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Sample records for digital hf radar

  1. Digital hf radar observations of equatorial spread-F

    SciTech Connect

    Argo, P.E.

    1984-01-01

    Modern digital ionosondes, with both direction finding and doppler capabilities can provide large scale pictures of the Spread-F irregularity regions. A morphological framework has been developed that allows interpretation of the hf radar data. A large scale irregularity structure is found to be nightward of the dusk terminator, stationary in the solar reference frame. As the plasma moves through this foehn-wall-like structure it descends, and irregularities may be generated. Localized upwellings, or bubbles, may be produced, and they drift with the background plasma. The spread-F irregularity region is found to be best characterized as a partly cloudy sky, due to the patchiness of the substructures. 13 references, 16 figures.

  2. All-digital radar architecture

    NASA Astrophysics Data System (ADS)

    Molchanov, Pavlo A.

    2014-10-01

    All digital radar architecture requires exclude mechanical scan system. The phase antenna array is necessarily large because the array elements must be co-located with very precise dimensions and will need high accuracy phase processing system for aggregate and distribute T/R modules data to/from antenna elements. Even phase array cannot provide wide field of view. New nature inspired all digital radar architecture proposed. The fly's eye consists of multiple angularly spaced sensors giving the fly simultaneously thee wide-area visual coverage it needs to detect and avoid the threats around him. Fly eye radar antenna array consist multiple directional antennas loose distributed along perimeter of ground vehicle or aircraft and coupled with receiving/transmitting front end modules connected by digital interface to central processor. Non-steering antenna array allows creating all-digital radar with extreme flexible architecture. Fly eye radar architecture provides wide possibility of digital modulation and different waveform generation. Simultaneous correlation and integration of thousands signals per second from each point of surveillance area allows not only detecting of low level signals ((low profile targets), but help to recognize and classify signals (targets) by using diversity signals, polarization modulation and intelligent processing. Proposed all digital radar architecture with distributed directional antenna array can provide a 3D space vector to the jammer by verification direction of arrival for signals sources and as result jam/spoof protection not only for radar systems, but for communication systems and any navigation constellation system, for both encrypted or unencrypted signals, for not limited number or close positioned jammers.

  3. European coordination for coastal HF radar data in EMODnet Physics

    NASA Astrophysics Data System (ADS)

    Mader, Julien; Novellino, Antonio; Gorringe, Patrick; Griffa, Annalisa; Schulz-Stellenfleth, Johannes; Montero, Pedro; Montovani, Carlo; Ayensa, Garbi; Vila, Begoña; Rubio, Anna; Sagarminaga, Yolanda

    2015-04-01

    Historically, joint effort has been put on observing open ocean, organizing, homogenizing, sharing and reinforcing the impact of the acquired information based on one technology: ARGO with profilers Argo floats, EuroSites, ESONET-NoE, FixO3 for deep water platforms, Ferrybox for stations in ships of opportunities, and GROOM for the more recent gliders. This kind of networking creates synergies and makes easier the implementation of this source of data in the European Data exchange services like EMODnet, ROOSs portals, or any applied services in the Blue economy. One main targeted improvement in the second phase of EMODnet projects is the assembling of data along coastline. In that sense, further coordination is recommended between platform operators around a specific technology in order to make easier the implementation of the data in the platforms (4th EuroGOOS DATAMEQ WG). HF radar is today recognized internationally as a cost-effective solution to provide high spatial and temporal resolution current maps (depending on the instrument operation frequency, covering from a few kilometres offshore up to 200 km) that are needed for many applications for issues related to ocean surface drift or sea state characterization. Significant heterogeneity still exists in Europe concerning technological configurations, data processing, quality standards and data availability. This makes more difficult the development of a significant network for achieving the needed accessibility to HF Radar data for a pan European use. EuroGOOS took the initiative to lead and coordinate activities within the various observation platforms by establishing a number of Ocean Observing Task Teams such as HF-Radars. The purpose is to coordinate and join the technological, scientific and operational HF radar communities at European level. The goal of the group is on the harmonization of systems requirements, systems design, data quality, improvement and proof of the readiness and standardization of

  4. Noise properties of HF radar measurement of ocean surface currents

    NASA Astrophysics Data System (ADS)

    Forget, Philippe

    2015-08-01

    High-frequency (HF) radars are commonly used for coastal circulation monitoring. The objective of the study is to assess what is the minimum timescale of variability of the geophysical surface currents that are accessible to the radar measurement given the intrinsic noise of this measurement. Noise properties are derived from the power density spectra (PDSs) of radial current records, which are compared to a model of the PDS of idealized currents contaminated by an additive white noise. The data were collected by two radar systems operating in the Northwestern Mediterranean. Periods of 3 weeks to 7 months are considered. Most of measured currents are affected by a white noise effect. Noise properties vary in time and space and are not specific to a particular radar station or to the radar signal processing method used (beam forming or direction finding). An increase of the noise level reduces the effective temporal resolution of radar-derived currents and then increases the minimum observable timescale of variability of geophysical currents. Our results are consistent with results of comparison found in literature between in situ sensors and radar measurements as well as between two radars operating along a same base line. The study suggests a self-sufficient method, requiring no external data, to estimate the minimum sampling period to consider for getting data sets having a minimized contamination by instrumental noise. This period can also be taken for smoothing or filtering measured currents.

  5. Customizable Digital Receivers for Radar

    NASA Technical Reports Server (NTRS)

    Moller, Delwyn; Heavey, Brandon; Sadowy, Gregory

    2008-01-01

    Compact, highly customizable digital receivers are being developed for the system described in 'Radar Interferometer for Topographic Mapping of Glaciers and Ice Sheets' (NPO-43962), NASA Tech Briefs, Vol. 31, No. 7 (August 2007), page 72. The receivers are required to operate in unison, sampling radar returns received by the antenna elements in a digital beam-forming (DBF) mode. The design of these receivers could also be adapted to commercial radar systems. At the time of reporting the information for this article, there were no commercially available digital receivers capable of satisfying all of the operational requirements and compact enough to be mounted directly on the antenna elements. A provided figure depicts the overall system of which the digital receivers are parts. Each digital receiver includes an analog-to-digital converter (ADC), a demultiplexer (DMUX), and a field-programmable gate array (FPGA). The ADC effects 10-bit band-pass sampling of input signals having frequencies up to 3.5 GHz. The input samples are demultiplexed at a user-selectable rate of 1:2 or 1:4, then buffered in part of the FPGA that functions as a first-in/first-out (FIFO) memory. Another part of the FPGA serves as a controller for the ADC, DMUX, and FIFO memory and as an interface between (1) the rest of the receiver and (2) a front-panel data port (FPDP) bus, which is an industry-standard parallel data bus that has a high data-rate capability and multichannel configuration suitable for DBF. Still other parts of the FPGA in each receiver perform signal-processing functions. The digital receivers can be configured to operate in a stand-alone mode, or in a multichannel mode as needed for DBF. The customizability of the receiver makes it applicable to a broad range of system architectures. The capability for operation of receivers in either a stand-alone or a DBF mode enables the use of the receivers in an unprecedentedly wide variety of radar systems.

  6. Mapping high-latitude plasma convection with coherent HF radars

    NASA Technical Reports Server (NTRS)

    Ruohoniemi, J. M.; Greenwald, R. A.; Baker, K. B.; Villain, J.-P.; Hanuise, C.

    1989-01-01

    Several methods developed for mapping high-latitude plasma convection with a high-latitude HF radar are described, which utilize coherent backscatter from electron density irregularities at F-region altitudes to observe convective plasma motion. Several examples of two-dimensional convection-velocity maps are presented, showing instances of L-shell-aligned flow in the dusk sector, the reversal of convection near magnetic midnight, and counterstreaming in the dayside cleft.

  7. HF radar observations of ionospheric backscatter during geomagnetically quiet periods

    NASA Astrophysics Data System (ADS)

    Kane, T. A.; Makarevich, R. A.; Devlin, J. C.

    2012-01-01

    The quiet-time coherent backscatter from the F-region observed by the Tasman International Geospace Environment Radar (TIGER) Bruny Island HF radar is analysed statistically in order to determine typical trends and controlling factors in the ionospheric echo occurrence. A comparison of the F-region peak density values from the IRI-2007 model and ionosonde measurements in the vicinity of the radar's footprint shows a very good agreement, particularly at subauroral and auroral latitudes, and model densities within the radar's footprint are used in the following analyses. The occurrence of F-region backscatter is shown to exhibit distinct diurnal, seasonal and solar cycle variations and these are compared with model trends in the F-region peak electron density and Pedersen conductance of the underlying ionosphere. The solar cycle effects in occurrence are demonstrated to be strong and more complex than a simple proportionality on a year-to-year basis. The diurnal and seasonal effects are strongly coupled to each other, with diurnal trends exhibiting a systematic gradual variation from month to month that can be explained when both electron density and conductance trends are considered. During the night, the echo occurrence is suggested to be controlled directly by the density conditions, with a direct proportionality observed between the occurrence and peak electron density. During the day, the echo occurrence appears to be controlled by both conductance and propagation conditions. It is shown that the range of echo occurrence values is smaller for larger conductances and that the electron density determines what value the echo occurrence takes in that range. These results suggest that the irregularity production rates are significantly reduced by the highly conducting E layer during the day while F-region density effects dominate during the night.

  8. Assimilation of HF radar data into the SWAN wave model

    NASA Astrophysics Data System (ADS)

    Siddons, L. A.; Wyatt, L. R.; Wolf, J.

    2009-05-01

    Data assimilation is a method used for optimally combining information to improve forecasting and model parameters. Three data assimilation algorithms are investigated and used for assimilating HF radar data into the SWAN wave model. The schemes under consideration are the Ensemble Kalman Filter, Ensemble Optimal Interpolation and a Three-Dimensional Variational scheme. Two approaches for updating the ocean wave spectrum are considered which consist of describing the spectrum using integral wave parameters of the whole spectrum and wave parameters within various frequency bands. The results show improvement in the wave parameters at the buoy location for the 3DVAR and ENS-OI scheme. The EnKF only shows good performance in one of the considered runs which leads to a conclusion that the methods used for calculating the errors for the EnKF scheme need further analysis.

  9. HF Doppler radar observations of low-latitude spread F

    NASA Astrophysics Data System (ADS)

    Reddi, C. R.; Sarma, M. S. S. R. K. N.; Niranjan, K.

    2009-06-01

    HF (5.5 MHz) Doppler radar observations of nonspread F and spread F echoes over Visakhapatnam (17.7°N, 83.3°E; dip 20°) are presented. The echoes appearing suddenly and nearly simultaneously in 16 successive range bins at 7.5 km intervals in association with spread F have been investigated. Two to five episodes of spread F activity were found to appear at intervals of 1-2 hours during individual nights. At the time of onset of spread F conditions, the Doppler velocity for each range bin changed rapidly from a negative maximum to a positive maximum followed by a gradual decrease to a steady ±10-15 m/s or to a large negative velocity and then again to a large positive. At the time of small constant velocity or velocity change from negative to positive, the spread F echoes were weak or even below the detection level of the radar. This disappearance in the higher ranges causes the decrease in range extent of spread F echoes. The positive and negative maximum velocities of spread F were in the range of +70 to -60 m/s. The maximum upward and downward velocity is not the same in all events of spread F activity. The width of the Doppler velocity spectrum for spread F echoes was found to vary with velocity. For zero velocity the width was a minimum of 50 m/s in contrast to 25 m/s for nonspread F events. These features were consistently observed for all spread F incidences. The observed results are compared with already reported HF/VHF observations and are discussed in the light of equatorial plasma dynamics during the growth phase of Rayleigh Taylor instability leading the incidence of spread F.

  10. Architecture for a 1-GHz Digital RADAR

    NASA Technical Reports Server (NTRS)

    Mallik, Udayan

    2011-01-01

    An architecture for a Direct RF-digitization Type Digital Mode RADAR was developed at GSFC in 2008. Two variations of a basic architecture were developed for use on RADAR imaging missions using aircraft and spacecraft. Both systems can operate with a pulse repetition rate up to 10 MHz with 8 received RF samples per pulse repetition interval, or at up to 19 kHz with 4K received RF samples per pulse repetition interval. The first design describes a computer architecture for a Continuous Mode RADAR transceiver with a real-time signal processing and display architecture. The architecture can operate at a high pulse repetition rate without interruption for an infinite amount of time. The second design describes a smaller and less costly burst mode RADAR that can transceive high pulse repetition rate RF signals without interruption for up to 37 seconds. The burst-mode RADAR was designed to operate on an off-line signal processing paradigm. The temporal distribution of RF samples acquired and reported to the RADAR processor remains uniform and free of distortion in both proposed architectures. The majority of the RADAR's electronics is implemented in digital CMOS (complementary metal oxide semiconductor), and analog circuits are restricted to signal amplification operations and analog to digital conversion. An implementation of the proposed systems will create a 1-GHz, Direct RF-digitization Type, L-Band Digital RADAR--the highest band achievable for Nyquist Rate, Direct RF-digitization Systems that do not implement an electronic IF downsample stage (after the receiver signal amplification stage), using commercially available off-the-shelf integrated circuits.

  11. Measurements of near surface ocean currents using HF radar

    NASA Astrophysics Data System (ADS)

    Laws, Kenneth Evans

    High Frequency (HF) radar is unique both in its ability to probe the ocean currents within the top few meters below the surface and to provide synoptic current maps covering thousands of square kilometers. This work focuses on the evaluation of ocean current measurement techniques, using the multi-frequency coastal radar (MCR), a system that operates on four frequencies (4.8, 6.8, 13.4 and 21.8 MHz) concurrently. Two methods of data processing, traditional beam forming and a direction finding approach, MUltiple SIgnal Characterization (MUSIC), are compared. Simulations and comparisons using real data are used to evaluate the application of MUSIC to the MCR and to design modifications to improve its performance. Uncertainties in the radar measurements as a function of radar operating frequency, sea state parameters and data processing method are estimated. Results show MUSIC to be applicable to the MCR and to outperform beam forming, particularly for the lower frequencies, over most of the real and simulated experiments examined. High resolution ocean wave spectral energy measurements are used to estimate the effect of Stokes drift on MCR measurements. The effect is shown to be small in magnitude relative to the expected errors in the MCR measurements and highly correlated with the wind. Although results show a correlation between the MCR measurements and the expected Stokes drift effect, the correlations could be the result of wind stress-induced currents. Using assumptions as to the form of the vertical current profile, estimates of the near-surface vertical shear are obtained from the MCR data. Analysis of the shear estimates casts doubt on the validity of a near-surface, logarithmic current profile for the open ocean. Further analysis of vertical shear estimates yields an estimate of the ocean current magnitude at the sea surface that is in agreement with the commonly accepted value of about 3% of the wind speed. Results of this work demonstrate a significant

  12. Digital Frequency Synthesizer For Radar Astronomy

    NASA Technical Reports Server (NTRS)

    Sadr, Ramin; Satorius, Edgar; Robinett, J. Loris, Jr.; Olson, Erlend

    1992-01-01

    Report discusses conceptual digital frequency synthesizer part of programmable local oscillator in radar-astronomy system. Phase must remain continuous during adjustments of frequency, phase noise must be low, and spectral purity must be high. Discusses theory of operation in some mathematical detail and presents new analysis of spectral purity of output.

  13. First results from the Blackstone HF radar in support of THEMIS

    NASA Astrophysics Data System (ADS)

    Lester, M.; Ruohoniemi, J. M.; Baker, J. B.; Barnes, R. J.; Clauer, C. R.; Greenwald, R. A.; Grocott, A.; Milan, S. E.; Yeoman, T. K.

    2008-12-01

    A new HF radar has been constructed and built in Blackstone, VA, as part of the SuperDARN/StormDARN programme specifically with the purpose of providing coverage over the Canadian ground sector in THEMIS. The new radar began operations in February 2008, an optimum time to support the first THEMIS tail campaign. This paper will discuss the importance of having radars at lower latitudes than the auroral zone locations of SuperDARN for substorm studies. Furthermore, the paper will also present the first results from this radar together with other SuperDARN observations during the THEMIS tail period.

  14. Inversion of swell frequency from a 1-year HF radar dataset collected in Brittany (France)

    NASA Astrophysics Data System (ADS)

    Wang, Weili; Forget, Philippe; Guan, Changlong

    2014-10-01

    This article presents long period ocean wave (swell) frequencies inverted from a 13-month dataset of high-frequency (HF) phased array radars and an assessment of these estimates by comparison with WAVEWATCH III model data. The method of swell frequency inversion from high-frequency radar sea echo Doppler spectra is described. Radar data were collected from a two-site HF Wellen Radar (WERA) radar system on the west coast of Brittany (France) operating at 12 MHz. A standard beam-forming processing technique has been used to obtain Doppler spectra of processed radar cells. Swell frequencies are obtained from the frequencies of particular spectral peaks of the second-order continuum in hourly averaged Doppler spectra. The data coverage of effective Doppler spectra considered for swell frequency estimates shows the influence of islands and shallow water effects. Swell estimates from both radar stations are in good agreement. The comparison of radar-derived results to WAVEWATCH III (WW3) estimates shows that radar measurements agree quite well with model results. The bias and standard deviation between two estimates are very small for swells with frequency less than 0.09 Hz (period >11 s), whereas radar estimates are generally lower than model estimates for shorter swells, along with higher standard deviation. Statistical analysis suggests that radar measurement uncertainty explains most of the difference between radar and model estimates. For each swell event, time series of frequency exhibits a quasi-linear frequency increase which is associated with the dispersive property of wave phase velocity. The use of swell frequency estimates from both radars on common radar cells only slightly increases the accuracy of swell frequency measurement.

  15. Ground backscatter characteristics model for SuperDARN Hokkaido HF radar

    NASA Astrophysics Data System (ADS)

    Oinats, Alexey; Nishitani, Nozomu; Ratovsky, Konstantin

    For the first time we present a model of diurnal and seasonal variations of ground backscatter signal propagation characteristics. There are minimal group range, corresponding elevation angle and other parameters. Model is developed for geographic location and specifications of SuperDARN Hokkaido HF radar. The model is based on HF ground backscatter signal calculation technique developed in the framework of waveguide approach. IRI-2007 model is used for calculation of background ionosphere. The main topic is a comparison of the presented model with an extensive dataset collected by SuperDARN Hokkaido radar during the whole its operation history since the late 2006 until 2014. The model is designed for both IRI testing and improvement of SuperDARN Hokkaido HF radar data interpretation. This work was done under financial support of the Russian Foundation for Basic Research (grants 14-05-00259-а and 14-05-00588-а).

  16. Digital exploitation of synthetic aperture radar

    NASA Technical Reports Server (NTRS)

    Wagner, H. L.; Shuchman, R. A.

    1977-01-01

    A digital processing and analysis scheme for use with digitized synthetic aperture radar data was developed. Using data from a four channel system, the imagery is preprocessed using specially designed software and then analyzed using preexisting facilities originally intended for use with MSS type data. Geometric and radiometric correction may be performed if desired, as well as classification analysis, Fast Fourier transform, filtering and level slice and display functions. The system provides low cost output in real time, permitting interactive imagery analysis. System information flow diagrams as well as sample output products are shown.

  17. Inner Shelf Current Structure Under Different Forcing Mechanisms— Combining ADCP and HF Radar Measurements

    NASA Astrophysics Data System (ADS)

    Kastner, S.; Kirincich, A.; Lentz, S. J.

    2014-12-01

    Our understanding of wind and wave driven currents in the coastal ocean has been limited by our inability to measure currents within a few meters of the surface. To improve our understanding of current dynamics in the upper few meters of the ocean we combine 8 months of ADCP measurements from the Martha's Vineyard Coastal Observatory with high-frequency (HF) radar measurements of surface currents. These techniques compliment each other, as the HF radar can only observe the surface velocities, and the ADCP cannot take accurate measurements in the upper few meters of the water column. We find that currents can vary significantly over the upper two meters of the inner shelf. Extrapolations to the surface based on the ADCP data are inconsistent with that observed by the HF radar. When different types of forcing conditions were examined, it was found that this difference is most evident in cases when wind stresses are weak (HF radar observations were onshore, in the opposite direction of the near-surface ADCP observations. Models indicate this difference can be attributed in part to Stokes' drift, measured by the HF radar but not the ADCP. When the ADCP velocities are corrected for Stokes' drift, the difference between the HF radar surface current and the top ADCP current is consistent with a simple model of near-surface wind-driven current shear. This suggests future attempts to extrapolate ADCP currents toward the surface should consider wind-driven shear. This result can be used to more accurately estimate onshore transport, which has applications in calculating nutrient and pollutant transport.

  18. Effects of production and loss of electrons on HF Doppler radar measurements of vertical plasma drifts

    NASA Astrophysics Data System (ADS)

    Jaya, A. S.; Nayar, S. R. P.; Rao, P. B.

    1993-04-01

    The measurements of vertical plasma drifts at magnetic equator using HF Doppler radar include contributions due to production and loss of electrons and also due to the equatorial electric field. From the computation of the electron density profiles, the temporal variation of electron density changes has been studied and the contribution of production and loss of electrons to the vertical plasma drift measurements using HF Doppler radar during daytime has been evaluated. The evaluation of vertical drifts has been made for different conditions of the ionosphere and for different zenith angles.

  19. Artificial Ionization and UHF Radar Response Associated with HF Frequencies near Electron Gyro-Harmonics (Invited)

    NASA Astrophysics Data System (ADS)

    Watkins, B. J.; Fallen, C. T.; Secan, J. A.

    2013-12-01

    We present new results from O-mode ionospheric heating experiments at the HAARP facility in Alaska to demonstrate that the magnitude of artificial ionization production is critically dependent on the choice of HF frequency near gyro-harmonics. For O-mode heating in the lower F-region ionosphere, typically about 200 km altitude, artificial ionization enhancements are observed in the lower ionosphere (about 150 - 220 km) and also in the topside ionosphere above about 500 km. Lower ionosphere density enhancements are inferred from HF-enhanced ion and plasma-line signals observed with UHF radar. Upper ionospheric density enhancements have been observed with TEC (total electron content) experiments by monitoring satellite radio beacons where signal paths traverse the HF-modified ionosphere. Both density enhancements and corresponding upward plasma fluxes have also been observed in the upper ionosphere via in-situ satellite observations. The data presented focus mainly on observations near the third and fourth gyro-harmonics. The specific values of the height-dependent gyro-harmonics have been computed from a magnetic model of the field line through the HF heated volume. Experiments with several closely spaced HF frequencies around the gyro-harmonic frequency region show that the magnitude of the lower-ionosphere artificial ionization production maximizes for HF frequencies about 1.0 - 1.5 MHz above the gyro-harmonic frequency. The response is progressively larger as the HF frequency is increased in the frequency region near the gyro-harmonics. For HF frequencies that are initially greater than the gyro-harmonic value the UHF radar scattering cross-section is relatively small, and non-existent or very weak signals are observed; as the signal returns drop in altitude due to density enhancements the HF interaction region passes through lower altitudes where the HF frequency is less than the gyro-harmonic value, for these conditions the radar scattering cross-section is

  20. Digital frequency synthesizer for radar astronomy

    NASA Technical Reports Server (NTRS)

    Sadr, R.; Satorius, E.; Robinett, L.; Olson, E.

    1990-01-01

    The digital frequency synthesizer (DFS) is an integral part of the programmable local oscillator (PLO) which is being developed for the NASA's Deep Space Network (DSN) and radar astronomy. Here, the theory of operation and the design of the DFS are discussed, and the design parameters in application for the Goldstone Solar System Radar (GSSR) are specified. The spectral purity of the DFS is evaluated by analytically evaluating the output spectrum of the DFS. A novel architecture is proposed for the design of the DFS with a frequency resolution of 1/2(exp 48) of the clock frequency (0.35 mu Hz at 100 MHz), a phase resolution of 0.0056 degrees (16 bits), and a frequency spur attenuation of -96 dBc.

  1. Improving Navigation information for the Rotterdam Harbour access through a 3D Model and HF radar

    NASA Astrophysics Data System (ADS)

    Schroevers, Marinus

    2015-04-01

    The Port of Rotterdam is one of the largest harbours in the world and a gateway to Europe. For the access to Rotterdam harbour, information on hydrodynamic and meteorological conditions is of vital importance for safe and swift navigation. This information focuses on the deep navigation channel in the shallow foreshore, which accommodates large seagoing vessels. Due to a large seaward extension of the Port of Rotterdam area in 2011, current patterns have changed. A re-evaluation of the information needed, showed a need for an improved accuracy of the cross channel currents and swell, and an extended forecast horizon. To obtain this, new information system was designed based on a three dimensional hydrodynamic model which produces a 72 hour forecast. Furthermore, the system will assimilate HF radars surface current to optimize the short term forecast. The project has started in 2013 by specifying data needed from the HF radar. At the same time (temporary) buoys were deployed to monitor vertical current profiles. The HF radar will be operational in July 2015, while the model development starts beginning 2015. A pre operational version of the system is presently planned for the end of 2016. A full operational version which assimilates the HF radar data is planned for 2017.

  2. E-region decameter-scale plasma waves observed by the dual TIGER HF radars

    NASA Astrophysics Data System (ADS)

    Carter, B. A.; Makarevich, R. A.

    2009-01-01

    The dual Tasman International Geospace Environment Radar (TIGER) HF radars regularly observe E-region echoes at sub-auroral magnetic latitudes 58°-60° S including during geomagnetic storms. We present a statistical analysis of E-region backscatter observed in a period of ~2 years (late 2004-2006) by the TIGER Bruny Island and Unwin HF radars, with particular emphasis on storm-time backscatter. It is found that the HF echoes normally form a 300-km-wide band at ranges 225-540 km. In the evening sector during geomagnetic storms, however, the HF echoes form a curved band joining to the F-region band at ~700 km. The curved band lies close to the locations where the geometric aspect angle is zero, implying little to no refraction during geomagnetic storms, which is an opposite result to what has been reported in the past. The echo occurrence, Doppler velocity, and spectral width of the HF echoes are examined in order to determine whether new HF echo types are observed at sub-auroral latitudes, particularly during geomagnetic storms. The datasets of both TIGER radars are found to be dominated by low-velocity echoes. A separate population of storm-time echoes is also identified within the datasets of both radars with most of these echoes showing similar characteristics to the low-velocity echo population. The storm-time backscatter observed by the Bruny Island radar, on the other hand, includes near-range echoes (r<405 km) that exhibit some characteristics of what has been previously termed the High Aspect angle Irregularity Region (HAIR) echoes. We show that these echoes appear to be a storm-time phenomenon and further investigate this population by comparing their Doppler velocity with the simultaneously measured F- and E-region irregularity velocities. It is suggested that the HAIR-like echoes are observed only by HF radars with relatively poor geometric aspect angles when electron density is low and when the electric field is particularly high.

  3. Improved statistical prediction of surface currents based on historic HF-radar observations

    NASA Astrophysics Data System (ADS)

    Frolov, Sergey; Paduan, Jeffrey; Cook, Michael; Bellingham, James

    2012-07-01

    Accurate short-term prediction of surface currents can improve the efficiency of search-and-rescue operations, oil-spill response, and marine operations. We developed a linear statistical model for predicting surface currents (up to 48 h in the future) based on a short time history of past HF-radar observations (past 48 h) and an optional forecast of surface winds. Our model used empirical orthogonal functions (EOFs) to capture spatial correlations in the HF-radar data and used a linear autoregression model to predict the temporal dynamics of the EOF coefficients. We tested the developed statistical model using historical observations of surface currents in Monterey Bay, California. The predicted particle trajectories separated from particles advected with HF-radar data at a rate of 4.4 km/day. The developed model was more accurate than an existing statistical model (drifter separation of 5.5 km/day) and a circulation model (drifter separation of 8.9 km/day). When the wind forecast was not available, the accuracy of our model degraded slightly (drifter separation of 4.9 km/day), but was still better than existing models. We found that the minimal length of the HF-radar data required to train an accurate statistical model was between 1 and 2 years, depending on the accuracy desired. Our evaluation showed that the developed model is accurate, is easier to implement and maintain than existing statistical and circulation models, and can be relocated to other coastal systems of similar complexity that have a sufficient history of HF-radar observations.

  4. Weighting in digital synthetic aperture radar processing

    NASA Technical Reports Server (NTRS)

    Dicenzo, A.

    1979-01-01

    Weighting is employed in synthetic aperture radar (SAR) processing to reduce the sidelobe response at the expense of peak center response height and mainlobe resolution. The weighting effectiveness in digital processing depends not only on the choice of weighting function, but on the fineness of sampling and quantization, on the time bandwidth product, on the quadratic phase error, and on the azimuth antenna pattern. The results of simulations conducted to uncover the effect of these parameters on azimuth weighting effectiveness are presented. In particular, it is shown that multilook capabilities of future SAR systems may obviate the need for consideration of the antenna pattern, and that azimuth time-bandwidth products of over 200 are probably required before the digital results begin to approach the ideal results.

  5. APQ-102 imaging radar digital image quality study

    NASA Astrophysics Data System (ADS)

    Griffin, C. R.; Estes, J. M.

    1982-11-01

    A modified APQ-102 sidelooking radar collected synthetic aperture radar (SAR) data which was digitized and recorded on wideband magnetic tape. These tapes were then ground processed into computer compatible tapes (CCT's). The CCT's may then be processed into high resolution radar images by software on the CYBER computer.

  6. APQ-102 imaging radar digital image quality study

    NASA Technical Reports Server (NTRS)

    Griffin, C. R.; Estes, J. M.

    1982-01-01

    A modified APQ-102 sidelooking radar collected synthetic aperture radar (SAR) data which was digitized and recorded on wideband magnetic tape. These tapes were then ground processed into computer compatible tapes (CCT's). The CCT's may then be processed into high resolution radar images by software on the CYBER computer.

  7. F region ionosphere effects on the mapping accuracy of SuperDARN HF radar echoes

    NASA Astrophysics Data System (ADS)

    Chen, X.-C.; Lorentzen, D. A.; Moen, J. I.; Oksavik, K.; Baddeley, L. J.; Lester, M.

    2016-05-01

    Structured particle precipitation in the cusp is an important source for the generation of F region ionospheric irregularities. The equatorward boundaries of broad Doppler spectral width in Super Dual Auroral Radar Network (SuperDARN) data and the concurrent OI 630.0 nm auroral emission are good empirical proxies for the dayside open-closed field line boundary. However, SuperDARN currently employs a simple virtual model to determine the location of its echoes, instead of a direct calculation of the radio wave path. The varying ionospheric conditions could influence the final mapping accuracy of SuperDARN echoes. A statistical comparison of the offsets between the SuperDARN Finland radar spectral width boundary (SWB) and the OI 630.0 nm auroral emission boundary (AEB) from a meridian-scanning photometer (MSP) on Svalbard is performed in this paper. By restricting the location of the 630.0 nm data to be near local zenith where the MSP has the highest spatial resolution, the optical mapping errors were significantly reduced. The variation of the SWB-AEB offset confirms that there is a close relationship between the mapping accuracy of the HF radar echoes and solar activity. The asymmetric variation of the SWB-AEB offset versus magnetic local time suggests that the intake of high-density solar extreme ultraviolet ionized plasma from postnoon at subauroral latitudes could result in a stronger refraction of the HF radar signals in the noon sector, while changing the HF radar operating frequency also has a refraction effect that contributes to the final location of the HF radar echoes.

  8. F-region ionosphere effects on the mapping accuracy of SuperDARN HF radar echoes

    NASA Astrophysics Data System (ADS)

    Chen, Xiangcai; Lorentzen, Dag; Moen, Jøran; Oksavik, Kjellmar; Baddeley, Lisa; Lester, Mark

    2016-04-01

    Structured particle precipitation in the cusp is an important source for the generation of F -region ionospheric irregularities. The equatorward boundaries of broad Doppler spectral width in Super Dual Auroral Radar Network (SuperDARN) data and the concurrent OI 630.0 nm auroral emission are good empirical proxies for the dayside open-closed field line boundary (OCB). However, SuperDARN currently employs a simple virtual model to determine the location of its echoes, instead of a direct calculation of the radio wave path. The varying ionospheric conditions could influence the final mapping accuracy of SuperDARN echoes. A statistical comparison of the offsets between the SuperDARN Finland radar spectral width boundary (SWB) and the OI 630.0 nm auroral emission boundary (AEB) from a meridian-scanning photometer (MSP) in Longyearbyen from December 1995 to January 2014 in wintertime is performed. By restricting the location of the OI 630.0 nm data to be near local zenith, where the MSP has the highest spatial resolution, the mapping errors were significantly reduced for the AEB. The variation of the SWB - AEB offset confirms that there is a close relationship between the mapping accuracy of the HF radar echoes and solar activity. The asymmetric variation of the SWB - AEB offset versus magnetic local time suggests that the intake of high density solar extreme ultraviolet ionized plasma from post-noon at sub-auroral latitudes could result in a stronger refraction of the HF radar signals in the noon sector. The changing HF radar operating frequency also has a refraction effect that contributes to the final location of the HF radar echoes.

  9. Inversion and assessment of swell waveheights from HF radar spectra in the Iroise Sea

    NASA Astrophysics Data System (ADS)

    Wang, Weili; Forget, Philippe; Guan, Changlong

    2016-04-01

    As an extension of previous work in Wang et al. (Ocean Dyn 64:1447-1456, 2014), this article presents significant waveheights of swell inverted from a 13 month dataset of two high-frequency (HF) phased array radars. As an important intermediate variable in the calculation of significant waveheights, relative swell directions obtained by two different methods from a single radar station are also presented. The impact of the inaccuracy of relative swell direction on the calculation of waveheight is investigated and an alternative way of using constant swell direction is proposed. Radar-inverted swell significant waveheights using different ranges of relative swell directions are investigated. Results are assessed by WAVEWATCH III model hind casts. Analysis of the complete database shows that radar-inverted swell significant waveheights agree reasonably well with model estimates with large scatter. Standard deviation of the difference between the two estimations increases with waveheight, whereas the relative standard deviation, normalized by waveheight, keeps nearly constant. The constant direction scheme of waveheight inversion gives good estimations except for energetic swell exceeding the small perturbation assumption. Statistical analysis suggests that radar measurement uncertainty explains a considerable part of the difference between radar and model estimates. Swell estimates from both radar stations are consistent. This enables combined use of both radar spectra at common radar cells. Use of double spectra solves the ambiguity of relative swell direction, i.e., absolute swell direction is obtained, and effectively improves the accuracy of swell direction by the least-squares method.

  10. A Multi-frequency Beam-forming HF Radar for Tsunami Detection

    NASA Astrophysics Data System (ADS)

    Trizna, D. B.

    2007-05-01

    We discuss a new multi-frequency beam-forming HF radar design for robust detection and tracking of tsunami waves from 200 km distances, providing continuous coverage of the tsunami wave pattern after it impinges on the continental shelf. The method works by mapping ocean currents at long range using traditional HF radar method of radial Bragg line Doppler shift measurements. The tsunami is detected by anomalous spatial patterns of higher than normal Bragg-line shifts due to the large orbital wave of the series of tsunami wave crests as they impinge on the continental shelf. An approach using beam forming of 16 or 32 antenna elements provides an update every five minutes or less, while Direction-of-Arrival method systems using just a few antenna elements inherently require of the order of 30 to 60 minutes for a reliable current map. The multi-frequency radar provides a more robust capability than the single frequency HF radar for at least two reasons. First, because the HF channel user spectrum suffers diurnal variability in channel occupancy due to the ionosphere changing with time of day, low frequencies can become contaminated with user noise, so that maximum range for reliable detection not achieved. Under this condition, one would rely on quiet higher HF frequencies that lie above the Maximum Usable Frequency (MUF) for ionospheric reflection propagation. Alternatively, for daylight operation when low frequency utilization can be used to minimize surface wave propagation loss, the sea state might not be sufficiently active to allow long range coverage needed for reliable detection, due to the lack of ocean wave spectral energy at the Bragg-resonant wave frequency. Thus, single- frequency radars, operating in the 4-6 MHz range to minimize propagation losses to achieve long-range coverage, would suffer due to low wind conditions. The multi-frequency HF radar discussed here allows one to dynamically choose the optimum frequency from a set of 8 to 16, as allowed by

  11. Applications of spectral estimation techniques to radar Doppler processing: Simulation and analysis of HF (High-frquency) skywave radar data

    NASA Astrophysics Data System (ADS)

    Trizna, D. B.; McNeal, G. D.

    1985-12-01

    This work is the second paper in a series of studies of the application of spectral estimations techniques to Doppler processing of coherent radar signals. In this work, simulated high-frequency (HF) radar sea scatter time series are generated and processed by use of three different spectral estimation algorithms and the fast Fourier transform (FFT). The sea clutter is simulated by narrowband filtering a wideband Gaussian noise spectrum in the frequency domain, with filter widths appropriate to describe first-order Bragg lines and second-order continuum. Targets are introduced as sinusoids, stepped by 5 dB for eight different echo power values, and stepped in Doppler frequency for four different values relative to the clutter. These simulations identify problems that appear unique to Doppler processing of coherent radar data in the presence of broadband clutter, and are in distinction to the application of spectral estimation to processing in the spatial domain. In the latter case, the spectral contributions are generally narrowly confined in the angular power spectral estimate, and the aim is to separate these contributions in the presence of noise. The HF radar application is concerned with separation of weak targets in the presence of stronger clutter returns, which are relati vely broad compared to the target return. It appears that the Burg maximum entropy method allows the detection of targets in clutter under conditions which the FFT is incapable of detection with any degree of accuracy.

  12. Digital Beamforming Synthetic Aperture Radar (DBSAR) Polarimetric Upgrade

    NASA Technical Reports Server (NTRS)

    Rincon, Rafael F.; Perrine, Martin; McLinden, Matthew; Valett, Susan

    2011-01-01

    The Digital Beamforming Synthetic Aperture Radar (DBSAR) is a state-of-the-art radar system developed at NASA/Goddard Space Flight Center for the development and implementation of digital beamforming radar techniques. DBSAR was recently upgraded to polarimetric operation in order to enhance its capability as a science instrument. Two polarimetric approaches were carried out which will be demonstrated in upcoming flight campaigns.

  13. Potential Use of HF Radar for Tsunami Detection in the Central and Eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Cokacar, Tulay; Necmioglu, Ocal; Ozer, Ceren

    2016-04-01

    Today, HF radar is recognized as internationally cost-effective and efficient solution to provide near-real time measurements that cover a large area continuously over time for ocean hazards warning and long term ocean monitoring studies such as, seasonal forecasts of climate, hurricanes, s torm surges and large-scale ocean circulation changes. These radar systems recently became an operational tool in coastal monitoring worldwide. They are used for many operational applications that include ship detection, tracking, guidance, distribution of pollutants, fishery and oceanography. HF radar data used for the tsunami warnings, can also be used for the other purposes and be of potential interest to wide application area users and stakeholders. Moreover multi user applications will ensure the system is maintained operationally over the long term. Hence the system is cost effective also with regards to maintenance. New algorithms allow useful detection and verification for tsunami detection. While technical monitoring capacity and the algorithms for tsunami detection is improved significantly, further studies are required to obtain complete wave height determination. We analysed the available technology and algorithms for the purpose of tsunami detection in the central-eastern Mediterranean and its connected Seas (Aegean and Black Sea). Since the study area is characterized by narrow continental shelf area, the HF radar observation for the purpose of tsunami detection is possible in restricted areas. While extensive continental shelves in the northeastern Black Sea and along the coast of Tunisia in the central Mediterranean let tsunami detection 2.5 hours before tsunami waves hit the coast, the detection is possible around 1 hr or less in advance for the remaining basins with wide continental shelf areas. The bathymetric structure is important for deciding the applicability of HF radar systems for the tsunami detection in continental shelf areas, which can be covered by

  14. Digital image transformation and rectification of spacecraft and radar images

    NASA Astrophysics Data System (ADS)

    Wu, S. S. C.

    1985-12-01

    The application of digital processing techniques to spacecraft television pictures and radar images is discussed. The use of digital rectification to produce contour maps from spacecraft pictures is described; images with azimuth and elevation angles are converted into point-perspective frame pictures. The digital correction of the slant angle of radar images to ground scale is examined. The development of orthophoto and stereoscopic shaded relief maps from digital terrain and digital image data is analyzed. Digital image transformations and rectifications are utilized on Viking Orbiter and Lander pictures of Mars.

  15. Digital image transformation and rectification of spacecraft and radar images

    NASA Technical Reports Server (NTRS)

    Wu, S. S. C.

    1985-01-01

    The application of digital processing techniques to spacecraft television pictures and radar images is discussed. The use of digital rectification to produce contour maps from spacecraft pictures is described; images with azimuth and elevation angles are converted into point-perspective frame pictures. The digital correction of the slant angle of radar images to ground scale is examined. The development of orthophoto and stereoscopic shaded relief maps from digital terrain and digital image data is analyzed. Digital image transformations and rectifications are utilized on Viking Orbiter and Lander pictures of Mars.

  16. Measurement of ocean wave height and direction by means of HF radar: An empirical approach

    NASA Astrophysics Data System (ADS)

    Essen, H.-H.; Gurgel, K.-W.; Schlick, T.

    1999-12-01

    High-frequency (HF) radar has been used for 20 years for remote sensing of ocean surface currents and ocean waves. Backscattered Doppler spectra contain two discrete lines, whose frequencies (Bragg frequency) determine the current speed, and four continuous side bands enabling inversion techniques to be used for retrieving ocean wave spectra. Recently, a new HF radar has been developed at the University of Hamburg (Germany). Data of a 34-day experiment reveal a high correlation between the standard deviation of the Bragg frequencies and the significant wave height weighted by an azimuthal function. Applying empirical regression curves it is possible to determine the significant wave height and the mean wave direction from intersecting beams of two radar stations. Compared to inversion techniques, the new method is applicable to data with a lower signal-to-noise ratio, i.e. it allows larger ranges. Two radar sites are required for current measurements. The optimum distance between two 30 MHz radars is about 20 km and, with the new method, needs not be reduced for the purpose of simultaneous wave measurements.

  17. Developing tools for digital radar image data evaluation

    NASA Technical Reports Server (NTRS)

    Domik, G.; Leberl, F.; Raggam, J.

    1986-01-01

    The refinement of radar image analysis methods has led to a need for a systems approach to radar image processing software. Developments stimulated through satellite radar are combined with standard image processing techniques to create a user environment to manipulate and analyze airborne and satellite radar images. One aim is to create radar products for the user from the original data to enhance the ease of understanding the contents. The results are called secondary image products and derive from the original digital images. Another aim is to support interactive SAR image analysis. Software methods permit use of a digital height model to create ortho images, synthetic images, stereo-ortho images, radar maps or color combinations of different component products. Efforts are ongoing to integrate individual tools into a combined hardware/software environment for interactive radar image analysis.

  18. Digital image transformation and rectification of spacecraft and radar images

    USGS Publications Warehouse

    Wu, S.S.C.

    1985-01-01

    Digital image transformation and rectification can be described in three categories: (1) digital rectification of spacecraft pictures on workable stereoplotters; (2) digital correction of radar image geometry; and (3) digital reconstruction of shaded relief maps and perspective views including stereograms. Digital rectification can make high-oblique pictures workable on stereoplotters that would otherwise not accommodate such extreme tilt angles. It also enables panoramic line-scan geometry to be used to compile contour maps with photogrammetric plotters. Rectifications were digitally processed on both Viking Orbiter and Lander pictures of Mars as well as radar images taken by various radar systems. By merging digital terrain data with image data, perspective and three-dimensional views of Olympus Mons and Tithonium Chasma, also of Mars, are reconstructed through digital image processing. ?? 1985.

  19. Radar scattering statistics for digital terrain models

    NASA Astrophysics Data System (ADS)

    Wilson, Kelce; Patrick, Dale; Blair, James

    2005-05-01

    The statistic results for a digital terrain model are presented that closely match measurements for 77% of the 189 possible combinations of 7 radar bands, 3 polarizations, and 9 terrain types. The model produces realistic backscatter coefficient values for the scenarios over all incidence angles from normal to grazing. The generator was created using measured data sets reported in the Handbook of Radar Scattering Statistics for Terrain covering L, C, S, X, Ka, Ku, and W frequency bands; HH, HV, and VV polarizations; and soil and rock, shrub, tree, short vegetation, grass, dry snow, wet snow, road surface, and urban area terrain types. The first two statistical moments match published values precisely, and a Chi-Square histogram test failed to reject the generator at a 95% confidence level for the 146 terrain models implemented. A Sea State model provides the grazing angle extension for predictions beyond the available measurements. This work will contain a comprehensive set of plots of mean and standard deviation versus incidence angle.

  20. Neural networks for automated classification of ionospheric irregularities in HF radar backscattered signals

    NASA Astrophysics Data System (ADS)

    Wing, S.; Greenwald, R. A.; Meng, C.-I.; Sigillito, V. G.; Hutton, L. V.

    2003-08-01

    The classification of high frequency (HF) radar backscattered signals from the ionospheric irregularities (clutters) into those suitable, or not, for further analysis, is a time-consuming task even by experts in the field. We tested several different feedforward neural networks on this task, investigating the effects of network type (single layer versus multilayer) and number of hidden nodes upon performance. As expected, the multilayer feedforward networks (MLFNs) outperformed the single-layer networks. The MLFNs achieved performance levels of 100% correct on the training set and up to 98% correct on the testing set. Comparable figures for the single-layer networks were 94.5% and 92%, respectively. When measures of sensitivity, specificity, and proportion of variance accounted for by the model are considered, the superiority of the MLFNs over the single-layer networks is much more striking. Our results suggest that such neural networks could aid many HF radar operations such as frequency search, space weather, etc.

  1. Characterizing the surface circulation in the Ebro Delta using a HF radar data-model approach

    NASA Astrophysics Data System (ADS)

    Lorente Jimenez, Pablo; Piedracoba Varela, Silvia; Soto-Navarro, Javier; Garcia-Sotillo, Marcos; Alvarez Fanjul, Enrique

    2016-04-01

    One year-long (2014) quality-controlled current observations from a CODAR SeaSonde High Frequency (HF) radar network deployed in the Ebro Delta (northwestern Mediterranean) were combined with operational products provided by a regional ocean forecasting system named IBI (Iberia-Biscay-Ireland) in order to comprehensively portray the ocean state and its variability. First, accurate HF radar data were used as benchmark for the rigorous validation of IBI performance by means of the computation of skill metrics and quality indicators. The analysis of the monthly averaged current maps for 2014 showed that IBI properly captured the prevailing dynamic features of the coastal circulation observed by the HF radar, according to the resemblance of circulation patterns and the eddy kinetic energy spatial distribution. The model skill assessment was completed with an exploration of dominant modes of variability both in time and space. The EOF analysis confirmed that the modeled surface current field evolved in space and time according to three significantly dominant modes of variability which accounted for the 49.2% of the total variance, in close agreement with the results obtained for the HF radar (46.1%). The response of the subtidal surface current field to prevalent wind regimes in the study area was examined in terms of induced circulation structures by performing a conditional averaging approach. This data-model synergistic approach has proved to be valid to operationally monitor and describe the complex coastal circulation in Ebro Delta despite the observed model drawbacks in terms of reduced energy content in surface currents and some inaccuracies in the wind-driven low frequency response. This integrated methodology constitutes a powerful tool for improving operational ocean forecasting systems at European level within the frame of the Copernicus Marine Environment Monitoring Service (CMEMS). It also facilitates high-stakes decision-making for coastal management and

  2. Improving current forecasts for the German Bight using HF radar measurements

    NASA Astrophysics Data System (ADS)

    Schulz-Stellenfleth, Johannes; Stanev, Emil; Staneva, Joanna

    2015-04-01

    Three HF radar stations located at the islands of Wangerooge and Sylt as well as on the mainland in Büsum are operated in the German Bight as part of COSYNA system. The WERA system operates at 12.4 MHz and provides surface current measurements every 20 min. The observations are merged with numerical model data to optimise state estimates on a pre-operational basis. The presentation introduces the spatio temporal interpolation (STOI) method, which is a statistical approach to correct data from a free model run using an analysis window of typically one tidal cycle. The technique is thus able to resolve intra-tidal time scales. The scheme is based on an EOF analysis to estimate the model error background statistics and is capable of providing improved short term forecasts. Statistics of the free model run, the HF radar data and the STOI analysis are shown for several month. Both the three dimensional primitive equation model GETM and the operational BSH model are used to provide free model run data. GETM setups with boundary forcing from the MYOCEAN North West Shelf model are used. Maps of innovation and residuals are presented. Furthermore forecast errors for different forecast horizons are discussed. Results are also compared to independent measurements taken at the FINO-1 and FINO-2 platforms. The impact of the analysis is, e.g., illustrated by drifter trajectory simulations. First results are also shown regarding an extension of the STOI method, which includes a model restart to further improve the dynamical consistency of the results. Issues related to the treatment of the boundary forcing and the meteo forcing used during the forecast period are discussed. The impact of the HF radar data on water level estimates are analysed. Furthermore, some results concerning the potential impact of existing and hypothetical HF radar systems are presented, which were obtained making use of the STOI method as well as statistical OSE and OSSE techniques.

  3. HF Doppler radar observations of equatorial plasma drifts and spread-F

    NASA Astrophysics Data System (ADS)

    Jayachandran, B.; Namboothiri, S. P.; Balan, N.; Rao, P. B.; Sastri, J. H.

    Vertical plasma drift measurements have been made by an HF Doppler radar at the equatorial station of Trivandrum. For magnetically quiet conditions, Doppler observations are presented dealing with (1) the postsunset vertical plasma drifts and their seasonal dependence, (2) the prereversal enhancement in the vertical plasma drift and the occurrence of equatorial spread-F, and (3) the vector plasma drift measurements for a sample equinoctial day.

  4. Digital orthogonal receiver for wideband radar based on compressed sensing

    NASA Astrophysics Data System (ADS)

    Hou, Qingkai; Liu, Yang; Chen, Zengping; Su, Shaoying

    2014-10-01

    Digital orthogonal receiver is one of the key techniques in digital receiver of soft radar, and compressed sensing is attracting more and more attention in radar signal processing. In this paper, we propose a CS digital orthogonal receiver for wideband radar which utilizes compressed sampling in the acquisition of radar raw data. In order to reconstruct complex signal from sub-sampled raw data, a novel sparse dictionary is proposed to represent the real-valued radar raw signal sparsely. Using our dictionary and CS algorithm, we can reconstruct the complex-valued radar signal from sub-sampled echoes. Compared with conventional digital orthogonal radar receiver, the architecture of receiver in this paper is more simplified and the sampling frequency of ADC is reduced sharply. At the same time, the range profile can be obtained during the reconstruction, so the matched filtering can be eliminated in the receiver. Some experiments on ISAR imaging based on simulated data prove that the phase information of radar echoes is well reserved in our orthogonal receiver and the whole design is effective for wideband radar.

  5. STRING: A new drifter for HF radar validation.

    NASA Astrophysics Data System (ADS)

    Rammou, Anna-Maria; Zervakis, Vassilis; Bellomo, Lucio; Kokkini, Zoi; Quentin, Celine; Mantovani, Carlo; Kalampokis, Alkiviadis

    2015-04-01

    High-Frequency radars (HFR) are an effective mean of remotely monitoring sea-surface currents, based on recording the Doppler-shift of radio-waves backscattered on the sea surface. Validation of HFRs' measurements takes place via comparisons either with in-situ Eulerian velocity data (usually obtained by surface current-meters attached on moorings) or to Lagrangian velocity fields (recorded by surface drifters). The most common surface drifter used for this purpose is the CODE-type drifter (Davis, 1985), an industry-standard design to record the vertical average velocity of the upper 1 m layer of the water column. In this work we claim that the observed differences between the HFR-derived velocities and Lagrangian measurements can be attributed not just to the different spatial scales recorded by the above instruments but also due to the fact that while the HFR-derived velocity corresponds to exponentially weighted vertical average of the velocity field from the surface to 1 m depth (Stewart and Joy, 1974) the velocity estimated by the CODE drifters corresponds to boxcar-type weighted vertical average due to the orthogonal shape of the CODE drifters' sails. After analyzing the theoretical behavior of a drifter under the influence of wind and current, we proceed to propose a new design of exponentially-shaped sails for the drogues of CODE-based drifters, so that the HFR-derived velocities and the drifter-based velocities will be directly comparable, regarding the way of vertically averaging the velocity field.The new drifter, codenamed STRING, exhibits identical behavior to the classical CODE design under relatively homogeneous conditions in the upper 1 m layer, however it is expected to follow a significantly different track in conditions of high vertical shear and stratification. Thus, we suggest that the new design is the instrument of choice for validation of HFR installations, as it can be used in all conditions and behaves identically to CODEs when vertical

  6. Surface current patterns in the Ibiza Channel with the use of High Frequency (HF) Radar system

    NASA Astrophysics Data System (ADS)

    Lana, Arancha; Fernández, Vicente; Troupin, Charles; Pascual, Ananda; Orfila, Alejandro; Tintoré, Joaquín

    2014-05-01

    The Ibiza Channel located between the East Coast of the Iberian Peninsula, and the West Coast of Ibiza, at the Balearic Islands, is a well-known biodiversity hot spot. This area is relevant due to the interaction of water masses coming from the Atlantic Ocean - ascending through the Iberian Peninsula coast - with the older Atlantic waters descending from the Gulf of Lion. In 2012, the installation of Coastal HF Radar in the area provides valuable information for the study of the surface transport along the channel. The Coastal HF Radar operates since June 2012, and provides hourly surface current maps with a spatial resolution of approximately 3 km and a range reaching up to 70 km offshore. The instrument forms part of a monitoring multi-platform system, which is completed with satellite-derived data, gliders, modelling and fixed and lagrangian buoys. All HF Radar data are processed with standard quality control methods. Drifter velocity obtained from lagrangian buoys for two oceanographic campaigns, satellite-derived data and currentmeter data from a fixed buoy in the Ibiza Channel are used to validate the HF Radar data. All surface current data are used to perform a spectrum analysis in order to show the physical processes, at the main temporal periods. The contribution of the different temporal scales to the total Kinetic Energy has been analysed for the first time at different seasonal intervals. This served to evaluate the energetic importance of the different components of the surface currents. The inertial currents have a lower contribution to the total KE during winter, compared with the summer period. Besides, the spatial distribution of the inertial component to the total KE varies seasonally, and according to the bathymetry of the area. The low-pass (sub-inertial) filtered HF Radar currents show a predominant northern current during the summer months in the channel, and a mean southern current during the winter period. These results are discussed and

  7. Traveling Ionospheric Disturbance Characteristics Over Texas Using the TIDDBIT HF Doppler Radar

    NASA Astrophysics Data System (ADS)

    Wene, G.; Crowley, G.; Fessler, B.; Bronn, J.

    2004-05-01

    Atmospheric gravity waves (AGW) are generated by numerous lower atmospheric processes, such as storms, and by auroral processes in the ionosphere. At ionospheric heights, the motion of the neutral gas in the AGW sets the ionosphere into motion. The waves displace the isoionic contours, resulting in a travelling ionospheric disturbance (TID). TIDs can be thought of as traveling corrugations in the ionosphere, and they can seriously affect HF radio communications and surveillance systems. Consequently, one of the most sensitive methods for detecting transient changes in the ionosphere is the HF Doppler technique operating in the 3-10 MHz band. A simple Doppler system consists of a CW (continuous wave) radio transmitter and receiver, which are highly frequency-stable. When a HF radio wave is reflected from the ionosphere, movement of the reflection point during passage of a TID produces a change in phase path and a Doppler shift proportional to the time rate of change of the phase path. The Doppler system is sensitive to motions of the ionospheric reflection point, and it therefore provides an accurate measure of both the TID and AGW periods. Similarly, because the TID velocity is determined simply from triangulation using the time-delays between perturbations at different reflection points, the TID velocities are also an accurate estimate of the underlying gravity wave horizontal and vertical trace velocities. HF Doppler systems have advantages over all other techniques for the measurement of TID characteristics. They are more amenable to analysis than data from ionosonde chains, and their time resolution (30 sec) is much higher than that of ionosondes . Unlike total electron content (TEC) methods, which respond to height-integrated TID effects, the HF Doppler radar responds to TIDs at the altitude of the radio reflection point. Finally, HF Doppler systems have low power consumption, so that both spatial and temporal resolution can be maintained for many days without

  8. Waves study in the Gulf of Naples by HF radar and buoy measurements

    NASA Astrophysics Data System (ADS)

    Saviano, Simona; Kalampokis, Alkiviadis; Uttieri, Marco; Zambianchi, Enrico

    2016-04-01

    An HF radar (25 MHz SeaSonde manufactured by CODAR Ocean Sensors Ltd.) has been operating in the Gulf of Naples (GoN) (Southeastern Tyrrhenian Sea) since 2004. HF radars use first-order echoes to determine surface currents, while second-order ones can be exploited to estimate the main parameters characterizing the wave field: wave direction, significant height (hs) and period (ps). Waves were studied in the GoN at three radar sites over a range cell located between 5 and 6 km from the coast. This choice, based upon preliminary sensitivity studies, allowed us to analyze the surface gravity wave field over an area of the basin where the depth is deep enough to avoid breaking, but at the same time close to the coast where the sea echo intensity is sufficiently high to ensure good data quality. The data acquired in the reference year 2012 are compared with the measurements collected over the same period by a directional waverider buoy installed offshore Capri island and managed by the Civil Protection Department of the Campania Region. The analysis aims at investigating the accuracy and the seasonal patterns of the wave parameters, showing the different responses of the wave field in different sectors of the GoN, and at verifying the agreement between the recordings of the two platforms. In addition, a coastal storm is studied to test the responsiveness of HF radars in critical environmental conditions. This work is a contribution to the Flagship Project RITMARE - The Italian Research for the Sea.

  9. Statistical study of TIDs using HF radar ground backscatter data and chirp sounding network MUF data

    NASA Astrophysics Data System (ADS)

    Oinats, Alexey; Kurkin, Vladimir; Nishitani, Nozomu; Ratovsky, Konstantin; Ivanova, Vera; Berngardt, Oleg

    We present statistical characteristics of traveling ionospheric disturbances (TIDs) revealed from the data of ground mid-latitude high frequency (HF) facilities that cover a wide longitudinal sector. Firstly, we analyzed an extensive dataset collected by SuperDARN Hokkaido HF radar since the late 2006 until 2014. A technique based on the cross-correlation analysis of minimal group range variations was used. We discuss diurnal and seasonal dependencies of predominant TIDs azimuth and apparent horizontal velocity as well as its solar and geomagnetic activity dependence. Further, we compare these statistical results with the same obtained using the first Russian SuperDARN Ekaterinburg HF radar data during 2013. In addition, we analyzed maximum usable frequency (MUF) series obtained by Russian oblique chirp sounding network. The network includes transmitters in Magadan, Norilsk, Khabarovsk and receiver in Tory (Irkutsk) and allow us to reveal large-scale TIDs characteristics in 2010-2011. This work was done under financial support of the Russian Foundation for Basic Research (grants 14-05-00259-a, 12-05-00865-a and 14-05-00588-a).

  10. UHF and HF Radar Studies of Langmuir Turbulence Experiments at HAARP

    NASA Astrophysics Data System (ADS)

    Sheerin, J. P.; Gerres, J. M.; Troyer, J. S.; Oyama, S. I.; Watkins, B. J.; Turnquist, J. E.; Bristow, W. A.; Heinselman, C. J.

    2007-05-01

    High power HF transmitters induce a number of plasma instabilities in the interaction region of overdense ionospheric plasma. Radars such as SuperDARN have been used to study artificial field-aligned irregularities (AFAI) created by the high power HF radiowave at the HAARP Ionospheric Observatory, Gakona, AK. A new Modular UHF Ionospheric Radar (MUIR) sited at HAARP, may now be used to monitor changes in the Langmuir plasma waves detected in the UHF backscatter. We report the results from recent campaigns using these new facilities in coordinated and comprehensive studies of strong Langmuir turbulence (SLT). Among the effects observed and studied are: SLT spectra including the outshifted plasma line or free-mode, appearance of a short timescale ponderomotive overshoot effect, temporal evolution of SLT, dependence of SLT on growth or suppression of AFAI, dependence of AFAI and MUIR backscatter on HAARP pulselength and duty-cycle, aspect angle dependence of the intensity of the plasma line. In particular, we explore the observed magnetic-zenith effect of increased turbulence with the HF wave directed up the field line. Langmuir modes parallel to the geomagnetic field are proposed to explain other features in stimulated electromagnetic emissions (SEE). These plasma waves are theorized to play a key role in certain features of radio-induced aurora. Experimental results are then compared to previous high latitude experiments and predictions from recent modeling efforts.

  11. UHF and HF Radar Studies of Langmuir Turbulence Experiments at HAARP

    NASA Astrophysics Data System (ADS)

    Sheerin, J. P.; Gerres, J. M.; Bacon, M. E.; Watkins, B. J.; Bristow, W. A.; Turnquist, J. E.; Oyama, S. I.; Heinselman, C. J.

    2007-12-01

    High power HF transmitters induce a number of plasma instabilities in the interaction region of overdense ionospheric plasma. Radars such as SuperDARN have been used to study artificial field-aligned irregularities (AFAI) created by the high power HF radiowave at the HAARP Ionospheric Observatory, Gakona, AK. A new Modular UHF Ionospheric Radar (MUIR) sited at HAARP, may now be used to monitor changes in the Langmuir plasma waves detected in the UHF backscatter. We report the results from recent campaigns using these new facilities in coordinated and comprehensive studies of strong Langmuir turbulence (SLT). Among the effects observed and studied are: SLT spectra including cascade, collapse, the outshifted plasma line or free-mode, appearance of a short timescale ponderomotive overshoot effect, temporal evolution of SLT, dependence of SLT on growth or suppression of AFAI, dependence of AFAI and MUIR backscatter on HAARP pulselength, duty-cycle, and aspect angle. In particular, we explore the aspect angle effect of increased turbulence with the HF wave directed at small angles to the field line. Langmuir modes parallel to the geomagnetic field are proposed to explain other features in stimulated electromagnetic emissions (SEE). These plasma waves are theorized to play a key role in certain features of radio-induced aurora. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.

  12. UHF and HF Radar Studies of Langmuir Turbulence Experiments at HAARP

    NASA Astrophysics Data System (ADS)

    Sheerin, J. P.; Gerres, J. M.; Troyer, J. S.; Oyama, S.; Watkins, B. J.; Turnquist, J. E.; Bristow, W. A.; Heinselman, C. J.

    2006-12-01

    High power HF transmitters induce a number of plasma instabilities in the interaction region of overdense ionospheric plasma. Radars such as SuperDARN have been used to study artificial field-aligned irregularities (AFAI) created by the high power HF radiowave at the HAARP Ionospheric Observatory, Gakona, AK. A new Modular UHF Ionospheric Radar (MUIR) sited at HAARP, may now be used to monitor changes in the Langmuir plasma waves detected in the UHF backscatter. We report the results from recent campaigns using these new facilities in coordinated and comprehensive studies of strong Langmuir turbulence (SLT). Among the effects observed and studied are: SLT spectra including the outshifted plasma line or `free- mode', appearance of a short timescale ponderomotive overshoot effect, temporal evolution of SLT, dependence of SLT on growth or suppression of AFAI, dependence of AFAI and MUIR backscatter on HAARP pulselength and duty-cycle, aspect angle dependence of the intensity of the plasma line. In particular, we explore the observed `magnetic-zenith' effect of increased turbulence with the HF wave directed up the field line. Langmuir modes parallel to the geomagnetic field are proposed to explain other features in stimulated electromagnetic emissions (SEE). These plasma waves are theorized to play a key role in certain features of radio-induced aurora. Experimental results are then compared to previous high latitude experiments and predictions from recent modeling efforts.

  13. Measurements of hf auroral clutter using the verona ava linear array radar (VALAR). Report for June 1990-June 1991

    SciTech Connect

    Choi, D.S.; Weijers, B.; Myers, N.B.

    1994-03-01

    Measurements of high frequency (HF) auroral clutter using the Verona Ava Linear Array Radar (VALAR) system are presented. VALAR is an experimental HF backscatter system capable of obtaining high resolution synoptic mapping of HF auroral clutter. The receive system includes a 700 meter long linear array. providing the high azimuthal resolution required for determining the spatial distribution of HF auroral clutter. Since the completion of the system at the end of 1989, data acquisition campaigns have been carried out on a near-monthly basis. In this report, the authors provide a brief description of VALAR and present preliminary measurements of three types of phenomena: ground backscatter, slant-F, and auroral backscatter.

  14. Determination of ionospheric parameters in real time using SuperDARN HF Radars

    NASA Astrophysics Data System (ADS)

    Bland, Emma C.; McDonald, Andrew J.; Larquier, Sebastien; Devlin, John C.

    2014-07-01

    A technique for determining key ionospheric parameters from high-frequency (HF) over-the-horizon radar ground scatter data is investigated using two Southern Hemisphere SuperDARN radars and also a Northern Hemisphere SuperDARN radar with reliable elevation angle-of-arrival capability. Ground scatter data are analyzed over a range of frequencies from 8 to 18 MHz to determine the maximum usable frequency and the vertical critical frequency over a wide geographical area within the radar field of view. The technique is shown to be well suited to middle to high latitudes where backscatter echoes from the ground dominate over those from ionospheric scattering targets. However, the technique is shown to break down during the winter months and away from solar maximum. It is shown that the use of reliable elevation angles can greatly enhance such methods allowing discrimination between ground scatter propagating via the E and F regions. It is also shown that contamination from very low velocity ionospheric scatter and ground scatter originating from the back lobe of the radar can be effectively filtered out, with the use of reliable elevation angles. This greatly improves the reliability of the ionospheric data products and allows for a high degree of automation of the process.

  15. Characterization of ocean surface current properties from single site HF/VHF radar

    NASA Astrophysics Data System (ADS)

    Marmain, Julien; Forget, Philippe; Molcard, Anne

    2011-11-01

    Surface current mapping from HF/VHF coastal radars traditionally requires at least two distant sites. Vector velocities are estimated by combining the radial velocity components measured by the radars. In many circumstances (e.g., failures, interferences, logistics constraints), such a combination is not possible by lack of data from one station. Two methods are evaluated to get information on surface circulation from a single site radar: the Vectorial Reconstruction Method (VRM) for current vector mapping and the Vortex Identification Method (VIM) for detecting eddy-like structures. The VRM assumes a non-divergent horizontal surface current, and the VIM analyzes radial velocities and their radial and orthoradial gradients. These two methods are tested on modeled and measured data sets in the Northwestern Mediterranean Sea where both high-resolution ocean circulation model and radar campaigns are available. The VRM performance is strongly limited by the divergence-free hypothesis which was not satisfied in our real data. The VIM succeeded in detection of vortex in the Gulf of Lions and from an operating single site radar located on the Provence coasts in summer.

  16. HF Radar Observations of Space Weather Effects in the Low and Mid-latitude Ionosphere

    NASA Astrophysics Data System (ADS)

    Menk, F. W.

    2015-12-01

    The ionosphere is dynamically coupled to the magnetosphere and hence diurnal and seasonal processes in the ionosphere are strongly influenced by space weather effects. These may vary the electron density distribution and cause changes in the reflection and absorption of HF radio signals. Other consequences include the formation of enhanced convective flows and irregularity features which may contribute to Doppler clutter. While there has been much discussion on the ionospheric signatures of magnetic storms at high latitudes, this presentation focuses on effects detected using mid- and low-latitude HF radars which examine field lines mapping to the vicinity of the ring current. Characteristic features include travelling ionospheric disturbances, high velocity flows and sustained irregular and quasi-sinusoidal 5 - 20 mHz waves recorded near the plasmapause. Such observations provide new insight on complex M-I coupling dynamics.

  17. Validation of HF Radar ocean surface currents in the Ibiza Channel using lagrangian drifters, moored current meter and underwater gliders

    NASA Astrophysics Data System (ADS)

    Lana, Arancha; Fernández, Vicente; Orfila, Alejandro; Troupin, Charles; Tintoré, Joaquín

    2015-04-01

    SOCIB High Frequency (HF) radar is one component of a multi-platform system located in the Balearic Islands and made up of Lagrangian platforms (profilers and drifting buoys), fixed stations (sea-level, weather, mooring and coastal), beach monitoring (camera), gliders, a research vessel as well as an ocean forecast system (waves and hydrodynamics). The HF radar system overlooks the Ibiza Channel, known as a 'choke point" where Atlantic and Mediterranean water masses interact and where meridional exchanges of water mass properties between the Balearic and the Algerian sub-basins take place. In order to determine the reliability of surface velocity measurements in this area, a quality assessment of the HF Radar is essential. We present the results of several validation experiments performed in the Ibiza Channel in 2013 and 2014. Of particular interest is an experiment started in September 2014 when a set of 13 surface drifters with different shapes and drogue lengths were released in the area covered by the HF radar. The drifter trajectories can be examined following the SOCIB Deployment Application (DAPP): http://apps.socib.es/dapp. Additionally, a 1-year long time series of surface currents obtained from a moored surface current-meter located in the Ibiza Channel, inside the area covered by the HF radar, was also used as a useful complementary validation exercise. Direct comparison between both radial surface currents from each radar station and total derived velocities against drifters and moored current meter velocities provides an assessment of the HF radar data quality at different temporal periods and geographical areas. Statistics from these comparisons give good correlation and low root-mean-square deviation. The results will be discussed for different months, geographical areas and types of surface drifters and wind exposure. Moreover, autonomous underwater glider constitutes an additional source of information for the validation of the observed velocity

  18. Reduction of ambiguities in HF radar results through a revised receiving antenna array and sounding pattern

    NASA Astrophysics Data System (ADS)

    Jarvis, M. J.; Dudeney, J. R.

