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1

Digital hf radar observations of equatorial spread-F  

SciTech Connect

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.

Argo, P.E.

1984-01-01

2

WAVE-DRIVEN SURFACE FROM HF RADAR  

E-print Network

FEATURE INTERNAL CURRENTS WAVE-DRIVEN SURFACE FROM HF RADAR By Lynn K. Shay Observations from-fre- quency (HF) radar have revealed that not only are the low-frequency and tidal currents resolved of the horizontal flow structure from HF radar pro- vides the spatial context for moored and ship- based

Miami, University of

3

Application of HF radar currents to oil spill modelling  

Microsoft Academic Search

In this work, the benefits of high-frequency (HF) radar currents for oil spill modeling and trajectory analysis of floating objects are analyzed. The HF radar performance is evaluated by means of comparison between a drifter buoy trajectory and the one simulated using a Lagrangian trajectory model. A methodology to optimize the transport model performance and to calculate the search area

Ana J. Abascal; Sonia Castanedo; Raul Medina; Inigo J. Losada; Enrique Alvarez-Fanjul

2009-01-01

4

Multifrequency HF radar observations of currents and current shears  

Microsoft Academic Search

Techniques have been developed for using high-frequency (HF) surface-wave radar to measure ocean currents and vertical current shears in the upper 1 or 2 m of the ocean surface. An HF radar can precisely measure the phase velocity and direction of propagation of ocean waves whose wavelength is one.half the radar wavelength. In the absence of a current, the speed

C. Teague

1986-01-01

5

Application of HF radar currents to oil spill modelling.  

PubMed

In this work, the benefits of high-frequency (HF) radar currents for oil spill modeling and trajectory analysis of floating objects are analyzed. The HF radar performance is evaluated by means of comparison between a drifter buoy trajectory and the one simulated using a Lagrangian trajectory model. A methodology to optimize the transport model performance and to calculate the search area of the predicted positions is proposed. This method is applied to data collected during the Galicia HF Radar Experience. This experiment was carried out to explore the capabilities of this technology for operational monitoring along the Spanish coast. Two long-range HF radar stations were installed and operated between November 2005 and February 2006 on the Galician coast. In addition, a drifter buoy was released inside the coverage area of the radar. The HF radar currents, as well as numerical wind data were used to simulate the buoy trajectory using the TESEO oil spill transport model. In order to evaluate the contribution of HF radar currents to trajectory analysis, two simulation alternatives were carried out. In the first one, wind data were used to simulate the motion of the buoy. In the second alternative, surface currents from the HF radar were also taken into account. For each alternative, the model was calibrated by means of the global optimization algorithm SCEM-UA (Shuffled Complex Evolution Metropolis) in order to obtain the probability density function of the model parameters. The buoy trajectory was computed for 24h intervals using a Monte Carlo approach based on the results provided in the calibration process. A bivariate kernel estimator was applied to determine the 95% confidence areas. The analysis performed showed that simulated trajectories integrating HF radar currents are more accurate than those obtained considering only wind numerical data. After a 24h period, the error in the final simulated position improves using HF radar currents. Averaging the information from all the simulated daily periods, the mean search and rescue area calculated using HF radar currents, is reduced by approximately a 62% in comparison with the search area calculated without these data. These results show the positive contribution of HF radar currents for trajectory analysis, and demonstrate that these data combined with atmospheric forecast models, are of value for trajectory analysis of oil spills or floating objects. PMID:18996546

Abascal, Ana J; Castanedo, Sonia; Medina, Raul; Losada, Inigo J; Alvarez-Fanjul, Enrique

2009-02-01

6

Digital Array Radar panel development  

Microsoft Academic Search

The Army Digital Array Radar (DAR) project's goal is to demonstrate how wide-bandgap semiconductor technology, highly-integrated transceivers, and the ever-increasing capabilities of commercial digital components can be leveraged to provide new capabilities and enhanced performance in future low-cost phased array systems. A 16-element, S-band subarray has been developed with panel-integrated, plastic-packaged gallium-nitride (GaN) amplifiers, multi-channel transceiver ICs, and digitization at

William Chappell; Caleb Fulton

2010-01-01

7

All-digital radar architecture  

NASA Astrophysics Data System (ADS)

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.

Molchanov, Pavlo A.

2014-10-01

8

HF Radar Sea-echo from Shallow Water  

PubMed Central

HF radar systems are widely and routinely used for the measurement of ocean surface currents and waves. Analysis methods presently in use are based on the assumption of infinite water depth, and may therefore be inadequate close to shore where the radar echo is strongest. In this paper, we treat the situation when the radar echo is returned from ocean waves that interact with the ocean floor. Simulations are described which demonstrate the effect of shallow water on radar sea-echo. These are used to investigate limits on the existing theory and to define water depths at which shallow-water effects become significant. The second-order spectral energy increases relative to the first-order as the water depth decreases, resulting in spectral saturation when the waveheight exceeds a limit defined by the radar transmit frequency. This effect is particularly marked for lower radar transmit frequencies. The saturation limit on waveheight is less for shallow water. Shallow water affects second-order spectra (which gives wave information) far more than first-order (which gives information on current velocities), the latter being significantly affected only for the lowest radar transmit frequencies for extremely shallow water. We describe analysis of radar echo from shallow water measured by a Rutgers University HF radar system to give ocean wave spectral estimates. Radar-derived wave height, period and direction are compared with simultaneous shallow-water in-situ measurements.

Lipa, Belinda; Nyden, Bruce; Barrick, Don; Kohut, Josh

2008-01-01

9

HF radar in French Mediterranean Sea: an element of MOOSE Mediterranean Ocean Observing System on Environment  

E-print Network

HF radar in French Mediterranean Sea: an element of MOOSE Mediterranean Ocean Observing System), the Mediterranean Institute of Oceanography is operating HF radars on the North Western Mediterranean coast of HF radars is to provide synoptic observation as sea surface current map every hour and over long

Boyer, Edmond

10

Results from UHF and HF Radar Studies of Ionospheric Interaction Experiments at HAARP  

Microsoft Academic Search

High power HF radiowave experiments have begun at the HAARP Ionospheric Research Observatory in Gakona, Alaska. The SuperDARN HF radar station in Kodiak, Alaska is now routinely employed to monitor HF backscatter from irregularities formed in the interaction volume over HAARP. A 16-panel prototype of a new UHF incoherent scatter radar facility, AMISR, has recently become operational on the HAARP

J. P. Sheerin; R. Ilie; E. L. Roesler; W. A. Bristow; B. J. Watkins; S. Oyama

2005-01-01

11

Mapping high-latitude plasma convection with coherent HF radars  

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

12

HF Doppler radar observations of low-latitude spread F  

Microsoft Academic Search

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

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

2009-01-01

13

Waveform design considerations for transmission of digital voice over HF  

Microsoft Academic Search

The development of digital voice (DV) technology has had a significant impact on high frequency (HF) voice communications. The secure features of DV in combination with the benefits of modern digital signal processing (i. e. equalization, narrow-band interference suppression, FEC, interleaving, etc) have provided users with some great advantages when communicating over challenging HF links. A new, higher quality, DV

John W. Nieto

2004-01-01

14

Simultaneous HF-radar and DMSP observations of the cusp  

NASA Technical Reports Server (NTRS)

The Geospace Environment Modeling (GEM) Program is directed toward modeling the coupled solar wind/magnetosphere/ionosphere system. The inter-calibration of ground-based observations of the ionosphere and satellite observations has been identified as an essential step in tying together the data to produce a global picture of geospace. On October 10, 1988 the DMSP-F9 satellite passed through the Southern Hemisphere cusp while a coheret scatter HF-radar was observing 10-m scale irregularities present in the ionosphere. The combined data indicate that these irregularities were being generated in the cusp, and that the cusp was a region of greater than normal electric field turbulence. The radar data indicate that the cusp was colocated with the region where the ionospheric convection rotated from sunward to anti-sunward with increasing latitude. These observations provide an unambiguous case where simultaneous satellite and ground-based observations of the cusp can be compared.

Baker, K. B.; Greenwald, R. A.; Ruohoniemi, J. M.; Dudeney, J. R.; Pinnock, M.

1990-01-01

15

UHF and HF Radar Studies of Langmuir Turbulence Experiments at HAARP  

Microsoft Academic Search

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

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

2007-01-01

16

UHF and HF Radar Studies of Langmuir Turbulence Experiments at HAARP  

Microsoft Academic Search

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

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

2006-01-01

17

Surface current measurements by HF radar over fresh water at Lake Michigan and Lake Tahoe  

Microsoft Academic Search

HF radar is widely used over salt water to measure surface currents, winds and waves. The authors report results over fresh water in Lakes Michigan and Tahoe. Although these pilot experiments were brief, they established that useful HF radar observations of surface currents can be obtained out to ranges of about 10 to 15 km with wave heights corresponding to

John F. Vesecky; Lorelle A. Meadows; Jason M. Daida; Peter E. Hansen; Calvin C. Teague; Daniel M. Fernandez; Jeffrey D. Paduan

1999-01-01

18

Assessment of WERA long-range HF-radar performance from the user's perspective  

Microsoft Academic Search

Since April 2006, long range (8.3MHz) WERA HF radars have been operated on the Southeastern United States coastline, as part of the U.S. Integrated Ocean Observing System (IOOS) and in particular the national HF Radar network. These radars measure currents operationally, and waves and winds experimentally across the wide continental shelf of Georgia (GA) and South Carolina (SC). Half-hourly data

D. Savidge; J. Amft; A. Gargett; M. Archer; D. Conley; G. Voulgaris; L. Wyatt; K.-W. Gurgel

2011-01-01

19

Architecture for a 1-GHz Digital RADAR  

NASA Technical Reports Server (NTRS)

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.

Mallik, Udayan

2011-01-01

20

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

E-print Network

HF radar observations of small-scale surface current variability in the Straits of Florida A. B-frequency Wellen radar (WERA), transmitting at 16.045 MHz, was deployed along the eastern Florida Shelf current measurements within the radar footprint along the shelf break at 86-m depth. The shallowest ADCP

Miami, University of

21

First in-situ measurements of HF radar echoing targets  

NASA Astrophysics Data System (ADS)

The sounding rocket Investigation of Cusp Irregularities 2 (ICI-2) was launched into the cusp ionosphere over Svalbard to investigate the production of decameter scale irregularities in the electron plasma associated with HF radar backscatter. The main mission objective was to obtain high-resolution measurements of decameter scale electron plasma irregularities and to quantify the growth rate for the gradient drift instability (GDI). At the 5.7 kHz sampling rate of the absolute density measurements, ICI-2 has provided the first documentation in terms of absolute electron density measurements of how 10-m structures are located on km scale electron density gradients. ICI-2 traversed a cusp electron density structure created by ongoing soft precipitation. 10-m scale irregularities were generated at km scale density gradients. The estimated growth time for the GDI process was 10-50 seconds.

Moen, J.; Oksavik, K.; Abe, T.; Lester, M.; Saito, Y.; Bekkeng, T. A.; Jacobsen, K. S.

2012-04-01

22

HF radar observations of surface circulation off Bodega Bay (northern California, USA)  

Microsoft Academic Search

Two high-frequency radar stations (CODAR) were installed along the northern California coast in May 2001. Comparisons of radar data with acoustic Doppler current profiler (ADCP) current data and near-surface drifter tracks indicate considerable agreement, with minimum RMS differences of order 0.05–0.15 m\\/s and average drifter-HF-radar track separation rates of 5 ± 3 km\\/d. Radar data resolve the three main sources

David M. Kaplan; John Largier; Louis W. Botsford

2005-01-01

23

Measuring rms Wave Height and the Scalar Ocean Wave Spectrum With HF Skywave Radar  

Microsoft Academic Search

Estimates of rms wave height and the scalar ocean wave frequency spectrum were made by inverting high-frequency (HF) skywave radar-measured sea-echo Doppler spectra. Whereas low-power surface- wave radars can make these measurements out to approximately 100 km from the radar, coverage out to 3000 km can be obtained with skywave radars that illuminate the sea via a single ionospheric reflection.

Joseph W. Maresca; T. M. Georges

1980-01-01

24

HF omnidirectional spectral CW auroral radar (HF-OSCAR) at very high latitude. Part 1: Technique  

NASA Astrophysics Data System (ADS)

An HF system for studies of very high latitude ionospheric irregularities was described. Radio aurora from field-aligned E-region irregularities of the Slant E Condition type were discussed. The complete system combines an ionosonde, a 12 MHz pulse radar and a 12 MHz bistatic CW Doppler-range set-up. The two latter units use alternately a 360 deg rotating Yagi antenna. High precision oscillators secure the frequency stability of the Doppler system in which the received signal is mixed down to a center frequency of 500 Hz. The Doppler shift range is max + or - 500 Hz. The received signal is recorded in analog form on magnetic tape and may be monitored visually and audibly. Echo range of the CW Doppler signal is obtained by a 150 Hz amplitude modulation of the transmitted signal and phase comparison with the backscattered signal.

Olesen, J. K.; Jacobsen, K. E.; Stauning, P.; Henriksen, S.

1983-12-01

25

The synthesis of travelling ionospheric disturbance (TID) signatures in HF radar observations using ray tracing  

E-print Network

The synthesis of travelling ionospheric disturbance (TID) signatures in HF radar observations using-time-intensity plots when travelling ionospheric disturbances (TIDs) are present. These signatures, in particular- iments. Key words. Ionosphere (auroral ionosphere; ionosphere ±atmosphere interactions; ionospheric

Paris-Sud XI, Université de

26

Persistent enhancement of the HF pump-induced plasma line measured with a UHF diagnostic radar at HAARP  

Microsoft Academic Search

Plasma lines excited by a powerful, high-frequency (HF) radio wave are studied using data obtained with an ultrahigh frequency (UHF) radar at HAARP (High Frequency Active Auroral Research Program) from 3 to 5 February 2005. Of particular interest is persistent enhancement of the radar backscatter power during HF on at several HF frequencies. The persistent enhancement is induced with the

S. Oyama; B. J. Watkins; F. T. Djuth; M. J. Kosch; P. A. Bernhardt; C. J. Heinselman

2006-01-01

27

Mesosphere summer echoes observed with the SuperDARN Hokkaido HF radar at Rikubetsu, Japan (43.5°N)  

NASA Astrophysics Data System (ADS)

Using the SuperDARN Hokkaido HF radar located at Rikubetsu in Hokkaido, Japan (43.5°N), we present first oblique-incidence observations of midlatitude mesosphere summer echoes (MSE) at the HF band (HF-MSE). Three HF-MSE events in June 2009 are case-studied. Analyses of HF-MSE data together with VHF and MF radar data obtained at Wakkanai, 260 km northwest of Rikubetsu, indicate the following: (1) in two events HF-MSE were accompanied by MSE at VHF (VHF-MSE), and in one event only HF-MSE were observed. (2) In accordance with southward neutral winds observed with the MF radar, HF-MSE exhibited high Doppler velocities with a maximum of about 60 m/s toward the south, and also HF-MSE regions moved southward with time, suggesting that irregularities and/or cold ice particles responsible for the radar wave scattering might be advected southward from higher latitudes.

Ogawa, Tadahiko; Nishitani, Nozomu; Kawamura, Seiji; Murayama, Yasuhiro

2013-12-01

28

Marrying quantitative and graphic tidal analysis tools with HF radar current map outputs  

Microsoft Academic Search

Separating off the tidal portion of flow from measured data and resolving into its individual constituents is an important part of coastal oceanographic analyses. HF radar surface-current maps taken hourly over many weeks or months offer a wealth of tidal information. Recent findings by several groups - based on HF current maps - show striking relations for the M2 tidal

D. Barrick; D. James; J. Isaacson

2003-01-01

29

Near-Real Time Quality Control of surface current maps from High-Frequency (HF) radars  

NASA Astrophysics Data System (ADS)

A method for real-time quality control and despiking of sea surface current maps from High-Frequency (HF) SeaSonde radars based on the Signal-to-Noise ratios of the Doppler velocities from individual radar stations is proposed and discussed. Benefits of using a conservative weighted least-squares versus a more traditional least-squares approach for the total vector derivation are demonstrated on a network of radars operating in the Northern Adriatic Sea

Cosoli, S.; Bolzon, G.

2009-04-01

30

Simulation and detection of tsunami signatures in ocean surface currents measured by HF radar  

NASA Astrophysics Data System (ADS)

High-frequency (HF) surface wave radars provide the unique capability to continuously monitor the coastal environment far beyond the range of conventional microwave radars. Bragg-resonant backscattering by ocean waves with half the electromagnetic radar wavelength allows ocean surface currents to be measured at distances up to 200 km. When a tsunami propagates from the deep ocean to shallow water, a specific ocean current signature is generated throughout the water column. Due to the long range of an HF radar, it is possible to detect this current signature at the shelf edge. When the shelf edge is about 100 km in front of the coastline, the radar can detect the tsunami about 45 min before it hits the coast, leaving enough time to issue an early warning. As up to now no HF radar measurements of an approaching tsunami exist, a simulation study has been done to fix parameters like the required spatial resolution or the maximum coherent integration time allowed. The simulation involves several steps, starting with the Hamburg Shelf Ocean Model (HAMSOM) which is used to estimate the tsunami-induced current velocity at 1 km spatial resolution and 1 s time step. This ocean current signal is then superimposed to modelled and measured HF radar backscatter signals using a new modulation technique. After applying conventional HF radar signal processing techniques, the surface current maps contain the rapidly changing tsunami-induced current features, which can be compared to the HAMSOM data. The specific radial tsunami current signatures can clearly be observed in these maps, if appropriate spatial and temporal resolution is used. Based on the entropy of the ocean current maps, a tsunami detection algorithm is described which can be used to issue an automated tsunami warning message.

Gurgel, Klaus-Werner; Dzvonkovskaya, Anna; Pohlmann, Thomas; Schlick, Thomas; Gill, Eric

2011-10-01

31

Ground backscatter characteristics model for SuperDARN Hokkaido HF radar  

NASA Astrophysics Data System (ADS)

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-? and 14-05-00588-?).

Oinats, Alexey; Nishitani, Nozomu; Ratovsky, Konstantin

32

Frequency and power dependency of HF-induced ionization signatures in incoherent scatter radar observations  

NASA Astrophysics Data System (ADS)

Incoherent scatter radar observations of high-power HF radio-wave induced enhancements in backscatter from ion-acoustic and plasma waves have been observed with the EISCAT UHF radar during Heating experiments where the pump-frequency passed through the 3rd and 4th harmonic of the electron gyro-frequency. The altitude-variation of the enhancement indicate an asymmetry in HF-induced ionization between pump-frequencies below and above a gyro-resonance. Models for ionospheric electron density response to ionization from HF-accelerated electrons is compared to the very precise observations of the altitude variation of the matching-altitudes. Optical observations of radio induced optical emissions are used to determine the electron acceleration by HF-radio waves.

Gustavsson, Bjorn; Sergienko, Tima; Rietveld, Michael; Brandstrom, Urban; Senior, Andrew; Vickers, Hannah; Kosch, Michael

33

A frequency averaging method to improve sea-state measurements with an HF skywave radar  

Microsoft Academic Search

A frequency averaging method which can improve the quality of averaged spectra of HF signals scattered by the sea is described. The method is compared to the classical single-frequency pulse-radar. Using the skywave radar of Valensole, France, the statistical independence of signals scattered by the sea at close frequencies is experimentally verified. Spectra of signals reflected by an F2 ionospheric

Jacques Parent

1987-01-01

34

HF Radar Performance on a Low Energy Environment as Found Using CODAR SeaSonde on the West Florida Shelf  

NASA Astrophysics Data System (ADS)

A network of three CODAR (Coastal Ocean Dynamics Application Radar) SeaSonde HF radars operating at 4.925 MHz has operated on the West Florida Shelf since 2003. HF Radar performance is evaluated in terms of percentage of data returns and RMS differences between the HF radar radial currents and an array of velocity measurements by moored acoustic Doppler current profilers (ADCP). Temporal variation of the radial current coverage is described and possible factors affecting the HF radar observations on this low energy (current and wave) shelf are discussed. Despite the challenge of achieving more backscatter from this low energy shelf, the data quality is good when the acquired HF radial currents are compared with the ADCP top bins. The RMS difference is in the range of 6 - 11 cm/s for hourly and 3 - 6 cm/s for 36-hour low-pass filtered radial currents, respectively.

Liu, Y.; Merz, C. R.; Weisberg, R. H.

2008-12-01

35

Design and applications of a versatile HF radar calibration target in low Earth orbit  

NASA Astrophysics Data System (ADS)

High frequency (HF) radars are used to detect ionospheric irregularities, meteor trails, and moving targets. The Precision Expandable Radar Calibration Sphere (PERCS) is a simple radar target in space to help determine the operational parameters of ground HF radars. PERCS will have a known radar cross section that is independent of observation direction within 0.5 dB. The PERCS satellite can be launched in a stowed configuration that has about 1 m in diameter. After launch, the PERCS will expand to a diameter of almost 10 m. Upon expansion, a stable wire frame is formed to act as a radar scatter target in the form of a polyhedral sphere. The simplest version of the sphere has 60 vertices (V60) that are joined to 90 rigid segments. Each segment is hinged so that the PERCS can be folded into a compact package for launch. Analysis of the V60 wire frame with a 10 m diameter shows that the radar cross section (RCS) is nearly independent of viewing angle up to 30 MHz. Another design with 240 vertices produces even better performance. Radar systems will be calibrated using the radar echo data and the precise knowledge of the target RCS, position, and velocity. The PERCS can reflect radar signals from natural targets such as field aligned and current driven irregularities not presently accessible from ground-based radars. The wire frame structure has several advantages over a metalized spheroid "balloon" with (1) much less drag, (2) larger radar cross section, and (3) lower fabrication cost.

Bernhardt, Paul A.; Siefring, Carl L.; Thomason, Joe F.; Rodriquez, Serafin P.; Nicholas, Andrew C.; Koss, Steven M.; Nurnberger, Mike; Hoberman, Chuck; Davis, Matthew; Hysell, David L.; Kelley, Michael C.

2008-02-01

36

Finland HF and Esrange MST radar observations of polar mesosphere summer echoes  

E-print Network

Finland HF and Esrange MST radar observations of polar mesosphere summer echoes Tadahiko Ogawa1/000061 Offset requests to: T. Ogawa Solar­Terrestrial Environment Laboratory Nagoya University, Japan #12;AG Ogawa1 , Neil F. Arnold2 , Sheila Kirkwood3 , Nozomu Nishitani1 , and Mark Lester2 1 Solar

Kirkwood, Sheila

37

Data assimilation of partitioned HF radar wave data into Wavewatch III  

NASA Astrophysics Data System (ADS)

In this study the assimilation of HF radar data into a high resolution, coastal Wavewatch III model is investigated. An optimal interpolation scheme is used to assimilate the data and the design of a background error covariance matrix which reflects the local conditions and difficulties associated with a coastal domain is discussed. Two assimilation schemes are trialled; a scheme which assimilates mean parameters from the HF radar data and a scheme which assimilates partitioned spectral HF radar data. This study demonstrates the feasibility of assimilating partitioned wave data into a coastal domain. The results show that the assimilation schemes provide satisfactory improvements to significant wave heights but more mixed results for mean periods. The best improvements are seen during a stormy period with turning winds. During this period the model is deficient at capturing the change in wave directions and the peak in the waveheights, while the high sea state ensures good quality HF radar data for assimilation. The study also suggests that there are both physical and practical advantages to assimilating partitioned wave data compared to assimilating mean parameters for the whole spectrum.

Waters, Jennifer; Wyatt, Lucy R.; Wolf, Judith; Hines, Adrian

2013-12-01

38

Surface circulation in the Iroise Sea (W. Brittany) from high resolution HF radar mapping  

E-print Network

Surface circulation in the Iroise Sea (W. Brittany) from high resolution HF radar mapping Alexei available. Refined resolution enabled to iden- tify fine-scale structures of surface circulation spatial intermittence in polarization of the tidal current ellipses. The analyzed data span two month

39

HF Stimulated Electromagnetic Emissions and radar observations of ionospheric heating from HAARP  

Microsoft Academic Search

High power radio waves excite electrostatic waves in the ionosphere. Electrostatic waves can be detected either by mode conversion into Stimulated Electromagnetic Emission (SEE) or scatter of radar signals. We present the results of SEE observations conducted through high-power HF heating experiments at the High-Frequency Active Auroral Research Program. Multiple receiving instruments have been used to observe many low frequency

S. J. Briczinski; P. A. Bernhardt; C. A. Selcher; B. J. Watkins

2011-01-01

40

HF Radar Observation of Wave Directional Spectra in a Strong Current Regime  

Microsoft Academic Search

Dual Wellen HF Radar (WERA) systems have been observing near-surface currents and wave parameters over the Southeast Florida shelf since June 2004 as a part of the Southeast Atlantic Coastal Ocean Observing System (SEACOOS). The region of coverage includes the Florida Straits and the Florida Current (FC) which typically has maximum surface velocities approaching 2 ms\\

Brian K. Haus; Mei Wang; L. K. Shay; L. R. Wyatt

2007-01-01

41

Digital Beamforming Synthetic Aperture Radar (DBSAR) Polarimetric Upgrade  

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

42

Ionospheric Cusp Polar Cap phenomena of particular relevance for generation of HF radar backscatter targets (Invited)  

NASA Astrophysics Data System (ADS)

High density polar cap patches are associated with enhanced backscatter power observed by the SuperDARN HF radars. How decametre scale HF radar echoing targets form is still a matter of debate. The Gradient Drift Instability (GDI) is usually regarded as the dominant mode for generating HF backscatter irregularities in the F-region cusp ionosphere. However, observations by EISCAT Svalbard Radar indicate that reversed flow events (RFEs), 100-200 km wide flow channels opposing the background convection, occur up to 40% of the time near the cusp inflow region. Here we present the first documentation of the RFE phenomenon by SuperDARN. When the RFE flow disturbance expands in longitude there is an immediate response in enhanced level of backscatter power, to within the one minute resolution of the radar. This gives experimental support to the new idea that the Kelvin-Helmholtz Instability (KHI) forms 0.1-10 km seed structures on which other instabilities like the GDI can operate more efficiently. However, high-resolution in-situ measurements by sounding rockets are really needed to reliably evaluate the relative importance of various plasma instability modes. The first results from the ICI-2 sounding rocket launched from Svalbard 5 December 2008 will be presented. The payload was equipped with Langmuir probes, AC and DC electric field experiment, plasma wave experiment, particle spectrometers for electrons (10 eV-10keV & >30keV) and ions (>30 keV). It intersected 3 regions of HF backscatter during its 10 min flight reaching an apogee of 330 km. With University of Oslo’s novel multi-Needle Langmuir probe experiment we performed absolute electron density measurements of decametre scale HF backscatter targets. Each HF backscatter region was associated with an inverted V precipitation region which opens for current driven instabilities.

Moen, J.

2009-12-01

43

Rates of scattering occurrence in routine HF radar observations during solar cycle maximum  

NASA Astrophysics Data System (ADS)

The HF radars of the Super Dual Auroral Radar Network (SuperDARN) provide continuous monitoring of the high-latitude ionosphere over large areas in both the northern and southern hemispheres. The HF technique generates estimates of the E×B convective drift of ionospheric plasma when suitable small-scale (˜10 m) irregularities are present and viewed under favorable magnetic aspect conditions (radar k vector ? to B). In this paper we report on the statistics of HF scattering occurrence. The study period encompasses 5.5 years (1988 to mid-1993) of routine observations with the HF radar located at Goose Bay, Labrador, Canada, and corresponds to the most recent period of solar cycle maximum. The data were carefully filtered for those instances when high-confidence F region velocity measurements were obtained within 1°×3° magnetic latitude/longitude regions and 12-min UT intervals. For average conditions the rates at which scatter occurred at particular values of invariant latitude ranged from <10% to >40% with MLT. The probability of making velocity measurements somewhere in the radar field of view varied from ˜80% on the nightside to ˜45% on the noon meridian. When scatter was detected, the average latitudinal coverage varied from a minimum of 4° ? on the dayside to over 6° ? on the nightside. There were significant dependencies on Kp and season. The highest occurrence rates (>60%) were obtained on the nightside for quiet conditions and in the afternoon for disturbed conditions. Winter was the most active season. HF scattering was limited by the equatorward boundary of the Feldstein oval but extended poleward of the oval into the polar cap. Scattering in the noon sector was associated with the aggregate cusp/mantle/low-latitude boundary layer region. The scattering activity was notably suppressed in the morning sector under disturbed conditions and in the noon and afternoon sectors in summer. We discuss the geophysical factors that influence the likelihood of generating HF scatter. These results have value for the design of experiments involving the SuperDARN HF radars.