    1986-02-01

    The reconfiguration of both the receiver dipole array and the pulse set used by the National Oceanic and Atmospheric Administration (NOAA) HF radar enables all ambiguity in polarization to be removed. Further, it enables the aliasing of Doppler velocities to be reduced by a factor of 2, which allows more flexibility in the pulse repetition rate used and permits lower velocities to be detected above the noise. The revised four-dipole array is L-shaped, with a crossed dipole at the corner. The addition of two extra dipoles provides the facility for unambiguous 'sky map' echo location.

  19. Investigation of height gradient in vertical plasma drift at equatorial ionosphere using multifrequency HF Doppler radar

    NASA Astrophysics Data System (ADS)

    Prabhakaran Nayar, S. R.; Sreehari, C. V.

    2004-12-01

    A multifrequency HF Doppler radar installed at the magnetic equatorial station Trivandrum provides an opportunity to study the height gradient in vertical plasma drift at the bottomside of equatorial F region during evening time. The multifrequency radar gives near-simultaneous observation of vertical plasma drift at three close by F region heights above the sounding station. The height gradient of the vertical drift shows a negative value during the prereversal enhancement (PRE) period and turns to positive value after the prereversal enhancement. The average height gradient in vertical plasma drift remains negative around PRE and its magnitude decreases with altitude, below F peak. This could be a clear-cut manifestation of the curl-free nature of the low-latitude electric field, and it could also indicate a partial signature of the postsunset velocity vortex at the equatorial F region. The magnitude of the mean height gradient around PRE exhibits a seasonal variation.

  20. Synergistic surface current mapping by spaceborne stereo imaging and coastal HF radar

    NASA Astrophysics Data System (ADS)

    Matthews, John Philip; Yoshikawa, Yutaka

    2012-09-01

    Well validated optical and radar methods of surface current measurement at high spatial resolution (nominally <100 m) from space can greatly advance our ability to monitor earth's oceans, coastal zones, lakes and rivers. With interest growing in optical along-track stereo techniques for surface current and wave motion determinations, questions of how to interpret such data and how to relate them to measurements made by better validated techniques arise. Here we make the first systematic appraisal of surface currents derived from along-track stereo Sun glitter (ATSSG) imagery through comparisons with simultaneous synoptic flows observed by coastal HF radars working at frequencies of 13.9 and 24.5 MHz, which return averaged currents within surface layers of roughly 1 m and 2 m depth respectively. At our Tsushima Strait (Japan) test site, we found that these two techniques provided largely compatible surface current patterns, with the main difference apparent in current strength. Within the northwest (southern) comparison region, the magnitudes of the ATSSG current vectors derived for 13 August 2006 were on average 22% (40%) higher than the corresponding vectors for the 1-m (2-m) depth radar. These results reflect near-surface vertical current structure, differences in the flow components sensed by the two techniques and disparities in instrumental performance. The vertical profile constructed here from ATSSG, HF radar and ADCP data is the first to resolve downwind drift in the upper 2 m of the open ocean. The profile e-folding depth suggests Stokes drift from waves of 10-m wavelength visible in the images.

  1. HF Radar for Long-Range Monitoring of Ionospheric Irregularities in the Equatorial Region

    NASA Astrophysics Data System (ADS)

    Pedersen, T. R.; Parris, R. T.; Dao, E. V.

    2014-12-01

    Ionospheric instabilities associated with plasma bubbles in the equatorial region are one of the major space weather impacts, creating scintillation that affects satellite communications and navigation as well as spread-F and propagation effects on lower frequency systems. Coherent scatter radars can be used to detect the presence of irregularities at a scale size corresponding to half the wavelength of the radar when the raypaths are perpendicular to the magnetic field. A number of vertical incidence radars operating in the VHF range near the magnetic equator use this effect to map out vertical irregularity structure in bubbles, while at high latitudes in both the northern and more recently southern hemisphere, HF radars in the SuperDARN network have successfully used refraction along near-horizontal paths to reach perpendicularity with the near-vertical magnetic field and map out ionospheric convection and irregularity structure over fields of view thousands of km across. In the equatorial region, perpendicularity can be obtained anywhere within a near-vertical plane even without refraction, although refraction can be used to achieve long ranges after one or more reflections from the earth's surface and bottomside ionosphere. This potentially provides a means of detecting and monitoring equatorial plasma bubbles over the oceans from long ranges using a small number of ground-based sites. We discuss the possible echoes that could be detected by such a system, the likely propagation modes and characteristics, and means of obtaining and utilizing elevation angle information to correctly locate distant plasma bubbles.

  2. Observations of very-high-latitude ionospheric irregularities with the Goose Bay HF (high frequency) radar

    SciTech Connect

    Greenwald, R.A.; Baker, K.B.

    1985-06-07

    The Goose Bay HF radar is a sophisticated instrument capable of providing detailed information on very-high-latitude E- and F-region ionospheric electron-density irregularities which act as a source of clutter on OTH radar systems. Through the use of two parallel phased-array antennas, this instrument is able to image the location of these irregularities within a three-dimensional volume covering much of northeastern Canada and Greenland. It is also capable of following the temporal variability of these irregularities as well as determining unambiguously the Doppler shift and broadening of radar signals scattered by them. This paper presents initial results with a single phased-array antenna, which represent typical examples of the spatial intensity distribution of these irregularities at different local times. Examples are presented of Doppler spectra of the irregularities at different local times. Data of this type are of appreciable value in ascertaining the techniques that must be utilized to improve clutter mitigation on high-latitude radar systems.

  3. Characteristics of medium-scale traveling ionospheric disturbances observed near the Antarctic Peninsula by HF radar

    NASA Astrophysics Data System (ADS)

    Grocott, A.; Hosokawa, K.; Ishida, T.; Lester, M.; Milan, S. E.; Freeman, M. P.; Sato, N.; Yukimatu, A. S.

    2013-09-01

    We present a survey of medium-scale traveling ionospheric disturbances (MSTIDs) observed by a Super Dual Auroral Radar Network HF radar located in the Falkland Islands between May 2010 and April 2011. The radar has a field of view that overlooks the Antarctic Peninsula, a known hot spot of gravity wave activity. We present observations of radar ground-backscatter data, in which the signatures of MSTIDs are manifested as structured enhancements in echo power. Observed periods were in the range 30-80 min, corresponding to frequencies of 0.2-0.6 mHz. Wavelengths were generally in the range 200-800 km and phase speeds in the range 100-300 m s-1. These values are within the ranges typically associated with medium-scale gravity waves. We find a primary population of northward (equatorward) propagating MSTIDs, which demonstrate an association with enhanced solar wind-magnetosphere coupling and a smaller, westward propagating population, that could be associated with atmospheric gravity waves excited by winds over the Andean and Antarctic Peninsula mountains or by the high winds of the Antarctic Polar Vortex.

  4. Quality assurance and control issues for HF radar wave and current measurements

    NASA Astrophysics Data System (ADS)

    Wyatt, Lucy

    2015-04-01

    HF radars are now widely used to provide surface current measurements over wide areas of the coastal ocean for scientific and operational applications. In general data quality is acceptable for these applications but there remain issues that impact on the quantity and quality of the data. These include problems with calibration and interference which impact on both phased array (e.g. WERA, Pisces) and direction-finding (e.g. SeaSonde) radars. These same issues and others (e.g. signal-to-noise, in-cell current variability, antenna sidelobes) also impact on the quality and quantity of wave data that can be obtained. These issues will be discussed in this paper, illustrated with examples from deployments of WERA, Pisces and SeaSonde radars in the UK, Europe, USA and Australia. These issues involve both quality assurance (making sure the radars perform to spec and the software is fully operational) and in quality control (identifying problems with the data due to radar hardware or software performance issues and flagging these in the provided data streams). Recommendations for the former, and current practice (of the author and within the Australian Coastal Ocean Radar Network, ACORN*) for the latter, will be discussed. The quality control processes for wave measurement are not yet as well developed as those for currents and data from some deployments can be rather noisy. Some new methods, currently under development by SeaView Sensing Ltd and being tested with ACORN data, will be described and results presented. *ACORN is a facility of the Australian Integrated Marine Observing System, IMOS. IMOS is a national collaborative research infrastructure, supported by Australian Government. It is led by University of Tasmania in partnership with the Australian marine and climate science community.

  5. The Long Wavelength Array (LWA): A Large HF/VHF Array for Solar Physics, Ionospheric Science, and Solar Radar

    NASA Astrophysics Data System (ADS)

    Kassim, N.; White, S.; Rodriquez, P.; Hartman, J.; Hicks, B.; Lazio, J.; Stewart, K.; Craig, J.; Taylor, G.; Cormier, C.; Romero, V.; Jenet, F.

    2010-09-01

    The Long Wavelength Array (LWA), currently under construction in New Mexico, will be an imaging HF/VHF interferometer providing a new approach for studying the Sun-Earth environment from the surface of the sun to the Earth’s ionosphere. The LWA will be a powerful tool for solar physics and space weather investigations, through its ability to characterize a diverse range of low-frequency, solar-related emissions, thereby increasing our understanding of particle acceleration and shocks in the solar atmosphere along with their impact on the Sun-Earth environment. As a passive receiver the LWA will directly detect Coronal Mass Ejections (CMEs) in emission, and indirectly through the scattering of cosmic background sources as they propagate towards Earth. If coupled with a suitable transmitter, the LWA would be an excellent receiver for solar radar, potentially demonstrating accurate geomagnetic storm prediction from the Earth’s surface. Both radar and passive receiving techniques could monitor the Sun-Earth environment during daytime as a compliment to nighttime space weather remote sensing techniques. The LWA will also naturally provide a measure of small-scale spatial and temporal ionospheric structure, a pre-requisite for accurate calibration and imaging of solar and space weather phenomena. As a sensitive monitor of differences in total electron content (TEC) through the ionosphere, the LWA will provide an unprecedented characterization of ionospheric turbulence and waves, capable of testing predictions of global ionospheric models with an aim towards improving their accuracy through input to physics-based models. As a fully digital, multi-beaming instrument, the LWA can monitor the Sun daily with a dedicated solar beam, while simultaneously pursuing ionospheric and astrophysics science programs both day and night. In this paper we present an overview of the LWA, currently under construction in New Mexico, and discuss the scientific goals of the project in the

  6. Causes of HF Backscatter Loss During Large Geomagnetic Storms: Comparisons between Northern and Southern Hemisphere SuperDARN Radars

    NASA Astrophysics Data System (ADS)

    Currie, J. L.; Waters, C. L.; Menk, F. W.; Sciffer, M. D.

    2015-12-01

    HF communication and surveillance systems are known to experience difficulty during geomagnetic storm conditions. The Super Dual Auroral Radar Network (SuperDARN) comprises over 35, HF (8-12 MHz) over-the-horizon radars used to study ionosphere dynamics and HF propagation. It is well known that SuperDARN radars experience a loss of backscatter during geomagnetic storm events, yet details of the reasons why this occurs are not clear. Loss of HF backscatter during geomagnetic storms is often attributed to D region absorption. However, the data shows that during intense geomagnetic storms, SuperDARN radars return high signal/noise ratio, backscatter from ranges out to ~800 km, inconsistent with loss due to absorption in the D region. Examples of SuperDARN backscatter during large storms will be presented and discussed together with HF ray-tracing, ionosonde and riometer data. Data from Kodiak in the north and Bruny Island in the south hemisphere are compared. These reveal properties of the ionosphere as the storm progresses and show hemisphere similarities and differences. Possible backscatter loss mechanisms will be discussed, given the evidence derived from the experimental data.

  7. Mapping ionospheric backscatter measured by the SuperDARN HF radars - Part 2: Assessing SuperDARN virtual height models

    NASA Astrophysics Data System (ADS)

    Yeoman, T. K.; Chisham, G.; Baddeley, L. J.; Dhillon, R. S.; Karhunen, T. J. T.; Robinson, T. R.; Senior, A.; Wright, D. M.

    2008-05-01

    The Super Dual Auroral Radar Network (SuperDARN) network of HF coherent backscatter radars form a unique global diagnostic of large-scale ionospheric and magnetospheric dynamics in the Northern and Southern Hemispheres. Currently the ground projections of the HF radar returns are routinely determined by a simple rangefinding algorithm, which takes no account of the prevailing, or indeed the average, HF propagation conditions. This is in spite of the fact that both direct E- and F-region backscatter and 1 1/2-hop E- and F-region backscatter are commonly used in geophysical interpretation of the data. In a companion paper, Chisham et al. (2008) have suggested a new virtual height model for SuperDARN, based on average measured propagation paths. Over shorter propagation paths the existing rangefinding algorithm is adequate, but mapping errors become significant for longer paths where the roundness of the Earth becomes important, and a correct assumption of virtual height becomes more difficult. The SuperDARN radar at Hankasalmi has a propagation path to high power HF ionospheric modification facilities at both Tromsø on a 1/2-hop path and SPEAR on a 1 1/2-hop path. The SuperDARN radar at Þykkvibǽr has propagation paths to both facilities over 1 1/2-hop paths. These paths provide an opportunity to quantitatively test the available SuperDARN virtual height models. It is also possible to use HF radar backscatter which has been artificially induced by the ionospheric heaters as an accurate calibration point for the Hankasalmi elevation angle of arrival data, providing a range correction algorithm for the SuperDARN radars which directly uses elevation angle. These developments enable the accurate mappings of the SuperDARN electric field measurements which are required for the growing number of multi-instrument studies of the Earth's ionosphere and magnetosphere.

  8. HF Doppler and VHF radar observations of upper atmospheric disturbances caused by weak cold front during winter time

    NASA Technical Reports Server (NTRS)

    Hung, R. J.; Lee, C. C.; Gao, M.; Johnson, D. L.; Yang, F. W.

    1990-01-01

    The simultaneous use of the Taiwan VHF radar and the HF Doppler sounder for remote measurement of three-dimensional winds, gravity waves, and density perturbations at mesospheric and thermospheric heights is demonstrated. A special event of atmospheric disturbances caused by propagating gravity waves excited by weak convective motions in winter time were investigated. The three-dimensional wind velocities at different heights were determined, and the frequency, horizontal wavelength, vertical wavelength, and phase velocity of the gravity waves were measured. The subtropical, low-latitude site makes the VHF radar and HF Doppler array systems unique, and the observations especially valuable for space projects dealing with low-latitude atmosphere.

  9. Surface circulation patterns at the southeastern Bay of Biscay: new observations from HF radar data

    NASA Astrophysics Data System (ADS)

    Solabarrieta, L.; Rubio, A.; Medina, R.; Paduan, J. D.; Castanedo, S.; Fontán, A.; Cook, M.; González, M.

    2012-12-01

    A CODAR Seasonde High Frequency (HF) radar network has been operational since the beginning of 2009 for the oceanic region of the Basque Country, Spain (south-eastern Bay of Biscay, Atlantic Ocean). It forms part of the Basque operational data acquisition system, established by the Directorate of Emergency Attention and Meteorology of the Basque Government. It is made up of two antennas, at the capes Higer (43d 23.554' N, 1d 47.745' W) and Matxitxako (43d 7.350' N, 2d 45.163' W), emitting at 4.525 MHz frequency and 30 kHz bandwidth. This system provides hourly surface currents with 5.12 km spatial resolution, covering 10,000 km2. Space- and time-covering measurements have been available in the study area since 2009. The data contribute considerably to the study of surface current patterns and the main physical processes in the area. Additional applications relate to security of navigation, maritime rescue, validation and improvement of numerical models, etc. For comparison with other validation studies and to obtain an estimate of the performance of the Basque system, statistical and spectral analysis of the surface currents obtained through the HF radar and different in-situ platforms have been conducted. The analyses show values of comparison between the different measuring systems consistent with those done by other authors (Paduan and Rosenfeld, 1996; Kaplan et al., 2005). The radar is able to reproduce the time evolution of the currents with a reasonable accuracy; likewise, the main three spectral peaks (inertial, semidiurnal and diurnal) are well resolved. In this context, the aim of this work is to show the HF radar ability to measure accurately the surface currents in the south-eastern Bay of Biscay and to study the ocean circulation in the area (figures 1 and 2). Surface current patterns are analysed and described for the period 2009-2011, for different timescales. A clear seasonality at a large-scale has been observed in accordance with previous work

  10. HF radar signatures of the cusp and low-latitude boundary layer

    NASA Technical Reports Server (NTRS)

    Baker, K. B.; Dudeney, J. R.; Greenwald, R. A.; Pinnock, M.; Newell, P. T.; Rodger, A. S.; Mattin, N.; Meng, C.-I.

    1995-01-01

    Continuous ground-based observations of ionospheric and magnetospheric regions are critical to the Geospace Environmental Modeling (GEM) program. It is therefore important to establish clear intercalibrations between different ground-based instruments and satellites in order to clearly place the ground-based observations in context with the corresponding in situ satellite measurements. HF-radars operating at high latitudes are capable of observing very large spatial regions of the ionosphere on a nearly continuous basis. In this paper we report on an intercalibration study made using the Polar Anglo-American Conjugate Radar Experiment radars located at Goose Bay, Labrador, and Halley Station, Antarctica, and the Defense Meteorological Satellite Program (DMSP) satellites. The DMSP satellite data are used to provide clear identifications of the ionospheric cusp and the low-latitude boundary layer (LLBL). The radar data for eight cusp events and eight LLBL events have been examined in order to determine a radar signature of these ionospheric regions. This intercalibraion indicates that the cusp is always characterized by wide, complex Doppler power spectra, whereas the LLBL is usually found to have spectra dominated by a single component. The distribution of spectral widths in the cusp is of a generally Gaussian form with a peak at about 220 m/s. The distribution of spectral widths in the LLBL is more like an exponential distribution, with the peak of the distribution occurring at about 50 m/s. There are a few cases in the LLBL where the Doppler power spectra are strikingly similar to those observed in the cusp.

  11. Currents, Tides and Waves measured by an HF Radar in the Gulf of Naples

    NASA Astrophysics Data System (ADS)

    Falco, Pierpaolo; Buonocore, Berardino; Cianelli, Daniela; Di Lemma, Roberta; Giordano, Alberto; Iermano, Ilaria; Kalampokis, Alkiviadis; Saviano, Simona; Uttieri, Marco; Zambardino, Giovanni; Zambianchi, Enrico

    2015-04-01

    An HF radar has been operating in the Gulf of Naples (Southeastern Tyrrhenian Sea) since 2004. The system is a SeaSonde manufactured by CODAR Ocean Sensors Ltd. Three mono-static radar units working at about 25 Mhz ensure the surface current mapping over nearly the entire Gulf of Naples area. The grid resolution is 1 Km with a range of approximately 40 Km. From continuous observations of the surface current fields several characteristics of the surface circulation were assessed. One of the most prominent evidences is the wind field forcing of the surface current, which determines different but recurrent circulation patterns affecting the transport and the off-in shore exchanges. The analysis of long and continuous current observations has revealed significant tidal currents. Previous studies regarding the tide magnitude in the Southern Tyrrhenian Sea showed a very limited tidal contribution to the current field. The determination of tidal current in the Gulf of Naples has pointed out a prevalent diurnal contribution and intensity values up to a maximum of 10 cm/s. Waves are one of the most important elements in a coastal management framework. HF radar may provide an estimate of the main parameters characterizing the wave field: wave direction, significant height and period. Waves were studied in the Gulf of Naples over a range cell located between 5 and 6 km from the coast. This choice, based upon preliminary sensitivity studies, allowed us to analyze the surface gravity wave field over an area of the Gulf where the depth is not too shallow and the sea echo intensity is sufficiently high to ensure good data quality. A pluriannual wave observation time series was studied in order to depict typical seasonal patterns.

  12. Kilometric irregularities in the E and R regions of the daytime equatorial ionosphere observed by a high resolution HF radar

    SciTech Connect

    Blanc, E.; Mercandalli, B.; Houngninou, E.

    1996-03-15

    The authors describe results from a vertically oriented HF radar operated in the Ivory Coast, which studied irregularities in the E and F regions of the equatorial ionosphere. The authors report on irregularity observations at heights consistent with the equatorial electrojet, and at heights above the electrojet, and into the F1 layer. They observe irregularities into the F region in this work. The radar operated in the frequency range from 1 to 8 MHz.

  13. Evolution of the Detached Westward Flow Channel as Observed by the Unwin HF Radar

    NASA Astrophysics Data System (ADS)

    Makarevich, R. A.; Dyson, P. L.

    2005-12-01

    We examine the spatial and temporal evolution of latitudinally narrow regions with enhanced Doppler velocity observed by the Unwin TIGER HF radar equatorward of Auroral Westward Flow Channels. AWFCs were detected by both the Bruny Island and New Zealand (Unwin) TIGER radars as regions with enhanced westward convection, at about -62 deg MLAT. A second, more equatorward (~ -60 deg MLAT) channel with enhanced westward convection was detected only by the Unwin radar. The spatio-temporal behaviour of the second channel and its characteristics were found to be significantly different from those of AWFCs, e.g. both the channel and flow directions were significantly non-L-shell-aligned. We also investigate the relationship between the flow speeds within the two types of flow channels. In all cases, the second channel appeared to originate within or close to the AWFC, with the flow deviation from the magnetic L-shell direction and latitudinal separation between channels increasing with time. In sharp contrast to the AWFC that persisted for 2-3 hours, the second channel was recognizable only for 30-50 min. A relation between multiple flow channels and other subauroral phenomena such as subauroral ion drifts (SAID) and subauroral polarization streams (SAPS), and the implications of observations for models of SAID and SAPS formation are discussed.

  14. An MF/HF radio array for radio and radar imaging of the ionosphere

    NASA Astrophysics Data System (ADS)

    Isham, Brett; Gustavsson, Bjorn; Belyey, Vasyl; Bullett, Terrence

    2016-07-01

    The Aguadilla Radio Array will be installed at the Interamerican University Aguadilla Campus, located in northwestern Puerto Rico. The array is intended for broad-band medium and high-frequency (MF/HF, roughly 2 to 25 MHz) radio and bistatic radar observations of the ionosphere. The main array consists of 20 antenna elements, arranged in a semi-random pattern providing a good distribution of baseline vectors, with 6-meter minimum spacing to eliminate spacial aliasing. A relocatable 6-element array is also being developed, in which each element consists of a crossed pair of active electric dipoles and all associated electronics for phase-coherent radio measurements. A primary scientific goal of the array is to create images of the region of ionospheric radio emissions stimulated by the new Arecibo Observatory high-power high-frequency radio transmitter. A second primary goal is the study of ionospheric structure and dynamics via coherent radar imaging of the ionosphere in collaboration with the University of Colorado / NOAA Versatile Interferometric Pulsed Ionospheric Radar (VIPIR), located at the USGS San Juan Observatory in Cayey, Puerto Rico. In addition to ionospheric research in collaboration with the Cayey and Arecibo Observatories, the goals of the project include the development of radio sounding, polarization, interferometry, and imaging techniques, and training of students at the university and high school levels.

  15. UHF Radar observations at HAARP with HF pump frequencies near electron gyro-harmonics and associated ionospheric effects

    NASA Astrophysics Data System (ADS)

    Watkins, Brenton; Fallen, Christopher; Secan, James

    Results for HF modification experiments at the HAARP facility in Alaska are presented for experiments with the HF pump frequency near third and fourth electron gyro-harmonics. A UHF diagnostic radar with range resolution of 600 m was used to determine time-dependent altitudes of scattering from plasma turbulence during heating experiments. Experiments were conducted with multiple HF frequencies stepped by 20 kHz above and below the gyro-harmonic values. During times of HF heating the HAARP facility has sufficient power to enhance large-scale ionospheric densities in the lower ionosphere (about 150-200 km altitude) and also in the topside ionosphere (above about 350 km). In the lower ionosphere, time-dependent decreases of the altitude of radar scatter result from electron density enhancements. The effects are substantially different even for relatively small frequency steps of 20 kHz. In all cases the time-varying altitude decrease of radar scatter stops about 5-10 km below the gyro-harmonic altitude that is frequency dependent; we infer that electron density enhancements stop at this altitude where the radar signals stop decreasing with altitude. Experiments with corresponding total electron content (TEC) data show that for HF interaction altitudes above about 170 km there is substantial topside electron density increases due to upward electron thermal conduction. For lower altitudes of HF interaction the majority of the thermal energy is transferred to the neutral gas and no significant topside density increases are observed. By selecting an appropriate HF frequency a little greater than the gyro-harmonic value we have demonstrated that the ionospheric response to HF heating is a self-oscillating mode where the HF interaction altitude moves up and down with a period of several minutes. If the interaction region is above about 170 km this also produces a continuously enhanced topside electron density and upward plasma flux. Experiments using an FM scan with the HF

  16. HF (HIGH FREQUENCY) RADAR MEASUREMENTS OF CIRCULATION IN THE EASTERN STRAIT OF JUAN DE FUCA (AUGUST, 1978)

    EPA Science Inventory

    During August, 1978, the surface currents in the Eastern Strait of Juan de Fuca were mapped with a High Frequency (HF) radar system (CODAR). The surface currents were measured simultaneously over several hundred square kilometers at one hour intervals continuously for five days. ...

  17. HF (HIGH FREQUENCY) RADAR MEASUREMENTS OF CIRCULATION IN THE EASTERN STRAIT OF JUAN DE FUCA NEAR PROTECTION ISLAND (JULY, 1979)

    EPA Science Inventory

    During July 1979 the surface currents in the Eastern Strait of Juan de Fuca were mapped with a High Frequency (HF) radar system (CODAR). These currents were measured simultaneously over several hundred square kilometers continuously for five days. The strong tidal currents and es...

  18. Occurrence characteristics of Mesosphere Summer Echoes observed by the SuperDARN Hokkaido HF radar

    NASA Astrophysics Data System (ADS)

    Tsuya, T.; Nishitani, N.; Ogawa, T.; Tsutsumi, M.; Yukimatu, A. S.

    2013-12-01

    At high latitudes in summer, neutral temperature of the mesopause around the 85 km altitude goes below about 150 K, heavy charged ice aerosol particles are generated, which reduce electron diffusivity. Neutral air turbulence in combination with the reduced electron diffusivity leads to the creation of structures which backscatter radio waves (Rapp and Lübken, ACP, 2004). As a result, the echoes backscattered near the mesopause are frequently observed in summer in the polar region as Polar Mesosphere Summer Echoes (PMSEs). In recent years mesosphere echoes have been observed not only in the polar region but also at midlatitudes as Mesosphere Summer Echoes (MSEs) (Ogawa et al., JASTP, 2011). In this study, we present a statistical analysis of MSEs observed by the midlatitude SuperDARN Hokkaido HF radar (geographic latitude: +43.53 N deg). We make use of the criteria for identifying MSEs adopted by Ogawa et al. (EPS, in press) who have performed an event study of MSE using the SuperDARN Hokkaido radar. As a result, MSEs are observed more frequently in the daytime (07 to 18 LT) and summer (in particular June and July) than other local times and seasons. This result is similar to the characteristics of PMSEs previously reported by Hosokawa et al. (GRL, 2005) using high latitude SuperDARN radars. MSEs are often contaminated with echoes from the Es layer. In order to identify MSEs exactly and understand the generation mechanisms of MSEs at midlatitudes, it is important to obtain neutral wind information near the mesopause because some MSE structures might be transported from higher latitudes by neutral winds (Singer et al., ASR, 2003), which affect the Doppler velocity of MSEs. If the Doppler velocity of MSEs is consistent with neutral wind velocity, it becomes credible that the echoes are MSEs. In this aspect we can set more appropriate criterion for identifying MSEs by accounting for the altitude distribution of neutral winds. We use the technique employed by Yukimatu

  19. Validation of HF radar probing of the vertical shear of surface currents by acoustic Doppler current profiler measurements

    NASA Astrophysics Data System (ADS)

    Ivonin, Dmitry V.; Broche, Pierre; Devenon, Jean-Luc; Shrira, Victor I.

    2004-04-01

    There exists no practical way of measuring vertical shear in the water just below the air/sea interface that contains information on air/water momentum fluxes. The paper is concerned with the validation of a recently proposed method of remote sensing of sea subsurface shear by means of a commonly used single-frequency HF radar based on the use of the second-order Bragg echo. To this end a dedicated field experiment was carried out off the French Mediterranean coast. In parallel with the HF radar probing, the independent simultaneous measurements of the subsurface shear profile were obtained by means of acoustic Doppler current profiler mounted on a floating platform, whose position was monitored by GPS. The comparison shows a fairly good agreement of the results (the discrepancy does not exceed 15%) and suggests a higher accuracy of the HF probing.

  20. 74. Transmitter building no. 102, view of radar digital test ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    74. Transmitter building no. 102, view of radar digital test and maintenance cabinet area control panel and date storage system showing ampex tape storage devices. - Clear Air Force Station, Ballistic Missile Early Warning System Site II, One mile west of mile marker 293.5 on Parks Highway, 5 miles southwest of Anderson, Anderson, Denali Borough, AK

  1. Spatial and temporal behavior of ULF pulsations observed by the Goose Bay HF radar

    NASA Technical Reports Server (NTRS)

    Walker, A. D. M.; Ruohoniemi, J. M.; Baker, K. B.; Greenwald, R. A.; Samson, J. C.

    1992-01-01

    Techniques which allow the instantaneous amplitude and phase to be determined as functions of geomagnetic lattitude, longitude, and time are employed to carry out a detailed analysis of HF radar data of a ULF pulsation event in the postmidnight sector on January 11, 1989. Field line resonances with several different frequencies occur simultaneously at different latitudes. These can be associated with cavity mode frequencies of 1.3 mHz, 1.9 mHz, 2.7 mGz, and 3.3 mHz. These frequencies are constant to better than 10 percent over a local time period of nearly 4 hr. The field-aligned currents driven by the resonances can be as large as 5 micro-A/sq m at ionospheric heights. The data support a picture of modes driven by solar wind impulses.

  2. Effects of geomagnetic pulsations on the Doppler shift of HF backscatter radar echoes

    NASA Astrophysics Data System (ADS)

    Bourdillon, A.; Delloue, J.; Parent, J.

    1989-04-01

    Three mechanisms are considered for studying the effects of geomagnetic pulsations on the Doppler shifts of HF backscatter radar echoes: (1) variation of the phase refractive index under the influence of the varying magnetic component, (2) modulation of the plasma density, and (3) electrodynamic drift of the ionosphere. The electrodynamic drift is shown to be the most probable efficient mechanism to account for the measured Doppler shifts. In this model the Doppler shift on F-region propagation modes is sensitive to the eastward electric field of the wave, while E-region propagation modes are sensitive to the northward and eastward components with weights depending on the reflection height. Pi 2 and Pc 3 effects on the Doppler shift are presented, along with an example of the effects of Pi 2 pulsations on F-region and Es-region propagation modes.

  3. Wave parameters comparisons between High Frequency (HF) radar system and an in situ buoy: a case study

    NASA Astrophysics Data System (ADS)

    Fernandes, Maria; Alonso-Martirena, Andrés; Agostinho, Pedro; Sanchez, Jorge; Ferrer, Macu; Fernandes, Carlos

    2015-04-01

    The coastal zone is an important area for the development of maritime countries, either in terms of recreation, energy exploitation, weather forecasting or national security. Field measurements are in the basis of understanding how coastal and oceanic processes occur. Most processes occur over long timescales and over large spatial ranges, like the variation of mean sea level. These processes also involve a variety of factors such as waves, winds, tides, storm surges, currents, etc., that cause huge interference on such phenomena. Measurement of waves have been carried out using different techniques. The instruments used to measure wave parameters can be very different, i.e. buoys, ship base equipment like sonar and satellites. Each equipment has its own advantage and disadvantage depending on the study subject. The purpose of this study is to evaluate the behaviour of a different technology available and presently adopted in wave measurement. In the past few years the measurement of waves using High Frequency (HF) Radars has had several developments. Such a method is already established as a powerful tool for measuring the pattern of surface current, but its use in wave measurements, especially in the dual arrangement is recent. Measurement of the backscatter of HF radar wave provides the raw dataset which is analyzed to give directional data of surface elevation at each range cell. Buoys and radars have advantages, disadvantages and its accuracy is discussed in this presentation. A major advantage with HF radar systems is that they are unaffected by weather, clouds or changing ocean conditions. The HF radar system is a very useful tool for the measurement of waves over a wide area with real-time observation, but it still lacks a method to check its accuracy. The primary goal of this study was to show how the HF radar system responds to high energetic variations when compared to wave buoy data. The bulk wave parameters used (significant wave height, period and

  4. HF Doppler radar observations of sporadic E at an Indian low latitude station, Visakhapatnam

    NASA Astrophysics Data System (ADS)

    Sarma, M. S. S. R. K. N.; Raghava Reddy, C.; Niranjan, K.

    2009-02-01

    5.5 MHz HF Doppler radar observations of Sporadic E over an Indian low latitude station, Visakhapatnam (17.7° N, 83.3° E and Dip 20°) with 10 s resolution showed quasi-periodic variations of the echo strength and Doppler velocity variations with periods of a few minutes to a few tens of minutes. The echo strength and Doppler velocity variations with time in different range bins of the ES echo showed variations which are some times similar and some times significantly different in successive range bins at intervals of 7.5 km. The ES echo occurs with the height of maximum echo strength in the range of 100 km to 120 km and some times at 130 km. The altitude variation of the average Doppler velocity is highly variable and the height of maximum echo strength is not the same as the height of maximum Doppler velocity. Observations of ES echoes at different times of the day are presented to bring out the differences between the day and night time ES echoes. The relationship between Radar and ES parameters derived from Ionograms is poorer than that of mid latitudes which is quite consistent with the expectations based on gradient drift instability.

  5. Digital filter design for radar image formation

    NASA Technical Reports Server (NTRS)

    Adams, John W.; Nelson, Jeffrey E.; Banh, N. D.; Moncada, John J.; Bayma, Robert W.

    1989-01-01

    Novel weighted-least-squares approaches to the design of digital filters for SAR applications are presented. The filters belong to three different categories according to their combinations of minimax passband, least-squares stopband, minimax stopband, and maximally-flat passband. For real-time applications, it is important to design the sets of digital filter coefficient tables in an offline environment; the appropriate precomputed filter is then selected for each SAR signal-processing function, as a function of both mode and mapping geometry during real-time processing.

  6. Evaluation Digital Elevation Model Generated by Synthetic Aperture Radar Data

    NASA Astrophysics Data System (ADS)

    Makineci, H. B.; Karabörk, H.

    2016-06-01

    Digital elevation model, showing the physical and topographical situation of the earth, is defined a tree-dimensional digital model obtained from the elevation of the surface by using of selected an appropriate interpolation method. DEMs are used in many areas such as management of natural resources, engineering and infrastructure projects, disaster and risk analysis, archaeology, security, aviation, forestry, energy, topographic mapping, landslide and flood analysis, Geographic Information Systems (GIS). Digital elevation models, which are the fundamental components of cartography, is calculated by many methods. Digital elevation models can be obtained terrestrial methods or data obtained by digitization of maps by processing the digital platform in general. Today, Digital elevation model data is generated by the processing of stereo optical satellite images, radar images (radargrammetry, interferometry) and lidar data using remote sensing and photogrammetric techniques with the help of improving technology. One of the fundamental components of remote sensing radar technology is very advanced nowadays. In response to this progress it began to be used more frequently in various fields. Determining the shape of topography and creating digital elevation model comes the beginning topics of these areas. It is aimed in this work , the differences of evaluation of quality between Sentinel-1A SAR image ,which is sent by European Space Agency ESA and Interferometry Wide Swath imaging mode and C band type , and DTED-2 (Digital Terrain Elevation Data) and application between them. The application includes RMS static method for detecting precision of data. Results show us to variance of points make a high decrease from mountain area to plane area.

  7. Statistical study of high-latitude E-region Doppler spectra obtained with the SHERPA HF radar

    NASA Astrophysics Data System (ADS)

    Hanuise, C.; Villain, J. P.; Cerisier, J. C.; Senior, C.; Ruohoniemi, J. M.; Greenwald, R. A.; Baker, K. B.

    1991-04-01

    A large number of Doppler spectra obtained at six HF frequencies in the E region with the SHERPA HF radar are analyzed statistically. They are characterized by their total power, their mean velocity and their spectral width. The observations cover geomagnetic conditions varying from quiet to disturbed. Due to the location of the auroral oval relative to the radar field of view, echoes are preferentially detected in the morning westward electrojet, with radial velocities away from the radar. This results in an asymmetrical velocity distribution. Both usual Type 1 and Type 2 Doppler spectra, associated with two-stream and gradient-drift waves, respectively, are at the origin of the two peaks in the distribution. Other spectral types do not appear in the statistics. Spectral widths remain narrow for both types. This is explained by a longer lifetime of wave trains compared to higher frequency waves detected by VHF radars. A decrease of the Doppler velocity with radar frequency is related to gradient effects on threshold, as predicted by the linear dispersion equation for the two-stream instability.

  8. Synthetic aperture radar and digital processing: An introduction

    NASA Technical Reports Server (NTRS)

    Dicenzo, A.

    1981-01-01

    A tutorial on synthetic aperture radar (SAR) is presented with emphasis on digital data collection and processing. Background information on waveform frequency and phase notation, mixing, Q conversion, sampling and cross correlation operations is included for clarity. The fate of a SAR signal from transmission to processed image is traced in detail, using the model of a single bright point target against a dark background. Some of the principal problems connected with SAR processing are also discussed.

  9. Fully digital foliage-penetrating synthetic aperature radar processor

    NASA Astrophysics Data System (ADS)

    Arnold, Stephen; Hsu, Charles C.; Zaghloul, Mona E.; Szu, Harold H.; Karangelen, Nicholas E.; Buss, James R.

    2001-03-01

    A high performance, fully digital Foliage Penetrating Synthetic Aperture Radar (FOPEN SAR) system is described. The FOPEN SAR algorithm is illustrated using Matlab. Digital implementation is derived and simulated using VHDL. The complex mathematical functions required by the algorithm have been demonstrated. Simulations have achieved an SNR equals 290 dB when compared to the baseline results from Matlab. The accuracy of the simulation was limited by the resolution of certain trigonometric and exponential functions implemented using VHDL, and thus can be improved upon. This would allow greater flexibility between speed/area considerations without degradation of the target resolution (100dB-signal accuracy).

  10. Evaluation of two algorithms for a network of coastal HF radars in the Mid-Atlantic Bight

    NASA Astrophysics Data System (ADS)

    Kohut, Josh; Roarty, Hugh; Randall-Goodwin, Evan; Glenn, Scott; Lichtenwalner, C. Sage

    2012-06-01

    The National High Frequency (HF) Surface Current Mapping Radar Network is being developed as a backbone system within the U.S. Integrated Ocean Observing System. This paper focuses on the application of HF radar-derived surface current maps to U.S. Coast Guard Search and Rescue operations along the Mid-Atlantic coast of the USA. In that context, we evaluated two algorithms used to combine maps of radial currents into a single map of total vector currents. In situ data provided by seven drifter deployments and four bottom-mounted current meters were used to (1) evaluate the well-established unweighted least squares (UWLS) and the more recently adapted optimal interpolation (OI) algorithms and (2) quantify the sensitivity of the OI algorithm to varying decorrelation scales and error thresholds. Results with both algorithms were shown to depend on the location within the HF radar data footprint. The comparisons near the center of the HF radar coverage showed no significant difference between the two algorithms. The most significant distinction between the two was seen in the drifter trajectories. With these simulations, the weighting of radial velocities by distance in the OI implementation was very effective at reducing both the distance between the actual drifter and the cluster of simulated particles as well as the scale of the search area that encompasses them. In this study, the OI further reduced the already improved UWLS-based search areas by an additional factor of 2. The results also indicated that the OI output was relatively insensitive to the varying decorrelation scales and error thresholds tested.

  11. Comparison of D-region Doppler drift winds measured by the SuperDARN Finland HF radar over an annual cycle using the Kiruna VHF meteor radar

    NASA Astrophysics Data System (ADS)

    Arnold, N. F.; Cook, P. A.; Robinson, T. R.; Lester, M.; Chapman, P. J.; Mitchell, N.

    2003-10-01

    The SuperDARN chain of oblique HF radars has provided an opportunity to generate a unique climatology of horizontal winds near the mesopause at a number of high latitude locations, via the Doppler shifted echoes from sources of ionisation in the D-region. Ablating meteor trails form the bulk of these targets, but other phenomena also contribute to the observations. Due to the poor vertical resolution of the radars, care must be taken to reduce possible biases from sporadic-E layers and Polar Mesospheric Summer echoes that can affect the effective altitude of the geophysical parameters being observed. Second, there is strong theoretical and observational evidence to suggest that the radars are picking up echoes from the backward looking direction that will tend to reduce the measured wind strengths. The effect is strongly frequency dependent, resulting in a 20% reduction at 12 MHz and a 50% reduction at 10 MHz. A comparison of the climatologies observed by the Super-DARN Finland radar between September 1999 and September 2000 and that obtained from the adjacent VHF meteor radar located at Kiruna is also presented. The agreement between the two instruments was very good. Extending the analysis to the SuperDARN Iceland East radar indicated that the principles outlined above could be applied successfully to the rest of the SuperDARN network.

  12. Experimental investigation of the relationship between HF radar measurements of currents and the dynamical properties of the upper ocean.

    NASA Astrophysics Data System (ADS)

    Fraunie, Philippe

    2014-05-01

    Forget P., Barbin Y., Bellomo L., Doglioli, *Lecuyer E., Fraunié P., Malengros D., Marmain J., Molcard A., Petrenko A., Quentin C., *Sentchev A. Mediterranean Institute of Oceanography-MIO UM 110 UTLN - AMU - CNRS/INSU 7294 - IRD 235 BP 20132 F-83957 La Garde cedex *Laboratoire d'Océanologie et Géosciences CNRS UMR 8187 LOG Université du Littoral - Côte d'Opale 32 avenue Foch, 62930 Wimereux The increasing application of HF radio-oceanography for coastal circulation monitoring requires a validation of the radar derived current velocities using independent velocity estimates. Surface currents measured by radar, as they are relative to some finite patch of the sea (the radar cell), depend on the spatial distribution of the current within the radar cell, its time variability, its vertical structure near the surface and the presence of ocean waves. We present an experimental investigation conducted in the NW Mediterranean to measure radial surface currents by HF radar simultaneously to the dynamical properties of the surface ocean. These latter included high resolution current profiling by ADCP, microprofiling of temperature/salinity by SCAMP and Lagrangian velocities from surface drifting buoys. All the data were GPS geo-localized. The current profiling by towed ADCP was performed along the radar beam directions. The poster shows the first results of the experiment and presents samples of the 3D structure of the horizontal current (down to 15m and over some km2) and of the stratification. The spatial distribution of the surface currents is described from Lagrangian measurements. The radar derived surface currents are discussed on the basis of these in situ data. Acknowledgements : This research was supported by the LEFE IMAGO program of CNRS -INSU, project SUBCORAD.

  13. Model of the Long Island Sound outflow: Comparison with year-long HF radar and Doppler current observations

    NASA Astrophysics Data System (ADS)

    Mau, Jenq-Chi; Wang, Dong-Ping; Ullman, David S.; Codiga, Daniel L.

    2008-08-01

    A three-dimensional primitive-equation model is used to simulate the Long Island Sound (LIS) outflow for a 1-year (2001) period. The model domain includes LIS and New York Bight (NYB). Tidal and wind forcing are included, and seasonal salinity and temperature variations are assimilated. The model results are validated with the HF radar, moored acoustic Doppler current profiler (ADCP), and ferry-based ADCP observations. The agreement between simulated and observed flow patterns generally is very good. The difference in seasonal mean currents between the model and moored ADCP is about 0.01 m/s; the correlation of dominant velocity fluctuations between the model and HF radar is 0.83; and the difference in mean LIS transport between the model and shipboard ADCP is about 5%. However, the model predicts a prominent tidally generated headland eddy not supported by the HF radar observation. The model sensitivity study indicates that the tides, winds, and ambient coastal front all have important impact on the buoyant outflow. The tides and winds cause stronger vertical mixing, which reduces the surface plume strength. The ambient coastal front, on the other hand, tends to enhance the plume.

  14. An EOF analysis of HF Doppler radar current measurements of the Chesapeake Bay buoyant outflow

    NASA Astrophysics Data System (ADS)

    Marmorino, G. O.; Shay, L. K.; Haus, B. K.; Handler, R. A.; Graber, H. C.; Horne, M. P.

    1999-02-01

    Surface currents measured by HF Doppler radar as part of a study of the Chesapeake Bay outflow plume are examined using a 'real-vector' empirical orthogonal function (EOF) analysis (Kaihatu et al., 1998). Based on about 23 days of nearly continuous data, the analysis shows that the first three EOF modes, judged to be the only significant modes, account for 76% of the variance in the data set. The buoyant outflow occurs primarily in the mean flow field. The first EOF mode is dominated by wind forcing and the second mode by across-shelf semi-diurnal tidal forcing. The third mode exhibits a large-scale horizontal shear and contains a curved region of weak relative flow which appears to delineate the offshore edge of the plume; also, the third-mode response varies over the spring-neap cycle, suggesting a modulation of the outflow plume by a tidal residual eddy. The analysis therefore has provided a useful, exploratory examination of this dataset of surface currents.

  15. 47 CFR 73.758 - System specifications for digitally modulated emissions in the HF broadcasting service.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 4 2013-10-01 2013-10-01 false System specifications for digitally modulated emissions in the HF broadcasting service. 73.758 Section 73.758 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES RADIO BROADCAST SERVICES International Broadcast Stations § 73.758 System specifications...

  16. 47 CFR 73.758 - System specifications for digitally modulated emissions in the HF broadcasting service.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 4 2012-10-01 2012-10-01 false System specifications for digitally modulated emissions in the HF broadcasting service. 73.758 Section 73.758 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES RADIO BROADCAST SERVICES International Broadcast Stations § 73.758 System specifications...

  17. Coherent HF radar backscatter from small-scale irregularities in the dusk sector of the subauroral ionosphere

    NASA Technical Reports Server (NTRS)

    Ruohoniemi, J. M.; Greenwald, R. A.; Villain, J.-P.; Baker, K. B.; Newell, P. T.

    1988-01-01

    This paper describes the characteristics of backscatter from decameter-scale ionospheric plasma density irregualarities, observed with an impressive regularity by the Goose Bay (Labrador) high-frequency (HF) radar in the dusk sector of the winter ionosphere, and discusses the relation of the scatter to the midlatitude trough. It is shown that this dusk scatter can be readily distinguished from other types of late afternoon/early evening scatter by the extreme equatorward position of its source region and by the low values of its associated radar Doppler velocities (not above 200 m/s) and spectral widths (not more than 200 m/s). A comparison of the radar observations with nearly simultaneous particle precipitation data obtained with the DMSP F6 satellite demonstrated that the source region of the backscatter lies within the subauroral ionosphere. It is shown that the characteristics of dusk scatter are compatible with the Spiro et al. (1978) model of the electrodynamics of the midlatitude trough.

  18. Interference-Detection Module in a Digital Radar Receiver

    NASA Technical Reports Server (NTRS)

    Fischman, Mark; Berkun, Andrew; Chu, Anhua; Freedman, Adam; Jourdan, Michael; McWatters, Dalia; Paller, Mimi

    2009-01-01

    A digital receiver in a 1.26-GHz spaceborne radar scatterometer now undergoing development includes a module for detecting radio-frequency interference (RFI) that could contaminate scientific data intended to be acquired by the scatterometer. The role of the RFI-detection module is to identify time intervals during which the received signal is likely to be contaminated by RFI and thereby to enable exclusion, from further scientific data processing, of signal data acquired during those intervals. The underlying concepts of detection of RFI and rejection of RFI-contaminated signal data are also potentially applicable in advanced terrestrial radio receivers, including software-defined radio receivers in general, receivers in cellular telephones and other wireless consumer electronic devices, and receivers in automotive collision-avoidance radar systems.

  19. Characterization of HF Propagation for Digital Audio Broadcasting

    NASA Technical Reports Server (NTRS)

    Vaisnys, Arvydas

    1997-01-01

    The purpose of this presentation is to give a brief overview of some propagation measurements in the Short Wave (3-30 MHz) bands, made in support of a digital audio transmission system design for the Voice of America. This task is a follow on to the Digital Broadcast Satellite Radio task, during which several mitigation techniques would be applicable to digital audio in the Short Wave bands as well, in spite of the differences in propagation impairments in these two bands. Two series of propagation measurements were made to quantify the range of impairments that could be expected. An assessment of the performance of a prototype version of the receiver was also made.

  20. Observation by HF radar of the Phillips resonance mechanism for generation of wind waves

    SciTech Connect

    Trizna, D.B.; Bogle, R.W.; Moore, J.C.; Howe, C.M.

    1980-09-20

    Measurements are reported of directional ocean wave spectra made over 80/sup 0/ of viewing angle by an HF radar, operating in the surface wave mode in an area 22.5 km north of San Clemente Island, California. Ten azimuths from 280/sup 0/ to 360/sup 0/ true bearing were simultaneously measured for 10 wave frequencies ranging from 0.14 Hz (75 m waves) to 0.35 Hz (13 m waves). A Waverider buoy was used to measure omnidirectional energy in the region, and first-order radar Bragg lines were used to determine the spreading of wave energy with angle. Data are presented in which a bimodal spectrum was present: an attenuated spectrum with wave components to 0.10 Hz from a storm at sea at 270/sup 0/ bearing; plus a transient local wind spectrum, stronger in amplitude at the higher frequencies, with wave cutoff near 0.14 Hz, and running from 315/sup 0/ bearing. Just after the onset of local winds, the westerly spectrum fitted a cosine squared spread at the lowest measured frequencies. With the development of local wind, which blew at a 12--14 kn (6--7 m s/sup -1/) speed for a period of 12 hours, the wave spectrum spread about the wind direction as cosine thirty-second at the lowest frequencies measured, 0.14 Hz, and cosine sixty-fourth at the highest frequencies measured, 0.35 Hz. For 0.28 Hz waves the Phillips resonance mechanism for wave generation is proposed to explain the twin peaks in amplitude observed, equally spaced either side of the wind direction. These were dominant for the earliest measurement period and still were major contributions for later measurement periods. This mechanism was found to contribute also at the higher wave frequencies, as predicted by theory. Coherence times are derived from the angular widths of the Phillips resonances based on predictions of Stewart and Manton and are found to agree quite well with theory.

  1. Development of a digital receiver for range imaging atmospheric radar

    NASA Astrophysics Data System (ADS)

    Yamamoto, Masayuki K.; Fujita, Toshiyuki; Abdul Aziz, Noor Hafizah Binti; Gan, Tong; Hashiguchi, Hiroyuki; Yu, Tian-You; Yamamoto, Mamoru

    2014-10-01

    In this paper, we describe a new digital receiver developed for a 1.3-GHz range imaging atmospheric radar. The digital receiver comprises a general-purpose software-defined radio receiver referred to as the Universal Software Radio Peripheral 2 (USRP2) and a commercial personal computer (PC). The receiver is designed to collect received signals at an intermediate frequency (IF) of 130 MHz with a sample rate of 10 MS s-1. The USRP2 digitizes IF received signals, produces IQ time series, and then transfers the IQ time series to the PC through Gigabit Ethernet. The PC receives the IQ time series, performs range sampling, carries out filtering in the range direction, decodes the phase-modulated received signals, integrates the received signals in time, and finally saves the processed data to the hard disk drive (HDD). Because only sequential data transfer from the USRP2 to the PC is available, the range sampling is triggered by transmitted pulses leaked to the receiver. For range imaging, the digital receiver performs real-time signal processing for each of the time series collected at different frequencies. Further, the receiver is able to decode phase-modulated oversampled signals. Because the program code for real-time signal processing is written in a popular programming language (C++) and widely used libraries, the signal processing is easy to implement, reconfigure, and reuse. From radar experiments using a 1-μs subpulse width and 1-MHz frequency span (i.e., 2-MHz frequency bandwidth), we demonstrate that range imaging in combination with oversampling, which was implemented for the first time by the digital receiver, is able to resolve the fine-scale structure of turbulence with a vertical scale as small as 100 m or finer.

  2. Nonlinear inversion of the integral equation to estimate ocean wave spectra from HF radar

    NASA Astrophysics Data System (ADS)

    Hisaki, Yukiharu

    1996-01-01

    Since all ocean wave components contribute to the second-order scattering of a high-frequency radio wave by the sea surface, it is theoretically possible to estimate the ocean wave spectrum from first- and second-order scattering in the Doppler spectrum measured with an HF ocean radar. To extract the wave spectral information, however, it is necessary to solve a nonlinear integral equation. This paper describes in detail how to solve the nonlinear integral equation without linearization or approximation. We show that the problem of solving the nonlinear integral equation can be converted into a nonlinear optimization problem. An algorithm to find the optimal solution is described. Examples of the algorithm applied to simulated data and measured data are shown. The wave frequency spectrum can be estimated even if the Doppler spectrum is available in only a single direction. In this case, however, the solution of the two-dimensional wavenumber spectrum tends to converge to a spectrum that is symmetrical to the beam direction. Even if the wave spectrum is dominant in a single direction, the solution may give two peaks in the wavenumber spectrum. One of them is the true peak and the other is the mirror image of it with respect to the beam direction. This ambiguity can be avoided by using Doppler spectra measured in at least two different directions. Although there is still some room for improvement in the practical application of this method, it can be applied to estimate the wave directional spectrum up to a rather high frequency, or Bragg frequency.

  3. Spatial and temporal behavior of ULF pulsations observed by the Goose Bay HF radar

    SciTech Connect

    Walker, A.D.M.; Ruohoniemi, J.M.; Baker, K.B.; Greenwald, R.A. ); Samson, J.C. )

    1992-08-01

    A detailed analysis of HF radar data of a ULF pulsation event in the postmidnight sector on January 11, 1989, has been carried out using techniques which allow the instantaneous amplitude and phase to be determined as functions of geomagnetic latitude, longitude, and time. Field line resonances with several different frequencies occur simultaneously at different latitudes. These can be associated with cavity mode frequencies of 1.3 mHz, 1.9 mHz, 2.7 mHz, and 3.3 mHz. In addition there is a resonance at 0.8 mHz which does not fit well with a cavity picture. These frequencies are constant to better than 10% over a local time period of nearly 4 hours. They show a packet structure as would be expected if they were triggered by a succession of impulses. The phase changes arbitrarily from packet to packet, but the frequency remains constant. The position of the maximum of the resonance as a function of time changes systematically. It is shown that this arises as the length of the field line changes with time; the resonance remains on the field line having appropriate length and Alfven speed. The field-aligned currents driven by the resonances can be as large as 5 {mu}A m{sup {minus}2} at ionospheric heights. The data support a picture of modes driven by solar wind impulses. It may be more appropriate to speak of a waveguide rather than a cavity with the phase velocity of the mode matching the velocity of the impulse along the magnetopause. A difficulty associated with this picture is that the great reproducibility of the frequencies is not consistent with the variability of the magnetopause, which forms one of the boundaries of the assumed resonator. It is, however, difficult to conceive of other resonators, for example in the magnetotail, which would provide a better explanation of the observations.

  4. Validation of Orthorectified Interferometric Radar Imagery and Digital Elevation Models

    NASA Technical Reports Server (NTRS)

    Smith Charles M.

    2004-01-01

    This work was performed under NASA's Verification and Validation (V&V) Program as an independent check of data supplied by EarthWatch, Incorporated, through the Earth Science Enterprise Scientific Data Purchase (SDP) Program. This document serves as the basis of reporting results associated with validation of orthorectified interferometric interferometric radar imagery and digital elevation models (DEM). This validation covers all datasets provided under the first campaign (Central America & Virginia Beach) plus three earlier missions (Indonesia, Red River: and Denver) for a total of 13 missions.

  5. Statistical characteristics of medium-scale traveling ionospheric disturbances revealed from the Hokkaido East and Ekaterinburg HF radar data

    NASA Astrophysics Data System (ADS)

    Oinats, Alexey V.; Nishitani, Nozomu; Ponomarenko, Pavlo; Berngardt, Oleg I.; Ratovsky, Konstantin G.

    2016-01-01

    We present a statistical study of medium-scale traveling ionospheric disturbances (MSTIDs) using the Hokkaido East (43.53° N, 143.61° E) and Ekaterinburg (56.42° N, 58.53° E) high-frequency (HF) radar data. Radar datasets are available from 2007 to 2014 for the Hokkaido and from 2013 to 2014 for the Ekaterinburg radar. In the case of the Hokkaido East radar, we have utilized the elevation angle information to study the MSTIDs propagating at the heights of the E and F ionospheric regions separately. We have analyzed the diurnal and seasonal behavior of the following medium-scale traveling ionospheric disturbance (MSTID) parameters: propagation direction, apparent horizontal velocity and wavelength, period, and relative amplitude. The F region MSTID azimuthal patterns were observed to be quite similar by the two radars. The E region northwestward MSTIDs (from 280° to 320°) were typical of summer daytime. Comparison with the horizontal wind model (HWM07) has showed that the dominant MSTID propagation directions match the anti-wind direction well, at least during sunlight hours. We have also found that the wavelength and period tend to decrease with an increase in solar activity. On the contrary, the relative amplitude increases with an increase in solar activity. Moreover, the relative amplitude tends to increase with increasing auroral electrojet (AE) index, as do the wavelength and velocity.

  6. Elliptical storm cell modeling of digital radar data

    NASA Technical Reports Server (NTRS)

    Altman, F. J.

    1972-01-01

    A model for spatial distributions of reflectivity in storm cells was fitted to digital radar data. The data were taken with a modified WSR-57 weather radar with 2.6-km resolution. The data consisted of modified B-scan records on magnetic tape of storm cells tracked at 0 deg elevation for several hours. The MIT L-band radar with 0.8-km resolution produced cross-section data on several cells at 1/2 deg elevation intervals. The model developed uses ellipses for contours of constant effective-reflectivity factor Z with constant orientation and eccentricity within a horizontal cell cross section at a given time and elevation. The centers of the ellipses are assumed to be uniformly spaced on a straight line, with areas linearly related to log Z. All cross sections are similar at different heights (except for cell tops, bottoms, and splitting cells), especially for the highest reflectivities; wind shear causes some translation and rotation between levels. Goodness-of-fit measures and parameters of interest for 204 ellipses are considered.

  7. Digital Radar-Signal Processors Implemented in FPGAs

    NASA Technical Reports Server (NTRS)

    Berkun, Andrew; Andraka, Ray

    2004-01-01

    High-performance digital electronic circuits for onboard processing of return signals in an airborne precipitation- measuring radar system have been implemented in commercially available field-programmable gate arrays (FPGAs). Previously, it was standard practice to downlink the radar-return data to a ground station for postprocessing a costly practice that prevents the nearly-real-time use of the data for automated targeting. In principle, the onboard processing could be performed by a system of about 20 personal- computer-type microprocessors; relative to such a system, the present FPGA-based processor is much smaller and consumes much less power. Alternatively, the onboard processing could be performed by an application-specific integrated circuit (ASIC), but in comparison with an ASIC implementation, the present FPGA implementation offers the advantages of (1) greater flexibility for research applications like the present one and (2) lower cost in the small production volumes typical of research applications. The generation and processing of signals in the airborne precipitation measuring radar system in question involves the following especially notable steps: The system utilizes a total of four channels two carrier frequencies and two polarizations at each frequency. The system uses pulse compression: that is, the transmitted pulse is spread out in time and the received echo of the pulse is processed with a matched filter to despread it. The return signal is band-limited and digitally demodulated to a complex baseband signal that, for each pulse, comprises a large number of samples. Each complex pair of samples (denoted a range gate in radar terminology) is associated with a numerical index that corresponds to a specific time offset from the beginning of the radar pulse, so that each such pair represents the energy reflected from a specific range. This energy and the average echo power are computed. The phase of each range bin is compared to the previous echo

  8. Digital HF communications for the polar regions - a low-cost alternative to satellite?

    NASA Astrophysics Data System (ADS)

    Prior-Jones, Michael; Warrington, Mike

    2010-05-01

    Digital HF communications for the polar regions - a low-cost alternative to satellite? Prior-Jones, M.R. and Warrington, E. M Communications within the polar regions pose unique technical challenges, due to the physical isolation, lack of infrastructure and extreme weather conditions. Geostationary satellite links are widely used, but they cannot function poleward of 80 degrees due to the curvature of the Earth. Low-earth-orbit systems like Iridium and ARGOS will function all the way to the poles. However, they are expensive, particularly for experiments requiring long time-series. Transferring data by Iridium satellite phone costs of the order of 60USD per megabyte. HF (i.e. 3-30 MHz) radio signals propagate via the ionosphere, allowing long distance transmission beyond the horizon. Ranges of thousands of kilometres can be easily achieved with relatively low transmission powers when propagation is favourable. The polar ionosphere is, however, a challenging environment for radio signals - the signals often reflect from multiple regions of the ionosphere and by multiple hops with intermediate ground reflections producing multipath effects. As the ionosphere is moving, these signals are also subject to very significant Doppler shifts that add to the complexity of the environment. These effects may make data communications at polar latitudes difficult or impossible at times and often only at low data rates. In this paper we discuss our experiments to use modern signal-processing and modulation techniques for digital transmission on HF, offering a similar speed to satellite but without paying the high cost of satellite airtime. Using an HF channel simulator developed by Warrington et al based on measurements of propagation at high latitudes, we have tested the performance of an OFDM-based modem derived from the Digital Radio Mondiale standard used for digital HF broadcasting and found that it outperforms current military modems developed by NATO (STANAG 4285 and 4539

  9. Advanced ground-penetrating radar for digital soil mapping

    NASA Astrophysics Data System (ADS)

    Lambot, S.; Minet, J.; Jadoon, K. Z.; Slob, E.; Vereecken, H.

    2009-04-01

    Sustainable and optimal agricultural and environmental management of water and land resources particularly relies on the description and understanding of soil water distribution and dynamics at different scales. We present an advanced ground penetrating radar (GPR) method for mapping the shallow soil water content and unsaturated hydraulic properties at the field scale. The radar system is based on vector network analyzer technology, for which calibration is simple and constitutes an international standard. A directive horn antenna is used as both transmitter and receiver and operates off the ground. A full-waveform model describes accurately the radar signal, and is based on a linear system of complex transfer functions for efficiently describing electromagnetic phenomena within the antenna and its interaction with soil, and a specific solution of the three-dimensional Maxwell's equations for wave propagation in multilayered media. The soil electromagnetic properties and their vertical distribution are estimated by resorting to full-waveform inverse modeling using iterative global optimization methods. The proposed methodology has been validated for a series of model configurations of increasing complexity. The method is now routinely used for real-time mapping of soil surface water content and reconstruct a few number of shallow soil layers. For more complex configurations, it is necessary to regularize the inverse problem. We have shown that constraining radar data inversion using soil hydrodynamic modeling has the potential to reconstruct time-lapse, continuously variable, vertical soil water content profiles and identify the shallow unsaturated hydraulic properties. The proposed approach shows great promise for quantitative imaging of the soil properties at the field scale. The technique will be combined with electromagnetic induction in a mechanistic data fusion framework to further extend its capabilities in a digital soil mapping context.

  10. Surface circulation in the Strait of Gibraltar: a comparison study between HF radar and high resolution model data.

    NASA Astrophysics Data System (ADS)

    Soto-Navarro, Javier; Lorente, Pablo; Álvarez-Fanjul, Enrique; Ruiz-Gil de la Serna, M. Isabel

    2015-04-01

    Surface currents from the HF radar system deployed by Puertos del Estado (PdE) at the Strait of Gibraltar and an operational high resolution configuration of the MIT global circulation model, implemented in the strait area in the frame of the SAMPA project, have been analyzed and compared in the period February 2013 - September 2014. The comparison have been carried out in the time and frequency domains, by statistical a geophysical (tide ellipses, wind forcing, EOF) methods. Results show good agreement between both current fields in the strait axis, with correlation around 0.6 (reaching 0.9 in the low frequency band). Higher discrepancies are found in the boundaries of the domain, due to the differences in the meridional components, likely related to the sparser and less accurate radar measurements in these areas. Rotary spectral analysis show a very good agreement between both systems, which is reflected in a very similar and realistic representation of the main tide constituents (M2, S2 and K1). The wind forced circulation pattern, of special interest in the mouth of the Bay of Algeciras, is also precisely represented by radar and model. Finally, the spatial patterns of the first four EOF modes of both fields are rather close, reinforcing the previous results. As conclusion, the analysis points out the proper representation of the surface circulation of the area performed by the PdE HF radar system and the SAMPA model. However, weak and strong points are found in both, stressing the importance of having two complementary tools in the area.

  11. Mapping ionospheric backscatter measured by the SuperDARN HF radars - Part 1: A new empirical virtual height model

    NASA Astrophysics Data System (ADS)

    Chisham, G.; Yeoman, T. K.; Sofko, G. J.

    2008-05-01

    Accurately mapping the location of ionospheric backscatter targets (density irregularities) identified by the Super Dual Auroral Radar Network (SuperDARN) HF radars can be a major problem, particularly at far ranges for which the radio propagation paths are longer and more uncertain. Assessing and increasing the accuracy of the mapping of scattering locations is crucial for the measurement of two-dimensional velocity structures on the small and meso-scale, for which overlapping velocity measurements from two radars need to be combined, and for studies in which SuperDARN data are used in conjunction with measurements from other instruments. The co-ordinates of scattering locations are presently estimated using a combination of the measured range and a model virtual height, assuming a straight line virtual propagation path. By studying elevation angle of arrival information of backscatterred signals from 5 years of data (1997-2001) from the Saskatoon SuperDARN radar we have determined the actual distribution of the backscatter target locations in range-virtual height space. This has allowed the derivation of a new empirical virtual height model that allows for a more accurate mapping of the locations of backscatter targets.

  12. Methods for the extraction of long-period ocean wave parameters from narrow beam HF radar sea echo

    NASA Astrophysics Data System (ADS)

    Lipa, Belinda; Barrick, Donald

    1980-07-01

    This paper describes inversion methods for HF radar sea echo Doppler spectra, giving parameters of the ocean wave spectrum in the important long-wavelength region. Radar spectra exhibiting very narrow spikes in the higher-order structure adjacent to the first-order lines are indicative of ocean wave components with a single dominant wavelength. In the simplest method of interpretation these components are assumed to be unidirectional; in this case we show how to extract wave period, direction, and rms wave height. If this simple model does not provide a good fit to the data or if the radar side bands have the form of broad peaks, we use a model for the wave spectrum with a cardioid distribution in direction and a Gaussian distribution in wave frequency. Parameters identifiable from this model include the rms wave height, dominant direction and period, and the angular spread in the direction and frequency distributions. In normal surface wave experiments the major source of error or noise is the random surface height of the sea; we describe the resulting statistics of the radar spectrum and trace the propagation of uncertainty to the derived ocean parameters.

  13. Surface circulation in the Iroise Sea (western Brittany) derived from high resolution current mapping by HF radars

    NASA Astrophysics Data System (ADS)

    Sentchev, Alexei; Forget, Philippe; Barbin, Yves; Marié, Louis; Ardhuin, Fabrice

    2010-05-01

    The use of high frequency radar (HFR) systems for near-real-time coastal ocean monitoring necessities that short time scale motions of the radar-derived velocities are better understood. While the ocean radar systems are able to describe coastal flow patterns with unprecedented details, the data they produce are often too sparse or gappy for applications such as the identification of coherent structures and fronts or understanding transport and mixing processes. In this study, we address two challenges. First, we report results from the HF radar system (WERA) which is routinely operating since 2006 on the western Brittany coast to monitor surface circulation in the Iroise Sea, over an area extending up to 100 km offshore. To obtain more reliable records of vector current fields at high space and time resolution, the Multiple Signal Classification (MUSIC) direction finding algorithm is employed in conjunction with the variational interpolation (2dVar) of radar-derived velocities. This provides surface current maps at 1 km spacing and time resolution of 20 min. Removing the influence of the sea state on radar-derived current measurements is discussed and performed on some data sequences. Second, we examine in deep continuous 2d velocity records for a number of periods, exploring the different modes of variability of surface currents in the region. Given the extent, duration, and resolution of surface current velocity measurements, new quantitative insights from various time series and spatial analysis on higher frequency kinematics will be discussed. By better characterizing the full spectrum of flow regimes that contribute to the surface currents and their shears, a more complete picture of the circulation in the Iroise Sea can be obtained.

  14. Surface current patterns observed by HF radar: methodology and analysis of currents to the north of the Yaeyama Islands, East China Sea

    NASA Astrophysics Data System (ADS)

    Hisaki, Yukiharu; Kashima, Motohiko; Kojima, Shoichiro

    2016-03-01

    A new method was developed to compare the classifications of different kind of data maps based on the self-organizing map (SOM) analysis. The surface current maps of the northern coast of Ishigaki and Iriomote Islands, East China Sea, observed by high-frequency (HF) radar were classified by SOM. Winds, sea surface temperatures (SST), and reanalysis data were also classified by SOM. The optimum area for classification was determined objectively by the new method, which relates these patterns to HF radar current patterns. We found two typical surface patterns: the first was that northeastward flows are dominant in the observation area and the second was that a clockwise eddy was also dominant in this area. The southwestward wind pattern was strongly related to the dominant clockwise eddy pattern of the HF radar current field.

  15. Comparison with oblique sounder data of high-latitude HF propagation predictions from RADAR C and AMBCOM computer program

    NASA Astrophysics Data System (ADS)

    Dave, Nikhil

    1988-06-01

    A study is done using two High Frequency (HF) propagation prediction programs - RADAR C and AMBCOM - to determine how well they predict median values of oblique sounder data of maximum observed frequencies (MOF) at high latitudes. The main differences between RADAR C and AMBCOM are the inclusion in the latter of high-latitude ionosphere and auroral absorption models, as well as a more sophisticated and accurate ray-tracing scheme. The data used for comparison are taken for the Winnipeg-Resolute Bay path in the year 1959 and for the Andoya-Ft. Monmouth and Andoya-College paths in 1964. The data for the Winnipeg-Resolute Bay corresponds to high sunspot number, while the others correspond to low sunspot number. Hence, this study provides information on the performance of the two programs for various high-latitude paths at both high and low sunspot number. AMBCOM was found to give generally better agreement with the above data than did RADAR C. Comparison of details of model predictions from the two computer programs for the above data-base is used to form an understanding of this improvement in prediction capability.

  16. Characteristics of daytime mid-latitude travelling ionospheric disturbances observed over the Antarctic peninsular with HF radar

    NASA Astrophysics Data System (ADS)

    Grocott, A.; Hosokawa, K.; Ishida, T.; Lester, M.; Milan, S. E.; Sato, N.; Yukimatu, A. S.

    2012-12-01

    We present a survey of travelling ionospheric disturbances (TIDs) observed by an HF radar located in the Falkland Islands between March 2010 and September 2011. The radar has a field of view that overlooks the Antarctic peninsular, a known hotspot of gravity wave activity. We present observations of radar ground backscatter data, in which the signatures of TIDs are manifest as structured enhancements in received backscattered power. Often, multiple TID signals are observed during an interval of observations and we discuss a new approach to their interpretation. Observed periods were in the range 30 - 60 minutes, corresponding to frequencies of 0.3 - 0.6 mHz. Wavelengths were generally in the range 250 - 400 km and phase speeds in the range 50 - 200 m/s. These values are within the ranges typically associated with medium-scale gravity waves. We discuss these results in terms of seasonal and diurnal variations, as well as in terms of their relationship to the local topography and large-scale geomagnetic activity.

  17. 38. Perimeter acquisition radar building room #414, digital/electrical repair shop; ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    38. Perimeter acquisition radar building room #414, digital/electrical repair shop; showing work areas available for maintenance and equipment repair - Stanley R. Mickelsen Safeguard Complex, Perimeter Acquisition Radar Building, Limited Access Area, between Limited Access Patrol Road & Service Road A, Nekoma, Cavalier County, ND

  18. Mapping near-inertial variability in the SE Bay of Biscay from HF radar data and two offshore moored buoys

    NASA Astrophysics Data System (ADS)

    Rubio, A.; Reverdin, G.; Fontán, A.; González, M.; Mader, J.

    2011-10-01

    HF radar surface current data together with data from two operational offshore oceanographic buoys located over the slope are used to map the variability associated with the near-inertial waves, during a target year (2009), in the SE Bay of Biscay. The results obtained show the complex 4D distribution of inertial oscillations in this area. We find a very pronounced horizontal structure across the area with ranges of a factor 5 in near-inertial kinetic energy. This pattern presents also strong seasonal variability, with a peak in KE closer to the shelf-break in summer, whereas winter maximum is weaker and located further to the north-east. The mooring data indicate more trapping near the surface in summer. These patterns are discussed in relation to the known seasonal differences in atmospheric/buoyancy forcing and the characteristics of the sub-inertial surface velocity field.

  19. A combined QC methodology in Ebro Delta HF radar system: real time web monitoring of diagnostic parameters and offline validation of current data

    NASA Astrophysics Data System (ADS)

    Lorente, Pablo; Piedracoba, Silvia; Soto-Navarro, Javier; Ruiz, Maria Isabel; Alvarez Fanjul, Enrique

    2015-04-01

    Over recent years, special attention has been focused on the development of protocols for near real-time quality control (QC) of HF radar derived current measurements. However, no agreement has been worldwide achieved to date to establish a standardized QC methodology, although a number of valuable international initiatives have been launched. In this context, Puertos del Estado (PdE) aims to implement a fully operational HF radar network with four different Codar SeaSonde HF radar systems by means of: - The development of a best-practices robust protocol for data processing and QC procedures to routinely monitor sites performance under a wide variety of ocean conditions. - The execution of validation works with in-situ observations to assess the accuracy of HF radar-derived current measurements. The main goal of the present work is to show this combined methodology for the specific case of Ebro HF radar (although easily expandable to the rest of PdE radar systems), deployed to manage Ebro River deltaic area and promote the conservation of an important aquatic ecosystem exposed to a severe erosion and reshape. To this aim, a web interface has been developed to efficiently monitor in real time the evolution of several diagnostic parameters provided by the manufacturer (CODAR) and used as indicators of HF radar system health. This web, updated automatically every hour, examines sites performance on different time basis in terms of: - Hardware parameters: power and temperature. - Radial parameters, among others: Signal-to-Noise Ratio (SNR), number of radial vectors provided by time step, maximum radial range and bearing. - Total uncertainty metrics provided by CODAR: zonal and meridional standard deviations and covariance between both components. - Additionally, a widget embedded in the web interface executes queries against PdE database, providing the chance to compare current time series observed by Tarragona buoy (located within Ebro HF radar spatial domain) and

  20. Passive all-sky imaging radar in the HF regime with WWV and the first station of the Long Wavelength Array

    NASA Astrophysics Data System (ADS)

    Helmboldt, J. F.; Clarke, T. E.; Craig, J.; Dowell, J. D.; Ellingson, S. W.; Hartman, J. M.; Hicks, B. C.; Kassim, N. E.; Taylor, G. B.; Wolfe, C. N.

    2013-09-01

    We present a new passive, bistatic high-frequency (HF) radar system consisting of the transmitters for the radio station WWV and the dipole antenna array that comprises the first station of the Long Wavelength Array (LWA) or "LWA1." We demonstrate that these two existing facilities, which are operated for separate purposes, can be used together as a unique HF radar imager, capable of monitoring the entire visible sky. In this paper, we describe in detail the techniques used to develop all-sky radar capability at 10, 15, and 20 MHz. We show that this radar system can be a useful tool for probing ionospheric structure and its effect on over-the-horizon (OTH) geolocation. The LWA1+WWV radar system appears to be especially adept at detecting and characterizing structures associated with sporadic-E. In addition, we also demonstrate how this system may be used for long-distance, OTH mapping of terrain/ocean HF reflectivity. Finally, we discuss the potential improvements in the utility of these applications as more LWA stations are added.

  1. Surface circulation at the Strait of Gibraltar: A combined HF radar and high resolution model study

    NASA Astrophysics Data System (ADS)

    Soto-Navarro, Javier; Lorente, Pablo; Álvarez Fanjul, Enrique; Carlos Sánchez-Garrido, Jose; García-Lafuente, Jesús

    2016-03-01

    Observations from a high frequency radar system and outputs from a high resolution operational ocean model working at the Strait of Gibraltar have been analyzed and compared during the period February 2013 to September 2014 in order to evaluate their capability to resolve the surface circulation of the region. The description of the mean circulation patterns has been statistically assessed, showing good agreement, particularly in the central region of the strait corresponding with the Atlantic Jet (AJ) stream, although some short scale features are not reproduced by the model. In the frequency domain very high concordance is observed. Tidal maps of diurnal and semidiurnal constituents are in good agreement with previous observations. The analysis of the model and radar response to the wind forcing reveals that the low resolution of the model wind-forcing field and its deeper superficial level smoothes the wind effect on the simulated currents. The first three EOF modes account for the 86% of model and radar variances. The coincidence between the observed and simulated patterns is very significant for the first two modes, which account for the mean velocity field and the latitudinal shifting of the AJ consequence of the flow-topography interaction. The third mode captures the wind-induced circulation, and greater discrepancies are found in this case. Results underline the complementary character of both systems: radar observations improve the model description, resolving short scale processes, while the model completes the radar information when the time or spatial coverage is poorer.

  2. Analysis of post-sunset F-region vertical plasma drifts during Counter Electrojet days using multi frequency HF Doppler Radar

    NASA Astrophysics Data System (ADS)

    Simi, K. G.; Vineeth, C.; Pant, T. K.

    2014-08-01

    In this paper, through a case study, an attempt has been made to bring out the relationship between post noon E-region electric field and post sunset F-region vertical plasma drift on quiet time Counter Electrojet (CEJ) days. Study carried out using the data from a multi frequency HF Doppler Radar and Digital Ionosonde located over Trivandrum (8.5° N; 77° E; 0.5° N dip lat.) a geomagnetic dip equatorial station in India during quite time CEJ days of the years 2004 and 2006, revealed some interesting aspects of the E region electrodynamics and post sunset F region electrodynamics. It has been observed that, in contrast to the normal electrojet (EEJ) days, the Pre-Reversal Enhancement (PRE) is either weakened or inhibited on CEJ days and the field reversal takes place much earlier than that on a normal day. It is suggested that even after the effects of the field reversal ceases to show up in the ground magnetic data, the reversed field may persist and shows up as a decrease in the PRE experienced by the F-region. In other words, the study indicates that the EEJ associated electrodynamics have a significant role in controlling the PRE.

  3. Correlated observations of the boundary between polar cap and nightside auroral zone by HF radars and the DMSP satellite

    SciTech Connect

    Senior, C.; Cerisier, J.C. ); Hanuise, C. ); Villain, J.P. ); Greenwald, R.G.; Newell, P.T. ); Rich, F.J. )

    1994-02-01

    Simultaneous observations from HF radars and the DMSP satellite have been used to relate the ionospheric convection pattern and the nightside precipitation at the polar cap-auroral zone boundary. The convection is eastward in the poleward part of the radars field of view and predominantly westward at lower latitudes. The DMSP-F9 particle spectrograms exhibit energetic precipitating protons at the poleward edge of an inverted V'. The downward H[sup +] flow displays spatial filtering effects with a clear energy-latitude dispersion. Single-particle trajectory simulations in appropriate field models demonstrate that these ions were ejected from the neutral sheet near 120 R[sub E] geocentric distance. Most notably, the simulations reveal significant azimuthal dispersion during transport, and the source region in the magnetotail is found to extend over several Earth radii in the dawn-dusk direction, less energetic particles originating duskward of the high-energy ones. The longitudinal spread of the tail source suggests particle precipitation in the ionosphere over at least one hour magnetic local time. Also, as the downflowing protons travel near the lobeward edge of the plasma sheet, the observations suggest that the convection reversal lies inside the boundary layer plasma sheet (PSBL). 11 refs., 3 figs.

  4. HF radar observations of Pc 5 field line resonances in the midnight/early morning MLT sector

    NASA Technical Reports Server (NTRS)

    Ruohoniemi, J. M.; Greenwald, R. A.; Baker, K. B.; Samson, J. C.

    1991-01-01

    The technique of F region sounding by HF coherent radar is applied to the study of field line resonances equatorward of a region of shear flow in the early morning sector. The motions were predominantly in the geomagnetic east-west direction, indicating north-south electric fields. These oscillations had pronounced peaks in their latitudinal power distribution. For the pulsation at 1.95 mHz, a latitudinal phase shift of 180 deg was observed across the peaks in all the look directions of the radar, and a longitudinal wavelength corresponding to an m value of 3 was obtained. For the 2.6-mHz pulsation, the phase shifts across the peaks had a variation with a look direction that indicated a significant longitudinal as well as latitudinal variation; for this activity, an m value of about 16 is estimated. These features are interpreted in terms of the field line resonance theory, and the possible sources of the pulsation energy are discussed.

  5. Development of NASA's Next Generation L-Band Digital Beamforming Synthetic Aperture Radar (DBSAR-2)

    NASA Technical Reports Server (NTRS)

    Rincon, Rafael; Fatoyinbo, Temilola; Osmanoglu, Batuhan; Lee, Seung-Kuk; Ranson, K. Jon; Marrero, Victor; Yeary, Mark

    2014-01-01

    NASA's Next generation Digital Beamforming SAR (DBSAR-2) is a state-of-the-art airborne L-band radar developed at the NASA Goddard Space Flight Center (GSFC). The instrument builds upon the advanced architectures in NASA's DBSAR-1 and EcoSAR instruments. The new instrument employs a 16-channel radar architecture characterized by multi-mode operation, software defined waveform generation, digital beamforming, and configurable radar parameters. The instrument has been design to support several disciplines in Earth and Planetary sciences. The instrument was recently completed, and tested and calibrated in a anechoic chamber.

  6. Development of a ground signal processor for digital synthetic array radar data

    NASA Technical Reports Server (NTRS)

    Griffin, C. R.; Estes, J. M.

    1981-01-01

    A modified APQ-102 sidelooking array radar (SLAR) in a B-57 aircraft test bed is used, with other optical and infrared sensors, in remote sensing of Earth surface features for various users at NASA Johnson Space Center. The video from the radar is normally recorded on photographic film and subsequently processed photographically into high resolution radar images. Using a high speed sampling (digitizing) system, the two receiver channels of cross-and co-polarized video are recorded on wideband magnetic tape along with radar and platform parameters. These data are subsequently reformatted and processed into digital synthetic aperture radar images with the image data available on magnetic tape for subsequent analysis by investigators. The system design and results obtained are described.

  7. A short-term predictive system for surface currents from a rapidly deployed coastal HF radar network

    NASA Astrophysics Data System (ADS)

    Barrick, Donald; Fernandez, Vicente; Ferrer, Maria I.; Whelan, Chad; Breivik, Øyvind

    2012-05-01

    In order to address the need for surface trajectory forecasts following deployment of coastal HF radar systems during emergency-response situations (e.g., search and rescue, oil spill), a short-term predictive system (STPS) based on only a few hours data background is presented. First, open-modal analysis (OMA) coefficients are fitted to 1-D surface currents from all available radar stations at each time interval. OMA has the effect of applying a spatial low-pass filter to the data, fills gaps, and can extend coverage to areas where radial vectors are available from a single radar only. Then, a set of temporal modes is fitted to the time series of OMA coefficients, typically over a short 12-h trailing period. These modes include tidal and inertial harmonics, as well as constant and linear trends. This temporal model is the STPS basis for producing up to a 12-h current vector forecast from which a trajectory forecast can be derived. We show results of this method applied to data gathered during the September 2010 rapid-response demonstration in northern Norway. Forecasted coefficients, currents, and trajectories are compared with the same measured quantities, and statistics of skill are assessed employing 16 24-h data sets. Forecasted and measured kinetic variances of the OMA coefficients typically agreed to within 10-15%. In one case where errors were larger, strong wind changes are suspected and examined as the cause. Sudden wind variability is not included properly within the STPS attack we presently employ and will be a subject for future improvement.

  8. A Digital Bistatic Radar Instrument for High-Latitude Ionospheric E-region Research

    NASA Astrophysics Data System (ADS)

    Huyghebaert, D. R.; Hussey, G. C.; McWilliams, K. A.; St-Maurice, J. P.

    2015-12-01

    A new 50 MHz ionospheric E-region radar is currently being developed and will be operational for the summer of 2016. The radar group in the Institute of Space and Atmospheric Studies (ISAS) at the University of Saskatchewan is designing and building the radar which will be located near the university in Saskatoon, SK, Canada and will have a field of view over Wollaston Lake in northern Saskatchewan. This novel radar will simultaneously obtain high spatial and temporal resolution through the use of a bistatic setup and pulse modulation techniques. The bistatic setup allows the radar to transmit and receive continuously, while pulse modulation techniques allow for enhanced spatial resolution, only constrained by the radio bandwidth licensing available. A ten antenna array will be used on both the transmitter and receiver sides, with each antenna having an independent radio path. This enables complete digital control of the transmitted 1 kW signal at each antenna, allowing for digital beam steering and multimode broadcasting. On the receiver side the raw digitized signal will be recorded from each antenna, allowing for complete digital post-processing to be performed on the data. From the measurements provided using these modern digital radar capabilities, further insights into the physics of E-region phenomena, such as Alfvén waves propagating from the magnetosphere above and ionospheric irregularities, may be investigated.

  9. Complexity in the high latitude HF radar spectral width boundary region

    NASA Astrophysics Data System (ADS)

    Parkinson, M. L.; Hannah, K. M.; Dyson, P. L.

    2008-05-01

    SuperDARN radars are sensitive to the collective Doppler characteristics of decametre-scale irregularities in the high latitude ionosphere. The radars routinely observe a distinct transition from large spectral width (>100 m s-1) located at higher latitudes to low spectral width (<50 m s-1) located at lower latitudes. Because of its equatorward location, the TIGER Tasmanian radar is very sensitive to the detection of the spectral width boundary (SWB) in the nightside auroral ionosphere. An analysis of the line-of-sight velocities and 2-D beam-swinging vectors suggests the meso-scale (~100 km) convection is more erratic in the high spectral width region, but slower and more homogeneous in the low spectral width region. The radar autocorrelation functions are better modelled using Lorentzian Doppler spectra in the high spectral width region, and Gaussian Doppler spectra in the low spectral width region. However, paradoxically, Gaussian Doppler spectra are associated with the largest spectral widths. Application of the Burg maximum entropy method suggests the occurrence of double-peaked Doppler spectra is greater in the high spectral width region, implying the small-scale (~10 km) velocity fluctuations are more intense above the SWB. These observations combined with collective wave scattering theory imply there is a transition from a fast flowing, turbulent plasma with a correlation length of velocity fluctuations less than the scattering wavelength, to a slower moving plasma with a correlation length greater than the scattering wavelength. Peak scaling and structure function analysis of fluctuations in the SWB itself reveals approximately scale-free behaviour across temporal scales of ~10 s to ~34 min. Preliminary scaling exponents for these fluctuations, αGSF=0.18±0.02 and αGSF=0.09±0.01, are even smaller than that expected for MHD turbulence.

  10. Perturbed Angular Correlation of the stretched cascade in the decay of 180mHf using a digital spectrometer

    NASA Astrophysics Data System (ADS)

    Jäger, Markus; Butz, Tilman

    2012-05-01

    We report on the measurement of the nuclear quadrupole interaction (NQI) at Hf sites using the nuclear probe 180mHf in HfF4·HF·2H2O at 300 K by exploiting all possible start quanta in the stretched cascade with a digital Time Differential Perturbed Angular Correlation (TDPAC) spectrometer. With conventional spectrometers, multiple prompt start signals would paralyze the router. The gain in coincidence rate is about a factor of 5 compared to a conventional spectrometer using a single start only. With multiple starts 180mHf is a promising new isomeric nuclear probe in TDPAC experiments. As an additional feature we implemented the possibility to measure up to four cascades simultaneously in order to save data collection time or to measure isobaric contaminations like 111mCd and 111In.

  11. The digital signal processor for the ALCOR millimeter wave radar

    NASA Astrophysics Data System (ADS)

    Ford, R. A.

    1980-11-01

    This report describes the use of an array processor for real time radar signal processing. Pulse compression, range marking, and monopulse error computation are some of the functions that will be performed in the array processor for the millimeter wave ALCOR radar augmentation. Real time software design, processor architecture, and system interfaces are discussed in the report.

  12. Interpretation of HF radar ionospheric Doppler spectra by collective wave scattering theory

    NASA Astrophysics Data System (ADS)

    Hanuise, C.; Villain, J. P.; Gresillon, D.; Cabrit, B.; Greenwald, R. A.; Baker, K. B.

    1993-01-01

    The correlation length and time constant of turbulent plasma motion is determined using the coherent radar autocorrelation function (ACF) in the framework of collective wave scattering theory by a nonuniform plasma. It is concluded that the observed Doppler spectra have either a Lorentzian shape or a Gaussian shape according to the size of the correlation length of the plasma motion as compared to the observed fluctuation wavelength. Observations indicate that the Lorentzian shape is most common. When the correlation length of the plasma motion is much greater than the observed fluctuation wavelength, the Doppler spectrum becomes Gaussian shaped.

  13. Characterizing the coastal dynamics behaviour within the Gulf of Naples using modelling, HF radar and in situ measurements

    NASA Astrophysics Data System (ADS)

    Iermano, Ilaria; Cianelli, Daniela; Falco, Pierpaolo; Uttieri, Marco; Zambianchi, Enrico

    2013-04-01

    The integration of numerical models in coastal observatories represents a current challenge for the scientific community, constituting a frontier both for research purposes and for a variety of practical applications, ranging from coastal protection to search and rescue activities, or support to engineering works and operational structures. Here we present the monitoring network installed in the Gulf of Naples, our recent advances in coastal and in-situ observations and the integrated ocean-atmosphere modelling approach, through connections to the state of the art and still opened research issues that will be the challenges for the next years. Currently, the monitoring network of the Gulf of Naples is composed of moored instrumentation and a HF radar system composed of three antennas that provide hourly data of surface currents for the entire Gulf at a spatial resolution of 1 km. The ocean model configuration is a ROMS (Regional Ocean Modeling System)-based code, configured on the region (~13-15E, 40-42N). The increasing availability of long-term observations, the large dataset recently acquired in sea-truth campaigns and numerical output from meteorological and ocean models allow us to use these integrated tools to characterize the coastal dynamics processes, and thus provide quantitative support to decision makers in the field of management strategy on oil spill and search and rescue operations, vulnerability of coasts and correct management strategies of the environmental heritage. This talk presents diverse scientific issues recently addressed by the DiSAm (University of Naples Parthenope) in the broad activity of developing and tuning of the oceanic components of modeling system. We will show some numerical model results in the Gulf of Naples basin in response to high resolution atmospheric forcing provided by the SKIRON model focusing mainly on the seasonal circulation and on the mesoscale and submesoscale variability associated with the current system of the

  14. HF radar observations of small-scale surface current variability in the Straits of Florida

    NASA Astrophysics Data System (ADS)

    Parks, A. B.; Shay, L. K.; Johns, W. E.; Martinez-Pedraja, J.; Gurgel, K.-W.

    2009-08-01

    A dual-station high-frequency Wellen radar (WERA), transmitting at 16.045 MHz, was deployed along the eastern Florida Shelf and operated and maintained by the University of Miami's Rosenstiel School of Marine and Atmospheric Science. From September 2004 to June 2005, a moored acoustic Doppler current profiler (ADCP) acquired subsurface current measurements within the radar footprint along the shelf break at 86-m depth. The shallowest ADCP bin located at 14-m depth was used as a comparison for the WERA surface measurements. RMS differences ranged from 0.1 to 0.3 m s-1 between the surface and 14-m depth, with good agreement over most of the period. Regression analyses indicated slopes near unity in the north-south (v) component and ≈0.5 for the east-west (u) component velocities. When utilized in tandem with the ADCP subsurface measurements, WERA enables three-dimensional snapshots of coastal oceanographic features to be resolved. For example, from December 2004 through February 2005, three energetic circulation patterns were observed: (1) a subsurface stratified countercurrent, (2) a submesoscale coherent vortex, and (3) a mesoscale circulation feature, i.e., a propagating Tortugas gyre. These features represent the significant current variability along the western flank of the Florida Current that impacts the coastal ocean.

  15. A Study of Clutter Reduction Techniques in Wide Bandwidth HF/VHF Deep Ground Penetrating Radar

    NASA Astrophysics Data System (ADS)

    Hammett, Darien J.

    2002-08-01

    Reducing clutter is one of the most daunting problems a radar processing engineer faces. Clutter causes a significant problem when attempting to detect sub-surface targets, as any significant change in the ground dielectric will produce a return at the receiver. The difficulty in reducing the clutter is compounded by the fact that the spectral characteristics of the clutter are similar to that of the target. While there are many methods that exist to reduce clutter, few do not require a prior information of either the target or the clutter. There are applications, of interest to the electromagnetic community, that are restricted in the amount of a prior information available to them. Estimation-subtraction filters calculate an estimate of the clutter from the statistics of the data collected and subtract that estimate from the original data. The Wiener filter has long been used as a way to suppress noise signals when a target reference is known. Using it to reduce clutter is a relatively new area of research. This research proposes estimation-subtraction filters and an application of the Wiener filter, which do not require a priori information to reduce the clutter of a bi-static synthetic aperture based, wideband deep ground penetrating radar system. The results of applying these filters to data collected in this way, at these depths, are illustrated here for the first time. x

  16. Assessing the fidelity of surface currents from a coastal ocean model and HF radar using drifting buoys in the Middle Atlantic Bight

    NASA Astrophysics Data System (ADS)

    Kuang, Liang; Blumberg, Alan F.; Georgas, Nickitas

    2012-08-01

    The rapid expansion of urbanization along the world's coastal areas requires a more comprehensive and accurate understanding of the coastal ocean. Over the past several decades, numerical ocean circulation models have tried to provide such insight, based on our developing understanding of physical ocean processes. The systematic establishment of coastal ocean observation systems adopting cutting-edge technology, such as high frequency (HF) radar, satellite sensing, and gliders, has put such ocean model predictions to the test, by providing comprehensive observational datasets for the validation of numerical model forecasts. The New York Harbor Observing and Prediction System (NYHOPS) is a comprehensive system for understanding coastal ocean processes on the continental shelf waters of New York and New Jersey. To increase confidence in the system's ocean circulation predictions in that area, a detailed validation exercise was carried out using HF radar and Lagrangian drifter-derived surface currents from three drifters obtained between March and October 2010. During that period, the root mean square (RMS) differences of both the east-west and north-south currents between NYHOPS and HF radar were approximately 15 cm s-1. Harmonic analysis of NYHOPS and HF radar surface currents shows similar tidal ellipse parameters for the dominant M2 tide, with a mean difference of 2.4 cm s-1 in the semi-major axis and 1.4 cm s-1 in the semi-minor axis and 3° in orientation and 10° in phase. Surface currents derived independently from drifters along their trajectories showed that NYHOPS and HF radar yielded similarly accurate results. RMS errors when compared to currents derived along the trajectory of the three drifters were approximately 10 cm s-1. Overall, the analysis suggests that NYHOPS and HF radar had similar skill in estimating the currents over the continental shelf waters of the Middle Atlantic Bight during this time period. An ensemble-based set of particle tracking

  17. Digital signal processing of data from conventional weather radar: The DISPLACE method

    NASA Astrophysics Data System (ADS)

    Terblanche, Deon Etienne

    1997-09-01

    This thesis describes the development, testing and implementation of a new method to process the output from a weather radar's logarithmic receiver. The processing method, called DISPLACE, has proven to have many applications, and is computationally efficient and accurate. Its applications include the processing of digitized logarithmic receiver output in order to simulate different receiver transfer functions, the processing of multi-parameter radar measurements and the filtering of ground clutter. It facilitates the computation of CAPPI's and radar-rainfall accumulation. The thesis also deals with the upgrading of South African weather radars since about 1990 through the in-house developed radar data acquisition system and the procedures established to ensure accurate calibrations. In addition, the hydrometeorological infrastructure deployed in the Bethlehem research are is used in an integrated manner to verify data obtained using the new method. This work is well timed to address the needs that are now emerging in South Africa and clearly illustrate the role the NPRP played in reviving radar meteorology. The DISPLACE method is proving once again that the potential of conventional weather radar has not been fully exploited. It has also stimulated the interest of young technicians and scientists in the field of radar meteorology. This augurs well for the future use of weather radar in South Africa, both in the field of rainfall stimulation and as an integral part of systems designed to forecast and to help manage the effects of severe weather conditions.

  18. Combination of Manually Digitized Radar and GOES IR for Real-Time Display of Rainfall Intensity.

    NASA Astrophysics Data System (ADS)

    Heinemann, Paul H.; Martsolf, J. David; Gerber, John F.; Smith, Daniel L.

    1987-08-01

    Manually Digitized Radar (MDR) and Geostationary Operational Environmental Satellite (GOES) thermal infrared (IR) data were merged to form a higher-resolution radar/IR product than that represented by the MDR. The combination MDR/IR maps were processed into a color coded map form and disseminated on a real-time basis through a computer network to users in the Florida agricultural community.

  19. Assimilation of HF radar data in a regional model of the Ligurian Sea

    NASA Astrophysics Data System (ADS)

    Vandenbulcke, Luc; Barth, Alexander; Beckers, Jean-Marie

    2015-04-01

    An ensemble of ROMS models with 1/60 degree resolution, covering the Ligurian Sea, and nested in the Mediterranean Forecasting System, is coupled with two WERA high-frequency radars run by the NATO Undersea Research Center (now CMRE). The following perturbations are applied to the members of the ensemble: the wind forcing field, the open sea boundary conditions, and a supplementary term in the momentum equation. An ensemble Kalman (EnKF) filter is then used to assimilate hourly-averaged radial currents into the model. A observation operator extracts the corresponding model radial currents from the model currents, then smooths them in the azimuthal direction as a function of distance to the radar. The observations are spatially dense, and not uncorrelated to one another, which is approximated in our experiment by increasing the observation error variance. Different cases are run, with the estimation vector containing the model state (in which case it is called the state vector) or multiple model states at different time steps. In the latter case, the filter is closely related to the Ensemble Smoother and the Asynchronous EnKF. The impact of different parameters is studied: the correlation length of the localization function, the (experimentally determined) total observational error, the stochastic perturbation in the momentum equation, the assimilation window length, etc. The update vector generated by the data assimilation scheme is analyzed to examine whether inertial oscillations are present and corrected. The model surface temperature is also compared with satellite images in order to assess the impact of assimilating one variable (surface currents) on another one (surface temperature).

  20. Towards a synthesis of substorm electrodynamics: HF radar and auroral observations

    NASA Astrophysics Data System (ADS)

    Grocott, A.; Lester, M.; Parkinson, M. L.; Yeoman, T. K.; Dyson, P. L.; Devlin, J. C.; Frey, H. U.

    2006-12-01

    At 08:35 UT on 21 November 2004, the onset of an interval of substorm activity was captured in the southern hemisphere by the Far UltraViolet (FUV) instrument on board the IMAGE spacecraft. This was accompanied by the onset of Pi2 activity and subsequent magnetic bays, evident in ground magnetic data from both hemispheres. Further intensifications were then observed in both the auroral and ground magnetic data over the following ~3 h. During this interval the fields-of-view of the two southern hemisphere Tasman International Geospace Enviroment Radars (TIGER) moved through the evening sector towards midnight. Whilst initially low, the amount of backscatter from TIGER increased considerably during the early stages of the expansion phase such that by ~09:20 UT an enhanced dusk flow cell was clearly evident. During the expansion phase the equatorward portion of this flow cell developed into a narrow high-speed flow channel, indicative of the auroral and sub-auroral flows identified in previous studies (e.g. Freeman et al., 1992; Parkinson et al., 2003). At the same time, higher latitude transient flow features were observed and as the interval progressed the flow reversal region and Harang discontinuity became very well defined. Overall, this study has enabled the spatial and temporal development of many different elements of the substorm process to be resolved and placed within a simple conceptual framework of magnetospheric convection. Specifically, the detailed observations of ionospheric flows have illustrated the complex interplay between substorm electric fields and associated auroral dynamics. They have helped define the distinct nature of different substorm current systems such as the traditional substorm current wedge and the more equatorward currents associated with polarisation electric fields. Additionally, they have revealed a radar signature of nightside reconnection which provides the promise of quantifying nightside reconnection in a way which has

  1. HF radar detection of infrasonic waves generated in the ionosphere by the 28 March 2005 Sumatra earthquake

    NASA Astrophysics Data System (ADS)

    Bourdillon, Alain; Occhipinti, Giovanni; Molinié, Jean-Philippe; Rannou, Véronique

    2014-03-01

    Surface waves generated by earthquakes create atmospheric waves detectable in the ionosphere using radio waves techniques: i.e., HF Doppler sounding, GPS and altimeter TEC measurements, as well as radar measurements. We present observations performed with the over-the-horizon (OTH) radar NOSTRADAMUS after the very strong earthquake (M=8.6) that occurred in Sumatra on March 28, 2005. An original method based on the analysis of the RTD (Range-Time-Doppler) image is suggested to identify the multi-chromatic ionospheric signature of the Rayleigh wave. The proposed method presents the advantage to preserve the information on the range variation and time evolution, and provides comprehensive results, as well as easy identification of the waves. In essence, a Burg algorithm of order 1 is proposed to compute the Doppler shift of the radar signal, resulting in sensitivity as good as obtained with higher orders. The multi-chromatic observation of the ionospheric signature of Rayleigh wave allows to extrapolate information coherent with the dispersion curve of Rayleigh waves, that is, we observe two components of the Rayleigh waves with estimated group velocities of 3.8 km/s and 3.6 km/s associated to 28 mHz (T~36 s) and 6.1 mHz (T~164 s) waves, respectively. Spectral analysis of the RTD image reveals anyway the presence of several oscillations at frequencies between 3 and 8 mHz clearly associated to the transfer of energy from the solid-Earth to the atmosphere, and nominally described by the normal modes theory for a complete planet with atmosphere. Oscillations at frequencies larger than 8 mHz are also observed in the spectrum but with smaller amplitudes. Particular attention is pointed out to normal modes 0S29 and 0S37 which are strongly involved in the coupling process. As the proposed method is frequency free, it could be used not only for detection of ionospheric perturbations induced by earthquakes, but also by other natural phenomena as well as volcanic explosions and

  2. Spurious effects of analog-to-digital conversion nonlinearities on radar range-Doppler maps

    NASA Astrophysics Data System (ADS)

    Doerry, A. W.; Dubbert, D. F.; Tise, B. L.

    2015-05-01

    High-performance radar operation, particularly Ground Moving Target Indicator (GMTI) radar modes, are very sensitive to anomalous effects of system nonlinearities. System nonlinearities generate harmonic spurs that at best degrade, and at worst generate false target detections. One significant source of nonlinear behavior is the Analog to Digital Converter (ADC). One measure of its undesired nonlinearity is its Integral Nonlinearity (INL) specification. We examine in this paper the relationship of INL to radar performance; in particular its manifestation in a range-Doppler map or image.

  3. Improvement of sea-environment sounding technology and signal processing method for HF ground-wave radar

    NASA Astrophysics Data System (ADS)

    Liu, Jinggao; Zheng, Zhengqi; Wang, Chengfa; Yin, Jieyi

    1998-08-01

    In the research of using HF ground wave radar to detect sea environment, we adopt symmetrical Yagi antenna array, correct the influence on antenna beam direction by platform on-sea and sea surface, optimize the schemes in the post- processing, which include multiple correlation, Bragg- Doppler spectrum identification and reconstruction processing. During the signal gathering, the statistical character of slow sea-state variation is utilized. It facilitates the multiple correlation integration and satisfy the requirement for reconstruction processing. So the reliability of extracting sea echo data and articulation of Bragg-Doppler spectrum are greatly improved. We simulate how platform on-sea and sea surface influence beam direction with scale model. And under varied conditions the rise degree of main beam is measured. These data can help us correct the direction of vertical antenna during practical erecting. With these data, we do the inversion of sea surface flow field and wave field parameters. The result agrees with what the standard scaling machine measure.

  4. HF radar observations of Pc 5 field line resonances in the midnight/early morning MLT sector

    SciTech Connect

    Ruohoniemi, J.M.; Greenwald, R.A.; Baker, K.B. ); Samson, J.C. )

    1991-09-01

    On a number of occasions The Johns Hopkins University/Applied Physics Laboratory HF radar at Goose Bay, Labrador, has observed the effects of field line resonances on the drift velocities of irregularities in the F region of the high-latitude ionosphere. One of the most interesting sets of resonances occurs near midnight MLT and may be associated with shear in the convective flow in the magnetotail. This paper discusses in detail a particularly clear example which shows field line resonance equatorward of a region of shear flow in the early morning sector. The motions were predominantly in the geomagnetic east-west direction, indicating north-south electric fields. As expected of field line resonance pulsations, these oscillations had pronounced peaks in their latitudinal power distribution. The pulsations could occur simultaneously but remained distinct as the latitude of peak response was observed to vary inversely with the frequency of the pulsation. The authors interpret these features in terms of field line resonance theory and discuss the possible sources of the pulsation energy.

  5. Use of 'velocity projection' to estimate the variation of sea-surface height from HF Doppler radar current measurements

    NASA Astrophysics Data System (ADS)

    Marmorino, G. O.; Shen, C. Y.; Evans, T. E.; Lindemann, G. J.; Hallock, Z. R.; Shay, L. K.

    2004-02-01

    The technique of 'velocity projection' (J. Geophys. Res. 106 (2001) 6973) is used to estimate the sea-surface height field and its change over time from measurements of surface velocity made using a shore-based HF Doppler radar over a 30×30-km region of the continental shelf located near the mouth of the Chesapeake Bay (USA). Projected current profiles are compared with measured currents from an array of acoustic Doppler current profilers, and the consistency and sensitivity of the projections to model assumptions are also examined. Using projected values of the local surface slope, a model sea-surface η( x, y) is least-squares fit over the study region at each measurement time. The error associated with these fits provides an internal check on the validity of the projection results. The slope of the model sea-surface shows a set-up toward the mouth of the Chesapeake Bay during downwelling-favorable winds and a counterclockwise rotation over the tidal cycle that is consistent with linear, shallow-water dynamics. A time series of sea-level difference extracted from the η maps shows a dominant M 2 tidal signal that compares well with measurements of bottom pressure made at two moorings. With proper attention to limits of applicability, such projection-based sea-surface slope fields (as well as other projection results) may be useful in diagnostic calculations or as nowcasts for use with prognostic models.

  6. Characteristics of zonal plasma drift during post-sunset hours observed using mult-frequency HF Doppler radar

    NASA Astrophysics Data System (ADS)

    Mathew, Tiju Joseph; Prabhakaran Nayar, S. R.

    F-region zonal plasma drifts near the magnetic equator around sunset period have been observed at multiple altitudes using the HF Doppler radar. The pattern of the plasma flow is such that it starts with a westward drift at the pre-sunset times followed by an eastward drift shortly after the E-region sunset. The striking feature of the zonal drift is the altitude dependence of the zonal drift and the presence of a vertical shear around the post sunset period at the F-region. The shear region is found to be in the altitude range of 200-300 km where the F and E -region compete for dominance. The negative gradient in the vertical drift and shear in the zonal drift are the deterministic features of the evening equatorial ionosphere to maintain the curl-free nature of the electric field. The simultaneous observation of the vertical and zonal plasma drifts suggests the existence of a post sunset velocity vortex over the equator.

  7. A technique for calculating ionospheric Doppler shifts from standard ionograms suitable for scientific, HF communication, and OTH radar applications

    NASA Astrophysics Data System (ADS)

    Lynn, K. J. W.

    2009-12-01

    High-resolution Doppler ionograms taken at 5 min intervals were obtained from a KEL IPS 71 ionosonde operating over a full ionosonde sweep range. The ionograms were converted into true height profiles using the program POLAN. POLAN also produced an equivalent parabolic layer model of best fit to the true height profile. A parabolic layer model of the ionosphere is defined by three parameters, namely, peak height, maximum electron density/critical frequency, and parabolic thickness. Equations for calculating Doppler shift from a time-varying parabolic layer model have long been known but have seen remarkably little use in the absence of suitable input data and a means of verifying the results. This paper shows that these equations can provide an accurate means of calculating ionospheric Doppler shift based on standard ionospheric ionograms taken at a 5 min rate over a 24 h period when compared with actual Doppler measurements. Apart from its scientific interest, the demonstrated technique will prove particularly valuable in deriving Doppler shift and associated signal fading for the real-time control of over-the-horizon radar and HF communication links.

  8. Wind influence on surface current variability in the Ibiza Channel from HF Radar

    NASA Astrophysics Data System (ADS)

    Lana, Arancha; Marmain, Julien; Fernández, Vicente; Tintoré, Joaquin; Orfila, Alejandro

    2016-04-01

    Surface current variability is investigated using 2.5 years of continuous velocity measurements from an high frequency radar (HFR) located in the Ibiza Channel (Western Mediterranean Sea). The Ibiza Channel is identified as a key geographical feature for the exchange of water masses but still poorly documented. Operational, quality controlled, HFR derived velocities are provided by the Balearic Islands Coastal Observing and Forecasting System (SOCIB). They are assessed by performing statistical comparisons with current-meter, ADCP, and surface lagrangian drifters. HFR system does not show significant bias, and its accuracy is in accordance with previous studies performed in other areas. The main surface circulation patterns are deduced from an EOF analysis. The first three modes represent almost 70 % of the total variability. A cross-correlation analysis between zonal and meridional wind components and the temporal amplitudes of the first three modes reveal that the first two modes are mainly driven by local winds, with immediate effects of wind forcing and veering following Ekman effect. The first mode (37 % of total variability) is the response of meridional wind while the second mode (24 % of total variability) is linked primarily with zonal winds. The third and higher order modes are related to mesoscale circulation features. HFR derived surface transport presents a markedly seasonal variability being mostly southwards. Its comparison with Ekman-induced transport shows that wind contribution to the total surface transport is on average around 65 %.

  9. Geometric rectification of radar imagery using digital elevation models

    NASA Technical Reports Server (NTRS)

    Naraghi, M.; Stromberg, W.; Daily, M.

    1983-01-01

    Geologic analysis of radar imagery requires accurate spatial rectification to allow rock type discrimination and meaningful exploitation of multisensor data files. A procedure is described which removes distortions produced by most sources including the heretofore elusive problem of terrain induced effects. Rectified imagery is presented which displays geologic features not apparent in the distorted data.

  10. A New 50-MHz VHF Digital Bistatic Radar for E-region Space Physics Research

    NASA Astrophysics Data System (ADS)

    Hussey, G. C.; Huyghebaert, D. R.; St-Maurice, J. P.; McWilliams, K. A.

    2015-12-01

    A new fully digital bistatic 50-MHz VHF radar is currently being developed by the radar group in the Institute of Space and Atmospheric Studies (ISAS) at the University of Saskatchewan. This paper presents the scientific motivation for the new radar. Traditionally bistatic radars have had excellent time resolution, but were significantly lacking in range resolution. With the now available accurate timing abilities and advanced pulse modulation techniques, bistatic radar configurations with both excellent temporal and spatial resolution are able to map or 'image' the E-region. The E-region portion of the ionosphere being the base of the magnetosphere has both global (ionosphere-magnetosphere system) and local phenomena of interest. The currents in the magnetosphere close in the E-region. Field-aligned currents (FACs) and Alfven waves are phenomena with origins in the magnetosphere which present their 'signatures' in the E-region. For example, Alfven waves (produced by the Alfven wave resonator) have different time scales, from less than a Hertz to periods of tens of minutes --- and the high temporal and spatial resolution of this new digital E-region radar will be able to detect them all. The E-region is also a dynamic plasma medium with the two-steam and gradient drift instabilities present and the improved measurement abilities will give fresh physical insight.

  11. An atlas of November 1978 synthetic aperture radar digitized imagery for oil spill studies

    NASA Technical Reports Server (NTRS)

    Maurer, H. E.; Oderman, W.; Crosswell, W. F.

    1982-01-01

    A data set is described which consists of digitized synthetic aperture radar (SAR) imagery plus correlative data and some preliminary analysis results. This data set should be of value to experimenters who are interested in the SAR instrument and its application to the detection and monitoring of oil on water and other distributed targets.

  12. Interferometric synthetic aperture radar and the Data Collection System Digital Terrain Elevation Demonstration

    NASA Astrophysics Data System (ADS)

    Heidelbach, Robert; Bolus, R.; Chadwick, J.

    1994-08-01

    Digital Terrain Elevations (DTE) that can be rapidly generated, and that have better fidelity and accuracy than Digital Terrain Elevation Data (DTED) Levels 1 or 2, would be extremely beneficial to Department of Defense (DOD) military operations, civil works programs, and various commercial applications. As a result, the Advanced Research Projects Agency (ARPA), along with the U.S. Army Topographic Engineering Center (TEC), are developing an Interferometric Synthetic Aperture Radar (IFSAR) elevation mapping capability. This system, the Interferometric Synthetic Aperture Radar for Digital Radar Elevations (IFSARE), is capable of collecting and providing data in all weather (reasonable), in day or night scenarios, and where obscurants are present. The IFSARE, which is currently undergoing Integration and Test, will allow for rapid on-line automatic processing of the collected digital radar data into DTE and high quality imagery. The prime contractor is the Environmental Research Institute of Michigan (ERIM). This paper addresses the proof of concept for civil works applications by analyzing a data set taken by the Wright Labs/ERIM Data Collection System (DCS). The objective was to demonstrate the capability of an IFSAR system to provide high fidelity, fine resolution DTE that can be employed in hydraulic models of the Mississippi River watershed. The demonstration was sponsored by ARPA and TEC.

  13. The application of digital signal processing techniques to a teleoperator radar system

    NASA Technical Reports Server (NTRS)

    Pujol, A.

    1982-01-01

    A digital signal processing system was studied for the determination of the spectral frequency distribution of echo signals from a teleoperator radar system. The system consisted of a sample and hold circuit, an analog to digital converter, a digital filter, and a Fast Fourier Transform. The system is interfaced to a 16 bit microprocessor. The microprocessor is programmed to control the complete digital signal processing. The digital filtering and Fast Fourier Transform functions are implemented by a S2815 digital filter/utility peripheral chip and a S2814A Fast Fourier Transform chip. The S2815 initially simulates a low-pass Butterworth filter with later expansion to complete filter circuit (bandpass and highpass) synthesizing.

  14. Development of wide band digital receiver for atmospheric radars using COTS board based SDR

    NASA Astrophysics Data System (ADS)

    Yasodha, Polisetti; Jayaraman, Achuthan; Thriveni, A.

    2016-07-01

    Digital receiver extracts the received echo signal information, and is a potential subsystem for atmospheric radar, also referred to as wind profiling radar (WPR), which provides the vertical profiles of 3-dimensional wind vector in the atmosphere. This paper presents the development of digital receiver using COTS board based Software Defined Radio technique, which can be used for atmospheric radars. The developmental work is being carried out at National Atmospheric Research Laboratory (NARL), Gadanki. The digital receiver consists of a commercially available software defined radio (SDR) board called as universal software radio peripheral B210 (USRP B210) and a personal computer. USRP B210 operates over a wider frequency range from 70 MHz to 6 GHz and hence can be used for variety of radars like Doppler weather radars operating in S/C bands, in addition to wind profiling radars operating in VHF, UHF and L bands. Due to the flexibility and re-configurability of SDR, where the component functionalities are implemented in software, it is easy to modify the software to receive the echoes and process them as per the requirement suitable for the type of the radar intended. Hence, USRP B210 board along with the computer forms a versatile digital receiver from 70 MHz to 6 GHz. It has an inbuilt direct conversion transceiver with two transmit and two receive channels, which can be operated in fully coherent 2x2 MIMO fashion and thus it can be used as a two channel receiver. Multiple USRP B210 boards can be synchronized using the pulse per second (PPS) input provided on the board, to configure multi-channel digital receiver system. RF gain of the transceiver can be varied from 0 to 70 dB. The board can be controlled from the computer via USB 3.0 interface through USRP hardware driver (UHD), which is an open source cross platform driver. The USRP B210 board is connected to the personal computer through USB 3.0. Reference (10 MHz) clock signal from the radar master oscillator

  15. A novel digital receiver concept for ISRO's future remote sensing radars

    NASA Astrophysics Data System (ADS)

    Desai, Nilesh; Vachhani, J. G.; Soin, Sumit; Agrawal, Rinku; Rao, C. V. N.; Gujraty, Virendra; Rana, Surindersingh

    2006-12-01

    Technology development related to digital, antenna and RF subsystems for Microwave Radar Sensors like Synthetic Aperture Radar, Scatterometer, Altimeter and Radiometer is one of the major activities under ISRO's microwave remote sensing programme, since 1980s. These technologies are now being gainfully utilized for building ISRO's operational Earth Observation missions involving microwave sensors like Radar Imaging Satellite, RISAT SAR, Oceansat-2 Scatterometer, Megha-Tropiques, MADRAS and Airborne SAR for Disaster Management, DMSAR. Concurrently, advanced technology developments in these fields are underway to meet the major technological challenges of building ISRO's proposed advanced microwave missions like ultra-high resolution SAR's, Synthetic Aperture Radiometer (SARAD), Milli-meter and sub-millimeter wave sounders and SAR Constellations for Disaster management as well as Interferometric, Polarmetric and polarmetric interferometry applications. Also, these hardware are being designed with core radar electronics concept, in which the same RF and digital hardware sub-units / modules will be utilized to build different microwave radar sensors. One of the major and common requirements for all these active and passive microwave sensors is the moderate to highspeed data acquisition and signal processing system. Traditionally, the Data acquisition units for all these radar sensors are implemented as stand-alone units, following the radar receivers. For ISRO's C-band airborne SAR (ASAR) and RISAT high resolution SAR, we have designed and developed High Speed 8-bit ADC based I/Q Digitisers, operating at 30.814 MHz and 250 MHz sampling rates, respectively. With the increasing demand of wide bandwidth and ultra-high resolution in imaging and non-imaging radar systems, the technology trend worldwide is towards a digital receiver, involving bandpass or IF sampling, thus eliminating the need for RF down converters and analog IQ demodulators. In order to evolve a generic

  16. On the spatiotemporal evolution of the ionospheric backscatter during magnetically disturbed periods as observed by the TIGER Bruny Island HF radar

    NASA Astrophysics Data System (ADS)

    Kumar, V. V.; Makarevich, R. A.; Kane, T. A.; Ye, H.; Devlin, J. C.; Dyson, P. L.

    2011-08-01

    The Superposed Epoch Analysis (SEA) method is used to examine a 4-year database (2000-2003) of the TIGER Bruny Island radar (MLON=226.78°E, MLAT=55.06°S) measurements to determine typical patterns of the spatiotemporal evolution of ionospheric backscatter during geomagnetically disturbed periods. SEA is performed separately for three disturbance categories: short-, medium-, and long-duration magnetic disturbances, based on the Dst index variation. Prior to SEA, the diurnal, seasonal, and solar cycle effects have been accounted for by subtracting the nominal quiet-time values. It is found that the occurrence of ionospheric HF backscatter exhibited strongest enhancements near t=0 h between 65°S and 70°S MLAT (range of 800-2500 km) during short-duration magnetic disturbance. In contrast, a reduction in echo occurrence first occurred near t=0 h at higher ranges (r≥2500 km) and expanded equatorwards during the recovery phase of the magnetic disturbances. This reduction in occurrence became progressively stronger and prolonged for medium- and long-duration magnetic disturbances. These categories also showed clear enhancements in the E-region backscatter (r<765 km) commencing from t=0 h. These observations can be explained by three main factors: (1) an enhancement in the E-region densities due to high-energy particle precipitation during magnetically disturbed periods causing the HF radar waves to refract from smaller altitudes and closer ranges, (2) a variability in the F-region densities associated with magnetic disturbances also affecting the propagation of the HF radar waves, and (3) a short-lived strong enhancement in growth rate of decametre-scale ionospheric irregularities when IMF turned southwards causing the highest echo occurrence near t=0 h during SEA.

  17. Near-Subsurface Science from a Digital Beamforming Polarimetric Synthetic Aperture Radar

    NASA Astrophysics Data System (ADS)

    Carter, L. M.; Rincon, R. F.

    2015-10-01

    Many important questions in planetary science depends on our ability to detect and map surface and subsurface layers of planetary bodies. We are developing a P-band (435 MHz, 70 cm wavelength) digital beamforming radar, called Space Exploration SAR (SESAR), capable of providing the measurement flexibility needed to address multiple types of science goals. SESAR will provide high spatial resolution imaging, full polarimetry, multibeam scatterometry and altimetry of planetary targets such as the Moon and Mars by using beamforming technology that can adjust the radar experiment to meet the specific science goals of each target.

  18. Drift Velocity of Small-Scale Artificial Ionospheric Irregularities According to Multifrequency HF Doppler Radar. I. Method of Calculation and Its Hardware Implementation

    NASA Astrophysics Data System (ADS)

    Vertogradov, G. G.; Uryadov, V. P.; Vertogradov, V. G.; Vertogradova, E. G.; Kubatko, S. V.

    2015-10-01

    The method of calculating the total drift velocity vector of small-scale artificial ionospheric irregularities as measured by the effective Doppler frequency shift of aspect-scattered signals from several diagnostic illumination transmitters operated at different frequencies is discussed. The technique of adaptive simulation of decameter radio waves propagating in an inhomogeneous magnetized ionosphere with allowance for the aspect scattering effects due to small-scale field-aligned irregularities is developed. A multifrequency HF Doppler radar for simultaneous measurement of the Doppler spectra of radio signals at a set of frequencies is described.

  19. Drift Velocity of Small-Scale Artificial Ionospheric Irregularities According to a Multifrequency HF Doppler Radar. II. Observation and Modeling Results

    NASA Astrophysics Data System (ADS)

    Vertogradov, G. G.; Uryadov, V. P.; Vertogradov, V. G.; Vertogradova, E. G.; Kubatko, S. V.

    2015-11-01

    We present the results of observations of the Doppler frequency shift for the radar radio signals of broadcast and exact-time RWM stations, which are scattered by small-scale artificial ionospheric irregularities. By the method described in our previous paper [1] and using the multifrequency HF Doppler radar, estimates were made for a three-dimensional vector of the drift velocity of irregularities. It is shown that the drift velocity of irregularities can vary considerably both in magnitude and direction for short periods of time. The velocity lies in a wide range of values, 20-270 m/s, but sometimes it exceeds 500-700 m/s. The most probable drift velocity ranges from 40 to 70 m/s.

  20. MAS2-8 radar and digital control unit

    NASA Technical Reports Server (NTRS)

    Oberg, J. M.; Ulaby, F. T.

    1974-01-01

    The design of the MAS 2-8 (2 to 8 GHz microwave-active spectrometer), a ground-based sensor system, is presented. A major modification in 1974 to the MAS 2-8, that of a control subsystem to automate the data-taking operation, is the prime focus. The digital control unit automatically changes all system parameters except FM rate and records the return signal on paper tape. The overall system operation and a detailed discussion of the design and operation of the digital control unit are presented.

  1. Observations by the CUTLASS radar, HF Doppler, oblique ionospheric sounding, and TEC from GPS during a magnetic storm

    NASA Astrophysics Data System (ADS)

    Blagoveshchensky, D. V.; Lester, M.; Kornienko, V. A.; Shagimuratov, I. I.; Stocker, A. J.; Warrington, E. M.

    2005-07-01

    Multi-diagnostic observations, covering a significant area of northwest Europe, were made during the magnetic storm interval (28 29 April 2001) that occurred during the High Rate SolarMax IGS/GPS-campaign. HF radio observations were made with vertical sounders (St. Petersburg and Sodankyla), oblique incidence sounders (OIS), on paths from Murmansk to St. Petersburg, 1050 km, and Inskip to Leicester, 170 km, Doppler sounders, on paths from Cyprus to St. Petersburg, 2800 km, and Murmansk to St. Petersburg, and a coherent scatter radar (CUTLASS, Hankasalmi, Finland). These, together with total electron content (TEC) measurements made at GPS stations from the Euref network in northwest Europe, are presented in this paper. A broad comparison of radio propagation data with ionospheric data at high and mid latitudes, under quiet and disturbed conditions, was undertaken. This analysis, together with a geophysical interpretation, allow us to better understand the nature of the ionospheric processes which occur during geomagnetic storms. The peculiarity of the storm was that it comprised of three individual substorms, the first of which appears to have been triggered by a compression of the magnetosphere. Besides the storm effects, we have also studied substorm effects in the observations separately, providing an improved understanding of the storm/substorm relationship. The main results of the investigations are the following. A narrow trough is formed some 10h after the storm onset in the TEC which is most likely a result of enhanced ionospheric convection. An enhancement in TEC some 2 3 h after the storm onset is most likely a result of heating and upwelling of the auroral ionosphere caused by enhanced currents. The so-called main effect on ionospheric propagation was observed at mid-latitudes during the first two substorms, but only during the first substorm at high latitudes. Ionospheric irregularities observed by CUTLASS were clearly related to the gradient in TEC

  2. Multi-DSP and FPGA based Multi-channel Direct IF/RF Digital receiver for atmospheric radar

    NASA Astrophysics Data System (ADS)

    Yasodha, Polisetti; Jayaraman, Achuthan; Kamaraj, Pandian; Durga rao, Meka; Thriveni, A.

    2016-07-01

    Modern phased array radars depend highly on digital signal processing (DSP) to extract the echo signal information and to accomplish reliability along with programmability and flexibility. The advent of ASIC technology has made various digital signal processing steps to be realized in one DSP chip, which can be programmed as per the application and can handle high data rates, to be used in the radar receiver to process the received signal. Further, recent days field programmable gate array (FPGA) chips, which can be re-programmed, also present an opportunity to utilize them to process the radar signal. A multi-channel direct IF/RF digital receiver (MCDRx) is developed at NARL, taking the advantage of high speed ADCs and high performance DSP chips/FPGAs, to be used for atmospheric radars working in HF/VHF bands. Multiple channels facilitate the radar t be operated in multi-receiver modes and also to obtain the wind vector with improved time resolution, without switching the antenna beam. MCDRx has six channels, implemented on a custom built digital board, which is realized using six numbers of ADCs for simultaneous processing of the six input signals, Xilinx vertex5 FPGA and Spartan6 FPGA, and two ADSPTS201 DSP chips, each of which performs one phase of processing. MCDRx unit interfaces with the data storage/display computer via two gigabit ethernet (GbE) links. One of the six channels is used for Doppler beam swinging (DBS) mode and the other five channels are used for multi-receiver mode operations, dedicatedly. Each channel has (i) ADC block, to digitize RF/IF signal, (ii) DDC block for digital down conversion of the digitized signal, (iii) decoding block to decode the phase coded signal, and (iv) coherent integration block for integrating the data preserving phase intact. ADC block consists of Analog devices make AD9467 16-bit ADCs, to digitize the input signal at 80 MSPS. The output of ADC is centered around (80 MHz - input frequency). The digitized data is fed

  3. A digital system to produce imagery from SAR data. [Synthetic Aperture Radar

    NASA Technical Reports Server (NTRS)

    Wu, C.

    1976-01-01

    This paper describes a digital processing algorithm and its associated system design for producing images from Synthetic Aperture Radar (SAR) data. The proposed system uses the Fast Fourier Transform (FFT) approach to perform the two-dimensional correlation process. The range migration problem, which is often a major obstacle to efficient processing, can be alleviated by approximating the locus of echoes from a point target by several linear segments. SAR data corresponding to each segment is correlated separately, and the results are coherently summed to produce full-resolution images. This processing approach exhibits greatly improved computation efficiency relative to conventional digital processing methods.

  4. 47 CFR 73.758 - System specifications for digitally modulated emissions in the HF broadcasting service.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...) For digitally modulated emissions, the Digital Radio Mondiale (DRM) standard shall be employed. Both digital audio broadcasting and datacasting are authorized. The RF requirements for the DRM system are... require that the digital spectral power density (and total power) be lower by several dB than is...

  5. 47 CFR 73.758 - System specifications for digitally modulated emissions in the HF broadcasting service.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ...) For digitally modulated emissions, the Digital Radio Mondiale (DRM) standard shall be employed. Both digital audio broadcasting and datacasting are authorized. The RF requirements for the DRM system are... require that the digital spectral power density (and total power) be lower by several dB than is...

  6. 47 CFR 73.758 - System specifications for digitally modulated emissions in the HF broadcasting service.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ...) For digitally modulated emissions, the Digital Radio Mondiale (DRM) standard shall be employed. Both digital audio broadcasting and datacasting are authorized. The RF requirements for the DRM system are... require that the digital spectral power density (and total power) be lower by several dB than is...

  7. A Statistical study of the Doppler spectral width of high-latitude ionospheric F-region echoes recorded with SuperDARN coherent HF radars

    NASA Astrophysics Data System (ADS)

    Villain, J.-P.; André, R.; Pinnock, M.; Greenwald, R. A.; Hanuise, C.

    2002-11-01

    The HF radars of the Super Dual Auroral Radar Network (SuperDARN) provide measurements of the E × B drift of ionospheric plasma over extended regions of the high-latitude ionosphere. We have conducted a statistical study of the associated Doppler spectral width of ionospheric F-region echoes. The study has been conducted with all available radars from the Northern Hemisphere for 2 specific periods of time. Period 1 corresponds to the winter months of 1994, while period 2 covers October 1996 to March 1997. The distributions of data points and average spectral width are presented as a function of Magnetic Latitude and Magnetic Local Time. The databases are very consistent and exhibit the same features. The most stringent features are: a region of very high spectral width, collocated with the ionospheric LLBL/cusp/mantle region; an oval shaped region of high spectral width, whose equator-ward boundary matches the poleward limit of the Holzworth and Meng auroral oval. A simulation has been conducted to evaluate the geometrical and instrumental effects on the spectral width. It shows that these effects cannot account for the observed spectral features. It is then concluded that these specific spectral width characteristics are the signature of ionospheric/magnetospheric coupling phenomena.

  8. Digital tapped delay lines for HWIL testing of matched filter radar receivers

    NASA Astrophysics Data System (ADS)

    Olson, Richard F.; Braselton, William J.; Mohlere, Richard D.

    2009-05-01

    Matched filter processing for pulse compression of phase coded waveforms is a classic method for increasing radar range measurement resolution. A generic approach for simulating high resolution range extended radar scenes in a Hardware in the Loop (HWIL) test environment is to pass the phase coded radar transmit pulse through an RF tapped delay line comprised of individually amplitude- and phase-weighted output taps. In the generic approach, the taps are closely spaced relative to time intervals equivalent to the range resolution of the compressed radar pulse. For a range-extended high resolution clutter scene, the increased number of these taps can make an analog implementation of an RF tapped delay system impractical. Engineers at the U.S. Army Aviation and Missile Research, Development and Engineering Center (AMRDEC) have addressed this problem by transferring RF tapped delay line signal operations to the digital domain. New digital tapped delay line (DTDL) systems have been designed and demonstrated which are physically compact compared to analog RF TDLs, leverage low cost FPGA and data converter technology, and may be readily expanded using open slots in a VME card cage. In initial HWIL applications, the new DTDLs have been shown to produce better dynamic range in pulse compressed range profiles than their analog TDL predecessors. This paper describes the signal requirements and system architecture for digital tapped delay lines. Implementation, performance, and HWIL simulation integration issues for AMRDEC's first generation DTDLs are addressed. The paper concludes with future requirements and plans for ongoing DTDL technology development at AMRDEC.

  9. The response of the high-latitude ionosphere to the coronal mass ejection event of April 6, 2000: A practical demonstration of space weather nowcasting with the Super Dual Auroral Radar Network HF radars

    NASA Astrophysics Data System (ADS)

    Ruohoniemi, J. M.; Barnes, R. J.; Greenwald, R. A.; Shepherd, S. G.

    2001-12-01

    The ionosphere at high latitudes is the site of important effects in space weather. These include strong electrical currents that may disrupt power systems through induced currents and density irregularities that can degrade HF and satellite communication links. With the impetus provided by the National Space Weather Program, the radars of the Super Dual Auroral Radar Network have been applied to the real-time specification (``nowcasting'') of conditions in the high-latitude ionosphere. A map of the plasma convection in the northern high-latitude ionosphere is continually generated at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) SuperDARN web site using data downloaded in real time from the radars via Internet connections. Other nowcast items include information on the conditions of HF propagation, the spatial extent of auroral effects, and the total cross polar cap potential variation. Time series of various parameters and an animated replay of the last 2 hours of convection patterns are also available for review. By comparing with simultaneous measurements from an upstream satellite, it is possible to infer the effective delay from the detection of changes in the solar wind at the satellite to the arrival of related effects in the high-latitude ionosphere. We discuss the space weather products available from the JHU/APL SuperDARN web site and their uses by simulating a nowcast of the ionosphere on April 6, 2000, during the arrival of a coronal mass ejection (CME) -related shock. The nowcast convection pattern in particular satisfies a critical need for timely, comprehensive information on ionospheric electric fields.

  10. Complementary code and digital filtering for detection of weak VHF radar signals from the mesoscale. [SOUSY-VHF radar, Harz Mountains, Germany

    NASA Technical Reports Server (NTRS)

    Schmidt, G.; Ruster, R.; Czechowsky, P.

    1983-01-01

    The SOUSY-VHF-Radar operates at a frequency of 53.5 MHz in a valley in the Harz mountains, Germany, 90 km from Hanover. The radar controller, which is programmed by a 16-bit computer holds 1024 program steps in core and controls, via 8 channels, the whole radar system: in particular the master oscillator, the transmitter, the transmit-receive-switch, the receiver, the analog to digital converter, and the hardware adder. The high-sensitivity receiver has a dynamic range of 70 dB and a video bandwidth of 1 MHz. Phase coding schemes are applied, in particular for investigations at mesospheric heights, in order to carry out measurements with the maximum duty cycle and the maximum height resolution. The computer takes the data from the adder to store it in magnetic tape or disc. The radar controller is programmed by the computer using simple FORTRAN IV statements. After the program has been loaded and the computer has started the radar controller, it runs automatically, stopping at the program end. In case of errors or failures occurring during the radar operation, the radar controller is shut off caused either by a safety circuit or by a power failure circuit or by a parity check system.

  11. Ionospheric Pc5 plasma oscillations observed by the King Salmon HF radar and their comparison with geomagnetic pulsations on the ground and in geostationary orbit

    NASA Astrophysics Data System (ADS)

    Sakaguchi, K.; Nagatsuma, T.; Ogawa, T.; Obara, T.; Troshichev, O. A.

    2012-03-01

    We analyzed Pc5 (1.7-6.7 mHz) oscillations of ionospheric Doppler plasma velocity observed on a westward pointing beam 3 of the SuperDARN King Salmon HF radar in Alaska during the solar maximum in 2002 and the minimum in 2007. Local time distributions of the ionospheric Pc5 oscillations showed peculiar asymmetric characteristics in both years; that is, the occurrence probability had a maximum around the magnetic midnight, whereas backscatter echoes exhibited almost no oscillation on the dayside. We compared these ionospheric Pc5 events with magnetic field variations on the ground under the radar beam at Pebek and King Salmon and the geostationary ETS-8 satellite at almost conjugate longitude. We found only a few nightside events where both the radar and magnetometers detected similar sinusoidal oscillations. On the other hand, from statistical spectral analyses we found that there were positive correlations between the integrated Pc5 range spectral power of velocity oscillations and the geomagnetic pulsations both on the ground and in geostationary orbit although the pulsation powers were quite low. For these ionospheric Pc5 events, we found that both solar wind bulk flow speed and dynamic pressure showed no correlation with the spectral power and more than half of the Pc5 events were observed when the geomagnetic activities were low as inferred from the AE and Dst indices. These results indicate that the azimuthal Pc5 oscillation in the ionospheric plasma flow does not represent well-known characteristics of Pc5 pulsations driven by solar wind changes. We consider that the nightside occurrence peak of the ionospheric Pc5 oscillation might be related to diurnal changes in the ionospheric conductivity, which controls the amplitude of wave electric fields in the ionosphere. Therefore, the Pc5 wave power distributions obtained by radar observations provide features different from those obtained from magnetic field observations.

  12. Synthetic Aperture Radar Interferometry for Digital Elevation Model of Kuwait Desert - Analysis of Errors

    NASA Astrophysics Data System (ADS)

    Jassar, H. K. Al; Rao, K. S.