Ruohoniemi, J. M.; Greenwald, R. A.

1997-05-01

44

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

NASA Astrophysics Data System (ADS)

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 local radio frequency allocation authorities, assuming just a single frequency is used at a time. Alternatively, one may choose four to eight frequencies operating simultaneously, to allow the clearest channel and best signal strength channel for enhanced processing. We will discuss the tradeoffs on multiple frequency use versus single optimum frequency use, both using a multi-frequency radar capability. Results of preliminary testing of a prototype system at Duck, NC will also be presented.

Trizna, D. B.

2007-05-01

45

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

NASA Astrophysics Data System (ADS)

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.

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

1985-12-01

46

The use of digital RF memories in radar signal processing  

NASA Astrophysics Data System (ADS)

This paper describes the use that may be made of Digital RF Memories in developing and evaluating new radar systems. It outlines the basic DRFM technology showing how a DRFM works and the sort of performance that may be expected. The application of this technology to radar is then discussed showing the advantages that may be obtained through the use of coherent digital IF processing. Finally some experimental DRFM based radar configurations are described illustrating the results that have been achieved and the implications that these might have on future radar systems.

Clark, D. G. D.; Ingram, P. M.

47

Ion acoustic HF radar echoes at high latitudes and far ranges  

NASA Astrophysics Data System (ADS)

Using data taken over 18 months with the Iceland East (CUT-LASS/Iceland) Super Dual Auroral Radar Network (SuperDARN) HF radar we have made a statistical study of a class of echoes which occur at ranges typically associated with F region echoes, but which have Doppler speeds near the ion acoustic speed Cs typical of E region echoes [Milan et al., 1997]. Comparison of the seasonal, diurnal, and range distributions of these echoes with the predictions of propagation models show that these are, indeed, E region echoes, differing in morphology from similar echoes at nearer ranges mainly because of the propagation conditions which are required to observe them. For the particular radar geometry of this study, conventional theory predicts that the effects of ionospheric gradients will result in phase velocities (radar Doppler velocities) which differ significantly from Cs, in disagreement with these observations. However, the observations are consistent with a new nonlinear theory of St.-Maurice and Hamza [2001].

Lacroix, P. J.; Moorcroft, D. R.

2001-12-01

48

Observations of very high latitutde ionospheric irregularities with the Good Bay HF radar  

NASA Astrophysics Data System (ADS)

The Goose Bay HF radar is a sophisticated instrument capableof 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 ocation 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. Initial results with a single phased array antenna which represent typical examples of the spatial intensity distribution of these irregularities at different local times are presented. Examples of Doppler spectra of the irregularities at different local times are given. 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.

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

1985-11-01

49

Assimilation of HF radar surface currents to optimize forcing in the northwestern Mediterranean Sea  

NASA Astrophysics Data System (ADS)

HF radar measurements are used to optimize surface wind forcing and baroclinic open boundary condition forcing in order to constrain model coastal surface currents. This method is applied to a northwestern Mediterranean (NWM) regional primitive equation model configuration. A new radar data set, provided by two radars deployed in the Toulon area (France), is used. To our knowledge, this is the first time that radar measurements of the NWM Sea are assimilated into a circulation model. Special attention has been paid to the improvement of the model coastal current in terms of speed and position. The data assimilation method uses an ensemble Kalman smoother to optimize forcing in order to improve the model trajectory. Twin experiments are initially performed to evaluate the method skills. Real measurements are then fed into the circulation model and significant improvements to the modeled surface currents, when compared to observations, are obtained.

Marmain, J.; Molcard, A.; Forget, P.; Barth, A.; Ourmières, Y.

2014-06-01

50

Observations of the broadening and coherence of MF\\/lower HF surface-radar ocean echoes  

Microsoft Academic Search

Known broadening mechanisms for the first-order Bragg peaks in high-frequency (HF: 3-30 MHz) and very-high-frequency (VHF: 30-300 MHz) Doppler spectra of radar echoes from the sea surface are summarized. Observations of medium-frequency (MF: 0.3-3 MHz)\\/lower HF sea echoes were made with a surface-wave phased-antenna array transmitting Gaussian pulses of width ≈40 and 70 ?s at frequencies 1.98, 3.84, and 5.80

Murray L. Parkinson

1997-01-01

51

DIGITAL VISION he advent of phased array radars and space-time adaptive processing has given radar  

E-print Network

© DIGITAL VISION T he advent of phased array radars and space-time adaptive processing has given radar designers the ability make radars adaptable on receive. The current state of radar technolo- gy of pairs of complementary sequences. Shortly thereafter, Welti proposed to use Golay sequences in radar

Nehorai, Arye

52

Surface water circulation patterns in the southeastern Bay of Biscay: New evidences from HF radar data  

NASA Astrophysics Data System (ADS)

High frequency (HF) radar stations have been working operationally in the southeastern part of the Bay of Biscay since 2009. The (2) systems provide hourly surface currents, with 5 km spatial resolution and a radial coverage lying close to 180 km. The detailed and quantitative description of the spatial patterns observed by the HF radar offers new evidence on the main ocean processes, at different time scales, affecting a study area where surface currents show marked temporal and spatial variability. A clear seasonality in terms of sea surface currents and along-slope circulation is observed, with cyclonic and anticyclonic patterns during the winter and summer months, respectively. From the analysis of low-pass filtered currents, a key component of this seasonal variability is associated with the surface signature of the slope current (Iberian Poleward Current (IPC)). Clearly intensified over the upper part of the slope, this current circulates eastward off the Spanish coast and northward over the French shelves in winter.

Solabarrieta, Lohitzune; Rubio, Anna; Castanedo, Sonia; Medina, Raúl; Charria, Guillaume; Hernández, Carlos

2014-02-01

53

Trajectory prediction using HF radar surface currents: Monte Carlo simulations of prediction uncertainties  

Microsoft Academic Search

An important aspect of particle trajectory modeling in the ocean is the assessment of the uncertainty in the final particle position. Monte Carlo particle trajectory simulations using surface currents derived from standard-range and long-range CODAR HF radar systems were performed using random-walk and random-flight models of the unresolved velocities. Velocity statistics for these models were derived from the covariance functions

David S. Ullman; James O'Donnell; Josh Kohut; Todd Fake; Arthur Allen

2006-01-01

54

The first in-situ observations of echoing HF radar backscatter targets  

NASA Astrophysics Data System (ADS)

The first direct measurements of HF-backscatter echoing electron density structures were conduced by the ICI-2 sounding rocket launched into the cusp ionosphere over Svalbard 5 December 2008. The echoing targets for coherent HF radars are 10-m scale electron density structures, half the operating radar wave length. Descending from ~300-200 km altitude, ICI-2 traversed volumes of HF backscatter detected by the CUTLASS radar, near the poleward boundary of the active cusp. ICI-2 carried a novel 4-Needle Langmuir Probe system capable to measure absolute electron density at 5.7 kHz sampling rate which means sub-meter resolution along the trajectory. The payload was also equipped with a high resolution electron spectrometer to resolve fine scale structures in the cusp auroral precipitation, and it carried an electric field experiment to measure the plasma drift surrounding the space craft. The 10-m plasma irregularities were observed near the trailing edge of km scale gradients in the electron density, which is in favour of the gradient drift instability. The electron density gradients on which the gradient drift instability could operate were apparently modulated by the electron precipitation. Furthermore, plasma structuring also occurred near the centre of the inverted V electron beam, indicating that a current driven instability process is also to be considered.

Moen, J. I.; Oksavik, K.; Abe, T.; Lester, M.; Saito, Y.; Bekkeng, J. K.; Jacobsen, K. S.; Bekkeng, T. A.

2010-12-01

55

A digital leakage cancellation scheme for monostatic FMCW radar  

Microsoft Academic Search

A novel heterodyne scheme based on real-time digital signal processing is proposed for leakage cancellation in monostatic frequency modulated continuous wave (FMCW) radars. Compared to conventional analog implementation, the advantages of the proposed scheme include that the DC offset existing in analog mixers affecting the cancellation performance are eliminated. A radar test bed at 26 GHz has been built. The

Kaihui Lin; Razmig Hagop Messerian; Yuanxun Wang

2004-01-01

56

Digitized dual wavelength radar data from a Texas thunderstorm  

E-print Network

DIGITIZED DUAL WAVL'LENGTH RADAR DATA FROM A TEXAS THUNDERSTORM A Thesis ROBIN ANN RADLEIN Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirement for the degree ol MASTER OF SCIENCE December 1977... Major Suhiect: Meteorology DTGlTTZED DUAL WAVELENGTH RADAR DATA FROM A TEXAS THUNDERSTORM A Thesis Approved as to style and content by: (Chairman of Co ' ee l. g. (Head of Departmen (Member ) (Member) Dece~'ber 1977 ABSTRACT Digitized Dual...

Radlein, Robin Ann

1977-01-01

57

An airborne digital processor for radar scatterometer data  

E-print Network

AN AIRBORNE DIGITAL PROCESSOR FOR RADAR SCATTEROMETER DATA A Thesis by DAVID STEVEN YEADON Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August 1977... Major Subject: Electrical Engineering AN AIRBORNE DIGITAL PROCESSOR FOR RADAR SCATTEROMETER DATA A Thesis by DAVID STEVEN YEADON Approved as to style and content by: (Chairman o Committee) Head of epartment) ( (Member ) (Member) August 1977...

Yeadon, David Steven

1977-01-01

58

Digital meteorological radar data compared with digital infrared data from a geostationary meteorological satellite  

E-print Network

DIGITAL METEOROLOGICAL RADAR DATA COMPARED WITH DIGITAL INFRARED DATA FROM A GEOSTATIONARY METEOROLOGICAL SATELLITE A Thesis by RODNEY STUART HENDFRSON Submitted to the Graduate College of Texas A&M University in partial fulfillment... of the requirement for the degree of MASTER OF SCIFNCE May I979 Ma jor Subject: Meteorology DIGITAL METEOROLOGICAL RADAR DATA COMPARED WITH DIGITAL INFRARED DATA FROM A GEOSTATIONAFY METEOROLOGICAL SATELLITE A Thesis by RODNEY STUART HENDERSON Approved...

Henderson, Rodney Stuart

1979-01-01

59

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

NASA Astrophysics Data System (ADS)

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 related with the external forcing, and bathymetry distribution, according to coastal or open ocean data.

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

2014-05-01

60

Radio science issues surrounding HF/VHF/UHF radar meteor studies  

NASA Astrophysics Data System (ADS)

Classical meteor radars depend on coherent (Fresnel) scattering from a meteor trail oriented perpendicular to the radar wave vector at closest approach to the radar. Meteor trails viewed in this manner are described as ``classical'' radar meteors with under/over-dense trails. While meteor ``head-echoes'' are rarely seen with classical low-power, wide-beam HF meteor radars, they are essentially always seen by large aperture (narrow-beam), high-power VHF/UHF radars. We discuss the expected radar scattering cross-sections (RCSs) of head-versus trail-echoes and how equilibrium concepts such as plasma frequency are of limited use in describing the results. Particular attention is given to the frequency dependence of the RCS and how the frequency dependence may yield considerable new information regarding the plasma distribution in the ``coma'' surrounding the meteoroid. As the head-echo is directly associated with the meteoroid, instantaneous (single-pulse) Doppler observations are possible. In the case of classical trail-echoes, the time evolution of the RCS as a function of frequency may provide new information on the plasma diffusion rate and thus on atmospheric density and temperature. Information from the time evolution of the trail must however be considered in light of new results showing that the trail rapidly B-field-aligns in a manner apparently driven by plasma instabilities that develop in 10-100ms after trail deposition. It is in the context of instability-driven B-field alignment of the trails that we discuss anomalous trail-echoes. The anomalous trail-echo is a range-spread chaotic (non-classical) trail-echo derived from a meteor that travels at an arbitrary angle relative to the radar wave vector. We present theoretical simulations illustrating these concepts.

Mathews, J. D.

2004-02-01

61

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

SciTech Connect

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.

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

1994-03-01

62

Digital vs. optical techniques in synthetic aperture radar data processing  

Microsoft Academic Search

The basic aspects of synthetic aperture radar image formation are reviewed. The required processing consists of a two-dimensional matched filtering operation which can be implemented either optically or digitally. An examination of the standard tilted-plane optical processing approach reveals that the required procedure can be performed in a conceptually simple, yet elegant, manner. The less mature digital technology can also

D. A. Ausherman

1977-01-01

63

Determination of ionospheric parameters in real time using SuperDARN HF Radars  

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

64

Long-term observations of meteor winds by the SuperDARN HF radar network  

NASA Astrophysics Data System (ADS)

The HF Super Dual Auroral Radar Network (SuperDARN) radars detect a category of backscatter that is due to meteor trails in the mesosphere. The motion of the neutral atmosphere can be inferred and applied to the study of atmospheric tides and planetary waves. The current configurations of longitudinal radar chains in the northern and southern hemispheres have accumulated mesospheric wind measurements continuously since the last solar cycle maximum while the archives of some of the radars span more than a solar cycle. We have analyzed the occurrence of mesospheric tides, planetary wave, and gravity wave activity in the meteor wind data over long periods at several radar stations in both hemispheres. Understanding the behavior of planetary waves and tides is not only crucial to characterizing mesopause variability but also transport in the mesosphere and lower thermosphere. in the mesosphere and lower thermosphere. We examine the seasonal and inter-annual variations of the diurnal, semidiurnal and terdiurnal tides, and planetary waves. We find connections to the quasi-biennial oscillation and to sudden stratospheric warming (SSW) events. We present examples of intensified planetary wave activity that occurred during SSWs. Additionally, we examine the variability in tidal and planetary wave activity over the past solar cycle and correlations with lower atmospheric phenomena and other datasets.

Talaat, Elsayed; Ruohoniemi, J. Michael; McCubbin, Elizabeth; Azeem, S. M. Irfan; Greenwald, Raymond

2012-07-01

65

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

NASA Astrophysics Data System (ADS)

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).

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

66

Simulation of radar returns from land using a digital technique  

NASA Astrophysics Data System (ADS)

For some time, radar echo simulators have been employed in the training of naval and air personnel. A solely digital method was developed in connection with the requirement to provide simulators for highly mobile airborne radars in which terrain has to be mapped in three dimensions. The resulting land simulator package is linked to the target echo generator hardware and a host computer. The developed procedure is also readily adaptable for the simulation of weather and chaff corridor effects. Attention is given to the reasons for considering a solely digital method, an outline of the digital method, details of simulator operation, sea clutter, limitations of the simulator, and clouds and chaff corridors.

Morgan, J. R.; Sherlock, P. E.; Hill, D. J.

67

HF radar observations of temporal variations in the high latitude convection  

NASA Astrophysics Data System (ADS)

Coherent HF radars are presently in operation at Goose Bay and Schefferville (Canada) to study the convection in the high latitude ionosphere. From the line of sight components of the plasma velocity measured by beach radar over a common field of view nearly instantaneous maps of the two dimensional plasma flow are obtained over the auroral zone and the polar cap. These maps have a time resolution of a few minutes. They drift in MLT with the Earth rotation. From a time series of such convection maps, the variation with universal time (UT) of the latitudinal velocity profile at a fixed MLT are obtained. These represent 'true' UT time variations of the convection. Examples of such variations are shown.

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

68

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

NASA Astrophysics Data System (ADS)

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.

Matthews, John Philip; Yoshikawa, Yutaka

2012-09-01

69

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

SciTech Connect

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.

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

1985-06-07

70

GPS ionospheric scintillation and HF radar backscatter - A comparison between GISTM network and SuperDARN at high latitudes  

NASA Astrophysics Data System (ADS)

The occurrence of GPS ionospheric scintillation at high latitudes over Scandinavia in 2003 and 2008 is compared with the occurrence of HF radar backscatter from field-aligned irregularities as a function of magnetic local time and geomagnetic latitude for the same two years. The scintillation was observed using GPS Ionospheric Scintillation and TEC Monitors (GISTM) included in a network extending from high to mid latitudes. Both the HF radar backscatter and GPS scintillation predominantly occur in the night portion of the auroral oval and the ionospheric footprint of the cusp. Data subsets for geomagnetically quiet and disturbed periods show the expected shift in latitude of the ionospheric regions both in the occurrence of phase scintillation and the HF radar backscatter from ionospheric irregularities.

Prikryl, Paul; Spogli, Luca; Alfonsi, Lucilla; Romano, Vincenzo; Aquino, Marcio

2010-05-01

71

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

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

72

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

NASA Astrophysics Data System (ADS)

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, with an intense poleward circulation over the slope during winter and weaker equatorward currents during summer. Recurrent mesoscale structures and high frequency processes (i.e. barotropic tides and inertial currents) add spatial and temporal complexity to this global scheme.;

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

2012-12-01

73

Propagating tsunami wave and subsequent resonant response signals detected by HF radar in the Kii Channel, Japan  

Microsoft Academic Search

Signals from the tsunami waves induced by the March 11, 2011 moment magnitude (Mw) 9.0 Tohoku-Oki earthquake and from subsequent resonances were detected as radial velocity variability by a high-frequency ocean surface radar (HF radar) installed on the eastern coast of the Kii Channel, at a range of about 1000 km from the epicenter along the eastern to southern coasts of

Hirofumi Hinata; Satoshi Fujii; Keita Furukawa; Tomoya Kataoka; Masafumi Miyata; Takashi Kobayashi; Masahiro Mizutani; Takahiro Kokai; Nobuyoshi Kanatsu

2011-01-01

74

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

SciTech Connect

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.

Blanc, E.; Mercandalli, B. [Laboratorie de Detection et de Geophysique, Bruyeres le Chatel (France)] [Laboratorie de Detection et de Geophysique, Bruyeres le Chatel (France); Houngninou, E.

1996-03-15

75

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

Microsoft Academic Search

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

Belinda Lipa; Donald Barrick

1980-01-01

76

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

NASA Technical Reports Server (NTRS)

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.

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

77

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

78

The digital processing of Seasat synthetic aperture radar data  

Microsoft Academic Search

An experimental digital Seasat synthetic aperture radar (SAR) processor is described which overcomes such defects of present systems as small dynamic range, low resolution of film recordings, optical systems light diffusion and difficulties in automatic focusing. The main problem to be overcome in the design of a spaceborne SAR data processor is range migration, in which the slant angle variations

J. R. Bennett; I. G. Cumming; R. A. Deane

1980-01-01

79

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. ...

80

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...

81

The potential of bistatic HF surface wave radar system for the surveillance of water-entry area along coastline  

Microsoft Academic Search

A bistatic\\/monostatic HF surface wave radar (HFSWR) experiment was conducted using both the transmit and receive systems of the HFSWR at Cape Race, Newfoundland and the receive system of the HFSWR at Cape Bonavista, Newfoundland. While the HFSWR at Cape Race operated in the monostatic mode, the transmitter at Cape Race and the receiver at Cape Bonavista were synchronized via

H. Leong

2006-01-01

82

A relaxation method for integral inversion applied to HF radar measurement of the ocean wave directional spectrum  

Microsoft Academic Search

The Chahine-Twomey relaxation method for inversion of the atmospheric radiative transfer equation is extended to provide an inverse solution to Barrick's equation describing second order scatter of high frequency (HF) radio waves from the ocean surface. The success of the method is demonstrated here using synthesised radar Doppler spectra obtained by solving the direct problem with wave buoy directional spectrum

LUCY R. WYATT

1990-01-01

83

HF radar observations of surface circulation off Bodega Bay (northern California, USA)  

NASA Astrophysics Data System (ADS)

Two high-frequency radar stations (CODAR) were installed along the northern California coast in May 2001. Comparisons of radar data with acoustic Doppler current profiler (ADCP) current data and near-surface drifter tracks indicate considerable agreement, with minimum RMS differences of order 0.05-0.15 m/s and average drifter-HF-radar track separation rates of 5 ± 3 km/d. Radar data resolve the three main sources of intraseasonal current variability in the area: (1) upwelling/relaxation dynamics, (2) tidal and diurnal forcing, and (3) inertial currents. Subtidal fluctuations are the largest component of variability, accounting for 45-75% of the variance. Wind-driven dynamics are the dominant source of this subtidal variability (67% of subtidal variability). Both upwelling and relaxation periods exhibit consistent patterns of surface velocity, with nearshore currents being slower and more poleward than offshore currents, which are strongly equatorward. Analysis of tidal and inertial variability indicate that current fluctuations are polarized toward clockwise rotation and are generally weaker and more linearly polarized near the coast. M2 tidal current ellipses switch direction of rotation at the shelf break, suggesting the presence of internal tidal waves. Currents in all frequency bands are deflected and accelerated around Pt. Reyes, and there are indications of increased current variability and changes in flow direction near Cordell Bank. The presence of considerable cross-shore and alongshore gradients in the strength and direction of surface flow patterns, and in particular weak poleward currents over the inner shelf, could have important consequences for plankton retention in the area.

Kaplan, David M.; Largier, John; Botsford, Louis W.

2005-10-01

84

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

NASA Astrophysics Data System (ADS)

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 and Tsutsumi (GRL, 2002) and Tsutsumi et al. (Radio Sci., 2009) to obtain neutral wind information from meteor echoes using SuperDARN radars. We are in the process of comparing Doppler velocity of HF echoes with neutral wind velocity and will present the results of this analysis. The altitude distribution of echoes can be obtained from interferometer array data, which is useful for distinguishing between MSEs and E region echoes. The detailed results with their interpretation will be presented.

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

2013-12-01

85

Propagating tsunami wave and subsequent resonant response signals detected by HF radar in the Kii Channel, Japan  

NASA Astrophysics Data System (ADS)

Signals from the tsunami waves induced by the March 11, 2011 moment magnitude ( M w) 9.0 Tohoku-Oki earthquake and from subsequent resonances were detected as radial velocity variability by a high-frequency ocean surface radar (HF radar) installed on the eastern coast of the Kii Channel, at a range of about 1000 km from the epicenter along the eastern to southern coasts of Honshu Island. A time-distance diagram of band-passed (9-200 min) radial velocity along the beam reveals that the tsunami waves propagated from the continental shelf slope to the inner channel as progressive waves for the first three waves, and then natural oscillations were excited by the waves; and that the direction of the tsunami wave propagation and the axis of the natural oscillations differed from that of the radar beam. In addition, spectral analyses of the radial velocities and sea surface heights obtained in the channel and on the continental shelf slope suggest complex natural oscillation modes excited by the tsunami waves. The major advantage of the HF radars as tsunami detection is early warning as the tsunami is still far offshore. There is no doubt on this importance beside still technical and operational studies are needed. Our results adds a new role of the HF radars to measure the detailed surface current fields with high spatiotemporal resolution toward understanding detailed processes of resonant response to tsunami waves in coastal regions.

Hinata, Hirofumi; Fujii, Satoshi; Furukawa, Keita; Kataoka, Tomoya; Miyata, Masafumi; Kobayashi, Takashi; Mizutani, Masahiro; Kokai, Takahiro; Kanatsu, Nobuyoshi

2011-11-01

86

Mesopheric turbulence intensities measured with a HF radar at 35 deg S. Part 2  

NASA Technical Reports Server (NTRS)

A theory was developed for extracting turbulence energy dissipation rates from spectra measured with a radar. It is shown that factors apart from turbulence contribute to the observed spectral widths, and that these factors must be considered if accurate estimates of energy dissipation rates are to be obtained. In particular, beam-width broadening and shear broadening are important. The first results obtained with this theory are presented. The rules were obtained using the large HF array at Adelaide, Australia, primarily during the Southern Hemisphere winter of 1981. Results are consistent with rocket measurements of turbulence, with typical values varying between 0.01 and 1/0.2 W kg at 80-90 km altitude.

Hocking, W. K.

1983-01-01

87

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

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

88

Roundoff noise analysis for digital Doppler processors in radar scatterometers  

NASA Technical Reports Server (NTRS)

The noise due to finite word length effects for digital Doppler processors (DPP) in radar scatterometers, is analyzed. The roundoff noise-to-signal ratio in the measurement of the radar return signal power is derived. Computer simulations which validate the analytical results are presented. The results can be used in tradeoff studies of hardware design such as number of bits required at each processing stage. The results are used in the design of a DPP for the NASA scatterometer planned to be launched in 1990.

Chi, Chong-Yung; Long, D.; Fuk, K. LI

1986-01-01

89

Three-Frequency Nonlinear Heterodyne Detection. 2: Digital Communications and Pulsed Radar  

E-print Network

Three-Frequency Nonlinear Heterodyne Detection. 2: Digital Communications and Pulsed Radar Malvin Carl Teich and Rainfield Y. Yen Part 1 of this paper [Appl. Opt. 14,666 (1975)]dealt with the cw radar the technique for a number of specificpulsed radar and digital communications applications. Both the vacuum

Teich, Malvin C.

90

Digital filter design for radar image formation  

NASA Astrophysics Data System (ADS)

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.

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

1989-08-01

91

Synthetic aperture radar and digital processing: An introduction  

NASA Technical Reports Server (NTRS)

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.

Dicenzo, A.

1981-01-01

92

Surface transport in the Northeastern Adriatic Sea from FSLE analysis of HF radar measurements  

NASA Astrophysics Data System (ADS)

This study focuses on the surface transport in the Northeastern Adriatic Sea and the related hydrodynamic connectivity with the Gulf of Trieste (GoT) under calm or typical wind conditions: Bora (from the NE) and Sirocco (from the SE). The surface transport in the area has been investigated by evaluating the Finite-Size Lyapunov Exponents (FSLE) on the current field measured by the High Frequency (HF) coastal radar network. FSLE allow us to estimate Lagrangian Coherent Structures (LCSs), which provide information on the transport patterns associated with the flow and identify regions characterized by different dynamics. This work includes the development and set-up of the FSLE algorithm applied for the first time to the specific Adriatic area considered. The FSLE analysis during calm wind reveals an attractive LCS crossing the GoT entrance, marking the convergence between the Northern Adriatic and the outflowing gulf waters. During Bora episodes this attractive LCS is displaced westward with respect to the calm wind case, indicating that Bora drives an extended coherent outflow from the GoT. On the other hand, Sirocco wind piles up the water along the northern end of the basin. In this area an attractive LCS is found, extending mainly in the SW-NE direction. The sirocco-induced inflow of Adriatic waters in the GoT is mainly driven along its northern (Italian) side, as evidenced by the orientation of the LCS. Under Sirocco condition, as in the Bora case, there is no barrier in front of the gulf. No relevant LCSs are observed in the southern radar coverage area except for Bora cases, when a repulsive LCS develops in front of the Istrian coast separating water masses to the North and the South of it.

Berta, Maristella; Ursella, Laura; Nencioli, Francesco; Doglioli, Andrea M.; Petrenko, Anne A.; Cosoli, Simone

2014-04-01

93

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

NASA Astrophysics Data System (ADS)

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.

Fraunie, Philippe

2014-05-01

94

Building a Digital Meteor Radar for Aeronomic Research  

NASA Astrophysics Data System (ADS)

Many billions of meteors enter the atmosphere of the earth every day. At altitudes near 100km these meteors ablate creating an ionized trail that drifts with the neutral wind and diffuses. Using electromagnetic waves near 30MHz the structure of these trails can be probed providing information about the structure of the earth's atmosphere around 100km. Specifically details about the winds and temperature can be extracted. Radar systems measuring meteor parameters have existed for many decades but the recent advances in high speed digital acquisition systems has enabled the development of software agile digital receivers. This paper details the lessons learned regarding a career proposal focusing on the development of a digital receiver for atmospheric research. One key aspect of this project that will be discussed is the bridging of science and engineering in this research. The challenges and benefits of this research will also be addressed.