    2012-07-01

    Using different combinations of 29 Advanced Synthetic Aperture Radar (ASAR) images, 43 Digital Elevations Models (DEM) were generated adopting SAR Interferometry (InSAR) technique. Due to sand movement in desert terrain, there is a poor phase correlation between different SAR images. Therefore, suitable methodology for generating DEMs of Kuwait desert terrain using InSAR technique were worked out. Time series analysis was adopted to derive the best DEM out of 43 DEMs. The problems related to phase de-correlation over desert terrain are discussed. Various errors associated with the DEM generation are discussed which include atmospheric effects, penetration into soil medium, sand movement. The DEM of Shuttle Radar Topography Mission (SRTM) is used as a reference. The noise levels of DEM of SRTM are presented.

  13. Effects of Analog-to-Digital Converter Nonlinearities on Radar Range-Doppler Maps.

    SciTech Connect

    Doerry, Armin Walter; Dubbert, Dale F.; Tise, Bertice L.

    2014-07-01

    Radar operation, particularly Ground Moving Target Indicator (GMTI) radar modes, are very sensitive to anomalous effects of system nonlinearities. These throw off harmonic spurs that are sometimes detected as false alarms. One significant source of nonlinear behavior is the Analog to Digital Converter (ADC). One measure of its undesired nonlinearity is its Integral Nonlinearity (INL) specification. We examine in this report the rela tionship of INL to GMTI performance. - 4 - Acknowledgements This report is the result of a n unfunded Research and Development effort . Sandia National Laboratories is a multi - program laboratory managed and operated by Sandia Corporation, a wholly owned subsidia ry of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE - AC04 - 94AL85000.

  14. Occurrence characteristics of subauroral westward plasma flows and lowest speed threshold of SAPS observed by the SuperDARN Hokkaido HF radar

    NASA Astrophysics Data System (ADS)

    Nagano, H.; Nishitani, N.; Hori, T.

    2014-12-01

    Westward rapid plasma flows in the ionosphere at subauroral latitudes are called "Sub-Auroral Polarization Stream (SAPS) [Foster and Burke, 2002]". SAPS is a manifestation of the Magnetosphere-Ionosphere (M-I) coupling. Therefore, it is important to know occurrence characteristics of SAPS in order to understand the details of M-I coupling system. As a result of the present analysis of SAPS using the SuperDARN Hokkaido HF radar, Kataoka et al. [2009] reported that positions of SAPS shifts toward lower latitude with decreasing Dst index. We investigate the characteristics of SAPS, with focus on the relationship between occurrence characteristics of SAPS and a variety of solar wind and geomagnetic parameters, using the SuperDARN Hokkaido HF radar with a field of view covering Far East Russia, which has been in operation since 2006. In particular, we identify the lowest limit of SAPS speed, which has not been discussed in the previous literatures. This is to examine the lowest threshold of electric field to generate SAPS as a result of M-I coupling. In order to investigate SAPS occurrence characteristics comprehensively, we analyzed events with wider ranges of velocity and MLAT than those in the previous studies. As a result of statistical analysis, we found two categories of westward flows that were reasonably separated with a speed threshold of ~150-200 m/s. For the faster flows above the threshold there is a clear correlation between MLAT and Dst index, whereas for the slower flows there is no such correlation. Similar correlation is found for MLT and AL index as well. The faster flows are considered to be SAPS, whereas the slower flows are probably associated with midlatitude F-region ionospheric irregularities not directly related to storms / substorms.

  15. Combined flatland ST radar and digital-barometer network observations of mesoscale processes

    NASA Technical Reports Server (NTRS)

    Clark, W. L.; Vanzandt, T. E.; Gage, K. S.; Einaudi, F. E.; Rottman, J. W.; Hollinger, S. E.

    1991-01-01

    The paper describes a six-station digital-barometer network centered on the Flatland ST radar to support observational studies of gravity waves and other mesoscale features at the Flatland Atmospheric Observatory in central Illinois. The network's current mode of operation is examined, and a preliminary example of an apparent group of waves evident throughout the network as well as throughout the troposphere is presented. Preliminary results demonstrate the capabilities of the current operational system to study wave convection, wave-front, and other coherent mesoscale interactions and processes throughout the troposphere. Unfiltered traces for the pressure and horizontal zonal wind, for days 351 to 353 UT, 1990, are illustrated.

  16. Digital processing of orbital radar data to enhance geologic structure - Examples from the Canadian Shield

    NASA Technical Reports Server (NTRS)

    Masuoka, Penny M.; Harris, Jeff; Lowman, Paul D., Jr.; Blodget, Herbert W.

    1988-01-01

    Various digital enhancement techniques for SAR are compared using SIR-B and Seasat images of the Canadian Shield. The three best methods for enhancing geological structure were found to be: (1) a simple linear contrast stretch; (2) a mean or median low-pass filter to reduce speckle prior to edge enhancement or a K nearest-neighbor average to cosmetically reduce speckle; and (3) a modification of the Moore-Waltz (1983) technique. Three look directions were coregistered and several means of data display were investigated as means of compensating for radar azimuth biasing.

  17. Modern Radar Techniques for Geophysical Applications: Two Examples

    NASA Technical Reports Server (NTRS)

    Arokiasamy, B. J.; Bianchi, C.; Sciacca, U.; Tutone, G.; Zirizzotti, A.; Zuccheretti, E.

    2005-01-01

    The last decade of the evolution of radar was heavily influenced by the rapid increase in the information processing capabilities. Advances in solid state radio HF devices, digital technology, computing architectures and software offered the designers to develop very efficient radars. In designing modern radars the emphasis goes towards the simplification of the system hardware, reduction of overall power, which is compensated by coding and real time signal processing techniques. Radars are commonly employed in geophysical radio soundings like probing the ionosphere; stratosphere-mesosphere measurement, weather forecast, GPR and radio-glaciology etc. In the laboratorio di Geofisica Ambientale of the Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome, Italy, we developed two pulse compression radars. The first is a HF radar called AIS-INGV; Advanced Ionospheric Sounder designed both for the purpose of research and for routine service of the HF radio wave propagation forecast. The second is a VHF radar called GLACIORADAR, which will be substituting the high power envelope radar used by the Italian Glaciological group. This will be employed in studying the sub glacial structures of Antarctica, giving information about layering, the bed rock and sub glacial lakes if present. These are low power radars, which heavily rely on advanced hardware and powerful real time signal processing. Additional information is included in the original extended abstract.

  18. Digital Terrestrial Video Broadcast Interference Suppression in Forward-Looking Ground Penetrating Radar Systems

    NASA Astrophysics Data System (ADS)

    Rial, F. I.; Mendez-Rial, Roi; Lawadka, Lukasz; Gonzalez-Huici, Maria A.

    2014-11-01

    In this paper we show how radio frequency interference (RFI) generated by digital video broadcasting terrestrial and digital audio broadcasting transmitters can be an important noise source for forward-looking ground penetrating radar (FLGPR) systems. Even in remote locations the average interference power sometimes exceeds ultra-wideband signals by many dB, becoming the limiting factor in the system sensitivity. The overall problem of RFI and its impact in GPR systems is briefly described and several signal processing approaches to removal of RFI are discussed. These include spectral estimation and coherent subtraction algorithms and various filter approaches which have been developed and applied by the research community in similar contexts. We evaluate the performance of these methods by simulating two different scenarios submitted to real RFI acquired with a FLGPR system developed at the Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR), (GER). The effectiveness of these algorithms in removing RFI is presented using some performance indices after suppression.

  19. Digital Beamforming Synthetic Aperture Radar (DBSAR): Performance Analysis During the Eco-3D 2011 and Summer 2012 Flight Campaigns

    NASA Technical Reports Server (NTRS)

    Rincon, Rafael F.; Fatoyinbo, Temilola; Carter, Lynn; Ranson, K. Jon; Vega, Manuel; Osmanoglu, Batuhan; Lee, SeungKuk; Sun, Guoqing

    2014-01-01

    The Digital Beamforming Synthetic Aperture radar (DBSAR) is a state-of-the-art airborne radar developed at NASA/Goddard for the implementation, and testing of digital beamforming techniques applicable to Earth and planetary sciences. The DBSAR measurements have been employed to study: The estimation of vegetation biomass and structure - critical parameters in the study of the carbon cycle; The measurement of geological features - to explore its applicability to planetary science by measuring planetary analogue targets. The instrument flew two test campaigns over the East coast of the United States in 2011, and 2012. During the campaigns the instrument operated in full polarimetric mode collecting data from vegetation and topography features.

  20. Dynamical critical scaling of electric field fluctuations in the greater cusp and magnetotail implied by HF radar observations of F-region Doppler velocity

    NASA Astrophysics Data System (ADS)

    Parkinson, M. L.

    2006-03-01

    Akasofu's solar wind ɛ parameter describes the coupling of solar wind energy to the magnetosphere and ionosphere. Analysis of fluctuations in ɛ using model independent scaling techniques including the peaks of probability density functions (PDFs) and generalised structure function (GSF) analysis show the fluctuations were self-affine (mono-fractal, single exponent scaling) over 9 octaves of time scale from ~46 s to ~9.1 h. However, the peak scaling exponent α0 was a function of the fluctuation bin size, so caution is required when comparing the exponents for different data sets sampled in different ways. The same generic scaling techniques revealed the organisation and functional form of concurrent fluctuations in azimuthal magnetospheric electric fields implied by SuperDARN HF radar measurements of line-of-sight Doppler velocity, vLOS, made in the high-latitude austral ionosphere. The PDFs of vLOS fluctuation were calculated for time scales between 1 min and 256 min, and were sorted into noon sector results obtained with the Halley radar, and midnight sector results obtained with the TIGER radar. The PDFs were further sorted according to the orientation of the interplanetary magnetic field, as well as ionospheric regions of high and low Doppler spectral width. High spectral widths tend to occur at higher latitude, mostly on open field lines but also on closed field lines just equatorward of the open-closed boundary, whereas low spectral widths are concentrated on closed field lines deeper inside the magnetosphere. The vLOS fluctuations were most self-affine (i.e. like the solar wind ɛ parameter) on the high spectral width field lines in the noon sector ionosphere (i.e. the greater cusp), but suggested multi-fractal behaviour on closed field lines in the midnight sector (i.e. the central plasma sheet). Long tails in the PDFs imply that "microbursts" in ionospheric convection occur far more frequently, especially on open field lines, than can be captured using

  1. FMCW channel sounder with digital processing for measuring the coherence of wideband HF radio links

    NASA Astrophysics Data System (ADS)

    Salous, S.

    1986-08-01

    Multipath propagation, and in particular, the interference between the ordinary and the extraordinary waves, places a fundamental constraint on the performance of wideband HF skywave radio links. Furthermore, the dispersive nature of ionospheric propagation causes phase nonlinearity and hence distortion of narrow pulses. In this paper, an FMCW wideband sounder built for the purposes of characterizing the channel is described. Spectral analysis of the audio output of the sounder via the FFT algorithm is shown to permit measurement of thef amplitude/frequency function, the polarization bandwidth, the fade rate, the fade depth and the distortion of a narrow pulse, all for a desired isolated ionospheric propagation mode. The sounder was used to collect data over an oblique path in the UK. The results of applying the FFT processing technique to the experimental data are presented.

  2. Digital image processing system for a high-powered CO2 laser radar

    NASA Astrophysics Data System (ADS)

    Corbett, Francis J.; Groden, Michael; Dryden, Gordon L.; Pfeiffer, George; Boos, Robert; Youmans, Douglas G.

    1996-11-01

    Textron has designed and built a high-powered CO2 laser radar for long range targeting and remote sensing. This is a coherent, multi-wavelength system with a 2D, wide-band image processing capability. The digital processor produces several output products from the transmitter return signals including range, velocity, angle, and 2D range-Doppler images of hard-body targets (LADAR mode). In addition, the processor sorts and reports on data acquired from gaseous targets by wavelength and integrated path absorption (LIDAR mode). The digital processor has been developed from commercial components with a SUN SPARC 20 serving as the operator workstation and display. The digital output products are produced in real time and stored off-line for post-mission analysis and further target enhancements. This LADAR is distinguished from other designs primarily by the waveforms produced by the laser for target interrogation. The digital processing algorithms are designed to extract certain features through operation on each of the two waveforms. The waveforms are a pulse-tone and a pulse-burst designed for target acquisition and track, and 2D imaging respectively. The algorithms are categorized by function as acquisition/track, 2D imaging, integrated absorption for gaseous targets, and post mission enhancements such as tomographic reconstruction for multiple looks at targets from different perspectives. Field tests are now in process and results acquired from Feb.-June '96 will be reported on. The digital imaging system, its architecture, algorithms, simulations, and products will be described.

  3. Simultaneous ground-based optical and HF radar observations of the ionospheric footprint of the open/closed field line boundary along the geomagnetic meridian

    NASA Astrophysics Data System (ADS)

    Chen, X.-C.; Lorentzen, D. A.; Moen, J. I.; Oksavik, K.; Baddeley, L. J.

    2015-11-01

    Previous studies have confirmed that the equatorward boundaries of OI 630.0 nm auroral emissions and broad Doppler spectral widths in Super Dual Auroral Radar Network (SuperDARN) data, the so-called spectral width boundary (SWB), are good empirical proxies for the dayside open/closed field line boundary (OCB) in the ionosphere. However, both observational techniques are associated with mapping errors. SuperDARN uses a virtual height model for mapping, but it is not well known how the mapping error responds to a changing background ionosphere or transient reconnection events. Optical instruments, such as the meridian-scanning photometers, have high spatial resolution near zenith, where the mapping error due to the assumed OI 630.0 nm auroral emission height becomes small by comparison. In this work, an adjusted method is introduced to identify the SWB, which does not require temporal smoothing across several scans. The difference in latitude between the SWB, as identified using this method, and the simultaneously observed OI 630.0 nm auroral emission boundary along a common line of sight is compared. Utilizing the OI 630.0 nm boundary as a reference location, we present two case studies observed at different levels of solar activity. In both instances the latitude offset of SWB from the reference location is discussed in relation to the background ionospheric electron density. The compared results indicate that the intake of high-density solar extreme ultraviolet ionized plasma from subauroral latitudes causes a refraction of the HF radar beam path, which results in an overestimation of range mapping. The adjusted method would thus be a useful tool for identifying the OCB under changing ionospheric conditions in the cusp region.

  4. Atmospheric density remote sensing of mesosphere and thermosphere to be used for spacecraft design by adopting VHF radar and HF Doppler sounder at low latitude west Pacific site during winter time

    NASA Technical Reports Server (NTRS)

    Hung, R. J.; Tsao, Y. D.; Johnson, D. L.; Chen, A. J.; Lee, C. C.

    1989-01-01

    Simultaneous observations of VHF radar and HF Doppler array systems located at Chung Li (Taiwan) are used to observe three-dimensional wind speeds and gravity waves. The density perturbations are determined at different altitudes of the mesosphere and thermosphere during weak convective motions of the cold front in the winter. The present observations are believed to be valuable for space projects dealing with the low-latitude atmosphere.

  5. Integration of radar altimeter, precision navigation, and digital terrain data for low-altitude flight

    NASA Technical Reports Server (NTRS)

    Zelenka, Richard E.

    1992-01-01

    Avionic systems that depend on digitized terrain elevation data for guidance generation or navigational reference require accurate absolute and relative distance measurements to the terrain, especially as they approach lower altitudes. This is particularly exacting in low-altitude helicopter missions, where aggressive terrain hugging maneuvers create minimal horizontal and vertical clearances and demand precise terrain positioning. Sole reliance on airborne precision navigation and stored terrain elevation data for above-ground-level (AGL) positioning severely limits the operational altitude of such systems. A Kalman filter is presented which blends radar altimeter returns, precision navigation, and stored terrain elevation data for AGL positioning. The filter is evaluated using low-altitude helicopter flight test data acquired over moderately rugged terrain. The proposed Kalman filter is found to remove large disparities in predicted AGL altitude (i.e., from airborne navigation and terrain elevation data) in the presence of measurement anomalies and dropouts. Previous work suggested a minimum clearance altitude of 220 ft AGL for a near-terrain guidance system; integration of a radar altimeter allows for operation of that system below 50 ft, subject to obstacle-avoidance limitations.

  6. Pc 3-4 Pulsations Near the Cusp: Observations using Search Coil Magnetometers and HF Radars on Svalbard

    NASA Astrophysics Data System (ADS)

    Engebretson, M. J.; Lu, F.; Posch, J.; Lessard, M. R.; Kim, H.; Wright, D.; Yeoman, T.; Johnson, J.

    2008-12-01

    Pc 3-4 pulsations (f ~10-100 mHz) originating in the ion foreshock upstream of Earth's bow shock due to the interaction between reflected ions and the solar wind frequently are observed in dayside ground magnetometer records at high latitudes. Many early studies noted increased Pc 3-4 wave power in the vicinity of the dayside cusp and inferred entry via the cusp, but later studies have revealed a more complex picture. In this study, we examined power near local noon at Pc 3-4 frequencies observed by search coil magnetometers at three closely-spaced stations on Svalbard (Ny Alesund, Longyearbyen, and Hornsund). Nineteen days with clear band-limited Pc 3-4 wave power near local noon, and thirteen days with only broadband wave power, were selected for which clear cusp signatures were available in data from the Finland SuperDARN radar, which was used to accurately determine the cusp latitude. 3-s resolution fixed- beam mode data from a radar beam viewing over Svalbard also made it possible to determine Pc 3-4 periodicity in regions of the cusp and auroral zone ionosphere that returned sufficient signal. Band-limited (Pc 3-4) and broadband ULF signals in near-noon magnetometer data showed a similar latitude distribution: wave power peaked about 4-5 degrees south of the cusp. Radar backscatter from the cusp showed no evidence of Pc 3-4 modulation in this region during any of these intervals, whereas two intervals of data at lower latitudes did show modulation at Pc 3-4 frequencies. These observations are consistent not with entry via the cusp proper but along field lines equatorward of the cusp which map to the low-latitude boundary layer or outer magnetosphere. Because this location is similar to that observed for the maximum power of traveling convection vortex events / magnetic impulse events (TCVs/MIEs), we suggest that similar physics may play a role in transmitting perturbations from the upstream solar wind into the dayside magnetosphere in both cases.

  7. A comparison study of zonal drift velocities measurements as seen by MF spaced antenna and HF Doppler radar in the Indian dip equatorial mesospheric and lower thermospheric (80-100 km) region

    NASA Astrophysics Data System (ADS)

    Ramkumar, T. K.; Gurubaran, S.; Rajaram, R.; Tiwari, D.; Viswanathan, K. S.

    2010-02-01

    The simultaneous measurements of zonal drift velocities, observed in the heights of 84-98 km in the Indian geomagnetic dip equatorial region by an medium frequency (MF, 1.98 MHz) spaced antenna and a high-frequency (HF, 18 MHz) Doppler radars, are compared on selected few days in the solar maximum years of 1998, 1999, and 2000. The agreement between the two radar measurements is found to be good below about 88 km, where the neutral turbulence induced ionospheric irregularities are more predominant. Above 90 km, however, the agreement becomes poor and at the highest height of 98 km it becomes the least. At this height, more often the HF Doppler radar shows a westward drift of about 200 m/s whereas the MF spaced antenna radar values lie within ±10 m/s and sometimes attain maximum values of ±50 m/s. Detailed discussions are made on the possible sources of underestimation of the drift velocities measured by the MF radar and the nature of scattering irregularities that are produced because of large neutral turbulences and plasma instabilities. It is suggested that these neutral and plasma turbulences (particularly type II plasma irregularities) contribute in a different manner to different radar frequencies and techniques and hence very different drift velocities in the heights of 90-100 km particularly in the geomagnetic dip equatorial region. Discussions are also made on (1) the real atmospheric and ionospheric physical process prevailing in the 90-100 km region and (2) the technical aspects of the radars that limits them to measure only particular types of motion in this region.

  8. The application of the ADSP-21020 40-bit floating point DSP microprocessor in a digital Doppler radar

    SciTech Connect

    Robinson, S.H.; Morrison, R.E.

    1991-08-26

    A continuous wave doppler radar system has been designed which is portable, easily deployable and can be remotely controlled. The system is immune to ground clutter and is used for wind speed detection and direction determination. Nearly real time digital signal processing is performed by an Analog Devices ADSP-21020, a 40-bit floating point Digital Signal Processing (DSP) microprocessor. This paper provides an overview of the design of the system including the radio frequency (RF) to digital interface. The various DSP detection algorithms are discussed and compared to system performance and sensitivity. Finally, DSP performance is compared to the performance of an earlier system using Analog Device's ADSP-2100. 6 refs.

  9. Digital processing considerations for extraction of ocean wave image spectra from raw synthetic aperture radar data

    NASA Technical Reports Server (NTRS)

    Lahaie, I. J.; Dias, A. R.; Darling, G. D.

    1984-01-01

    The digital processing requirements of several algorithms for extracting the spectrum of a detected synthetic aperture radar (SAR) image from the raw SAR data are described and compared. The most efficient algorithms for image spectrum extraction from raw SAR data appear to be those containing an intermediate image formation step. It is shown that a recently developed compact formulation of the image spectrum in terms of the raw data is computationally inefficient when evaluated directly, in comparison with the classical method where matched-filter image formation is an intermediate result. It is also shown that a proposed indirect procedure for digitally implementing the same compact formulation is somewhat more efficient than the classical matched-filtering approach. However, this indirect procedure includes the image formation process as part of the total algorithm. Indeed, the computational savings afforded by the indirect implementation are identical to those obtained in SAR image formation processing when the matched-filtering algorithm is replaced by the well-known 'dechirp-Fourier transform' technique. Furthermore, corrections to account for slant-to-ground range conversion, spherical earth, etc., are often best implemented in the image domain, making intermediate image formation a valuable processing feature.

  10. Novel deep-space radar systems and topside HF wave measurements as new sources of data for Space Weather services

    NASA Astrophysics Data System (ADS)

    Rothkaehl, H.; Thidé, B.; Baan, W. A.; Bergman, J.; Hanuise, C.; Moussas, X.; Watermann, J.

    To understand the properties of the solar terrestrial environment and to develop a quantitative model of the magnetosphere-ionosphere-thermosphere subsystem which is strongly coupled via the electric field particle precipitation heat flows and small scale interaction it is necessary to design and build new generation multi-point and multi-type sensor diagnostics as the LOFAR-LOIS system Ground-based multi-frequency and multi-polarisation netted radio and radar facilities and observation clusters in space will be helpful to find solutions to problems in space physics and to detect long-term environmental changes The innovative radio spectrometer on board the COMPASS satellite was designed to investigate the still largely unknown mechanisms which govern these turbulent interactions of natural and man-made origin Future simultaneous investigation and monitoring of the Earth environment by the combined LOIS-LOFAR system will be coordinated with space-borne low orbiting experiments Real-time access to such high-resolution multi-region data is likely to improve the quality of different types of space related services

  11. The Future of HF-Interaction Experiments at EISCAT

    NASA Astrophysics Data System (ADS)

    Rietveld, M. T.

    2007-05-01

    The EISCAT HF facility, co-located with two incoherent scatter radars, has some of the best diagnostics available for doing research in plasma physics and actively probing the ionosphere, upper atmosphere and magnetosphere. The facility is presently undergoing some improvements which will keep it at the forefront of such research. Direct digital synthesis of the HF wave will allow fast changes of frequency and beam direction, and increased flexibility in pulsing. Some of the more important recent results are outlined, and the directions for further progress are suggested. These results include the effect of electron heating on the charging of mesospheric dust which changes the strength of VHF radar echoes from the polar summer mesosphere. Other results involve Langmuir and thermal plasma instabilities from the F region which show a rich variety of dependences on pumping frequency and direction to the Earth's magnetic field. Some of the geometrical effects observed in plasma line observations and artificial optical emissions remain largely unexplained.

  12. Seasonal variation of a coastal jet in the Long Island Sound outflow region based on HF radar and Doppler current observations

    NASA Astrophysics Data System (ADS)

    Ullman, D. S.; Codiga, D. L.

    2004-07-01

    Surface current (HF radar) and velocity profile observations, obtained as part of the Front-Resolving Observational Network with Telemetry (FRONT) project over an approximately 2-year period, are used to describe the seasonal variability of a coastal jet in the Long Island Sound outflow region. The jet is observed in an area of the continental shelf where surface thermal fronts are frequently detected during both summer and winter. The current jet is coincident with a band of high summer frontal probability, and apparently arises from the interaction between Long Island Sound outflow and larger-scale alongshore currents on the shelf. The jet reaches peak strength in summer (transport of ˜0.07 Sv) and is weak or non-existent in winter. Flow is strongest near the surface and weakens with depth, with only moderate seasonal variations in the vertical shear. The relatively long data set of currents combined with historical hydrographic measurements and buoy wind observations is analyzed to examine the seasonal variability of the terms in the depth-averaged momentum balance. The depth-averaged pressure gradient is partitioned into a steric component, evaluated from the hydrography, and a non-steric component that is estimated as the residual of the computed terms in the momentum equation. The depth-averaged momentum balance is found to be approximately geostrophic in the across-shore direction. The seasonal variability in the jet arises due to the shifting balance between buoyancy-driven flow that is always downshelf but intensifies somewhat in summer and wind-driven flow which dominates in winter when wind stress becomes strongly upwelling favorable.

  13. The derivation of a sub-canopy digital terrain model of a flooded forest using synthetic aperture radar

    NASA Technical Reports Server (NTRS)

    Imhoff, Marc Lee; Gesch, Dean B.

    1990-01-01

    Synthetic aperture radar data from the Shuttle Imaging Radar-B Mission were combined with the tide surface information to create a digital terrain model for a 70-km by 40-km section of the Mouths of the Ganges forests in southern Bangladesh. The dominance of the interaction phenomenon (canopy to surface or surface to canopy reflection) in flooded forests was exploited to create sub-canopy flood boundary maps for two different tide times. The boundary maps were digitally combined in x, y, z space with tide elevation models created from tide gauge data gridding the survey site and used as input to interpolation routines to create a terrain model. The end product represents a significant step in our ability to characterize the topography and hydrology of wetland ecosystems. The model derived here can be used for simulating tidal flow and nutrient transport from the forest to the marine habitat.

  14. Hardware description ADSP-21020 40-bit floating point DSP as designed in a remotely controlled digital CW Doppler radar

    SciTech Connect

    Morrison, R.E.; Robinson, S.H.

    1991-01-01

    A continuous wave Doppler radar system has been designed which is portable, easily deployed, and remotely controlled. The heart of this system is a DSP/control board using Analog Devices ADSP-21020 40-bit floating point digital signal processor (DSP) microprocessor. Two 18-bit audio A/D converters provide digital input to the DSP/controller board for near real time target detection. Program memory for the DSP is dual ported with an Intel 87C51 microcontroller allowing DSP code to be up-loaded or down-loaded from a central controlling computer. The 87C51 provides overall system control for the remote radar and includes a time-of-day/day-of-year real time clock, system identification (ID) switches, and input/output (I/O) expansion by an Intel 82C55 I/O expander. 5 refs., 8 figs., 2 tabs.

  15. Digitally Calibrated TR Modules Enabling Real-Time Beamforming SweepSAR Architectures for DESDynI-Class Radar Instruments

    NASA Technical Reports Server (NTRS)

    Hoffman, James Patrick; Peral, Eva; Veilluex, Louise; Perkovic, Dragana; Shaffer, Scott

    2011-01-01

    Real-time digital beamforming, combined with lightweight, large aperture reflectors, enable SweepSAR architectures such as that of the proposed DESDynI [Deformation, Ecosystem Structure, and Dynamics of Ice] SAR [Synthetic Aperture Radar] Instrument (or DSI). SweepSAR promises significant increases in instrument capability for solid earth and biomass remote sensing, while reducing mission mass and cost. This new instrument concept requires new methods for calibrating the multiple channels, which must be combined on-board, in real-time. We are developing new methods for digitally calibrating digital beamforming arrays to reduce development time, risk and cost of precision calibrated TR modules for array architectures by accurately tracking modules' characteristics through closed-loop Digital Calibration, thus tracking systematic changes regardless of temperature

  16. High-resolution Precipitation and Lightning Monitoring by the Ku-band Broadband Radar and the VHF Broadband Digital Interferometer

    NASA Astrophysics Data System (ADS)

    Nakamura, Yoshitaka; Yoshikawa, Eiichi; Akita, Manabu; Morimoto, Takeshi; Ushio, Tomoo; Kawasaki, Zen-Ichiro; Saito, Toshiya; Nishida, Takashi; Sakazume, Norio

    We propose a high-resolution precipitation and lightning monitoring for meteorological application. This monitoring is mainly utilized the Ku-band broadband radar (BBR) and the VHF broadband digital interferometer (DITF). The BBR can accurately measure the radar reflectivity factor and the mean Doppler velocity with 5 m resolution over a range from 40 m to several kilometers for 10 W power using a pulse compression technique. The two or more DITFs make us visualize lightning channel propagations in three dimensions. Moreover, we add new functions that integrate these observation data and disclose integration analyses results with the quasi real-time information disclosure system. Initial observations for severe storms with lightning during summer and winter thunderstorm season by these monitoring instruments indicate that we obtain detailed precipitation distribution and detect active convective cells with lightning discharges.

  17. Atmospheric density remote sensing of mesosphere and thermosphere to be used for spacecraft design by adopting VHF radar and HF Doppler sounder at low latitude West Pacific site during winter

    NASA Astrophysics Data System (ADS)

    Hung, R. J.; Lee, C. C.; Chen, A. J.

    The VHF radar and HF Doppler sounder located at the subtropical and low latitude observing site of Taiwan has been used to make a simultaneous observation for atmospheric parameters from the troposphere, to the middle atmosphere, and then to the thermosphere during the time period of the weak convective motions of cold front in winter time. For observations at mesospheric heights, time dependent wind velocities with three-dimensional profiles are detected in the backscattered power, radial velocities and Doppler spectral width. For observations at thermospheric heights, time-dependent phase path change of high frequency radio wave reflected from ionospheric heights is used to measure Doppler frequency variation of gravity wave parameters. The density perturbations caused by the propagation of the gravity waves due to the weak convective motions in winter time were calculated from the VHF radar and HF Doppler sounder observations simultaneously. These short-term middle atmospheric and thermospheric density changes are a key element needed for space vehicle design purposes. Projects such as the Space Shuttle, Shuttle II, Tethered Satellite, Hubble Space Telescope, Aerobraking Orbital Transfer Vehicle, and Aeroassisted Flight Experiment will benefit from such studies.

  18. A digital elevation model of the Greenland Ice Sheet derived from combined laser and radar altimetry data

    NASA Astrophysics Data System (ADS)

    Fredenslund Levinsen, Joanna; Smith, Ben; Sørensen, Louise S.; Forsberg, René

    2014-05-01

    When estimating elevation changes of ice-covered surfaces from radar altimetry, it is important to correct for slope-induced errors. They cause the reflecting point of the pulse to move up-slope and thus return estimates in the wrong coordinates. Slope-induced errors can be corrected for by introducing a Digital Elevation Model (DEM). In this work, such a DEM is developed for the Greenland Ice Sheet using a combination of Envisat radar and ICESat laser altimetry. If time permits, CryoSat radar altimetry will be included as well. The reference year is 2010 and the spatial resolution 2.5 x 2.5 km. This is in accordance with the results obtained in the ESA Ice Sheets CCI project showing that a 5 x 5 km grid spacing is reasonable for ice sheet-wide change detection (Levinsen et al., 2013). Separate DEMs will be created for the given data sets, and the geostatistical spatial interpolation method collocation will be used to merge them, thus adjusting for potential inter-satellite biases. The final DEM is validated with temporally and spatially agreeing airborne lidar data acquired in the NASA IceBridge and ESA CryoVex campaigns. The motivation for developing a new DEM is based on 1) large surface changes presently being observed, and mainly in margin regions, hence necessitating updated topography maps for accurately deriving and correcting surface elevation changes, and 2) although radar altimetry is subject to surface penetration of the signal into the snowpack, data is acquired continuously in time. This is not the case with e.g. ICESat, where laser altimetry data were obtained in periods of active lasers, i.e. three times a year with a 35-day repeat track. Previous DEMs e.g. have 2007 as the nominal reference year, or they are built merely from ICESat data. These have elevation errors as small as 10 cm, which is lower than for Envisat and CryoSat. The advantage of an updated DEM consisting of combined radar and laser altimetry therefore is the possibility of

  19. Low resolution radar digital interface. [with data recorder for precipitation measurements

    NASA Technical Reports Server (NTRS)

    1973-01-01

    This document describes the design and operation of a low resolution radar data recording system for precipitation measurements. This system records a full azimuth scan on seven track magnetic tapes every five minutes. It is designed to operate on a continuous basis with operator intervention required only for changing tape reels and calibration.

  20. Detection of Digital Elevation Model Errors Using X-band Weather Radar

    NASA Technical Reports Server (NTRS)

    Young, Steven D.; deHaag, Maatren Uijt

    2007-01-01

    Flight in Instrument Meteorological Conditions requires pilots to manipulate flight controls while referring to a Primary Flight Display. The Primary Flight Display indicates aircraft attitude along with, in some cases, many other state variables such as altitude, speed, and guidance cues. Synthetic Vision Systems have been proposed that overlay the traditional information provided on Primary Flight Displays onto a scene depicting the location of terrain and other geo-spatial features.Terrain models used by these displays must have sufficient quality to avoid providing misleading information. This paper describes how X-band radar measurements can be used as part of a monitor, and/or maintenance system, to quantify the integrity of terrain models that are used by systems such as Synthetic Vision. Terrain shadowing effects, as seen by the radar, are compared in a statistical manner against estimated shadow feature elements extracted from the stored terrain model from the perspective of the airborne observer. A test statistic is defined that enables detection of errors as small as the range resolution of the radar. Experimental results obtained from two aircraft platforms hosting certified commercial-off-the-shelf X-band radars test the premise and illustrate its potential.

  1. High resolution vertical profiles of wind, temperature and humidity obtained by computer processing and digital filtering of radiosonde and radar tracking data from the ITCZ experiment of 1977

    NASA Technical Reports Server (NTRS)

    Danielson, E. F.; Hipskind, R. S.; Gaines, S. E.

    1980-01-01

    Results are presented from computer processing and digital filtering of radiosonde and radar tracking data obtained during the ITCZ experiment when coordinated measurements were taken daily over a 16 day period across the Panama Canal Zone. The temperature relative humidity and wind velocity profiles are discussed.

  2. Using X-band Weather Radar Measurements to Monitor the Integrity of Digital Elevation Models for Synthetic Vision Systems

    NASA Technical Reports Server (NTRS)

    Young, Steve; UijtdeHaag, Maarten; Sayre, Jonathon

    2003-01-01

    Synthetic Vision Systems (SVS) provide pilots with displays of stored geo-spatial data representing terrain, obstacles, and cultural features. As comprehensive validation is impractical, these databases typically have no quantifiable level of integrity. Further, updates to the databases may not be provided as changes occur. These issues limit the certification level and constrain the operational context of SVS for civil aviation. Previous work demonstrated the feasibility of using a realtime monitor to bound the integrity of Digital Elevation Models (DEMs) by using radar altimeter measurements during flight. This paper describes an extension of this concept to include X-band Weather Radar (WxR) measurements. This enables the monitor to detect additional classes of DEM errors and to reduce the exposure time associated with integrity threats. Feature extraction techniques are used along with a statistical assessment of similarity measures between the sensed and stored features that are detected. Recent flight-testing in the area around the Juneau, Alaska Airport (JNU) has resulted in a comprehensive set of sensor data that is being used to assess the feasibility of the proposed monitor technology. Initial results of this assessment are presented.

  3. Monthly and seasonal occurrences of potential flash flood-producing rains determined from Manually Digitized Radar data

    NASA Technical Reports Server (NTRS)

    Wilson, G. S.

    1980-01-01

    An analysis is conducted of a small 4-year climatological data base of Manually Digitized Radar (MDR) data to infer the monthly and seasonal distributions of the relative frequency of occurrence of potential flash flood-producing rains over the Central and Eastern U.S. Some possible meteorological mechanisms for producing potential flash flooding rains are discussed in terms of the relative maxima and minima in the monthly and seasonal frequency distributions over the MDR network. Frequencies were found to be generally higher in more southern locations and lower farther north in all months and seasons. However, most locations experienced an annual cycle in the frequency of occurrence with maxima in summer and minima in winter. In given seasons and months, local areas of maximum and minimum occurrences may be related to quasi-stationary meteorological processes that trigger and organize intense convection over a common area.

  4. Channel calibration for digital array radar in the presence of amplitude-phase and mutual coupling errors

    NASA Astrophysics Data System (ADS)

    Li, Weixing; Zhang, Yue; Lin, Jianzhi; Chen, Zengping

    2015-10-01

    Amplitude-phase errors and mutual coupling errors among multi-channels in digital array radar (DAR) will seriously deteriorate the performance of signal processing such as digital beam-forming (DBF) and high resolution direction finding. In this paper, a combined algorithm for error calibration in DAR has been demonstrated. The algorithm firstly estimates the amplitude-phase errors of each channel using interior calibration sources with the help of the calibration network. Then the signals from far field are received and the amplitude-phase errors are compensated. According to the subspace theories, the relationship between the principle eigenvectors and distorted steering vectors is expressed, and the cost function containing the mutual coupling matrix (MCM) and incident directions is established. Making use of the properties of MCM of uniform linear array, Gauss-Newton method is implied to iteratively compute the MCM and the direction of arrival (DOA). Simulation results have shown the effectiveness and performance of proposed algorithm. Based on an 8-elements DAR test-bed, experiments are carried out in anechoic chamber. The results illustrate that the algorithm is feasible in actual systems.

  5. Excitation thresholds of field-aligned irregularities and associated ionospheric hysteresis at very high latitudes observed using SPEAR-induced HF radar backscatter

    NASA Astrophysics Data System (ADS)

    Wright, D. M.; Dhillon, R. S.; Yeoman, T. K.; Robinson, T. R.; Thomas, E. C.; Baddeley, L. J.; Imber, S.

    2009-07-01

    On 10 October 2006 the SPEAR high power radar facility was operated in a power-stepping mode where both CUTLASS radars were detecting backscatter from the SPEAR-induced field-aligned irregularities (FAIs). The effective radiated power of SPEAR was varied from 1-10 MW. The aim of the experiment was to investigate the power thresholds for excitation (Pt) and collapse (Pc) of artificially-induced FAIs in the ionosphere over Svalbard. It was demonstrated that FAI could be excited by a SPEAR ERP of only 1 MW, representing only 1/30th of SPEAR's total capability, and that once created the irregularities could be maintained for even lower powers. The experiment also demonstrated that the very high latitude ionosphere exhibits hysteresis, where the down-going part of the power cycle provided a higher density of irregularities than for the equivalent part of the up-going cycle. Although this second result is similar to that observed previously by CUTLASS in conjunction with the Tromsø heater, the same is not true for the equivalent incoherent scatter measurements. The EISCAT Svalbard Radar (ESR) failed to detect any hysteresis in the plasma parameters over Svalbard in stark contract with the measurements made using the Tromsø UHF.

  6. Digital interpolators for polar format processing. [of synthetic aperture radar images

    NASA Technical Reports Server (NTRS)

    Adams, John W.; Hudson, Ralph E.; Bayma, Robert W.; Nelson, Jeffrey E.

    1989-01-01

    The polar format approach to SAR image formation requires data to be interpolated from a warped grid onto a Cartesian lattice. In general, this requires that data be interpolated between varying sampling rates. In this paper, frequency-domain optimality criteria for polar format interpolators are defined and justified, and an approach to designing the corresponding digital filters is described.

  7. A Digital Elevation Model of the Greenland Ice Sheet based on Envisat and CryoSat-2 Radar Altimetry

    NASA Astrophysics Data System (ADS)

    Levinsen, J. F.; Smith, B. E.; Sandberg Sørensen, L.; Khvorostovsky, K.; Forsberg, R.

    2014-12-01

    With the launch of the first radar altimeter by ESA in 1992, more than two decades of radar altimetry data are now available. Therefore, one goal of ESA's Ice Sheet Climate Change Initiative is the estimation of surface elevation changes of the Greenland Ice Sheet (GrIS) based on ERS-1, -2, Envisat, CryoSat-2, and, in the longer term, Sentinel-3 data. This will create a data record from 1992 until present date. In addition to elevation-change records, such data can be processed to produce digital elevation models, or DEMs, of the ice sheets. The DEMs can be used to correct radar altimetry data for slope-induced errors resulting from the large footprint (e.g. 2-10 km for Envisat vs. 60 m for ICESat laser altimetry) or to correct for the underlying surface topography when applying the repeat-track method. DEMs also provide key information in e.g. SAR remote sensing of ice velocities to remove the interferograms' topographic signal or in regional climate modeling. This work focuses on the development of a GrIS DEM from Envisat and CryoSat-2 altimetry, corrected with temporally and spatially coincident NASA ICESat, ATM, and LVIS laser data. The spatial resolution is 2 x 2 km and the reference year 2010. It is based on 2009 and 2010 data, the 2009 data adjusted to 2010 by accounting for the intermediate elevation changes. This increases the spatial data coverage and reduces data errors. The GIMP DEM has been corrected for negative elevations and errors in the north, and used to constrain the final DEM. The recently acquired observations and increased data coverage give a strong advantage to this DEM relative to previous models, based on lower-resolution, more temporally scattered data (e.g. a decade of observations or only ICESat data, limited to three annual 35-day acquisition periods). Furthermore, as surface changes occur continuously, an up-to-date DEM is necessary to correctly constrain the observations, thereby ensuring an accurate change detection or modeling

  8. Simulation of post-ADC digital beamforming for large aperture array radars

    NASA Astrophysics Data System (ADS)

    Johansson, G.; Borg, J.; Johansson, J.; Lundberg Nordenvaad, M.; Wannberg, G.

    2010-06-01

    This paper presents simulations and methods developed to investigate the feasibility of using a Fractional-Sample-Delay (FSD) system in the planned EISCAT_3D incoherent scatter radar. Key requirements include a frequency-independent beam direction over a 30 MHz band centered around 220 MHz, with correct reconstruction of pulse lengths down to 200 ns. The clock jitter from sample to sample must be extremely low for the integer sample delays. The FSD must also be able to delay the 30 MHz wide signal band by 1/1024th of a sample without introducing phase shifts, and it must operate entirely in baseband. An extensive simulation system based on mathematical models has been developed, with inclusion of performance-degrading aspects such as noise, timing error, and bandwidth. Finite Impulse Response (FIR) filters in the baseband of a band-pass-sampled signal have been used to apply true time delay beamforming. It has been confirmed that such use is both possible and well behaved. The target beam-pointing accuracy of 0.06° is achievable using optimized FIR filters with lengths of 36 taps and an 18 bit coefficient resolution. Even though the minimum fractional delay step necessary for beamforming is ˜13.1 ps, the maximum sampling timing error allowed in the array is found to be σ ≤ 120 ps if the errors are close to statistically independent.

  9. Simultaneous observation of HF-enhanced plasma waves and HF-wave self-focusing

    SciTech Connect

    Frey, A.; Duncan, L.M.

    1984-07-01

    Intense HF-radiowaves of the ordinary mode transmitted from the ground enhance plasma waves near the reflection height. These have been extensively studied in the past by the use of Incohernt-Scatter-Radars. Intense HF-radiowaves propagating in the ionosphere also produce electron density irregularities with scale sizes much larger than the HF wavelength of approx.60 m. These have been observed by radio star intensity scintillations. For the past 2 years a new method was used at Arecibo, P.R. which allows radar- and scintillation-measurements at 430 MHz to be performed simultaneously along the same line of sight. The scale sizes deduced from the scintillation measurements are shorter than the scale sizes observed with the radar and are inconsistent with the HF-power density thresholds predicted by existing theories.

  10. First results from HF (High-Frequency) oblique backscatter soundings to the northwest of College, Alaska using a modified ULCAR digisonde D-256

    NASA Astrophysics Data System (ADS)

    Hunsucker, Robert D.; Delana, Brett S.

    1989-03-01

    The modified air Weather Service Digital Ionospheric Sounding System (DISS, AN/FMQ12) is described in detail. The HF sounding system at College, Alaska is used to investigate the behavior of ground scatter, plus E and F-region direct backscatter caused by high latitude ionospheric irregularities. These echoes may manifest themselves as clutter in the proposed Alaskan OTH radar system. Soundings to the northwest of College were identified as ground scatter plus several types of auroral clutter echoes.

  11. Performance Analysis of a Digital Image Synthesizer as a Counter-Measure Against Inverse Synthetic Aperture Radar

    NASA Astrophysics Data System (ADS)

    LeDantec, Fernando A.

    2002-09-01

    This thesis is concerned with the development of a model to analyze a Digital Image Synthesizer (DIS) integrated circuit designed to create false target images to deceive Inverse Synthetic Aperture Radar (ISAR). The DIS is able to recreate the scattering effect of a moving target by using appropriate phase and gain modulations on an intercepted ISAR chirp signal before retransmitting it with the proper time delay. The DIS signal processing and the ISAR compression of the modulated return are modeled to examine the range-Doppler profile of a synthesized false target image. The image is representative of the image that would appear on an ISAR display. ISAR image quality is used to evaluate different DIS architectures and bit formats. Evaluation of the image quality is based on the deviation from an infinite resolution false target image. The results obtained from evaluating different DIS architectures indicate that the design is tolerant of significant quantization errors. The model is used to validate the architecture of the integrated circuit being fabricated. Finally, various different ISAR integration times and pulse repetition frequencies are used to confirm the integrity of the model.

  12. Comparison between nighttime ionosonde, incoherent scatter radar, AE-E satellite, and HF Doppler observations of F region vertical electrodynamic plasma drifts in the vicinity of the magnetic equator

    NASA Astrophysics Data System (ADS)

    Oyekola, Oyedemi S.

    2006-11-01

    Nighttime F region vertical drifts were made using an ionosonde for the equatorial station Ibadan (7.4°N, 3.9°E, 6°S dip) from 1 year of data during 1957-1958 International Geophysical Year (IGY) that corresponds to a period of solar maximum for undisturbed condition. We compare the seasonal vertical drifts with measurements made by incoherent scatter radar, AE-E satellite, and HF Doppler for equatorial F region vertical drifts. We find a comparable variability pattern during periods of high F layer heights during equinox and the December solstice, and the opposite behavior occurs during June solstice. The drifts are predominantly downward between 2000 and 0500 LT intervals. Ionosonde drifts are smaller in values by either a factor of two or three than other methods, except for consistent June solstice ionosonde and satellite magnitudes. The equinoctial average prereversal enhancements measured by the four techniques are roughly comparable (about 36 m/s) and occur at the same local time (1900 LT) for all the seasons. The evening reversal times are similar, apart from June solstice that exhibits large variations. The morning reversal times are also in accord except for the equinoctial Jicamarca drift. Our observations indicate that ionosonde drifts measurements are in better agreement with vertical drifts results at other equatorial stations.

  13. The MST Radar Technique

    NASA Technical Reports Server (NTRS)

    Roettger, J.

    1984-01-01

    The coherent radar technique is reviewed with special emphasis to mesosphere-stratosphere-troposphere (MST) radars operating in the VHF band. Some basic introduction to Doppler radar measurements and the radar equation is followed by an outline of the characteristics of atmospheric turbulence, viewed from the scattering and reflection processes of radar signals. Radar signal acquisition and preprocessing, namely coherent detection, digital sampling, pre-integration and coding, is briefly discussed. The data analysis is represented in terms of the correlation and spectrum analysis, yielding the essential parameters: power, signal-to-noise ratio, average and fluctuating velocity and persistency. The techniques to measure wind velocities, viz. the different modes of the Doppler method as well as the space antenna method are surveyed and the feasibilities of the MST radar interferometer technique are elucidated. A general view on the criteria to design phased array antennas is given. An outline of the hardware of a typical MST radar system is presented.

  14. Identification of topographic elements composition based on landform boundaries from radar interferometry segmentation (preliminary study on digital landform mapping)

    NASA Astrophysics Data System (ADS)

    Widyatmanti, Wirastuti; Wicaksono, Ikhsan; Dinta Rahma Syam, Prima

    2016-06-01

    Dense vegetation that covers most landscapes in Indonesia becomes a common limitation in mapping the landforms in tropical region. This paper aims to examine the use of radar interferometry for landform mapping in tropical region; to examine the application of segmentation method to develop landform type boundaries; and to identify the topographic elements composition for each type of landform. Using Idrisi® and “eCognition ®” softwares, toposhape analysis, segmentation and multi-spectral classification were applied to identify the composition of topographic elements i.e. the types of land-cover from Landsat 8, elevation, slope, relief intensity and curvatures from SRTM (DEM). Visual interpretation on DEM and land-cover fusion imagery was conducted to derive basic control maps of landform and land-cover. The result shows that in segmentation method, shape and compactness levels are essential in obtaining land-cover, elevation, and slope class units to determine the most accurate class borders of each element. Despite a complex procedure applied in determining landform classification, the combination of topographic elements segmentation result presents a distinct border of each landform class. The comparison between landform maps derived from segmentation process and visual interpretation method demonstrates slight dissimilarities, meaning that multi-stage segmentation approach can improve and provide more effective digital landform mapping method in tropical region. Topographic elements on each type of landforms show distinctive composition key containing the percentage of each curvature elements per area unit. Supported by GIS programming and modeling in the future, this finding is significant in reducing effort in landform mapping using visual interpretation method for a very large coverage but in detail scale level.

  15. The Arecibo Observatory as an MST radar

    NASA Technical Reports Server (NTRS)

    Woodman, R. F.

    1983-01-01

    The radars and other systems at the Arecibo Observatory were designed and built, originally, for incoherent-scatter and radio-astronomy research. More recently, important additions have been made for planetary radar and artificial RF heating of the ionosphere. Although designed and built for a different application, these systems have shown to be very powerful tools for tropospheric, stratospheric and mesospheric research. The Observatory at present has two main radars: one at 430 and the other at 2380 MHz. In addition, 50-MHz MST radar work has been done using portable transmitters brought to the Observatory for this purpose. This capability will become permanent with the recent acquisition of a transmitter at this frequency. Furthermore, control and data processing systems have been developed to use the powerful HF transmitter and antennas of the HF-heating facility as an HF bistatic radar. A brief description of the four radars available at the Observatory is presented.

  16. Decoders for MST radars

    NASA Technical Reports Server (NTRS)

    Woodman, R. F.

    1983-01-01

    Decoding techniques and equipment used by MST radars are described and some recommendations for new systems are presented. Decoding can be done either by software in special-purpose (array processors, etc.) or general-purpose computers or in specially designed digital decoders. Both software and hardware decoders are discussed and the special case of decoding for bistatic radars is examined.

  17. Radar data processing and analysis

    NASA Technical Reports Server (NTRS)

    Ausherman, D.; Larson, R.; Liskow, C.

    1976-01-01

    Digitized four-channel radar images corresponding to particular areas from the Phoenix and Huntington test sites were generated in conjunction with prior experiments performed to collect X- and L-band synthetic aperture radar imagery of these two areas. The methods for generating this imagery are documented. A secondary objective was the investigation of digital processing techniques for extraction of information from the multiband radar image data. Following the digitization, the remaining resources permitted a preliminary machine analysis to be performed on portions of the radar image data. The results, although necessarily limited, are reported.

  18. High frequency radar software reference manual for Product Two

    NASA Astrophysics Data System (ADS)

    Walden, D. C.; Winkelman, J. R.; Matheson, L. D.; Grubb, R. N.

    1984-03-01

    The Space Environment Laboratory (SEL) of NOAA developed a general purpose High Frequency (HF) Radar system capable of making most of the measurements of the ionosphere that can be made by coherent monostatic or bistatic radio wave sounding. This capability is provided by combining a very flexible, frequency-agile transmitter and receiver system with a digital control and signal processing system containing a general purpose 16-bit minicomputer for operator interaction and control. A manual is given which describes the software operating system written by the SEL staff to permit the Radar to be used for quite a wide range of standard measurements under simple operator control. The control language enables the user to exploit most of the capabilities of the instrument without having to program the system in detail. The manual is primarily directed at the user who needs to understand and use this capability. Secondarily, if used in conjunction with the computer manufacturer's system and language manuals, the SEL HF Radar Hardware manuals and the SEL source code listings, it should enable an experienced user to customize the software for special purposes or to produce new operating software.

  19. Temperate Ice Depth Sounding Radar (TIDSoR)

    NASA Astrophysics Data System (ADS)

    Jara, V.; Player, K.; Gogineni, S.; Rodriguez, F.; Thompson, L.

    2007-12-01

    Glaciers in several parts of the world are reported to be retreating and thinning rapidly over the last few years. A key variable in the study of glacier dynamics is ice thickness. A few attempts have been made to develop airborne sounding radars for temperate-ice thickness measurements [Arcone et al., 2000]. There is an urgent need for compact radar for routine ice thickness measurements from ground-based and airborne platforms. Radars (Radio Detection and Ranging) have been widely used to measure ice thickness in Greenland and Antarctica. However, the radars used in these areas operate in the VHF and UHF part of the electromagnetic spectrum. Due to the composition of temperate ice, the attenuation and back-scatter from large pockets of water makes UHF and VHF ineffective in sounding of its thickness. Radars operating in lower part of the HF spectrum are required for sounding temperate ice. We are designing and developing a Temperate Ice Depth-Sounding Radar (TIDSoR) that can penetrate through the water pockets and provide a more accurate measurement of the ice thickness. TIDSoR is a light-weight system for ground-based operations in mountainous terrain or aerial surveys in which weight is an important factor, such as in an UAV. TIDSoR operates on two channels in the HF spectrum using two-linear, frequency-modulated chirp waveforms. The two chirp frequency ranges are 7 to 8 MHz and 13.5 to 14.5 MHz. The radar will operate from a 12-V battery and is designed to weigh less than 2 kg, excluding the battery. The radar consists of three main sections: Digital, RF and antenna. The digital-section generates the transmitter waveforms, timing and control signals, and digitizes processes and stores the received signal. The RF-section consists of a transmitter with a 20-W peak-power amplifier, band-pass filters, and a switching system for a shared antenna. The receiver consists of a blanking switch, a limiter, a low-noise amplifier, a band-pass filter and a data acquisition

  20. Doppler shift simulation of scattered HF signals during the Tromsø HF pumping experiment on 16 February 1996

    NASA Astrophysics Data System (ADS)

    Borisova, T. D.; Blagoveshchenskaya, N. F.; Moskvin, I. V.; Rietveld, M. T.; Kosch, M. J.; Thidé, B.

    2002-09-01

    Comparisons between bistatic scatter measurements and simulation results during the Tromsø HF pumping experiment on 16 February 1996 are made. Doppler measurements of an HF diagnostic signal scattered from the field-aligned irregularities (FAIs) in the auroral E-region were carried out on the London Tromsø St. Petersburg path at 9410 kHz from 21:00 to 22:00 UT. The scattered signals were observed both from natural and artificial ionospheric irregularities located in the vicinity of Tromsø. To simulate the Doppler frequency shifts, fd , of scattered signals, a radio channel model, named CONE, was developed. The model allows for ray tracing, group and phase paths, and Doppler frequency shift calculations. The calculated Doppler shifts were analyzed for dependence on the magnitude and direction of plasma velocities in the scattering volume. It was found that the velocity components in the north-south direction are crucial for explaining the Doppler frequency shifts of the scattered diagnostic signals. To simulate fd , real velocities obtained from the EISCAT UHF radar at an altitude of 278 km and from the digital all-sky imager during the experiment were employed. The simulation results of Doppler frequency shift variations with time are in reasonable agreement with the experimental Doppler shifts of scattered signals on the London Tromsø St. Petersburg path.

  1. Temperate Ice Depth-Sounding Radar

    NASA Astrophysics Data System (ADS)

    Jara-Olivares, V. A.; Player, K.; Rodriguez-Morales, F.; Gogineni, P.

    2008-12-01

    Glaciers in several parts of the world are reported to be retreating and thinning rapidly over the last decade. Radar instruments can be used to provide a wealth of information regarding the internal and basal conditions of large and small ice masses. These instruments typically operate in the VHF and UHF regions of the electromagnetic spectrum. For temperate-ice sounding, however, the high water content produces scattering and attenuation in propagating radar waves at VHF and UHF frequencies, which significantly reduce the penetration depths. Radars operating in the HF band are better suited for systematic surveys of the thickness and sub-glacial topography of temperate-ice regions. We are developing a dual-frequency Temperate-Ice-Depth Sounding Radar (TIDSoR) that can penetrate through water pockets, thus providing more accurate measurements of temperate ice properties such as thickness and basal conditions. The radar is a light-weight, low power consumption portable system for surface-based observations in mountainous terrain or aerial surveys. TIDSoR operates at two different center frequencies: 7.7 MHz and 14 MHz, with a maximum output peak power of 20 W. The transmit waveform is a digitally generated linear frequency-modulated chirp with 1 MHz bandwidth. The radar can be installed on aircrafts such as the CReSIS UAV [1], DCH-6 (Twin Otter), or P-3 Orion for aerial surveys, where it could be supported by the airplane power system. For surface based experiments, TIDSoR can operate in a backpack configuration powered by a compact battery system. The system can also be installed on a sled towed by a motorized vehicle, in which case the power supply can be replaced by a diesel generator. The radar consists of three functional blocks: the digital section, the radio-frequency (RF) section, and the antenna, and is designed to weigh less than 2 kg, excluding the power supply. The digital section generates the transmit waveforms as well as timing and control signals

  2. Mitigating Doppler shift effect in HF multitone data modem

    NASA Astrophysics Data System (ADS)

    Sonlu, Yasar

    1989-09-01

    Digital communications over High Frequency (HF) radio channels are getting important in recent years. Current HF requirements are for data transmission at rates 2.4 kbps or more to accommodate computer data links and digital secure voice. HF modems which were produced to meet these speeds are, serial modems and parallel modems. On the other hand, the HF sky-wave communication medium, the ionosphere, has some propagation problems such as multipath and Doppler shift. The effect of Doppler shift in a parallel modem which employs Differential Quadrature Phase Shift Keying (DQPSK) modulation is considered and a correction method to mitigate the Doppler Shift effect is introduced.

  3. Superconductor Digital-RF Receiver Systems

    NASA Astrophysics Data System (ADS)

    Mukhanov, Oleg A.; Kirichenko, Dmitri; Vernik, Igor V.; Filippov, Timur V.; Kirichenko, Alexander; Webber, Robert; Dotsenko, Vladimir; Talalaevskii, Andrei; Tang, Jia Cao; Sahu, Anubhav; Shevchenko, Pavel; Miller, Robert; Kaplan, Steven B.; Sarwana, Saad; Gupta, Deepnarayan

    Digital superconductor electronics has been experiencing rapid maturation with the emergence of smaller-scale, lower-cost communications applications which became the major technology drivers. These applications are primarily in the area of wireless communications, radar, and surveillance as well as in imaging and sensor systems. In these areas, the fundamental advantages of superconductivity translate into system benefits through novel Digital-RF architectures with direct digitization of wide band, high frequency radio frequency (RF) signals. At the same time the availability of relatively small 4K cryocoolers has lowered the foremost market barrier for cryogenically-cooled digital electronic systems. Recently, we have achieved a major breakthrough in the development, demonstration, and successful delivery of the cryocooled superconductor digital-RF receivers directly digitizing signals in a broad range from kilohertz to gigahertz. These essentially hybrid-technology systems combine a variety of superconductor and semiconductor technologies packaged with two-stage commercial cryocoolers: cryogenic Nb mixed-signal and digital circuits based on Rapid Single Flux Quantum (RSFQ) technology, room-temperature amplifiers, FPGA processing and control circuitry. The demonstrated cryocooled digital-RF systems are the world's first and fastest directly digitizing receivers operating with live satellite signals in X-band and performing signal acquisition in HF to L-band at ˜30GHz clock frequencies.

  4. Lunar Radar Cross Section at Low Frequency

    NASA Technical Reports Server (NTRS)

    Rodriguez, P.; Kennedy, E. J.; Kossey, P.; McCarrick, M.; Kaiser, M. L.; Bougeret, J.-L.; Tokarev, Y. V.

    2002-01-01

    Recent bistatic measurements of the lunar radar cross-section have extended the spectrum to long radio wavelength. We have utilized the HF Active Auroral Research Program (HAARP) radar facility near Gakona, Alaska to transmit high power pulses at 8.075 MHz to the Moon; the echo pulses were received onboard the NASA/WIND spacecraft by the WAVES HF receiver. This lunar radar experiment follows our previous use of earth-based HF radar with satellites to conduct space experiments. The spacecraft was approaching the Moon for a scheduled orbit perturbation when our experiment of 13 September 2001 was conducted. During the two-hour experiment, the radial distance of the satellite from the Moon varied from 28 to 24 Rm, where Rm is in lunar radii.

  5. Large phased-array radars

    SciTech Connect

    Brookner, D.E.

    1988-12-15

    Large phased-array radars can play a very important part in arms control. They can be used to determine the number of RVs being deployed, the type of targeting of the RVs (the same or different targets), the shape of the deployed objects, and possibly the weight and yields of the deployed RVs. They can provide this information at night as well as during the day and during rain and cloud covered conditions. The radar can be on the ground, on a ship, in an airplane, or space-borne. Airborne and space-borne radars can provide high resolution map images of the ground for reconnaissance, of anti-ballistic missile (ABM) ground radar installations, missile launch sites, and tactical targets such as trucks and tanks. The large ground based radars can have microwave carrier frequencies or be at HF (high frequency). For a ground-based HF radar the signal is reflected off the ionosphere so as to provide over-the-horizon (OTH) viewing of targets. OTH radars can potentially be used to monitor stealth targets and missile traffic.

  6. Investigation and Development of Data-Driven D-Region Model for HF Systems Impacts

    NASA Technical Reports Server (NTRS)

    Eccles, J. V.; Rice, D.; Sojka, J. J.; Hunsucker, R. D.

    2002-01-01

    Space Environment Corporation (SEC) and RP Consultants (RPC) are to develop and validate a weather-capable D region model for making High Frequency (HF) absorption predictions in support of the HF communications and radar communities. The weather-capable model will assimilate solar and earth space observations from NASA satellites. The model will account for solar-induced impacts on HF absorption, including X-rays, Solar Proton Events (SPE's), and auroral precipitation. The work plan includes: I . Optimize D-region model to quickly obtain ion and electron densities for proper HF absorption calculations. 2. Develop indices-driven modules for D-region ionization sources for low, mid, & high latitudes including X-rays, cosmic rays, auroral precipitation, & solar protons. (Note: solar spectrum & auroral modules already exist). 3. Setup low-cost monitors of existing HF beacons and add one single-frequency beacon. 4. Use PENEX HF-link database with HF monitor data to validate D-region/HF absorption model using climatological ionization drivers. 5. Develop algorithms to assimilate NASA satellite data of solar, interplanetary, and auroral observations into ionization source modules. 6. Use PENEX HF-link & HF-beacon data for skill score comparison of assimilation versus climatological D-region/HF absorption model. Only some satellites are available for the PENEX time period, thus, HF-beacon data is necessary. 7. Use HF beacon monitors to develop HF-link data assimilation algorithms for regional improvement to the D-region/HF absorption model.

  7. SMAP's Radar OBP Algorithm Development

    NASA Technical Reports Server (NTRS)

    Le, Charles; Spencer, Michael W.; Veilleux, Louise; Chan, Samuel; He, Yutao; Zheng, Jason; Nguyen, Kayla

    2009-01-01

    An approach for algorithm specifications and development is described for SMAP's radar onboard processor with multi-stage demodulation and decimation bandpass digital filter. Point target simulation is used to verify and validate the filter design with the usual radar performance parameters. Preliminary FPGA implementation is also discussed.

  8. Satellite Remote Sensing of Landscape Freeze/Thaw State Dynamics for Complex Topography and Fire Disturbance Areas Using Multi-Sensor Radar and SRTM Digital Elevation Models

    NASA Astrophysics Data System (ADS)

    Podest, E.; McDonald, K.; Kimball, J.; Randerson, J. T.

    2003-12-01

    The annual freeze/thaw cycle drives the length of the growing season in the boreal forest, and is a major factor determining annual productivity and associated exchange of CO2 with the atmosphere. Variations in freeze/thaw processes are spatially and temporally complex in boreal environments, particularly in areas of complex topography and in fire disturbance regimes. We investigate the spatial and temporal characteristics of seasonal freeze/thaw dynamics in complex boreal landscapes, as derived from radar backscatter measured with ERS (C-band, VV polarization, 200m resolution) and JERS-1 (L-band, HH polarization, 100m resolution) Synthetic Aperture Radars (SARs), and with the SeaWinds scatterometer (Ku-band, 25km resolution). C- and L-band backscatter are applied to characterize freeze/thaw transitions for a chronosequence of recovering burn sites near Delta Junction, Alaska, and for a region of complex topography on the Kenai Peninsula, Alaska. We characterize differences in radar-derived freeze/thaw state, examining transitions over complex terrain and landscape disturbance regimes. In areas of complex terrain, we explore freeze/thaw dynamics related to elevation, slope aspect and varying landcover. In the burned regions, we explore the timing of seasonal freeze/thaw transition as related to the recovering landscape, relative to that of a nearby control site. We apply in situ biophysical measurements, including flux tower measurements to validate and interpret the remotely sensed parameters. A multi-scale analysis is performed relating high-resolution SAR backscatter and moderate resolution scatterometer measurements to assess trade-offs in spatial and temporal resolution in the remotely sensed fields. A temporal change discriminator is applied to classify time series radar imagery to classify the landscape freeze-thaw state. We apply a 30m-resolution digital elevation model (DEM) derived from Shuttle Radar Topography Mission (SRTM) data to orthorectify the time

  9. Radar and Lidar Radar DEM

    NASA Technical Reports Server (NTRS)

    Liskovich, Diana; Simard, Marc

    2011-01-01

    Using radar and lidar data, the aim is to improve 3D rendering of terrain, including digital elevation models (DEM) and estimates of vegetation height and biomass in a variety of forest types and terrains. The 3D mapping of vegetation structure and the analysis are useful to determine the role of forest in climate change (carbon cycle), in providing habitat and as a provider of socio-economic services. This in turn will lead to potential for development of more effective land-use management. The first part of the project was to characterize the Shuttle Radar Topography Mission DEM error with respect to ICESat/GLAS point estimates of elevation. We investigated potential trends with latitude, canopy height, signal to noise ratio (SNR), number of LiDAR waveform peaks, and maximum peak width. Scatter plots were produced for each variable and were fitted with 1st and 2nd degree polynomials. Higher order trends were visually inspected through filtering with a mean and median filter. We also assessed trends in the DEM error variance. Finally, a map showing how DEM error was geographically distributed globally was created.

  10. The Newcastle meteor radar

    NASA Technical Reports Server (NTRS)

    Keay, Colin

    1987-01-01

    A brief history and development of the Newcastle Meteor Radar system is given. Also described are its geographical coordinates and its method of operation. The initial objective when the project was commenced was to develop an entirely digital analyzer capable of recognizing meteor echo signals and recording as many of their parameters as possible. This objective was achieved.

  11. The accuracy of using the spectral width boundary measured in off-meridional SuperDARN HF radar beams as a proxy for the open-closed field line boundary

    NASA Astrophysics Data System (ADS)

    Chisham, G.; Freeman, M. P.; Sotirelis, T.; Greenwald, R. A.

    2005-10-01

    Determining reliable proxies for the ionospheric signature of the open-closed field line boundary (OCB) is crucial for making accurate measurements of magnetic reconnection. This study compares the latitudes of spectral width boundaries (SWBs) measured by different beams of the Goose Bay radar of the Super Dual Auroral Radar Network (SuperDARN), with the latitudes of OCBs determined using the low-altitude Defense Meteorological Satellite Program (DMSP) spacecraft, in order to determine whether the accuracy of the SWB as a proxy for the ionospheric projection of the OCB depends on the line-of-sight direction of the radar beam. The latitudes of SWBs and OCBs were identified using automated algorithms applied to 5 years (1997 2001) of data measured in the 1000 1400 magnetic local time (MLT) range. Six different Goose Bay radar beams were used, ranging from those aligned in the geomagnetic meridional direction to those aligned in an almost zonal direction. The results show that the SWB is a good proxy for the OCB in near-meridionally-aligned beams but becomes progressively more unreliable for beams greater than 4 beams away from the meridional direction. We propose that SWBs are identified at latitudes lower than the OCB in the off-meridional beams due to the presence of high spectral width values that result from changes in the orientation of the beams with respect to the gradient in the large-scale ionospheric convection pattern. Keywords. Ionosphere (Instruments and techniques; Plasma convection) Magnetospheric physics (Magnetopause, cusp and boundary layers)

  12. Application of ground-penetrating radar, digital optical borehole images, and cores for characterization of porosity hydraulic conductivity and paleokarst in the Biscayne aquifer, southeastern Florida, USA

    USGS Publications Warehouse

    Cunningham, K.J.

    2004-01-01

    This paper presents examples of ground-penetrating radar (GPR) data from two study sites in southeastern Florida where karstic Pleistocene platform carbonates that comprise the unconfined Biscayne aquifer were imaged. Important features shown on resultant GPR profiles include: (1) upward and lateral qualitative interpretative distribution of porosity and hydraulic conductivity; (2) paleotopographic relief on karstic subaerial exposure surfaces; and (3) vertical stacking of chronostratigraphic high-frequency cycles (HFCs). These characteristics were verified by comparison to rock properties observed and measured in core samples, and identified in digital optical borehole images. Results demonstrate that an empirical relation exists between measured whole-core porosity and hydraulic conductivity, observed porosity on digital optical borehole images, formation conductivity, and GPR reflection amplitudes-as porosity and hydraulic conductivity determined from core and borehole images increases, formation conductivity increases, and GPR reflection amplitude decreases. This relation allows for qualitative interpretation of the vertical and lateral distribution of porosity and hydraulic conductivity within HFCs. Two subtidal HFCs in the uppermost Biscayne aquifer have significantly unique populations of whole-core porosity values and vertical hydraulic conductivity values. Porosity measurements from one cycle has a median value about two to three times greater than the values from the other HFC, and median values of vertical hydraulic-conductivity about three orders of magnitude higher than the other HFC. The HFC with the higher porosity and hydraulic conductivity values is shown as a discrete package of relatively low-amplitude reflections, whereas the HFC characterized by lower porosity and hydraulic-conductivity measurements is expressed by higher amplitude reflections. Porosity and hydraulic-conductivity values measured from whole-core samples, and vuggy porosity

  13. Radar applications overview

    NASA Astrophysics Data System (ADS)

    Greenspan, Marshall

    1996-06-01

    During the fifty years since its initial development as a means of providing early warning of airborne attacks against allied countries during World War II, radar systems have developed to the point of being highly mobile and versatile systems capable of supporting a wide variety of remote sensing applications. Instead of being tied to stationary land-based sites, radar systems have found their way into highly mobile land vehicles as well as into aircraft, missiles, and ships of all sizes. Of all these applications, however, the most exciting revolution has occurred in the airborne platform arena where advanced technology radars can be found in all shapes and sizes...ranging from the large AWACS and Joint STARS long range surveillance and targeting systems to small millimeter wave multi-spectral sensors on smart weapons that can detect and identify their targets through the use of highly sophisticated digital signal processing hardware and software. This paper presents an overview of these radar applications with the emphasis on modern airborne sensors that span the RF spectrum. It will identify and describe the factors that influence the parameters of low frequency and ultra wide band radars designed to penetrate ground and dense foliage environments and locate within them buried mines, enemy armor, and other concealed or camouflaged weapons of war. It will similarly examine the factors that lead to the development of airborne radar systems that support long range extended endurance airborne surveillance platforms designed to detect and precision-located both small high speed airborne threats as well as highly mobile time critical moving and stationary surface vehicles. The mission needs and associated radar design impacts will be contrasted with those of radar systems designed for high maneuverability rapid acquisition tactical strike warfare platforms, and shorter range cued air-to-surface weapons with integral smart radar sensors.

  14. Radar frequency radiation

    NASA Astrophysics Data System (ADS)

    Malowicki, E.

    1981-11-01

    A method is presented for the determination of radar frequency radiation power densities that the PAVE PAWS radar system could produce in its air and ground environment. The effort was prompted by the concern of the people in the vicinity of OTIS AFB MA and BEALE AFB CA about the possible radar frequency radiation hazard of the PAVE PAWS radar. The method is based on the following main assumptions that: (a) the total field can be computed as the vector summation of the individual fields due to each antenna element; (b) the individual field can be calculated using distances for which the field point is in the far field of the antenna element. An RFR computer program was coded for the RADC HE 6180 digital computer and exercised to calculate the radiation levels in the air and ground space for the present baseline and the possible Six DB and 10 DB growth systems of the PAVE PAWS radar system at OTIS AFB MA. The average radiation levels due to the surveillance fence were computed for three regions: in the air space in front of the radar, at the radar hazard fence at OTIS AFB MA and at representative ground points in the OTIS AFB vicinity. It was concluded that the radar frequency radiation of PAVE PAWS does not present a hazard to personnel provided there is no entry to the air hazard zone or to the area within the hazard fence. The method developed offers a cost effective way to determine radiation levels from a phased array radar especially in the near field and transition regions.

  15. Digital Base Band Converter As Radar Vlbi Backend / Dbbc Kā Ciparošanas Sistēma Radara Vlbi Novērojumiem

    NASA Astrophysics Data System (ADS)

    Tuccari, G.; Bezrukovs, Vl.; Nechaeva, M.

    2012-12-01

    A digital base band converter (DBBC) system has been developed by the Istituto di Radioastronomia (Noto, Italy) for increasing the sensitivity of European VLBI Network (EVN) by expanding the full observed bandwidth using numerical methods. The output data rate of this VLBI-backend is raised from 1 to 4 Gbps for each radiotelescope. All operations related to the signal processing (frequency translation, amplification, frequency generation with local oscillators, etc.) are transferred to the digital domain, which allows - in addition to well-known advantages coming from digital technologies - achieving better repeatability, precision, simplicity, etc. The maximum input band of DBBC system is 3.5 GHz, and the instantaneous bandwidth is up to 1 GHz for each radio frequency/intermediate frequency (RF/IF) out of the eight possible. This backend is a highly powerful platform for other radioastronomy applications, and a number of additional so-called personalities have been developed and used. This includes PFB (polyphase filter bank) receivers and Spectra for high resolution spectroscopy. An additional new development with the same aim - to use the DBBC system as a multi-purpose backend - is related to the bi-static radar observations including Radar VLBI. In such observations it is possible to study the population of space debris, with detection of even centimetre class fragments. A powerful transmitter is used to illuminate the sky region to be analyzed, and the echoes coming from known or unknown objects are reflected to one or more groundbased telescopes thus producing a single-dish or interferometric detection. The DBBC Radar VLBI personality is able to realize a high-resolution spectrum analysis, maintaining in the central area the echo signal at the expected frequency including the Doppler shift of frequency. For extremely weak signals a very large integration time is needed, so for this personality different input parameters are provided. The realtime information

  16. Error analysis in the digital elevation model of Kuwait desert derived from repeat pass synthetic aperture radar interferometry

    NASA Astrophysics Data System (ADS)

    Rao, Kota S.; Al Jassar, Hala K.

    2010-09-01

    The aim of this paper is to analyze the errors in the Digital Elevation Models (DEMs) derived through repeat pass SAR interferometry (InSAR). Out of 29 ASAR images available to us, 8 are selected for this study which has unique data set forming 7 InSAR pairs with single master image. The perpendicular component of baseline (B highmod) varies between 200 to 400 m to generate good quality DEMs. The Temporal baseline (T) varies from 35 days to 525 days to see the effect of temporal decorrelation. It is expected that all the DEMs be similar to each other spatially with in the noise limits. However, they differ very much with one another. The 7 DEMs are compared with the DEM of SRTM for the estimation of errors. The spatial and temporal distribution of errors in the DEM is analyzed by considering several case studies. Spatial and temporal variability of precipitable water vapour is analysed. Precipitable water vapour (PWV) corrections to the DEMs are implemented and found to have no significant effect. The reasons are explained. Temporal decorrelation of phases and soil moisture variations seem to have influence on the accuracy of the derived DEM. It is suggested that installing a number of corner reflectors (CRs) and the use of Permanent Scatter approach may improve the accuracy of the results in desert test sites.

  17. Supermarine Spitfire HF VII

    NASA Technical Reports Server (NTRS)

    1944-01-01

    Supermarine Spitfire HF VII: This Supermarine Spitfire HF VII was one of high-altitude versions of the famous fighter, its normal elliptical wingtips replaced by extended 'pointed' tips for its high-altitude role. This is one of the Langley aircraft that has survived. It is in the Smithsonian Institution's National Air and Space Museum's collection.

  18. Terminal Doppler weather radar

    NASA Astrophysics Data System (ADS)

    Michelson, M.; Shrader, W. W.; Wieler, J. G.

    1990-02-01

    The terminal Doppler weather radar (TDWR) system, now under development, will provide automatic detection of microbursts and low-level wind shear. This paper discusses the TDWR performance parameters and describes its structural elements, including the antenna subsystem, the transmitter, the receiver/exciter, the digital signal processor, and the radar product generator/remote monitoring subsystem. Attention is also given to the processes of the base data formation, point target removal, signal-to-noise thresholding, and velocity de-aliasing and to the TDWR algorithms and displays. A schematic diagram of the TDWR system is presented.

  19. The potential of flood forecasting using a variable-resolution global Digital Terrain Model and flood extents from Synthetic Aperture Radar images.

    NASA Astrophysics Data System (ADS)

    Mason, David; Garcia-Pintado, Javier; Cloke, Hannah; Dance, Sarah

    2015-08-01

    A basic data requirement of a river flood inundation model is a Digital Terrain Model (DTM) of the reach being studied. The scale at which modeling is required determines the accuracy required of the DTM. For modeling floods in urban areas, a high resolution DTM such as that produced by airborne LiDAR (Light Detection And Ranging) is most useful, and large parts of many developed countries have now been mapped using LiDAR. In remoter areas, it is possible to model flooding on a larger scale using a lower resolution DTM, and in the near future the DTM of choice is likely to be that derived from the TanDEM-X Digital Elevation Model (DEM). A variable-resolution global DTM obtained by combining existing high and low resolution data sets would be useful for modeling flood water dynamics globally, at high resolution wherever possible and at lower resolution over larger rivers in remote areas. A further important data resource used in flood modeling is the flood extent, commonly derived from Synthetic Aperture Radar (SAR) images. Flood extents become more useful if they are intersected with the DTM, when water level observations (WLOs) at the flood boundary can be estimated at various points along the river reach. To illustrate the utility of such a global DTM, two examples of recent research involving WLOs at opposite ends of the spatial scale are discussed. The first requires high resolution spatial data, and involves the assimilation of WLOs from a real sequence of high resolution SAR images into a flood model to update the model state with observations over time, and to estimate river discharge and model parameters, including river bathymetry and friction. The results indicate the feasibility of such an Earth Observation-based flood forecasting system. The second example is at a larger scale, and uses SAR-derived WLOs to improve the lower-resolution TanDEM-X DEM in the area covered by the flood extents. The resulting reduction in random height error is significant.

  20. Mode S baseline radar tracking

    NASA Astrophysics Data System (ADS)

    Mancus, E. F.; Baker, L. H.

    1982-11-01

    The baseline performance characteristics of the moving target detector (MTD) and radar data acquisition system (RDAS) as an integral part of the Mode S sensor, were determined. The MTD and RDAS were separately evaluated to determine their capability to provide radar data suitable for utilization by the Mode S sensor and automated radar terminal system (ARTS). The design modifications made to the Mode S sensor to provide the capability of interfacing to either an MTD or RDAS were evaluated to determine if they were in compliance with the Federal Aviation Administration engineering requirement, FAA-ER-240-26. Radar baseline technical performance data was provided to characterize the MTD, RDAS, Mode S, and ARTS. The minimum radar tracking requirements are studied to determine if they are adequate to provide reliable radar track data to an air traffic control facility. It was concluded that the Mode S sensor, when integrated with an MTD-2 radar digitizer, can provide reliable primary radar track data to the ARTS III system for automated radar track acquisition.

  1. HF sounding of the auroral magnetosphere

    NASA Astrophysics Data System (ADS)

    Gurevich, A. V.; Babichenko, A. M.; Karashtin, A. N.; Rapoport, V. O.

    1992-06-01

    Results are presented from incoherent scatter radar measurements in the magnetosphere, using the Radiophysical Research Institute 'Sura' heating facility operated in the frequency range 4.5-9 MHz. The first magnetosphere sounding experiments were carried out on February 21, 1989; a frequency of 9.310 MHz was used for the sounding, while the effective radiated power was about 30 MW. The results of analyses of the scattered signal spectra showed that, in the auroral region of the polar magnetosphere, ion acoustic oscillations are excited and that the HF sounding technique used in this study was an effective method for magnetosphere sounding.

  2. Planetary Radar

    NASA Technical Reports Server (NTRS)

    Neish, Catherine D.; Carter, Lynn M.

    2015-01-01

    This chapter describes the principles of planetary radar, and the primary scientific discoveries that have been made using this technique. The chapter starts by describing the different types of radar systems and how they are used to acquire images and accurate topography of planetary surfaces and probe their subsurface structure. It then explains how these products can be used to understand the properties of the target being investigated. Several examples of discoveries made with planetary radar are then summarized, covering solar system objects from Mercury to Saturn. Finally, opportunities for future discoveries in planetary radar are outlined and discussed.

  3. Modeling the interference environment in the HF band

    NASA Astrophysics Data System (ADS)

    Pederick, L. H.; Cervera, M. A.

    2016-02-01

    The performance of systems using high frequency (HF) radio waves, such as over-the-horizon radars (OTHR), can be strongly affected by external interferers at great distances (thousands of kilometers) from the systems receiver. However, the propagation of interference has complex behavior and is known to vary with location, time, season, sunspot number, and radio frequency. Understanding how the level of interference varies with all of these factors is important for the design of new systems such as next generation OTHR. By combining databases of known transmitters, ray-tracing propagation, and a model ionosphere, a model of the behavior of interference at HF has been developed.

  4. Decorrelation in interferometric radar echoes

    NASA Technical Reports Server (NTRS)

    Zebker, Howard A.; Villasensor, John

    1992-01-01

    A radar interferometric technique for topographic mapping of surfaces promises a high resolution, globally consistent approach to generation of digital elevation models. One implementation approach, that of utilizing a single SAR system in a nearly repeating orbit, is attractive not only for cost and complexity reasons but also in that it permits inference of changes in the surface over the orbit repeat cycle from the correlation properties of the radar echoes. The various sources contributing to the echo correlation statistics are characterized, and the term which most closely describes surficial change is isolated. There is decorrelation increasing with time, but digital terrain model generation remains feasible.

  5. Estimation of the Doppler frequency and direction of arrival of the ionospherically propagated HF signals

    NASA Astrophysics Data System (ADS)

    Su, Hongtao; Liu, Hongwei; Shui, Penglang; Bao, Zheng

    2009-08-01

    High-frequency (HF) signals reflected from different points within each ionospheric layer may have slightly different Doppler frequencies and angles of arrival. The superposition of these signals leads to time varying and nonplanar wavefronts. Investigation of temporal and spatial characteristics of the ionospherically propagated HF signals plays an important role in designing the signal processing algorithms for the HF over-the-horizon radar (OTHR). A cost-efficient superresolution algorithm for simultaneously estimating the Doppler frequencies and angles of arrival of the ionospherically propagated HF signals is proposed in this paper. The effectiveness of the proposed algorithm is verified by the experimental data from a trial HF OTHR. Furthermore, the superposition model with the HF signal reflected by a smooth ionospheric layer consisting of a number of submode signals is also confirmed by the experimental data processing results.

  6. Spaceborne radar

    NASA Technical Reports Server (NTRS)

    Moore, R. K.; Eckerman, J.; Meneghini, R.; Atlas, D.; Boerner, W. M.; Cherry, S.; Clark, J. F.; Doviak, R. J.; Goldhirsh, J.; Lhermitte, R. M.

    1981-01-01

    The spaceborne radar panel considered how radar could be used to measure precipitation from satellites. The emphasis was on how radar could be used with radiometry (at microwave, visible (VIS), and infrared (IR) wavelengths) to reduce the uncertainties of measuring precipitation with radiometry alone. In addition, the fundamental electromagnetic interactions involved in the measurements were discussed to determine the key work areas for research and development to produce effective instruments. Various approaches to implementing radar systems on satellites were considered for both shared and dedicated instruments. Finally, a research and development strategy was proposed for establishing the parametric relations and retrieval algorithms required for extracting precipitation information from the radar and associated radiometric data.

  7. Data volume reduction for imaging radar polarimetry

    NASA Technical Reports Server (NTRS)

    Zebker, Howard A. (Inventor); Held, Daniel N. (Inventor); Vanzyl, Jakob J. (Inventor); Dubois, Pascale C. (Inventor); Norikane, Lynne (Inventor)

    1988-01-01

    Two alternative methods are presented for digital reduction of synthetic aperture multipolarized radar data using scattering matrices, or using Stokes matrices, of four consecutive along-track pixels to produce averaged data for generating a synthetic polarization image.

  8. Superconductor Digital Electronics: -- Current Status, Future Prospects

    NASA Astrophysics Data System (ADS)

    Mukhanov, Oleg

    2011-03-01

    Two major applications of superconductor electronics: communications and supercomputing will be presented. These areas hold a significant promise of a large impact on electronics state-of-the-art for the defense and commercial markets stemming from the fundamental advantages of superconductivity: simultaneous high speed and low power, lossless interconnect, natural quantization, and high sensitivity. The availability of relatively small cryocoolers lowered the foremost market barrier for cryogenically-cooled superconductor electronic systems. These fundamental advantages enabled a novel Digital-RF architecture - a disruptive technological approach changing wireless communications, radar, and surveillance system architectures dramatically. Practical results were achieved for Digital-RF systems in which wide-band, multi-band radio frequency signals are directly digitized and digital domain is expanded throughout the entire system. Digital-RF systems combine digital and mixed signal integrated circuits based on Rapid Single Flux Quantum (RSFQ) technology, superconductor analog filter circuits, and semiconductor post-processing circuits. The demonstrated cryocooled Digital-RF systems are the world's first and fastest directly digitizing receivers operating with live satellite signals, enabling multi-net data links, and performing signal acquisition from HF to L-band with 30 GHz clock frequencies. In supercomputing, superconductivity leads to the highest energy efficiencies per operation. Superconductor technology based on manipulation and ballistic transfer of magnetic flux quanta provides a superior low-power alternative to CMOS and other charge-transfer based device technologies. The fundamental energy consumption in SFQ circuits defined by flux quanta energy 2 x 10-19 J. Recently, a novel energy-efficient zero-static-power SFQ technology, eSFQ/ERSFQ was invented, which retains all advantages of standard RSFQ circuits: high-speed, dc power, internal memory. The

  9. Observations of HF backscatter decay rates from HAARP generated FAI

    NASA Astrophysics Data System (ADS)

    Bristow, William; Hysell, David

    2016-07-01

    Suitable experiments at the High-frequency Active Auroral Research Program (HAARP) facilities in Gakona, Alaska, create a region of ionospheric Field-Aligned Irregularities (FAI) that produces strong radar backscatter observed by the SuperDARN radar on Kodiak Island, Alaska. Creation of FAI in HF ionospheric modification experiments has been studied by a number of authors who have developed a rich theoretical background. The decay of the irregularities, however, has not been so widely studied yet it has the potential for providing estimates of the parameters of natural irregularity diffusion, which are difficult measure by other means. Hysell, et al. [1996] demonstrated using the decay of radar scatter above the Sura heating facility to estimate irregularity diffusion. A large database of radar backscatter from HAARP generated FAI has been collected over the years. Experiments often cycled the heater power on and off in a way that allowed estimates of the FAI decay rate. The database has been examined to extract decay time estimates and diffusion rates over a range of ionospheric conditions. This presentation will summarize the database and the estimated diffusion rates, and will discuss the potential for targeted experiments for aeronomy measurements. Hysell, D. L., M. C. Kelley, Y. M. Yampolski, V. S. Beley, A. V. Koloskov, P. V. Ponomarenko, and O. F. Tyrnov, HF radar observations of decaying artificial field aligned irregularities, J. Geophys. Res. , 101, 26,981, 1996.

  10. Temporal Development of HF-Excited Langmuir and Ion Turbulence at Arecibo

    NASA Astrophysics Data System (ADS)

    Djuth, F. T.; DuBois, D. F.

    2015-10-01

    The Arecibo high-power, high-frequency (HF) facility and 430 MHz radar are used to examine the temporal development of the HF-induced Langmuir and ion turbulences from 1 ms to many minutes after the turn-on of the HF beam in the F region. All HF observations begin in a smooth, stratified, stable plasma. "Cold start" HF transmissions are employed to avoid remnant irregularities from prior HF transmissions. HF-excited plasma line (HFPL) and ion line echoes are used to monitor the evolution of the turbulence. In the evening/nighttime the HFPL develops in three reproducible stages. Over time scales of 0 to 10-20 ms (possibly 40 ms), the smooth plasma conditions are maintained, and the results are consistent with theoretical models of the excitation of strong Langmuir turbulence near HF reflection. This entails the initiation of the so-called "caviton production cycle." The turbulence from the parametric decay instability is detected at lower altitudes where the radar wave vector matches those of the HF-enhanced waves. The data suggests that the two processes coexist in the region in between. After ~40 ms the "overshoot process" begins and consists of a downward extension of the HFPL from the HF reflection region to heights ~1.1 km below followed by a retreat back to the reflection region. The whole overshoot process takes place over a time scale of ~3 s. Thereafter the echo remains near HF reflection for 20-90 s after HF turn-on. The HFPL echo subsequently breaks up into patches because of the formation of large-scale electron density structures in the plasma. New kinetic models indicate that suprathermal electrons excited in the plasma by, for example, caviton burn-out serve to regulate plasma turbulence in the modified ionospheric volume.

  11. Magnetic zenith effect in the ionospheric modification by an X-mode HF heater wave

    NASA Astrophysics Data System (ADS)

    Blagoveshchenskaya, N. F.; Borisova, T. D.; Haggstrom, I.; Rietveld, M. T.; Yeoman, T. K.

    2013-12-01

    We report experimental results aimed at an investigation of the magnetic zenith effect in the high latitude ionosphere F region from ionospheric modification by powerful HF heater wave with X-polarization. The ionospheric modification was produced by the HF heating facility at Tromsø (Norway) using the phased array with a narrow beam with of 6 degrees. Effective radiated power was varied between 450 and 1000 MW. The HF pump wave radiated in different directions relative to the magnetic field from 90 degrees (vertical) to 78 degrees (magnetic zenith) at frequencies near or above the ordinary-mode critical frequency. The response of the ionosphere plasma to the HF pump wave impact was checked by the UHF incoherent scatter radar located in the immediate vicinity of the HF heater. UHF radar was probing the plasma parameters, such as electron density and temperature (Ne and Te), HF-induced plasma and ion lines in the altitude range from 90 to 600 km. It was running in a scanning mode when UHF radar look angles were changed from 74 to 90 degrees by 1 or 2 degree step. It was clearly demonstrated that the strongest heater-induced effects took place in the magnetic field-aligned direction when HF pointing was also to the magnetic zenith. It was found that strong Ne enhancement of up to 80 % along magnetic field (artificial density ducts) were excited only under HF pumping towards magnetic zenith. The width of the artificial ducts comes to only 2 degrees. The Ne increases were accompanied by the Te enhancements of up to about 50 %. Less pronounced Te increases were also observed in the directions of 84 and 90 degrees. Strong Ne enhancements can be accompanied by excitation of strong HF-induced plasma and ion lines. Thus experimental results obtained points to the strong magnetic zenith effect due to self-focusing powerful HF radio wave with X-mode polarization.

  12. A combined quality-control methodology in Ebro Delta (NE Spain) high frequency radar system

    NASA Astrophysics Data System (ADS)

    Lorente, P.; Piedracoba, S.; Soto-Navarro, J.; Alvarez-Fanjul, E.

    2015-08-01

    Ebro River Delta is a relevant marine protected area in the western Mediterranean. In order to promote the conservation of its ecosystem and support operational decision making in this sensitive area, a three site standard-range (13.5 MHz) CODAR SeaSonde High Frequency (HF) radar was deployed in 2013. Since there is a growing demand for reliable HF radar surface current measurements, the main goal of this work is to present a combined quality control methodology. Firstly, one year-long (2014) real-time web monitoring of nonvelocity-based diagnostic parameters is conducted in order to infer both radar site status and HF radar system performance. Signal-to-noise ratio at the monopole exhibited a consistent monthly evolution although some abrupt decreases (below 10 dB), occasionally detected in June for one of the radar sites, impacted negatively on the spatiotemporal coverage of total current vectors. It seemed to be a sporadic episode since radar site overall performance was found to be robust during 2014. Secondly, a validation of HF radar data with independent in situ observations from a moored current meter was attempted for May-October 2014. The accuracy assessment of radial and total vectors revealed a consistently high agreement. The directional accuracy of the HF radar was rated at better than 8°. The correlation coefficient and RMSE values emerged in the ranges 0.58-0.83 and 4.02-18.31 cm s-1, respectively. The analysis of the monthly averaged current maps for 2014 showed that the HF radar properly represented basic oceanographic features previously reported, namely: the predominant southwestward flow, the coastal clockwise eddy confined south of Ebro Delta mouth or the Ebro River impulsive-type freshwater discharge. Future works should include the use of verified HF radar data for the rigorous skill assessment of operational ocean circulation systems currently running in Ebro estuarine region like MyOcean IBI.

  13. Application of ground scatter returns for calibration of HF interferometry data

    NASA Astrophysics Data System (ADS)

    Ponomarenko, Pavlo; Nishitani, Nozomu; Oinats, Alexey V.; Tsuya, Taishi; St.-Maurice, Jean-Pierre

    2015-08-01

    Information on the vertical angle of arrival (elevation) is crucial in determining propagation modes of high-frequency (HF, 3-30 MHz) radio waves travelling through the ionosphere. The most advanced network of ionospheric HF radars, SuperDARN (Super Dual Auroral Radar Network), relies on interferometry to measure elevation, but this information is rarely used due to intrinsic difficulties with phase calibration as well as with the physical interpretation of the measured elevation patterns. In this work, we propose an empirical method of calibration for SuperDARN interferometry. The method utilises a well-defined dependence of elevation on range of ground scatter returns. "Fine tuning" of the phase is achieved based on a detailed analysis of phase fluctuation effects at very low elevation angles. The proposed technique has been successfully applied to data from the mid-latitude Hokkaido East SuperDARN radar. It can also be used at any other installation that utilises HF interferometry.

  14. Automotive radar

    NASA Astrophysics Data System (ADS)

    Rohling, Hermann

    2004-07-01

    Radar networks for automtovie short-range applications (up to 30m) based on powerful but inexpensive 24GHz high range resolution pulse or FMCW radar systems have been developed at the Technical University of Hamburg-Harburg. The described system has been integrated in to an experimental vehicle and tested in real street environment. This paper considers the general network design, the individual pulse or FMCW radar sensors, the network signal processing scheme, the tracking procedure and possible automotive applications, respectively. Object position estimation is accomplished by the very precise range measurement of each individual sensor and additional trilateration procedures. The paper concludes with some results obtained in realistic traffic conditions with multiple target situations using 24 GHz radar network.

  15. Radar history

    NASA Astrophysics Data System (ADS)

    Putley, Ernest

    2008-07-01

    The invention of radar, as mentioned in Chris Lavers' article on warship stealth technology (March pp21-25), continues to be a subject of discussion. Here in Malvern we have just unveiled a blue plaque to commemorate the physicist Albert Percival Rowe, who arrived in 1942 as the head of the Telecommunications Research Establishment (TRE), which was the Air Ministry research facility responsible for the first British radar systems.

  16. Lightweight SAR GMTI radar technology development

    NASA Astrophysics Data System (ADS)

    Kirk, John C.; Lin, Kai; Gray, Andrew; Hseih, Chung; Darden, Scott; Kwong, Winston; Majumder, Uttam; Scarborough, Steven

    2013-05-01

    A small and lightweight dual-channel radar has been developed for SAR data collections. Using standard Displaced Phase Center Antenna (DPCA) radar digital signal processing, SAR GMTI images have been obtained. The prototype radar weighs 5-lbs and has demonstrated the extraction of ground moving targets (GMTs) embedded in high-resolution SAR imagery data. Heretofore this type of capability has been reserved for much larger systems such as the JSTARS. Previously, small lightweight SARs featured only a single channel and only displayed SAR imagery. Now, with the advent of this new capability, SAR GMTI performance is now possible for small UAV class radars.

  17. Illumination of the Air Environment Using Radiation of HF Broadcast Stations

    NASA Astrophysics Data System (ADS)

    Lutsenko, V. I.; Lutsenko, I. V.; Popov, I. V.

    2015-06-01

    We consider the possibility of using illumination of the HF broadcast stations for location of air objects. The relationships for estimation of the detection range are obtained and requirements for the degree of suppression of a direct signal from the broadcast station are determined. Spectral characteristics of the signals from HF broadcast stations are studied experimentally for different polarizations of the received radiation. The possibility of air object detection using the Doppler effect is shown. Theoretical estimates of the radar cross section of air objects for different polarizations of the incident radiation are given. It is found experimentally that the radar cross section is about the same for the vertical and horizontal polarizations.

  18. Mid-latitude Ionospheric HF Channel Reciprocity: Evidence from the Ionospheric Oblique Incidence Sounding Experiments

    NASA Astrophysics Data System (ADS)

    Zhou, Chen; Zhao, Zhengyu; Zhang, Yuannong

    The mid-latitude ionospheric HF channel reciprocity is studied in this paper through theoret-ical considerations and ionospheric oblique incidence sounding experiments. The reciprocity of ionospheric HF channel experiments were carried out by using two identical Wuhan Iono-spheric Oblique Incidence Sounding Systems (WIOISS) located in Wuhan (30° 32N, 114° 21E) and Wanning (18° 58N, 110° 31E) respectively. The comparisons of group distance and Doppler shift between Wuhan-Wanning and Wanning-Wuhan HF ionospheric propagation paths show that the reciprocity of ionospheric HF channel is satisfied to some extent. The group dis-tances of two paths are calculated by a 3-D ray tracing simulation as well. The theoretical and experimental results could be widely used for HF communication systems and sky wave over-the-horizon radar.

  19. Midlatitude ionospheric HF channel reciprocity: Evidence from the ionospheric oblique incidence sounding experiments

    NASA Astrophysics Data System (ADS)

    Zhou, Chen; Zhao, Zhengyu; Deng, Feng; Ni, Binbin; Chen, Gang

    2010-12-01

    Ionospheric HF channel reciprocity is investigated at middle latitudes on the basis of ionospheric oblique incidence sounding experiments. Two identical Wuhan Ionospheric Oblique Incidence Sounding Systems (WIOISS), located at Wuhan (30°32'N, 114°21'E) and Wanning (18°58'N, 110°31'E), are used to carry out the campaign. Comparisons of group distance and Doppler shift between Wuhan-Wanning and Wanning-Wuhan HF ionospheric propagation paths indicate that the reciprocity of the ionospheric HF channel is satisfied at midlatitude region. A 3-D ray tracing simulation is also implemented to evaluate the group distances of the two paths. Midlatitude ionospheric HF channel reciprocity, as verified both experimentally and theoretically in the present study, can be useful for HF communication systems and sky wave over-the-horizon radars.

  20. Simultaneous Hf and Mf Sounding of The Mid-latitude Mesosphere At Sura

    NASA Astrophysics Data System (ADS)

    Karashtin, A. N.; Belikovich, V. V.; Shlyugaev, Yu. V.; Komrakov, G. P.

    Mesosphere sounding was carried out at SURA (56 N) in August 1999 using HF SURA radar, operated at 8.9 MHz, and co-located partial reflection facility, operated at 2.95 MHz. Sporadic enhancements of HF echoes correspondent to MSE were not registered during observational period. Both radars covered approximately the same volume and used same temporal (0.2 s) and spatial (3 km) resolutions. Layered echoes usually observed by HF radar were sometimes registered at MF also, but no correlation between them were found both in height and time. This indicates different prevailing mechanisms of echo formation at used frequencies -- Fresnel reflection at MF and turbulent scattering at HF. Only strong meteor echoes were correlated at both radars. HF sounding data were also compared with electron density profile derived from the partial reflectrion data. It is shown that echo intensity and electron density profiles are similar at long time scales (several hours) up to the heights of about 85 km. Decreas- ing of echo intensity above 85 km can be explained in terms of increased magnetizing of electrons. At shorter time scales (several minutes) echo intensity and electron den- sity profiles can differ substantionally that can be caused by temporal variations of atmospheric turbulence. HF echoes below 80 km were observed sporadically and only in case of non-monotonic behavior of electron density, namely, from the regions of density depletions. It should be mentioned that an existence of density depletion does not lead itself to HF echo from correspondent altitude. Described work was supported by RFBR through the Grant 99­05­64483.

  1. Requirements for space shuttle scatter radar experiments

    NASA Technical Reports Server (NTRS)

    Harker, K. J.

    1975-01-01

    The feasibility of carrying out scatter radar experiments on the space shuttle was analyzed. Design criteria considered were the required average transmitter power, frequency resolution, spatial resolution, and statistical accuracy. Experiments analyzed were measurement of the naturally enhanced plasma line and the ion component of the incoherent scatter spectrum, and the plasma line artificially enhanced by an intense HF radio wave. The ion component measurement does not appear feasible, while the other two appear reasonable for short ranges only.

  2. Planetary radar

    NASA Technical Reports Server (NTRS)

    Taylor, R. M.

    1980-01-01

    The radar astronomy activities supported by the Deep Space Network during June, July, and August 1980 are reported. The planetary bodies observed were Venus, Mercury, and the asteroid Toro. Data were obtained at both S and X band, and the observations were considered successful.

  3. Digital communications study

    NASA Technical Reports Server (NTRS)

    Boorstyn, R. R.

    1973-01-01

    Research is reported dealing with problems of digital data transmission and computer communications networks. The results of four individual studies are presented which include: (1) signal processing with finite state machines, (2) signal parameter estimation from discrete-time observations, (3) digital filtering for radar signal processing applications, and (4) multiple server queues where all servers are not identical.

  4. Digital processing of bandpass signals

    NASA Astrophysics Data System (ADS)

    Jackson, M. C.; Matthewson, P.

    Modern radar and radio systems rely on digital signal processing to enhance the quality of received signals. Prior to such processing, these signals must be converted to digital form. The historical development of signal digitization is briefly discussed in this paper and leads to a description of some current work on digital mixing. A method of directly sampling a band-limited intermediate frequency (i.f.) signal is presented, using a pair of digital mixer channels to produce complex low-pass samples of the signal envelope. The method is found to produce well matched channel outputs. Finally, the applicability of the method to radar is discussed.

  5. Empirical Study of the Multiaxial, Thermomechanical Behavior of NiTiHf Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Shukla, Dhwanil; Noebe, Ronald D.; Stebner Aaron P.

    2013-01-01

    An empirical study was conducted to characterize the multiaxial, thermomechanical responses of new high temperature NiTiHf alloys. The experimentation included loading thin walled tube Ni(sub 50.3)Ti(sub 29.7)Hf(sub 20) alloy samples along both proportional and nonproportional axial-torsion paths at different temperatures while measuring surface strains using stereo digital image correlation. A Ni(sub 50.3)Ti(sub 33.7)Hf(sub 16) alloy was also studied in tension and compression to document the effect of slightly depleting the Hf content on the constitutive responses of NiTiHf alloys. Samples of both alloys were made from nearly texture free polycrystalline material processed by hot extrusion. Analysis of the data shows that very small changes in composition significantly alter NiTiHf alloy properties, as the austenite finish (Af) temperature of the 16-at Hf alloy was found to be approximately 60 C less than the 20-at Hf alloy (approximately 120 C vs. 180 C). In addition, the 16-at Hf alloy exhibited smaller compressive transformation strains (2 vs. 2.5 percent). Multi-axial characterization of the 20-at % Hf alloy showed that while the random polycrystal transformation strains in tension (4 percent) and compression (2.5 percent) are modest in comparison with binary NiTi (6 percent, 4 percent), the torsion performance is superior (7 vs. 4 shear strain width to the pseudoelastic plateau).

  6. Pulsed inductive HF laser

    NASA Astrophysics Data System (ADS)

    Razhev, A. M.; Churkin, D. S.; Kargapol'tsev, E. S.; Demchuk, S. V.

    2016-03-01

    We report the results of experimentally investigated dependences of temporal, spectral and spatial characteristics of an inductive HF-laser generation on the pump conditions. Gas mixtures H2 – F2(NF3 or SF66) and He(Ne) – H2 – F2(NF3 or SF6) were used as active media. The FWHM pulse duration reached 0.42 μs. This value corresponded to a pulsed power of 45 kW. For the first time, the emission spectrum of an inductive HF laser was investigated, which consisted of seven groups of bands with centres around the wavelengths of 2732, 2736, 2739, 2835, 2837, 2893 and 2913 nm. The cross section profile of the laser beam was a ring with a diameter of about 20 mm and width of about 5 mm. Parameters of laser operation in the repetitively pulsed regime were sufficiently stable. The amplitude instability of light pulses was no greater than 5% – 6%.

  7. TRMM radar

    NASA Technical Reports Server (NTRS)

    Okamoto, Kenichi

    1993-01-01

    The results of a conceptual design study and the performance of key components of the Bread Board Model (BBM) of the Tropical Rainfall Measuring Mission (TRMM) radar are presented. The radar, which operates at 13.8 GHz and is designed to meet TRMM mission objectives, has a minimum measurable rain rate of 0.5 mm/h with a range resolution of 250 m, a horizontal resolution of about 4 km, and a swath width of 220 km. A 128-element active phased array system is adopted to achieve contiguous scanning within the swath. The basic characteristics of BBM were confirmed by experiments. The development of EM started with the cooperation of NASDA and CRL.

  8. High frequency radar software reference manual for product one

    NASA Astrophysics Data System (ADS)

    Walden, D. C.; Winkelman, J. R.; Matheson, L. D.; Schultz, L. D.; Merrill, R. G.

    1984-02-01

    This manual for use with the HF Radar Product 1 software was first distributed to users in draft form in 1978. It has been updated several times since then as the software has evolved. It is being formally published now to record the achievement and to form a more convenient reference manual for the use of this product.

  9. Satellite remote sensing of landscape freeze/thaw state dynamics for complex Topography and Fire Disturbance Areas Using multi-sensor radar and SRTM digital elevation models

    NASA Technical Reports Server (NTRS)

    Podest, Erika; McDonald, Kyle; Kimball, John; Randerson, James

    2003-01-01

    We characterize differences in radar-derived freeze/thaw state, examining transitions over complex terrain and landscape disturbance regimes. In areas of complex terrain, we explore freezekhaw dynamics related to elevation, slope aspect and varying landcover. In the burned regions, we explore the timing of seasonal freeze/thaw transition as related to the recovering landscape, relative to that of a nearby control site. We apply in situ biophysical measurements, including flux tower measurements to validate and interpret the remotely sensed parameters. A multi-scale analysis is performed relating high-resolution SAR backscatter and moderate resolution scatterometer measurements to assess trade-offs in spatial and temporal resolution in the remotely sensed fields.

  10. UAS-Based Radar Sounding of Ice

    NASA Astrophysics Data System (ADS)

    Hale, R. D.; Keshmiri, S.; Leuschen, C.; Ewing, M.; Yan, J. B.; Rodriguez-Morales, F.; Gogineni, S.

    2014-12-01

    The University of Kansas Center for Remote Sensing of Ice Sheets developed two Unmanned Aerial Systems (UASs) to support polar research. We developed a mid-range UAS, called the Meridian, for operating a radar depth sounder/imager at 195 MHz with an eight-element antenna array. The Meridian weighs 1,100 lbs, has a 26-foot wingspan, and a range of 950 nm at its full payload capacity of 120 lbs. Ice-penetrating radar performance drove the configuration design, though additional payloads and sensors were considered to ensure adaptation to multi-mission science payloads. We also developed a short range UAS called the G1X for operating a low-frequency radar sounder that operates at 14 and 35 MHz. The G1X weighs 85 lbs, has a 17-foot wingspan, and a range of about 60 nm per gallon of fuel. The dual-frequency HF/VHF radar depth sounder transmits at 100 W peak power at a pulse repetition frequency of 10 KHz and weighs approximately 4.5 lbs. We conducted flight tests of the G1X integrated with the radar at the Sub-glacial Lake Whillans ice stream and the WISSARD drill site. The tests included pilot-controlled and fully autonomous flights to collect data over closely-spaced lines to synthesize a 2-D aperture. We obtained clear bed echoes with a signal-to-noise (S/N) ratio of more than 50 dB at this location. These are the first-ever successful soundings of glacial ice with a UAS-based radar. Although ice attenuation losses in this location are low in comparison to more challenging targets, in-field performance improvements to the UAS and HF/VHF radar system enabled significant gains in the signal-to-noise ratio, such that the system can now be demonstrated on more challenging outlet glaciers. We are upgrading the G1X UAS and radar system for further tests and data collection in Greenland. We are reducing the weight and volume of the radar, which, when coupled with further reductions in airframe and avionics weight and a larger fuel bladder, will offer extended range. Finally

  11. Analysis of synthetic aperture radar imagery

    NASA Technical Reports Server (NTRS)

    Blanchard, B. J. (Principal Investigator)

    1976-01-01

    The author has identified the following significant results. Average radar response for L-band like polarized system appeared to be related to the watershed runoff coefficients when the viewing angle was approximately 42 deg off nadir. Four requirements for radar systems used to verify applications of active microwave for water resources were identified: (1) first generation digital data will be required; (2) radar should be calibrated both internally and externally; (3) new systems should avoid radom use; and (4) images should be geometrically rectified prior to delivery to the user.

  12. The Italian involvement in Cassini radar

    NASA Astrophysics Data System (ADS)

    Nirchio, F.; Pernice, B.; Borgarelli, L.; Dionisio, C.

    1991-12-01

    The Radio Frequency Electronic Subsystem (RFES) of the Cassini radar is described. The requirements of the Cassini radar are summarized. The design parameters taken into consideration in developing the RFES are described. The RFES interfaces with the High Gain Antenna (HGA) for signal transmission and reception. The operational parameters of the Cassini radar are presented. The front end electronics (FEE), microwave receiver (MR), high power amplifier (HPA), frequency generator (FG), digital chip generator (DCG), Chirp Up Converter and Amplifier (CUCA) and power supply of the RFES are described.

  13. Multispectral microwave imaging radar for remote sensing applications

    NASA Technical Reports Server (NTRS)

    Larson, R. W.; Rawson, R.; Ausherman, D.; Bryan, L.; Porcello, L.

    1974-01-01

    A multispectral airborne microwave radar imaging system, capable of obtaining four images simultaneously is described. The system has been successfully demonstrated in several experiments and one example of results obtained, fresh water ice, is given. Consideration of the digitization of the imagery is given and an image digitizing system described briefly. Preliminary results of digitization experiments are included.

  14. Generating nonlinear FM chirp radar signals by multiple integrations

    DOEpatents

    Doerry, Armin W.

    2011-02-01

    A phase component of a nonlinear frequency modulated (NLFM) chirp radar pulse can be produced by performing digital integration operations over a time interval defined by the pulse width. Each digital integration operation includes applying to a respectively corresponding input parameter value a respectively corresponding number of instances of digital integration.

  15. Radar observations of F region equatorial irregularities

    NASA Technical Reports Server (NTRS)

    Woodman, R. F.; La Hoz, C.

    1976-01-01

    The paper presents some results of backscatter observations of the F region irregularities made with the large 50-MHz radar at Jicamarca, Peru, during a few days of observations. The results were obtained by using three observational techniques: the modified range-time-intensity technique, the digital power mapping technique, and the digital raw data recording technique. Backscatter intensity maps as a function of altitude and time are presented, which can be interpreted as radar pictures of F region irregularities. A classification of spread F spectral signatures resulting from approximately 30,000 spectra obtained in sets of 64 simultaneous heights under a variety of conditions is also given.

  16. Application of polarimetric sounding to HF ionospheric remote sensing

    NASA Astrophysics Data System (ADS)

    Bezrodny, V. G.; Ponomarenko, P. V.; Yampolski, Y. M.

    1997-01-01

    It is shown that the scattering of electromagnetic waves by refractive index inhomogeneities in a continuous random medium is accompanied by a certain polarimetric phenomenon that is analogous to the Brewster effect of classic electrodynamics. In this paper, an observational method and results are discussed for the case of bistatic HF radar sounding of small-scale ionospheric inhomogeneities at frequencies above MUF. The height of the scattering layer, its thickness, and characteristic plasma drift velocity in the ionosphere are estimated as a result of statistical processing.

  17. Flood delineation from synthetic aperture radar data with the help of a priori knowledge from historical acquisitions and digital elevation models in support of near-real-time flood mapping

    NASA Astrophysics Data System (ADS)

    Schlaffer, Stefan; Hollaus, Markus; Wagner, Wolfgang; Matgen, Patrick

    2012-10-01

    The monitoring of flood events with synthetic aperture radar (SAR) sensors has attracted a considerable amount of attention during the last decade, owing to the growing interest in using spaceborne data in near-real time flood management. Most existing methods for classifying flood extent from SAR data rely on pure image processing techniques. In this paper, we propose a method involving a priori knowledge about an area taken from a multitemporal time series and a digital elevation model. A time series consisting of ENVISAT ASAR acquisitions was geocoded and coregistered. Then, a harmonic model was fitted to each pixel time series. The standardised residuals of the model were classified as flooded when exceeding a certain threshold value. Additionally, the classified flood extent was limited to flood-prone areas which were derived from a freely available DEM using the height above nearest drainage (HAND) index. Comparison with two different reference datasets for two different flood events showed that the approach yielded realistic results but underestimated the inundation extent. Among the possible reasons for this are the rather coarse resolution of 150 m and the sparse data coverage for a substantial part of the time series. Nevertheless, the study shows the potential for production of rapid overviews in near-real time in support of early response to flood crises.

  18. INTEGRATED CONTROL OF COMBINED SEWER REGULATORS USING WEATHER RADAR

    EPA Science Inventory

    Integrated operation was simulated of ten dynamic combined sewer regulators on a Montreal interceptor. Detailed review of digital recording weather radar capabilities indicated that it is potentially the best rainfall estimation means for accomplishing the runoff prediction that ...

  19. Marburg Hemorrhagic Fever (Marburg HF)

    MedlinePlus

    ... The CDC Cancel Submit Search The CDC Marburg hemorrhagic fever (Marburg HF) Note: Javascript is disabled or is ... was first recognized in 1967, when outbreaks of hemorrhagic fever occurred simultaneously in laboratories in Marburg and Frankfurt, ...

  20. Phenomena in the high latitude ionosphere induced by an X-mode HF heater wave

    NASA Astrophysics Data System (ADS)

    Blagoveshchenskaya, N. F.; Borisova, T. D.; Yeoman, T. K.; Rietveld, M. T.

    2011-12-01

    New experimental results are presented from high power ionospheric modification experiments with the EISCAT/Heating HF facility at Tromsø, Norway. The experiments were conducted in the course of Russian EISCAT HF heating campaigns in 2009 - 2011 using the following diagnostic tools: the EISCAT UHF incoherent scatter radar at Tromsø, the CUTLASS (SuperDARN) HF coherent radar, bi-static HF Doppler radio scatter and the EISCAT ionosonde (dynasonde). The effects on the high-latitude F region of the ionosphere by X-mode powerful HF radio waves injected towards the magnetic zenith (MZ) are analysed. We present the first experimental evidence for strong plasma modifications induced by the X-mode powerful HF radio waves. The distinctive feature of modification experiments is that the heater frequency is choosen by a special way, namely, it is above the ordinary-mode critical frequency but comparable with the extraordinary-mode critical frequency. The results show that the X-mode HF pump wave can generate very strong small-scale artificial field aligned irregularities (AFAIs) in the F-region of the high-latitude ionosphere. These irregularities, with spatial scales across the geomagnetic field of the order of 8 - 15 m, appeared 10 s - 4 min after the heater is turned on. They had the unusually long decay time which varied in a wide range between 3 and 30 min. The generation of the X-mode AFAIs was accompanied by electron temperature (Te) enhancements up to 50 % above the background level and an increase in the electron density (Ne) by up to 30 %. Such electron density enhancements can be attributed to HF-induced ionization production rather than the change of the density distribution due to the thermal diffusion. The analysis of the incoherent backscatter spectra obtained with the EISCAT UHF radar during X-mode HF pumping demonstrated the strongly enhanced ion line shoulders (upshifted and downshifted spectral peaks) observed during the whole 10 min heater-on period

  1. Radar image processing module development program, phase 3

    NASA Technical Reports Server (NTRS)

    1977-01-01

    The feasibility of using charge coupled devices in an IPM for processing synthetic aperture radar signals onboard the NASA Convair 990 (CV990) aircraft was demonstrated. Radar data onboard the aircraft was recorded and processed using a CCD sampler and digital tape recorder. A description of equipment and testing was provided. The derivation of the digital presum filter was documented. Photographs of the sampler/tape recorder, real time display and circuit boards in the IPM were also included.

  2. A computer based ionospheric sounding and HF noise measuring system

    NASA Astrophysics Data System (ADS)

    Earl, G. F.

    1980-09-01

    A system for the automated collection of ionospheric backscatter sounding and HF noise measurement data is described. The system was configured around a PDP 11/40 minicomputer and modified Barry Research FMCW sounding equipment. The real time digital signal processing associated with the backscatter sounder and noise measurement systems is discussed. The data are displayed and recorded in a calibrated mode, and examples are presented.

  3. Proposal for ionospheric tomography technique using a new HF radio source

    NASA Astrophysics Data System (ADS)

    Wang, L.; MacDougall, J. W.

    Ionospheric tomography has developed near 20 years from a theoretical concept to a powerful experimental method and it has been used successfully to image a wide range of ionospheric structures over altitude-versus-latitude planes Measurements of the line integral of the electron density along ray paths from ground transmitter to satellite i e TEC are inverted in a reconstruction algorithm to create an image of the spatial distribution of the density over the region of interest Recent ionospheric tomography experiments use VHF UHF signals transmitted from NNSS or GPS satellite networks We propose a new signal source using transmission from ground HF radar networks and received by a satellite HF signals carry rich information about the ionosphere and sensitive to small changes HF measurements such as signal amplitude group delay DOA and Doppler frequency shift provide a priori knowledge for the tomographic image reconstruction The initial phase problem inherent in the phase or TEC measurement can be eliminated by Faraday rotation measurements and the relative rotations on two adjacent frequencies solves the ambiguity problems at HF frequencies We are currently working on the simulations and the transmitter design A great opportunity to implement this idea will come from the launch of the CASSIOPE a multi-purpose small satellite that receives HF signals from ground radar fertilities in 2007

  4. Radar studies related to the earth resources program. [remote sensing programs

    NASA Technical Reports Server (NTRS)

    Holtzman, J.

    1972-01-01

    The radar systems research discussed is directed toward achieving successful application of radar to remote sensing problems in such areas as geology, hydrology, agriculture, geography, forestry, and oceanography. Topics discussed include imaging radar and evaluation of its modification, study of digital processing for synthetic aperture system, digital simulation of synthetic aperture system, averaging techniques studies, ultrasonic modeling of panchromatic system, panchromatic radar/radar spectrometer development, measuring octave-bandwidth response of selected targets, scatterometer system analysis, and a model Fresnel-zone processor for synthetic aperture imagery.

  5. Integration of WERA Ocean Radar into Tsunami Early Warning Systems

    NASA Astrophysics Data System (ADS)

    Dzvonkovskaya, Anna; Helzel, Thomas; Kniephoff, Matthias; Petersen, Leif; Weber, Bernd

    2016-04-01

    High-frequency (HF) ocean radars give a unique capability to deliver simultaneous wide area measurements of ocean surface current fields and sea state parameters far beyond the horizon. The WERA® ocean radar system is a shore-based remote sensing system to monitor ocean surface in near real-time and at all-weather conditions up to 300 km offshore. Tsunami induced surface currents cause increasing orbital velocities comparing to normal oceanographic situation and affect the measured radar spectra. The theoretical approach about tsunami influence on radar spectra showed that a tsunami wave train generates a specific unusual pattern in the HF radar spectra. While the tsunami wave is approaching the beach, the surface current pattern changes slightly in deep water and significantly in the shelf area as it was shown in theoretical considerations and later proved during the 2011 Japan tsunami. These observed tsunami signatures showed that the velocity of tsunami currents depended on a tsunami wave height and bathymetry. The HF ocean radar doesn't measure the approaching wave height of a tsunami; however, it can resolve the surface current velocity signature, which is generated when tsunami reaches the shelf edge. This strong change of the surface current can be detected by a phased-array WERA system in real-time; thus the WERA ocean radar is a valuable tool to support Tsunami Early Warning Systems (TEWS). Based on real tsunami measurements, requirements for the integration of ocean radar systems into TEWS are already defined. The requirements include a high range resolution, a narrow beam directivity of phased-array antennas and an accelerated data update mode to provide a possibility of offshore tsunami detection in real-time. The developed software package allows reconstructing an ocean surface current map of the area observed by HF radar based on the radar power spectrum processing. This fact gives an opportunity to issue an automated tsunami identification message

  6. Soviet oceanographic synthetic aperture radar (SAR) research

    SciTech Connect

    Held, D.N.; Gasparovic, R.F.; Mansfield, A.W.; Melville, W.K.; Mollo-Christensen, E.L.; Zebker, H.A.

    1991-01-01

    Radar non-acoustic anti-submarine warfare (NAASW) became the subject of considerable scientific investigation and controversy in the West subsequent to the discovery by the Seasat satellite in 1978 that manifestations of underwater topography, thought to be hidden from the radar, were visible in synthetic aperture radar (SAR) images of the ocean. In addition, the Seasat radar produced images of ship wakes where the observed angle between the wake arms was much smaller than expected from classical Kelvin wake theory. These observations cast doubt on the radar oceanography community's ability to adequately explain these phenomena, and by extension on the ability of existing hydrodynamic and radar scattering models to accurately predict the observability of submarine-induced signatures. If one is of the opinion that radar NAASW is indeed a potentially significant tool in detecting submerged operational submarines, then the Soviet capability, as evidenced throughout this report, will be somewhat daunting. It will be shown that the Soviets have extremely fine capabilities in both theoretical and experimental hydrodynamics, that Soviet researchers have been conducting at-sea radar remote sensing experiments on a scale comparable to those of the United States for several years longer than we have, and that they have both an airborne and spaceborne SAR capability. The only discipline that the Soviet Union appears to be lacking is in the area of digital radar signal processing. If one is of the opinion that radar NAASW can have at most a minimal impact on the detection of submerged submarines, then the Soviet effort is of little consequence and poses not threat. 280 refs., 31 figs., 12 tabs.

  7. Observation and theory of the radar aurora

    SciTech Connect

    Sahr, J.D.

    1990-01-01

    Plasma density irregularities occurring near the Aurora Borealis cause scattering of HF, VHF, and UHF radio waves. Analysis of the resulting radar signal provides great detail about the spatial and temporal characteristics of these auroral E region irregularities. Observations are presented of the radar aurora from recent campaigns in northern Sweden. After reviewing the basic theory and observations of auroral electrojet irregularities, a simple nonlinear fluid theory of electrojet ion-acoustic waves is introduced, and reduced to a form of the three-wave interaction equations. This theory provides a simple mechanism for excitation of linearly stable waves at large aspect and flow angles, as well as a prediction of the power spectra that a coherent scatter radar should observe. In addition, this theory may be able to account for type 3 waves without resorting to ion gyro modes, such as the electrostatic ion-cyclotron wave. During the course of the research a simple new radar transmitting mode and signal processing algorithm was generated which very simply solves a frequency aliasing problem that often occurs in CUPRI auroral radar studies. Several new radar data analysis routines were developed, including the principally cross-beam image and scatter plots of the second versus first moments of the power spectrum of the irregularities. Analysis of vertical interferometer data shows that type 3 waves originate at ordinary electrojet altitudes, not in the upper E region, from which it is concluded that the electrostatic ion-cyclotron mode does not generate type 3 waves. The measured height of type 3 waves and other spectral analyses provide support for the pure ion-acoustic theory of type 3 waves. Suggestions are offered for hardware improvements to the CUPRI radar, new experiments to test new and existing theories.

  8. Radar echo processing with partitioned de-ramp

    SciTech Connect

    Dubbert, Dale F.; Tise, Bertice L.

    2013-03-19

    The spurious-free dynamic range of a wideband radar system is increased by apportioning de-ramp processing across analog and digital processing domains. A chirp rate offset is applied between the received waveform and the reference waveform that is used for downconversion to the intermediate frequency (IF) range. The chirp rate offset results in a residual chirp in the IF signal prior to digitization. After digitization, the residual IF chirp is removed with digital signal processing.

  9. Processing for spaceborne synthetic aperture radar imagery

    NASA Technical Reports Server (NTRS)

    Lybanon, M.

    1973-01-01

    The data handling and processing in using synthetic aperture radar as a satellite-borne earth resources remote sensor is considered. The discussion covers the nature of the problem, the theory, both conventional and potential advanced processing techniques, and a complete computer simulation. It is shown that digital processing is a real possibility and suggests some future directions for research.

  10. Shuttle imaging radar-C science plan

    NASA Technical Reports Server (NTRS)

    1986-01-01

    The Shuttle Imaging Radar-C (SIR-C) mission will yield new and advanced scientific studies of the Earth. SIR-C will be the first instrument to simultaneously acquire images at L-band and C-band with HH, VV, HV, or VH polarizations, as well as images of the phase difference between HH and VV polarizations. These data will be digitally encoded and recorded using onboard high-density digital tape recorders and will later be digitally processed into images using the JPL Advanced Digital SAR Processor. SIR-C geologic studies include cold-region geomorphology, fluvial geomorphology, rock weathering and erosional processes, tectonics and geologic boundaries, geobotany, and radar stereogrammetry. Hydrology investigations cover arid, humid, wetland, snow-covered, and high-latitude regions. Additionally, SIR-C will provide the data to identify and map vegetation types, interpret landscape patterns and processes, assess the biophysical properties of plant canopies, and determine the degree of radar penetration of plant canopies. In oceanography, SIR-C will provide the information necessary to: forecast ocean directional wave spectra; better understand internal wave-current interactions; study the relationship of ocean-bottom features to surface expressions and the correlation of wind signatures to radar backscatter; and detect current-system boundaries, oceanic fronts, and mesoscale eddies. And, as the first spaceborne SAR with multi-frequency, multipolarization imaging capabilities, whole new areas of glaciology will be opened for study when SIR-C is flown in a polar orbit.

  11. Auxiliary signal processing system for a multiparameter radar

    NASA Technical Reports Server (NTRS)

    Chandrasekar, V.; Gray, G. R.; Caylor, I. J.

    1993-01-01

    The design of an auxiliary signal processor for a multiparameter radar is described with emphasis on low cost, quick development, and minimum disruption of radar operations. The processor is based around a low-cost digital signal processor card and personal computer controller. With the use of such a concept, an auxiliary processor was implemented for the NCAR CP-2 radar during a 1991 summer field campaign and allowed measurement of additional polarimetric parameters, namely, the differential phase and the copolar cross correlation. Sample data are presented from both the auxiliary and existing radar signal processors.

  12. Wavelet based hierarchical coding scheme for radar image compression

    NASA Astrophysics Data System (ADS)

    Sheng, Wen; Jiao, Xiaoli; He, Jifeng

    2007-12-01

    This paper presents a wavelet based hierarchical coding scheme for radar image compression. Radar signal is firstly quantized to digital signal, and reorganized as raster-scanned image according to radar's repeated period frequency. After reorganization, the reformed image is decomposed to image blocks with different frequency band by 2-D wavelet transformation, each block is quantized and coded by the Huffman coding scheme. A demonstrating system is developed, showing that under the requirement of real time processing, the compression ratio can be very high, while with no significant loss of target signal in restored radar image.

  13. Phenomena induced by powerful HF pumping towards magnetic zenith with a frequency near the F-region critical frequency and the third electron gyro harmonic frequency

    NASA Astrophysics Data System (ADS)

    Blagoveshchenskaya, N. F.; Carlson, H. C.; Kornienko, V. A.; Borisova, T. D.; Rietveld, M. T.; Yeoman, T. K.; Brekke, A.

    2009-01-01

    Multi-instrument observational data from an experiment on 13 October 2006 at the EISCAT/HEATING facility at Tromsø, Norway are analysed. The experiment was carried out in the evening hours when the electron density in the F-region dropped, and the HF pump frequency fH was near and then above the critical frequency of the F2 layer. The distinctive feature of this experiment is that the pump frequency was just below the third electron gyro harmonic frequency, while both the HF pump beam and UHF radar beam were directed towards the magnetic zenith (MZ). The HF pump-induced phenomena were diagnosed with several instruments: the bi-static HF radio scatter on the London-Tromsø-St. Petersburg path, the CUTLASS radar in Hankasalmi (Finland), the European Incoherent Scatter (EISCAT) UHF radar at Tromsø and the Tromsø ionosonde (dynasonde). The results show thermal electron excitation of the HF-induced striations seen simultaneously from HF bi-static scatter and CUTLASS radar observations, accompanied by increases of electron temperature when the heater frequency was near and then above the critical frequency of the F2 layer by up to 0.4 MHz. An increase of the electron density up to 25% accompanied by strong HF-induced electron heating was observed, only when the heater frequency was near the critical frequency and just below the third electron gyro harmonic frequency. It is concluded that the combined effect of upper hybrid resonance and gyro resonance at the same altitude gives rise to strong electron heating, the excitation of striations, HF ray trapping and extension of HF waves to altitudes where they can excite Langmuir turbulence and fluxes of electrons accelerated to energies that produce ionization.

  14. Bistatic observations of large and small scale ULF waves in SPEAR-induced HF coherent backscatter

    NASA Astrophysics Data System (ADS)

    Yeoman, T. K.; Baddeley, L. J.; Dhillon, R. S.; Robinson, T. R.; Wright, D. M.

    2008-08-01

    HF radar backscatter which has been artificially-induced by a high power RF facility has been demonstrated to provide ionospheric electric field data of unprecedented temporal resolution and accuracy. Here such data, induced by the SPEAR high power radar on Svalbard, are used to investigate ULF wave processes observed by the CUTLASS HF radars. Observations are presented of both waves with a large-scale nature, driven externally to the magnetosphere and those with small azimuthal scale lengths, driven by wave-particle interactions. For ULF wave events with large azimuthal scale lengths an excellent agreement in the observed wave polarisation ellipse is found between the radar observations and ground-based magnetometer data. In contrast, for the small scale events, no ground-based magnetic counterpart is observed. Indeed the data from the two CUTLASS radars seem inconsistent, and each radar must be interpreted separately, as the spatial resolution of the radars is sufficient to resolve the wave characteristics along the radar beams, but insufficient to resolve the wave characteristics across the beams. A high azimuthal wave number (m) wave with a period of 300 s and m~-60 is observed to occur over Svalbard at ~14:00 magnetic local time. This confirms the existence of waves driven by wave-particle interactions with trapped particle populations in the outer magnetosphere. A comparison of the observed wave characteristics with previous, lower latitude, observations suggests that these high latitude waves have a similar azimuthal scale size to those generated in the inner magnetosphere; the azimuthal wave number of -60 observed in the present study is comparable to previous values of -20 -50, but suggests an increase of m with latitude. A similar energy source in drifting proton populations is also suggested, but with lower characteristic proton energies of 10 keV implicated at high latitude, compared to the 20 60 keV energies invoked for previous lower latitude

  15. Fault growth and propagation during incipient continental rifting: Insights from a combined aeromagnetic and Shuttle Radar Topography Mission digital elevation model investigation of the Okavango Rift Zone, northwest Botswana

    NASA Astrophysics Data System (ADS)

    Kinabo, B. D.; Hogan, J. P.; Atekwana, E. A.; Abdelsalam, M. G.; Modisi, M. P.

    2008-06-01

    Digital Elevation Models (DEM) extracted from the Shuttle Radar Topography Mission (SRTM) data and high-resolution aeromagnetic data are used to characterize the growth and propagation of faults associated with the early stages of continental extension in the Okavango Rift Zone (ORZ), northwest Botswana. Significant differences in the height of fault scarps and the throws across the faults in the basement indicate extended fault histories accompanied by sediment accumulation within the rift graben. Faults in the center of the rift either lack topographic expressions or are interpreted to have become inactive, or have large throws and small scarp heights indicating waning activity. Faults on the outer margins of the rift exhibit either (1) large throws or significant scarp heights and are considered older and active or (2) throws and scarp heights that are in closer agreement and are considered young and active. Fault linkages between major fault systems through a process of "fault piracy" have combined to establish an immature border fault for the ORZ. Thus, in addition to growing in length (by along-axis linkage of segments), the rift is also growing in width (by transferring motion to younger faults along the outer margins while abandoning older faults in the middle). Finally, utilization of preexisting zones of weakness allowed the development of very long faults (>100 km) at a very early stage of continental rifting, explaining the apparent paradox between the fault length versus throw for this young rift. This study clearly demonstrates that the integration of the SRTM DEM and aeromagnetic data provides a 3-D view of the faults and fault systems, providing new insight into fault growth and propagation during the nascent stages of continental rifting.

  16. Signature of 3-4 day planetary waves in the equatorial ionospheric F layer height and medium frequency radar winds over Tirunelveli (8.7oN)

    NASA Astrophysics Data System (ADS)

    Sundararaman, Sathishkumar

    Signature of 3-4 day planetary waves in the equatorial ionospheric F layer height and medium frequency radar winds over Tirunelveli (8.7oN) S. Sathishkumar1, R. Dhanya1, K. Emperumal1, D. Tiwari2, S. Gurubaran1 and A. Bhattacharyya2 1. Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Tirunelveli, India 2. Indian Institute of Geomagnetism, Navi Mumbai, India Email: sathishmaths@gmail.com Abstract The equatorial atmosphere-ionosphere system has been studied theoretically and observationally in the past. In the equatorial atmosphere, oscillations with periods of 3-4 days are often observed in the medium frequency (MF) radar over Tirunelveli (8.7oN, 77.8oE, 1.34oN geomag. lat.). Earlier observations show the clear evidence that these waves can propagate from the stratosphere to ionosphere. A digital ionosonde has been providing useful information on several ionospheric parameters from the same site. Simultaneous observations of mesospheric winds using medium frequency radar and F-layer height (h'F) from ionosonde reveal that the 3-4 day wave was evident in both the component during the 01 June 2007 and 31 July 2007. The 3-4 day wave could have an important role in the day to day variability of the equatorial ionosphere evening uplift. Results from an extensive analysis that is being carried out in the direction of 3-4 day wave present in the ionosphere will be presented.

  17. HF ground scatter from the polar cap: Ionospheric propagation and ground surface effects

    NASA Astrophysics Data System (ADS)

    Ponomarenko, P. V.; St. Maurice, J.-P.; Hussey, G. C.; Koustov, A. V.

    2010-10-01

    In addition to being scattered by the ionospheric field-aligned irregularities, HF radar signals can be reflected by the ionosphere toward the Earth and then scattered back to the radar by the rugged ground surface. These ground scatter (GS) echoes are responsible for a substantial part of the returns observed by HF radars making up the Super Dual Auroral Radar Network (SuperDARN). While a GS component is conventionally used in studying ionosphere dynamics (e.g., traveling ionospheric disturbances, ULF waves), its potential in monitoring the state of the scattering surface remains largely unexploited. To fill this gap, we investigated diurnal and seasonal variation of the ground echo occurrence and location from a poleward-looking SuperDARN radar at Rankin Inlet, Canada. Using colocated ionosonde information, we have shown that seasonal and diurnal changes in the high-latitude ionosphere periodically modulate the overall echo occurrence rate and spatial coverage. In addition, characteristics of GS from a particular geographic location are strongly affected by the state of the underlying ground surface. We have shown that (1) ice sheets rarely produce detectable backscatter, (2) mountain ranges are the major source of GS as they can produce echoes at all seasons of the year, and (3) sea surface becomes a significant source of GS once the Arctic sea ice has melted away. Finally, we discuss how the obtained results can expand SuperDARN abilities in monitoring both the ionosphere and ground surface.

  18. Estimation of planetary surface roughness by HF sounder observation

    NASA Astrophysics Data System (ADS)

    Kobayashi, T.; Ono, T.

    Japanese Martian exploration project "Nozomi" was to carry out several science missions. Plasma Wave Sounder, one of those onboard missions, was an HF sounder to study Martian plasma environment, and Martian surface with the altimetry mode (Oya and Ono, 1998) as well. The altimetry mode observation was studied by means of computer simulations utilizing the KiSS code which had been originally designed to simulate the SELENE Lunar Radar Sounder, a spaceborne HF GPR, based on Kirchhoff approximation theory (Kobayashi, Oya and Ono, 2002). We found an empirical power law for the standard deviation of observed altitudes over Gaussian random rough surfaces: it varies in proportion to the square of the RMS gradient of the surface √{2} hRMS{λ_0, where hRMS and λ_0 are the RMS height of the surface and the correlation distance of the surface, respectively. We applied Geometrical optics to understand this empirical power law, and derived a square power law for the standard deviation of the observed altitude. Our Geometrical optics model assumed the followings: 1) the observed surface is a Gaussian random rough surface, 2) the mean surface is a flat horizontal plane, 3) the observed surface echo is the back scattering echoes, 4) the observed altitude is the mean value of the apparent range of those back scattering echoes. These results imply that HF sounder may be utilized to measure the surface roughness of planetary bodies in terms of the RMS gradient of the surface. Refrence: H. Oya and T. Ono, A new altimeter for Mars land shape observations utilizing the ionospheric sounder system onboard the Planet-B spacecraft, Earth Planets Space, Vol. 50, pp.229-234, 1998 T. Kobayashi, H. Oya, and T. Ono, A-scope analysis of subsurface radar sounding of lunar mare region, Earth Planets Space, Vol. 54, pp.973-982, 2002

  19. HF echoes from ionization potentially produced by high-altitude discharges

    SciTech Connect

    Roussel-Dupre, R.; Fitzgerald, T.J.; Symbalisty, E.