Palo, S. E.

2011-12-01

95

A Cascaded Approach for Correcting Ionospheric Contamination with Large Amplitude in HF Skywave Radars  

PubMed Central

Ionospheric phase perturbation with large amplitude causes broadening sea clutter's Bragg peaks to overlap each other; the performance of traditional decontamination methods about filtering Bragg peak is poor, which greatly limits the detection performance of HF skywave radars. In view of the ionospheric phase perturbation with large amplitude, this paper proposes a cascaded approach based on improved S-method to correct the ionospheric phase contamination. This approach consists of two correction steps. At the first step, a time-frequency distribution method based on improved S-method is adopted and an optimal detection method is designed to obtain a coarse ionospheric modulation estimation from the time-frequency distribution. At the second correction step, based on the phase gradient algorithm (PGA) is exploited to eliminate the residual contamination. Finally, use the measured data to verify the effectiveness of the method. Simulation results show the time-frequency resolution of this method is high and is not affected by the interference of the cross term; ionospheric phase perturbation with large amplitude can be corrected in low signal-to-noise (SNR); such a cascade correction method has a good effect. PMID:24578656

Wei, Yinsheng; Guo, Rujiang; Xu, Rongqing; Tang, Xiudong

2014-01-01

96

A cascaded approach for correcting ionospheric contamination with large amplitude in HF skywave radars.  

PubMed

Ionospheric phase perturbation with large amplitude causes broadening sea clutter's Bragg peaks to overlap each other; the performance of traditional decontamination methods about filtering Bragg peak is poor, which greatly limits the detection performance of HF skywave radars. In view of the ionospheric phase perturbation with large amplitude, this paper proposes a cascaded approach based on improved S-method to correct the ionospheric phase contamination. This approach consists of two correction steps. At the first step, a time-frequency distribution method based on improved S-method is adopted and an optimal detection method is designed to obtain a coarse ionospheric modulation estimation from the time-frequency distribution. At the second correction step, based on the phase gradient algorithm (PGA) is exploited to eliminate the residual contamination. Finally, use the measured data to verify the effectiveness of the method. Simulation results show the time-frequency resolution of this method is high and is not affected by the interference of the cross term; ionospheric phase perturbation with large amplitude can be corrected in low signal-to-noise (SNR); such a cascade correction method has a good effect. PMID:24578656

Li, Yajun; Wei, Yinsheng; Guo, Rujiang; Xu, Rongqing; Wang, Zhuoqun; Tang, Xiudong

2014-01-01

97

Interference-Detection Module in a Digital Radar Receiver  

NASA Technical Reports Server (NTRS)

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.

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

2009-01-01

98

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

99

Hokkaido HF radar signatures of periodically reoccurring nighttime medium-scale traveling ionospheric disturbances detected at short ranges  

NASA Astrophysics Data System (ADS)

The Super Dual Auroral Radar Network Hokkaido HF radar often detects periodically reoccurring E region echoing regions propagating toward or away from it. In this work, we consider 117 of such events identified for 2008-2012. These are shown to occur at nighttime, preferentially during summer, although significant number for events was found for winter. Statistics for the local time of occurrence, magnitude of the speed and polarity of progressions, and temporal and spatial periodicities are presented. We show that the power of echoes is linearly related to their Doppler velocity which makes it possible to identify the events on both power and Doppler velocity plots. Other peculiar characteristics of echoes are discussed. The onset of events is associated with gravity waves propagation through the radar field of view.

Koustov, A. V.; Yakymenko, K. N.; Nishitani, N.; Ponomarenko, P. V.

2014-02-01

100

Development of a digital receiver for range imaging atmospheric radar  

NASA Astrophysics Data System (ADS)

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-?s 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.

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

2014-10-01

101

Elliptical storm cell modeling of digital radar data  

NASA Technical Reports Server (NTRS)

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.

Altman, F. J.

1972-01-01

102

Digital Radar-Signal Processors Implemented in FPGAs  

NASA Technical Reports Server (NTRS)

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 by complex conjugate multiplication to obtain the mean Doppler shift (and hence the mean and variance of the velocity of precipitation) of the echo at that range.

Berkun, Andrew; Andraka, Ray

2004-01-01

103

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

SciTech Connect

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.

Walker, A.D.M.; Ruohoniemi, J.M.; Baker, K.B.; Greenwald, R.A. (Johns Hopkins Univ. Applied Physics Lab., Laurel, MD (United States)); Samson, J.C. (Univ. of Alberta, Edmonton (Canada))

1992-08-01

104

Advanced ground-penetrating radar for digital soil mapping  

NASA Astrophysics Data System (ADS)

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.

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

2009-04-01

105

A Digital Array Radar with a Hierarchical System Architecture Caleb Fulton, Patrick Clough, Vijay Pai, and William Chappell  

E-print Network

A Digital Array Radar with a Hierarchical System Architecture Caleb Fulton, Patrick Clough, Vijay -- A digital array radar system prototype is pre sented that makes use of a hierarchical digital backend for future radars that fully embrace the concept of lowcost inte gration in a panelized platform

106

Hardware implementation of a high-performance programmable digital processing system for radar proximity fuze  

Microsoft Academic Search

A new type of digital processing system for a radar proximity fuze is described. By utilizing high-speed real-time digital signal processing devices and a special FFT processor, a high-performance system has been developed which provides digital signal processing for a radar proximity fuze. Reasonable overall architecture and programmable processors used in this system notably improve its programmability and scalability. This

Di Wu; Zhang'e Ma; Xiutan Wang; Hainan Diao

2001-01-01

107

Coherent HF radar backscatter characteristics associated with auroral forms identified by incoherent radar techniques: A comparison of CUTLASS and EISCAT observations  

NASA Astrophysics Data System (ADS)

Backscatter from decameter-wavelength field-aligned F region irregularities, as measured by the Cooperative UK Twin Located Auroral Sounding System (CUTLASS) Finland HF coherent radar, is compared with common volume plasma parameters and the electric field deduced by the European Incoherent Scatter (EISCAT) UHF incoherent radar system, for a 12 hour period from June 18 to June 19, 1996. During this interval we find an excellent agreement between irregularity Doppler velocity and bulk ion drift resolved along the CUTLASS beam. Backscatter is found to exist only in regions of nonzero electric field, as the E×B instability growth rate is dependent on E. Following a substorm expansion phase onset, backscatter largely disappears for a period of several hours, thought to be a consequence of nondeviative absorption of the HF radio wave in the D region or a quenching of the F region instability mechanism by enhanced E region Pedersen conductivity. Finally, the presence of auroral arcs within the scatter volume increases the intensity of backscatter returns and introduces a subsidiary peak, displaced from the preexisting peak, in the backscatter spectra; this subsidiary peak results in an increase in the apparent spectral width of the backscatter. We show how this allows the location of precipitation features within the field of view to be determined.

Milan, S. E.; Davies, J. A.; Lester, M.

1999-10-01

108

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

NASA Astrophysics Data System (ADS)

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.

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

2010-05-01

109

The shuttle radar topography mission—a new class of digital elevation models acquired by spaceborne radar  

Microsoft Academic Search

For 11 days in February 2000, the Shuttle Radar Topography Mission (SRTM) successfully recorded by interferometric synthetic aperture radar (InSAR) data of the entire land mass of the earth between 60°N and 57°S. The data acquired in C- and X-bands are processed into the first global digital elevation models (DEMs) at 1 arc sec resolution, by NASA-JPL and German aerospace

Bernhard Rabus; Michael Eineder; Achim Roth; Richard Bamler

2003-01-01

110

Performance analysis of pulse Doppler digital radars with application to the Shuttle Ku-band system  

NASA Technical Reports Server (NTRS)

A pulse Doppler digital radar is one of the primary components of the Ku-band integrated radar and communication equipment on the Space Shuttle. The performance of the Ku-band rendezvous radar to be used on the Space Shuttle is analyzed in four parts. First an overall functional block diagram description is presented to illustrate the signal processing in the detection and the tracking modes. The detection capabilities and limitations of the radar are investigated taking all of the system losses into account. A new unified analysis of digital radar tracking loops is developed which takes into consideration the effects of a scintillating target and receiver front end noise. The behavior of the radar is discussed in the presence of thermal noise, amplitude scintillation, and target glint.

Alem, W. K.; Weber, C. L.

1978-01-01

111

The HF surface wave radar WERA. Part I: Statistical analysis of recorded data  

Microsoft Academic Search

Surface wave (SW) over-the-horizon (OTH) radars are not only widely used for ocean remote sensing, but they can also be exploited in integrated maritime surveillance systems. This paper represents the first part of the description of the statistical and spectral analysis performed on sea backscattered signals recorded by the oceanographic WEllen RAdar (WERA) system. Data were collected on May 13th

Salvatore Maresca; Maria Greco; Fulvio Gini; R. Grasso; S. Coraluppi; N. Thomas

2010-01-01

112

Moving target detection via digital time domain correlation of random noise radar signals  

Microsoft Academic Search

Ultra-wideband random noise radar theoretically has a thumbtack ambiguity function, which cannot be realized due to hardware, processing, and environmental limitations. Velocity estimation using traditional Doppler processing is not practicable for ultra-wideband random noise radar because of the large fractional bandwidth. Through analysis, this paper explores moving target detection using digital correlation processing of random noise signals in the time

James R. Lievsay; Geoffrey A. Akers

2011-01-01

113

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

114

Ionospheric and auroral clutter models for HF surface wave and over-the-horizon radar systems  

NASA Astrophysics Data System (ADS)

The detection performance of high frequency surface wave radar (HFSWR) and high frequency over-the-horizon radar (OTHR) systems is heavily influenced by the presence of radar clutter. In HFSWR systems, the clutter has its origins in vertical-incidence ionospheric reflections, whereas in OTHR systems, the origin is Bragg backscatter from plasma structures in the auroral zone. This paper models the spreading of the radar clutter signal in the Doppler and angle-of-arrival domains that arises from forward-scattering effects as the radar pulse propagates through regions of ionospheric plasma irregularities. The models use a geometric optics approach to determine the power spectrum of the radar signal phase. This power spectrum is then used to simulate three-dimensional space-time-range radar data cubes. The accuracy of the models is tested by comparing the simulated data to measured data cubes. As an application, the data are then used to evaluate the performance of the newly developed fast fully adaptive (FFA) space-time adaptive processing (STAP) scheme to improve the extraction of target echoes from a clutter background.

Ravan, M.; Riddolls, R. J.; Adve, R. S.

2012-01-01

115

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

Microsoft Academic Search

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

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

2009-01-01

116

Adaptive digital beamforming (ADBF) architecture for wideband phased-array radars  

NASA Astrophysics Data System (ADS)

The practical application of adaptive digital beamforming (ADBF) to phased array radar systems has been demonstrated by several systems, most notably MESAR. However, MESAR and the other fielded radar systems employing ADBF are limited to narrow bandwidth operation. The next generation of defense radar systems currently under development are considering ADBF architecture, but with wideband waveforms. New radar system architectures are mandated by the requirement for simultaneously accomplishing wide bandwidth and ADBF, particularly for the precision measurement and tracking environment of ballistic missile defense. This paper describes approaches to developing wideband architectures suitable for this and similar applications.

Mitchell, Mark A.; Howard, Robert L.; Tarran, Chris

1999-07-01

117

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

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

118

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

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

119

Plasma wave activity in the polar E-region: New insights from HF radar observations in Antarctica  

NASA Astrophysics Data System (ADS)

Plasma structuring at small scales (decameter wavelengths and below) in the high-latitude E-region is normally attributed to plasma instability processes under conditions of strong electric fields and/or favorable plasma density gradients. Establishing the electric field dependence of the wave activity in particular is both fundamentally important and experimentally challenging. In this report, we present direct observations of the polar E-region wave activity in conjunction with the electric field measurements with the recently-deployed SuperDARN South Pole (SPS) and McMurdo (MCM) HF radars. The ability of all Antarctic SuperDARN radars to observe E-region plasma waves is assessed first by modeling their magnetic aspect angle conditions. The diurnal variation of E region echo occurrence is analyzed and shown to be distinctly different between SPS and MCM. It is demonstrated that E-region echo occurrence is largely controlled by the electric field strength which behaves differently at SPS and MCM. The contribution of the E-region plasma waves of different spectral properties and physical origins to the SPS and MCM datasets and their electric field control are also investigated. The results suggest that the electric field control of E-region wave activity is present but perhaps indirect. One possible scenario is a two-step process in which primary waves are generated under strong electric field conditions and create strong polarization electric fields that in turn are responsible for secondary wave generation. The new radar observations in Antarctica suggest that such a process is perhaps more common than previously thought and may be responsible for generation of the large majority of small-scale waves in the polar E-region.

Makarevich, R. A.

2013-12-01

120

The relationship between strength of turbulence and backscattering radar power at HF and VHF  

NASA Technical Reports Server (NTRS)

The formulae relating turbulence and other atmospheric parameters to backscattered power for radar observations are reviewed. Emphasis is on the case of scatter from turbulent irregularities which have scales corresponding to the range of isotropic, inertial range turbulence. The applicability of this assumption is discussed. A formula is introduced for the mesosphere which relates ionospheric electron densities to backscattered power.

Hocking, W. K.

1983-01-01

121

Nature of Near-Inertial Motions in the Upper Ocean and a Possible Route towards HF Radar Probing of Seasonal Stratification  

NASA Astrophysics Data System (ADS)

Inertial band response of the upper ocean to changing wind is studied both theoretically and by analysis of observations in the Gulf of Lyons. The theoretical examination is carried out within the framework of the linearized Euler equations on the non-traditional f-plane. Due to the horizontal component of the Earth rotation for near-inertial waves with frequencies slightly below the local inertial frequency f there is a waveguide in the mixed layer confined from below by the pycnocline. When the stratification is shallow and strong these near-inertial motions are the ones most easily and strongly excited by the changing winds. The linear model predicts that in the presence of seasonal stratification the inertial band response of the upper ocean is dominated by these sub-inertial motions. These motions have been overlooked in the previous studies since they are absent under the traditional approximation. The in situ observations which employed buoys with thermistors, ADCPs, HF radars and SST data were carried out in the Gulf of Lyons in April-June 2006. The observations support the theoretical picture: a pronounced inertial band response occurs only in the presence of strong shallow stratification and is sharply localized near the surface. The surface signatures of these motions are easily captured by HF radars. The sensitivity of the inertial band response (as seen by HF radars) to the upper ocean stratification provides a possibility for developing HF radar probing of seasonal stratification. An analysis of continuous two year HF observations near the Porquerolle island confirms that the seasonal stratification is indeed the necessary condition for a strong inertial band response.

Shrira, Victor; Forget, Philippe

2014-05-01

122

Measuring surface wind direction by monostatic HF ground-wave radar at the eastern China Sea  

Microsoft Academic Search

The extraction of full wind vectors from data obtained by single-site (monostatic) high-frequency ground-wave radar (HFGWR) is an ongoing challenge because of the inherent directional ambiguities. Here, a new algorithm for resolving the ambiguity of wind direction from monostatic data is presented. The true wind direction is determined by minimizing the sum of the difference among three wind directions derived

Weimin Huang; Eric Gill; Shicai Wu; Biyang Wen; Zijie Yang; Jiechang Hou

2004-01-01

123

Complexity in the high latitude HF radar spectral width boundary region  

NASA Astrophysics Data System (ADS)

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, ?GSF=0.18±0.02 and ?GSF=0.09±0.01, are even smaller than that expected for MHD turbulence.

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

2008-05-01

124

Wavefront Adaptive Raymode Processing for Over-the-Horizon HF Radar Clutter Mitigation  

Microsoft Academic Search

Detection of surface targets using over-the-horizon radar (OTHR) is extremely challenging due to ionospherically-induced Doppler spread clutter. In particular, low Doppler targets are often masked by ground clutter arriving via multipath propagation at different elevation angles, each with a different ionospheric Doppler shift. The wavefront adaptive raymode processing (WARP) approach presented here exploits the azimuthally distributed nature of the clutter

O. Kazanci; I. Bilik; J. Krolik

2007-01-01

125

A compact low cost, high-power broad band SPDT switch for HF and VHF radar  

NASA Astrophysics Data System (ADS)

The high power SPDT (single pole double throw) switch is extremely useful as a building block for forming linear and circular polarized beams in high power radars. It can also be used simply as a switch to route the RF to two different feeder lines. This paper brings out the detailed design and development of a broad band, low loss, SPDT switch for high power applications using vacuum relay. This fabricated unit is comparatively economical as the only purchased item is a vacuum relay. The size is also compact and two outputs are adjacent to each other as per the requirements. The constructed SPDT switch operates well from dc to VHF range (200 MHz) and has an insertion loss of less than 0.5 dB and isolation better than 35 dB up to 200 MHz. This switch has been tested for 120 kW peak power at 53 MHz with the load VSWR of 2:1 without any trace of breakdown and is already connected with the Indian MST Radar system. There are 32 such units in the whole radar system.

Agarwal, Arvind; Sarkar, B. K.

1993-08-01

126

Digital topography of volcanoes from radar interferometry: an example from Mt Vesuvius, Italy  

Microsoft Academic Search

A new airborne radar technique can generate digital topographic data for volcanoes at a scale of 10 m spatial and 1–5 m vertical, with a swath width of ~6.4 km. Called TOPSAR, the intrument is an interferometric radar flown on the NASA DC-8 aircraft. TOPSAR data permit the quantification of volcano slopes, volumes, and heights, and as such will be

Peter J. Mouginis-Mark; Harold Garbeil

1993-01-01

127

A digital demodulation scheme for use in a high dynamic range radar system  

NASA Astrophysics Data System (ADS)

Digital demodulation is a technique whereby the positive frequency component of a narrowband signal is translated to baseband by digital means. With this technique, the dynamic range of some radar systems can be greatly increased. A digital demodulation scheme suitable for an airborne radar system is described, and some of the major design issues in its implementation are analyzed. The demodulation process first involves downconversion of the signal to an intermediate frequency (IF), filtering the resulting signal to reduce its frequency sidelobes, mixing the filtered signal to a second IF, digitizing the second IF signal, and filtering the digital signal with a lowpass finite impulse response filter. An expression for the optimal filter is derived, maximizing the ratio of the positive frequency clutter power to the negative frequency clutter plus noise power. Simulated input and output spectra are shown. The simulation results were validated by a simple experiment.

Rempel, Glen; Haslam, George

128

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

NASA Astrophysics Data System (ADS)

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 particularly tsunamis, for future oceanic monitoring and tsunami warning systems.

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

2014-03-01

129

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

SciTech Connect

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.

Ruohoniemi, J.M.; Greenwald, R.A.; Baker, K.B. (Johns Hopkins Univ., Laurel, MD (United States)); Samson, J.C. (Univ. of Alberta, Edmonton (Canada))

1991-09-01

130

Variability of the Kuroshio Current south of Sagami Bay as observed using long-range coastal HF radars  

NASA Astrophysics Data System (ADS)

Ocean surface currents between Cape Nojima and Hachijo Island have been mapped since fall 2000 using a pair of SeaSonde long-range HF radars. During September 2000 through December 2001, the no large meander (NLM) nearshore (n) and offshore (o) modes were observed. The surface current maps allowed new details to be observed in the structure of these modes and the transitions between them. Two noteworthy phenomena include blocking of the surface currents when the Kuroshio was in an extreme nearshore position behind the Zenisu Ridge and the "Kyucho" pattern when the current retroflexed from the NLMo position. In early 2004, a large meander (LM) developed and was well established in its historical position south of Honshu by August 2004. Subsequently, the LM continued propagating downstream, but stopped when it encountered the Izu Ridge. It then moved back to its original position near 137.5°E, and the process repeated itself. This east-west oscillation resulted in two common positions for the LM south of Sagami Bay: from its more westerly position (LMw, for west) the Kuroshio had a very favorable approach to the deep gap between Miyake Island and the Zenisu Ridge, and the currents were strongly toward the northeast through the region. When the meander moved up against the ridge (LMe, for east), a strong along-ridge current toward the northwest was evident, which turned sharply northeast when it encountered the shallow Zenisu Ridge. The dominant timescale for this within-mode variability was about 30 days.

Ramp, Steven R.; Barrick, Donald E.; Ito, Tomotaka; Cook, Michael S.

2008-06-01

131

Multiple frequency radar observations of high-latitude E region irregularities in the HF modified ionosphere  

NASA Technical Reports Server (NTRS)

This paper discusses the results of the September 1983 observations of artificial field-aligned irregularities (AFAIs) in the Tromso, Norway region, made by backscatter radars operating at 46.9, 143.8, 21.4, and 140.0 MHz. Four classes of resonant instability processes at work in the E and F regions are examined in detail: (1) the coupling of parametric decay instability waves across geomagnetic field lines, (2) thermal parametric instability, (3) four-wave interaction thermal parametric instability, and (4) the resonance instability. The characteristics of the AFAI scatter are described, with special attention given to the growth and decay time constants, functional dependence on the heater power and polarization, and the scattering cross sections of the irregularities.

Noble, S. T.; Gordon, W. E.; Djuth, F. T.; Jost, R. J.; Hedberg, A.

1987-01-01

132

First observations of the temporal/spatial variation of the sub-auroral polarization stream from the SuperDARN Wallops HF radar  

NASA Astrophysics Data System (ADS)

In this letter we present the first two-dimensional observations of sub-auroral ion drift (SAID) variability within the sub-auroral polarization stream (SAPS) using a new mid-latitude SuperDARN radar located at Wallops Island, VA. The radar data are complemented with observations from the DMSP F15, TIMED, and NOAA-18 spacecraft to confirm that a backscatter feature observed at the equatorward edge of the auroral oval is a manifestation of SAPS/SAID. During a several hour long period on August 6, 2005, the velocity data indicate that significant changes in the SAPS flow occurred on time scales of a few minutes. The Wallops HF radar observations demonstrate that the SAPS phenomenon is a source of small-scale irregularities extending over many hours of MLT and that the electric fields associated with SAID in particular are highly variable.

Oksavik, K.; Greenwald, R. A.; Ruohoniemi, J. M.; Hairston, M. R.; Paxton, L. J.; Baker, J. B. H.; Gjerloev, J. W.; Barnes, R. J.

2006-06-01

133

Performance of a digital signal processor with impulse noise suppression (meteor radar detection system appl.)  

Microsoft Academic Search

Scanning systems which produce records of electromagnetic input signals are usually subject to random impulse interference which may seriously degrade the records. An impulse noise suppressor employing digital techniques has been developed which has general applicability to such systems and which has been employed with success in a meteor radar installation and a thermal infrared scanning system. The results of

C. S. L. Keay; J. E. Butler; J. A. Kennewell

1976-01-01

134

An assessment of shuttle radar topography mission digital elevation data for studies of volcano morphology  

E-print Network

An assessment of shuttle radar topography mission digital elevation data for studies of volcano's volcanoes. Although these data were acquired with a nominal spatial resolution of 30 m, such data are only available for volcanoes located within the U.S.A. and its Territories. For the overwhelming majority

Wright, Robert

135

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

NASA Technical Reports Server (NTRS)

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.

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

1982-01-01

136

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

NASA Technical Reports Server (NTRS)

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.

Pujol, A.

1982-01-01

137

Surface circulation in the Iroise Sea (W. Brittany) from high resolution HF radar mapping  

NASA Astrophysics Data System (ADS)

The data from two high-frequency radars (HFR) operating in the Iroise Sea are re-processed by applying an improved version of the direction finding algorithm, removing wave-induced surface currents and the variational interpolation on a regular grid. Combining these processing techniques allowed reconstruction of the surface currents at a level of details that was not previously available. Refined resolution enabled to identify fine-scale structures of surface circulation, to quantify the variability of tidal currents and the residual (time averaged) velocity field, and to explain spatial intermittence in polarization of the tidal current ellipses. The analyzed data span two month-long periods in spring and late summer of 2007. The major findings include (a) a dipole structure in the vorticity field characterized by two oppositely rotating eddies, generated on the leeward side of the Ushant Island at flood (negative polarity) and at ebb (positive polarity); (b) an extremely strong fortnightly variability of tidal currents northwest of the Ushant Island with the highest velocity magnitude of 3.9 m/s caused by the interference of the major semi-diurnal tidal constituents; (c) a significant contribution of the higher order nonlinear tidal harmonics to the surface currents in the Fromveur strait, which maintains strong tidal currents and affects the shape of their fortnightly modulation. The residual circulation is characterized by two distinct zones approximately separated by the 100 m isobath: in the offshore zone the residual currents have a significant contribution of the wind-driven component, whereas the nearshore zone is characterized by extremely strong (up to 0.4 m/s) time-independent residual circulation featuring two permanent anticyclonic eddies: north of the western extremity of the Sein archipelago, and north the Ushant Island. The acquired data and the presented results could be useful for regional model validation and studies of the local eddy dynamics, tidal fronts, and passive tracer transport in the region.

Sentchev, Alexei; Forget, Philippe; Barbin, Yves; Yaremchuk, Max

2013-01-01

138

Characterizing observed circulation patterns within a bay using HF radar and numerical model simulations  

NASA Astrophysics Data System (ADS)

In this study, High Frequency Radar (HFR), observations in conjunction with numerical model simulations investigate surface flow dynamics in a tidally-active, wind-driven bay; Galway Bay situated on the West coast of Ireland. Comparisons against ADCP sensor data permit an independent assessment of HFR and model performance, respectively. Results show root-mean-square (rms) differences in the range 10 - 12cm/s while model rms equalled 12 - 14cm/s. Subsequent analysis focus on a detailed comparison of HFR and model output. Harmonic analysis decompose both sets of surface currents based on distinct flow process, enabling a correlation analysis between the resultant output and dominant forcing parameters. Comparisons of barotropic model simulations and HFR tidal signal demonstrate consistently high agreement, particularly of the dominant M2 tidal signal. Analysis of residual flows demonstrate considerably poorer agreement, with the model failing to replicate complex flows. A number of hypotheses explaining this discrepancy are discussed, namely: discrepancies between regional-scale, coastal-ocean models and globally-influenced bay-scale dynamics; model uncertainties arising from highly-variable wind-driven flows across alarge body of water forced by point measurements of wind vectors; and the high dependence of model simulations on empirical wind-stress coefficients. The research demonstrates that an advanced, widely-used hydro-environmental model does not accurately reproduce aspects of surface flow processes, particularly with regards wind forcing. Considering the significance of surface boundary conditions in both coastal and open ocean dynamics, the viability of using a systematic analysis of results to improve model predictions is discussed.

O'Donncha, Fearghal; Hartnett, Michael; Nash, Stephen; Ren, Lei; Ragnoli, Emanuele

2015-02-01

139

High Frequency (HF) upgrade study for the Canadian Regional Operations Control Center (ROCC) AWACS Digital Information Link (RADIL) project  

NASA Astrophysics Data System (ADS)

The Regional Operations Control Center AWACS Digital Information Link/Rapidly Deployable Integrated Command and Control System (RADIL/RADIC) System Program Office, Canadian RADIL Program, has acquired high-frequency (HF) radio equipment for two Canadian ground stations under the RADIL Project. This equipment will allow those stations to carry out Tactical Digital Information Link (TADIL) A data transmissions assisted by MIL-STD-188-141A automatic link establishment (ALE). The MITRE Corporation has been tasked to study whether U.S. TADIL stations should be equipped with similar HF-ALE modems. This report analyzes the improvements in performance over northern links that can be expected from the addition of ALE to the TADIL A system. Since there is only a small amount of data on ALE-assisted digital communications in northern regions, the analysis combines a probabilistic approach to comparison of ALE and conventional linking techniques with actual HF propagation data from links in Canada, Iceland, and Norway. The report also assesses the risks to effective communications of using an ALE-TADIL A system in the north and recommends several improvements in hardware and software that can lower those risks.