    1997-04-01

    In this paper the authors report on recent radar measurements taken during the month of October 1994 with the LDG HF radar in the Ivory Coast, Africa as part of the International Equatorial Electrojet Year. The purpose of this experimental effort in part was to study the effects of thunderstorms on the ionosphere. At the same time, the authors decided to carry out a set of experiments of an exploratory nature to look for echoes that could potentially arise from ionization produced in the mesosphere. The two leading candidates for producing transient ionization in the mesosphere are meteors and high-altitude discharges. Each is discussed in the context of these measurements.

  20. The Shuttle Radar Topography Mission

    NASA Astrophysics Data System (ADS)

    Farr, T. G.; Kobrick, M.

    2001-05-01

    The Shuttle Radar Topography Mission (SRTM), which flew successfully aboard Endeavour in February 2000, is a cooperative project between NASA and the National Imagery and Mapping Agency (NIMA). The mission was designed to use a single-pass radar interferometer to produce a digital elevation model of the Earth's land surface between about 60 degrees north and 56 degrees south latitude. The DEM will have 30 m horizontal resolution and about 15 m vertical errors. Two ortho-rectified C-band image mosaics are also planned. SRTM used a modification of the radar instrument that comprised the Spaceborne Radar Laboratory that flew twice on the Shuttle Endeavour in 1994. To collect the interferometric data, a 60 m mast, additional C-band antenna, and improved tracking and navigation devices were added. A second X-band antenna was also added by the German Space Agency, and produced higher resolution topographic measurements in strips nested within the full, C-band coverage. First results indicate that the radars and ancillary instruments worked very well. Data played back to the ground during the flight were processed to DEMs and products released hours after acquisition. An extensive program for calibration and verification of the SRTM data is now underway. When complete later this year, systematic processing of the data will begin, with final products emerging a continent at a time. Data processing will be completed by the end of 2002. Products will be transferred to the US Geological Survey's EROS Data Center for civilian archive and distribution. NIMA will handle Department of Defense distribution. * Work performed under contract to NASA.

  1. The Shuttle Radar Topography Mission

    NASA Astrophysics Data System (ADS)

    Farr, T. G.; Kobrick, M.

    2001-12-01

    The Shuttle Radar Topography Mission (SRTM), which flew successfully aboard Endeavour in February 2000, is a cooperative project between NASA, the National Imagery and Mapping Agency, and the German and Italian Space Agencies. The mission was designed to use a single-pass radar interferometer to produce a digital elevation model of the Earth's land surface between about 60 degrees north and 56 degrees south latitude. The DEM will have 30 m horizontal resolution and better than 15 m vertical errors. Two ortho-rectified C-band image mosaics are also planned. Data processing will be completed by the end of 2002. SRTM used a modification of the radar instrument that comprised the Spaceborne Radar Laboratory that flew twice on the Shuttle Endeavour in 1994. To collect the interferometric data, a 60 m mast, additional C-band antenna, and improved tracking and navigation devices were added. A second X-band antenna was also added by the German Space Agency, and produced higher resolution topographic measurements in strips nested within the full, C-band coverage. First results indicate that the radars and ancillary instruments worked very well. Data played back to the ground during the flight were processed to DEMs and products released hours after acquisition. An extensive program for calibration and verification of the SRTM data is now underway. When complete later this year, systematic processing of the data will begin, with final products emerging a continent at a time. Products will be transferred to the US Geological Survey's EROS Data Center for civilian archive and distribution. NIMA will handle Department of Defense distribution. * Work performed under contract to NASA.

  2. A directional HF noise model: Calibration and validation in the Australian region

    NASA Astrophysics Data System (ADS)

    Pederick, L. H.; Cervera, M. A.

    2016-01-01

    The performance of systems using HF (high frequency) radio waves, such as over-the-horizon radars, is strongly dependent on the external noise environment. However, this environment has complex behavior and is known to vary with location, time, season, sunspot number, and radio frequency. It is also highly anisotropic, with the directional variation of noise being very important for the design and development of next generation over-the-horizon radar. By combining global maps of lightning occurrence, raytracing propagation, a model background ionosphere and ionospheric absorption, the behavior of noise at HF may be modeled. This article outlines the principles, techniques, and current progress of the model and calibrates it against a 5 year data set of background noise measurements. The calibrated model is then compared with data at a second site.

  3. High-resolution studies of the HF ionospheric modification interaction region

    NASA Technical Reports Server (NTRS)

    Duncan, L. M.; Sheerin, J. P.

    1985-01-01

    The use of the pulse edge analysis technique to explain ionospheric modifications caused by high-power HF radio waves is discussed. The technique, implemented at the Arecibo Observatory, uses long radar pulses and very rapid data sampling. A comparison of the pulse leading and trailing edge characteristics is obtained and the comparison is used to estimate the relative changes in the interaction region height and layer width; an example utilizing this technique is provided. Main plasma line overshoot and miniovershoot were studied from the pulse edge observations; the observations at various HF pulsings and radar resolutions are graphically presented. From the pulse edge data the development and the occurrence of main plasma line overshoot and miniovershoot are explained. The theories of soliton formation and collapse, wave ducting, profile modification, and parametric instabilities are examined as a means of explaining main plasma line overshoots and miniovershoots.

  4. VHF and HF sea echo Doppler spectrum for a finite illuminated area

    NASA Astrophysics Data System (ADS)

    Hisaki, Yukiharu; Tokuda, Masayuki

    2001-05-01

    The prediction of the sea echo Doppler spectrum of VHF and HF radio waves is important for the ocean wave remote sensing by VHF and HF radars. The authors extended the theory of the sea echo Doppler spectrum. In previous theories it is assumed that the scale of the illuminated area is much larger than the dominant wavelength. However, the effect of the finite illuminated area may not be negligible. The authors considered the effect to predict second-order sea echo Doppler spectrum and extended previous theories. Furthermore, the authors developed the numerical technique to compute radar cross sections of the extended theory. As a result, the agreement between measured and predicted Doppler spectra is improved.

  5. KAGUYA Lunar Radar Sounder (LRS) observation of lunar surface echo and its calibration

    NASA Astrophysics Data System (ADS)

    Kobayashi, Takao; Ryeol Lee, Seung

    2015-04-01

    Lunar Radar Sounder (LRS) is an HF radar of which the center frequency of transmitted pulse is 5 MHz. LRS was installed to KAGUYA which flew to the Moon in 2007. During the operation period of 19 months, LRS performed radar sounding observation from the orbit at the nominal altitude of 100 km to cover whole surface of the Moon with its foot print. The total number of LRS observations (pulse transmissions) exceeded 10^8. We extracted the nadir surface echo out of each observation which made a surface echo map of the Moon, i.e. a mosaic image of the Moon of an HF frequency (5 MHz). The observed surface echoes carry information regarding lunar surface and that of shallow subsurface (near-surface) whose depth scale is smaller than the range resolution of the LRS (~ 150 m in vacuum). An inversion algorithm is applied to extract such information. However, inversion algorithms often assume a simple model of Fresnel reflection. One should remove the effect of surface roughness from the LRS data before practicing inversion. For this purpose, we carried out simulation of LRS observation to evaluate the surface roughness effect on the LRS data quantitatively. The simulation is based on Kirchhoff approximation theory. Digital Elevation Model (DEM) of KAGUYA Terrain Camera (TC) mission was used in the simulation to simulate the actual lunar terrain. LRS observation simulation was performed in the range from -90 to 70 degrees in longitude and in the range from -30 to 70 degrees in latitude at every 0.1 degree interval in both directions. The simulation revealed 1) LRS surface echo observation is sensible to the surface terrain: even wrinkle ridges and small craters are well recognized in the mosaic image of simulation surface echo map. 2) Little difference was found in the mosaic image of an old mare surface and a young mare surface. 3) However, apparent difference was found in the shape of the distribution functions of echo intensity of an old mare surface and a young mare

  6. Radar investigation of barium releases over Arecibo Observatory, Puerto Rico

    NASA Technical Reports Server (NTRS)

    Djuth, Frank T.

    1995-01-01

    The NASA Combined Release and Radiation Effects Satellite (CRRES) El Coqui rocket campaign was successfully carried out in Puerto Rico during the period 18 May through 12 July 1992. This report describes five chemical release experiments in the upper ionosphere supported by Geospace Research, Inc. during the El Coqui campaign. Additional spin-off science is also discussed. The El Coqui releases are designated AA-1 (rocket 36-082), AA-2 (rocket 36-081), AA-3b (rocket 36-064), AA-4 (rocket 36-065), and AA-7 (rocket 36-083). Particular attention is paid to releases AA-2 and AA-4. These two experiments involved the illumination of ionospheric release regions with powerful high-frequency (HF) radio waves transmitted from the Arecibo HF facility. In the AA-2 experiment, microinstabilities excited by the HF wave in a Ba(+) plasma were examined. This release yielded a smooth plasma cloud that helped clarify several fundamental issues regarding the physics of wave plasma instabilities. During AA-2 extremely strong HF-induced Langmuir turbulence was detected with the Arecibo 430 MHz radar. CF3Br was released in the AA-4 study to create an ionospheric hole that focused the HF beam. This experiment successfully explored wave-plasma coupling in an O(+) ionosphere under conditions of very high HF electric field strengths.

  7. Doppler radar results

    NASA Technical Reports Server (NTRS)

    Bracalente, Emedio M.

    1992-01-01

    The topics are covered in viewgraph form and include the following: (1) a summary of radar flight data collected; (2) a video of combined aft cockpit, nose camera, and radar hazard displays; (3) a comparison of airborne radar F-factor measurements with in situ and Terminal Doppler Weather Radar (TDWR) F-factors for some sample events; and (4) a summary of wind shear detection performance.

  8. Thermal response of the F region ionosphere in artificial modification experiments by HF radio waves

    NASA Technical Reports Server (NTRS)

    Mantas, G. P.; Lahoz, C. H.; Carlson, H. C., Jr.

    1981-01-01

    The thermal response of the nighttime F region ionosphere to local heating by HF radio waves has been observed with the incoherent scatter radar at Arecibo, Puerto Rico. The observations consist of high-resolution space and time variation of the electron temperature as a high-power HF transmitter is switched on and off with a period 240 s. As soon as the HF transmitter is turned on, the electron temperature begins to rise rapidly in a narrow altitude region near 300 km, below the F2 layer peak. The electron temperature perturbation subsequently spreads over a broader altitude region. The observations are compared with the anticipated thermal response of the ionosphere based on numerical solutions of the coupled time-dependent heat conduction equations for the electron and composite ion gases and are found to be in good agreement over the entire altitude region covered by the observations.

  9. Lunar radar backscatter studies

    NASA Technical Reports Server (NTRS)

    Thompson, T. W.

    1979-01-01

    The lunar surface material in the Plato area is characterized using Earth based visual, infrared, and radar signatures. Radar scattering in the lunar regolith with an existing optical scattering computer program is modeled. Mapping with 1 to 2 km resolution of the Moon using a 70 cm Arecibo radar is presented.

  10. Radar: Human Safety Net

    ERIC Educational Resources Information Center

    Ritz, John M.

    2016-01-01

    Radar is a technology that can be used to detect distant objects not visible to the human eye. A predecessor of radar, called the telemobiloscope, was first used to detect ships in the fog in 1904 off the German coast. Many scientists have worked on the development and refinement of radar (Hertz with electromagnetic waves; Popov with determining…

  11. Radar images analysis for scattering surfaces characterization

    NASA Astrophysics Data System (ADS)

    Piazza, Enrico

    1998-10-01

    According to the different problems and techniques related to the detection and recognition of airplanes and vehicles moving on the Airport surface, the present work mainly deals with the processing of images gathered by a high-resolution radar sensor. The radar images used to test the investigated algorithms are relative to sequence of images obtained in some field experiments carried out by the Electronic Engineering Department of the University of Florence. The radar is the Ka band radar operating in the'Leonardo da Vinci' Airport in Fiumicino (Rome). The images obtained from the radar scan converter are digitized and putted in x, y, (pixel) co- ordinates. For a correct matching of the images, these are corrected in true geometrical co-ordinates (meters) on the basis of fixed points on an airport map. Correlating the airplane 2-D multipoint template with actual radar images, the value of the signal in the points involved in the template can be extracted. Results for a lot of observation show a typical response for the main section of the fuselage and the wings. For the fuselage, the back-scattered echo is low at the prow, became larger near the center on the aircraft and than it decrease again toward the tail. For the wings the signal is growing with a pretty regular slope from the fuselage to the tips, where the signal is the strongest.

  12. Radar Range Sidelobe Reduction Using Adaptive Pulse Compression Technique

    NASA Technical Reports Server (NTRS)

    Li, Lihua; Coon, Michael; McLinden, Matthew

    2013-01-01

    Pulse compression has been widely used in radars so that low-power, long RF pulses can be transmitted, rather than a highpower short pulse. Pulse compression radars offer a number of advantages over high-power short pulsed radars, such as no need of high-power RF circuitry, no need of high-voltage electronics, compact size and light weight, better range resolution, and better reliability. However, range sidelobe associated with pulse compression has prevented the use of this technique on spaceborne radars since surface returns detected by range sidelobes may mask the returns from a nearby weak cloud or precipitation particles. Research on adaptive pulse compression was carried out utilizing a field-programmable gate array (FPGA) waveform generation board and a radar transceiver simulator. The results have shown significant improvements in pulse compression sidelobe performance. Microwave and millimeter-wave radars present many technological challenges for Earth and planetary science applications. The traditional tube-based radars use high-voltage power supply/modulators and high-power RF transmitters; therefore, these radars usually have large size, heavy weight, and reliability issues for space and airborne platforms. Pulse compression technology has provided a path toward meeting many of these radar challenges. Recent advances in digital waveform generation, digital receivers, and solid-state power amplifiers have opened a new era for applying pulse compression to the development of compact and high-performance airborne and spaceborne remote sensing radars. The primary objective of this innovative effort is to develop and test a new pulse compression technique to achieve ultrarange sidelobes so that this technique can be applied to spaceborne, airborne, and ground-based remote sensing radars to meet future science requirements. By using digital waveform generation, digital receiver, and solid-state power amplifier technologies, this improved pulse compression

  13. Space Radar Image of Saline Valley, California

    NASA Technical Reports Server (NTRS)

    1999-01-01

    This is a three-dimensional perspective view of Saline Valley, about 30 km (19 miles) east of the town of Independence, California created by combining two spaceborne radar images using a technique known as interferometry. Visualizations like this one are helpful to scientists because they clarify the relationships of the different types of surfaces detected by the radar and the shapes of the topographic features such as mountains and valleys. The view is looking southwest across Saline Valley. The high peaks in the background are the Inyo Mountains, which rise more than 3,000 meters (10,000 feet) above the valley floor. The dark blue patch near the center of the image is an area of sand dunes. The brighter patches to the left of the dunes are the dry, salty lake beds of Saline Valley. The brown and orange areas are deposits of boulders, gravel and sand known as alluvial fans. The image was constructed by overlaying a color composite radar image on top of a digital elevation map. The radar image was taken by the Spaceborne Imaging Radar-C/X-bandSynthetic Aperture Radar (SIR-C/X-SAR) on board the space shuttleEndeavour in October 1994. The digital elevation map was producedusing radar interferometry, a process in which radar data are acquired on different passes of the space shuttle. The two data passes are compared to obtain elevation information. The elevation data were derived from a 1,500-km-long (930-mile) digital topographic map processed at JPL. Radar image data are draped over the topography to provide the color with the following assignments: red is L-band vertically transmitted, vertically received; green is C-band vertically transmitted, vetically received; and blue is the ratio of C-band vertically transmitted, vertically received to L-band vertically transmitted, vertically received. This image is centered near 36.8 degrees north latitude and 117.7 degrees west longitude. No vertical exaggeration factor has been applied to the data. SIR-C/X-SAR, a joint

  14. Signal Processing Techniques for a Planetary Subsurface Radar Onboard Satellite

    NASA Astrophysics Data System (ADS)

    Yagitani, S.; Ishikawa, T.; Nagano, I.; Kojima, H.; Matsumoto, H.

    2001-12-01

    We are developing a satellite-borne HF ( ~ 10 MHz) radar system to be used to investigate planetary subsurface layered structures. Before deciding the design of a high-performance subsurface radar system, in this study we calculate the propagation and reflection characteristics of various HF radar pulses through subsurface layer models, in order to examine the wave forms and frequencies of the radar pulses suitable to discriminate and pick up weak subsurface echoes buried in stronger surface reflection and scattering echoes. In the numerical calculations the wave form of a transmitted radar pulse is first Fourier-transformed into a number of elementary plane waves having different frequencies, for each of which the propagation and reflection characteristics through subsurface layer models are calculated by a full wave analysis. Then the wave form of the reflected radar echo is constructed by synthesizing all of the elementary plane waves. As the transmitted pulses, we use several different types of wave form modulation to realize the radar pulse compression to improve the signal-to-noise (S/N) ratio and time resolution of the subsurface echoes: the linear FM chirp (conventional), the M (maximal-length) sequence and the complementary sequences. We will discuss the characteristics of these pulse compression techniques, such as the improvement in the S/N ratio and the time resolution to identify the subsurface echoes. We will also present the possibility of applying the Multiple Signal Classification (MUSIC) method to further improve both the S/N ratio and time resolution to extract the weaker subsurface echoes.

  15. Imaging Radar Applications in the Death Valley Region

    NASA Technical Reports Server (NTRS)

    Farr, Tom G.

    1996-01-01

    Death Valley has had a long history as a testbed for remote sensing techniques (Gillespie, this conference). Along with visible-near infrared and thermal IR sensors, imaging radars have flown and orbited over the valley since the 1970's, yielding new insights into the geologic applications of that technology. More recently, radar interferometry has been used to derive digital topographic maps of the area, supplementing the USGS 7.5' digital quadrangles currently available for nearly the entire area. As for their shorter-wavelength brethren, imaging radars were tested early in their civilian history in Death Valley because it has a variety of surface types in a small area without the confounding effects of vegetation. In one of the classic references of these early radar studies, in a semi-quantitative way the response of an imaging radar to surface roughness near the radar wavelength, which typically ranges from about 1 cm to 1 m was explained. This laid the groundwork for applications of airborne and spaceborne radars to geologic problems in and regions. Radar's main advantages over other sensors stems from its active nature- supplying its own illumination makes it independent of solar illumination and it can also control the imaging geometry more accurately. Finally, its long wavelength allows it to peer through clouds, eliminating some of the problems of optical sensors, especially in perennially cloudy and polar areas.

  16. Ultrawideband radar clutter measurements of forested terrain, 1991--1992

    SciTech Connect

    Sheen, D.M.; Severtsen, R.H.; Prince, J.M.; Davis, K.C.; Collins, H.D.

    1993-06-01

    The ultrawideband (UWB) radar clutter measurements project was conducted to provide radar clutter data for new ultrawideband radar systems which are currently under development. A particular goal of this project is to determine if conventional narrow band clutter data may be extrapolated to the UWB case. This report documents measurements conducted in 1991 and additional measurements conducted in 1992. The original project consisted of clutter measurements of forested terrain in the Olympic National Forest near Sequim, WA. The impulse radar system used a 30 kW peak impulse source with a 2 Gigasample/second digitizer to form a UHF (300--1000 MHz) ultrawideband impulse radar system. Additional measurements were conducted in parallel using a Systems Planning Corporation (SPC) step-chirp radar system. This system utilized pulse widths of 1330 nanoseconds over a bandwidth of 300--1000 MHz to obtain similar resolution to the impulse system. Due to the slow digitizer data throughput in the impulse radar system, data collection rates were significantly higher using the step-chirp system. Additional forest clutter measurements were undertaken in 1992 to increase the amount of data available, and especially to increase the amount of data from the impulse radar system.

  17. Cloud and Precipitation Radar

    NASA Astrophysics Data System (ADS)

    Hagen, Martin; Höller, Hartmut; Schmidt, Kersten

    Precipitation or weather radar is an essential tool for research, diagnosis, and nowcasting of precipitation events like fronts or thunderstorms. Only with weather radar is it possible to gain insights into the three-dimensional structure of thunderstorms and to investigate processes like hail formation or tornado genesis. A number of different radar products are available to analyze the structure, dynamics and microphysics of precipitation systems. Cloud radars use short wavelengths to enable detection of small ice particles or cloud droplets. Their applications differ from weather radar as they are mostly orientated vertically, where different retrieval techniques can be applied.

  18. Radar Location Equipment Development Program: Phase I

    SciTech Connect

    Sandness, G.A.; Davis, K.C.

    1985-06-01

    The work described in this report represents the first phase of a planned three-phase project designed to develop a radar system for monitoring waste canisters stored in a thick layer of bedded salt at the Waste Isolation Pilot Plant near Carlsbad, New Mexico. The canisters will be contained in holes drilled into the floor of the underground waste storage facility. It is hoped that these measurements can be made to accuracies of +-5 cm and +-2/sup 0/, respectively. The initial phase of this project was primarily a feasibility study. Its principal objective was to evaluate the potential effectiveness of the radar method in the planned canister monitoring application. Its scope included an investigation of the characteristics of radar signals backscattered from waste canisters, a test of preliminary data analysis methods, an assessment of the effects of salt and bentonite (a proposed backfill material) on the propagation of the radar signals, and a review of current ground-penetrating radar technology. A laboratory experiment was performed in which radar signals were backscattered from simulated waste canisters. The radar data were recorded by a digital data acquisition system and were subsequently analyzed by three different computer-based methods to extract estimates of canister location and tilt. Each of these methods yielded results that were accurate within a few centimeters in canister location and within 1/sup 0/ in canister tilt. Measurements were also made to determine the signal propagation velocities in salt and bentonite (actually a bentonite/sand mixture) and to estimate the signal attenuation rate in the bentonite. Finally, a product survey and a literature search were made to identify available ground-penetrating radar systems and alternative antenna designs that may be particularly suitable for this unique application. 10 refs., 21 figs., 4 tabs.

  19. HF Channel Availability under Ionospheric Disturbances: Model, Method and Measurements as Contributions

    NASA Astrophysics Data System (ADS)

    Tulunay, E.; Senalp, E. T.; Tulunay, Y.; Warrington, E. M.; Sari, M. O.

    2009-04-01

    A small group at METU has been developing data driven models in order to forecast some critical parameters, which affect the communication and navigation systems, since 1990. The background on the subjects supports new achievements in terms of theoretical and experimental basis contributing the COST 296 WG2 activities. This work mentions the representative contributions. (i) A method has been proposed for the assessment of HF Channel Availability under ionospheric disturbances. Signal to Noise Ratio (SNR), Doppler Spread and Modified Power Delay Spread were considered. The study relates the modem performance to ionospheric disturbances. Ionospheric disturbance was characterised by Disturbance Storm Type (DST) index. Radar data including Effective Multipath Spread, Composite Doppler Spread and SNR values were obtained from the experiment conducted between Leicester UK (52.63° N; 1.08° W) and Uppsala, Sweden (59.92° N; 17.63° E) in the year 2001. First, joint probability density function (PDF) of SNR, Doppler Spread, and Effective Multipath Spread versus DST were considered. It was demonstrated by determining the conditional PDFs, and by using Bayes' Theorem, that there were dependencies between DST and the above mentioned parameters [Sari, 2006]. Thus, it is concluded that the availability of the HF channel is a function of DST. As examples of modem characterizations, Military Standards were considered. Given a magnetic condition, the modem availability was calculated. The model developed represents the ionospheric HF channel, and it is based on a stochastic approach. Depending on the new experimental data, the conditional PDFs could be updated continuously. The HF channel availability under various ionospheric Space Weather (SW) conditions can be determined using the model. The proposed method is general and can include other indices as well. The method can also be applied to a variety of other processes. (ii) The effects of space weather conditions on the

  20. Modification of the high latitude F region of the ionosphere by X-mode powerful HF radio waves: Experimental results from multi-instrument diagnostics

    NASA Astrophysics Data System (ADS)

    Blagoveshchenskaya, Nataly; Rietveld, Michael; Haggstrom, Ingemar; Borisova, Tatiana; Yeoman, Tim

    We present the experimental results for strong plasma modifications induced by the X-mode powerful HF radio waves injected towards the magnetic zenith into the high latitude F region of the ionosphere. A large number of experiments in the course of Russian EISCAT heating campaigns were conducted in 2009 - 2013 under different background conditions in a wide heater frequency range from 4 to 8 MHz. The EISCAT UHF incoherent scatter radar at Tromsø, the CUTLASS (SuperDARN) HF coherent radar in Finland, SEE receiver at Tromsø, the HF Doppler equipment near St. Petersburg, and the EISCAT ionosonde (dynasonde) were used as diagnostic instruments. The results show that the X-mode HF pump wave can generate: (1) strong small-scale artificial field aligned irregularities (AFAIs); (2) HF-induced plasma and HF-enhanced ion lines (HFPLs and HFILs) from UHF radar spectra; (3) strong electron density enhancements along magnetic field line in a wide altitude range; (4) spectral components (few tens of Hz) in the Doppler spectra of the heater signal measured at a distance of 1200 km from the Tromsø HF heating facility. The experimental results obtained points to the strong magnetic zenith effect due to self-focusing powerful HF radio wave with X-mode polarization. For heater frequencies in the range of about 4 - 6 MHz the mentioned above phenomena are generated when the heater frequency is equal or above the ordinary-mode critical frequency (foF2). Under high background electron density and the heater frequencies used of 6.5 - 8.0 MHz, the strong X-mode HF-induced phenomena were observed both when the heater frequency is equal or above the foF2 and the heater frequency is below the foF2.

  1. HfS: Hyperfine Structure fitting tool

    NASA Astrophysics Data System (ADS)

    Estalella, Robert

    2016-07-01

    HfS fits the hyperfine structure of spectral lines, with multiple velocity components. The HfS_nh3 procedures included in HfS fit simultaneously the hyperfine structure of the NH3 (J,K)= (1,1) and (2,2) inversion transitions, and perform a standard analysis to derive the NH3 column density, rotational temperature Trot, and kinetic temperature Tk. HfS uses a Monte Carlo approach for fitting the line parameters, with special attention to the derivation of the parameter uncertainties. HfS includes procedures that make use of parallel computing for fitting spectra from a data cube.

  2. The CRRES AA 2 release: HF wave-plasma interactions in a dense Ba+ cloud

    NASA Astrophysics Data System (ADS)

    Djuth, F. T.; Sulzer, M. P.; Elder, J. H.; Groves, K. M.

    1995-09-01

    An ionospheric chemical release, designated AA 2, was performed on July 12, 1992, as part of the NASA Combined Release and Radiation Effects Satellite (CRRES) El Coqui rocket campaign. The purpose of the AA 2 experiment was to study the interaction between a powerful radio wave and a high ion mass (Ba+), ``collisionless'' plasma. Approximately 35 kg of Ba were explosively released near the center of the Arecibo high-frequency (HF) beam at 253 km altitude. This was the largest Ba release of the CRRES experiments; it yielded a distinctive ionospheric layer having a maximum plasma frequency of 11 MHz. At early times (<1 min after the release) the HF beam produced the strongest Langmuir waves ever detected with the Arecibo 430-MHz radar. Resonantly enhanced Langmuir waves were observed to be excited principally at the upshifted plasma line (i.e., near 430 MHz+fHF, where fHF is the frequency of the modifying HF wave), and only weakly excited waves were apparent at the downshifted plasma line (430 MHz-fHF). The upshifted plasma-line spectrum contained a dominant peak at the ``decay line,'' that is, at the frequency 430 MHz+fHF-δ, where δ is close to the Ba+ ion-acoustic frequency (~2 kHz). Downshifted plasma-line echoes occurred at frequencies near 430 MHz-fHF and 430 MHz-fHF-1 kHz and exhibited little or no signal strength at the decay line (430 MHz-fHF+δ). During an initial period of intense upshifted plasma-line excitation, the power asymmetry between the upshifted and downshifted plasma lines was of the order of 105 at the decay line. The upshifted plasma line was accompanied by strong HF-enhanced ion waves that were present only at the downshifted acoustic sideband. After geomagnetic field-aligned irregularities formed in the plasma the amplitudes of the upshifted and downshifted plasma lines equalized, and each exhibited spectra characteristic of the parametric decay instability. At early times in the Ba+ plasma the symmetry of wave excitation anticipated for a

  3. A simple digital TDPAC spectrometer

    NASA Astrophysics Data System (ADS)

    Webb, T. A.; Nikkinen, Leo; Gallego, Juan; Ryan, D. H.

    2013-05-01

    We present a simplified digital time differential perturbed γ - γ angular correlation (TDPAC) spectrometer that demonstrates that such instruments can be built using primarily commercial components and with relatively modest coding effort. The system handles data rates of 70 kcps/detector with a timing resolution of better than 500 ps, and has been used with both 111In and 181Hf.

  4. Environmentally friendly HF (DF) lasers

    NASA Astrophysics Data System (ADS)

    Apollonov, V. V.

    2016-08-01

    Dedicated to the 100th anniversary of the birth of Academician A M Prokhorov, this paper reviews the physics of self-sustained volume discharge without preionization—self-initiated volume discharge (SIVD)—in the working mixtures of non-chain hydrofluoride HF (deuterofluoride (DF)) lasers. The dynamics of SIVD in discharge gaps with different geometries is thoroughly described. The mechanisms for the restriction of current density in a diffuse channel in electric discharges in SF6 and SF6 based mixtures (which determines whether SIVD is possible) are proposed and analyzed using simple models. The most probable mechanisms are the electron impact dissociation of SF6 and other mixture components, electron–ion recombination and electron attachment to vibrationally excited SF6 molecules. Starting from a comparative analysis of the rate coefficients of these processes, it is shown that electron–ion recombination is capable of compensating for electron detachment from negative ions via electron impact. It is also established that SIVD is not only observed in SF6, but also in other strongly electronegative gases. The factors that determine the uniformity of the active medium in non-chain HF (DF) lasers are analyzed. Some special features of non-chain HF (DF) lasers with different apertures operating are carefully examined. Consideration is given to the problem of increasing the aperture and discharge volume of non-chain HF (DF) lasers. Based on our experimental results, the possibility of increasing the energy of such lasers to ~1 kJ and above is shown.

  5. Delineate subsurface structures with ground penetrating radar

    SciTech Connect

    Wyatt, D.E.; Hu, L.Z.; Ramaswamy, M.; Sexton, B.G.

    1992-10-01

    High resolution ground penetrating radar (GPR) surveys were conducted at the Savannah River Site in South Carolina in late 1991 to demonstrate the radar techniques in imaging shallow utility and soil structures. Targets of interest at two selected sites, designated as H- and D-areas, were a buried backfilled trench, buried drums, geologic stratas, and water table. Multiple offset 2-D and single offset 3-D survey methods were used to acquire high resolution radar data. This digital data was processed using standard seismic processing software to enhance signal quality and improve resolution. Finally, using a graphics workstation, the 3D data was interpreted. In addition, a small 3D survey was acquired in The Woodlands, Texas, with very dense spatial sampling. This data set adequately demonstrated the potential of this technology in imaging subsurface features.

  6. Delineate subsurface structures with ground penetrating radar

    SciTech Connect

    Wyatt, D.E. ); Hu, L.Z. ); Ramaswamy, M. ); Sexton, B.G. )

    1992-01-01

    High resolution ground penetrating radar (GPR) surveys were conducted at the Savannah River Site in South Carolina in late 1991 to demonstrate the radar techniques in imaging shallow utility and soil structures. Targets of interest at two selected sites, designated as H- and D-areas, were a buried backfilled trench, buried drums, geologic stratas, and water table. Multiple offset 2-D and single offset 3-D survey methods were used to acquire high resolution radar data. This digital data was processed using standard seismic processing software to enhance signal quality and improve resolution. Finally, using a graphics workstation, the 3D data was interpreted. In addition, a small 3D survey was acquired in The Woodlands, Texas, with very dense spatial sampling. This data set adequately demonstrated the potential of this technology in imaging subsurface features.

  7. Radar image analysis utilizing junctive image metamorphosis

    NASA Astrophysics Data System (ADS)

    Krueger, Peter G.; Gouge, Sally B.; Gouge, Jim O.

    1998-09-01

    A feasibility study was initiated to investigate the ability of algorithms developed for medical sonogram image analysis, to be trained for extraction of cartographic information from synthetic aperture radar imagery. BioComputer Research Inc. has applied proprietary `junctive image metamorphosis' algorithms to cancer cell recognition and identification in ultrasound prostate images. These algorithms have been shown to support automatic radar image feature detection and identification. Training set images were used to develop determinants for representative point, line and area features, which were used on test images to identify and localize the features of interest. The software is computationally conservative; operating on a PC platform in real time. The algorithms are robust; having applicability to be trained for feature recognition on any digital imagery, not just those formed from reflected energy, such as sonograms and radar images. Applications include land mass characterization, feature identification, target recognition, and change detection.

  8. space Radar Image of Long Valley, California

    NASA Technical Reports Server (NTRS)

    1994-01-01

    An area near Long Valley, California, was mapped by the Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar aboard the space shuttle Endeavor on April 13, 1994, during the first flight of the radar instrument, and on October 4, 1994, during the second flight of the radar instrument. The orbital configurations of the two data sets were ideal for interferometric combination -- that is overlaying the data from one image onto a second image of the same area to create an elevation map and obtain estimates of topography. Once the topography is known, any radar-induced distortions can be removed and the radar data can be geometrically projected directly onto a standard map grid for use in a geographical information system. The 50 kilometer by 50 kilometer (31 miles by 31 miles) map shown here is entirely derived from SIR-C L-band radar (horizontally transmitted and received) results. The color shown in this image is produced from the interferometrically determined elevations, while the brightness is determined by the radar backscatter. The map is in Universal Transverse Mercator (UTM) coordinates. Elevation contour lines are shown every 50 meters (164 feet). Crowley Lake is the dark feature near the south edge of the map. The Adobe Valley in the north and the Long Valley in the south are separated by the Glass Mountain Ridge, which runs through the center of the image. The height accuracy of the interferometrically derived digital elevation model is estimated to be 20 meters (66 feet) in this image. Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars illuminate Earth with microwaves, allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-band (24 cm), C-band (6 cm) and X-band (3 cm). The multi-frequency data will be used by the international scientific community to better understand the global

  9. 2. VIEW SOUTHWEST, prime search radar tower, height finder radar ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. VIEW SOUTHWEST, prime search radar tower, height finder radar towards, height finder radar towers, and radar tower (unknown function) - Fort Custer Military Reservation, P-67 Radar Station, .25 mile north of Dickman Road, east of Clark Road, Battle Creek, Calhoun County, MI

  10. The GEO-HF project

    NASA Astrophysics Data System (ADS)

    Willke, B.; Ajith, P.; Allen, B.; Aufmuth, P.; Aulbert, C.; Babak, S.; Balasubramanian, R.; Barr, B. W.; Berukoff, S.; Bunkowski, A.; Cagnoli, G.; Cantley, C. A.; Casey, M. M.; Chelkowski, S.; Chen, Y.; Churches, D.; Cokelaer, T.; Colacino, C. N.; Crooks, D. R. M.; Cutler, C.; Danzmann, K.; Dupuis, R. J.; Elliffe, E.; Fallnich, C.; Franzen, A.; Freise, A.; Gholami, I.; Goßler, S.; Grant, A.; Grote, H.; Grunewald, S.; Harms, J.; Hage, B.; Heinzel, G.; Heng, I. S.; Hepstonstall, A.; Heurs, M.; Hewitson, M.; Hild, S.; Hough, J.; Itoh, Y.; Jones, G.; Jones, R.; Huttner, S. H.; Kötter, K.; Krishnan, B.; Kwee, P.; Lück, H.; Luna, M.; Machenschalk, B.; Malec, M.; Mercer, R. A.; Meier, T.; Messenger, C.; Mohanty, S.; Mossavi, K.; Mukherjee, S.; Murray, P.; Newton, G. P.; Papa, M. A.; Perreur-Lloyd, M.; Pitkin, M.; Plissi, M. V.; Prix, R.; Quetschke, V.; Re, V.; Regimbau, T.; Rehbein, H.; Reid, S.; Ribichini, L.; Robertson, D. I.; Robertson, N. A.; Robinson, C.; Romano, J. D.; Rowan, S.; Rüdiger, A.; Sathyaprakash, B. S.; Schilling, R.; Schnabel, R.; Schutz, B. F.; Seifert, F.; Sintes, A. M.; Smith, J. R.; Sneddon, P. H.; Strain, K. A.; Taylor, I.; Taylor, R.; Thüring, A.; Ungarelli, C.; Vahlbruch, H.; Vecchio, A.; Veitch, J.; Ward, H.; Weiland, U.; Welling, H.; Wen, L.; Williams, P.; Winkler, W.; Woan, G.; Zhu, R.

    2006-04-01

    The GEO 600 gravitational wave detector uses advanced technologies including signal recycling and monolithic fused-silica suspensions to achieve a sensitivity close to the kilometre scale LIGO and VIRGO detectors. As soon as the design sensitivity of GEO 600 is reached, the detector will be operated as part of the worldwide network to acquire data of scientific interest. The limited infrastructure at the GEO site does not allow for a major upgrade of the detector. Hence the GEO collaboration decided to improve the sensitivity of the GEO detector by small sequential upgrades some of which will be tested in prototypes first. The development, test and installation of these upgrades are named 'The GEO-HF Project.' This paper describes the upgrades considered in the GEO-HF project as well as their scientific reasons. We will describe the changes in the GEO 600 infrastructure and the prototype work that is planned to support these upgrades. Finally, we will point to some laboratory research that identifies new technologies or optical configurations that might undergo a transition into detector subsystems within the GEO-HF project.

  11. Satellite radar interferometry - Two-dimensional phase unwrapping

    NASA Technical Reports Server (NTRS)

    Goldstein, Richard M.; Zebker, Howard A.; Werner, Charles L.

    1988-01-01

    Interferometric synthetic aperture radar observations provide a means for obtaining high-resolution digital topographic maps from measurements of amplitude and phase of two complex radar images. The phase of the radar echoes may only be measured modulo 2 pi; however, the whole phase at each point in the image is needed to obtain elevations. An approach to 'unwrapping' the 2 pi ambiguities in the two-dimensional data set is presented. It is found that noise and geometrical radar layover corrupt measurements locally, and these local errors can propagate to form global phase errors that affect the entire image. It is shown that the local errors, or residues, can be readily identified and avoided in the global phase estimation. A rectified digital topographic map derived from the unwrapped phase values is presented.

  12. Simultaneous Multi-angle Radar Observations of Langmuir Turbulence Excited by RF Ionospheric Interactions at HAARP

    NASA Astrophysics Data System (ADS)

    Sheerin, J. P.; Watanabe, N.; Rayyan, N.; Spry, D.; Adham, N.; Watkins, B. J.; Bristow, W. A.; Spaleta, J.; Bernhardt, P. A.

    2012-12-01

    The high power HAARP HF transmitter is employed to generate and study strong Langmuir turbulence (SLT) in the interaction region of overdense ionospheric plasma. Diagnostics included the Modular UHF Ionospheric Radar (MUIR) sited at HAARP, the SuperDARN-Kodiak HF radar, and HF receivers to record stimulated electromagnetic emissions (SEE). Dependence of diagnostic signals on HAARP HF parameters, including pulselength, duty-cycle, aspect angle, and frequency were recorded. Short pulse, low duty cycle experiments demonstrate control of artificial field-aligned irregularities (AFAI) and isolation of ponderomotive effects. Among the effects observed and studied are: SLT spectra including cascade, collapse, and co-existence spectra and an outshifted plasma line under certain ionospheric conditions. High time resolution studies of the temporal evolution of the plasma line reveal the appearance of an overshoot effect on ponderomotive timescales. Bursty turbulence is observed in the collapse and cascade lines. For the first time, simultaneous multi-angle radar measurements of plasma line spectra are recorded demonstrating marked dependence on aspect angle with the strongest interaction region observed displaced southward of the HF zenith pointing angle. Numerous measurements of the outshifted plasma line are observed. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.

  13. Simultaneous Multi-angle Radar Observations of Langmuir Turbulence Excited by RF Ionospheric Interactions at HAARP

    NASA Astrophysics Data System (ADS)

    Sheerin, J. P.; Rayyan, N.; Watanabe, N.; Watkins, B. J.; Bristow, W. A.; Bernhardt, P. A.

    2013-10-01

    The high power HAARP HF transmitter is employed to generate and study strong Langmuir turbulence (SLT) in the interaction region of overdense ionospheric plasma. Diagnostics included the Modular UHF Ionospheric Radar (MUIR) sited at HAARP, the SuperDARN-Kodiak HF radar, and HF receivers to record stimulated electromagnetic emissions (SEE). Dependence of diagnostic signals on HAARP HF parameters, including pulselength, duty-cycle, aspect angle, and frequency were recorded. Short pulse, low duty cycle experiments demonstrate control of artificial field-aligned irregularities (AFAI) and isolation of ponderomotive effects. Among the effects observed and studied are: SLT spectra including cascade, collapse, and co-existence spectra and an outshifted plasma line under certain ionospheric conditions. High time resolution studies of the temporal evolution of the plasma line reveal the appearance of an overshoot effect on ponderomotive timescales. Bursty turbulence is observed in the collapse and cascade lines. For the first time, simultaneous multi-angle radar measurements of plasma line spectra are recorded demonstrating marked dependence on aspect angle with the strongest interaction region observed displaced southward of the HF zenith pointing angle. Numerous measurements of the outshifted plasma line are observed. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.

  14. Clinical trials update from the American Heart Association meeting 2010: EMPHASIS-HF, RAFT, TIM-HF, Tele-HF, ASCEND-HF, ROCKET-AF, and PROTECT.

    PubMed

    Cleland, John G F; Coletta, Alison P; Buga, Laszlo; Antony, Renjith; Pellicori, Pierpaolo; Freemantle, Nick; Clark, Andrew L

    2011-04-01

    This article provides information and a commentary on key trials relevant to the pathophysiology, prevention, and treatment of heart failure presented at the annual meeting of the American Heart Association held in Chicago in 2010. Unpublished reports should be considered as preliminary, since analyses may change in the final publication. In patients with mild heart failure (HF), EMPHASIS-HF showed that the addition of eplerenone to standard therapy was well tolerated and reduced both the risk of death and hospitalization. The addition of cardiac resynchronization therapy to implantable cardioverter defibrillator (ICD) therapy reduced the incidence of all-cause mortality and HF hospitalizations in patients with NYHA class II-III HF compared with ICD alone in RAFT. Telemonitoring failed to improve outcome compared with a high standard of conventional care in patients with chronic HF (TIM-HF study) and a telephone-based interactive voice response system failed to improve outcome in patients recently hospitalized for HF (Tele-HF study). ASCEND-HF suggested that nesiritide was ineffective but safe in patients with acute decompensated HF. ROCKET-AF suggests that the factor-Xa inhibitor rivaroxaban may be as effective as warfarin in patients with atrial fibrillation. The PROTECT study provided more data to suggest that amino-terminal B-type natriuretic peptide guided therapy may be beneficial in patients with left ventricular systolic dysfunction. PMID:21436363

  15. Laser radar in robotics

    SciTech Connect

    Carmer, D.C.; Peterson, L.M.

    1996-02-01

    In this paper the authors describe the basic operating principles of laser radar sensors and the typical algorithms used to process laser radar imagery for robotic applications. The authors review 12 laser radar sensors to illustrate the variety of systems that have been applied to robotic applications wherein information extracted from the laser radar data is used to automatically control a mechanism or process. Next, they describe selected robotic applications in seven areas: autonomous vehicle navigation, walking machine foot placement, automated service vehicles, manufacturing and inspection, automotive, military, and agriculture. They conclude with a discussion of the status of laser radar technology and suggest trends seen in the application of laser radar sensors to robotics. Many new applications are expected as the maturity level progresses and system costs are reduced.

  16. Planetary radar studies

    NASA Technical Reports Server (NTRS)

    Thompson, T. W.; Cutts, J. A.

    1981-01-01

    A catalog of lunar and radar anomalies was generated to provide a base for comparison with Venusian radar signatures. The relationships between lunar radar anomalies and regolith processes were investigated, and a consortium was formed to compare lunar and Venusian radar images of craters. Time was scheduled at the Arecibo Observatory to use the 430 MHz radar to obtain high resolution radar maps of six areas of the lunar suface. Data from 1978 observations of Mare Serenitas and Plato are being analyzed on a PDP 11/70 computer to construct the computer program library necessary for the eventual reduction of the May 1981 and subsequent data acquisitions. Papers accepted for publication are presented.

  17. 3. VIEW NORTHWEST, height finder radar towers, and radar tower ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. VIEW NORTHWEST, height finder radar towers, and radar tower (unknown function) - Fort Custer Military Reservation, P-67 Radar Station, .25 mile north of Dickman Road, east of Clark Road, Battle Creek, Calhoun County, MI

  18. 30. Perimeter acquisition radar building room #318, showing radar control. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    30. Perimeter acquisition radar building room #318, showing radar control. Console and line printers - Stanley R. Mickelsen Safeguard Complex, Perimeter Acquisition Radar Building, Limited Access Area, between Limited Access Patrol Road & Service Road A, Nekoma, Cavalier County, ND

  19. 1999 IEEE radar conference

    SciTech Connect

    1999-07-01

    This conference addresses the stringent radar technology demands facing the next century: target detection, tracking and identification; changing target environment; increased clutter mitigation techniques; air traffic control; transportation; drug smuggling; remote sensing, and other consumer oriented applications. A timely discussion covers how to minimize costs for these emerging areas. Advanced radar technology theory and applications are also presented. Topics covered include: signal processing; space time adaptive processing/antennas; surveillance technology; radar systems; dual use; and phenomenology.

  20. The Condor equatorial electrojet campaign - Radar results

    NASA Astrophysics Data System (ADS)

    Kudeki, Erhan; Fejer, Bela G.; Farley, Donald T.; Hanuise, Christian

    1987-12-01

    The results of two Condor equatorial electrojet experiments (i.e., a daytime and a nighttime experiments on March 12, 1983), in which Condor rocked turbulence measurements were obtained simultaneously with VHF radar interferometer and HF radar backscatter observations, are discussed. The daytime Condor experiment showed that the electrojet could be made turbulent by either the gradient drift or the two-stream instability, or both. Pure two-stream turbulence was observed on the topside layer in the daytime electrojet suggesting that mode coupling processes should be included in nonlinear saturation theories of two-stream waves. In the nighttime experiment, radar data showed a bifurcated layer with the two parts having comparable echo strength but oppositely directed zonal drift velocities. The lower layer showed narrow backscatter spectra, while the upper layer was characterized by kilometer scale waves and vertically propagating type one waves. The characteristics of the topside large-scale waves were consistent with the predictions of nonlocal gradient drift instability theories.

  1. Signal processing techniques for surveillance radar - An overview

    NASA Astrophysics Data System (ADS)

    Farina, A.; Galati, G.

    1985-06-01

    The present paper is concerned with a survey of the signal processing techniques presently employed in modern air defense and surveillance radars and those techniques likely to be applied in the future. Attention is given to the requirements for enhancing performance in surveillance radar, current processing techniques, advanced techniques, low probability of intercept (LPI) and anti-ARM (anti-radiation missile), anti-stealth, digital beamforming (DBF), adaptivity, high directivity and high resolution, multidimensional processing, target classification, and fieldability. Stealth is the term given to means of reducing the radar cross section of a target and the reduction of infrared emissions from the engine exhaust.

  2. The application of systolic arrays to radar signal processing

    NASA Astrophysics Data System (ADS)

    Spearman, R.; Spracklen, C. T.; Miles, J. H.

    The design of a systolic array processor radar system is examined, and its performance is compared to that of a conventional radar processor. It is shown how systolic arrays can be used to replace the boards of high speed logic normally associated with a high performance radar and to implement all of the normal processing functions associated with such a system. Multifunctional systolic arrays are presented that have the flexibility associated with a general purpose digital processor but the speed associated with fixed function logic arrays.

  3. Ground penetrating radar for asparagus detection

    NASA Astrophysics Data System (ADS)

    Seyfried, Daniel; Schoebel, Joerg

    2016-03-01

    Ground penetrating radar is a promising technique for detection of buried objects. Recently, radar has more and more been identified to provide benefits for a plurality of applications, where it can increase efficiency of operation. One of these fields is the industrial automatic harvesting process of asparagus, which is performed so far by cutting the soil ridge at a certain height including all the asparagus spears and subsequently sieving the latter out of the soil. However, the height where the soil is cut is a critical parameter, since a wrong value leads to either damage of the roots of the asparagus plants or to a reduced crop yield as a consequence of too much biomass remaining in the soil. In this paper we present a new approach which utilizes ground penetrating radar for non-invasive sensing in order to obtain information on the optimal height for cutting the soil. Hence, asparagus spears of maximal length can be obtained, while keeping the roots at the same time undamaged. We describe our radar system as well as the subsequent digital signal processing steps utilized for extracting the information required from the recorded radar data, which then can be fed into some harvesting unit for setting up the optimal cutting height.

  4. Rendezvous radar for the orbital maneuvering vehicle

    NASA Technical Reports Server (NTRS)

    Locke, John W.; Olds, Keith; Parks, Howard

    1991-01-01

    This paper describes the development of the Rendezvous Radar Set (RRS) for the Orbital Maneuvering Vehicle (OMV) for the National Aeronautics and Space Administration (NASA). The RRS was to be used to locate, and then provide vectoring information to, target satellites (or Shuttle or Space Station) to aid the OMV in making a minimum-fuel-consumption approach and rendezvous. The RRS design is that of an X-Band, all solid-state, monopulse tracking, frequency hopping, pulse-Doppler radar system. The development of the radar was terminated when the OMV prime contract to TRW was terminated by NASA. At the time of the termination, the development was in the circuit design stage. The system design was virtually completed, the PDR had been held. The RRS design was based on Motorola's experiences, both in the design and production of radar systems for the US Army and in the design and production of hi-rel communications systems for NASA space programs. Experience in these fields was combined with the latest digital signal processor and micro-processor technology to design a light-weight, low-power, spaceborne radar. The antenna and antenna positioner (gimbals) technology developed for the RRS is now being used in the satellite-to-satellite communication link design for Motorola's Iridium telecommunications system.

  5. Radar Technology Development at NASA/JPL

    NASA Technical Reports Server (NTRS)

    Rosen, Paul A.

    2011-01-01

    Radar at JPL and worldwide is enjoying a period of unprecedented development. JPL's science-driven program focuses on exploiting commercially available components to build new technologies to meet NASA's science goals. Investments in onboard-processing, advanced digital systems, and efficient high-power devices, point to a new generation of high-performance scientific SAR systems in the US. Partnerships are a key strategy for US missions in the coming decade

  6. HF channel modeling for real-time packet transmission

    NASA Astrophysics Data System (ADS)

    Rostami, Mehdi; Angeja, Joao; Tavares, Joao; Navarro, Antonio

    2003-07-01

    The recent rapid growth of multimedia communications has efficiently allowed delivering different services, formats and contents over an enormous variety of digital networks with IP acting as an integration protocol. The main objective of this research work is to evaluate the performance of an high frequency (HF) wireless network for transporting multimedia services according to UDP/IP protocol stack. Besides, allowing civil/amateur communications, HF bands are also used for long distance wireless military communications. Therefore, our work is based on NATO Link and Physical layer standards, STANAG 5066 and STANAG 4539, respectively. A typical transmission bandwidth is about 3 kHz resulting in a varying bit rate in the range between 75 and 12800 bps. This very low bit rate by itself imposes serious challenges for reliable real time multimedia communications. This paper discusses optimal combinations of channel coders, modulators and packet sizes in order to achieve the greatest throughput in function of the signal-to-noise ratio and HF channel conditions.

  7. Planetary radar astronomy

    NASA Astrophysics Data System (ADS)

    Ostro, S. J.

    1983-03-01

    The present investigation is concerned with planetary radar research reported during the time from 1979 to 1982. A brief synopsis of radar definitions and technical terminology is also provided. In connection with the proximity of the moon to earth, lunar radar studies have been performed over a wider range of wavelengths than radar investigations of other planetary targets. The most recent study of lunar quasispecular scattering is due to Simpson and Tyler (1982). The latest efforts to interpret the lunar radar maps focus on maria-highlands regolith differences and models of crater ejecta evolution. The highly successful Pioneer Venus Radar Mapper experiment has provided a first look at Venus' global distributions of topography, lambda 17-cm radar reflectivity, and rms surface slopes. Attention is given to recent comparisons of Viking Orbiter images of Mars to groundbased radar altimetry of the planet, the icy Galilean satellites, radar observations of asteroids and comets, and lambda 4-cm and lambda 13-cm observations of Saturn's rings.

  8. IEEE National Radar Conference, 3rd, University of Michigan, Ann Arbor, MI, Apr. 20, 21, 1988, Proceedings

    NASA Astrophysics Data System (ADS)

    The present conference discusses topics in radar systems and subsystems, radar techniques, radar signal processing, and radar phenomenology. Attention is given to mm-wave radar system tradeoffs, polarimetric X/L/C-band SAR, a VHF radar for tropical jungle terrain elevation modeling, low probability of intercept techniques and implementations, target tracking in maneuver-centered coordinates, advanced techniques for extension of SAR depth-of-focus under arbitrary aircraft maneuvers, and iterative noncoherent angular superresolution. Also discussed are the effect of codebook size on the vector quantization of SAR data, the application of knowledge-based systems to surveillance, digital filters for SAR, novel radar pulse compression waveforms, the theory and application of SAR oceanography, autoregressive modeling of radar data with application to target identification, and a coherent model of radar weather clutter.

  9. A fully photonics-based coherent radar system

    NASA Astrophysics Data System (ADS)

    Ghelfi, Paolo; Laghezza, Francesco; Scotti, Filippo; Serafino, Giovanni; Capria, Amerigo; Pinna, Sergio; Onori, Daniel; Porzi, Claudio; Scaffardi, Mirco; Malacarne, Antonio; Vercesi, Valeria; Lazzeri, Emma; Berizzi, Fabrizio; Bogoni, Antonella

    2014-03-01

    The next generation of radar (radio detection and ranging) systems needs to be based on software-defined radio to adapt to variable environments, with higher carrier frequencies for smaller antennas and broadened bandwidth for increased resolution. Today's digital microwave components (synthesizers and analogue-to-digital converters) suffer from limited bandwidth with high noise at increasing frequencies, so that fully digital radar systems can work up to only a few gigahertz, and noisy analogue up- and downconversions are necessary for higher frequencies. In contrast, photonics provide high precision and ultrawide bandwidth, allowing both the flexible generation of extremely stable radio-frequency signals with arbitrary waveforms up to millimetre waves, and the detection of such signals and their precise direct digitization without downconversion. Until now, the photonics-based generation and detection of radio-frequency signals have been studied separately and have not been tested in a radar system. Here we present the development and the field trial results of a fully photonics-based coherent radar demonstrator carried out within the project PHODIR. The proposed architecture exploits a single pulsed laser for generating tunable radar signals and receiving their echoes, avoiding radio-frequency up- and downconversion and guaranteeing both the software-defined approach and high resolution. Its performance exceeds state-of-the-art electronics at carrier frequencies above two gigahertz, and the detection of non-cooperating aeroplanes confirms the effectiveness and expected precision of the system.

  10. A fully photonics-based coherent radar system.

    PubMed

    Ghelfi, Paolo; Laghezza, Francesco; Scotti, Filippo; Serafino, Giovanni; Capria, Amerigo; Pinna, Sergio; Onori, Daniel; Porzi, Claudio; Scaffardi, Mirco; Malacarne, Antonio; Vercesi, Valeria; Lazzeri, Emma; Berizzi, Fabrizio; Bogoni, Antonella

    2014-03-20

    The next generation of radar (radio detection and ranging) systems needs to be based on software-defined radio to adapt to variable environments, with higher carrier frequencies for smaller antennas and broadened bandwidth for increased resolution. Today's digital microwave components (synthesizers and analogue-to-digital converters) suffer from limited bandwidth with high noise at increasing frequencies, so that fully digital radar systems can work up to only a few gigahertz, and noisy analogue up- and downconversions are necessary for higher frequencies. In contrast, photonics provide high precision and ultrawide bandwidth, allowing both the flexible generation of extremely stable radio-frequency signals with arbitrary waveforms up to millimetre waves, and the detection of such signals and their precise direct digitization without downconversion. Until now, the photonics-based generation and detection of radio-frequency signals have been studied separately and have not been tested in a radar system. Here we present the development and the field trial results of a fully photonics-based coherent radar demonstrator carried out within the project PHODIR. The proposed architecture exploits a single pulsed laser for generating tunable radar signals and receiving their echoes, avoiding radio-frequency up- and downconversion and guaranteeing both the software-defined approach and high resolution. Its performance exceeds state-of-the-art electronics at carrier frequencies above two gigahertz, and the detection of non-cooperating aeroplanes confirms the effectiveness and expected precision of the system. PMID:24646997

  11. Radar cross calibration investigation TAMU radar polarimeter calibration measurements

    NASA Astrophysics Data System (ADS)

    Blanchard, A. J.; Newton, R. W.; Bong, S.; Kronke, C.; Warren, G. L.; Carey, D.

    1982-10-01

    A short pulse, 20 MHz bandwidth, three frequency radar polarimeter system (RPS) operates at center frequencies of 10.003 GHz, 4.75 GHz, and 1.6 GHz and utilizes dual polarized transmit and receive antennas for each frequency. The basic lay-out of the RPS is different from other truck mounted systems in that it uses a pulse compression IF section common to all three RF heads. Separate transmit and receive antennas are used to improve the cross-polarization isolation at each particular frequency. The receive is a digitally controlled gain modulated subsystem and is interfaced directly with a microprocesser computer for control and data manipulation. Antenna focusing distance, focusing each antenna pair, rf head stability, and polarization characteristics of RPS antennas are discussed. Platform and data acquisition procedures are described.

  12. The PROUST radar

    NASA Technical Reports Server (NTRS)

    Bertin, F.; Glass, M.; Ney, R.; Petitdidier, M.

    1986-01-01

    The Stratosphere-Troposphere (ST) radar called PROUST works at 935 MHz using the same klystron and antenna as the coherent-scatter radar. The use of this equipment for ST work has required some important modifications of the transmitting system and the development of receiving, data processing and acquisition (1984,1985) equipment. The modifications are discussed.

  13. Determination of radar MTF

    SciTech Connect

    Chambers, D.

    1994-11-15

    The ultimate goal of the Current Meter Array (CMA) is to be able to compare the current patterns detected with the array with radar images of the water surface. The internal wave current patterns modulate the waves on the water surface giving a detectable modulation of the radar cross-section (RCS). The function relating the RCS modulations to the current patterns is the Modulation Transfer Function (MTF). By comparing radar images directly with co-located CMA measurements the MTF can be determined. In this talk radar images and CMA measurements from a recent experiment at Loch Linnhe, Scotland, will be used to make the first direct determination of MTF for an X and S band radar at low grazing angles. The technical problems associated with comparing radar images to CMA data will be explained and the solution method discussed. The results suggest the both current and strain rate contribute equally to the radar modulation for X band. For S band, the strain rate contributes more than the current. The magnitude of the MTF and the RCS modulations are consistent with previous estimates when the wind is blowing perpendicular to the radar look direction.

  14. Java Radar Analysis Tool

    NASA Technical Reports Server (NTRS)

    Zaczek, Mariusz P.

    2005-01-01

    Java Radar Analysis Tool (JRAT) is a computer program for analyzing two-dimensional (2D) scatter plots derived from radar returns showing pieces of the disintegrating Space Shuttle Columbia. JRAT can also be applied to similar plots representing radar returns showing aviation accidents, and to scatter plots in general. The 2D scatter plots include overhead map views and side altitude views. The superposition of points in these views makes searching difficult. JRAT enables three-dimensional (3D) viewing: by use of a mouse and keyboard, the user can rotate to any desired viewing angle. The 3D view can include overlaid trajectories and search footprints to enhance situational awareness in searching for pieces. JRAT also enables playback: time-tagged radar-return data can be displayed in time order and an animated 3D model can be moved through the scene to show the locations of the Columbia (or other vehicle) at the times of the corresponding radar events. The combination of overlays and playback enables the user to correlate a radar return with a position of the vehicle to determine whether the return is valid. JRAT can optionally filter single radar returns, enabling the user to selectively hide or highlight a desired radar return.

  15. Radar illusion via metamaterials.

    PubMed

    Jiang, Wei Xiang; Cui, Tie Jun

    2011-02-01

    An optical illusion is an image of a real target perceived by the eye that is deceptive or misleading due to a physiological illusion or a specific visual trick. The recently developed metamaterials provide efficient approaches to generate a perfect optical illusion. However, all existing research on metamaterial illusions has been limited to theory and numerical simulations. Here, we propose the concept of a radar illusion, which can make the electromagnetic (EM) image of a target gathered by radar look like a different target, and we realize a radar illusion device experimentally to change the radar image of a metallic target into a dielectric target with predesigned size and material parameters. It is well known that the radar signatures of metallic and dielectric objects are significantly different. However, when a metallic target is enclosed by the proposed illusion device, its EM scattering characteristics will be identical to that of a predesigned dielectric object under the illumination of radar waves. Such an illusion device will confuse the radar, and hence the real EM properties of the metallic target cannot be perceived. We designed and fabricated the radar illusion device using artificial metamaterials in the microwave frequency, and good illusion performances are observed in the experimental results. PMID:21405918

  16. Measurement of TID and Gravity Wave Parameters Using An HF Doppler System

    NASA Astrophysics Data System (ADS)

    Wene, G. P.; Crowley, G.; Fessler, B. W.; Bronn, J. S.

    2005-05-01

    The manifestation of atmospheric gravity waves (AGWs) in the ionosphere is called a traveling ionospheric disturbance (TID). TIDs can be thought of as traveling corrugations in the ionosphere, and as such can seriously affect HF radio communications and surveillance systems. They may indirectly play a greater role in disrupting communications by triggering the growth of ionospheric instabilities, resulting in scintillation of radio signals. It is therefore of great interest to monitor TIDs on a routine basis, and to correlate their properties with other phenomena. In this paper, we present data from a unique radio technique for measuring TID properties such as their spectrum, and their spectrally resolved propagation characteristics. One of the most sensitive methods for detecting transient changes in the ionosphere is the HF Doppler technique operating in the 3-10 MHz band. HF Doppler systems have advantages over all other techniques for the measurement of TID characteristics. They are more amenable to analysis than data from ionosonde chains, and their time resolution (30 sec) is much higher than that of ionosondes . Unlike total electron content (TEC) methods, which respond to height-integrated TID effects, the HF Doppler radar responds to TIDs at the altitude of the radio reflection point. Finally, HF Doppler systems have low power consumption, so that both spatial and temporal resolution can be maintained for many days without the costs that would be associated with an incoherent-scatter radar. SwRI recently designed, built and deployed an HF Doppler sounding system in Texas, to investigate TIDs. The TIDDBIT radar consisted of three transmitters (Austin, Uvalde and St. Hedwig) and a receiver in San Antonio, Texas. Using a cross-spectral analysis technique, TID speeds and azimuths were obtained for each wave frequency. We provide a synoptic survey of the TID characteristics observed over Texas during January-March 2002. The Doppler system provides an accurate

  17. Equatorial MU Radar project

    NASA Astrophysics Data System (ADS)

    Yamamoto, Mamoru; Hashiguchi, H.; Tsuda, Toshitaka; Yamamoto, Masayuki

    Research Institute for Sustainable Humanosphere, Kyoto University (RISH) has been studying the atmosphere by using radars. The first big facility was the MU (Middle and Upper atmosphere) radar installed in Shiga, Japan in 1984. This is one of the most powerful and multi-functional radar, and is successful of revealing importance of atmospheric waves for the dynamical vertical coupling processes. The next big radar was the Equatorial Atmosphere Radar (EAR) installed at Kototabang, West Sumatra, Indonesia in 2001. The EAR was operated under close collaboration with LAPAN (Indonesia National Institute for Aeronautics and Space), and conducted the long-term continuous observations of the equatorial atmosphere/ionosphere for more than 10 years. The MU radar and the EAR are both utilized for inter-university and international collaborative research program for long time. National Institute for Polar Research (NIPR) joined EISCAT Scientific Association together with Nagoya University, and developed the PANSY radar at Syowa base in Antarctica as a joint project with University of Tokyo. These are the efforts of radar study of the atmosphere/ionosphere in the polar region. Now we can find that Japan holds a global network of big atmospheric/ionospheric radars. The EAR has the limitation of lower sensitivity compared with the other big radars shown above. RISH now proposes a plan of Equatorial MU Radar (EMU) that is to establish the MU-radar class radar next to the EAR. The EMU will have an active phased array antenna with the 163m diameter and 1055 cross-element Yagis. Total output power of the EMU will be more than 500kW. The EMU can detect turbulent echoes from the mesosphere (60-80km). In the ionosphere incoherent-scatter observations of plasma density, drift, and temperature would be possible. Multi-channel receivers will realize radar-imaging observations. The EMU is one of the key facilities in the project "Study of coupling processes in the solar-terrestrial system

  18. Integrating a Microwave Radiometer into Radar Hardware for Simultaneous Data Collection Between the Instruments

    NASA Technical Reports Server (NTRS)

    McLinden, Matthew; Piepmeier, Jeffrey

    2013-01-01

    The conventional method for integrating a radiometer into radar hardware is to share the RF front end between the instruments, and to have separate IF receivers that take data at separate times. Alternatively, the radar and radiometer could share the antenna through the use of a diplexer, but have completely independent receivers. This novel method shares the radar's RF electronics and digital receiver with the radiometer, while allowing for simultaneous operation of the radar and radiometer. Radars and radiometers, while often having near-identical RF receivers, generally have substantially different IF and baseband receivers. Operation of the two instruments simultaneously is difficult, since airborne radars will pulse at a rate of hundreds of microseconds. Radiometer integration time is typically 10s or 100s of milliseconds. The bandwidth of radar may be 1 to 25 MHz, while a radiometer will have an RF bandwidth of up to a GHz. As such, the conventional method of integrating radar and radiometer hardware is to share the highfrequency RF receiver, but to have separate IF subsystems and digitizers. To avoid corruption of the radiometer data, the radar is turned off during the radiometer dwell time. This method utilizes a modern radar digital receiver to allow simultaneous operation of a radiometer and radar with a shared RF front end and digital receiver. The radiometer signal is coupled out after the first down-conversion stage. From there, the radar transmit frequencies are heavily filtered, and the bands outside the transmit filter are amplified and passed to a detector diode. This diode produces a DC output proportional to the input power. For a conventional radiometer, this level would be digitized. By taking this DC output and mixing it with a system oscillator at 10 MHz, the signal can instead be digitized by a second channel on the radar digital receiver (which typically do not accept DC inputs), and can be down-converted to a DC level again digitally. This

  19. Laser radar improvements

    NASA Astrophysics Data System (ADS)

    Jelalian, A. V.

    1981-11-01

    A short history of the uses of various laser radars is presented, and appropriate applications of laser and microwave radars are discussed. CO2 laser radar, operating at 10.6 microns, is considered for use in aircraft navigation systems, fire-control systems for armored vehicle and aircraft, missile guidance, severe storm research, line-of-sight command of missiles, wind turbine site surveys, clear-air turbulence monitors for aircraft, and satellite tracking. Microwave radar is all-weather, but is subject to multipath inaccuracies, countermeasures, and angular resolution limitations, so hybrid laser microwave systems look promising for microwave target acquisition and laser tracking. Advantages and disadvantages of the use of ruby, YAG, and CO2 lasers in varying atmospheric conditions are discussed. Development of a laser radar pod for obstacle detection, Doppler navigation, automatic terrain following, hover control, weapon delivery, and precision searching is noted.

  20. Intelligent radar data processing

    NASA Astrophysics Data System (ADS)

    Holzbaur, Ulrich D.

    The application of artificial intelligence principles to the processing of radar signals is considered theoretically. The main capabilities required are learning and adaptation in a changing environment, processing and modeling information (especially dynamics and uncertainty), and decision-making based on all available information (taking its reliability into account). For the application to combat-aircraft radar systems, the tasks include the combination of data from different types of sensors, reacting to electronic counter-countermeasures, evaluation of how much data should be acquired (energy and radiation management), control of the radar, tracking, and identification. Also discussed are related uses such as monitoring the avionics systems, supporting pilot decisions with respect to the radar system, and general applications in radar-system R&D.