Wickwire, Kenneth

1995-04-01

140

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

NASA Astrophysics Data System (ADS)

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 configuration for all the microwave sensors, we have initiated design and development of a generic L-band digital receiver, consisting of receiver elements (LNA, digital attenuator and Bandpass filter) followed by Analog-to-Digital Converter. The digitised data can then be output in parallel or serial format. Additionally, a digital signal processor performing tasks like data compression, convolution or correlation and formatting can also be integrated with this generic digital receiver. The front end of the receiver is wide-band, catering to bandwidths of upto 2 GHz while the digitisation rates are also of the order of 1-2 GHz. It is proposed to standardize the design and use this generic receiver for front end data acquisition of all the future microwave sensors. It will meet the digitisation requirements of 500 MHz to 1 GHz for ultra-high resolution (0.25-0.5 meter) SAR as well as direct sampling of the signal around 1.4GHz for L-band Synthetic Aperture Radiometer. After initial prototyping using discrete receiver elements and ultra-high speed 8-bit ADC, it will be taken up as a custom ASIC or multi-chip module consisting of RF MMIC's and a mixed signal ADC ASIC. These designs will be fabricated using InP, GaAs or SiGe process technologies at competent foundries like GATEC, SCL, Infineon/Germany, X-Fab/Germany and Ommic-Philips/France. This novel digital receiver will offer several advantages like flexibility, stability, reduced RF hardware and miniaturisation. This paper describes the ultra-high speed design requirements, configuration details and target specifications and salient features of this generic L-band digital receiver for ISRO's future spaceborne and airborne radar missions. It also addresses the associated signal integrity, EMI/EMC and thermal issues.

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

2006-12-01

141

Model analysis of influence of wave-current interaction on current measurement of HF ocean surface radar for isolated eddy and upwelling  

NASA Astrophysics Data System (ADS)

The influence of wave-current interaction on the current measurement of HF ocean surface radar (HFOSR) is analyzed by a simulation of the Doppler velocity spectra of the first-order echo. The Doppler velocity spectra is a product of the spatial integration of the radial velocity weighted by the radar sensitivity and the normalized radar cross section (NRCS). As a result of the wave number change due to the wave-current interaction and the extension of the wave packet due to the divergence of ocean currents, the NRCS distribution becomes nonuniform. The artificial component is produced around the center of the current phenomena in the simulated radial velocity field because the nonuniformity of the NRCS distribution distorts the spectral shape of the first-order echo. The artificial component flows in the opposite direction of the propagation of the causal ocean waves. The intensity of the artificial component depends on the spatial scale ratio of the radar sensitivity distribution to the current phenomenon. In addition, the spatial averaging effect caused by the radar sensitivity distribution leads the antisymmetric component of the radial velocity difference, which weakens the intensity of the simulated current phenomena. The averaging of the two radial velocities extracted from the two first-order echoes, corresponding to the approaching and receding causal ocean waves, is effective in reducing the artificial component in the measured radial current velocity by HFOSR, because the artificial components in the simulated radial velocities have almost the same spatial distributions with the opposite direction of flow.

Nadai, Akitsugu

2006-10-01

142

Digital multi-channel high resolution phase locked loop for surveillance radar systems  

NASA Astrophysics Data System (ADS)

This paper present a multi-channel, high resolution, fast lock phase locked loop (PLL) for surveillance radar applications. Phase detector based PLLs are simple to design, suffer no systematic phase error, and can run at the highest speed. Reducing loop gain can proportionally improve jitter performance, but also reduces locking time and pull-in range. The proposed system is based on digital process and control the error signal to the voltage controlled oscillator (VCO) adaptively to control its gain in order to achieve fast lock times while improving in lock jitter performance. Under certain circumstances the design also improves the frequency agility capability of the radar system. The results show a fast lock, high resolution PLL with transient time less than 10 µ sec which is suitable to radar applications.

Rizk, Mohamed; Shaaban, Shawky; Abou-El-Nadar, Usama M.; Hafez, Alaa El-Din Sayed

143

Estimating Lagrangian transport blending drifters with HF radar data and models: Results from the TOSCA experiment in the Ligurian Current (North Western Mediterranean Sea)  

NASA Astrophysics Data System (ADS)

Lagrangian transport estimates are investigated using results from HF radar, model and drifter data during a dedicated experiment in the Ligurian Current in the Toulon area (North Western Mediterranean Sea). Uncertainty estimates on particle position, D(t), are computed and compared to absolute dispersion, D0(t), that provides an indication of the uncertainty in case of zero prior knowledge. In agreement with previous studies, radar results show that D(t)?1/2D0(t) (i.e. ?6 km after 24 h). Model results are less reliable, as it can be expected in highly nonlinear coastal flows without local data assimilation. The central result of this paper is that when drifters are promptly deployed in an area of interest, their data can be used to significantly improve transport estimates using the Lagrangian blending algorithm LAVA with velocity fields from models or radar. Uncertainty can be reduced to ?1/6D0(t), (i.e. ?2 km after 24 h) for both radar and model, implying a much reduced search range in case of operational applications. The method is also found to have some forecasting skills with uncertainty ?1/2D0(t) during the first ?6 h. Sensitivity tests provide indications on relevant time and space scales of predictability and provide suggestions for appropriate drifter sampling strategies.

Berta, Maristella; Bellomo, Lucio; Magaldi, Marcello G.; Griffa, Annalisa; Molcard, Anne; Marmain, Julien; Borghini, Mireno; Taillandier, Vincent

2014-11-01

144

Temporal variability in intensity-height profiles of a severe storm using digital radar data  

E-print Network

under study. These results will be related to existing atmospheric conditions, and a theory will be advanced as to the possible cause of the explosive growth associated with an observed tornado. CHAPTER II DESCRIPTION OF THE SYNOPTIC CONDITIONS... of the real potential of the digital radar will be presented for a thunderstorm system observed on April 26, 1969, that produced a confirmed tornado and rains of considerable intensity at 1700 CST at Ninnekah, Oklahoma. Between 1600 CST and 1700 CST, two...

Canipe, Yates Julio

1972-01-01

145

Estimating Water Slope in Amazon River Tributaries Using the Shuttle Radar Topography Mission Digital Elevation Model  

Microsoft Academic Search

Extracting river height from the Shuttle Radar Topography Mission digital elevation model (SRTM DEM) for four Amazon River tributaries found water surface elevation standard deviations of 6.16 m for the Madeira River, 7.47 m for the Purus River, 5.28 m for the Negro River, and 5.35 m for the Branco River. Standard deviations and slopes were found for the Madeira,

J. Hamski; G. Lefavour; D. Alsdorf; T. Pavelsky

2006-01-01

146

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

NASA Technical Reports Server (NTRS)

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.

Wu, C.

1976-01-01

147

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

NASA Astrophysics Data System (ADS)

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.

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

2009-05-01

148

Digital and optical systolic architectures for airborne adaptive radars  

NASA Astrophysics Data System (ADS)

Systolic architectures for digital and analog, electronic and optical signal processing are presented along with specific applications to adaptive nulling. It is shown how the various architectures provide for the implementation of adaptive algorithms and how technologies affect performance. Their effects on adaptive degrees of freedom, convergence time, null depth, signal to noise ratio are presented along with size, weight, and required power. Adaptive algorithms covered are of two basic types: feedback/iterative and direct methods. Examples of each include the least mean square (LMS) for the iterative type and the QU factorization based on the Givens method for the direct method. Simulation results have verified the performance of the least squares and the systolic array for QU factorization by Givens method. Improved performance was obtained using the modified minimum variance distortionless response algorithm based on the maximum likelihood criteria. An optical implementation of the least squares algorithm over a continuously adaptive multi-path was experimentally evaluated. Thus far, 24 dB of cancellation was achieved over a 7 micro-second multi-path window for 10 mega-Hertz instantaneous bandwidth. Adaptivity in the spatial, temporal and Doppler domains are illustrated and their embodiment into the various architectures are presented. For example, an analog optical processor which generates weights in the spatial and temporal (multi-path) domains for broadband systems is shown. Also shown is a digital systolic architecture which is applied to a direct decomposition method for generation of adaptive weights in the spatial and Doppler domains. A description of brassboard models representing both architectures is included.

Lis, Stanley; Vannicola, Vincent C.; Graniero, John A.; Medoff, Barry P.; Penn, William A.

1986-07-01

149

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

NASA Astrophysics Data System (ADS)

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.

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

2012-07-01

150

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

E-print Network

, and Solar Radar Namir E. Kassim Naval Research Laboratory, Washington, DC 20375 Stephen M. White AFRL, Kirtland AFB, Albuquerque, NM 87117 Paul Rodriguez Consultant, Washington, DC 20375 Jacob M. Hartman, Brian

Ellingson, Steven W.

151

Hf phased-array radar for studying small-scale structure in the high-latitude ionosphere  

Microsoft Academic Search

Since October 1983, a new coherent backscatter radar has been in operation at Goose Bay, Labrador, for the purpose of studying small-scale electron density structure in the high-latitude ionosphere. This radar operates over a frequency band that extends from 8 to 20 MHz, and it uses an electronically phased array of 16 log-periodic antennas for both transmission and reception. The

R. A. Greenwald; K. B. Baker; R. A. Hutchins; C. Hanuise

1985-01-01

152

A comparison of multifrequency HF radar and ADCP measurements of near-surface currents during COPE3  

Microsoft Academic Search

A high-frequency multifrequency coastal radar operating at four frequencies between 4.8 and 21.8 MHz was used as part of the third Chesapeake Bay Outflow Plume Experiment (COPE-3) during October and November, 1997. The radar system surveyed the open ocean east of the coast and just south of the mouth of Chesapeake Bay from two sites separated by about 20 km.

Calvin C. Teague; John F. Vesecky; Zachariah R. Hallock

2001-01-01

153

Hf phased-array radar for studying small-scale structure in the high-latitude ionosphere  

SciTech Connect

Since October 1983, a new coherent backscatter radar has been in operation at Goose Bay, Labrador, for the purpose of studying small-scale electron density structure in the high-latitude ionosphere. This radar operates over a frequency band that extends from 8 to 20 MHz, and it uses an electronically phased array of 16 log-periodic antennas for both transmission and reception. The radar transmits a seven-pulse pattern that enables one to determine 17-lag complex autocorrelation functions of the backscattered signals as a function of range and azimuth. This paper presents a complete description of the radar including explanations of the operation of the phasing matrix, the techniques of data acquisition and analysis as implemented in the radar microcomputer, and the possible on-line and automatic operating modes that may be instituted. Also presented are examples of some of the initial results obtained with the radar during the afternoon and late evening hours. These examples include images of the two-dimensional distribution of small-scale structure and of their associated mean Doppler motion. Examples of F-region Doppler spectra derived from the complex autocorrelation functions are also presented. These Doppler spectra show interesting differences from those of high-latitude E-region irregularities.

Greenwald, R.A.; Baker, K.B.; Hutchins, R.A.; Hanuise, C.

1985-02-01

154

Modern Radar Techniques for Geophysical Applications: Two Examples  

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

155

Applications of digital radar in the analysis of severe local storms  

E-print Network

August 1973 Major Subject: Meteorology APPLICATIONS OF DIGITAL RADAR IN THE ANALYSIS OF SEVERE LOCAL STORMS A Thesis JOHN EVERETT VOGEL Approved as to style and content by: (Co-Chairman of Committee) / /. Lier &. i i . 3 I r1 ~ '-d (ri 'i ~ ~ i... characteristics of the thunder- storm-cell structure. In two of the cases studied, on April 26, 1969 and April 29 and 30, 1970, tornadoes and other severe weather events were observed. In each of the three tornado occurrences reported, an "explosive...

Vogel, John Everett

1973-01-01

156

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

NASA Technical Reports Server (NTRS)

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.

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

2014-01-01

157

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

Code of Federal Regulations, 2011 CFR

...3) Audio-frequency band. The quality of service, using digital source coding within a 10 kHz bandwidth, taking into account the need to adapt the emission coding for various levels of error avoidance, detection and correction, can...

2011-10-01

158

A Special-Purpose Digital Radar Simulation and Performance Prediction Model  

Microsoft Academic Search

A special-purpose radar model has been developed to provide interim capability in the evaluation of Army radar performance. This irterim model is designed to be used pending development of the radar scoring facility and will be replaced by the empirical prediction model developed from the radar scoring facility. The radar model has three basic sections: (1) cross section and signal

Merle E. Parmer

1968-01-01

159

A Model for Radar Images and Its Application to Adaptive Digital Filtering of Multiplicative Noise  

Microsoft Academic Search

Standard image processing techniques which are used to enhance noncoherent optically produced images are not applicable to radar images due to the coherent nature of the radar imaging process. A model for the radar imaging process is derived in this paper and a method for smoothing noisy radar images is also presented. The imaging model shows that the radar image

Victor S. Frost; Josephine Abbott Stiles; K. S. Shanmugan; Julian C. Holtzman

1982-01-01

160

HF RADAR observations of coastal currents induced by the 29-30 September 2009 tsunami South of O’ahu  

NASA Astrophysics Data System (ADS)

A High-Frequency RADAR collected radial current observations at 1.5 km resolution every 15 minutes along O’ahu’s South Shore. Following the arrival of the tsunami generated by the September 29 Samoan earthquake, radial currents fluctuations of up to 4 cm/s were recorded 25-35 km off shore. The bursts of shoreward surface current associated with the tsunami are located at the transition between deep and shallower water on Penguin Bank, a submerged bank extending westward from the Lanai-Molokai group. The RADAR currents and supporting sea level data from other sensors in the area, showed oscillations at a dominant period of 500 sec. excited by the tsunami, which persisted for more than 8 hours after the tsunami’s initial arrival.

Flament, P. J.; Cass, J. L.; Merrifield, M. A.; Gurgel, K.

2009-12-01

161

Detecting and quantifying mountain permafrost creep from in situ inventory, space-borne radar interferometry and airborne digital photogrammetry  

Microsoft Academic Search

In this paper three different techniques for detecting and quantifying mountain permafrost creep are compared: (1) rock glacier inventory and characterization from in situ indicators, (2) space-borne radar interferometry, and (3) digital processing of repeated airborne imagery. The specific char- acteristics of the three methods and their complementarity are investigated for the Fletschhorn mountain range in the Simplon\\/Saas valley region,

R. Frauenfelder; T. Strozzi; A. Kääb

2004-01-01

162

A 3D Optimal Interpolation Assimilation Scheme of HF Radar Current Data into a Numerical Ocean Model  

NASA Astrophysics Data System (ADS)

In this work a technique for the 3D assimilation of ocean surface current measurements into a numerical ocean model based on data from High Frequency Radar (HFR) systems is presented. The technique is the combination of supplementary forcing on the surface and of and Ekman layer projection of the correction in the depth. Optimal interpolation through BLUE (Best Linear Unbiased Estimator) of the model predicted velocity and HFR observations is computed in order to derive a supplementary forcing applied at the surface boundary. In the depth the assimilation is propagated using an additional Ekman pumping (vertical velocity) based on the correction achieved by BLUE. In this work a HFR data assimilation system for hydrodynamic modelling of Galway Bay in Ireland is developed; it demonstrates the viability of adopting data assimilation techniques to improve the performance of numerical models in regions characterized by significant wind-driven flows. A network of CODAR Seasonde high frequency radars (HFR) deployed within Galway Bay, on the West Coast of Ireland, provides flow measurements adopted for this study. This system provides real-time synoptic measurements of both ocean surface currents and ocean surface waves in regions of the bay where radials from two or more radars intersect. Radar systems have a number of unique advantages in ocean modelling data assimilation schemes, namely, the ability to provide two-dimensional mapping of surface currents at resolutions that capture the complex structure related to coastal topography and the intrinsic instability scales of coastal circulation at a relatively low-cost. The radar system used in this study operates at a frequency of 25MHz which provides a sampling range of 25km at a spatial resolution of 300m.A detailed dataset of HFR observed velocities is collected at 60 minute intervals for a period chosen for comparison due to frequent occurrences of highly-energetic, storm-force events. In conjunction with this, a comprehensive weather station, tide gauge and river monitoring program is conducted. The data are then used to maintain density fields within the model and to force the wind direction and magnitude on flows. The Data Assimilation scheme is then assessed and validated via HFR surface flow measurements.

Ragnoli, Emanuele; Zhuk, Sergiy; Donncha, Fearghal O.; Suits, Frank; Hartnett, Michael

2013-04-01

163

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

Code of Federal Regulations, 2010 CFR

...Broadcast Stations § 73.758 System specifications for digitally...RF requirements for the DRM system are specified in paragraphs...of this section. (b) System parameters —(1) Channel...emission is not to the same geographical area as either of the...

2010-10-01

164

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

SciTech Connect

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.

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

1991-08-26

165

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)

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.

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

1989-01-01

166

Estimating Water Slope in Amazon River Tributaries Using the Shuttle Radar Topography Mission Digital Elevation Model  

NASA Astrophysics Data System (ADS)

Extracting river height from the Shuttle Radar Topography Mission digital elevation model (SRTM DEM) for four Amazon River tributaries found water surface elevation standard deviations of 6.16 m for the Madeira River, 7.47 m for the Purus River, 5.28 m for the Negro River, and 5.35 m for the Branco River. Standard deviations and slopes were found for the Madeira, Purus, and Branco rivers by fitting a simple, straight line to the SRTM heights with ~1000 km of flow distance. A second order polynomial was used for the Negro River. Resulting water surface slopes are 3.63 cm/km for the Madeira, 2.83 cm/km for the Purus, and 6.95 cm/km for the Branco whereas a range in slope from 7.00 to 2.10 cm/km was found for the Negro. Using a conservative, annual minimum water slope estimate of 2 cm/km for each tributary leads to reach length requirements of 616 km for the Madiera, 747 km for the Purus, 528 km for the Negro, and 535 km for the Branco to clearly delineate slope. The Global Rain Forest Mapping project's synthetic aperture radar mosaics (GRFM SAR) provide river width. Channel width is computed at each GRFM SAR pixel along a center line obtained by thresholding the Laplacian of an image containing the distance from each channel pixel to the nearest bank pixel. For the Purus River a depth estimate of 15 m and a Manning's n of 0.03 are assumed in calculating river flow velocities using Manning's equation. Using the estimated velocity of 1.04 m/s, the calculated Purus River discharge is 8500 m3/s. state.edu/water/

Hamski, J.; Lefavour, G.; Alsdorf, D.; Pavelsky, T.

2006-12-01

167

Topographic constraints on impact crater morphology on Venus from high-resolution stereo synthetic aperture radar digital elevation models  

Microsoft Academic Search

High-resolution digital elevation models (DEMs) derived from Magellan Left-Left Stereo synthetic aperture radar data of Venus for a set of impact craters ranging in rim diameter from 5 to 300 km exhibit depths broadly as expected from theory but with significant departures for both large and small craters. In craters larger than 38 km diameter, rim-floor depth becomes independent of

Christopher G. Cochrane; Richard C. Ghail

2006-01-01

168

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

Microsoft Academic Search

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

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

2009-01-01

169

Space Plasma Exploration by Active Radar (SPEAR): an overview of a future radar facility  

E-print Network

Space Plasma Exploration by Active Radar (SPEAR): an overview of a future radar facility D. M is a new polar cap HF radar facility which is to be deployed on Svalbard. The principal capabilities of SPEAR will include the generation of arti®cial plasma irregularities, operation as an `all-sky' HF radar

Paris-Sud XI, Université de

170

A West Florida Shelf ROMS Nested into HYCOM: Ensemble-based Assimilation of HF-Radar Surface Currents and a 2005 Red Tide Case Study with Simulated Drifters  

NASA Astrophysics Data System (ADS)

A West Florida Shelf (WFS) model is constructed by nesting the Regional Ocean Model System (ROMS) in the Atlantic Hybrid Coordinate Ocean Model (HYCOM) to include both local and deep-ocean forcing, particularly the Gulf of Mexico Loop Current (LC). Hindcast experiments from 2004 to 2006 are presented and compared to observed temperature (moorings and BSOP profiling floats), ADCP velocity time series and HF-Radar surface currents. Two different mixing schemes (Mellor Yamada level 2.5 and K-Profile Parameterization, KPP) are tested and the importance of the vertical resolution for mixing is addressed. The model results of those different configurations are compared to temperature observations on the shelf. Results obtained with the Mellor Yamada scheme are closer to observations during winter (negative buoyancy flux and strong winds) while in summer (positive buoyancy flux and in general weaker wind) the KPP scheme produces more realistic results. Given the present HYCOM configuration we assessed the benefit of nesting ROMS in HYCOM compared to nesting ROMS in climatology. The model solutions on the shelf were compared to various in situ data. The model performed best when using the HYCOM boundary values. Simulated trajectories for drifters deployed off Tampa Bay and Sarasota were used to address the evolution of Karenia brevis concentrations during the 2005 red tide. Near surface drifters were advected offshore, whereas drifters deployed in the bottom Ekman layer matched the subsequently observed Karenia brevis distributions, showing the importance of the 3D structure of coastal ocean currents for red tide on the WFS. As a first attempt at assimilating CODAR surface currents we used an ensemble simulation carried out under different wind forcings to estimate the error covariance of the model state vector and the covariance between the ocean currents and the wind. Improvements were obtained for the modeled currents, not only at the surface, but also at depth.

Barth, A.; Alvera-Azcarate, A.; Weisberg, R. H.

2007-05-01

171

A digital beamforming processor for the joint DoD/NASA space based radar mission  

NASA Technical Reports Server (NTRS)

The Space Based Radar (SBR) program includes a joint technology demonstration between NASA and the Air Force to design a low-earth orbiting, 2x50 m L-band radar system for both Earth science and intelligence related observations.

Fischman, Mark A.; Le, Charles; Rosen, Paul A.

2004-01-01

172

A combined analogue and digital pulse compression system using large time bandwidth product signals for use in synthetic aperture radar  

NASA Astrophysics Data System (ADS)

Pulse compression, widely used in modern radar systems, has the advantage in that it allows the use of long duration low-power pulses which facilitate low-power transmission. A synthetic aperture radar (SAR) pulse compression system able to compress very large time bandwidth product signals while still retaining high dynamic range capability and flexibility would be very advantageous. The possibility of implementing the compression in two stages is investigated, in which the first stage compression processing is done by an analog device followed by digital techniques in the second stage. Various signal coding methods were evaluated to determine those most suitable to the two-stage process, and various means of implementing the second stage were compared. A two-stage pulse compression system was then designed and built to generate arbitrarily coded expanded pulses with bandwidths in excess of 200 MHz. Its performance was evaluated in the presence of tone, noise, and jamming. It was shown that the two-stage pulse compression system exhibited greater resistance to quantizer saturation than a comparable digital system. The processing effort required to implement the compression using a digital adaptive matched filter was found to be slightly less than double that of a basic pulse compression system.

Godbole, Pushkar E.

1989-07-01

173

In-flight detection of errors for enhanced aircraft flight safety and vertical accuracy improvement using digital terrain elevation data with an inertial navigation system, global positioning system and radar altimeter  

Microsoft Academic Search

This dissertation discusses integration architectures using digital terrain elevation data (DTED) with an inertial navigation system (INS), a global positioning system (GPS) and a radar altimeter. Two integration architectures are considered: DTED with INS, GPS and radar altimeter for aircraft vertical accuracy improvement during the final approach; and DTED with kinematic GPS (KGPS) and a radar altimeter for enhanced aircraft

Robert Anthony Gray

1999-01-01

174

Simulation of Post-ADC Digital BeamForming for Large Area Radar Receiver Arrays  

Microsoft Academic Search

In order to provide instantaneous three-dimensional radar measurements spanning the entire vertical extent of the ionosphere, the planned EIS-CAT_3D incoherent scatter radar system includes multiple receive-only antenna arrays, situated at 90-280 km from the main transmit\\/receive site. These employs band-pass sampling at 80 MHz, with the input signal spectrum contained in the 6th Nyquist zone. This paper presents simulations and

Gustav Stenberg; Johan Borg; J. Johansson; G. Wannber

2006-01-01

175

A Digital Processor for the Production of Seasat Synthetic Aperture Radar Imagery  

Microsoft Academic Search

With the launch of Seasat-A in June, 1978, the first spaceborne Synthetic Aperture Radar data was made available to the remote sensing community. While the mission only lasted 3+ months, a large volume of SAR data was recorded during this period, and recent image production is beginning to show the remarkable clarity of the data.\\u000aSynthetic Aperture Radar processing requires

John R. Bennett; Ian G. Cumming

1979-01-01

176

Large-scale traveling ionospheric disturbance observed by superDARN Hokkaido HF radar and GPS networks on 15 December 2006  

Microsoft Academic Search

On 15 December 2006, during the main phase of a relatively large storm, Doppler velocity data from the Super Dual Aural Radar Network (SuperDARN) Hokkaido radar, together with total electron content (TEC) data from the GPS Earth Observation Network (GEONET), recorded daytime large-scale traveling ionospheric disturbances (LSTIDs). We studied two disturbances propagating southward and one disturbance propagating northward between 0000

H. Hayashi; N. Nishitani; T. Ogawa; Y. Otsuka; T. Tsugawa; K. Hosokawa; A. Saito

2010-01-01

177

Radar Imaging Systems Joseph Charpentier  

E-print Network

Radar Imaging Systems Joseph Charpentier Department of Computing Sciences Villanova University types of radar imaging systems; synthetic aperture radar (SAR), through-the-wall radar, and digital holographic near field radar. Each system surveyed experiments that improved the quality of the resulting

178

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

NASA Astrophysics Data System (ADS)

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 achieving a high spatial and temporal coverage, as well as the opportunity to continuously map surface changes relative to an updated topography and slopes. References: Levinsen, J. F., Khvorostovsky, K., Ticconi, F., Shepherd, A., Forsberg, R., Sørensen, L. S., Muir, A., Pie, N., Felikson, D., Flament, T., Hurkmans, R., Moholdt, G., Gunter, B., Lindenbergh, R. C., and Kleinherenbrink, M.: ESA's Ice Sheets CCI: validation and inter-comparison of surface elevation changes derived from laser and radar altimetry over Jakobshavn Isbræ, Greenland - Round Robin results, The Cryosphere Discuss., 7, 5433-5460, 2013.

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

2014-05-01

179

HF radio oceanography — A review  

Microsoft Academic Search

The understanding and utilization of HF radar sea-echo have enjoyed steady progress since the experimental discovery of the underlying radar\\/sea interaction process over two decades ago. The agreement of theory with measured data confirms the correctness of currently accepted explanations for both the first-order and second-order portions of the sea-echo Doppler spectrum in terms of the wave-height directional spectrum. Furthermore,

Donald E. Barrick

1978-01-01

180

First observations of the temporal\\/spatial variation of the sub-auroral polarization stream from the SuperDARN Wallops HF radar  

Microsoft Academic Search

In this letter we present the first two-dimensional observations of sub-auroral ion drift (SAID) variability within the sub-auroral polarization stream (SAPS) using a new mid-latitude SuperDARN radar located at Wallops Island, VA. The radar data are complemented with observations from the DMSP F15, TIMED, and NOAA-18 spacecraft to confirm that a backscatter feature observed at the equatorward edge of the

K. Oksavik; R. A. Greenwald; J. M. Ruohoniemi; M. R. Hairston; L. J. Paxton; J. B. H. Baker; J. W. Gjerloev; R. J. Barnes

2006-01-01

181

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)

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.

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

1980-01-01

182

Digital Signal Generator and Receiver design For S-band Radar  

Microsoft Academic Search

The new generation of radar has to be equipped with a high performance exciters and receivers to cope with the threat in an Electronic Warfare scenario. The threat in a complex environment with interfering signals requires a reliable signal generation with proper frequency agility and efficient gain controls in receiver units. This is quite cumbersome to achieve in analog domain.

L. Prakasam; T. Roy; D. Meena

2007-01-01

183

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

NASA Technical Reports Server (NTRS)

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.

1973-01-01

184

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

NASA Technical Reports Server (NTRS)

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.

Young, Steve; UijtdeHaag, Maarten; Sayre, Jonathon

2003-01-01

185

Ka-band Digitally Beamformed Airborne Radar Using SweepSAR Technique  

NASA Technical Reports Server (NTRS)

A paper describes a frequency-scaled SweepSAR demonstration that operates at Ka-Band (35.6 GHz), and closely approximates the DESDynl mission antenna geometry, scaled by 28. The concept relies on the SweepSAR measurement technique. An array of digital receivers captures waveforms from a multiplicity of elements. These are combined using digital beamforming in elevation and SAR processing to produce imagery. Ka-band (35.6 GHz) airborne SweepSAR using array-fed reflector and digital beamforming features eight simultaneous receive beams generated by a 40-cm offset-fed reflector and eight-element active array feed, and eight digital receiver channels with all raw data recorded and later used for beamforming. Illumination of the swath is accomplished using a slotted-waveguide antenna radiating 250 W peak power. This experiment has been used to demonstrate digital beamforming SweepSAR systems.

Sadowy, Gregory A.; Chuang, Chung-Lun; Ghaemi, Hirad; Heavey, Brandon A.; Lin, Lung-Sheng S.; Quaddus, Momin

2012-01-01

186

An analysis of HF radar measured surface currents to determine tidal, wind-forced, and seasonal circulation in the Gulf of the Farallones, California, United States  

Microsoft Academic Search

A complete year of hourly 3 km resolution high-frequency radar measured surface currents covering the Gulf of the Farallones were analyzed with the following three primary objectives: (1) describe the seasonal surface circulation, (2) identify tidal currents, and (3) determine the influence of wind forcing. Three predominant seasonal circulation regimes were identified: relaxation, storm, and upwelling. The relaxation period exhibited

Matt K. Gough; Newell Garfield; Erika McPhee-Shaw

2010-01-01

187

VOLUME 78, NUMBER 5 P H Y S I C A L R E V I E W L E T T E R S 3 FEBRUARY 1997 Multifrequency Doppler Radar Observations of Electron Gyroharmonic Effects  

E-print Network

Doppler Radar Observations of Electron Gyroharmonic Effects during Electromagnetic Pumping the first detailed mul- tifrequency HF Doppler radar (MDR) studies of elec- tron gyroharmonic effects) Experimental results of multifrequency HF Doppler radar studies during electromagnetic pumping

188

The Shuttle Radar Topography Mission  

Microsoft Academic Search

The Shuttle Radar Topography Mission produced the most complete, highest-resolution digital elevation model of the Earth. The project was a joint endeavor of NASA, the National Geospatial-Intelligence Agency, and the German and Italian Space Agencies and flew in February 2000. It used dual radar antennas to acquire interferometric radar data, processed to digital topographic data at 1 arc sec resolution.

Tom G. Farr; Paul A. Rosen; Edward Caro; Robert Crippen; Riley Duren; Scott Hensley; Michael Kobrick; Mimi Paller; Ernesto Rodriguez; Ladislav Roth; David Seal; Scott Shaffer; Joanne Shimada; Jeffrey Umland; Marian Werner; Michael Oskin; Douglas Burbank; Douglas Alsdorf

2007-01-01

189

Digital ionosonde observations during equatorial spread F-italic  

Microsoft Academic Search

In this paper we present and discuss equatorial spread F-italic data taken with a digital ionosonde\\/HF radar located at Huancayo, Peru. A modified phenomenology is developed which uses the system's ability to do echo location. The onset of irregularities is seen to occur in the east and to move westward, while inside this large-scale structure the plasma is found to

P. E. Argo; M. C. Kelley

1986-01-01

190

HF, VHF, and UHF systems and technology  

Microsoft Academic Search

A wide variety of unique systems and components inhabits the HF, VHF, and UHF bands. Many communication systems (ionospheric, meteor-burst, and troposcatter) provide beyond-line-of-sight coverage and operate independently of external infrastructure. Broadcasting and over-the-horizon radar also operate in these bands. Magnetic-resonance imaging uses HF\\/VHF signals to see the interior of a human body, and RF heating is used in a

Frederick H. Raab; Robert Caverly; Richard Campbell; Murat Eron; James B. Hecht; Arturo Mediano; Daniel P. Myer; John L. B. Walker

2002-01-01

191

The Arecibo Observatory as an MST radar  

NASA Technical Reports Server (NTRS)

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.

Woodman, R. F.

1983-01-01

192

HF excited instabilities in space plasmas  

NASA Technical Reports Server (NTRS)

It has now become technologically feasible to construct ground-based HF radar systems which can deliver RF energy to the ionospheric plasma, with power densities sufficient to alter the ionospheric electron thermal budget and plasma characteristics. Effects produced by a ground-based transmitter of a power aperture of the order of 10,000 Mw sq m in the frequency range from 4 to 12 MHz are shown in a graph. Another graph presents a profile of electron gas temperature enhancement due to energy deposition by a high power HF transmitter. The conduction of high-power HF ionospheric plasma experiments is discussed. Attention is given to plasma instabilities, wave-particle acceleration effects, spacial and time scales, parametric instabilities, spread-F, and the possibility of placing high power-aperture radars on an orbiting space platform.

Carlson, H. C., Jr.; Duncan, L. M.

1977-01-01

193

Temperate Ice Depth Sounding Radar (TIDSoR)  

NASA Astrophysics Data System (ADS)

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 system to store the acquired data. At HF, a physically large-antenna is needed. TIDSoR takes advantage of the helix antenna concept to minimize its physical dimensions and weight. Moreover, the ability to achieve different polarizations (linear, circular and elliptical) was considered to maximize the performance of the radar system. Arcone, S. A., Lawson, D. E., Moran, M. and Delaney, A. J., 2000, 12-100-MHz profiles of ice depth and stratigraphy of three temperate glaciers. In: Proc. GPR 2000, Eighth Intl. Conf. Ground-Penetrating Radar, Gold Coast, Austral., 23-26 May, 2000.

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

2007-12-01

194

Remote sensing of sea state by radar  

Microsoft Academic Search

In recent years several radar techniques have evolved which allow the remote measurement of certain parameters important in the description of sea state. At MF and HF, monostatic and bistatic configurations employing satellites, ships, islands, and\\/or land based stations can measure the ocean waveheight spectrum with several frequencies via first-order Bragg scatter. At high HF and VHF, the ocean waveheight

D. Barrick

1972-01-01

195

Temperate Ice Depth-Sounding Radar  

NASA Astrophysics Data System (ADS)

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. It also digitizes the output signal from the receiver and stores the data in binary format using a portable computer. The RF-section consists of a high- power transmitter and a low-noise receiver with digitally controlled variable gain. The antenna is time-shared between the transmitter and receiver by means of a transmit/receive (T/R) switch. In regards to the antenna, we have made a survey study of various electrically small antennas (ESA) to choose the most suitable radiating structure for this application. Among the different alternatives that provide a good trade-off between electrical performance and small size, we have adopted an ESA dipole configuration for airborne platforms and a half-wavelength radiator for the surface-based version. The airborne antenna solution is given after studying the geometry of the aerial vehicle and its fuselage contribution to the antenna radiation pattern. Dipoles are made of 11.6 mm diameter cables (AWG 0000) or printed patches embedded into the aircraft fuselage, wings, or both. The system is currently being integrated and tested. TIDSoR is expected to be deployed during the spring 2008 either in Alaska or Greenland for surface based observations. In this paper, we will discuss our design considerations and current progress towards the development of this radar system. [1] Center for Remote Sensing of Ice Sheets (Cresis), Sept 2008, [Online]. Available: http://www.cresis.ku.edu

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

2008-12-01

196

Meteor observations with the European incoherent scatter UHF radar  

Microsoft Academic Search

The European Incoherent Scatter (EISCAT) UHF radar, which operates at a nominal frequency of 930 MHz, is introduced as a powerful meteor radar. Its high sensitivity is utilized to detect transient enhanced ionization trails caused by meteors of all orientations, in contrast to conventional HF and VHF backscatter radars, which observe only the meteor trails oriented approximately normal to the

Asta Pellinen-Wannberg; Gudmund Wannberg

1994-01-01

197

Lunar Radar Cross Section at Low Frequency  

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

198

Large phased-array radars  

SciTech Connect

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.

Brookner, D.E.

1988-12-15

199

Sea backscatter at HF: Interpretation and utilization of the echo  

Microsoft Academic Search

Theories and concepts for utilization of HF sea echo are compared and tested against surface-wave measurements made from San Clemente Island in the Pacific in a joint NRL\\/ITS\\/NOAA experiment. The use of first-order sea echo as a reference target for calibration of HF over-the-horizon radars is established. Features of the higher order Doppler spectrum can be employed to deduce the

DONALD E. BARRICK; JAMES M. HEADRICK; ROBERT W. BOGLE; DOUGLASS D. CROMBIE

1974-01-01

200

A new 1 km digital elevation model of the Antarctic derived from combined satellite radar and laser data - Part 1: Data and methods  

NASA Astrophysics Data System (ADS)

Digital elevation models (DEMs) of the whole of Antarctica have been derived, previously, from satellite radar altimetry (SRA) and limited terrestrial data. Near the ice sheet margins and in other areas of steep relief the SRA data tend to have relatively poor coverage and accuracy. To remedy this and to extend the coverage beyond the latitudinal limit of the SRA missions (81.5° S) we have combined laser altimeter measurements from the Geosciences Laser Altimeter System onboard ICESat with SRA data from the geodetic phase of the ERS-1 satellite mission. The former provide decimetre vertical accuracy but with poor spatial coverage. The latter have excellent spatial coverage but a poorer vertical accuracy. By combining the radar and laser data using an optimal approach we have maximised the vertical accuracy and spatial resolution of the DEM and minimised the number of grid cells with an interpolated elevation estimate. We assessed the optimum resolution for producing a DEM based on a trade-off between resolution and interpolated cells, which was found to be 1 km. This resulted in just under 32% of grid cells having an interpolated value. The accuracy of the final DEM was assessed using a suite of independent airborne altimeter data and used to produce an error map. The RMS error in the new DEM was found to be roughly half that of the best previous 5 km resolution, SRA-derived DEM, with marked improvements in the steeper marginal and mountainous areas and between 81.5 and 86° S. The DEM contains a wealth of information related to ice flow. This is particularly apparent for the two largest ice shelves - the Filchner-Ronne and Ross - where the surface expression of flow of ice streams and outlet glaciers can be traced from the grounding line to the calving front. The surface expression of subglacial lakes and other basal features are also illustrated. We also use the DEM to derive new estimates of balance velocities and ice divide locations.

Bamber, J. L.; Gomez-Dans, J. L.; Griggs, J. A.

2009-05-01

201

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

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

202

Digital ionosonde observations during equatorial spread F-italic  

SciTech Connect

In this paper we present and discuss equatorial spread F-italic data taken with a digital ionosonde/HF radar located at Huancayo, Peru. A modified phenomenology is developed which uses the system's ability to do echo location. The onset of irregularities is seen to occur in the east and to move westward, while inside this large-scale structure the plasma is found to drift eastward. A very curious difference has been identified between spread F-italic observations with the ionosonde and with the VHF radar at Jicamarca. At VHF, spread F-italic onset often occurs when the ionosphere is rising, whereas in all five examples presented here, the digital ionosonde detected onset when the apparent ionosphere motion was downward. The result even held on the one night of common data taking. The effect could be instrumental but may be related to the considerable orographic differences in the two sites. Isolated scattering patches are observed and are tentatively identified as detached or ''fossil'' plumes. At frequencies above the nominal f-italic/sub 0/F-italic/sub 2/ the system (and other ionosondes) may in fact function as a coherent radar. During one night, data were obtained simultaneously with the HF radar, a rocket, and the Jicamarca VHF radar. Comparisons of these data are discussed in detail. Finally, additional evidence is presented that acoustic gravity waves play a role in the development of equatorial spread F-italic and in the formation of detached plumes. To be self-consistent, the gravity waves must come from nearby sources such as the tropical rain forest to the east of Jicamarca.

Argo, P.E.; Kelley, M.C.

1986-05-01

203

Bistatic radar sea state monitoring  

NASA Technical Reports Server (NTRS)

Bistatic radar techniques were examined for remote measurement of the two-dimensional surface wave height spectrum of the ocean. One technique operates at high frequencies (HF), 3-30 MHz, and the other at ultrahigh frequencies (UHF), approximately 1 GHz. Only a preliminary theoretical examination of the UHF technique was performed; however the principle underlying the HF technique was demonstrated experimentally with results indicating that an HF bistatic system using a surface transmitter and an orbital receiver would be capable of measuring the two-dimensional wave height spectrum in the vicinity of the transmitter. An HF bistatic system could also be used with an airborne receiver for ground truth ocean wave spectrum measurements. Preliminary system requirements and hardware configurations are discussed for both an orbital system and an aircraft verification experiment.

Ruck, G. T.; Barrick, D. E.; Kaliszewski, T.

1972-01-01

204

An analysis of the data collection modes of a digital weather radar system with respect to significant severe weather features  

E-print Network

of Eq (4) is 2 log Z = 2 log r + log P ? log C~k~ e r (8) Using the values of C for the TA"}U radar- given below and that of 2 ~k~ given earlier, we have C = 1. 0089 x 10 3 C = 8. 609 x 10 Iog C ski = 9. 0 2 log C lkl = 10. 1 2= (6a) (6})) By... ke 0 0 L 4I D C 0 0 O I- L I- I 4 CC L 0 IV J IC 0 I g C 0 I IU U 0 C? C o 0 0 0 I 4 U K I 0 XX 'clo I Dl D K O 0 I g 8 I ID U Z E 4 I I- 0 I 8 0 V 0 E Dl x r N K X O 0 o 4 C 0 4 0 o ea 0 X O cJ Cf Dl cfl CJ...

Neyland, Michael Arthur

1978-01-01

205

Digital Base Band Converter As Radar Vlbi Backend / Dbbc K? Ciparošanas Sist?ma Radara Vlbi Nov?rojumiem  

NASA Astrophysics Data System (ADS)

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 can then allow exploring easily the desired range of search for unknown or not fully determined orbit objects. These features make Radar VLBI personality most useful in the space debris measurements. DBBC sist?ma izstr?d?ta Noto Radioastronomijas instit?t?. Sist?mas galvenaisuzdevums - palielin?t visa Eiropas VLBI t?kla jut?bu - realiz?ts, palielinotvisas nov?rojam?s joslas platumu un pielietojot ciparu sign?lu apstr?des metodes.Izejas datu pl?sma palielin?ta no 1 l?dz 4 Gbps katram radioteleskopam un visasoper?cijas, kas saist?tas ar sign?lu apstr?di (frekvences p?rveidošana, pastiprin?jums,iekš?jie ?eneratori, utt.), realiz?tas digit?l? form?, kas ?auj ieg?t noz?m?gusuzlabojumus atk?rtojam?b?, precizit?t?, vienk?rš?b?, nemaz neminot visp?rzin?m?spriekšroc?bas, ko nodrošina digit?lo tehnolo?iju izmantošana. Maksim?l? ieejassign?la frekven?u josla ir 3.5 GHz, un moment?nais joslas platums ir l?dz 1 GHz uzkatru no asto?iem iesp?jamajiem RF/IF kan?liem. Š? datu re?istr?cijas sist?ma ir?oti veiktsp?j?ga platforma ne tikai EVN, bet ar? citiem radioastronomijas pielietojumiem,un papildus tiek izstr?d?ta vesela virkne programmat?ras pakot?u, kasv?l vair?k paplašina sist?mas funkcionalit?ti. Tas ietver PFB (Polif?zes FiltruBanka) uztv?r?jus "Spectra”, kas piem?roti augstas izš?irtsp?jas spektroskopijasvajadz?b?m. Papildus realiz?ts jaunas programmat?ras risin?jums, ar m?r?iizmantot DBBC sist?mu k? daudzfunkcion?lu datu ciparošanas iek?rtu, kasizmantojama bistatiskiem radara nov?rojumiem, tai skait? ar? rad

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

2012-12-01

206

High-frequency radar observations of ocean surface currents.  

PubMed

This article reviews the discovery, development, and use of high-frequency (HF) radio wave backscatter in oceanography. HF radars, as the instruments are commonly called, remotely measure ocean surface currents by exploiting a Bragg resonant backscatter phenomenon. Electromagnetic waves in the HF band (3-30 MHz) have wavelengths that are commensurate with wind-driven gravity waves on the ocean surface; the ocean waves whose wavelengths are exactly half as long as those of the broadcast radio waves are responsible for the resonant backscatter. Networks of HF radar systems are capable of mapping surface currents hourly out to ranges approaching 200 km with a horizontal resolution of a few kilometers. Such information has many uses, including search and rescue support and oil-spill mitigation in real time and larval population connectivity assessment when viewed over many years. Today, HF radar networks form the backbone of many ocean observing systems, and the data are assimilated into ocean circulation models. PMID:22809196

Paduan, Jeffrey D; Washburn, Libe

2013-01-01

207

High-frequency radar measurements of coastal ocean surface currents  

Microsoft Academic Search

Long-term, high-frequency (HF) radar measurements of coastal ocean surface currents allow observation of large-scale coastal circulation events with a temporal and spatial resolution not readily available with conventional instrumentation. Additionally, HF radar is capable of measuring the directional distribution of ocean waves at a {open_quotes}resonant{close_quotes} frequency. These and other measurements using inversion techniques provide information useful for estimating a variety

1993-01-01

208

Studies of HF-induced Strong Plasma Turbulence at the HAARP Ionospheric Observatory  

Microsoft Academic Search

High power HF transmitters may induce a number of plasma instabilities in the interaction region of overdense ionospheric plasma. We report results from our recent experiments using over one gigawatt of HF power (ERP) to generate and study strong Langmuir turbulence (SLT) and particle acceleration at the HAARP Observatory, Gakona, Alaska. Among the effects observed and studied in UHF radar

J. P. Sheerin; N. Adham; R. G. E. Roe; M. R. Keith; B. J. Watkins; W. A. Bristow; P. A. Bernhardt; C. A. Selcher

2010-01-01

209

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

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 identified on digital borehole images from shallowing-upward, peritidal HFCs show that the highest porosity occurs at the base of the cycles, moderate porosity at the middle of the cycles, and lowest porosity occurs at the top of cycles. Hydraulic conductivity is also highest at the base of the peritidal cycles and lowest in the middle to upper parts of cycles. This change in porosity and hydraulic conductivity from bottom to top is visible as an upward variation in reflection amplitude on GPR profiles-lowest amplitudes at the base and highest at the cycle tops. This study demonstrates that GPR can be used to show the qualitative distribution of porosity and hydraulic conductivity within a cycle-stratigraphic framework composed of carbonate HFCs. The distribution of porosity and hydraulic conductivity within HFCs is related to depositional textures. The upward and lateral patterns of the rock facies within the HFCs can be translated to geophysical-log properties and radar facies configurations that could aid in interpretation and prediction of ground-water flow through a carbonate aquifer. ?? 2003 Elsevier B.V. All rights reserved.

Cunningham, K.J.

2004-01-01

210

Radar applications overview  

NASA Astrophysics Data System (ADS)

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.

Greenspan, Marshall

1996-06-01

211

Image compression and transmission for HF radio systems  

Microsoft Academic Search

This paper presents a novel image compression technique coupled with three HF transmission schemes. The image compression scheme is based on a phase dispersion technique originally developed for the design of pulse compression radar waveforms. The technique forms the basis for a lossless, invertible transform that converts sub-band coefficients to an intermediate domain. This image compression scheme generates significance map

Michael T. Kurdziel; William N. Furman

2002-01-01

212

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

NASA Astrophysics Data System (ADS)

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.

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

2010-09-01

213

The SHAllow RADar (SHARAD) Onboard the NASA MRO Mission  

Microsoft Academic Search

This paper describes the mission concepts, design, and achievements of the Italian Space Agency (ASI)- provided Mars SHAllow RADar (SHARAD) sounder high-fre- quency (HF) sounding radar, used onboard the National Aeronautics and Space Administration (NASA) Mars Reconnais- sance Orbiter (MRO) Spacecraft. Its goals are the detection of liquid or solid water below the surface, and the mapping of subsurface geologic

Renato Croci; Roberto Seu; Enrico Flamini; Enrico Russo

2011-01-01

214

Radar Entomology  

NSDL National Science Digital Library

Radar tracking used to profile insect migration, mating and flight patterns. Many links to various pages include current workers in radar entomology, historical uses of the technology, and many images.

0000-00-00

215

Radar principles  

NASA Technical Reports Server (NTRS)

Discussed here is a kind of radar called atmospheric radar, which has as its target clear air echoes from the earth's atmosphere produced by fluctuations of the atmospheric index of refraction. Topics reviewed include the vertical structure of the atmosphere, the radio refractive index and its fluctuations, the radar equation (a relation between transmitted and received power), radar equations for distributed targets and spectral echoes, near field correction, pulsed waveforms, the Doppler principle, and velocity field measurements.

Sato, Toru

1989-01-01

216

Temporal evolution of HF-enhanced plasma lines  

NASA Technical Reports Server (NTRS)

A theoretical investigation is conducted of the temporal evolution of HF-enhanced plasma lines (HFPLs). An extended theoretical model is presented which was originally intended to explain the intensity overshoot of the high frequency enhanced plasma line (HFPL). The extension takes into consideration the fact that nonresistant heating of plasma electrons by the parametrically excited Langmuir waves can yield an apparent increment in electron temperature. It is pointed out that the HFPLs refer to the radar echoes at frequencies near the sum and difference of the radar frequency and the HF heater wave frequency. It is suggested that backscatter of radar signals from plasma waves having a wavenumber of 18/m cause the enhanced spectral lines.

Kuo, S. P.; Ho, A. Y.; Lee, M. C.

1990-01-01

217

A theoretical model for the temporal evolution of HF-enhanced plasma lines  

NASA Technical Reports Server (NTRS)

The HF-enhanced plasma lines (HFPLs) observed in the Arecibo heating experiments refer to the radar returns at frequencies near the sum and difference of the radar frequency and the HF-heatear frequency. Those enhanced spectral lines are caused by backscatter of radar signals from parametrically excited plasma waves having a wavenumber of 18 n. A nonlinear theory was developed to describe the temporal evolution of those specified plasma waves and their originating altitude interval of HFPLs observed at Arecibo, Puerto Rico are explained. The theoretical resultsagree well with the observation (Djuth and Sulzer, 1989).

Kuo, S. P.; Ho, A. Y.; Lee, M. C.; Djuth, F. T.

1990-01-01

218

A radar image time series  

NASA Technical Reports Server (NTRS)

A set of ten side-looking radar images of a mining area in Arizona that were aquired over a period of 14 yr are studied to demonstrate the photogrammetric differential-rectification technique applied to radar images and to examine changes that occurred in the area over time. Five of the images are rectified by using ground control points and a digital height model taken from a map. Residual coordinate errors in ground control are reduced from several hundred meters in all cases to + or - 19 to 70 m. The contents of the radar images are compared with a Landsat image and with aerial photographs. Effects of radar system parameters on radar images are briefly reviewed.

Leberl, F.; Fuchs, H.; Ford, J. P.

1981-01-01

219

Decorrelation in interferometric radar echoes  

NASA Technical Reports Server (NTRS)

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.

Zebker, Howard A.; Villasensor, John

1992-01-01

220

Radar: the evolution since World War II  

Microsoft Academic Search

Modern radar design has benefited from the evolution of specialized digital processing, allowing high resolution ground mapping, target identification, and target tracking under many conditions. Air-to-air interception makes use of complex decision processes to select from many modes that depend on the clutter backgrounds and flight profiles. Today's multimode radars provide this information for each task while minimizing distractions. Fire

R. Strong

2005-01-01

221

Data volume reduction for imaging radar polarimetry  

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

222

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

NASA Astrophysics Data System (ADS)

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.

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

2009-08-01

223

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

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

224

Spaceborne radar  

NASA Technical Reports Server (NTRS)

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.

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

225

The meteor radar as a tool for upper atmosphere research  

NASA Technical Reports Server (NTRS)

Meteor radar provide measurements of the upper mesosphere and lower thermosphere neutral wind field by using the reflection of electromagnetic waves from meteor trails. These radars are relatively inexpensive and provide an excellent means of monitoring the mean winds and tides in the 80 to 100 km region. Recently new techniques were developed to detect meteor echoes from other ground based radar systems operating in the HF/VHF frequency range. The meteor echo information augments the data that are routinely collected by these radars. These new techniques are discussed.

Avery, S. K.

1989-01-01

226

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

227

Meridian Digital M2008/M2008HF  

E-print Network

.......................................................................................... 17 Speed Call on Private Lines .................................................................. 18 Line ...............................................................................................24 Receiving a call 27 Call Waiting

228

Meridian Digital M2008/M2008HF  

E-print Network

.......................................................................................... 17 Speed Call on Private Lines .................................................................. 18 Line ...............................................................................................24 Receiving a call 27 Call Waiting ................................................................................

Hayden, Nancy J.

229

Optical-radar-DEM remote sensing data integration for geological mapping in the Afar Depression, Ethiopia  

Microsoft Academic Search

The advantages of integrating optical (Landsat Enhanced Thematic Mapper Plus (ETM+) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)) and radar (Shuttle Imaging Radar (SIR) C, X-band Synthetic Aperture Radar (SAR) and RADARSAT-1) remote sensing data, and digital elevation models (DEMs) (Shuttle Radar Topography Mission (SRTM)) for geological mapping in arid regions such as the Afar Depression in Ethiopia

Allison K. Thurmond; Mohamed G. Abdelsalam; John B. Thurmond

2006-01-01

230

A high resolution multimode synthetic aperture radar  

NASA Astrophysics Data System (ADS)

Modifications to a high performance synthetic aperture mode for the AN/APS-506 radar are described. The modifications include improvements in the system coherency, the addition of demodulation and digitization circuitry, the installment of a strapdown inertial sensing system on the antenna, and the development of the real time motion compensation and airborne SAR processing subsystems. In the modified version of the radar pulse compression waveform generation is based on a digital waveform scheme that makes it possible to enhance the spectral purity of the radar signals and to obtain a great deal of flexibility in generating waveforms of various bandwidths.

Haslam, G. E.; vant, M. R.; Difilippo, D.

231

Longitudinal and seasonal variations in the occurrence of sunrise undulation at the dip equator: A study using Trivandrum and Jicamarca Digital Ionosonde and Jicamarca Incoherent Scatter radar measurements  

NASA Astrophysics Data System (ADS)

At night, the absence of photo ionization in combination with sustained downward plasma motion means that the F region can be severely depleted at the magnetic equator at the end of the night. As a result, there can be, at sunrise, a sudden upward jump in altitude of the F region peak which is then followed by a quick descent in association with the downward motion of the photo ionization production peak. This constitutes what has been described as the equatorial sunrise undulation. Its anecdotal existence has been reported over Jicamarca (120 S, 76.90 W, 1.70 S dip-latitude) while it has been seen repeatedly over Trivandrum (8.470 N, 76.920 E, 0.170 S dip latitude), India, particularly during equinox conditions. Seasonal variations in the occurrence of sunrise undulation in the F-region peak height (hmF2) at two longitudinally separated geomagnetic equatorial stations, namely Jicamarca and Trivandrum are being presented. Measurements from Digital ionosondes, located at these two stations, have been used in this study. A fast descends in hmF2 after the local F region sunrise was quite visible at both the stations. The frequency of occurrence of sunrise undulation at Trivandrum, however, was high compared to the same at Jicamarca. There were noticeable differences in the seasonal occurrence of sunrise undulation at the two places. While it was observed throughout the year at Trivandrum, there was a distinct seasonal preference of occurrence at Jicamarca, at least in the year 2010, a low solar active period. Its frequency of occurrence at Jicamarca was high during winter (June) solstice, low during equinox (March) and had almost negligible occurrence during summer solstice (December). We show that (1) plasma density during sunrise at Jicamarca on average was twice as much as at Trivandrum, and (2) average height of hmF2 during night at Jicamarca was higher (~100km ) during equinox and solstice months compared to the same at Trivandrum. Our results suggest that the background density plays an important role in the observation of a sunrise undulation in the F region peak which itself is quite sensitive to the electric field seen by the plasma between sunset and sunrise. Using incoherent backscatter radar data from Jicamarca we show that the sunrise undulation can be masked when remnant plasma from the previous night does not come down to low enough altitude. We argue that this is the reason behind the lack of sunrise undulations in December at Jicamarca, given the fact that there is often very strong plasma uplift in the evening at that time of year. Thus the seasonal and longitudinal variation of sunrise ionosphere is a proxy to understand the electro-dynamical features of the night before.