  1. Micropower impulse radar imaging

    SciTech Connect

    Hall, M.S.

    1995-11-01

    From designs developed at the Lawrence Livermore National Laboratory (LLNL) in radar and imaging technologies, there exists the potential for a variety of applications in both public and private sectors. Presently tests are being conducted for the detection of buried mines and the analysis of civil structures. These new systems use a patented ultra-wide band (impulse) radar technology known as Micropower Impulse Radar (GPR) imaging systems. LLNL has also developed signal processing software capable of producing 2-D and 3-D images of objects embedded in materials such as soil, wood and concrete. My assignment while at LLNL has focused on the testing of different radar configurations and applications, as well as assisting in the creation of computer algorithms which enable the radar to scan target areas of different geometeries.

  2. Spaceborne weather radar

    NASA Technical Reports Server (NTRS)

    Meneghini, Robert; Kozu, Toshiaki

    1990-01-01

    The present work on the development status of spaceborne weather radar systems and services discusses radar instrument complementarities, the current forms of equations for the characterization of such aspects of weather radar performance as surface and mirror-image returns, polarimetry, and Doppler considerations, and such essential factors in spaceborne weather radar design as frequency selection, scanning modes, and the application of SAR to rain detection. Attention is then given to radar signal absorption by the various atmospheric gases, rain drop size distribution and wind velocity determinations, and the characteristics of clouds, as well as the range of available estimation methods for backscattering, single- and dual-wavelength attenuation, and polarimetric and climatological characteristics.

  3. HF Radio Wave Propagation in the Ionosphere Observed with the ePOP RRI (Radio Receiver Instrument) -- SuperDARN Experiment

    NASA Astrophysics Data System (ADS)

    Hussey, G. C.; Gillies, R. G.; Ridley, C. G.; Yau, A. W.; McWilliams, K. A.; Sofko, G. J.

    2014-12-01

    The Radio Receiver Instrument (RRI) on the enhanced Polar Outflow Probe (ePOP) scientific payload of the recently launched CSA (Canadian Space Agency) CASSIOPE (Cascade Demonstrator Small-Sat and Ionospheric Polar Explorer) satellite mission and the Super Dual Auroral Radar Network (SuperDARN) of HF radars have successfully executed a number of experiments since the launch of ePOP in late September, 2013. This presentation investigates the propagation delays and timing associated with HF radio waves transversing the plasma in the terrestrial ionosphere. Both the relative and absolute timing of the co-ordinated SuperDARN-RRI experiments will be presented. This knowledge is essential for interpreting HF radio wave propagation effects such as range accuracy, mode-splitting and timing, Doppler shift, and delayed 'echo' signatures, for example.

  4. Programmable Analog-To-Digital Converter

    NASA Technical Reports Server (NTRS)

    Kist, Edward H., Jr.

    1993-01-01

    High-speed analog-to-digital converter with programmable voltage steps that can be changed during operation. Allows concentration of converter resolution over specific portion of waveform. Particularly useful in digitizing wind-shear radar and lidar return signals, in digital oscilloscopes, and other applications in which desirable to increase digital resolution over specific area of waveform while accepting lower resolution over rest of waveform. Effective increase in dynamic range achieved without increase in number of analog-to-digital converter bits. Enabling faster analog-to-digital conversion.

  5. Digital Optical Circuit Technology

    NASA Technical Reports Server (NTRS)

    Dove, B. L. (Editor)

    1985-01-01

    The Proceedings for the 48th Meeting of the AGARD Avionics Panel contain the 18 papers presented a Technical Evaluation Report, and discussions that followed the presentations of papers. Seven papers were presented in the session devoted to optical bistability. Optical logic was addressed by three papers. The session on sources, modulators and demodulators presented three papers. Five papers were given in the final session on all optical systems. The purpose of this Specialists' Meeting was to present the research and development status of digital optical circuit technology and to examine its relevance in the broad context of digital processing, communication, radar, avionics and flight control systems implementation.

  6. Compressive wideband microwave radar holography

    NASA Astrophysics Data System (ADS)

    Wilson, Scott A.; Narayanan, Ram M.

    2014-05-01

    Compressive sensing has emerged as a topic of great interest for radar applications requiring large amounts of data storage. Typically, full sets of data are collected at the Nyquist rate only to be compressed at some later point, where information-bearing data are retained and inconsequential data are discarded. However, under sparse conditions, it is possible to collect data at random sampling intervals less than the Nyquist rate and still gather enough meaningful data for accurate signal reconstruction. In this paper, we employ sparse sampling techniques in the recording of digital microwave holograms over a two-dimensional scanning aperture. Using a simple and fast non-linear interpolation scheme prior to image reconstruction, we show that the reconstituted image quality is well-retained with limited perceptual loss.

  7. Description and availability of airborne Doppler radar data

    NASA Technical Reports Server (NTRS)

    Harrah, S. D.; Bracalente, E. M.; Schaffner, P. R.; Baxa, E. G.

    1993-01-01

    An airborne, forward-looking, pulse, Doppler radar has been developed in conjunction with the joint FAA/NASA Wind Shear Program. This radar represents a first in an emerging technology. The radar was developed to assess the applicability of an airborne radar to detect low altitude hazardous wind shears for civil aviation applications. Such a radar must be capable of looking down into the ground clutter environment and extracting wind estimates from relatively low reflectivity weather targets. These weather targets often have reflectivities several orders of magnitude lower than the surrounding ground clutter. The NASA radar design incorporates numerous technological and engineering achievements in order to accomplish this task. The basic R/T unit evolved from a standard Collins 708 weather radar, which supports specific pulse widths of 1-7 microns and Pulse Repetition Frequencies (PRF) of less than 1-10 kHz. It was modified to allow for the output of the first IF signal, which fed a NASA developed receiver/detector subsystem. The NASA receiver incorporated a distributed, high-speed digital attenuator, producing a range bin to range bin automatic gain control system with 65 dB of dynamic range. Using group speed information supplied by the aircraft's navigation system, the radar signal is frequency demodulated back to base band (zero Doppler relative to stationary ground). The In-phase & Quadrature-phase (I/Q) components of the measured voltage signal are then digitized by a 12-bit A-D converter (producing an additional 36 dB of dynamic range). The raw I/Q signal for each range bin is then recorded (along with the current radar & aircraft state parameters) by a high-speed Kodak tape recorder.

  8. 5. VIEW EAST, height finder radar towers, radar tower (unknown ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. VIEW EAST, height finder radar towers, radar tower (unknown function), prime search radar tower, operations building, and central heating plant - Fort Custer Military Reservation, P-67 Radar Station, .25 mile north of Dickman Road, east of Clark Road, Battle Creek, Calhoun County, MI

  9. 4. VIEW NORTHEAST, radar tower (unknown function), prime search radar ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. VIEW NORTHEAST, radar tower (unknown function), prime search radar tower, emergency power building, and height finder radar tower - Fort Custer Military Reservation, P-67 Radar Station, .25 mile north of Dickman Road, east of Clark Road, Battle Creek, Calhoun County, MI

  10. Measurements of spatial and frequency coherence of an equatorial hf path during spread-F

    SciTech Connect

    Fitzgerald, T.J.; Argo, P.E.; Carlos, R.C.

    1993-01-01

    In August 1990, the authors set up an hf path on the equatorial path between Maloelap Atoll and Bikini Atoll. This path, which had a range of 702 km, reflected in the ionosphere approximately 100 km north of the Altair radar location on Kwajalein. Transmitters at Maloelap broadcasted four cw tones within bandwidth of either 4 kHz, 9 kHz, or 70 kHz to be used to determine frequency coherence and also a phase-coded pseudo random sequence with a bandwidth of 60 kHz (channel probe) to be used to determine time delay spread. A spatial array of antennas was deployed at Bikini to measure spatial and frequency coherence using the cw broadcasts. The system was run in the post-sunset time period over two weeks during which almost every night showed significant degradation due to spread F resulting in rapid fading, decreased spatial and frequency coherence, and increased time delay spread. Doppler spreads of greater than 20 Hz were not uncommon, and the spatial correlation distances and frequency coherence bandwidths became so small (50 meters and 1 kHz respectively) that the experiment had to be readjusted. Measurements taken by the Altair incoherent scatter radar and the CUPRI 50 MHz coherent scatter radar indicate that although the bistatic hf channel is affected by the large scale plume structures, most of the [open quotes]damage[close quotes] is done by the bottomside spread F.

  11. Range rate-Doppler correlation for HF propagation in traveling ionospheric disturbance environments

    NASA Astrophysics Data System (ADS)

    Nickisch, L. J.; Hausman, Mark A.; Fridman, Sergey V.

    2006-10-01

    Using ionospheric sounding together with fast computational inverse processing, it is now possible to obtain good real-time ionospheric models for use in geolocation for over-the-horizon (OTH) radar. However, deflection of HF propagation paths by traveling ionospheric disturbances (TIDs) remains a troubling cause of coordinate registration errors. Bandwidth and coverage limitations in ionospheric soundings preclude the ability to model TID structure in real time in most cases. It would be useful if TID-induced path deflections could be related to radar-measurable quantities like Doppler shift. As a first step in studying this possibility, we have considered the relationship between Doppler shift and group range rate for point-to-point HF propagation paths in TID environments. The nature of group range rate-Doppler correlation is exposed in three ways: (1) simple theoretical modeling, (2) ray tracing in simulated TID environments, and (3) analysis of OTH radar measurements of a fixed beacon. It is shown that group range rate and Doppler shift for fixed-point propagation paths are usually proportional with a ratio that depends on whether ionospheric motion or density changes predominate in the TID environment.

  12. Computing Ocean Surface Currents from Satellite Synthetic Aperture Radar Imagery

    NASA Astrophysics Data System (ADS)

    Qazi, Waqas A.

    Ocean surface currents play an important role in ocean-atmosphere interactions and global ocean circulation, and are also significant for fishing, ocean navigation, and search & rescue. Existing in-situ and remote sensing techniques for measuring ocean surface currents are limited by spatial and temporal data coverage, and thermal IR feature tracking methods are limited by clouds and weak thermal gradients. High-resolution spaceborne Synthetic Aperture Radar (SAR) offers repeatable cloud-penetrating measurements of the ocean surface. This research explores methods for ocean surface current measurement through satellite-based SAR. The major part of this research is concerned with the development and application of a semi-automated algorithm to generate ocean surface currents at ˜1.9 km resolution from sequential spaceborne C-band SAR intensity images using the Maximum Cross-Correlation(MCC) method. The primary geographical area of study is the coastal California Current System (CCS), and nearly two years (2008-2009) of 30-min lag data from the Envisat ASAR and ERS-2 AMI SAR sensors is analyzed. The velocity wavenumber spectrum of the derived MCC SAR currents agrees with the k-2 power law as predicted by submesoscale resolution models, and also shows seasonal mesoscale variability. The derived MCC SAR currents are validated against High frequency (HF) radar currents, and the two show some agreement in vector direction, with MCC SAR vectors oriented slightly anti-clockwise relative to HF radar vectors. The unimodal mean-symmetric residual histograms indicate that errors between the two datasets are random, except for a mean positive bias of ≈ 11 cm/s in MCC SAR currents relative to HF radar currents. This magnitude difference occurs primarily in the along-shore component ( ≈ 6 cm/s) and is negligible in the cross-shore component. Doppler Centroid Cross-Track (XT) radial currents from Envisat Wide Swath Mode (WSM) scenes are compared with HF radar radial currents

  13. Optical and ionospheric phenomena at EISCAT under continuous X-mode HF pumping

    NASA Astrophysics Data System (ADS)

    Blagoveshchenskaya, N. F.; Borisova, T. D.; Kosch, M.; Sergienko, T.; Brändström, U.; Yeoman, T. K.; Häggström, I.

    2014-12-01

    We present experimental results from multiinstrument observations in the high-latitude ionospheric F2 layer at the EISCAT (European Incoherent Scatter Scientific Association) heating facility. The results come from a set of experiments, when an X-polarized HF pump wave at high heater frequencies (fH > 6.0 MHz) was injected into the F region of the ionosphere toward the magnetic zenith. Experiments were carried out under quiet magnetic conditions with an effective radiated power of 458-548 MW. HF pumping was produced at different heater frequencies, away from electron gyroharmonic frequencies, and different durations of heater pulses. We show the first experimental evidence of the excitation of artificial optical emissions at red (630 nm) and green (557.7 nm) lines in the high-latitude ionospheric F2 layer induced by an X-polarized HF pump wave. Intensities at red and green lines varied in the range 110-950 R and 50-350 R, respectively, with a ratio of green to red line of 0.35-0.5. The results of optical observations are compared with behaviors of the HF-enhanced ion and plasma lines from EISCAT UHF incoherent scatter radar data and small-scale field-aligned artificial irregularities from Cooperative UK Twin Located Auroral Sounding System observations. It was found that the X-mode radio-induced optical emissions coexisted with HF-enhanced ion and plasma lines and strong artificial field-aligned irregularities throughout the whole heater pulse. It is indicative that parametric decay or oscillating two-stream instabilities were not quenched by fully established small-scale field-aligned artificial irregularities excited by an X-mode HF pump wave.

  14. Digital-Difference Processing For Collision Avoidance.

    NASA Technical Reports Server (NTRS)

    Shores, Paul; Lichtenberg, Chris; Kobayashi, Herbert S.; Cunningham, Allen R.

    1988-01-01

    Digital system for automotive crash avoidance measures and displays difference in frequency between two sinusoidal input signals of slightly different frequencies. Designed for use with Doppler radars. Characterized as digital mixer coupled to frequency counter measuring difference frequency in mixer output. Technique determines target path mathematically. Used for tracking cars, missiles, bullets, baseballs, and other fast-moving objects.

  15. Wind turbine clutter mitigation in coastal UHF radar.

    PubMed

    Yang, Jing; Pan, Chao; Wang, Caijun; Jiang, Dapeng; Wen, Biyang

    2014-01-01

    Coastal UHF radar provides a unique capability to measure the sea surface dynamic parameters and detect small moving targets, by exploiting the low energy loss of electromagnetic waves propagating along the salty and good conducting ocean surface. It could compensate the blind zone of HF surface wave radar at close range and reach further distance than microwave radars. However, its performance is susceptible to wind turbines which are usually installed on the shore. The size of a wind turbine is much larger than the wavelength of radio waves at UHF band, which results in large radar cross section. Furthermore, the rotation of blades adds time-varying Doppler frequency to the clutter and makes the suppression difficult. This paper proposes a mitigation method which is based on the specific periodicity of wind turbine clutter and performed mainly in the time-frequency domain. Field experimental data of a newly developed UHF radar are used to verify this method, and the results prove its effectiveness. PMID:24550709

  16. Wind Turbine Clutter Mitigation in Coastal UHF Radar

    PubMed Central

    Wang, Caijun; Jiang, Dapeng; Wen, Biyang

    2014-01-01

    Coastal UHF radar provides a unique capability to measure the sea surface dynamic parameters and detect small moving targets, by exploiting the low energy loss of electromagnetic waves propagating along the salty and good conducting ocean surface. It could compensate the blind zone of HF surface wave radar at close range and reach further distance than microwave radars. However, its performance is susceptible to wind turbines which are usually installed on the shore. The size of a wind turbine is much larger than the wavelength of radio waves at UHF band, which results in large radar cross section. Furthermore, the rotation of blades adds time-varying Doppler frequency to the clutter and makes the suppression difficult. This paper proposes a mitigation method which is based on the specific periodicity of wind turbine clutter and performed mainly in the time-frequency domain. Field experimental data of a newly developed UHF radar are used to verify this method, and the results prove its effectiveness. PMID:24550709

  17. Planetary Radar Astronomy

    NASA Technical Reports Server (NTRS)

    Ostro, Steven J.

    1993-01-01

    Radar is a powerful technique that has furnished otherwise unavailable information about solar system bodies for three decades. The advantages of radar in planetary astronomy result from: (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice. Planetary radar astronomy has primarily involved observations with Earth-based radar telescopes, but also includes some experiments with a spaceborne transmitter or receiver. In addition to providing a wealth of information about the geological and dynamical properties of asteroids, comets, the inner planets, and natural satellites, radar experiments have established the scale of the solar system, have contributed significantly to the accuracy of planetary ephemerides, and have helped to constrain theories of gravitation. This review outlines radar astronomical techniques and describes principal observational results.

  18. Ground-penetrating radar methods

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Ground-penetrating radar geophysical methods are finding greater and greater use in agriculture. With the ground-penetrating radar (GPR) method, an electromagnetic radio energy (radar) pulse is directed into the subsurface, followed by measurement of the elapsed time taken by the radar signal as it ...

  19. Radar remote sensing in biology

    USGS Publications Warehouse

    Moore, Richard K.; Simonett, David S.

    1967-01-01

    The present status of research on discrimination of natural and cultivated vegetation using radar imaging systems is sketched. The value of multiple polarization radar in improved discrimination of vegetation types over monoscopic radars is also documented. Possible future use of multi-frequency, multi-polarization radar systems for all weather agricultural survey is noted.

  20. The RITMARE coastal radar network and applications to monitor marine transport infrastructures

    NASA Astrophysics Data System (ADS)

    Carrara, Paola; Corgnati, Lorenzo; Cosoli, Simone; Griffa, Annalisa; Kalampokis, Alkiviadis; Mantovani, Carlo; Oggioni, Alessandro; Pepe, Monica; Raffa, Francesco; Serafino, Francesco; Uttieri, Marco; Zambianchi, Enrico

    2014-05-01

    Coastal radars provide information on the environmental state of oceans, namely maps of surface currents at time intervals of the order of one hour with spatial coverage of the order of several km, depending on the transmission frequency. The observations are of crucial importance for monitoring ports and ship tracks close to the coast, providing support for safe navigation in densely operated areas and fast response in case of accidents at sea, such as oil spill or search and rescue. Besides these applications, coastal radar observations provide fundamental support in MPAs surveillance, connectivity and marine population circulation. In the framework of the Italian RITMARE flagship project coordinated by CNR (Consiglio Nazionale delle Ricerche), a coastal radar network has been designed and implemented with a number of innovative characteristics. The network includes both HF and X-band radars, allowing coverage of wide areas with different spatial and temporal resolutions. HF radars cover up to 80 km with a spatial resolution ranging between 1 and 5 km, while X-band radars provide 5 km coverage with a spatial resolution of 10 m. Joining these two capabilities, the RITMARE coastal radar network enables both a highly effective coverage of wide coastal areas and integrated monitoring of different phenomena, thus allowing the collection of current and wave parameters and detection of bathymetries of both open sea and coastal areas. A dedicated action to foster interoperability among data providers has been undertaken within RITMARE; an IT framework is under development to provide software tools for data collection and data sharing. It suggests standard, data format definitions, Quality Control strategies, data management and dissemination policies. In particular, the implementation of tools exploits both standards of OGC (Open Geospatial Consortium) and web services offered to manage, access and deliver geospatial data. Radar data produced in RITMARE by the coastal

  1. Asteroid radar astrometry

    NASA Technical Reports Server (NTRS)

    Ostro, S. J.; Jurgens, R. F.; Rosema, K. D.; Winkler, R.; Yeomans, D. K.; Campbell, D. B.; Chandler, J. F.; Shapiro, I. I.; Hine, A. A.; Velez, R.

    1991-01-01

    Measurements of time delay and Doppler frequency are reported for asteroid-radar echoes obtained at Arecibo and Goldstone during 1980-1990. Radar astrometry is presented for 23 near-earth asteroids and three mainbelt asteroids. These measurements, which are orthogonal to optical, angular-position measurements, and typically have a fractional precision between 10 to the -5th and 10 to the -8th, permit significant improvement in estimates of orbits and hence in the accuracy of prediction ephemerides. Estimates are also reported of radar cross-section and circular polarization ratio for all asteroids observed astrometrically during 1980-1990.

  2. EISCAT Svalbard radar

    NASA Astrophysics Data System (ADS)

    Lehtinen, Markku; Kangas, Jorma

    1992-02-01

    The main fields of interest of the Finnish scientists in EISCAT research are listed. Finnish interests in the Polar Cap Radar (PMR) and areas where the Finnish contribution could be important are addressed: radar techniques; sporadic E layers in the polar cap; atmospheric models; auroral studies in the polar cap; nonthermal plasmas in the F region; coordinated measurements with the Cluster satellites; studies of the ionospheric traveling; convection vortices; polar cap absorption; studies of lower atmosphere; educational program. A report on the design specification of an ionospheric and atmospheric radar facility based on the archipelago of Svalbard (Norway) is summarized.

  3. A microprogrammable radar controller

    NASA Technical Reports Server (NTRS)

    Law, D. C.

    1986-01-01

    The Wave Propagation Lab. has completed the design and construction of a microprogrammable radar controller for atmospheric wind profiling. Unlike some radar controllers using state machines or hardwired logic for radar timing, this design is a high speed programmable sequencer with signal processing resources. A block diagram of the device is shown. The device is a single 8 1/2 inch by 10 1/2 inch printed circuit board and consists of three main subsections: (1) the host computer interface; (2) the microprogram sequencer; and (3) the signal processing circuitry. Each of these subsections are described in detail.

  4. Polarimetric Doppler Weather Radar

    NASA Astrophysics Data System (ADS)

    Bringi, V. N.; Chandrasekar, V.

    2001-10-01

    This work provides a detailed introduction to the principles of Doppler and polarimetric radar, focusing in particular on their use in the analysis of weather systems. The authors first discuss underlying topics such as electromagnetic scattering, polarization, and wave propagation. They then detail the engineering aspects of pulsed Doppler polarimetric radar, before examining key applications in meteorology and remote sensing. The book is aimed at graduate students of electrical engineering and atmospheric science as well as practitioners involved in the applications of polarimetric radar.

  5. A statistical channel model for adaptive HF communications via a severely disturbed ionosphere

    NASA Astrophysics Data System (ADS)

    Haines, D. M.

    1983-12-01

    Motivation for the resurgence of interest in improving HF communication is presented. This includes the continued widespread use of the HF band, and the new technology that now makes it feasible to vastly improve the historically poor quality of communications in this band. Non-conventional HF techniques or systems are classified into four general categories according to the technical specialties that spawned them. These categories are Adaptive Frequency Management. Digital Waveform Processing, Networking, and Adaptive Antennas. A 15 parameter channel model is presented which forms the basis for the on-going RADC measurement program. These parameters address the dispersion and dynamics of time, frequency and spatial distortion imposed by the skywave channel. Next, measurement techniques are evaluated for characterization of these parameters, resulting in the selection of a six station Arctic network of wideband pulse compression (matched filter) channel probes. A description of waveform generation, receiver signal processing and the program plans and schedule are presented.

  6. Evaluating the surface circulation in the Ebro delta (northeastern Spain) with quality-controlled high-frequency radar measurements

    NASA Astrophysics Data System (ADS)

    Lorente, P.; Piedracoba, S.; Soto-Navarro, J.; Alvarez-Fanjul, E.

    2015-11-01

    The Ebro River delta is a relevant marine protected area in the western Mediterranean. In order to promote the conservation of its ecosystem and support operational decision making in this sensitive area, a three-site standard-range (13.5 MHz) CODAR SeaSonde high-frequency (HF) radar was deployed in December 2013. The main goal of this work is to explore basic features of the sea surface circulation in the Ebro deltaic region as derived from reliable HF radar surface current measurements. For this aim, a combined quality control methodology was applied: firstly, 1-year long (2014) real-time web monitoring of nonvelocity-based diagnostic parameters was conducted to infer both radar site status and HF radar system performance. The signal-to-noise ratio at the monopole exhibited a consistent monthly evolution, although some abrupt decreases (below 10 dB), occasionally detected in June for one of the radar sites, impacted negatively on the spatiotemporal coverage of total current vectors. It seemed to be sporadic episodes since radar site overall performance was found to be robust during 2014. Secondly, a validation of HF radar data with independent in situ observations from a moored current meter was attempted for May-October 2014. The accuracy assessment of radial and total vectors revealed a consistently high agreement. The directional accuracy of the HF radar was rated at better than 8°. The correlation coefficient and root mean square error (RMSE) values emerged in the ranges [0.58-0.83] and [4.02-18.31] cm s-1, respectively. The analysis of the monthly averaged current maps for 2014 showed that the HF radar properly represented basic oceanographic features previously reported, namely, the predominant southwestward flow, the coastal clockwise eddy confined south of the Ebro delta mouth, or the Ebro River impulsive-type freshwater discharge. The EOF analysis related the flow response to local wind forcing and confirmed that the surface current field evolved in

  7. Generation of Artificial Acoustic-Gravity Waves and Traveling Ionospheric Disturbances in HF Heating Experiments

    NASA Astrophysics Data System (ADS)

    Pradipta, R.; Lee, M. C.; Cohen, J. A.; Watkins, B. J.

    2015-10-01

    We report the results of our ionospheric HF heating experiments to generate artificial acoustic-gravity waves (AGW) and traveling ionospheric disturbances (TID), which were conducted at the High-frequency Active Auroral Research Program facility in Gakona, Alaska. Based on the data from UHF radar, GPS total electron content, and ionosonde measurements, we found that artificial AGW/TID can be generated in ionospheric modification experiments by sinusoidally modulating the power envelope of the transmitted O-mode HF heater waves. In this case, the modulation frequency needs to be set below the characteristic Brunt-Vaisala frequency at the relevant altitudes. We avoided potential contamination from naturally-occurring AGW/TID of auroral origin by conducting the experiments during geomagnetically quiet time period. We determine that these artificial AGW/TID propagate away from the edge of the heated region with a horizontal speed of approximately 160 m/s.

  8. A comparison of EISCAT and HF Doppler observations of a ULF wave

    NASA Astrophysics Data System (ADS)

    Wright, D. M.; Yeoman, T. K.; Davies, J. A.

    1998-10-01

    Since the middle of 1995, an HF Doppler sounder has been running almost continuously in northern Norway, with the receiver at Ramfjordmoen and the transmitter at Seljelvnes. Concurrent operation of the EISCAT UHF radar in common programme (CP-1) mode has made it possible to study the ionospheric signature of a magnetospheric ULF wave. These are the first results of such wave signatures observed simultaneously in both instruments. It has been demonstrated that the observed Doppler signature was mainly due to the vertical bulk motion of the ionosphere caused by the electric field perturbation of the ULF wave and the first direct observational confirmation of a numerical simulation has been achieved. The wave, which was Alfvénic in nature, was detected by the instruments 8° equatorward of the broad resonance region. The implications for the deduced wave modes in the ionosphere and the mechanism producing the HF Doppler variations are discussed.

  9. Improved HF183 quantitative real-time PCR assay for characterization of human fecal pollution in ambient surface water samples.

    PubMed

    Green, Hyatt C; Haugland, Richard A; Varma, Manju; Millen, Hana T; Borchardt, Mark A; Field, Katharine G; Walters, William A; Knight, R; Sivaganesan, Mano; Kelty, Catherine A; Shanks, Orin C

    2014-05-01

    Quantitative real-time PCR (qPCR) assays that target the human-associated HF183 bacterial cluster within members of the genus Bacteroides are among the most widely used methods for the characterization of human fecal pollution in ambient surface waters. In this study, we show that a current TaqMan HF183 qPCR assay (HF183/BFDrev) routinely forms nonspecific amplification products and introduce a modified TaqMan assay (HF183/BacR287) that alleviates this problem. The performance of each qPCR assay was compared in head-to-head experiments investigating limits of detection, analytical precision, predicted hybridization to 16S rRNA gene sequences from a reference database, and relative marker concentrations in fecal and sewage samples. The performance of the modified HF183/BacR287 assay is equal to or improves upon that of the original HF183/BFDrev assay. In addition, a qPCR chemistry designed to combat amplification inhibition and a multiplexed internal amplification control are included. In light of the expanding use of PCR-based methods that rely on the detection of extremely low concentrations of DNA template, such as qPCR and digital PCR, the new TaqMan HF183/BacR287 assay should provide more accurate estimations of human-derived fecal contaminants in ambient surface waters. PMID:24610857

  10. The US open skies synthetic aperture radar (SAROS)

    SciTech Connect

    Fortner, K.R.; Hezeltine, P.L.

    1996-11-01

    This paper discusses the Synthetic Aperture Radar for Open Skies (SAROS), an airborne side-looking synthetic aperture radar (SAR) system installed on the U.S. OC-135B Open Skies Observation Aircraft. The paper discusses in detail how the SAROS is designed to meet the performance requirements and limits of the Treaty on Open Skies. The SAROS is based on the U.S. AN/APD-12 analog radar system which has been modified to digitally record radar, motion, and annotation data on magnetic tape and has been designated as the AN/APD-14. The theoretical performance of the AN/APD-12 SAR exceeds the three meter range and azimuth resolution allowed by the Treaty. The SAROS design will limit the performance of the SAR to no better than three meter`s through reduction in transmitted frequency bandwidth, reduction in azimuth bandwidth, and decimation of azimuth sampling prior to recording of the phase history data. 5 figs.

  11. Time-frequency analysis of synthetic aperture radar signals

    SciTech Connect

    Johnston, B.

    1996-08-01

    Synthetic aperture radar (SAR) has become an important tool for remote sensing of the environment. SAR is a set of digital signal processing algorithms that are used to focus the signal returned to the radar because radar systems in themselves cannot produce the high resolution images required in remote sensing applications. To reconstruct an image, several parameters must be estimated and the quality of output image depends on the degree of accuracy of these parameters. In this thesis, we derive the fundamental SAR algorithms and concentrate on the estimation of one of its critical parameters. We show that the common technique for estimating this particular parameter can sometimes lead to erroneous results and reduced quality images. We also employ time-frequency analysis techniques to examine variations in the radar signals caused by platform motion and show how these results can be used to improve output image quality.

  12. Model for optimal parallax in stereo radar imagery

    NASA Technical Reports Server (NTRS)

    Pisaruck, M. A.; Kaupp, V. H.; Macdonald, H. C.; Waite, W. P.

    1984-01-01

    Simulated stereo radar imagery is used to investigate parameters for a spaceborne imaging radar. Incidence angles ranging from small to intermediate to large are used with three digital terrain model areas which are representative of relatively flat, moderately rough, and mountaneous terrain. The simulated radar imagery was evaluated by interpreters for ease of stereo perception and information content, and rank ordered within each class of terrain. The interpreter's results are analyzed for trends between the height of a feature and either parallax or vertical exaggeration for a stereo pair. A model is developed which predicts the amount of parallax (or vertical exaggeration) an interpreter would desire for best stereo perception of a feature of a specific height. Results indicate the selection of angle of incidence and stereo intersection angle depend upon the relief of the terrain. Examples of the simulated stereo imagery are presented for a candidate spaceborne imaging radar having four selectable angles of incidence.

  13. A model for simulation and processing of radar images

    NASA Technical Reports Server (NTRS)

    Stiles, J. A.; Frost, V. S.; Shanmugam, K. S.; Holtzman, J. C.

    1981-01-01

    A model for recording, processing, presentation, and analysis of radar images in digital form is presented. The observed image is represented as having two random components, one which models the variation due to the coherent addition of electromagnetic energy scattered from different objects in the illuminated areas. This component is referred to as fading. The other component is a representation of the terrain variation which can be described as the actual signal which the radar is attempting to measure. The combination of these two components provides a description of radar images as being the output of a linear space-variant filter operating on the product of the fading and terrain random processes. In addition, the model is applied to a digital image processing problem using the design and implementation of enhancement scene. Finally, parallel approaches are being employed as possible means of solving other processing problems such as SAR image map-matching, data compression, and pattern recognition.

  14. RADAR performance experiments

    NASA Technical Reports Server (NTRS)

    Leroux, C.; Bertin, F.; Mounir, H.

    1991-01-01

    Theoretical studies and experimental results obtained at Coulommiers airport showed the capability of Proust radar to detect wind shears, in clear air condition as well as in presence of clouds or rain. Several examples are presented: in a blocking highs situation an atmospheric wave system at the Brunt-Vaisala frequency can be clearly distinguished; in a situation of clouds without rain the limit between clear air and clouds can be easily seen; and a windshear associated with a gust front in rainy conditions is shown. A comparison of 30 cm clear air radar Proust and 5 cm weather Doppler radar Ronsard will allow to select the best candidate for wind shear detection, taking into account the low sensibility to ground clutter of Ronsard radar.

  15. Laser Radar Animation

    NASA Video Gallery

    Laser and radar instruments aboard NASA aircraft provide measurements of the snow and ice surface and down to the bedrock under the ice. Lasers, with a shorter wavelength, measure the surface eleva...

  16. Distributed array radar

    NASA Astrophysics Data System (ADS)

    Heimiller, R. C.; Belyea, J. E.; Tomlinson, P. G.

    1983-11-01

    Distributed array radar (DAR) is a concept for efficiently accomplishing surveillance and tracking using coherently internetted mini-radars. They form a long baseline, very thinned array and are capable of very accurate location of targets. This paper describes the DAR concept. Factors involving two-way effective gain patterns for deterministic and random DAR arrays are analyzed and discussed. An analysis of factors affecting signal-to-noise ratio is presented and key technical and performance issues are briefly summarized.

  17. Downhole pulse radar

    DOEpatents

    Chang, Hsi-Tien

    1989-01-01

    A borehole logging tool generates a fast rise-time, short duration, high peak-power radar pulse having broad energy distribution between 30 MHz and 300 MHz through a directional transmitting and receiving antennas having barium titanate in the electromagnetically active region to reduce the wavelength to within an order of magnitude of the diameter of the antenna. Radar returns from geological discontinuities are sampled for transmission uphole.

  18. Downhole pulse radar

    DOEpatents

    Chang, Hsi-Tien

    1987-09-28

    A borehole logging tool generates a fast rise-time, short duration, high peak-power radar pulse having broad energy distribution between 30 MHz and 300 MHz through a directional transmitting and receiving antennas having barium titanate in the electromagnetically active region to reduce the wavelength to within an order of magnitude of the diameter of the antenna. Radar returns from geological discontinuities are sampled for transmission uphole. 7 figs.

  19. Advanced meteor wind observations using meteor and MST radars

    NASA Astrophysics Data System (ADS)

    Tsutsumi, M.; Aso, T.; Hall, C.; Nakamura, T.; Sato, K.; Sato, T.

    A few topics from recent developments of radio meteor observation techniques are presented The Nippon Norway Tromsoe Meteor Radar NTMR has been in continuous operation since November 2003 in Tromsoe 69N One of the major advantages of the present meteor radar is its high echo rate 6000-20000 echoes a day despite the relatively small transmitting power 7 5kW peak From ambipolar diffusion coefficients we have successfully extracted atmospheric temperature fluctuations due to gravity waves assuming the Boussinesq approximation The time and height resolutions of horizontal winds and temperature fluctuations at the altitude of 90 km are 1 hour and 2km high enough for the study of gravity waves with a period longer than a few hours Horizontal propagation characteristics of gravity waves are further studied using a theoretical phase relation between the wind and temperature fluctuations MST radars in the VHF band have a great potential in meteor echo observations due to their high transmitting power The meteor measurement can be conducted throughout a day and complement the turbulent echo measurement in the mesosphere which is limited to daylight hours only The MU radar of Kyoto University is one of those radars and has been successfully applied to meteor studies by utilizing its very high versatility The MU radar was recently renewed Its signal processing unit is up-graded from a 4 analog receiver system to a 25 digital receiver system In the present study we try to improve the MU radar meteor measurement

  20. DBF technique for the space synchronization of bistatic (multistatic) radars

    NASA Astrophysics Data System (ADS)

    Zhao, Shujie; Geng, Fulu; Gao, Ruyun; Xie, Changrong; Ma, Xudong; Chen, Jianchun

    The space synchronization is one of the key techniques of bistatic(multistatic) radars. The concept and main parameters in implementing the space synchronization by pulse chasing with digital beam forming (DBF) technique are discussed. A implementation scheme as well as some of the test results of a prototype are also given in this paper.

  1. Space Radar Image of Rocky Mountains, Montana

    NASA Technical Reports Server (NTRS)

    1994-01-01

    This is a three-dimensional perspective of the eastern front range of the Rocky Mountains, about 120 kilometers (75 miles) west of Great Falls, Montana. The image was created by combining two spaceborne radar images using a technique known as interferometry. Visualizations like this are useful to scientists because they show the shapes of the topographic features such as mountains and valleys. This technique helps to clarify the relationships of the different types of materials on the surface detected by the radar. The view is looking south-southeast. Along the right edge of the image is the valley of the north fork of the Sun River. The western edge of the Great Plains appears on the left side. The valleys in the lower center, running off into the plains on the left, are branches of the Teton River. The highest mountains are at elevations of 2,860 meters (9,390 feet), and the plains are about 1,400 meters (4,500 feet) above sea level. The dark brown areas are grasslands, bright green areas are farms, light brown, orange and purple areas are scrub and forest, and bright white and blue areas are steep rocky slopes. The two radar images were taken on successive days by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) on board the space shuttle Endeavour in October 1994. The digital elevation map was produced using radar interferometry, a process in which radar data are acquired on different passes of the space shuttle. The two data passes are compared to obtain elevation information. Radar image data are draped over the topography to provide the color with the following assignments: red is L-band vertically transmitted, vertically received; green is C-band vertically transmitted, vertically received; and blue are the differences seen in the L-band data between the two days. This image is centered near 47.7 degrees north latitude and 112.7 degrees west longitude. No vertical exaggeration factor has been applied to the data. SIR-C/X-SAR, a

  2. On wave radar measurement

    NASA Astrophysics Data System (ADS)

    Ewans, Kevin; Feld, Graham; Jonathan, Philip

    2014-09-01

    The SAAB REX WaveRadar sensor is widely used for platform-based wave measurement systems by the offshore oil and gas industry. It offers in situ surface elevation wave measurements at relatively low operational costs. Furthermore, there is adequate flexibility in sampling rates, allowing in principle sampling frequencies from 1 to 10 Hz, but with an angular microwave beam width of 10° and an implied ocean surface footprint in the order of metres, significant limitations on the spatial and temporal resolution might be expected. Indeed there are reports that the accuracy of the measurements from wave radars may not be as good as expected. We review the functionality of a WaveRadar using numerical simulations to better understand how WaveRadar estimates compare with known surface elevations. In addition, we review recent field measurements made with a WaveRadar set at the maximum sampling frequency, in the light of the expected functionality and the numerical simulations, and we include inter-comparisons between SAAB radars and buoy measurements for locations in the North Sea.

  3. The 94 GHz MMW imaging radar system

    NASA Technical Reports Server (NTRS)

    Alon, Yair; Ulmer, Lon

    1993-01-01

    The 94 GHz MMW airborne radar system that provides a runway image in adverse weather conditions is now undergoing tests at Wright-Patterson Air Force Base (WPAFB). This system, which consists of a solid state FMCW transceiver, antenna, and digital signal processor, has an update rate of 10 times per second, 0.35x azimuth resolution and up to 3.5 meter range resolution. The radar B scope (range versus azimuth) image, once converted to C scope (elevation versus azimuth), is compatible with the standard TV presentation and can be displayed on the Head Up Display (HUD) or Head Down Display (HDD) to aid the pilot during landing and takeoff in limited visibility conditions.

  4. A new type of Doppler velocity fluctuations in HF ground scatter from the polar cap

    NASA Astrophysics Data System (ADS)

    Scoular, G.; Ponomarenko, P. V.; St.-Maurice, J. P.

    2013-10-01

    We report a new type of variations in Doppler velocity of HF ground scatter echoes from the polar cap at f˜10 mHz. Similar fluctuations from lower latitudes are usually associated with large-scale dayside Pc3-4 ULF waves. However, the polar cap oscillations exhibit a puzzling anisotropy in spatial coherence along and across the radar's line of sight. Furthermore, in contrast to Pc3-4 waves, these fluctuations show no ground magnetic signatures and display a pronounced gap in power/occurrence around local noon. We hypothesize that localized, ≤100 km, auroral particle precipitations near the radar site can modulate Doppler shift of the radio waves entering the ionosphere. In the ground scatter returns, due to the geometrical spread of the rays propagating through the ionosphere to the ground, these variations would appear to have a much larger line-of-sight scale.

  5. Earth resources shuttle imaging radar. [systems analysis and design analysis of pulse radar for earth resources information system

    NASA Technical Reports Server (NTRS)

    1975-01-01

    A report is presented on a preliminary design of a Synthetic Array Radar (SAR) intended for experimental use with the space shuttle program. The radar is called Earth Resources Shuttle Imaging Radar (ERSIR). Its primary purpose is to determine the usefulness of SAR in monitoring and managing earth resources. The design of the ERSIR, along with tradeoffs made during its evolution is discussed. The ERSIR consists of a flight sensor for collecting the raw radar data and a ground sensor used both for reducing these radar data to images and for extracting earth resources information from the data. The flight sensor consists of two high powered coherent, pulse radars, one that operates at L and the other at X-band. Radar data, recorded on tape can be either transmitted via a digital data link to a ground terminal or the tape can be delivered to the ground station after the shuttle lands. A description of data processing equipment and display devices is given.

  6. Introduction to special section: Science and technology of over-the-horizon radar

    NASA Astrophysics Data System (ADS)

    Berkey, F. Tom

    1998-07-01

    The rationale for the development of over-the-horizon (OTH) radar systems operating at frequencies in the HF band arose out of a perceived need for an early-warning defense network. That need changed with the end of the Cold War; however, today OTH radars play a major role in the CounterDrug Program for the interdiction of drug-smuggling aircraft. This special section of Radio Science is devoted to a review of OTH radar technology, with emphasis on contemporary developments in this field. The collection of papers presented here has evolved largely from research and development efforts directed to improving the performance of OTH radar systems deployed both in the United States and in Australia.

  7. High frequency radar measurements of tidal currents flowing through San Pablo Strait, San Francisco Bay

    USGS Publications Warehouse

    Maresca, Joseph W., Jr.; Padden, Robin R.; Cheng, Ralph T.; Seibel, Erwin

    1980-01-01

    High frequency (HF) radar measurements of the surface current averaged over the upper 0.5 m in San Pablo Strait were compared with current meter measurements of the subsurface current made at 9.4 m below mean lower low water (MLLW) over two 12.4-h tidal cycles. After averaging the radar and current meter data over two tidal cycles, a southerly (ebbing direction) surface current of 32 cm·s−1 was deduced from the radar measurements and a northerly (flooding direction) subsurface current of 7 cm·s−1 from the current meter measurements. This nontidal flow is maintained by freshwater discharge from the Sacramento–San Joaquin Rivers into Suisun and San Pablo Bays. The radar measurement technique provides quantitative estimates of the surface currents that previously were determined only from surface drifter studies.

  8. Radar Ionospheric Impact Mitigation

    NASA Astrophysics Data System (ADS)

    Bishop, G.; Decker, D.; Baker, C.

    2006-12-01

    New ionospheric modeling technology is being developed to improve correction of ionospheric impacts on the performance of ground-based space-surveillance radars (SSRs) in near-real-time. These radars, which detect and track space objects, can experience significant target location errors due to ionospheric delay and refraction of the radar signals. Since these radars must detect and track targets essentially to the radar horizon, it is necessary to accurately model the ionosphere as the radar would observe it, down to the local horizon. To correct for spatial and temporal changes in the ionosphere the model must be able to update in near-real-time using ionospheric sensor data. Since many radars are in isolated locations, or may have requirements to operate autonomously, an additional required capability is to provide accurate ionospheric mitigation by exploiting only sensor data from the radar site. However, the model must also be able to update using additional data from other types of sensors that may be available. The original radar ionospheric mitigation approach employed the Bent climatological model. This 35-year-old technology is still the means employed in the many DoD SSRs today. One more recent approach used capabilities from the PRISM model. PRISM technology has today been surpassed by `assimilative models' which employ better physics and Kalman filtering techniques. These models are not necessarily tailored for SSR application which needs to optimize modeling of very small regions using only data from a single sensor, or very few. The goal is to develop and validate the performance of innovative and efficient ionospheric modeling approaches that are optimized for the small regions applicable to ground-based radar coverage (radius of ~2000 km at ionospheric altitudes) and somewhat beyond. These approaches must adapt a continuous modeling scheme in near-real-time to be consistent with all observational data that may become available, and degrade

  9. Statistical gamma transitions in {sup 174}Hf

    SciTech Connect

    Farris, L.P.; Cizewski, J.A.; Brinkman, M.J.; Henry, R.G.; Lee, C.S.; Khoo, T.L.; Janssens, R.V.F.; Moore, E.F.; Carpenter, M.P.; Ahmad, I.; Lauritsen, T.; Kolata, J.J.; Beard, K.B.; Ye, D.; Garg, U.; Kaplan, M.S.; Saladin, J.X.; Winchell, D.

    1992-08-01

    Statistical spectrum extracted from the {sup 172}Yb({alpha},2n){sup 174}Hf reaction was fit with Monte Carlo simulations using a modified GDR E1 strength function and several formulations of the level density.

  10. Statistical gamma transitions in sup 174 Hf

    SciTech Connect

    Farris, L.P.; Cizewski, J.A.; Brinkman, M.J.; Henry, R.G.; Lee, C.S. ); Khoo, T.L.; Janssens, R.V.F.; Moore, E.F.; Carpenter, M.P.; Ahmad, I.; Lauritsen, T. ); Kolata, J.J.; Beard, K.B.; Ye, D.; Garg, U. ); Kaplan, M.S.; Saladin, J.X.; Winchell, D. (Pittsburgh Univ., PA (Un

    1992-01-01

    Statistical spectrum extracted from the {sup 172}Yb({alpha},2n){sup 174}Hf reaction was fit with Monte Carlo simulations using a modified GDR E1 strength function and several formulations of the level density.

  11. Synthetic aperture radar interferometry of Okmok volcano, Alaska: radar observations

    USGS Publications Warehouse

    Lu, Zhong; Mann, Dörte; Freymueller, Jeffrey T.; Meyer, David

    2000-01-01

    ERS-1/ERS-2 synthetic aperture radar interferometry was used to study the 1997 eruption of Okmok volcano in Alaska. First, we derived an accurate digital elevation model (DEM) using a tandem ERS-1/ERS-2 image pair and the preexisting DEM. Second, by studying changes in interferometric coherence we found that the newly erupted lava lost radar coherence for 5-17 months after the eruption. This suggests changes in the surface backscattering characteristics and was probably related to cooling and compaction processes. Third, the atmospheric delay anomalies in the deformation interferograms were quantitatively assessed. Atmospheric delay anomalies in some of the interferograms were significant and consistently smaller than one to two fringes in magnitude. For this reason, repeat observations are important to confidently interpret small geophysical signals related to volcanic activities. Finally, using two-pass differential interferometry, we analyzed the preemptive inflation, coeruptive deflation, and posteruptive inflation and confirmed the observations using independent image pairs. We observed more than 140 cm of subsidence associated with the 1997 eruption. This subsidence occurred between 16 months before the eruption and 5 months after the eruption, was preceded by ∼18 cm of uplift between 1992 and 1995 centered in the same location, and was followed by ∼10 cm of uplift between September 1997 and 1998. The best fitting model suggests the magma reservoir resided at 2.7 km depth beneath the center of the caldera, which was ∼5 km from the eruptive vent. We estimated the volume of the erupted material to be 0.055 km3 and the average thickness of the erupted lava to be ∼7.4 m. Copyright 2000 by the American Geophysical Union.

  12. SPace Radar Image of Fort Irwin, California

    NASA Technical Reports Server (NTRS)

    1994-01-01

    This image of Fort Irwin in California's Mojave Desert compares interferometric radar signatures topography -- data that were obtained by multiple imaging of the same region to produce three-dimensional elevation maps -- as it was obtained on October 7-8, 1994 by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar aboard the space shuttle Endeavour. Data were acquired using the L-band (24 centimeter wavelength) and C-band (6 centimeter wavelength). The image covers an area about 25 kilometers by 70 kilometers (15.5 miles by 43 miles). North is to the lower right of the image. The color contours shown are proportional to the topographic elevation. With a wavelength one-fourth that of the L-band, the results from the C-band cycle through the color contours four times faster for a given elevation change. Detailed comparisons of these multiple frequency data over different terrain types will provide insights in the future into wavelength-dependent effects of penetration and scattering on the topography measurement accuracy. Fort Irwin is an ideal site for such detailed digital elevation model comparisons because a number of high precision digital models of the area already exist from conventional measurements as well as from airborne interferometric SAR data. Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars illuminate Earth with microwaves, allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-band (24 cm), C-band (6 cm) and X-band (3 cm). The multi-frequency data will be used by the international scientific community to better understand the global environment and how it is changing. The SIR-C/X-SAR data, complemented by aircraft and ground studies, will give scientists clearer insights into those environmental changes which are caused by nature and those changes which are induced by human

  13. Triangulation using synthetic aperture radar images

    NASA Technical Reports Server (NTRS)

    Wu, Sherman S. C.; Howington-Kraus, Annie E.

    1991-01-01

    For the extraction of topographic information about Venus from stereoradar images obtained from the Magellan Mission, a Synthetic Aperture Radar (SAR) compilation system was developed on analytical stereoplotters. The system software was extensively tested by using stereoradar images from various spacecraft and airborne radar systems, including Seasat, SIR-B, ERIM XCL, and STAR-1. Stereomodeling from radar images was proven feasible, and development is on a correct approach. During testing, the software was enhanced and modified to obtain more flexibility and better precision. Triangulation software for establishing control points by using SAR images was also developed through a joint effort with the Defense Mapping Agency. The SAR triangulation system comprises four main programs, TRIDATA, MODDATA, TRISAR, and SHEAR. The first two programs are used to sort and update the data; the third program, the main one, performs iterative statistical adjustment; and the fourth program analyzes the results. Also, input are flight data and data from the Global Positioning System and Inertial System (navigation information). The SAR triangulation system was tested with six strips of STAR-1 radar images on a VAX-750 computer. Each strip contains images of 10 minutes flight time (equivalent to a ground distance of 73.5 km); the images cover a ground width of 22.5 km. All images were collected from the same side. With an input of 44 primary control points, 441 ground control points were produced. The adjustment process converged after eight iterations. With a 6-m/pixel resolution of the radar images, the triangulation adjustment has an average standard elevation error of 81 m. Development of Magellan radargrammetry will be continued to convert both SAR compilation and triangulation systems into digital form.

  14. Digital correlator for the portable channel prober measurement instrument

    NASA Astrophysics Data System (ADS)

    Peo, George E., Jr.

    1987-12-01

    This document describes a Digital Correlator for the Portable Channel Prober Measurement Instrument being developed by the Naval Research Laboratory for use in experiments designed to characterize high frequency (HF) radio channels. This Digital Correlator is a digital signal processor designed and constructed by Stow Computer, 111 old Bolton Road, Stow, MA 01775, (617/508) 897-6838. Two Digital Correlators are integrated into the existing Digital Pre-processor to make a Portable Wideband HF Channel Analyzer. The Portable Wideband HF Channel Analyzer will be located at the receiving site of the channel probing experiment and is situated between the coherent radio receiver and the microcomputer used for data recording and analysis. The Portable Wideband HF Channel Analyzer computes the delay power spectrum of the received waveform. The in-phase and quadrature outputs of the receiver are sampled and converted to digital values by the Analog to Digital Converter, integrated by the Integrator, and correlated with a stored replica of the transmitted waveform by two Digital Correlators. The resulting tap gains are then read by the system microcomputer using the microcomputer interface.

  15. Current radar responsive tag development activities at Sandia National Laboratories.

    SciTech Connect

    Plummer, Kenneth W.; Ormesher, Richard C.

    2003-09-01

    Over the past ten years, Sandia has developed RF radar responsive tag systems and supporting technologies for various government agencies and industry partners. RF tags can function as RF transmitters or radar transponders that enable tagging, tracking, and location determination functions. Expertise in tag architecture, microwave and radar design, signal analysis and processing techniques, digital design, modeling and simulation, and testing have been directly applicable to these tag programs. In general, the radar responsive tag designs have emphasized low power, small package size, and the ability to be detected by the radar at long ranges. Recently, there has been an interest in using radar responsive tags for Blue Force tracking and Combat ID (CID). The main reason for this interest is to allow airborne surveillance radars to easily distinguish U.S. assets from those of opposing forces. A Blue Force tracking capability would add materially to situational awareness. Combat ID is also an issue, as evidenced by the fact that approximately one-quarter of all U.S. casualties in the Gulf War took the form of ground troops killed by friendly fire. Because the evolution of warfare in the intervening decade has made asymmetric warfare the norm rather than the exception, swarming engagements in which U.S. forces will be freely intermixed with opposing forces is a situation that must be anticipated. Increasing utilization of precision munitions can be expected to drive fires progressively closer to engaged allied troops at times when visual de-confliction is not an option. In view of these trends, it becomes increasingly important that U.S. ground forces have a widely proliferated all-weather radar responsive tag that communicates to all-weather surveillance. The purpose of this paper is to provide an overview of the recent, current, and future radar responsive research and development activities at Sandia National Laboratories that support both the Blue Force Tracking

  16. Soil moisture detection from radar imagery of the Phoenix, Arizona test site

    NASA Technical Reports Server (NTRS)

    Cihlar, J.; Ulaby, F. T.; Mueller, R.

    1975-01-01

    The Environmental Research Institute of Michigan (ERIM) dual-polarization X and L band radar was flown to acquire radar imagery over the Phoenix (Arizona) test site. The site was covered by a north-south pass and an east-west pass. Radar response to soil moisture was investigated. Since the ERIM radar does not have accurately measured antenna patterns, analysis of the L band data was performed separately for each of several strips along the flight line, each corresponding to a narrow angle of incidence. For the NS pass, good correlation between the radar return and mositure content was observed for each of the two nearest (to nadir) angular ranges. At higher angular ranges, no correlation was observed. The above procedure was not applied to the EW pass due to flight path misalignments. The results obtained stress the importance of radar calibration, the digitization process, and the angle of incidence.

  17. Sporadic E ionization layers observed with radar imaging and ionospheric modification

    NASA Astrophysics Data System (ADS)

    Hysell, D. L.; Munk, J.; McCarrick, M.

    2014-10-01

    Sporadic E ionization layers have been observed in the daytime subauroral ionospheric E layer by a 30 MHz radar in Alaska. The radar detects coherent backscatter from meter-scale field-aligned plasma density irregularities. The irregularities were generated by ionospheric modification—by the emission of strong HF electromagnetic waves directly beneath the layers—making the layers visible to the radar. Aperture-synthesis methods are used to generate imagery of the layers from the radar data. The layers are patchy, with patches organized along fronts spaced by tens of kilometers and propagating slowly toward the southwest. Similar, naturally occurring layers are commonly observed at middle latitudes at night in the absence of ionospheric modification. That the patchy layers can be found at high magnetic latitudes during the day argues that they are most likely produced through the interaction of the ionospheric layer with neutral atmospheric waves and instabilities. Attenuation of the radar echoes when the HF emission frequency exceeded the third harmonic of the electron gyrofrequency was observed and is discussed.

  18. A barrier radar concept

    NASA Astrophysics Data System (ADS)

    Marshall, J.; Ball, C.; Weissman, I.

    A description is given of a low power, light-weight radar that can be quickly set up and operated on batteries for extended periods of time to detect airborne intruders. With low equipment and operating costs, it becomes practical to employ a multiplicity of such radars to provide an unbroken intrusion fence over the desired perimeter. Each radar establishes a single transmitted fan beam extending vertically from horizon to horizon. The beam is generated by a two-face array antenna built in an A-frame configuration and is shaped, through phasing of the array elements, to concentrate the transmitter power in a manner consistent with the expected operating altitude ceiling of the targets of interest. The angular width of this beam in the dimension transverse to the fan depends on the radar transmission frequency and the antenna aperture dimension, but is typically wide enough so that a target at the maximum altitude or range will require tens of seconds to pass through the beam. A large number of independent samples of radar data will thus be available to provide many opportunities for target detection.

  19. Digital avionics: A cornerstone of aviation

    NASA Technical Reports Server (NTRS)

    Spitzer, Cary R.

    1990-01-01

    Digital avionics is continually expanding its role in communication (HF and VHF, satellite, data links), navigation (ground-based systems, inertial and satellite-based systems), and flight-by-wire control. Examples of electronic flight control system architecture, pitch, roll, and yaw control are presented. Modeling of complex hardware systems, electromagnetic interference, and software are discussed.

  20. 33. Perimeter acquisition radar building room #320, perimeter acquisition radar ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    33. Perimeter acquisition radar building room #320, perimeter acquisition radar operations center (PAROC), contains the tactical command and control group equipment required to control the par site. Showing spacetrack monitor console - Stanley R. Mickelsen Safeguard Complex, Perimeter Acquisition Radar Building, Limited Access Area, between Limited Access Patrol Road & Service Road A, Nekoma, Cavalier County, ND

  1. Phase modulating the Urbana radar

    NASA Technical Reports Server (NTRS)

    Herrington, L. J., Jr.; Bowhill, S. A.

    1983-01-01

    The design and operation of a switched phase modulation system for the Urbana Radar System are discussed. The system is implemented and demonstrated using a simple procedure. The radar system and circuits are described and analyzed.

  2. Mercury radar speckle dynamics

    NASA Astrophysics Data System (ADS)

    Holin, Igor V.

    2010-06-01

    Current data reveal that Mercury is a dynamic system with a core which has not yet solidified completely and is at least partially decoupled from the mantle. Radar speckle displacement experiments have demonstrated that the accuracy in spin-dynamics determination for Earth-like planets can approach 10 -5. The extended analysis of space-time correlation properties of radar echoes shows that the behavior of speckles does not prevent estimation of Mercury's instantaneous spin-vector components to accuracy of a few parts in 10 7. This limit can be reached with more powerful radar facilities and leads to constraining the interior in more detail from effects of spin dynamics, e.g., from observation of the core-mantle interplay through high precision monitoring of the 88-day spin-variation of Mercury's crust.

  3. The MST Radar Technique

    NASA Technical Reports Server (NTRS)

    Balsley, B. B.

    1985-01-01

    The past ten year have witnessed the development of a new radar technique to examine the structure and dynamics of the atmosphere between roughly 1 to 100 km on a continuous basis. The technique is known as the MST (for Mesosphere-Stratosphere-Troposphere) technique and is usable in all weather conditions, being unaffected by precipitation or cloud cover. MST radars make use of scattering from small scale structure in the atmospheric refractive index, with scales of the order of one-half the radar wavelength. Pertinent scale sizes for middle atmospheric studies typically range between a fraction of a meter and a few meters. The structure itself arises primarily from atmospheric turbulence. The technique is briefly described along with the meteorological parameters it measures.

  4. Characteristics of Sunset radar

    NASA Technical Reports Server (NTRS)

    Green, J. L.

    1983-01-01

    Located in a narrow canyon 15 km west of Boulder, Colorado, the Sunset pulsed Doppler radar was the first radar designed and constructed specifically as a VHF ST radar. The antenna system is a phased array of coaxial-colinear dopoles with computer-controlled phase shifters for each line of dipoles. It operates at a frequency of 40.475 MHz and a wavelength of 7.41M. Peak transmitter power is 100 kW. Aperture efficiency is 0.58 and resistive loss is 0.30 for its 3600 sq m area. The practical steering rate is 1 record/minute/position to any arbitrary antenna beam position. The first clear-air turbulence echoes and wind velocity measurements were obtained in 1974. Significant accomplishments are listed.

  5. Radar data smoothing filter study

    NASA Technical Reports Server (NTRS)

    White, J. V.

    1984-01-01

    The accuracy of the current Wallops Flight Facility (WFF) data smoothing techniques for a variety of radars and payloads is examined. Alternative data reduction techniques are given and recommendations are made for improving radar data processing at WFF. A data adaptive algorithm, based on Kalman filtering and smoothing techniques, is also developed for estimating payload trajectories above the atmosphere from noisy time varying radar data. This algorithm is tested and verified using radar tracking data from WFF.

  6. HF Accelerated Electron Fluxes, Spectra, and Ionization

    NASA Astrophysics Data System (ADS)

    Carlson, Herbert C.; Jensen, Joseph B.

    2015-10-01

    Wave particle interactions, an essential aspect of laboratory, terrestrial, and astrophysical plasmas, have been studied for decades by transmitting high power HF radio waves into Earth's weakly ionized space plasma, to use it as a laboratory without walls. Application to HF electron acceleration remains an active area of research (Gurevich in Usp Fizicheskikh Nauk 177(11):1145-1177, 2007) today. HF electron acceleration studies began when plasma line observations proved (Carlson et al. in J Atmos Terr Phys 44:1089-1100, 1982) that high power HF radio wave-excited processes accelerated electrons not to ~eV, but instead to -100 times thermal energy (10 s of eV), as a consequence of inelastic collision effects on electron transport. Gurevich et al (J Atmos Terr Phys 47:1057-1070, 1985) quantified the theory of this transport effect. Merging experiment with theory in plasma physics and aeronomy, enabled prediction (Carlson in Adv Space Res 13:1015-1024, 1993) of creating artificial ionospheres once ~GW HF effective radiated power could be achieved. Eventual confirmation of this prediction (Pedersen et al. in Geophys Res Lett 36:L18107, 2009; Pedersen et al. in Geophys Res Lett 37:L02106, 2010; Blagoveshchenskaya et al. in Ann Geophys 27:131-145, 2009) sparked renewed interest in optical inversion to estimate electron spectra in terrestrial (Hysell et al. in J Geophys Res Space Phys 119:2038-2045, 2014) and planetary (Simon et al. in Ann Geophys 29:187-195, 2011) atmospheres. Here we present our unpublished optical data, which combined with our modeling, lead to conclusions that should meaningfully improve future estimates of the spectrum of HF accelerated electron fluxes. Photometric imaging data can significantly improve detection of emissions near ionization threshold, and confirm depth of penetration of accelerated electrons many km below the excitation altitude. Comparing observed to modeled emission altitude shows future experiments need electron density profiles

  7. Radar Investigations of Asteroids

    NASA Technical Reports Server (NTRS)

    Ostro, S. J.

    1984-01-01

    Radar investigations of asteroids, including observations during 1984 to 1985 of at least 8 potential targets and continued analyses of radar data obtained during 1980 to 1984 for 30 other asteroids is proposed. The primary scientific objectives include estimation of echo strength, polarization, spectral shape, spectral bandwidth, and Doppler shift. These measurements yield estimates of target size, shape, and spin vector; place constraints on topography, morphology, density, and composition of the planetary surface; yield refined estimates of target orbital parameters; and reveals the presence of asteroidal satellites.

  8. Threat radar system simulations

    NASA Astrophysics Data System (ADS)

    Miller, L.

    The capabilities, requirements, and goals of radar emitter simulators are discussed. Simulators are used to evaluate competing receiver designs, to quantify the performance envelope of a radar system, and to model the characteristics of a transmitted signal waveform. A database of candidate threat systems is developed and, in concert with intelligence data on a given weapons system, permits upgrading simulators to new projected threat capabilities. Four currently available simulation techniques are summarized, noting the usefulness of developing modular software for fast controlled-cost upgrades of simulation capabilities.

  9. Microwave radar oceanographic investigations

    NASA Technical Reports Server (NTRS)

    Jackson, F. C.

    1988-01-01

    The Radar Ocean Wave Spectrometer (ROWS) technique was developed and demonstrated for measuring ocean wave directional spectra from air and space platforms. The measurement technique was well demonstrated with data collected in a number of flight experiments involving wave spectral comparisons with wave buoys and the Surface Contour Radar (SCR). Recent missions include the SIR-B underflight experiment (1984), FASINEX (1986), and LEWEX (1987). ROWS related activity is presently concentrating on using the aircraft instrument for wave-processes investigations and obtaining the necessary support (consensus) for a satellite instrument development program. Prospective platforms include EOS and the Canadian RADARSAT.

  10. Spaceborne Imaging Radar Symposium

    NASA Technical Reports Server (NTRS)

    Elachi, C.

    1983-01-01

    An overview of the present state of the art in the different scientific and technological fields related to spaceborne imaging radars was presented. The data acquired with the SEASAT SAR (1978) and Shuttle Imaging Radar, SIR-A (1981) clearly demonstrated the important emphasis in the 80's is going to be on in-depth research investigations conducted with the more flexible and sophisticated SIR series instruments and on long term monitoring of geophysical phenomena conducted from free-flying platforms such as ERS-1 and RADARSAT.

  11. 2-D inner-shelf current observations from a single VHF WEllen RAdar (WERA) station

    USGS Publications Warehouse

    Voulgaris, G.; Kumar, N.; Gurgel, K.-W.; Warner, J.C.; List, J.H.

    2011-01-01

    The majority of High Frequency (HF) radars used worldwide operate at medium to high frequencies (8 to 30 MHz) providing spatial resolutions ranging from 3 to 1.5 km and ranges from 150 to 50 km. This paper presents results from the deployment of a single Very High Frequency (VHF, 48 MHz) WEllen RAdar (WERA) radar with spatial resolution of 150 m and range 10-15 km, used in the nearshore off Cape Hatteras, NC, USA. It consisted of a linear array of 12 antennas operating in beam forming mode. Radial velocities were estimated from radar backscatter for a variety of wind and nearshore wave conditions. A methodology similar to that used for converting acoustically derived beam velocities to an orthogonal system is presented for obtaining 2-D current fields from a single station. The accuracy of the VHF radar-derived radial velocities is examined using a new statistical technique that evaluates the system over the range of measured velocities. The VHF radar velocities showed a bias of 3 to 7 cm/s over the experimental period explainable by the differences in radar penetration and in-situ measurement height. The 2-D current field shows good agreement with the in-situ measurements. Deviations and inaccuracies are well explained by the geometric dilution analysis. ?? 2011 IEEE.

  12. Systems and Methods for Radar Data Communication

    NASA Technical Reports Server (NTRS)

    Bunch, Brian (Inventor); Szeto, Roland (Inventor); Miller, Brad (Inventor)

    2013-01-01

    A radar information processing system is operable to process high bandwidth radar information received from a radar system into low bandwidth radar information that may be communicated to a low bandwidth connection coupled to an electronic flight bag (EFB). An exemplary embodiment receives radar information from a radar system, the radar information communicated from the radar system at a first bandwidth; processes the received radar information into processed radar information, the processed radar information configured for communication over a connection operable at a second bandwidth, the second bandwidth lower than the first bandwidth; and communicates the radar information from a radar system, the radar information communicated from the radar system at a first bandwidth.

  13. SEASAT Synthetic Aperture Radar Data

    NASA Technical Reports Server (NTRS)

    Henderson, F. M.

    1981-01-01

    The potential of radar imagery from space altitudes is discussed and the advantages of radar over passive sensor systems are outlined. Specific reference is made to the SEASAT synthetic aperture radar. Possible applications include oil spill monitoring, snow and ice reconnaissance, mineral exploration, and monitoring phenomena in the urban environment.

  14. Nonlinear synthetic aperture radar imaging using a harmonic radar

    NASA Astrophysics Data System (ADS)

    Gallagher, Kyle A.; Mazzaro, Gregory J.; Ranney, Kenneth I.; Nguyen, Lam H.; Martone, Anthony F.; Sherbondy, Kelly D.; Narayanan, Ram M.

    2015-05-01

    This paper presents synthetic aperture radar (SAR) images of linear and nonlinear targets. Data are collected using a linear/nonlinear step frequency radar. We show that it is indeed possible to produce SAR images using a nonlinear radar. Furthermore, it is shown that the nonlinear radar is able to reduce linear clutter by at least 80 dB compared to a linear radar. The nonlinear SAR images also show the system's ability to detect small electronic devices in the presence of large linear clutter. The system presented here has the ability to completely ignore a 20-inch trihedral corner reflector while detecting a RF mixer with a dipole antenna attached.

  15. Ultrawideband imaging radar based on OFDM: system simulation analysis

    NASA Astrophysics Data System (ADS)

    Garmatyuk, Dmitriy

    2006-05-01

    Orthogonal frequency division-multiplexing (OFDM) is rapidly emerging as a preferred method of UWB signaling in commercial applications aimed mainly at low-power, high data-rate communications. This paper explores the possibility of applying OFDM to use in imaging radar technology. Ultra-wideband nature of the signal provides for high resolution of the radar, whereas usage of multi-sub-carrier method of modulation allows for dynamic spectrum allocation. Robust multi-path performance of OFDM signals and heavy reliance of transceiver design on digital processors easily implemented in modern VLSI technology make a number of possible applications viable, e.g.: portable high-resolution indoor radar/movement monitoring system; through-the-wall/foliage synthetic aperture imaging radar with a capability of image transmission/broadcasting, etc. Our work is aimed to provide a proof-of-concept simulation scenario to explore numerous aspects of UWB-OFDM radar imaging through evaluating range and cross-range imaging performance of such a system with an eventual goal of software-defined radio (SDR) implementation. Stripmap SAR topology was chosen for modeling purposes. Range/cross-range profiles were obtained along with full 2-D images for multi-target in noise scenarios. Model set-up and results of UWB-OFDM radar imaging simulation study using Matlab/Simulink modeling are presented and discussed in this paper.