Ambili, K. M.; St-Maurice, Jean-Pierre; Choudhary, Raj Kumar

232

Radar interferometry: limits and potential  

Microsoft Academic Search

The contribution of radar interferometry to the field of digital terrain modeling is important because this technique offers specific features which optical instruments cannot attain. However, the complexity of the height restitution and the accuracy of the result strongly depend on the orbital geometry at the time of the data takes. The present study aims at assessing the potential of

Didier Massonnet; Thierry Rabaute

1993-01-01

233

Automotive radar  

NASA Astrophysics Data System (ADS)

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.

Rohling, Hermann

2004-07-01

234

The AN\\/GSC10 (KATHRYN) Variable Rate Data Modem for HF Radio  

Microsoft Academic Search

The AN\\/GSC-10 (KATHRYN) is a new modem equipment for digital data transmission on HF radio circuits. Its unique modulation technique provides a wide range of signal redundancy and data rate to allow optimum performance over the correspondingly wide range of propagation conditions characteristic of HF radio. Efficient detection is achieved at all levels of redundancy by utilizing a fully coherent

M. Zimmerman; A. Kirsch

1967-01-01

235

Stimulated Emission and Radar Observations of RF-Ionosphere Interaction Experiments at HAARP  

Microsoft Academic Search

High power HF radiowaves launched from ground-based transmitters interact with overdense ionospheric plasma to produce strong nonlinear effects. Where available, VHF\\/UHF radar data reveal several spatial and temporal signatures in the plasma line backscatter indicative of strong turbulence effects at many scales. Stimulated electromagnetic emissions (SEE) which propagate to HF receivers on the ground may provide information complementary to plasma

J. P. Sheerin; J. M. Parzych; J. P. Mills; W. A. Bristow; K. M. Groves

2003-01-01

236

Digital communications study  

NASA Technical Reports Server (NTRS)

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.

Boorstyn, R. R.

1973-01-01

237

Integrated photonic analog-to-digital converters  

E-print Network

Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical ...

Khilo, Anatol (Anatol M.)

2011-01-01

238

Survey of Chinese radars  

Microsoft Academic Search

Open information on about 200 Chinese radars including earlier radars is now available. By number of model types China is an important radar country. This Chinese radar survey paper shows that Chinese radars cover a wide spectrum of civilian and military applications. Chinese civilian radars include air-borne weather avoidance\\/navigation, air traffic control (ASR, ARSR, GCA, SSR), harbor surveillance, industrial applications,

S. L. Johnston

1995-01-01

239

Stimulated Emissions and Radar Scatter from Pulsed RF-Ionosphere Interactions at HAARP  

Microsoft Academic Search

High power HF radiowave pulses launched from ground-based transmitters interact with overdense quiescent ionospheric plasma to produce strong turbulence effects. These effects are evident in the ion and plasma lines detected by diagnostic radars. Several spatial and temporal signatures in the backscattered plasma lines show reproducible evidence of strong turbulence effects at many scales. Complementary to radar probe diagnostics are

J. P. Sheerin; J. P. Mills; K. M. Groves; W. A. Bristow; Jacqueline Pau; A. Y. Wong

2001-01-01

240

Optimal Pollution Mitigation in Monterey Bay Based on Coastal Radar Data and Nonlinear  

E-print Network

Optimal Pollution Mitigation in Monterey Bay Based on Coastal Radar Data and Nonlinear Dynamics run-off which is a typical source of pollution in the bay. We show that a HF radar-based pollution release scheme using this flow structure reduces the impact of pollution on the coastal envi- ronment

Marsden, Jerrold

241

Measurement of ocean wave spectra using narrow-beam HE radar  

Microsoft Academic Search

A data interpretation algorithm is developed to extract ocean wave information from HF radar backscatter observed by a narrow-beam antenna system. The basis of this measurement is the inversion of the integral equation representing the second-order radar cross section of the ocean surface. This equation is numerically inverted by approximating it as a matrix equation and pseudoinverting the kernel matrix

Randy Howell; John Walsh

1993-01-01

242

Requirements for space shuttle scatter radar experiments  

NASA Technical Reports Server (NTRS)

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.

Harker, K. J.

1975-01-01

243

PACE and EISCAT radar observations of short-lived flow bursts on the nightside  

NASA Technical Reports Server (NTRS)

Concurrent observations from two widely spaced radar experiments of quasi periodic flow bursts in the nightside are presented. The flow bursts closely resemble single radar observations reported by Williams et al. By using the Polar Anglo-American Conjugate Experiment (PACE) HF radar array at Halley Bay in conjunction with the EISCAT Common Program (CP) 2-D experiment, the flow bursts are shown to be a global phenomenon and important information as to their development and propagation can be determined.

Freeman, M. P.; Morelli, J. P.; Cowley, S. W. H.; Pinnock, M.; Williams, P. J. S.; Farrugia, C. J.

1991-01-01

244

Analysis of synthetic aperture radar imagery  

NASA Technical Reports Server (NTRS)

Some problems faced in applications of radar measurements in hydrology are: (1) adequate calibration of the radar systems and direct digital data will be required in order that repeatable data can be acquired for hydrologic applications; (2) quantitative hydrologic research on a large scale will be prohibitive with aircraft mounted synthetic aperture radar systems due to the system geometry; (3) spacecraft platforms appear to be the best platforms for radar systems when conducting research over watersheds larger than a few square kilometers; (4) experimental radar systems should be designed to avoid use of radomes; and (5) cross polarized X and L band data seem to discriminate between good and poor hydrologic cover better than like polarized data.

Blanchard, B. J.

1977-01-01

245

Generating nonlinear FM chirp radar signals by multiple integrations  

SciTech Connect

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.

Doerry, Armin W. (Albuquerque, NM)

2011-02-01

246

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

NASA Technical Reports Server (NTRS)

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).

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

2013-01-01

247

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)

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.

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

2003-01-01

248

Radars in space  

NASA Technical Reports Server (NTRS)

The capabilities of active microwave devices operating from space (typically, radar, scatterometers, interferometers, and altimeters) are discussed. General radar parameters and basic radar principles are explained. Applications of these parameters and principles are also explained. Trends in space radar technology, and where space radars and active microwave sensors in orbit are going are discussed.

Delnore, Victor E.

1990-01-01

249

Hf Transition Probabilities and Abundances  

E-print Network

Radiative lifetimes from laser-induced fluorescence measurements, accurate to about +/- 5 percent, are reported for 41 odd-parity levels of Hf II. The lifetimes are combined with branching fractions measured using Fourier transform spectrometry to determine transition probabilities for 150 lines of Hf II. Approximately half of these new transition probabilities overlap with recent independent measurements using a similar approach. The two sets of measurements are found to be in good agreement for measurements in common. Our new laboratory data are applied to refine the hafnium photospheric solar abundance and to determine hafnium abundances in 10 metal-poor giant stars with enhanced r-process abundances. For the Sun we derive log epsilon (Hf) = 0.88 +/- 0.08 from four lines; the uncertainty is dominated by the weakness of the lines and their blending by other spectral features. Within the uncertainties of our analysis, the r-process-rich stars possess constant Hf/La and Hf/Eu abundance ratios, log epsilon (Hf/La) = -0.13 +/- 0.02 (sigma = 0.06) and log epsilon (Hf/Eu) = +0.04 +/- 0.02 (sigma = 0.06). The observed average stellar abundance ratio of Hf/Eu and La/Eu is larger than previous estimates of the solar system r-process-only value, suggesting a somewhat larger contribution from the r-process to the production of Hf and La. The newly determined Hf values could be employed as part of the chronometer pair, Th/Hf, to determine radioactive stellar ages.

J. E. Lawler; E. A. Den Hartog; Z. E. Labby; C. Sneden; J. J. Cowan; I. I. Ivans

2006-11-01

250

Medium-scale traveling ionospheric disturbances observed with the SuperDARN Hokkaido radar, all-sky imager, and GPS network and their relation to concurrent sporadic E irregularities  

Microsoft Academic Search

We present midlatitude medium-scale traveling ionospheric disturbances (MSTIDs) observed with a Super Dual Auroral Radar Network (SuperDARN) HF radar at around 10 MHz in Hokkaido, Japan, in combination with a 630-nm all-sky imager and a GPS network (GEONET) that provides total electron content (TEC) data. MSTIDs propagating southward from high latitudes are detected at first with the HF radar and

T. Ogawa; N. Nishitani; Y. Otsuka; K. Shiokawa; T. Tsugawa; K. Hosokawa

2009-01-01

251

Data Acquisition System for Doppler Radar Vital-Sign Monitor  

Microsoft Academic Search

Automatic gain control (AGC) units increase the dynamic range of a system to compensate for the limited dynamic range of analog to digital converters. This problem is compounded in wireless systems in which large changes in signal strength are effects of a changing environment. These issues are evident in the direct-conversion Doppler radar vital- sign monitor. Utilizing microwave radar signals

Alexander M. Vergara; Victor M. Lubecke

2007-01-01

252

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 ...

253

Weather Radar Fundamentals  

NSDL National Science Digital Library

This 2-hour module presents the fundamental principles of Doppler weather radar operation and how to interpret common weather phenomena using radar imagery. This is accomplished via conceptual animations and many interactive radar examples in which the user can practice interpreting both radar reflectivity and radar velocity imagery. Although intended as an accelerated introduction to understanding and using basic Doppler weather radar products, the module can also serve as an excellent refresher for more experienced users.

2014-09-14

254

Combined synthetic aperture radar/Landsat imagery  

NASA Technical Reports Server (NTRS)

This paper presents the results of investigations into merging synthetic aperture radar (SAR) and Landsat multispectral scanner (MSS) images using optical and digital merging techniques. The unique characteristics of airborne and orbital SAR and Landsat MSS imagery are discussed. The case for merging the imagery is presented and tradeoffs between optical and digital merging techniques explored. Examples of Landsat and airborne SAR imagery are used to illustrate optical and digital merging. Analysis of the merged digital imagery illustrates the improved interpretability resulting from combining the outputs from the two sensor systems.

Marque, R. E.; Maurer, H. E.

1978-01-01

255

Current radar-responsive tag development activities at Sandia National Laboratories  

Microsoft Academic Search

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

Richard C. Ormesher; Kenneth W. Plummer; Lars M. Wells

2004-01-01

256

Coastal Current Observation in the Area of Abrupt Topographic Change with DBF Ocean Radar  

Microsoft Academic Search

A DBF ocean radar can detect the surface current pattern every 15 minutes. The tidal current and the residual current were investigated through the continuous observation of the DBF (digital beam forming) radar in the middle-west area of Ariake Bay in autumn 2005. For the validation of the surface current data by the DBF ocean radar the ship-board ADCP measurements

S. Sakai; T. Tsubono; M. Matsuyama; A. Tada; M. Mizunuma

2006-01-01

257

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)

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.

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

2012-10-01

258

HF mitigation via the Texaco-UOP HF additive technology  

SciTech Connect

Alkylation is one of the key processes used by refiners to produce high-octane gasoline. In the alkylation process, light olefins and isobutane are converted to alkylate, a high-octane, low-vapor-pressure, paraffinic gasoline-blending component. Because of its clean burning characteristics and ability to contribute to lower emissions, alkylate is a highly valued component in premium and reformulated gasolines. Alkylation process technology using hydrogen fluoride (HF) as a catalyst has been widely used for many years. Since the mid-1980s, a primary concern has been the tendency of HF to form an aerosol when HF is released to the atmosphere. Much effort has gone into the development of measures to ensure the safe handling of HF in the refinery environment. Texaco and UOP have under development an HF additive technology. The key to this technology is the discovery of a class of additives that form a complex with HF to significantly reduce the aerosol-forming tendency of the catalyst system and still maintain acceptable catalytic performance and product quality. The purpose of this paper is to provide an update on the development status of the Texaco-UOP HF additive technology. Aerosol reduction has been demonstrated in small-scale laboratory release tests as well as in larger scale wind tunnel release tests. The catalytic performance of the HF additive has been demonstrated in laboratory alkylation facilities and in a short-term experimental trial in a full-scale refinery unit. On the basis of the positive results obtained in the test program, a project is under way to implement the HF additive technology on a continuous basis in an existing Texaco alkylation unit by the third quarter of 1994.

Sheckler, J.C.; Hammershaimb, H.U. (UOP, Des Plaines, IL (United States)); Ross, L.J. (Texaco Refining and Marketing, Inc., El Dorado, KS (United States)); Comey, K.R. III (Texaco Inc., Port Arthur, TX (United States). Research and Development)

1994-01-01

259

Multipolarization Radar Images for Geologic Mapping and Vegetation Discrimination  

Microsoft Academic Search

The NASA\\/JPL airborne synthetic aperture radar system produces radar image data simultaneously in four linear polarizations (HH, VV, VH, HV) at 24.6-cm wavelength (L-band), with 10-m resolution, across a swath width of approximately 10 km. The signal data are recorded optically and digitally and annotated in each of the channels to facilitate a completely automated digital correlation. Both standard amplitude,

Diane Evans; Tom Farr; J. P. Ford; Thomas Thompson; C. L. Werner

1986-01-01

260

A Monostatic Ocean Scattering Cross Section for the Case of Surface Wave Radar Operating from a Floating Barge  

Microsoft Academic Search

An understanding of the parameters affecting the high frequency surface wave radar (HFSWR) cross sections of the ocean surface is essential to employing such formulations in remote sensing models. Available techniques to date have not explicitly included the effect of antenna motion on the ocean clutter spectra derived from HF Doppler radar data. Here, a model, which assumes the incident

John Walsh; Eric Gill; Weimin Huang

2008-01-01

261

Using a P2P architecture for voice and radar transportation in critical command and control systems  

Microsoft Academic Search

The Brazilian air traffic service is constituted by a civil and a military organization, which provide tracking (radar), voice and data communication (VHF, UHF and HF) services, through an integrated network. To optimize the management of its air traffic system, Brazil divides the airspace into four independent Regional Centers. In each of these regions, the existing sensors (radars and radios)

A. de Barros Barrete; E. T. Yano

2010-01-01

262

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

NASA Technical Reports Server (NTRS)

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.

Holtzman, J.

1972-01-01

263

Frequency stability associated with a cw HF laser.  

PubMed

The frequency stability of a cw, electrically initiated HF mixing laser was investigated using heterodyne and interferometric techniques. A stability corresponding to 1 part in 10(8) was achieved over an observation time of 150 msec. The data indicated that improved performance would be achieved by increasing the mechanical stability in the optical system. Long-term stability was demonstrated by locking the laser output to the Lamb dip of the lasing transition. Based upon these experiments, the cw chemical laser shows potential as a stable frequency local oscillator for applications such as laser radar and communications. PMID:20164992

Hinchen, J J; Freiberg, R J

1976-02-01

264

Radar echo processing with partitioned de-ramp  

DOEpatents

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.

Dubbert, Dale F.; Tise, Bertice L.

2013-03-19

265

Future Trends in Automotive Radar \\/ Imaging Radar  

Microsoft Academic Search

There is a growing interest of car manufacturers in sensors monitoring the car's surrounding area in order to improve safety systems from mere crash survival to crash prediction or prevention by early detection of hazardous situations. Therefore radar sensors have been intensively investigated for many years. A large variety of radar based vehicular sensors have been developed. Narrow-beam radars are

J. Wenger

1998-01-01

266

An analysis of simulated stereo radar imagery  

NASA Technical Reports Server (NTRS)

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 mountainous terrain. The simulated radar imagery was evaluated by interpreters for ease of stereo perception and information content, and rank order 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 relative relief of the terrain. Examples of the simulated stereo imagery are presented for a candidate spaceborne imaging radar having four selectable angles of incidence.

Pisaruck, M. A.; Kaupp, V. H.; Macdonald, H. C.; Waite, W. P.

1983-01-01

267

Marburg Hemorrhagic Fever (Marburg HF)  

MedlinePLUS

... a sighted, cave-dwelling bat widely distributed across Africa. Given the fruit bat's wide distribution, more areas ... Marburg HF typically appears in sporadic outbreaks throughout Africa; laboratory confirmed cases have been reported in Uganda, ...

268

Radar observations of F region equatorial irregularities  

Microsoft Academic Search

Experimental results obtained with the Jicamarca radar and a new digital processing system during spread F conditions are presented. The data consist of two-dimensional maps showing backscatter power and samples of frequency spectra of the backscatter signals as a function of altitude and time. Almost simultaneous spread F backscatter power and incoherent scatter observations of electron density and vertical drifts

Ronald F. Woodman; César La Hoz

1976-01-01

269

Shuttle imaging radar-C science plan  

NASA Technical Reports Server (NTRS)

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.

1986-01-01

270

Processing for spaceborne synthetic aperture radar imagery  

NASA Technical Reports Server (NTRS)

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.

Lybanon, M.

1973-01-01

271

Method for orthorectification of terrestrial radar maps  

NASA Astrophysics Data System (ADS)

The vehicle-based PELICAN radar system is used in the context of mobile mapping. The R-SLAM algorithm allows simultaneous retrieval of the vehicle trajectory and of the map of the environment. As the purpose of PELICAN is to provide a means for gathering spatial information, the impact of distortion caused by the topography is not negligible. This article proposes an orthorectification process to correct panoramic radar images and the consequent R-SLAM trajectory and radar map. The a priori knowledge of the area topography is provided by a digital elevation model. By applying the method to the data obtained from a path with large variations in altitude it is shown that the corrected panoramic radar images are contracted by the orthorectification process. The efficiency of the orthorectification process is assessed firstly by comparing R-SLAM trajectories to a GPS trajectory and secondly by comparing the position of Ground Control Points on the radar map with their GPS position. The RMS positioning error moves from 5.56 m for the raw radar map to 0.75 m for the orthorectified radar map.

Jaud, Marion; Rouveure, Raphaël; Faure, Patrice; Moiroux-Arvis, Laure; Monod, Marie-Odile

2014-11-01

272

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)

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.

Sundararaman, Sathishkumar

273

Constraining energetic slope currents through assimilation of high-frequency radar observations  

NASA Astrophysics Data System (ADS)

Assimilation of high-frequency (HF) radar current observations and CTD hydrography is performed with the 4D-Var analysis scheme implemented in the Regional Ocean Modeling System (ROMS). We consider both an idealized case, with a baroclinic slope current in a periodic channel, and a realistic case for the coast of Vesterålen in northern Norway. In the realistic case, the results of the data assimilation are compared with independent data from acoustic profilers and surface drifters. Best results are obtained when background error correlation scales are small (10 km or less) and when the data assimilation window is short, i.e. about 1 day. Furthermore, we find that the impact of assimilating HF radar currents is generally larger than the impact of CTD hydrography. However, combining the HF radar currents with a few hydrographic profiles gives significantly better results, which demonstrates the importance of complementing surface observations with observations of the vertical structure of the ocean.

Sperrevik, A. K.; Christensen, K. H.; Röhrs, J.

2015-03-01

274

Optimal pollution mitigation in Monterey Bay based on coastal radar data and nonlinear dynamics.  

PubMed

High-frequency (HF) radar technology produces detailed velocity maps near the surface of estuaries and bays. The use of velocity data in environmental prediction, nonetheless, remains unexplored. In this paper, we uncover a striking flow structure in coastal radar observations of Monterey Bay, along the California coastline. This complex structure governs the spread of organic contaminants, such as agricultural runoff which is a typical source of pollution in the bay. We show that a HF radar-based pollution release scheme using this flow structure reduces the impact of pollution on the coastal environment in the bay. We predict the motion of the Lagrangian flow structures from finite-time Lyapunov exponents of the coastal HF velocity data. From this prediction, we obtain optimal release times, at which pollution leaves the bay most efficiently. PMID:17948809

Coulliette, Chad; Lekien, Francois; Paduan, Jeffrey D; Haller, George; Marsden, Jerrold E

2007-09-15

275

CUTLASS observations of a high-m ULF wave and its consequences for the DOPE HF Doppler sounder  

Microsoft Academic Search

The CUTLASS (Co-operative UK Twin Located Auroral Sounding System) Finland HF radar, whilst operating in a high spatial and temporal resolu- tion mode, has measured the ionospheric signature of a naturally occurring ULF wave in scatter artificially generated by the Tromsø Heater. The wave had a period of 100 s and exhibited curved phase fronts across the heated volume (about

D. M. Wright; T. K. Yeoman

1999-01-01

276

Crop classification with a Landsat/radar sensor combination  

NASA Technical Reports Server (NTRS)

A combined Landsat/radar approach to classification of remotely sensed data, with emphasis on crops, was undertaken. Radar data were obtained by microwave radar spectrometers over fields near Eudora, Kansas and Landsat image data were obtained for the same test site. After Landsat digital images were registered and test-cells extracted, a comparable set of radar image pixels were simulated to match the Landsat pixels. The combined data set is then used for classification, and the results are examined with the best combination of sensor variables identified. Finally, the usefulness of radar in a simulated cloud-cover situation is demonstrated. The major conclusion derived from this study is that the combination of radar/optical sensors is superior to either one alone.

Li, R. Y.; Ulaby, F. T.; Eyton, J. R.

1980-01-01

277

SPREAD DOPPLER CLUTTER MITIGATION FOR OTH RADAR BY PHYSICS ASSISTED ADAPTIVE PROCESSING  

Microsoft Academic Search

The detection performance of skywave HF over-the-horizon radars is fundamentally limited by ionospheric motion which causes spreading of surface clutter returns in Doppler space. This paper exploits a model for HF propagation through ionospheric irregularities based on a thin phase screen formulation which is used to derive the Doppler spread and the spatio-temporal dependence in the received field due to

Dinesh R; Jeffrey L. Krolik

278

HF echoes from ionization potentially produced by high-altitude discharges  

SciTech Connect

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.

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

1997-04-01

279

Space shuttle synthetic aperture radar. [using real time  

NASA Technical Reports Server (NTRS)

Results of a feasibility study to investigate a digital signal processor for real-time operation with a synthetic aperture radar system aboard the space shuttle are presented. Pertinent digital processing theory, a description of the proposed system, and size, weight, power, scheduling, and development estimates are included.

1975-01-01

280

Radar electronic warfare  

NASA Astrophysics Data System (ADS)

An overview of radar and electronic warfare is given. Definitions, common terms, and principles of radar and electronic warfare, and simple analyses of interactions between radar systems and electronic countermeasures (ECM) are presented. Electronic counter-countermeasure and electronic support measures are discussed. Background material in mathematics, electromagnetics, and probability necessary for an understanding of radar and electronic warfare is given and radar tracking models are examined. The effects of various ECM emissions on radar systems are analyzed, including discussion of active ECM and angle scanning systems, angle measurement in monopulse, and automatic gain control.

Golden, August, Jr.

281

Radar observations of wave transformations in the vicinity of islands  

NASA Technical Reports Server (NTRS)

Remote sensing by ground-based HF radar and airborne synthetic aperture radar and in situ wave measurements performed on March 25, 1977 during the West Coast Experiment have made it possible to form an overall picture of the 7-sec-period wave climate over a 35,000 sq km region off the southern California coast. The picture which emerges from these measurements shows a broad deep-ocean directional distribution arriving from the west and being significantly modified as it travels coastward passing San Clemente and Santa Catalina islands.

Vesecky, J. F.; Teague, C. C.; Hsiao, S. V.; Shemdin, O. H.; Pawka, S. S.

1980-01-01

282

High-resolution studies of the HF ionospheric modification interaction region  

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

283

Radar Range Sidelobe Reduction Using Adaptive Pulse Compression Technique  

NASA Technical Reports Server (NTRS)

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 technique could bring significant impact on future radar development. The novel feature of this innovation is the non-linear FM (NLFM) waveform design. The traditional linear FM has the limit (-20 log BT -3 dB) for achieving ultra-low-range sidelobe in pulse compression. For this study, a different combination of 20- or 40-microsecond chirp pulse width and 2- or 4-MHz chirp bandwidth was used. These are typical operational parameters for airborne or spaceborne weather radars. The NLFM waveform design was then implemented on a FPGA board to generate a real chirp signal, which was then sent to the radar transceiver simulator. The final results have shown significant improvement on sidelobe performance compared to that obtained using a traditional linear FM chirp.

Li, Lihua; Coon, Michael; McLinden, Matthew

2013-01-01

284

Monitoring tsunami propagation using OTH radar  

NASA Astrophysics Data System (ADS)

Ionospheric anomalies following tsunamis are now observable after major events as Total Electron Content (TEC) fluctuations. GPS and altimeters are important tools for this purpose, but the detection depends on satellites-receivers geometry, when the line of sight crosses the moving perturbation parallel to the wave fronts. All these anomalies show the signature in the ionosphere of tsunami-generated internal gravity waves (IGW) propagating in the neutral atmosphere over oceanic regions. Most of these ionospheric anomalies are deterministic and reproducible by numerical modeling via the coupling mechanism between ocean, neutral atmosphere and ionosphere. This numerical modeling supplies useful information for the estimation of expected anomalies and to explore and identify new techniques to detect the ionospheric tsunami signature. [|#18#|][|#5#|][|#23#|]The Over-The-Horizon (OTH) radars recently proved to be able to measure seismic Rayleigh wave in the ionosphere, consequently we explore here numerically the possibility to detect the ionospheric signature of tsunamis. OTH operate in High Frequency (HF) band and can be used to monitor the bottomside ionosphere over large regions. Those regions can be strongly perturbed by tsunami generated IGW. We reproduce numerically those atmospheric/ionospheric waves as well as the effect that they produce on synthetic radar measurements. The effects of the tsunami directionality are analyzed underlining the radar capabilities to follow the ionospheric perturbations. The large coverage of OTH radar and its sensitivity to plasma anomalies open new perspectives in the future oceanic monitoring and tsunami warning systems.

Coisson, P.; Occhipinti, G.; Lognonne, P.; Rolland, L. M.

2010-12-01

285

Calibration and Validation of Direction-Finding High-Frequency Radar Ocean Surface Current Observations  

Microsoft Academic Search

This paper focuses on the validation of remotely sensed ocean surface currents from SeaSonde-type high-frequency (HF) radar systems. Hourly observations during the period July 22, 2003 through September 9, 2003 are used from four separate radar sites deployed around the shores of Monterey Bay, CA. Calibration of direction-finding techniques is addressed through the comparisons of results obtained using measured and

Jeffrey D. Paduan; Kyung Cheol Kim; Michael S. Cook; Francisco P. Chavez

2006-01-01

286

Current Structure Variations Detected by High-Frequency Radar and Vector-Measuring Current Meters  

Microsoft Academic Search

Ocean surface current measurements from high-frequency (HF) radar are assessed by comparing these data to near-surface current observations from 1 to 30 October 1994 at two moored subsurface current meter arrays (20 and 25 m) instrumented with vector-measuring current meters (VMCMs) and Seacat sensors during the Duck94 experiment. A dual-station ocean surface current radar (OSCR) mapped the current fields at

Lynn K. Shay; Steven J. Lentz; Hans C. Graber; Brian K. Haus

1998-01-01

287

Digital Doppler Processor For Spaceborne Scatterometer  

NASA Technical Reports Server (NTRS)

Report describes conceptual digital Doppler processor for NASA scatterometer (NSCAT), advanced version of SEASAT spaceborne radar scatterometer used to measure winds near surface of ocean. In NSCAT design, six antennas illuminate surface of ocean with fanshaped beams.

LONG. D. G.; Chi, Chong-Yung; Li, Fuk K.

1989-01-01

288

Radar/radiometer facilities for precipitation measurements  

NASA Technical Reports Server (NTRS)

The OSU ElectroScience Laboratory Radar/Radiometer Facilities are described. This instrumentation includes a high-resolution radar/radiometer system, a fully automated low-resolution radar system, and a small surveillance radar system. The high-resolution radar/radiometer system operates at 3, 9, and 15 GHz using two 9.1 m and one 4.6 m parabolic antennas, respectively. The low-resolution and surveillance radars operate at 9 and 15 GHz, respectively. Both the high- and low-resolution systems are interfaced to real-time digital processing and recording systems. This capability was developed for the measurement of the temporal and spatial characteristics of precipitation in conjunction with millimeter wavelength propagation studies utilizing the Advanced Technology Satellites. Precipitation characteristics derived from these measurements could also be of direct benefit in such diverse areas as: the atmospheric sciences, meteorology, water resources, flood control and warning, severe storm warning, agricultural crop studies, and urban and regional planning.

Hodge, D. B.; Taylor, R. C.

1973-01-01

289

Space Radar Image of Owens Valley, California  

NASA Technical Reports Server (NTRS)

This is a three-dimensional perspective view of Owens Valley, near the town of Bishop, California that was 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 southeast along the eastern edge of Owens Valley. The White Mountains are in the center of the image, and the Inyo Mountains loom in the background. The high peaks of the White Mountains rise more than 3,000 meters (10,000 feet) above the valley floor. The runways of the Bishop airport are visible at the right edge of the image. The meandering course of the Owens River and its tributaries appear light blue on the valley floor. Blue areas in the image are smooth, yellow areas are rock outcrops, and brown areas near the mountains 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 data were taken 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. 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, vertically 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 37.4 degrees north latitude and 118.3 degrees west longitude. No vertical exaggeration factor has been applied to the data. SIR-C/X-SAR, a joint mission of the German, Italian, and the United States space agencies, is part of NASA's Mission to Planet Earth.

1999-01-01

290

Space Radar Image of Saline Valley, California  

NASA Technical Reports Server (NTRS)

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 mission of the German, Italian, and the United States space agencies, is part of NASA's Mission to Planet Earth.

1999-01-01

291

Imaging Radar Applications in the Death Valley Region  

NASA Technical Reports Server (NTRS)

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.

Farr, Tom G.

1996-01-01

292

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

SciTech Connect

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.

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

1993-06-01

293

Radar investigation of barium releases over Arecibo Observatory, Puerto Rico  

NASA Technical Reports Server (NTRS)

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.

Djuth, Frank T.

1995-01-01

294

Ionospheric modification induced by high-power HF transmitters - A potential for extended range VHF-UHF communications and plasma physics research  

Microsoft Academic Search

Radio, radar, communications, and photometric experiments are summarized which have been conducted to determine the characteristics of a volume of the ionosphere that has been intentionally modified by high-power HF radio waves. The theoretical and physical bases for ionospheric modification are outlined, high-power HF facilities are described which have been designed for experimental modification of the F-region, and diagnostic measurements

W. F. Utlaut

1975-01-01

295

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

NASA Technical Reports Server (NTRS)

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.

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

1981-01-01

296

Remorque RADAR Description technique  

E-print Network

ANNEXE: Remorque RADAR Description technique Le but de la remorque est de transporter un RADAR et pour héberger l'électronique radar et son opérateur. Caractéristiques générales de la remorque : · PTC'un côté, une baie de l'autre. Un hublot sur le toit et une baie donnant sur la partie RADAR. Un plafonnier

Heurteaux, Yanick

297

Lunar radar backscatter studies  

NASA Technical Reports Server (NTRS)

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.

Thompson, T. W.

1979-01-01

298

Synthetic aperture radar interferometry  

Microsoft Academic Search

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 characteristic of the surface. By exploiting the phase of the coherent radar signal, interferometry has transformed radar remote sensing from a largely interpretive science to a quantitative tool, with applications in cartography, geodesy, land cover

PAUL A. ROSEN; SCOTT HENSLEY; IAN R. JOUGHIN; FUK K. LI; SØREN N. MADSEN; ERNESTO RODRÍGUEZ; RICHARD M. GOLDSTEIN

2000-01-01

299

Digital Media Developing Digital  

E-print Network

Developing Digital Media Developing Digital Media Digital Media Case Study During 2012, IT Services component of student and staff development." In terms of the use of digital media for teaching, Mark Dixon this digital content, mentorship of paramedic students was informal and delivered locally. According to Mairéad

300

Radar Location Equipment Development Program: Phase I  

SciTech Connect

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.

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

1985-06-01

301

The Precision Expandable Radar Calibration Sphere (PERCS) With Applications for Laser Imaging and Ranging  

NASA Astrophysics Data System (ADS)

The Naval Research Laboratory will provide an orbiting calibration sphere to be used with ground-based laser imaging telescopes and HF radio systems. The Precision Expandable Radar Calibration Sphere (PERCS) is a practical, reliable, high-performance HF calibration sphere and laser imaging target to orbit at about 600 km altitude. The sphere will be made of a spherical wire frame with aspect independent radar cross section in the 3 to 35 MHz frequency range. The necessary launch vehicle to place the PERCS in orbit will be provided by the Department of Defense Space Test Program. The expandable calibration target has a stowed diameter of 1 meter and a fully deployed diameter of 10.2 meters. A separate deployment mechanism is provided for the sphere. After deployment, the Precision Expandable Radar Calibration Sphere (PERCS) with 180 vertices will be in a high inclination orbit to scatter radio pulses from a number of ground systems, including (1) over-the-horizon (OTH) radars operated by the United States and Australia; (2) high power HF facilities such as HAARP in Alaska, EISCAT in Norway, and Arecibo in Puerto Rico; (3) the chain of high latitude SuperDARN radars used for auroral region mapping; and (4) HF direction finding for Navy ships. With the PERCS satellite, the accuracy of HF radars can be periodically checked for range, elevation, and azimuth errors. In addition, each of the 360 vertices on the PERCS sphere will support an optical retro-reflector for operations with ground laser facilities used to track satellites. The ground laser systems will be used to measure the precise location of the sphere within one cm accuracy and will provide the spatial orientation of the sphere as well as the rotation rate. The Department of Defense facilities that can use the corner-cube reflectors on the PERCS include (1) the Air Force Maui Optical Site (AMOS), (2) the Starfire Optical Range (SOR), and (3) the NRL Optical Test Facility (OTF).

Bernhardt, P.; Nicholas, A.; Thomas, L.; Davis, M.; Hoberman, C.; Davis, M.

302

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)

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.

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

303

Design and simulation of a scatterometer processor using digital filtering techniques  

E-print Network

-Chairmen of Advisory Committee: Dr. John W. Rouse, Jr. Dr. Jo W. Howze This report describes two digital filtering methods by which scatterometer data can be reprocessed. The processors are designed to operate on sampled data from a Doppler radar scatterometer... The Radar Scatterometer. Scope of this Report II. THE RYAN 13. 3 GHz DOPPLER RADAR SCATTEROMERER. 7 The Doppler Scatterometer. The Analog Processor The Digital Processor. III. DIGITAL FILTER DESIGN. Introduction The K-Transform. 13 19 24 24 26...

Galka, Walter

1975-01-01

304

Radar Meteorology Tutorial  

NSDL National Science Digital Library

Brian McNoldy at Multi-community Environmental Storm Observatory (MESO) educates the public about the use of radar in meteorology in this pdf document. After reading about the history of radar, visitors can find out how radar can detect storms by transmitting a high-power beam of radiation. Students can learn how scatter, absorption, frequencies, scan angles, and moments impact the radar display. With the help of many example images, the author also discusses how to interpret the images collected. At the end of the online document, visitors can learn about the characteristics and capabilities of NEXRAD WSR-88D, the radar used throughout the United States.

McNoldy, Brian

305

Noise and clutter rejection in radars and imaging sensors; Proceedings of the International Symposium, Tokyo, Japan, October 22-24, 1984  

NASA Astrophysics Data System (ADS)

Advanced techniques and systems for image processing and information extraction are considered along with subsurface radars, the polarization and statistical properties of clutter, characteristics of clutter properties, medical and acoustic imaging, remote sensing, radar signal processing, image processing, tracking techniques, antennas, and the imaging radar. Radar systems are discussed, taking into account radar image processing for surface aircraft recognition, clutter suppression in air traffic control radars, the Time Reference Scanning Beam (TRSB) Microwave Landing System (MLS) modelling and analysis in multipath environment, echo enhancement for a marine radar by new display techniques, compact FSK signals for radar clutter rejection, an energy efficient synthesis of an ambiguity surface, and experimental results on discrimination of radar signals by polarization. Attention is given to fast-scan processing in maritime surveillance radar, a distributed digital processing architecture for adaptive suppression of radar clutter and interference, and the noise properties of generators.

Musha, T.; Suzuki, T.; Ogura, H.

306

Delineate subsurface structures with ground penetrating radar  

SciTech Connect

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.

Wyatt, D.E. [Westinghouse Savannah River Co., Aiken, SC (United States); Hu, L.Z. [New Wave Technology, Houston, TX (United States); Ramaswamy, M. [Houston Advanced Research Center, Woodlands, TX (United States); Sexton, B.G. [Microseeps, Inc., Pittsburgh, PA (United States)

1992-10-01

307

space Radar Image of Long Valley, California  

NASA Technical Reports Server (NTRS)

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 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. X-SAR was developed by the Dornier and Alenia Spazio companies for the German space agency, Deutsche Agentur fuer Raumfahrtangelegenheiten (DARA), and the Italian space agency, Agenzia Spaziale Italiana (ASI), with the Deutsche Forschungsanstalt fuer Luft und Raumfahrt e.V.(DLR), the major partner in science, operations and data processing of X-SAR.

1994-01-01

308

Observation and Simulation of Small Earthquake Tsunami in Okinawa by Using Ocean Radar  

NASA Astrophysics Data System (ADS)

The present tsunami warning systems use seismic waves to detect tsunamis. To upgrade the systems, new detecting method by using the ocean radar has been studied. NiCT has observed an ocean current in Okinawa with the HF ocean radar installed in Ishigaki Island and Yonaguni Island. A small earthquake of Mw 6.0 occurred in the observing region on April 4, 2007 and generated a very weak tsunami. In this study, the Doppler spectrums of the ocean radar data and the simulated tsunami propagation are computed and compared.

Takahashi, T.; Konuma, T.; Kojima, S.

2008-12-01

309

Accuracy of topographic maps derived from ERS-1 interferometric radar  

Microsoft Academic Search

An interferometric radar technique for topographic mapping of surfaces promises a high-resolution approach to the generation of digital elevation models. The authors present analyses of data collected by the synthetic aperture radar instrument on-board the ERS-1 satellite on successive orbits. Use of a single satellite in a nearly repeating orbit is attractive for reducing cost and spaceborne hardware complexity; also

Howard A. Zebker; Charles L. Werner; Paul A. Rosen; Scott Hensley

1994-01-01

310

Applicability of radar observations to the prediction of storm runoff  

E-print Network

coefficient of 0. 97A. Digitized dis- tributions of radar observations are then used with this relationship to predict surface runoff from thxee storms over the Dittlo i~ashita River basin. The predicted values of runoff: are lowe? than the observed values...APPLICABILITY OF RADAR OBSERVATIONS TO THE PREDICTION OF STORM RUNOFF A Thesis ODZLL ld. JOHNSON CAPTAIN USAF Submitted tc the Graduate College of the Texas A&? University in partial fulfillment of the requirements for the degre. . of YESTER...

Johnson, Odell Monroe

1967-01-01

311

Low level range coverage performance prediction for VHF radar  

Microsoft Academic Search

A VHF radar frequencies the range coverage is not strictly limited by the quasi-optical horizon like at microwave radar frequencies but is extended due to diffraction propagation. This effect, here called beyond-the-horizon (BTH) detection capability is strongly dependent on the propagation path and thus on the terrain structure. The availability of digital terrain maps gives way to the use of

H. Kuschel

1989-01-01

312

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

313

Array processing without any space diversity: application in the HF band (3-30 MHz)  

Microsoft Academic Search

The paper presents an operational system of digital transmission within the HF frequency range, aiming at a significant increase of the data transfer rate compared with the current standard. Therefore, an array processing method performs with a set of four collocated sensors, the spatial responses of which are different one from each other. This diversity induces a well-conditioned problem of

Y. Erhel; A. Bisiaux; L. Bertel; D. Lemur

2002-01-01

314

A SOFTWARE-DEFINED RADIO IONOSPHERIC CHIRPSOUNDER FOR HF PROPAGATION ANALYSIS  

E-print Network

A SOFTWARE-DEFINED RADIO IONOSPHERIC CHIRPSOUNDER FOR HF PROPAGATION ANALYSIS Pradeep B. Nagaraju the flexibility of state-of-the art digital radio platforms. However, the advent of Software Defined Radio (SDR. In this paper, we report on our development of a prototype Software Defined Radio (SDR) chirpsounder system

Melodia, Tommaso

315

Coherent radar measurement of ocean currents from geostationary orbit  

NASA Technical Reports Server (NTRS)

A coherent HF radar system developed by Barrick has successfully measured ocean surface currents near shore. This innovative system, called CODAR, can map the current vector for coastal areas as large as 10,000 sq km. CODAR's range is limited owing to the strong attenuation suffered by HF ground waves. An alternate technique was proposed by Schuler, in which the cross-product power spectrum of two (different frequency) microwave signals is processed. The frequency of the resonant peak corresponds close by to the Doppler shift of an ocean gravity wave traveling toward the radar at the phase velocity, v(sub p). The slight difference between the frequency of the measured resonant delta K peak and the Doppler frequency shift caused by the motion of the gravity wave is attributed to be the current velocity in the pointing direction of the radar. The Microwave Remote Sensing Laboratory (MIRSL) has considered the feasibility of using this technique to measure ocean surface currents from geostationary satellite platforms. Problems are discussed that must be overcome if a satellite current measurement system is to be realized. MIRSL research activities that address some of these problem areas are discussed. Current measurements are presented that were made using a specially-designed C-Band, step-frequency delta K radar. These measurements suggest that progress is being achieved in detecting ocean surface current motion for a wide variety of ocean surface conditions.

Mcintosh, R. E.

1989-01-01

316

High frequency radar and its application to fresh water Lorelle A. Meadows a,  

E-print Network

over freshwater using CODAR Ocean Sensors SeaSondes, operating at 5 and 42 MHz with 21 W and 90 W order, the strong HF echo arises from a Bragg scattering interaction with ocean waves traveling radially gravity waves traveling radially toward or away from the radar. The presence of near-surface currents

Ruf, Christopher

317

Noncausal Adaptive Spatial Clutter Mitigation in Monostatic MIMO Radar: Fundamental Limitations  

Microsoft Academic Search

The problem of a point target detection masked by clutter distributed over range and Doppler, including the range and Doppler of the target, is considered for a multimode propagation scenario commonly encountered in quasimonostatic HF over-the-horizon radars (OTHR). Here, a clutter signal spread in Doppler frequency due to propagation via a disturbed ionospheric layer competes with a target and narrowband

Yuri I. Abramovich; Gordon J. Frazer; Ben A. Johnson

2010-01-01

318

Do you have a radar bill in your pocket?  

NSDL National Science Digital Library

This activity introduces students to radar bills (currency that has serial numbers that read the same forward and backward) and challenges them to estimate how frequently radar bills occur. The activity, part of the Figure This! collection of 80 math challenges emphasizing math in the real world, explains how symmetry and repeating patterns are important to mathematicians, scientists, and artists. The Hint tells students that our currency has eight-digit serial numbers, and the solution provides a table that shows the relationship between the number of digits in a serial number and the number of radar bills. Related questions ask students to solve similar problems with serial numbers that contain different numbers of digits. Answers to all questions and links to additional resources are provided. Copyright 2005 Eisenhower National Clearinghouse

National Council of Teachers of Mathematics (NCTM)

2002-01-01

319

Experimental phased array radar ELRA with extended flexibility  

NASA Astrophysics Data System (ADS)

An update of a phased array radar research project with the experimental system ELRA (electronic steerable radar) is given with respect to the extended and improved possibilities for performing measurements and evaluations for different types of radar operation. The variability of waveforms for solid-state transmitters is described. Flexible control of multifunction operation with various search and localization tasks is achieved with a network of microcomputers. Different means of signal processing are used for target detection and estimation. The active receiving array is divided into subarrays, and offers digital beamforming for pattern shaping and adaptive jammer suppression. Experimental results are presented.

Groeger, I.; Sander, W.; Wirth, W.-D.

1990-11-01

320

Data processing aspects of synthetic aperture radar  

Microsoft Academic Search

An introduction to the basic features of SAR and the problems of real-time synthetic aperture radar processing is presented. The SAR processing functions are described as well as some computational rates which are required for range and azimuth compression. A hardware pipeline concept consisting of standardized digital processing modules (e.g. two-dimensional storage unit, FIR filter, fast Fourier transformation) is introduced

Roland Schotter

1987-01-01

321

Radio HF precursors of Earthquakes  

Microsoft Academic Search

The high frequency (HF) earthquake electromagnetic precursors (40-55MHz band) were recorded by the four electromagnetic stations a few days (hours) prior the event associated with earthquakes with magnitude more than 5.0 at Crete Island. These experiments were performed continuously during 1998-2002 and specific peculiarities are found. This is underhorizon epicenter position for main part of events under question. Another unusual

Yu. Ruzhin; C. Nomicos; F. Vallianatos; V. Shpakovsky

2004-01-01

322

A fully photonics-based coherent radar system.  

PubMed

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

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

323

A fully photonics-based coherent radar system  

NASA Astrophysics Data System (ADS)

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.

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

324

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

325

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

326

Planetary radar studies  

NASA Technical Reports Server (NTRS)

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.

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

1981-01-01

327

Laser radar in robotics  

SciTech Connect

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.

Carmer, D.C.; Peterson, L.M. [Environmental Research Inst. of Michigan, Ann Arbor, MI (United States)

1996-02-01

328

CHIRP Doppler radar  

NASA Astrophysics Data System (ADS)

The present investigation is concerned with the concept of a combination of the clinical procedure of reconstruction tomography with the radar processing for linear FM pulse compression. An approach based on such a combination is to be employed to map radar backscatter energy. Radar systems employing pulse compression of linear frequency modulated (CHIRP) pulses are considered along with the inversion formula employed by reconstruction tomography. The conventional system enabling radar backscatter mapping is based on pulse-Doppler radar which basically incorporates range-gated spectrum analysis. CHIRP Doppler radar represents a potential alternative. Advantages are related to an absence of requirements to maintain coherence from pulse to pulse, and the suppression of interference due to second-time-around signals. Raabe (1976) has discussed an application involving the imaging of the wakes of reentering space vehicles.

Bernfeld, M.

1984-04-01

329

MIMO radar, SIMO radar, and IFIR radar: a P. P. Vaidyanathan and Piya Pal  

E-print Network

MIMO radar, SIMO radar, and IFIR radar: a comparison P. P. Vaidyanathan and Piya Pal Dept and SIMO radar systems for the case where the transmitter and receiver are collocated. The simplicity of the application allows one to see clearly where the advantages of MIMO radar come from, and what the tradeoffs are

Vaidyanathan, P. P.

330

Integrating a Microwave Radiometer into Radar Hardware for Simultaneous Data Collection Between the Instruments  

NASA Technical Reports Server (NTRS)

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 unintuitive step allows the digital receiver to sample both the radiometer and radar data at a rapid, synchronized data rate (greater than 1 MHz bandwidth). Once both signals are sampled by the same digital receiver, high-speed quality control can be performed on the radiometer data to allow it to take data simultaneously with the radar. The radiometer data can be blanked during radar transmit, or when the radar return is of a power level high enough to corrupt the radiometer data. Additionally, the receiver protection switches in the RF front end can double as radiometer calibration sources, the short (four-microsecond level) switching periods integrated over many seconds to estimate the radiometer offset. The major benefit of this innovation is that there is minimal impact on the radar performance due to the integration of the radiometer, and the radiometer performance is similarly minimally affected by the radar. As the radar and radiometer are able to operate simultaneously, there is no extended period of integration time loss for the radiometer (maximizing sensitivity), and the radar is able to maintain its full number of pulses (increasing sensitivity and decreasing measurement uncertainty).

McLinden, Matthew; Piepmeier, Jeffrey

2013-01-01

331

Improving on police radar  

Microsoft Academic Search

The use of lasers, cameras, and advanced signal processing to help isolate individual offenders on crowded highways is discussed. The limitations of the predominant radar in use today, namely down-the-road Doppler-radar in which the axis of the antenna is directed along the line of travel of the target vehicle, are described. The potential of video records, across-the-road radar, and both

P. D. Fisher

1992-01-01

332

Caribbean Radar Cases  

NSDL National Science Digital Library

This module presents radar case studies taken from events in the Caribbean that highlight radar signatures of severe weather. These cases include examples of deep convection, squall lines, bow echoes, tornadoes, and heavy rain resulting in flooding. Each case study includes a discussion of the conceptual models of each type of event as a review before showing the radar signatures and allowing the learner to analyze each one.

2014-09-14

333

Digital-Difference Processing For Collision Avoidance.  

NASA Technical Reports Server (NTRS)

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.

Shores, Paul; Lichtenberg, Chris; Kobayashi, Herbert S.; Cunningham, Allen R.

1988-01-01

334

The Invisible Radar Triangle  

NSDL National Science Digital Library

Students learn about radar imaging and its various military and civilian applications that include recognition and detection of human-made targets, and the monitoring of space, deforestation and oil spills. They learn how the concepts of similarity and scaling are used in radar imaging to create three-dimensional models of various targets. Students apply the critical attributes of similar figures to create scale models of a radar imaging scenario using infrared range sensors (to emulate radar functions) and toy airplanes (to emulate targets). They use technology tools to measure angles and distances, and relate the concept of similar figures to real-world applications.

2014-09-18

335

Detecting 1110th Scaled Structures in Dielectric Media Using Monostatic X-Band Radar Scattering Measurements  

E-print Network

Detecting 1110th Scaled Structures in Dielectric Media Using Monostatic X-Band Radar Scattering-GHz. The monostatic X-band measurements were acquired in an anechoic environment, and digital images Modeling, RCS Measurements, Compact Range, Ground Penetrating Radar, Monostatic Measurements

Massachusetts at Lowell, University of

336

Space-time adaptive processing from an airborne early warning radar perspective  

Microsoft Academic Search

Technology improvements over the last decade have made it feasible to consider digital space time adaptive processing, STAP, with associated sophisticated adaptive weight generation algorithms, for airborne early warning (AEW) radar The performance advantages to an AEW radar are significant because of the difficult interference environment it must operate in with large ground clutter returns combined with jamming and casual

J. K. Day

1995-01-01

337

Fusion of hyperspectral and radar data using the IHS transformation to enhance urban surface features  

Microsoft Academic Search

The Intensity–Hue–Saturation (IHS) transformation is used to integrate the high spectral resolution, provided by hyperspectral data (Airborne Visible Infrared Imaging Spectrometer, AVIRIS), and the surface texture information, derived from radar data (Topographic Synthetic Aperture Radar, TOPSAR), into a single image of an urban area. This transformed image is superimposed on the Digital Elevation Model (DEM) data derived from TOPSAR data

C.-M. Chen; G. F. Hepner; R. R. Forster

2003-01-01

338

OFDM waveforms for frequency agility and opportunities for Doppler processing in radar  

Microsoft Academic Search

Frequency agility is an important feature when radar operates in jammed environments. With the development of the orthogonal frequency division multiplexing (OFDM) waveform in the communications, the opportunity for a new generation of digital agile radar rises. Old and expensive multi-channel analog agile front ends could be replaced by simpler and cost effective single channel transceivers where the coherent switches

G. Lellouch; P. Tran; R. Pribic; P. van Genderen

2008-01-01

339

Generalized radar/radiometry imaging problems  

E-print Network

Paper Generalized radar/radiometry imaging problems Ivan Prudyus, Sviatoslav Voloshynovskiy, Andriy- ing simulation based on radar, synthetic aperture radar (SAR) and radiometry systems are presented systems, synthetic aperture radar, spatio-temporal imaging. 1. Introduction Resolution of radar

Genève, Université de

340

Characterization and comparison of the charge trapping in HfSiON and HfO2 gate dielectrics  

Microsoft Academic Search

Charge trapping in HfSiON and HfO2 gate dielectrics was studied using both DC and pulsed ID-VG characterization techniques. The data shows a significant amount of hysteresis in HfO2 but negligible instability in HfSiON. Constant voltage stress measurements of HfO2 and HfSiON films show that the threshold voltage shift in HfO2 films is as much as 10 times higher than that

A. Shanware; M. R. Visokay; J. J. Chambers; A. L. P. Rotondaro; J. McPherson; L. Colombo

2003-01-01

341

Radar cross calibration investigation TAMU radar polarimeter calibration measurements  

NASA Technical Reports Server (NTRS)

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.

Blanchard, A. J.; Newton, R. W.; Bong, S.; Kronke, C.; Warren, G. L.; Carey, D.

1982-01-01

342

Hf diversity in S-type granites  

NASA Astrophysics Data System (ADS)

The 176Hf/177Hf composition of inherited and magmatic zircon in the 538 Ma S-type Peninsula pluton (South Africa) has been determined at different scales. In the smallest rock samples investigated (<0.5 dm3), as well as within individual thin sections, magmatic zircon crystals exhibit the same wide range in ?Hf(538) as the pluton (8? units). In addition, across a significant range of bulk-rock compositions, both the range and average of the magmatic zircon Hf isotopic composition do not vary significantly with compositional parameters that are expected to scale with the proportion of mantle-derived magma addition (e.g., Mg# and Ca). At all scales, the ?Hf variability in the magmatic zircon fraction matches well with that portrayed by the time-evolved inherited zircon population [i.e., with the ?Hf(538) range of the inherited zircon cores]. This evidence suggests that the ?Hf heterogeneity of magmatic zircon is directly inherited from the source. However, the analysis of zircon core-rim pairs reveals that the 176Hf/177Hf composition of the inherited crystals does not directly transfer to their magmatic overgrowths. Small-scale modeling of zircon dissolution and re-precipitation in a static magma generates sub-mm melt domains having variable Zr content and Hf isotope composition. The composition of these domains is controlled by the size and isotope composition of the nearest dissolving zircon crystals and the cooling rate of the magma. These results suggest that in magma systems with a substantial inherited zircon load, zircon crystals within the same rock should record variable 176Hf/177Hf in the magmatic zircon fraction.

Farina, F.; Stevens, G.; Gerdes, A.; Frei, D.

2014-10-01

343

Java Radar Analysis Tool  

NASA Technical Reports Server (NTRS)

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.

Zaczek, Mariusz P.

2005-01-01

344

Phased-array radars  

Microsoft Academic Search

The operating principles, technology, and applications of phased-array radars are reviewed and illustrated with diagrams and photographs. Consideration is given to the antenna elements, circuitry for time delays, phase shifters, pulse coding and compression, and hybrid radars combining phased arrays with lenses to alter the beam characteristics. The capabilities and typical hardware of phased arrays are shown using the US

Eli Brookner

1985-01-01

345

Radar image interpretability analysis  

Microsoft Academic Search

The utility of radar images with respect to trained image interpreter ability to identify, classify and detect specific terrain features (linear, natural area, complex area features, and individual man-made features) was qualitatively determined. Further, radar images were evaluated with respect to their utility for determining vehicle movement potential and the level of activity within the test areas. Because there are

V. S. Frost; J. A. Stiles; J. C. Holtzman

1981-01-01

346

Noncooperative rendezvous radar system  

NASA Technical Reports Server (NTRS)

A fire control radar system was developed, assembled, and modified. The baseline system and modified angle tracking system are described along with the performance characteristics of the baseline and modified systems. Proposed changes to provide additional techniques for radar evaluation are presented along with flight test data.

1974-01-01

347

Asynchronous Transfer Mode over HF Radio (ATM\\/HF) A Network Architecture Proposal  

Microsoft Academic Search

The ATM\\/HF network architecture (1) is a HF radio broadcast network that utilizes three distinct MAC protocols. ATM\\/HF integrates into existing communications systems and supports existing and proposed traffic types. The frame and wireless packet structures are based upon a 128 kbps data rate and descriptions of the reference layer model and basic operations show how the network is established

Paul S. Giovanni

348

Asynchronous transfer mode over HF radio (ATM\\/HF): a network architecture proposal  

Microsoft Academic Search

The ATM\\/HF network architecture is a HF radio broadcast network that utilizes three distinct MAC protocols. ATM\\/HF integrates into existing communications systems and supports existing and proposed traffic types. The frame and wireless packet structures are based upon a 128 kbps data rate and descriptions of the reference layer model and basic operations show how the network is established and

Paul S. Giovanni; M. Airst

1999-01-01

349

Compressive wideband microwave radar holography  

NASA Astrophysics Data System (ADS)

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.

Wilson, Scott A.; Narayanan, Ram M.