  16. Fiber optic coherent laser radar 3d vision system

    SciTech Connect

    Sebastian, R.L.; Clark, R.B.; Simonson, D.L.

    1994-12-31

    Recent advances in fiber optic component technology and digital processing components have enabled the development of a new 3D vision system based upon a fiber optic FMCW coherent laser radar. The approach includes a compact scanner with no moving parts capable of randomly addressing all pixels. The system maintains the immunity to lighting and surface shading conditions which is characteristic of coherent laser radar. The random pixel addressability allows concentration of scanning and processing on the active areas of a scene, as is done by the human eye-brain system.

  17. Review of the homodyne technique for coherent radar

    NASA Astrophysics Data System (ADS)

    Christensen, E. Lintz; Madsen, S. Norvang; Skou, N.

    The merits of using homodyne techniques for coherent radar are examined. The influence of various component deficiencies is discussed with relation to the choice between homodyne and heterodyne. The use of digital IQ signal generation and processing to correct for some of the problems of modulator and demodulator design by predistortion, offset correction, etc. is briefly addressed. A 5.3-GHz synthetic aperture radar designed for strip mapping at High resolution is then considered to illustrate the use of the homodyne approach. Measurement results on quadrature modulators and demodulators at 300 MHz and 5.3 GHz are given to support the contention that the homodyne technique can be applied successfully.

  18. Imaging Radar in the Mojave Desert-Death Valley Region

    NASA Technical Reports Server (NTRS)

    Farr, Tom G.

    2001-01-01

    The Mojave Desert-Death Valley region has had a long history as a test bed for remote sensing techniques. Along with visible-near infrared and thermal IR sensors, imaging radars have flown and orbited over the area since the 1970's, yielding new insights into the geologic applications of these technologies. More recently, radar interferometry has been used to derive digital topographic maps of the area, supplementing the USGS 7.5' digital quadrangles currently available for nearly the entire area. As for their shorter-wavelength brethren, imaging radars were tested early in their civilian history in the Mojave Desert-Death Valley region because it contains a variety of surface types in a small area without the confounding effects of vegetation. The earliest imaging radars to be flown over the region included military tests of short-wavelength (3 cm) X-band sensors. Later, the Jet Propulsion Laboratory began its development of imaging radars with an airborne sensor, followed by the Seasat orbital radar in 1978. These systems were L-band (25 cm). Following Seasat, JPL embarked upon a series of Space Shuttle Imaging Radars: SIRA (1981), SIR-B (1984), and SIR-C (1994). The most recent in the series was the most capable radar sensor flown in space and acquired large numbers of data swaths in a variety of test areas around the world. The Mojave Desert-Death Valley region was one of those test areas, and was covered very well with 3 wavelengths, multiple polarizations, and at multiple angles. At the same time, the JPL aircraft radar program continued improving and collecting data over the Mojave Desert Death Valley region. Now called AIRSAR, the system includes 3 bands (P-band, 67 cm; L-band, 25 cm; C-band, 5 cm). Each band can collect all possible polarizations in a mode called polarimetry. In addition, AIRSAR can be operated in the TOPSAR mode wherein 2 antennas collect data interferometrically, yielding a digital elevation model (DEM). Both L-band and C-band can be

  19. Design guidelines for SAR digital receiver/exciter boards.

    SciTech Connect

    Dudley, Peter A.

    2009-08-01

    High resolution radar systems generally require combining fast analog to digital converters and digital to analog converters with very high performance digital signal processing logic. These mixed analog and digital printed circuit boards present special challenges with respect to electromagnetic interference. This document first describes the mechanisms of interference on such boards then follows up with a discussion of prevention techniques and finally provides a checklist for designers to help avoid common mistakes.

  20. Venus Radar Mapper (VRM): Multimode radar system design

    NASA Technical Reports Server (NTRS)

    Johnson, William T. K.; Edgerton, Alvin T.

    1986-01-01

    The surface of Venus has remained a relative mystery because of the very dense atmosphere that is opaque to visible radiation and, thus, normal photographic techniques used to explore the other terrestrial objects in the solar system are useless. The atmosphere is, however, almost transparent to radar waves and images of the surface have been produced via Earth-based and orbital radars. The technique of obtaining radar images of a surface is variously called side looking radar, imaging radar, or synthetic aperture radar (SAR). The radar requires a moving platform in which the antenna is side looking. High resolution is obtained in the cross-track or range direction by conventional radar pulse encoding. In the along-track or azimuth direction, the resolution would normally be the antenna beam width, but for the SAR case, a much longer antenna (or much sharper beam) is obtained by moving past a surface target as shown, and then combining the echoes from many pulses, by using the Doppler data, to obtain the images. The radar design of the Venus Radar Mapper (VRM) is discussed. It will acquire global radar imagery and altimetry data of the surface of Venus.

  1. Inversion to estimate ocean wave directional spectrum from high-frequency radar

    NASA Astrophysics Data System (ADS)

    Hisaki, Yukiharu

    2015-04-01

    An high-frequency (HF) radar observes ocean surface currents and waves by radiating HF radio waves to the sea surface and analyzing the backscattered signals. Ocean wave spectrum is estimated from the first- and the second-order scattering of Doppler spectra by the inversion. The estimation of ocean surface currents is robust, because the surface currents can be derived from the peak Doppler frequency of the first-order scattering in the Doppler spectrum. The method to estimate ocean wave spectra is complicated and the second-order scattering in the Doppler spectrum is fragile, which is affected by the noise in the Doppler spectrum. A new method to estimate ocean wave spectra from HF radar is developed. This method is the extension of Hisaki (1996, 2005, 2006, 2009, 2014). The new method can be applied to both the single radar and dual radar array case, while the previous methods can be applied only the single radar case (Hisaki, 2005, 2006, 2009, 2014) or dual radar case (Hisaki, 1996). Ocean wave spectra are estimated in the regular grid cells, while wave spectra are estimated on the polar grids points with the origin of the radar position in the previous method for single radar case. The governing equations for wave estimation are the integral equations which relate the wave spectrum to the Doppler spectrum, and the energy balance equation under the assumption of stationarity. The regularization constraints in the horizontal space and the wave frequency-direction space are also used for the estimation. The unknowns, which are spectral values, surface wind speeds and directions, are estimated by seeking the minimum of the objective function, which is defined as the sum of weighted squares of the equations. The signal to noise ratio in the Doppler spectrum for wave estimation must be high. We selected the Doppler spectra using the SOM (Self organization map ) analysis method. The method will be demonstrated by comparing with in-situ observed data, in which only

  2. Stepped-frequency radar signal processing

    NASA Astrophysics Data System (ADS)

    Seyfried, Daniel; Schoebel, Joerg

    2015-01-01

    Stepped-frequency radar is a prominent example of the class of continuous-wave radar systems. Since raw data are recorded in frequency-domain direct investigations referring to the frequency content can be done on the raw data. However, a transformation of these data is required in order to obtain a time-domain representation of the targets illuminated by the radar. In this paper we present different ways of arranging the raw data which then are processed by means of the inverse fast Fourier transform. On the basis of the time-domain result we discuss strengths and weaknesses of each of these data structures. Furthermore, we investigate the influence of phase noise on the time-domain signal by means of an appropriate model implemented in our simulation tool. We also demonstrate the effects of commonly known techniques of digital signal processing, such as windowing and zero-padding of frequency-domain data. Finally we present less commonly known methods, such as the processing gain of the (inverse) fast Fourier transform by means of which the signal to noise ratio of the time-domain signal can be increased.

  3. Impulse radar studfinder

    DOEpatents

    McEwan, T.E.

    1995-10-10

    An impulse radar studfinder propagates electromagnetic pulses and detects reflected pulses from a fixed range. Unmodulated pulses, about 200 ps wide, are emitted. A large number of reflected pulses are sampled and averaged. Background reflections are subtracted. Reflections from wall studs or other hidden objects are detected and displayed using light emitting diodes. 9 figs.

  4. Synthetic Aperture Radar Interferometry

    NASA Technical Reports Server (NTRS)

    Rosen, P. A.; Hensley, S.; Joughin, I. R.; Li, F.; Madsen, S. N.; Rodriguez, E.; Goldstein, R. M.

    1998-01-01

    Synthetic aperture radar interferometry is an imaging technique for measuring the topography of a surface, its changes over time, and other changes in the detailed characteristics of the surface. This paper reviews the techniques of interferometry, systems and limitations, and applications in a rapidly growing area of science and engineering.

  5. Impulse radar studfinder

    DOEpatents

    McEwan, Thomas E.

    1995-01-01

    An impulse radar studfinder propagates electromagnetic pulses and detects reflected pulses from a fixed range. Unmodulated pulses, about 200 ps wide, are emitted. A large number of reflected pulses are sampled and averaged. Background reflections are subtracted. Reflections from wall studs or other hidden objects are detected and displayed using light emitting diodes.

  6. Rain radar instrument definition

    NASA Astrophysics Data System (ADS)

    Vincent, Nicolas; Chenebault, J.; Suinot, Noel; Mancini, Paolo L.

    1996-12-01

    As a result of a pre-phase a study, founded by ESA, this paper presents the definition of a spaceborne Rain Radar, candidate instrument for earth explorer precipitation mission. Based upon the description of user requirements for such a dedicated mission, a mission analysis defines the most suitable space segment. At system level, a parametric analysis compares pros and cons of instrument concepts associated with rain rate retrieval algorithms in order to select the most performing one. Several trade-off analysis at subsystem level leads then to the definition of the proposed design. In particular, as pulse compression is implemented in order to increase the radar sensitivity, the selected method to achieve a pulse response with a side-lobe level below--60 dB is presented. Antenna is another critical rain radar subsystem and several designs are com pared: direct radiating array, single or dual reflector illuminated by single or dual feed arrays. At least, feasibility of centralized amplification using TWTA is compared with criticality of Tx/Rx modules for distributed amplification. Mass and power budgets of the designed instrument are summarized as well as standard deviations and bias of simulated rain rate retrieval profiles. The feasibility of a compliant rain radar instrument is therefore demonstrated.

  7. Passive bistatic radar analysis

    NASA Astrophysics Data System (ADS)

    O'Hagan, Daniel W.; Kuschel, H.; Schiller, Joachim

    2009-06-01

    Passive Bistatic Radar (PBR) research is at its zenith with several notable PBR systems currently operational, or available for deployment. Such PBRs include the Manastash Ridge Radar (MRR) developed for and by academia; Silent Sentry developed as a commercial concern by Lockheed Martin; and Homeland Alerter (HA100) also a commercial system developed by Thales. However at present, despite the existence of numerous PBR prototypes, take up of commercial passive radar technology remains slow. This is due in part to technology immaturity, in part to politics, and particularly due to the fact that monostatic radars perform so well. If PBRs are to enjoy longevity as a viable technology then it is imperative that they address certain niche application areas, with the aforementioned MRR being one prime example of this. The focus of this paper will be an analysis of a PBR system that utilised FM radio signals of opportunity to detect aircraft targets with an RCS generally not lower than 20 m2. The paper will demonstrate the theoretical detection coverage of an FM based PBR operating in a severe interference environment.

  8. Generation and detection of super small striations by F region HF heating

    NASA Astrophysics Data System (ADS)

    Najmi, A.; Milikh, G.; Secan, J.; Chiang, K.; Psiaki, M.; Bernhardt, P.; Briczinski, S.; Siefring, C.; Chang, C. L.; Papadopoulos, K.

    2014-07-01

    Recent theoretical models and preliminary observations indicate that super small striations (SSS) in the plasma density with scale size of 10 cm can be excited by F region HF heating at frequencies close to multiples of the electron gyrofrequency. We present here new experimental results using the High Frequency Active Auroral Research Program ionospheric heater at a frequency close to the fourth electron gyroharmonic with simultaneous GPS, Stimulated Electromagnetic Emission, ionosonde, and occasional Incoherent Radar Scattering diagnostics. Differential phase measurements of GPS signals through the heated region indicated the presence of SSS with extremely high amplitude (δn/n = 0.2-0.3) at scale size comparable to the electron gyroradius. The highest amplitude of GPS scintillations coincide with the highest level of the Broad Upshifted Maximum (BUM) and occurred when the HF frequency is slightly above the fourth harmonic of the electron cyclotron frequency. Frequency sweeps indicate that the scintillation amplitude exhibits hysteresis similar to that observed for the BUM amplitude when the HF frequency is cycled about the fourth harmonic of the cyclotron frequency. The results favor a four wave parametric process as the physical mechanism of the SSS. Additional experiments allowed the determination of the excitation and decay rates of the SSS.

  9. Estimation of dielectric constant of lunar material by HF sounder observation

    NASA Astrophysics Data System (ADS)

    Kobayashi, T.; Ono, T.

    Space borne radio sounding observation has been one of indispensable items in planetary missions An HF sounder Lunar Radar Sounder LRS will be onboard SELENE a lunar exploration program of Japan in 2007 Its primary objective is subsurface geologic structure of the Moon Especially mare regions are of strong interest of investigators because of its relatively smooth surface it is thought that smooth surface allows us to see subsurface feature with less difficulty However even if a clear subsurface image is obtained the data does not provide us with quantitative information unless the dielectric constant of the lunar subsurface material We propose a technique to estimate the dielectric constant of lunar material that utilizes HF sounder data of closely located multiple orbits The technique is applied to SAR images that are produced from HF sounder data and stands on the fact that the apparent position of subsurface object varies as a function of the dielectric constant of subsurface material Assuming a uniform subsurface material the displacement of images of a subsurface target should be consistent with that of observation orbits if the correct dielectric constant of the subsurface material is assumed A numerical model on geometrical optics estimates that the proposed technique requires a synthetic aperture larger than about 50km provided that the orbit altitude is 100km subsurface target depth is a few km and that the observation frequency is 5MHz with 2MHz bandwidth Some laboratory experiments were conducted to demonstrate validity of the

  10. HF Propagation Effects Caused by an Artificial Plasma Cloud in the Ionosphere

    NASA Astrophysics Data System (ADS)

    Joshi, D. R.; Groves, K. M.; McNeil, W. J.; Caton, R. G.; Parris, R. T.; Pedersen, T. R.; Cannon, P. S.; Angling, M. J.; Jackson-Booth, N. K.

    2014-12-01

    In a campaign carried out by the NASA sounding rocket team, the Air Force Research Laboratory (AFRL) launched two sounding rockets in the Kwajalein Atoll, Marshall Islands, in May 2013 known as the Metal Oxide Space Cloud (MOSC) experiment to study the interactions of artificial ionization and the background plasma and measure the effects on high frequency (HF) radio wave propagation. The rockets released samarium metal vapor in the lower F-region of the ionosphere that ionized forming a plasma cloud that persisted for tens of minutes to hours in the post-sunset period. Data from the experiments has been analyzed to understand the impacts of the artificial ionization on HF radio wave propagation. Swept frequency HF links transiting the artificial ionization region were employed to produce oblique ionograms that clearly showed the effects of the samarium cloud. Ray tracing has been used to successfully model the effects of the ionized cloud. Comparisons between observations and modeled results will be presented, including model output using the International Reference Ionosphere (IRI), the Parameterized Ionospheric Model (PIM) and PIM constrained by electron density profiles measured with the ALTAIR radar at Kwajalein. Observations and modeling confirm that the cloud acted as a divergent lens refracting energy away from direct propagation paths and scattering energy at large angles relative to the initial propagation direction. The results confirm that even small amounts of ionized material injected in the upper atmosphere can result in significant changes to the natural propagation environment.

  11. Augmented reality using ultra-wideband radar imagery

    NASA Astrophysics Data System (ADS)

    Nguyen, Lam; Koenig, Francois; Sherbondy, Kelly

    2011-06-01

    The U.S. Army Research Laboratory (ARL) has been investigating the utility of ultra-wideband (UWB) synthetic aperture radar (SAR) technology for detecting concealed targets in various applications. We have designed and built a vehicle-based, low-frequency UWB SAR radar for proof-of-concept demonstration in detecting obstacles for autonomous navigation, detecting concealed targets (mines, etc.), and mapping internal building structures to locate enemy activity. Although the low-frequency UWB radar technology offers valuable information to complement other technologies due to its penetration capability, it is very difficult to comprehend the radar imagery and correlate the detection list from the radar with the objects in the real world. Using augmented reality (AR) technology, we can superimpose the information from the radar onto the video image of the real world in real-time. Using this, Soldiers would view the environment and the superimposed graphics (SAR imagery, detection locations, digital map, etc.) via a standard display or a head-mounted display. The superimposed information would be constantly changed and adjusted for every perspective and movement of the user. ARL has been collaborating with ITT Industries to implement an AR system that integrates the video data captured from the real world and the information from the UWB radar. ARL conducted an experiment and demonstrated the real-time geo-registration of the two independent data streams. The integration of the AR sub-system into the radar system is underway. This paper presents the integration of the AR and SAR systems. It shows results that include the real-time embedding of the SAR imagery and other information into the video data stream.

  12. Comparison of HfCl4, HfI4, TEMA-Hf, and TDMA-Hf as precursors in early growing stages of HfO2 films deposited by ALD: A DFT study

    NASA Astrophysics Data System (ADS)

    Cortez-Valadez, M.; Fierro, C.; Farias-Mancilla, J. R.; Vargas-Ortiz, A.; Flores-Acosta, M.; Ramírez-Bon, R.; Enriquez-Carrejo, J. L.; Soubervielle-Montalvo, C.; Mani-Gonzalez, P. G.

    2016-06-01

    The final structure of HfO2 films grown by atomic layer deposition (ALD) after reaction with OH- ions has been analyzed by DFT (density functional theory). The interaction of the precursors: HfCl4 (hafnium tetrachloride), HfI4 (hafnium tetraiodide), TEMA-Hf (tetrakis-ethylmethylamino hafnium), and TDMA-Hf (tetrakis-dimethylamino hafnium) with HO-H was studied employing the B3LYP (Becke 3-parameter, Lee-Yang-Parr) hybrid functional and the PBE (Perdew-Burke-Ernzerhof) generalized gradient functional. The structural evolution at the Si(100) surface has been analyzed by LDA (local density approximation). The structural parameters: bond length and bond angle, and the vibrational parameters for the optimized structures are also reported. The presence of hafnium silicate at the interface was detected. The infrared spectra and structural parameters obtained in this work agree with previously reported experimental results.

  13. HF Radio Wave Production of Artificial Ionospheres

    NASA Astrophysics Data System (ADS)

    Carlson, Herbert

    In 1993 it was predicted that artificial ionospheres would be produced by high power HF radio waves, once HF transmitters approached a GWatt ERP. When that threshold was very recently achieved, such production was indeed detected and published at two high latitude high power HF facilities. Here we review: the first-principles logic behind that prediction, which aspects of such production are critically dependent on magnetic latitude, and which aspects of such production depend only on physical parameters independent of latitude. These distinctions follow directly from decomposition of the problem of ionization production into its components of: radio-wave propagation, wave-particle interactions, electron transport, and quantitative elastic/inelastic cross-sections. We outline this analysis to show that, within the context of early observations, the production of ionization is inevitable, and only a question of competing instability thresholds, and scale of ionization production. This illustrates complimentary aeronomy and plasma physics to advance understanding of both.

  14. Stepped frequency ground penetrating radar

    DOEpatents

    Vadnais, Kenneth G.; Bashforth, Michael B.; Lewallen, Tricia S.; Nammath, Sharyn R.

    1994-01-01

    A stepped frequency ground penetrating radar system is described comprising an RF signal generating section capable of producing stepped frequency signals in spaced and equal increments of time and frequency over a preselected bandwidth which serves as a common RF signal source for both a transmit portion and a receive portion of the system. In the transmit portion of the system the signal is processed into in-phase and quadrature signals which are then amplified and then transmitted toward a target. The reflected signals from the target are then received by a receive antenna and mixed with a reference signal from the common RF signal source in a mixer whose output is then fed through a low pass filter. The DC output, after amplification and demodulation, is digitized and converted into a frequency domain signal by a Fast Fourier Transform. A plot of the frequency domain signals from all of the stepped frequencies broadcast toward and received from the target yields information concerning the range (distance) and cross section (size) of the target.

  15. Ionization Energy Measurements and Spectroscopy of HfO and HfO^+

    NASA Astrophysics Data System (ADS)

    Merritt, J. M.; Bondybey, V. E.; Heaven, M. C.

    2009-06-01

    Rotationally resolved spectra of the HfO^+ cation have been recorded using the pulsed field ionization zero electron kinetic energy (PFI-ZEKE) technique. The F(0^+)← X^1Σ_g band system in HfO was resonantly excited to provide vibrational and rotational state selectivity in the two photon ionization process. Using the PFI-ZEKE technique a value of 7.91687(10) eV was determined for the ionization energy (IE) of HfO, 0.37 eV higher than the values reported previously using electron impact ionization measurements. Underestimation of the IE in the previous studies is attributed to ionization of thermally excited states. A progression in the HfO^+ stretching vibration up to ν^+ = 4 was observed in the PFI-ZEKE spectrum, allowing for determination of the ground electronic state vibrational frequency of ν_e = 1017.7(10) cm^{-1} and anharmonicity of ω_ex_e = 3.2(2) cm^{-1}. The rotational constant of HfO^+ was determined to be 0.403(5) cm^{-1}. Benchmark theoretical ab initio calculations were carried out in order to explore the effects of electron correlation on the predicted molecular properties. Survey scans utilizing laser induced fluorescence and resonance enhanced multiphoton ionization detection revealed many previously unassigned bands in the region of the F-X and G-X bands of HfO, which we attribute to nominally forbidden singlet - triplet transitions of HfO.

  16. Removal of uranium from aqueous HF solutions

    DOEpatents

    Pulley, Howard; Seltzer, Steven F.

    1980-01-01

    This invention is a simple and effective method for removing uranium from aqueous HF solutions containing trace quantities of the same. The method comprises contacting the solution with particulate calcium fluoride to form uranium-bearing particulates, permitting the particulates to settle, and separting the solution from the settled particulates. The CaF.sub.2 is selected to have a nitrogen surface area in a selected range and is employed in an amount providing a calcium fluoride/uranium weight ratio in a selected range. As applied to dilute HF solutions containing 120 ppm uranium, the method removes at least 92% of the uranium, without introducing contaminants to the product solution.

  17. Low Temperature Silicon Surface Cleaning by HF Etching/Ultraviolet Ozone Cleaning (HF/UVOC) Method (I)—Optimization of the HF Treatment—

    NASA Astrophysics Data System (ADS)

    Suemitsu, Maki; Kaneko, Tetsuya; Miyamoto, Nobuo

    1989-12-01

    Several variations of fluoric acid (HF) treatments of silicon substrates were examined for their adaptability as a pretreatment method for a silicon epitaxy process. Treatments with and without distilled, deionized (DI) water rinse, of different HF concentrations, and of different methods of HF supply were tested and their residual carbonic impurity contents were measured using RHEED. As a result, HF treatments by themselves were found to be insufficient in passivating the surface dangling bonds irrespective of the method of HF supply: dipping into the solution or exposure to the vapor. The optimum procedure of HF treatment thus proposed is a succession of (a) HF dipping, (b) DI-water rinsing, (c) nitrogen-gas blowing, and (d) UV-ozone cleaning.

  18. An MSK Radar Waveform

    NASA Technical Reports Server (NTRS)

    Quirk, Kevin J.; Srinivasan, Meera

    2012-01-01

    The minimum-shift-keying (MSK) radar waveform is formed by periodically extending a waveform that separately modulates the in-phase and quadrature- phase components of the carrier with offset pulse-shaped pseudo noise (PN) sequences. To generate this waveform, a pair of periodic PN sequences is each passed through a pulse-shaping filter with a half sinusoid impulse response. These shaped PN waveforms are then offset by half a chip time and are separately modulated on the in-phase and quadrature phase components of an RF carrier. This new radar waveform allows an increase in radar resolution without the need for additional spectrum. In addition, it provides self-interference suppression and configurable peak sidelobes. Compared strictly on the basis of the expressions for delay resolution, main-lobe bandwidth, effective Doppler bandwidth, and peak ambiguity sidelobe, it appears that bi-phase coded (BPC) outperforms the new MSK waveform. However, a radar waveform must meet certain constraints imposed by the transmission and reception of the modulation, as well as criteria dictated by the observation. In particular, the phase discontinuity of the BPC waveform presents a significant impediment to the achievement of finer resolutions in radar measurements a limitation that is overcome by using the continuous phase MSK waveform. The phase continuity, and the lower fractional out-of-band power of MSK, increases the allowable bandwidth compared with BPC, resulting in a factor of two increase in the range resolution of the radar. The MSK waveform also has been demonstrated to have an ambiguity sidelobe structure very similar to BPC, where the sidelobe levels can be decreased by increasing the length of the m-sequence used in its generation. This ability to set the peak sidelobe level is advantageous as it allows the system to be configured to a variety of targets, including those with a larger dynamic range. Other conventionally used waveforms that possess an even greater

  19. Description, characteristics and testing of the NASA airborne radar

    NASA Technical Reports Server (NTRS)

    Jones, W. R.; Altiz, O.; Schaffner, P.; Schrader, J. H.; Blume, H. J. C.

    1991-01-01

    Presented here is a description of a coherent radar scattermeter and its associated signal processing hardware, which have been specifically designed to detect microbursts and record their radar characteristics. Radar parameters, signal processing techniques and detection algorithms, all under computer control, combine to sense and process reflectivity, clutter, and microburst data. Also presented is the system's high density, high data rate recording system. This digital system is capable of recording many minutes of the in-phase and quadrature components and corresponding receiver gains of the scattered returns for selected spatial regions, as well as other aircraft and hardware related parameters of interest for post-flight analysis. Information is given in viewgraph form.

  20. The Shuttle Imaging Radar B (SIR-B) experiment report

    NASA Technical Reports Server (NTRS)

    Cimino, Jo Bea; Holt, Benjamin; Richardson, Annie

    1988-01-01

    The primary objective of the SIR-B experiment was to acquire multiple-incidence-angle radar imagery of a variety of Earth's surfaces to better understand the effects of imaging geometry on radar backscatter. A complementary objective was to map extensive regions of particular interest. Under these broad objectives, many specific scientific experiments were defined by the 43 SIR-B Science Team members, including studies in the area of geology, vegetation, radar penetration, oceanography, image analysis, and calibration technique development. Approximately 20 percent of the planned digital data were collected, meeting 40 percent of the scientific objectives. This report is an overview of the SIR-B experiment and includes the science investigations, hardware design, mission scenario, mission operations, events of the actual missions, astronaut participation, data products (including auxiliary data), calibrations, and a summary of the actual coverage. Also included are several image samples.

  1. Preliminary science results from the Shuttle Imaging Radar-B

    NASA Technical Reports Server (NTRS)

    Ruzek, M.

    1985-01-01

    Preliminary results of analyzing digital radar imagery data obtained by the SIR-B aboard the Space Shuttle Challenger STS 41-G are presented. The data cover 5 million square kilometers of the earth surface between 57 deg north and south latitudes. Radar imagery of the same target at different incidence angles was used to classify surfaces by their backscatter response as a function of incidence angle. The SIR-B proved to be useful for collecting multiple incidence angle data sets over a broad range of targets, providing information in the areas of geology, archeology, forestry, agriculture, oceanography, geography, and hydrology. The analysis is also used to optimize radar parameters such as look angle for future missions.

  2. Assessment of forest cover changes using multidate spaceborne imaging radar

    NASA Technical Reports Server (NTRS)

    Lee, Kyu-Sung; Hoffer, Roger M.

    1988-01-01

    Data obtained in 1978 by Seasat and in 1984 by SIR-B over a forested area in northern Florida are analyzed. The objective of the study was to determine the potential for detecting major changes in forest cover utilizing synthetic aperture radar obtained from satellite altitudes, and to define an effective methodology for processing and analyzing digital synthetic aperture radar data obtained on two different dates. It is found that multitemporal synthetic aperture radar data obtained from satellite altitudes can be used to detect major changes in forest cover conditions such as deforestation and reforestation. A suprisingly good level of detectivity was obtained for identifying areas of regrowth after they had been clearcut and replanted.

  3. Development of land based radar polarimeter processor system

    NASA Technical Reports Server (NTRS)

    Kronke, C. W.; Blanchard, A. J.

    1983-01-01

    The processing subsystem of a land based radar polarimeter was designed and constructed. This subsystem is labeled the remote data acquisition and distribution system (RDADS). The radar polarimeter, an experimental remote sensor, incorporates the RDADS to control all operations of the sensor. The RDADS uses industrial standard components including an 8-bit microprocessor based single board computer, analog input/output boards, a dynamic random access memory board, and power supplis. A high-speed digital electronics board was specially designed and constructed to control range-gating for the radar. A complete system of software programs was developed to operate the RDADS. The software uses a powerful real time, multi-tasking, executive package as an operating system. The hardware and software used in the RDADS are detailed. Future system improvements are recommended.

  4. Surface current patterns in the northern Adriatic extracted from high-frequency radar data using self-organizing map analysis

    NASA Astrophysics Data System (ADS)

    Mihanović, Hrvoje; Cosoli, Simone; Vilibić, Ivica; Ivanković, Damir; Dadić, Vlado; GačIć, Miroslav

    2011-08-01

    A network of high-frequency (HF) radars was installed in the northern Adriatic in the second half of 2007, aimed to measure surface currents in the framework of the North Adriatic Surface Current Mapping (NASCUM) project. This study includes a detailed analysis of current measurements from February to August 2008, a period in which three radars were simultaneously operational. Current patterns and temporal evolutions of different physical processes were extracted by using self-organizing map (SOM) analysis. The analysis focused on subtidal frequency band and extracted 12 different circulation patterns on a 4 × 3 rectangular SOM grid. The SOM was also applied on a joint data set that included contemporaneous surface wind data obtained from the operational hydrostatic mesoscale meteorological model ALADIN/HR. The strongest currents were recorded during energetic bora episodes, being recognized by several current patterns and having the characteristic downwind flow with magnitudes exceeding 35 cm/s at some grid points. Another characteristic wind, the sirocco, was represented by three current patterns, while the remaining current structures were attributed to weak winds and the residual thermohaline circulation. A strong resemblance has been found between SOM patterns extracted from HF radar data only and from combined HF radar and wind data sets, revealing the predominant wind influence to the surface circulation structures and their temporal changes in the northern Adriatic. These results show the SOM analysis being a valuable tool for extracting characteristic surface current patterns and forcing functions.

  5. Space Radar Image of Oetzal, Austria

    NASA Technical Reports Server (NTRS)

    1994-01-01

    This is a digital elevation model that was geometrically coded directly onto an X-band seasonal change image of the Oetztal supersite in Austria. The image is centered at 46.82 degrees north latitude and 10.79 degrees east longitude. This image is located in the Central Alps at the border between Switzerland, Italy and Austria, 50 kilometers (31 miles) southwest of Innsbruck. It was acquired by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture aboard the space shuttle Endeavour on April 14, 1994 and on October 5, 1994. It was produced by combining data from these two different data sets. Data obtained in April is green; data obtained in October appears in red and blue, and was used as an enhancement based on the ratio of the two data sets. Areas with a decrease in backscatter from April to October appear in light blue (cyan), such as the large Gepatschferner glacier seen at the left of the image center, and most of the other glaciers in this view. A light blue hue is also visible at the east border of the dark blue Lake Reschensee at the upper left side. This shows a significant rise in the water level. Magenta represents areas with an increase of backscatter from April 10 to October 5. Yellow indicates areas with high radar signal response during both passes, such as the mountain slopes facing the radar. Low radar backscatter signals refer to smooth surface (lakes) or radar grazing areas to radar shadow areas, seen in the southeast slopes. The area is approximately 29 kilometers by 21 kilometers (18 miles by 13.5 miles). The summit of the main peaks reaches elevations of 3,500 to 3,768 meters (xx feet to xx feet)above sea level. The test site's core area is the glacier region of Venter Valley, which is one of the most intensively studied areas for glacier research in the world. Research in Venter Valley (below center)includes studies of glacier dynamics, glacier-climate regions, snowpack conditions and glacier hydrology. About 25 percent of the core test

  6. X-mode HF Pump-induced Phenomena at High Heater Frequencies in the High Latitude Ionosphere F-region

    NASA Astrophysics Data System (ADS)

    Blagoveshchenskaya, N. F.; Borisova, T. D.; Kalishin, A. S.; Yeoman, T. K.; Häggström, I.

    2015-12-01

    Experimental results concentrating on X-mode HF-induced phenomena in the high latitude ionosphere F region are discussed. Experiments have been carried out at the HF Heating facility at Tromsø with an effective radiated power of 450 - 650 MW at high heater frequencies of 6.2 - 8.0 MHz. Multi-instriment diagnostics included the European Incoherent Scatter (EISCAT) UHF radar at 931 MHz at Tromsø, the Finland CUTLASS (Co-operative UK Twin Located Auroral Sounding System) radar, the stimulated electromagnetic emission (SEE) equipment at Tromsø, and the HF receiver near St. Petersburg for the observations of narrow band SEE features. The key parameter considered is the ratio between the heater frequency and critical frequency of the F2 layer (fH/foF2). We have analyzed the behaviors of small-scale artificial field-aligned irregularities (FAIs) and HF-enhanced plasma and ion lines (HFPLs and HFILs) depending on the pump proximity to the critical frequency. It was shown that the HFPLs and HFILs coexisted with FAIs throughout the whole heater pulse when fH/foF2 > 1 as well as fH/foF2 ≤ 1. It is indicative that parametric decay instability was not quenched by fully developed FAIs. The comparison between contrasting O/X mode HF-induced phenomena, when the heater frequency is below or near the critical frequency of F2 layer, is made. It was found that an X-mode HF pumping is able to excite different narrow band spectral components in the SEE spectra (within 1 kHz of pump frequency), such as ion acoustic, electrostatic ion cyclotron, and electrostatic ion cyclotron harmonic waves (otherwise known as neutralized ion Bernstein waves) observed at a long distance from the HF Heating facility. It was suggested that these spectral component can be attributed to the stimulated Brillion scatter (SBS) process. The results obtained show that an X-polarized electromagnetic wave scattered by SBS can propagate more than one thousand km without significant attenuation.

  7. A compressive radar system with chaotic-based FM signals using the Bernoulli map

    NASA Astrophysics Data System (ADS)

    Ochoa, Hector A.; Teja Enugula, Charan

    2013-05-01

    Matched filters are used in radar systems to identify echo signals embedded in noise. They allow us to extract range and Doppler information about the target from the reflected signal. In high frequency radars, matched filters make the system expensive and complex. For that reason, the radar research community is looking at techniques like compressive sensing or compressive sampling to eliminate the use of matched filters and high frequency analog-to-digital converters. In this work, compressive sensing is proposed as a method to increase the resolution and eliminate the use of matched filters in chaotic radars. Two basic scenarios are considered, one for stationary targets and one for non-stationary targets. For the stationary targets, the radar scene was a one dimensional vector, in which each element from the vector represents a target position. For the non-stationary targets, the radar scene was a two dimensional matrix, in which one direction of the matrix represents the target's range, and the other direction represents the target's velocity. Using optimization techniques, it was possible to recover both radar scenes from an under sampled echo signal. The reconstructed scenes were compared against a traditional matched filter system. In both cases, the matched filter was capable of recovering the radar scene. However, there was a considerable amount of artifacts introduced by the matched filter that made target identification a daunting task. On the other hand, using compressive sensing it was possible to recover both radar scenes perfectly, even when the echo signal was under sampled.

  8. Digital Libraries.

    ERIC Educational Resources Information Center

    Fox, Edward A.; Urs, Shalini R.

    2002-01-01

    Provides an overview of digital libraries research, practice, and literature. Highlights include new technologies; redefining roles; historical background; trends; creating digital content, including conversion; metadata; organizing digital resources; services; access; information retrieval; searching; natural language processing; visualization;…

  9. Model of Artificial Ionospheric Ducts due to the HF-heating

    NASA Astrophysics Data System (ADS)

    Vartanyan, A.; Milikh, G. M.; Demekhov, A. G.; Papadopoulos, K.; Huba, J.; Joyce, G. R.

    2009-12-01

    The presence of field aligned density striations plays a critical role in the propagation of whistler waves in the ionosphere. Such density structures have often been observed to extend over distances covering entire magnetic field lines, trapping, channeling and reflecting whistler waves between conjugate regions. The possibility for artificially creating such trans-hemispheric ducts was first discussed by Perrine et al. [2006]. They showed that long term (> 15 minutes) continuous HF-heating of the F-region by powerful ionospheric heaters such as HAARP generates a strong thermal wave in the ionospheric and magnetospheric plasma. This thermal wave propagates along the magnetic field line through the topside ionosphere and magnetosphere, driving ion outflows, displacing the ambient plasma and leading to the formation of density ducts. Two recent experiments detected large scale ducts caused by the HF-heating. One experiment was conducted at HAARP and used the low orbit satellite DEMETER as a diagnostic tool [Milikh et al., 2008]. The experiment shows in situ detected plasma ducts with the spatial scale of a few tens kilometers. Another heating experiment was conducted at the EISCAT HF facility and used UHF radar as a diagnostic tool [Rietveld et al., 2003]. As a result vertical profiles of electron and ion temperature were obtained in the height range 150-600 km. It is the objective of this paper to present the first detailed model of the formation of ionospheric ducts due to HF-heating. The model is checked against the observations made at EISCAT. The results show a good agreement between the model and observations. Milikh, G.M., K. Papadopoulos, et al. (2008), Geophys. Res. Lett, 35, doi:10.1029/2008GL034630. Perrine, R.P., G.M. Milikh, K. Papadopoulos, et al., Radio Sci. (2006), 41, doi:10.1029/2005RS003371. Rietveld, M.T., M.J. Kosch, et al., J. Geophys. Res. (2003), 108, doi:10.1029/2002JA009543.

  10. Floor-plan radar

    NASA Astrophysics Data System (ADS)

    Falconer, David G.; Ueberschaer, Ronald M.

    2000-07-01

    Urban-warfare specialists, law-enforcement officers, counter-drug agents, and counter-terrorism experts encounter operational situations where they must assault a target building and capture or rescue its occupants. To minimize potential casualties, the assault team needs a picture of the building's interior and a copy of its floor plan. With this need in mind, we constructed a scale model of a single- story house and imaged its interior using synthetic-aperture techniques. The interior and exterior walls nearest the radar set were imaged with good fidelity, but the distal ones appear poorly defined and surrounded by ghosts and artifacts. The latter defects are traceable to beam attenuation, wavefront distortion, multiple scattering, traveling waves, resonance phenomena, and other effects not accounted for in the traditional (noninteracting, isotropic point scatterer) model for radar imaging.

  11. New weather radar coming

    NASA Astrophysics Data System (ADS)

    Maggs, William Ward

    What would you call the next generation of radar for severe weather prediction? NEXRAD, of course. A prototype for the new system was recently completed in Norman, Okla., and by the early 1990s up to 195 stations around the United States will be tracking dangerous weather and sending faster, more accurate, and more detailed warnings to the public.NEXRAD is being built for the Departments of Commerce, Transportation, and Defense by the Unisys Corporation under a $450 million contract signed in December 1987. Th e system will be used by the National Weather Service, the Federal Aviation Administration (FAA), and the U.S. Air Force and Navy. The NEXRAD radar tower in Norman is expected to be operational in October.

  12. RADAR Reveals Titan Topography

    NASA Technical Reports Server (NTRS)

    Kirk, R. L.; Callahan, P.; Seu, R.; Lorenz, R. D.; Paganelli, F.; Lopes, R.; Elachi, C.

    2005-01-01

    The Cassini Titan RADAR Mapper is a K(sub u)-band (13.78 GHz, lambda = 2.17 cm) linear polarized RADAR instrument capable of operating in synthetic aperture (SAR), scatterometer, altimeter and radiometer modes. During the first targeted flyby of Titan on 26 October, 2004 (referred to as Ta) observations were made in all modes. Evidence for topographic relief based on the Ta altimetry and SAR data are presented here. Additional SAR and altimetry observations are planned for the T3 encounter on 15 February, 2005, but have not been carried out at this writing. Results from the T3 encounter relevant to topography will be included in our presentation. Data obtained in the Ta encounter include a SAR image swath

  13. Kuiper Belt Mapping Radar

    NASA Technical Reports Server (NTRS)

    Freeman, A.; Nilsen, E.

    2001-01-01

    Since their initial discovery in 1992, to date only a relatively small number of Kuiper Belt Objects (KBO's) have been discovered. Current detection techniques rely on frame-to-frame comparisons of images collected by optical telescopes such as Hubble, to detect KBO's as they move against the background stellar field. Another technique involving studies of KBO's through occultation of known stars has been proposed. Such techniques are serendipitous, not systematic, and may lead to an inadequate understanding of the size, range, and distribution of KBO's. In this paper, a future Kuiper Belt Mapping Radar is proposed as a solution to the problem of mapping the size distribution, extent, and range of KBO's. This approach can also be used to recover radar albedo and object rotation rates. Additional information is contained in the original extended abstract.

  14. GEOS-2 C-band radar system project. Spectral analysis as related to C-band radar data analysis

    NASA Technical Reports Server (NTRS)

    1972-01-01

    Work performed on spectral analysis of data from the C-band radars tracking GEOS-2 and on the development of a data compaction method for the GEOS-2 C-band radar data is described. The purposes of the spectral analysis study were to determine the optimum data recording and sampling rates for C-band radar data and to determine the optimum method of filtering and smoothing the data. The optimum data recording and sampling rate is defined as the rate which includes an optimum compromise between serial correlation and the effects of frequency folding. The goal in development of a data compaction method was to reduce to a minimum the amount of data stored, while maintaining all of the statistical information content of the non-compacted data. A digital computer program for computing estimates of the power spectral density function of sampled data was used to perform the spectral analysis study.

  15. Origin of Excess 176Hf in Meteorites

    NASA Astrophysics Data System (ADS)

    Thrane, Kristine; Connelly, James N.; Bizzarro, Martin; Meyer, Bradley S.; The, Lih-Sin

    2010-07-01

    After considerable controversy regarding the 176Lu decay constant (λ176Lu), there is now widespread agreement that (1.867 ± 0.008) × 10-11 yr-1 as confirmed by various terrestrial objects and a 4557 Myr meteorite is correct. This leaves the 176Hf excesses that are correlated with Lu/Hf elemental ratios in meteorites older than ~4.56 Ga meteorites unresolved. We attribute 176Hf excess in older meteorites to an accelerated decay of 176Lu caused by excitation of the long-lived 176Lu ground state to a short-lived 176m Lu isomer. The energy needed to cause this transition is ascribed to a post-crystallization spray of cosmic rays accelerated by nearby supernova(e) that occurred after 4564.5 Ma. The majority of these cosmic rays are estimated to penetrate accreted material down to 10-20 m, whereas a small fraction penetrate as deep as 100-200 m, predicting decreased excesses of 176Hf with depth of burial at the time of the irradiation event.

  16. Space Radar Image of Long Valley, California - 3D view

    NASA Technical Reports Server (NTRS)

    1994-01-01

    This is a three-dimensional perspective view of Long Valley, California by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar on board the space shuttle Endeavour. This view was constructed by overlaying a color composite SIR-C image on a digital elevation map. The digital elevation map was produced using radar interferometry, a process by which radar data are acquired on different passes of the space shuttle and, which then, are compared to obtain elevation information. The data were acquired on April 13, 1994 and on October 3, 1994, during the first and second flights of the SIR-C/X-SAR radar instrument. The color composite radar image was produced by assigning red to the C-band (horizontally transmitted and vertically received) polarization; green to the C-band (vertically transmitted and received) polarization; and blue to the ratio of the two data sets. Blue areas in the image are smooth and yellow areas are rock outcrops with varying amounts of snow and vegetation. The view is looking north along the northeastern edge of the Long Valley caldera, a volcanic collapse feature created 750,000 years ago and the site of continued subsurface activity. Crowley Lake is off the image to the left. Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars illuminate Earth with microwaves, allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-band (24 cm), C-band (6 cm) and X-band (3 cm). The multi-frequency data will be used by the international scientific community to better understand the global environment and how it is changing. The SIR-C/X-SAR data, complemented by aircraft and ground studies, will give scientists clearer insights into those environmental changes which are caused by nature and those changes which are induced by human activity. SIR-C was developed by NASA's Jet Propulsion Laboratory

  17. Space Radar Image of Long Valley, California in 3-D

    NASA Technical Reports Server (NTRS)

    1994-01-01

    This three-dimensional perspective view of Long Valley, California was created from data taken by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar on board the space shuttle Endeavour. This image was constructed by overlaying a color composite SIR-C radar image on a digital elevation map. The digital elevation map was produced using radar interferometry, a process by which radar data are acquired on different passes of the space shuttle. The two data passes are compared to obtain elevation information. The interferometry data were acquired on April 13,1994 and on October 3, 1994, during the first and second flights of the SIR-C/X-SAR instrument. The color composite radar image was taken in October and was produced by assigning red to the C-band (horizontally transmitted and vertically received) polarization; green to the C-band (vertically transmitted and received) polarization; and blue to the ratio of the two data sets. Blue areas in the image are smooth and yellow areas are rock outcrops with varying amounts of snow and vegetation. The view is looking north along the northeastern edge of the Long Valley caldera, a volcanic collapse feature created 750,000 years ago and the site of continued subsurface activity. Crowley Lake is the large dark feature in the foreground. Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars illuminate Earth with microwaves, allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-band (24 cm), C-band (6 cm) and X-band (3 cm). The multi-frequency data will be used by the international scientific community to better understand the global environment and how it is changing. The SIR-C/X-SAR data, complemented by aircraft and ground studies, will give scientists clearer insights into those environmental changes which are caused by nature and those changes which are

  18. A Comparative Time Differential Perturbed Angular Correlation Study of the Nuclear Quadrupole Interaction in HfF4·HF·2H2O Using 180mHf and 181Hf(β-)181Ta as Nuclear Probes: Is Ta an Innocent Spy?

    NASA Astrophysics Data System (ADS)

    Butz, Tilman; Das, Satyendra K.; Manzhur, Yurij

    2009-02-01

    We report on a comparative study of the nuclear quadrupole interaction of the nuclear probes 180mHf and 181Hf(β -)181Ta in HfF4・HF・2H2O using time differential perturbed angular correlations (TDPAC) at 300 K. For the first probe, assuming a Lorentzian frequency distribution, we obtained ωQ= 103(4) Mrad/s, an asymmetry parameter η = 0.68(3), a linewidth δ = 7.3(3.9)%, and full anisotropy within experimental accuracy. For the second probe, assuming a Lorentzian frequency distribution, we obtained three fractions: (1) with 56.5(7)%, ωQ= 126.64(4) Mrad/s and η = 0.9241(4) with a rather small distribution δ = 0.40(8)% which is attributed to HfF4・HF・2H2O; (2) with 4.6(4)%, ωQ = 161.7(3) Mrad/s and η = 0.761(4) assuming no line broadening which is tentatively attributed to a small admixture of Hf2OF6・H2O; (3) the remainder of 39.0(7)% accounts for a rapid loss of anisotropy and is modelled by a perturbation function with a sharp frequency multiplied by an exponential factor exp(-λ t) with λ = 0.55(2) ns-1. Whereas the small admixture of Hf2OF6・H2O escapes detection by the 180mHf probe, there is no rapid loss of roughly half the anisotropy as is the case with 181Hf(β -)181Ta. This loss could in principle be due to fluctuating electric field gradients originating from movements of nearest neighbour HF adducts and/or H2O molecules after nuclear transmutation to the foreign atom Ta which are absent for the isomeric probe. Alternatively, paramagnetic Ta ions could lead to fluctuating magnetic dipole fields which, when combined with fluctuating electric field gradients, could also lead to a rapid loss of anisotropy. In any case, Ta is not an "innocent spy" in this compound. Although 180mHf is not a convenient probe for conventional spectrometers, the use of fast digitizers and software coincidences would allow to use all γ -quanta in the stretched cascade which would greatly improve the efficiency of the spectrometer. 180mHf could also serve as a Pu

  19. Radar cross-sectional study using noise radar

    NASA Astrophysics Data System (ADS)

    Freundorfer, A. P.; Siddiqui, J. Y.; Antar, Y. M. M.

    2015-05-01

    A noise radar system is proposed with capabilities to measure and acquire the radar cross-section (RCS) of targets. The proposed system can cover a noise bandwidth of near DC to 50 GHz. The noise radar RCS measurements were conducted for selective targets like spheres and carpenter squares with and without dielectric bodies for a noise band of 400MHz-5000MHz. The bandwidth of operation was limited by the multiplier and the antennae used.

  20. 41. Perimeter acquisition radar building radar element and coaxial display, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    41. Perimeter acquisition radar building radar element and coaxial display, with drawing of typical antenna section. Drawing, from left to right, shows element, aluminum ground plane, cable connectors and hardware, cable, and back-up ring. Grey area is the concrete wall - Stanley R. Mickelsen Safeguard Complex, Perimeter Acquisition Radar Building, Limited Access Area, between Limited Access Patrol Road & Service Road A, Nekoma, Cavalier County, ND

  1. 51. View of upper radar scanner switch in radar scanner ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    51. View of upper radar scanner switch in radar scanner building 105 from upper catwalk level showing emanating waveguides from upper switch (upper one-fourth of photograph) and emanating waveguides from lower radar scanner switch in vertical runs. - Clear Air Force Station, Ballistic Missile Early Warning System Site II, One mile west of mile marker 293.5 on Parks Highway, 5 miles southwest of Anderson, Anderson, Denali Borough, AK

  2. Goldstone solar system radar

    NASA Technical Reports Server (NTRS)

    Jurgens, Raymond F.

    1991-01-01

    Caltech/Jet Propulsion Laboratory (JPL) radar astronomers made use of the Very Large Array (VLA) at Socorro, NM, during February 1990, to receive radio echoes from the planet Venus. The transmitter was the 70 meter antenna at the Goldstone complex northwest of Barstow, CA. These observations contain new information about the roughness of Venus at cm to decimeter scales and are complementary to information being obtained by the Magellan spacecraft. Asteroid observations are also discussed.

  3. Imaging synthetic aperture radar

    DOEpatents

    Burns, Bryan L.; Cordaro, J. Thomas

    1997-01-01

    A linear-FM SAR imaging radar method and apparatus to produce a real-time image by first arranging the returned signals into a plurality of subaperture arrays, the columns of each subaperture array having samples of dechirped baseband pulses, and further including a processing of each subaperture array to obtain coarse-resolution in azimuth, then fine-resolution in range, and lastly, to combine the processed subapertures to obtain the final fine-resolution in azimuth. Greater efficiency is achieved because both the transmitted signal and a local oscillator signal mixed with the returned signal can be varied on a pulse-to-pulse basis as a function of radar motion. Moreover, a novel circuit can adjust the sampling location and the A/D sample rate of the combined dechirped baseband signal which greatly reduces processing time and hardware. The processing steps include implementing a window function, stabilizing either a central reference point and/or all other points of a subaperture with respect to doppler frequency and/or range as a function of radar motion, sorting and compressing the signals using a standard fourier transforms. The stabilization of each processing part is accomplished with vector multiplication using waveforms generated as a function of radar motion wherein these waveforms may be synthesized in integrated circuits. Stabilization of range migration as a function of doppler frequency by simple vector multiplication is a particularly useful feature of the invention; as is stabilization of azimuth migration by correcting for spatially varying phase errors prior to the application of an autofocus process.

  4. Characteristics of HfO2/Hf-based bipolar resistive memories

    NASA Astrophysics Data System (ADS)

    Jinshun, Bi; Zhengsheng, Han

    2015-06-01

    Nano-scale Hf/HfO2-based resistive random-access-memory (RRAM) devices were fabricated. The cross-over between top and bottom electrodes of RRAM forms the metal-insulator-metal sandwich structure. The electrical responses of RRAM are studied in detail, including forming process, SET process and RESET process. The correlations between SET voltage and RESET voltage, high resistance state and low resistance state are discussed. The electrical characteristics of RRAM are in a strong relationship with the compliance current in the SET process. The conduction mechanism of nano-scale Hf/HfO2-based RRAM can be explained by the quantum point contact model. Project supported by the National Natural Science Foundation of China (Nos. 11179003, 61176095).

  5. A family of radars for advanced systems

    NASA Astrophysics Data System (ADS)

    Giaccari, Ennio; Penazzi, Carlo Alberto

    1989-04-01

    The military and air traffic control radars developed by Selenia are reviewed. The design, production, and testing aspects of the radar development process are discussed, focusing on shipborne, ground based, and air traffic control radars. An overview of radar subsystems is given, including the antenna, transmitter, receiver-exciter, signal processor, data processor, and radar controller subsystems.

  6. Spaceborne Imaging Radar Project

    NASA Technical Reports Server (NTRS)

    Herman, Neil

    1986-01-01

    In June of 1985 the Project Initiation Agreement was signed by the Jet Propulsion Laboratory and the NASA Office of Space Science and Applications for the Spaceborne Imaging Radar Project (SIR). The thrust of the Spaceborne Imaging Radar Project is to continue the evolution of synthetic aperture radar (SAR) science and technology developed during SEASAT, SIR-A and SIR-B missions to meet the needs of the Earth Observing System (EOS) in the mid 1990's. As originally formulated, the Project plans were for a reflight of the SIR-B in 1987, the development of a new SAR, SIR-C, for missions in mid 1989 and early 1990, and the upgrade of SIR-C to EOS configuration with a qualification flight aboard the shuttle in the 1993 time frame (SIR-D). However, the loss of the shuttle Challenger has delayed the first manifest for SIR to early 1990. This delay prompted the decision to drop SIR-B reflight plans and move ahead with SIR-C to more effectively utilize this first mission opportunity. The planning for this project is discussed.

  7. Radar gun hazards

    SciTech Connect

    Not Available

    1991-12-20

    Radar guns - hand-held units used by the law to nail speeders - have been in use since the early '60s. Now they've been accused of causing cancer. Police officers in several states have so far filed eight suits against the manufacturer, claiming that they have contracted rare forms of cancer, such as of the eyelid and the testicle, from frequent proximity to the devices. Spurred by concerns expressed by police groups, researchers at the Rochester Institute of Technology are conducting what they believe to be the first research of its kind in the nation. Last month psychologist John Violanti, an expert in policy psychology and health, sent out a one-page survey to 6,000 active and retired police officers in New York State, asking them about their health and their use of radar guns. Violanti says melanoma, leukemia, and lymph node cancer may be linked to these as well as other electromagnetic devices. The Food and Drug Administration earlier this year issued a warning about radar guns, telling users not to operate them closer than 6 inches from the body. But this may not be a sufficient safeguard since the instruments can give off crisscrossing wave emissions within a police vehicle. The survey will be used to help determine if it would be safer to mount the guns, which are currently either hand-held or mounted on dashboards, outside troopers' cars.

  8. An overview of current and advanced processing techniques for surveillance radar

    NASA Astrophysics Data System (ADS)

    Farina, A.; Galati, G.

    An evaluation is made of current and prospective signal processing techniques for air defense and surveillance radars, giving attention to surveillance performance-enhancement requirements, signal coding, and anticlutter and ECCM techniques for three-dimensional radars. Novel concepts and techniques anticipated for future application encompass low probability of intercept features, anti-ARM, and antistealth capabilities, digital beam forming, adaptivity, high resolution multidimensional processing, and target classification.

  9. 25. Perimeter acquisition radar building room #2M4, (mezzanine), power supply ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    25. Perimeter acquisition radar building room #2M4, (mezzanine), power supply room; computer power supply on left and water flow on right. This room is directly below data processing area (room #318). Sign on right reads: High purity water digital rack - Stanley R. Mickelsen Safeguard Complex, Perimeter Acquisition Radar Building, Limited Access Area, between Limited Access Patrol Road & Service Road A, Nekoma, Cavalier County, ND

  10. Considerations for Integration of a Physiological Radar Monitoring System with Gold Standard Clinical Sleep Monitoring Systems

    PubMed Central

    Singh, Aditya; Baboli, Mehran; Gao, Xiaomeng; Yavari, Ehsan; Padasdao, Bryson; Soll, Bruce; Boric-Lubecke, Olga; Lubecke, Victor M.

    2016-01-01

    A design for a physiological radar monitoring system (PRMS) that can be integrated with clinical sleep monitoring systems is presented. The PRMS uses two radar systems at 2.45GHz and 24 GHz to achieve both high sensitivity and high resolution. The system can acquire data, perform digital processing and output appropriate conventional analog outputs with a latency of 130 ms, which can be recorded and displayed by a gold standard sleep monitoring system, along with other standard sensor measurements. PMID:24110139

  11. Considerations for integration of a physiological radar monitoring system with gold standard clinical sleep monitoring systems.

    PubMed

    Singh, Aditya; Baboli, Mehran; Gao, Xiaomeng; Yavari, Ehsan; Padasdao, Bryson; Soll, Bruce; Boric-Lubecke, Olga; Lubecke, Victor

    2013-01-01

    A design for a physiological radar monitoring system (PRMS) that can be integrated with clinical sleep monitoring systems is presented. The PRMS uses two radar systems at 2.45 GHz and 24 GHz to achieve both high sensitivity and high resolution. The system can acquire data, perform digital processing and output appropriate conventional analog outputs with a latency of 130 ms, which can be recorded and displayed by a gold standard sleep monitoring system, along with other standard sensor measurements. PMID:24110139

  12. Survey of ULF wave signatures seen in the Tasman International Geospace Environment Radars data

    NASA Astrophysics Data System (ADS)

    Norouzi-Sedeh, L.; Waters, C. L.; Menk, F. W.

    2015-02-01

    Ultralow frequency (ULF) plasma waves propagate through the magnetosphere and ionosphere where they can alter the Doppler velocity of HF radar echoes. Data from the two Tasman International Geospace Environment Radars and the fluxgate and induction coil magnetometers located on Macquarie Island (54.5°S, 158.95°E geographic) over 2006-2009 show that ULF wave signatures are common. Using coincident radar and magnetometer data selection criteria, 194 events representing a total of 233.4 h were identified. The majority of ULF signatures seen in the radar data were detected between 06 and 12 UT (15 and 21 LT). Using the Maximum Entropy Method, the spectral content showed favored frequencies of 1.6, 2.1, 2.9, and 3.3 mHz but no obvious variation of frequency with latitude. Most of the observed frequencies were in the range 1-4 mHz. A class of Doppler velocity signatures that appeared as a zigzag shape in the radar range:time plots were identified and may be related to the expected plasmapause latitudes. Regularly spaced, favored frequencies appeared in the ground magnetometer data during the afternoon, night, and morning sectors for those days where ULF wave events were observed in the radar data.

  13. Gadanki Ionospheric Radar Interferometer (GIRI): System Description, Capabilities and Observations

    NASA Astrophysics Data System (ADS)

    Durga rao, Meka; Jayaraman, Achuthan; Patra, Amit; Kamaraj, Pandian; Jayaraj, Katta; Raghavendra, J.; Yasodha, Polisetti

    2016-07-01

    A 30-MHz radar has been developed at National Atmospheric Research Laboratory for dedicated probing of ionosphere and to study the low latitude ionospheric plasma irregularities. The radar has the beam steering capability to scan a larger part of the sky up to ±45o in East-West direction, which will overcome the limitation of slit camera picture obtained by the fixed beam of the Gadanki MST radar on the ionospheric plasma irregularity/structures. The system is also configured for pulse-to-pulse beam steering, employs multi-channel receiving system to carryout Interferometry/Imaging experiments. The radar system employs 20x8 phased antenna array, Direct Digital Synthesizers to generate pulse coded excitation signals, high power solid-state Transmit-Receive modules to generate a peak power of 150 kW, low loss coaxial beam forming and feeder network and multi-channel direct IF digital receiver. Round-the-clock observations are being made with uninterrupted operations and high quality E-and F-Region Range-Time-Intensity and conical maps are obtained with the system. In this paper we present, the system design philosophy, realization, initial observations and also the capability of the system to augment for Meteor observations.

  14. GeoSAR: A Radar Terrain Mapping System for the New Millennium

    NASA Technical Reports Server (NTRS)

    Thompson, Thomas; vanZyl, Jakob; Hensley, Scott; Reis, James; Munjy, Riadh; Burton, John; Yoha, Robert

    2000-01-01

    GeoSAR Geographic Synthetic Aperture Radar) is a new 3 year effort to build a unique, dual-frequency, airborne Interferometric SAR for mapping of terrain. This is being pursued via a Consortium of the Jet Propulsion Laboratory (JPL), Calgis, Inc., and the California Department of Conservation. The airborne portion of this system will operate on a Calgis Gulfstream-II aircraft outfitted with P- and X-band Interferometric SARs. The ground portions of this system will be a suite of Flight Planning Software, an IFSAR Processor and a Radar-GIS Workstation. The airborne P-band and X-band radars will be constructed by JPL with the goal of obtaining foliage penetration at the longer P-band wavelengths. The P-band and X-band radar will operate at frequencies of 350 Mhz and 9.71 Ghz with bandwidths of either 80 or 160 Mhz. The airborne radars will be complemented with airborne laser system for measuring antenna positions. Aircraft flight lines and radar operating instructions will be computed with the Flight Planning Software The ground processing will be a two-step step process. First, the raw radar data will be processed into radar images and interferometer derived Digital Elevation Models (DEMs). Second, these radar images and DEMs will be processed with a Radar GIS Workstation which performs processes such as Projection Transformations, Registration, Geometric Adjustment, Mosaicking, Merging and Database Management. JPL will construct the IFSAR Processor and Calgis, Inc. will construct the Radar GIS Workstation. The GeoSAR Project was underway in November 1996 with a goal of having the radars and laser systems fully integrated onto the Calgis Gulfstream-II aircraft in early 1999. Then, Engineering Checkout and Calibration-Characterization Flights will be conducted through November 1999. The system will be completed at the end of 1999 and ready for routine operations in the year 2000.

  15. Realistic simulations of tsunami detection by High-Frequency Radar in British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Grilli, Stéphan; Shelby, Michael; Grilli, Annette; Lado Insua, Tania; Guérin, Charles-Antoine

    2016-04-01

    A promising technique for long-range detection of tsunamis is the use of shore-based High Frequency (HF) surface wave radars, also simply referred to as oceanographic radars. These over-the-horizon radars are routinely used for real-time monitoring of ocean surface currents up to a 70-80 km range, based on the Doppler shift the latter cause in ocean waves at the radar Bragg frequency. Quite recently there has been convincing numerical and experimental evidence that oceanographic radars can also be used to detect tsunami-induced surface currents. However, these need to be at least 0.15-0.20 m/s to be detectable, when considering environmental noise and background currents (from tide and mesoscale circulation). This limits the actual detection of tsunami currents to the near range, that is essentially to the continental shelf over which tsunami currents become strong enough; in many cases this does not leave enough time to issue an efficient warning, unless there is a wide shelf. In recent work, some of the authors have proposed a detection algorithm that does not have this limitation and can detect an approaching tsunami in deeper water, beyond the continental shelf. This algorithm does not require "inverting" currents, but instead is based on spatial correlations of the raw signals recorded at two distant radar cells along the same wave ray, shifted in time by the tsunami propagation time along the ray. An elevated correlation would indicate the presence of a tsunami. We apply this algorithm to a realistic tsunami case study conducted, using a state-of-the-art long wave model, for sources (both seismic and landslide) and bathymetry off of Vancouver Island, BC. The propagation time between different radar cells is calculated with a Geometrical Optics approach using the Eikonal equation. This requires first determining wave rays' intersections with radar cells and computing a connectivity matrix between the latter. A model simulating the radar backscattered signal in

  16. Simulation of synthetic aperture radar 4: Summary and recommendations

    NASA Astrophysics Data System (ADS)

    Crane, Peter M.; Bell, Herbert H.

    1990-04-01

    Four experiments were conducted to identify digital feature data base requirements for simulating synthetic aperture radar (SAR). The results indicate that lines of communication and large areal features are the principal cues used in SAR image interpretation. The results also indicate that depiction of small, individual features is required to create a simulation with acceptable realism. These small individual features may be depicted generically without adversely affecting SAR operator task performance. This approach has been proposed by the Defense Mapping Agency (DMA) as the basis for a new Digital Feature Analysis Data (DFAD) product (Level 3-C) to support high-resolution radar simulation. We recommend that the Air Force accept the proposed Level 3-C DFAD specification for SAR simulation.

  17. Miniature L-Band Radar Transceiver

    NASA Technical Reports Server (NTRS)

    McWatters, Dalia; Price, Douglas; Edelstein, Wendy

    2007-01-01

    A miniature L-band transceiver that operates at a carrier frequency of 1.25 GHz has been developed as part of a generic radar electronics module (REM) that would constitute one unit in an array of many identical units in a very-large-aperture phased-array antenna. NASA and the Department of Defense are considering the deployment of such antennas in outer space; the underlying principles of operation, and some of those of design, also are applicable on Earth. The large dimensions of the antennas make it advantageous to distribute radio-frequency electronic circuitry into elements of the arrays. The design of the REM is intended to implement the distribution. The design also reflects a requirement to minimize the size and weight of the circuitry in order to minimize the weight of any such antenna. Other requirements include making the transceiver robust and radiation-hard and minimizing power demand. Figure 1 depicts the functional blocks of the REM, including the L-band transceiver. The key functions of the REM include signal generation, frequency translation, amplification, detection, handling of data, and radar control and timing. An arbitrary-waveform generator that includes logic circuitry and a digital-to-analog converter (DAC) generates a linear-frequency-modulation chirp waveform. A frequency synthesizer produces local-oscillator signals used for frequency conversion and clock signals for the arbitrary-waveform generator, for a digitizer [that is, an analog-to-digital converter (ADC)], and for a control and timing unit. Digital functions include command, timing, telemetry, filtering, and high-rate framing and serialization of data for a high-speed scientific-data interface. The aforementioned digital implementation of filtering is a key feature of the REM architecture. Digital filters, in contradistinction to analog ones, provide consistent and temperature-independent performance, which is particularly important when REMs are distributed throughout a large

  18. Cognitive processing for nonlinear radar

    NASA Astrophysics Data System (ADS)

    Martone, Anthony; Ranney, Kenneth; Hedden, Abigail; Mazzaro, Gregory; McNamara, David

    2013-05-01

    An increasingly cluttered electromagnetic environment (EME) is a growing problem for radar systems. This problem is becoming critical as the available frequency spectrum shrinks due to growing wireless communication device usage and changing regulations. A possible solution to these problems is cognitive radar, where the cognitive radar learns from the environment and intelligently modifies the transmit waveform. In this paper, a cognitive nonlinear radar processing framework is introduced where the main components of this framework consist of spectrum sensing processing, target detection and classification, and decision making. The emphasis of this paper is to introduce a spectrum sensing processing technique that identifies a transmit-receive frequency pair for nonlinear radar. It will be shown that the proposed technique successfully identifies a transmit-receive frequency pair for nonlinear radar from data collected from the EME.

  19. The effect of plasma density structure on HF radio wave propagation at auroral and polar latitudes measured by e-POP

    NASA Astrophysics Data System (ADS)

    Perry, G. W.; James, H. G.; Gillies, R.; McWilliams, K. A.; St-Maurice, J. P.; Yau, A. W.

    2015-12-01

    One of the scientific objectives of the enhanced Polar Outflow Probe (e-POP) Radio Receiver Instrument (RRI) is to study ionospheric density structure and its impact on High Frequency (HF) radio wave propagation. We present a survey of several ePOP RRI transits through isolated beams of the Super Dual Auroral Radar Network (SuperDARN) Saskatoon and Rankin Inlet radars. It reveals that the spreading of a SuperDARN beam beyond its nominal azimuthal beam width of 3.24° is a common occurrence at auroral and polar latitudes. Furthermore, on multiple occasions, lateral deviations of a beam's power peak by several beam widths was measured, indicating the presence of significant plasma density gradients along the ray path. The e-POP RRI measurements illustrate that our understanding and recognition of plasma density gradients and their influence on HF radio wave propagation is limited. We report on the results of employing HF ray tracing techniques to quantify the impact of ionospheric structuring on HF radio wave propagation, and consider the source of the gradients contributing to the spreading of the SuperDARN beams.

  20. Radar-aeolian roughness project

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Dobrovolskis, A.; Gaddis, L.; Iversen, J. D.; Lancaster, N.; Leach, Rodman N.; Rasnussen, K.; Saunders, S.; Vanzyl, J.; Wall, S.

    1991-01-01

    The objective is to establish an empirical relationship between measurements of radar, aeolian, and surface roughness on a variety of natural surfaces and to understand the underlying physical causes. This relationship will form the basis for developing a predictive equation to derive aeolian roughness from radar backscatter. Results are given from investigations carried out in 1989 on the principal elements of the project, with separate sections on field studies, radar data analysis, laboratory simulations, and development of theory for planetary applications.