2014-05-01

350

Looking at Radar Images  

NSDL National Science Digital Library

These activities pertain to the value of the different types of images, including a false color mosaic, a Compressed Stokes image, a vegetation map and key, and various ground photographs. Students are given specific directions on how to decide what features of a radar image indicate such structures as upland forest, clear-cut areas, and roads. In a second activity, students look at the radar images to see if they can produce a vegetation map similar to the one they have been given. The third activity introduces 15 Decade Volcanoes that pose a particular threat to humans. Using the Decade Volcanoes as examples, students view radar images of volcanoes that occur around the world. The final exercise is aimed at helping students distinguish the differences between radar image data and visible photographs. Students will look at radar data and photographs of three sites taken by the astronauts.

351

Measurements of spatial and frequency coherence of an equatorial hf path during spread-F  

SciTech Connect

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.

Fitzgerald, T.J.; Argo, P.E.; Carlos, R.C.

1993-01-01

352

Measurements of spatial and frequency coherence of an equatorial hf path during spread-F  

SciTech Connect

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.

Fitzgerald, T.J.; Argo, P.E.; Carlos, R.C.

1993-07-01

353

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

354

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

355

Browse > Conferences> Radar Conference, 2008. RADAR ... INDEX TERMS  

E-print Network

Browse > Conferences> Radar Conference, 2008. RADAR ... INDEX TERMS REFERENCES CITING DOCUMENTS Force, MorphoAnalysis in Signal Process. Lab., Salon-de-Provence This paper appears in: Radar Conference, 2008. RADAR '08. IEEE Issue Date: 26-30 May 2008 On page(s): 1 - 5 Location: Rome ISSN: 1097-5659 Print

Préaux, Jean-Philippe

356

Computing Ocean Surface Currents from Satellite Synthetic Aperture Radar Imagery  

NASA Astrophysics Data System (ADS)

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, and are seen to have much larger extreme values, which is attributed to the Doppler wind correction process. Ignoring the extreme values, errors between the two datasets appear to be random, with a near-zero mean bias, and are also linked with the Doppler radial estimation errors attributed to model wind corrections. Comparison of Doppler radials with MCC SAR radials for two ? 12-hour lag cases also shows promising results. Finally, experiments conducted with TerraSAR-X experimental Dual Receive Aperture (DRA) mode Along-Track Interferometry (ATI) datasets suggest possible solutions for the absolute phase calibration problem using interferometric phase over ocean only.

Qazi, Waqas A.

357

Wind Turbine Clutter Mitigation in Coastal UHF Radar  

PubMed Central

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

Wang, Caijun; Jiang, Dapeng; Wen, Biyang

2014-01-01

358

Wind turbine clutter mitigation in coastal UHF radar.  

PubMed

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

Yang, Jing; Pan, Chao; Wang, Caijun; Jiang, Dapeng; Wen, Biyang

2014-01-01

359

The RITMARE coastal radar network and applications to monitor marine transport infrastructures  

NASA Astrophysics Data System (ADS)

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 radar network represent a challenge to the nowadays definition of OGC web services: the network will suggest and test solutions.

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

360

Haloviruses HF1 and HF2: evidence for a recent and large recombination event.  

PubMed

Haloviruses HF1 and HF2 were isolated from the same saltern pond and are adapted to hypersaline conditions, where they infect a broad range of haloarchaeal species. The HF2 genome has previously been reported. The complete sequence of the HF1 genome has now been determined, mainly by PCR and primer walking. It was 75,898 bp in length and was 94.4% identical to the HF2 genome but about 1.8 kb shorter. A total of 117 open reading frames and five tRNA-like genes were predicted, and their database matches and characteristics were similar to those found in HF2. A comparison of the predicted restriction digest patterns based on nucleotide sequence with the observed restriction digest patterns of viral DNA showed that, unlike the case for HF2, some packaged HF1 DNA had cohesive termini. Except for a single base change, HF1 and HF2 were identical in sequence over the first 48 kb, a region that includes the early and middle genes. The remaining 28 kb of HF1 showed many differences from HF2, and the similarity of the two genomes over this late gene region was 87%. The abrupt shift in sequence similarity around 48 kb suggests a recent recombination event between either HF1 or HF2 and another HF-like halovirus that has swapped most of the right-end 28 kb. This example indicates there is a high level of recombination among viruses that live in this extreme environment. PMID:15090523

Tang, Sen-Lin; Nuttall, Stewart; Dyall-Smith, Mike

2004-05-01

361

Optical and ionospheric phenomena at EISCAT under continuous X-mode HF pumping  

NASA Astrophysics Data System (ADS)

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.

Blagoveshchenskaya, N. F.; Borisova, T. D.; Kosch, M.; Sergienko, T.; Brändström, U.; Yeoman, T. K.; Häggström, I.

2014-12-01

362

Use and Interpretation of Radar  

NSDL National Science Digital Library

This undergraduate meteorology tutorial from Texas A&M University discusses the basic principles of operation of weather radars, describes how to interpret radar mosaics, and discusses the use of radar in weather forecasting. Students learn the relationship between range and elevation and how to use radar images and mosaics in short-range forecasting.

John Nielsen-Gammon

1996-01-01

363

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 ...

364

Model for optimal parallax in stereo radar imagery  

NASA Technical Reports Server (NTRS)

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.

Pisaruck, M. A.; Kaupp, V. H.; Macdonald, H. C.; Waite, W. P.

1984-01-01

365

Time-frequency analysis of synthetic aperture radar signals  

SciTech Connect

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.

Johnston, B.

1996-08-01

366

Target Detection and Localization Using MIMO Radars and Sonars  

Microsoft Academic Search

In this paper, we propose a new space-time coding configuration for target detection and localization by radar or sonar systems. In common active array systems, the transmitted signal is usually coherent between the different elements of the array. This configuration does not allow array processing in the transmit mode. However, space-time coding of the transmitted signals allows to digitally steer

Ilya Bekkerman; Joseph Tabrikian

2006-01-01

367

Discrimination of geophysical phenomena in satellite radar interferograms  

Microsoft Academic Search

Various geophysical phenomena are recorded in the interference patterns formed by differencing two synthetic aperture radar (SAR) images. The fringes generated by the topographic relief can be removed using a digital elevation model (DEM). The remaining fringes map the change in satellite-to-ground range which occurred between the acquisition times of the two images. By comparing different pairs of images spanning

Didier Massonnet; Kurt L. Feigl

1995-01-01

368

Naval Research Laboratory flex processor for radar signal processing  

NASA Astrophysics Data System (ADS)

This paper describes a programmable radar signal processor architecture developed at the Naval Research Laboratory (NRL). The design incorporates T.I. TMS320C30 programmable digital signal processor devices, Xilinx programmable gate arrays, TRW FFT devices, and a parallel array of Inmos Transputer microprocessors. The architecture is extremely flexible and is applicable to a wide variety of applications.

Alter, James J.; Evins, James B.; Letellier, J. P.

1991-12-01

369

Spaceborne meteorological radar studies  

NASA Technical Reports Server (NTRS)

Various radar designs and methods are studied for the estimation of rainfall parameters from space. An immediate goal is to support the development of the spaceborne radar that has been proposed for the Tropical Rain Measuring Mission (TRMM). The effort is divided into two activities: a cooperative airborne rain measuring experiment with the Radio Research Laboratory of Japan (RRL), and the modelling of spaceborne weather radars. An airborne rain measuring experiment was conducted at Wallops Flight Facility in 1985 to 1986 using the dual-wavelength radar/radiometer developed by RRL. The data are presently being used to test a number of methods that are relevant to spaceborne weather radars. An example is shown of path-averaged rain rates as estimated from three methods: the standard reflectivity rain rate method (Z-R), a dual-wavelength method, and a surface reference method. The results from the experiment shows for the first time the feasibility of using attenuation methods from space. The purposes of the modelling are twofold: to understand in a quantitative manner the relationships between a particular radar design and its capability for estimating precipitation parameters and to help devise and test new methods. The models are being used to study the impact of various TRMM radar designs on the accuracy of rain rate estimation as well as to test the performance of range-profiling algorithms, the mirror-image method, and some recently devised graphical methods for the estimation of the drop size distribution.

Meneghini, R.

1988-01-01

370

Wuhan Atmosphere Radio Exploration (WARE) radar: System design and online winds measurements  

NASA Astrophysics Data System (ADS)

The basic configuration of the Wuhan MST (mesosphere-stratosphere-troposphere) radar, which was designed and constructed by the School of Electronic Information, Wuhan University, is preliminarily described in this paper. The Wuhan MST radar operates at very high frequency (VHF) band (53.8 MHz) by observing the real-time characteristics of turbulence and the wind field vector in the height range of 3.5-90 km (not including 25-60 km) with high temporal and height resolutions. This all-solid-state, all-coherent pulse Doppler radar is China's first independent development of an MST radar focusing on atmospheric observation. The subsystems of the Wuhan MST radar include an antenna system, a feeder line system, all-solid-state radar transmitters, digital receivers, a beam control system, a signal processing system, a data processing system, a product generation system, and a user terminal. Advanced radar technologies are used, including highly reliable all-solid-state transmitters, low-noise large dynamic range digital receivers, an active phased array, high-speed digital signal processing, and real-time graphic terminals. This paper describes the design and implementation of the radar. Preliminary online wind measurements and results of the comparison to simultaneous observations by a GPS rawinsonde are presented as well.

Zhengyu, Zhao; Chen, Zhou; Haiyin, Qing; Guobin, Yang; Yuannong, Zhang; Gang, Chen; Yaogai, Hu

2013-05-01

371

Generation of Artificial Acoustic-Gravity Waves and Traveling Ionospheric Disturbances in HF Heating Experiments  

NASA Astrophysics Data System (ADS)

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.

Pradipta, R.; Lee, M. C.; Cohen, J. A.; Watkins, B. J.

2015-02-01

372

A source mechanism producing HF-induced plasma lines (HFPLS) with up-shifted frequencies  

NASA Technical Reports Server (NTRS)

Attention is given to a nonlinear scattering process analyzed as a source mechanism producing the frequency up-shifted HFPLs observed in the Arecibo ionospheric heating experiments. A physical picture is offered to explain how Langmuir waves with frequencies greater than the HF heater wave frequency can be produced in the heating experiments and be detected by incoherent radars as frequency up-shifted HFPLs. Since the considered scattering process occurs in a region near the reflection height, it explains why the frequency up-shifted HFPLs should originate from the altitude near the reflection height as observed. The theory also shows that the amount of frequency up-shift is inversely proportional to the frequency of the HF heater and increases linearly with the electron temperature. The quantitative analysis of the theory shows a good agreement with the experimental results.

Kuo, S. P.; Lee, M. C.

1992-01-01

373

Radar Remote Sensing  

NASA Technical Reports Server (NTRS)

This lecture was just a taste of radar remote sensing techniques and applications. Other important areas include Stereo radar grammetry. PolInSAR for volumetric structure mapping. Agricultural monitoring, soil moisture, ice-mapping, etc. The broad range of sensor types, frequencies of observation and availability of sensors have enabled radar sensors to make significant contributions in a wide area of earth and planetary remote sensing sciences. The range of applications, both qualitative and quantitative, continue to expand with each new generation of sensors.

Rosen, Paul A.

2012-01-01

374

Space Radar Image of Rocky Mountains, Montana  

NASA Technical Reports Server (NTRS)

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 joint mission of the German, Italian and United States space agencies, is part of NASA's program entitled Mission to Planet Earth.

1994-01-01

375

Earth resources shuttle imaging radar. [systems analysis and design analysis of pulse radar for earth resources information system  

NASA Technical Reports Server (NTRS)

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.

1975-01-01

376

Experimental Evaluation of Adaptive Beamforming Methods and Interference Models for High Frequency Over-the-Horizon Radar Systems  

Microsoft Academic Search

This paper experimentally evaluates the interference cancellation performance of different adaptive beamforming schemes applicable to high frequency (HF) over-the-horizon (OTH) radar systems. Such systems are known to receive multipath and diffusely scattered radio frequency interference produced as a result of reflection from the stratified, dynamic and spatially inhomogeneous ionospheric propagation medium. Apart from quantifying the effectiveness of operational adaptive beamformers

G. A. Fabrizio; D. A. Gray; M. D. Turley

2003-01-01

377

Improved HF183 quantitative real-time PCR assay for characterization of human fecal pollution in ambient surface water samples.  

PubMed

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

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

378

Improved HF183 Quantitative Real-Time PCR Assay for Characterization of Human Fecal Pollution in Ambient Surface Water Samples  

PubMed Central

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

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.

2014-01-01

379

The 94 GHz MMW imaging radar system  

NASA Technical Reports Server (NTRS)

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.

Alon, Yair; Ulmer, Lon

1993-01-01

380

GMTI MIMO radar  

E-print Network

Multiple-input multiple-output (MIMO) extensions to radar systems enable a number of advantages compared to traditional approaches. These advantages include improved angle estimation and target detection. In this paper, ...

Bliss, Daniel W., Jr.

381

Caribbean Radar Products  

NSDL National Science Digital Library

This module provides examples of radar imagery from various locations in the Caribbean to demonstrate the different types of images available. Also, examples of different meteorological and non meteorological features are presented to show features seen in island locations.

COMET

2013-12-31

382

Imaging with Radar  

NSDL National Science Digital Library

This interactive activity from NOVA features synthetic aperture radar (SAR), which uses radio waves to create high-quality images. Examine SAR images of Washington, D.C., and learn about this technology's unique advantages.

WGBH Educational Foundation

2004-01-29

383

Soil moisture detection from radar imagery of the Phoenix, Arizona test site  

NASA Technical Reports Server (NTRS)

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.

Cihlar, J.; Ulaby, F. T.; Mueller, R.

1975-01-01

384

Digital Libraries  

NSDL National Science Digital Library

This projects introduces digital libraries, digital initiatives, search techniques, and the Instructional Architect Review Rubric. Digital Library Information : The Scope of the Digital Library D-Lib Journal article, 1998 2008 Joint Conference on Digital Libraries (JCDL) Annual meeting devoted to Digital Libraries Initiatives : Digital Libraries Initiative The Initiative's focus is to dramatically advance the means to collect, store, and organize information in digital forms, and make it available for searching, retrieval, and processing via communication networks -- all in ...

Heather

2008-09-29

385

Doppler Radar Technology  

NSDL National Science Digital Library

This resource provides an introduction to the function and uses of the The National Weather Service's (NWS) Weather Surveillance Doppler Radar (WSR-88D). Topics include the components of the system, an overview of the products and overlays the system creates, and some example images with captions explaining what is being shown. There are also links to radar meteorology tutorials and to information on training to use the system and interpret its imagery.

386

Downhole pulse radar  

DOEpatents

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.

Chang, Hsi-Tien

1987-09-28

387

Downhole pulse radar  

SciTech Connect

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.

Chang, Hsi-Tien (Albuquerque, NM)

1989-01-01

388

Adaptive MIMO radar waveforms  

Microsoft Academic Search

Multiple-Input, Multiple-Output (MIMO) radars enhance performance by transmitting and receiving coded waveforms from multiple locations. To date, the theoretical literature on MIMO radar has focused largely on the use of ldquoorthogonal waveforms.rdquo Practical approaches to approximate orthogonality (e.g., via waveforms characterized by low cross-correlation and low autocorrelation sidelobe levels) have also started to emerge. We show, however, that such waveforms

Daniel J. Rabideau; Lexington MA

2008-01-01

389

Statistical Analysis for VHF Radar Parameters at SÃO LUÍS, Jicamarca and Christmas Island Equatorial Stations  

NASA Astrophysics Data System (ADS)

Equatorial Spread F (ESF) is a manifestation of ionospheric interchange instabilities in the nighttime equatorial F region. These instabilities generate plasma density irregularities with scale sizes ranging from kilometers to thousands of kilometers. The irregularities can be detected from varieties of instruments such as digisonde, coherent and incoherent scatter radars, in situ space probes, and airglow photometers. In the present study, statistics of various aspects of spread F occurrence are presented from HF/VHF radar and incoherent scatter radar located at three equatorial stations: Christmas Island (2oN, 202.6oE, 2.9oN dip latitude, VHF radar), São Luís (2.59oS, 315.8oE, 0.5oS dip latitude, HF radar) and Jicamarca (12oS, 283.1oE, 0.6oN dip latitude, ISR). The radar parameters presented here are the onset altitude and onset time of the bottom-type and plume, and the peak altitude of the plume which are known to be associated with the spread F occurrence characteristics. The study reveals novel features namely, seasonal and solar flux dependence of spread F occurrence over Christmas island /São Luís, and longitudinal dependence of spread F occurrence characteristics from these three stations based on the chosen parameters. The importance of this work lies in the radar parameter empirical model developed combining statistical analysis of three equatorial and longitudinally separated stations, which is important to study the irregularity generation mechanisms, for space weather forecasting and nowcasting programs, and improving scintillation warning models. These parameters show generally linear correlation with solar flux index (F10.7 cm) and variation with season and magnetic declination angle. The fit correlation with F10.7cm is shown as useful information to implement one spread-F development empirical model based on small scale irregularities detected by VHF radars.

de la cruz cueva, R. Y.; Paula, E. R.; Kherani, E. A.

2013-05-01

390

On wave radar measurement  

NASA Astrophysics Data System (ADS)

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.

Ewans, Kevin; Feld, Graham; Jonathan, Philip

2014-08-01

391

On wave radar measurement  

NASA Astrophysics Data System (ADS)

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.

Ewans, Kevin; Feld, Graham; Jonathan, Philip

2014-09-01

392

SPace Radar Image of Fort Irwin, California  

NASA Technical Reports Server (NTRS)

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 activity. SIR-C was developed by NASA's Jet Propulsion Laboratory. X-SAR was developed by the Dornier and Alenia Spazio companies for the German space agency, Deutsche Agentur fuer Raumfahrtangelegenheiten (DARA), and the Italian space agency, Agenzia Spaziale Italiana (ASI), with the Deutsche Forschungsanstalt fuer Luft und Raumfahrt e.V.(DLR), the major partner in science, operations and data processing of X-SAR.

1994-01-01

393

Design guidelines for SAR digital receiver/exciter boards.  

SciTech Connect

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.

Dudley, Peter A.

2009-08-01

394

A photonic ADC for radar and EW applications based on modelocked laser  

Microsoft Academic Search

This paper presents a WDM architecture of a photonic analogue to digital converter (ADC) for direct RF sampling in radar and EW digital receiver, the architecture is based on the parallel operation of an array of state-of-the-art electronic ADCs while the photonic sampling is achieved using a mode locked laser (MLL). The parallelisation is implemented through a novel technique for

L. Pierno; M. Dispenza; G. Tonelli; A. Bogoni; P. Ghelfi; L. Poti

2008-01-01

395

Tsunami signature in the ionosphere: A simulation of OTH radar observations  

NASA Astrophysics Data System (ADS)

In the last ten years ionospheric anomalies following major earthquakes and tsunamis have been detected. Global Positioning System (GPS) and altimeters have been proven effective for this purpose, through Total Electron Content (TEC) measurement. Most of these ionospheric anomalies are deterministic and reproducible by numerical modeling via the coupling mechanism through ocean, neutral atmosphere and ionosphere. Numerical modeling supplies also useful support in the estimation of expected ionospheric effects and in the exploration and identification of new techniques to detect ionospheric tsunami signatures. We explore here a new ground-based technique, nominally the use of over-the-horizon (OTH) radars, for tsunami detection through ionospheric monitoring. OTH radars operate in High Frequency (HF) band and sounding the bottomside ionosphere they could anticipate the detection of tsunami-driven Internal Gravity Waves (IGW). To validate this hypothesis, we use HF numerical ray-tracing to simulate synthetic OTH radar measurements through a 3D tsunami-driven IGW ionospheric model. Our simulations clearly identify the tsunami signature in the OTH radar measurements one hour and a half before the tsunami arrival on the coast. The large coverage of OTH radar and its sensitivity to plasma anomalies open new perspectives in the oceanic monitoring and future tsunami warning systems.

CoïSson, Pierdavide; Occhipinti, Giovanni; Lognonné, Philippe; Molinié, Jean-Philippe; Rolland, Lucie M.

2011-12-01

396

Sporadic E ionization layers observed with radar imaging and ionospheric modification  

NASA Astrophysics Data System (ADS)

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.

Hysell, D. L.; Munk, J.; McCarrick, M.

2014-10-01

397

Can OTH Radar Help Tsunami Monitoring?  

NASA Astrophysics Data System (ADS)

Ionospheric anomalies following 2004 Sumatra tsunami have been detected and reported in the scientific literature (e.g., Liu et al. 2006; DasGupta et al. 2006; Occhipinti et al. 2006). Similar anomalies were also observed after the tsunamigenic earthquake in Peru in 2001 (Artru et al., 2005) and after earthquakes in Sumatra and Chile in 2007. All these anomalies show the signature in the ionosphere of tsunami-generated internal gravity waves (IGW) propagating in the neutral atmosphere over oceanic regions. Most of these ionospheric anomalies are deterministic and reproducible by numerical modeling (Occhipinti et al., 2006, 2008; Mai and Kiang, 2009; Hickey et al. 2009) via the coupling mechanism between ocean, neutral atmosphere and ionosphere. In addition, the numerical modeling supplies useful helps in the estimation of expected anomalies and to explore and identify new techniques to detect the ionospheric tsunami signature, other than GPS and altimeters. Here we present an overview of the physical coupling mechanism and the simulation environment that we developed to assess the capabilities of Over-The-Horizon (OTH) radars to detect these ionospheric anomalies. We use a full 3D approach, including empirical models of neutral atmosphere and ionosphere. Synthetic radar measurements are computed using HF numerical ray-tracing. The large coverage of OTH radar and its sensitivity to plasma anomalies open new perspectives in the future oceanic monitoring and tsunami warning system. [Artru et al., 2005] Geophys. J. Int., 160, 2005 [DasGupta et al., 2006] Earth Planet. Space, 35, 929-959. [Liu et al., 2006] J. Geophys. Res., 111, A05303. [Occhipinti et al., 2006] Geophys. Res. Lett., 33, L20104, 2006 [Occhipinti et al., 2008] Geophys. J. Int., 173, 3, 753-1135, 2008. [Mai and Kiang, 2009] Radio Sci., 44, RS3011 [Hickey et al., 2009] J. Geoophys. Res., 114, A08304

Coïsson, P.; Occhipinti, G.; Rolland, L. M.; Lognonne, P.

2009-12-01

398

Radar MeteorologyRadar Meteorology Feb 20, 1941 10 cm (S-band) radar used to track rain showers (Ligda)  

E-print Network

Radar MeteorologyRadar Meteorology Feb 20, 1941 10 cm (S-band) radar used to track rain showers similar observations in the early 1940's (U.S. Air Corps meteorologists receiving "radar" training at MIT in 1943 First operational weather radar, Panama, 1943 Science of radar meteorology born from WWII research

Rutledge, Steven

399

Analyzing the connectivity potential of landscape geomorphic systems: a radar remote sensing and GIS approach, Estufa Canyon, Texas, USA  

E-print Network

. The landscape gradient, which is extracted from the Digital Elevation Model (DEM), and the surface roughness, which is extracted from radar images, are used to analyze the connectivity potential of geomorphic systems in the landscape. Integration...

Ibrahim, ElSayed Ali Hermas

2005-11-01

400

The Multiple Doppler Radar Workshop, November 1979.  

NASA Astrophysics Data System (ADS)

The findings of the Multiple Doppler Radar Workshop are summarized by a series of six papers. Part I of this series briefly reviews the history of multiple Doppler experimentation, fundamental concepts of Doppler signal theory, and organization and objectives of the Workshop. Invited presentations by dynamicists and cloud physicists are also summarized.Experimental design and procedures (Part II) are shown to be of critical importance. Well-defined and limited experimental objectives are necessary in view of technological limitations. Specified radar scanning procedures that balance temporal and spatial resolution considerations are discussed in detail. Improved siting for suppression of ground clutter as well as scanning procedures to minimize errors at echo boundaries are discussed. The need for accelerated research using numerically simulated proxy data sets is emphasized.New technology to eliminate various sampling limitations is cited as an eventual solution to many current problems in Part III. Ground clutter contamination may be curtailed by means of full spectral processing, digital filters in real time, and/or variable pulse repetition frequency. Range and velocity ambiguities also may be minimized by various pulsing options as well as random phase transmission. Sidelobe contamination can be reduced through improvements in radomes, illumination patterns, and antenna feed types. Radar volume-scan time can be sharply reduced by means of wideband transmission, phased array antennas, multiple beam antennas, and frequency agility.Part IV deals with synthesis of data from several radars in the context of scientific requirements in cumulus clouds, widespread precipitation, and severe convective storms. The important temporal and spatial scales are examined together with the accuracy required for vertical air motion in each phenomenon. Factors that introduce errors in the vertical velocity field are identified and synthesis techniques are discussed separately for the dual Doppler and multiple Doppler cases. Various filters and techniques, including statistical and variational approaches, are mentioned. Emphasis is placed on the importance of experiment design and procedures, technological improvements, incorporation of all information from supporting sensors, and analysis priority for physically simple cases. Integrated reliability is proposed as an objective tool for radar siting.Verification of multiple Doppler-derived vertical velocity is discussed in Part V. Three categories of verification are defined as direct, deductive, and theoretical/numerical. Direct verification consists of zenith-pointing radar measurements (from either airborne or ground-based systems), air motion sensing aircraft, instrumented towers, and tracking of radar chaff. Deductive sources include mesonetworks, aircraft (thermodynamic and microphysical) measurements, satellite observations, radar reflectivity, multiple Doppler consistency, and atmospheric soundings. Theoretical/numerical sources of verification include proxy data simulation, momentum checking, and numerical cloud models. New technology, principally in the form of wide bandwidth radars, is seen as a development that may reduce the need for extensive verification of multiple Doppler-derived vertical air motions. Airborne Doppler radar is perceived as the single most important source of verification within the bounds of existing technology.Nine stages of data processing and display are identified in Part VI. The stages are identified as field checks, archival, selection, editing, coordinate transformation, synthesis of Cartesian fields, filtering, display, and physical analysis. Display of data is considered to be a problem critical to assimilation of data at all stages. Interactive computing systems and software are concluded to be very important, particularly for the editing stage. Three- and 4-dimensional displays are considered essential for data assimilation, particularly at the physical analysis stage. The concept of common data tape formats is approved both for data in radar s

Carbone, R. E.; Harris, F. I.; Hildebrand, P. H.; Kropfli, R. A.; Miller, L. J.; Moninger, W.; Strauch, R. G.; Doviak, R. J.; Johnson, K. W.; Nelson, S. P.; Ray, P. S.; Gilet, M.

1980-10-01

401

Geostat follow-on (GFO) radar altimeter  

NASA Astrophysics Data System (ADS)

This paper reflects the progress of the GFO altimeter design, first described by Walker et. al. The GFO altimeter uses a linear FM waveform, pulse repetition frequency, pulse compression technique, and alpha-beta tracker design similar to an earlier GEOSAT radar altimeter. The current design takes advantage of advanced RF and digital signal processing technologies to produce an instrument that is both light-weight and reliable. Analysis of the range, waveheight, and backscattering cross section performance indicates that the GFO altimeter will achieve equivalent GEOSAT performance in all areas.

Walker, Dan M.; Crowley, R. D.; Dobrzanski, J. R.

1994-06-01

402

66. VIEW SHOWING HOLD FOR RADAR CABLES AT RADAR SITE, ...  

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

66. VIEW SHOWING HOLD FOR RADAR CABLES AT RADAR SITE, LOOKING NORTH Everett Weinreb, photographer, March 1988 - Mount Gleason Nike Missile Site, Angeles National Forest, South of Soledad Canyon, Sylmar, Los Angeles County, CA

403

Multiple excitation modes in 163Hf  

NASA Astrophysics Data System (ADS)

Excited states of 163Hf were populated using the 94Zr(74Ge,5 n ) reaction and the decay ? rays were measured with the Gammasphere spectrometer. Two previously known bands were extended to higher spins, and nine new bands were identified. In addition to bands associated with three- and five-quasiparticle configurations, two ? - vibrational bands coupled to the i13 /2 excitation were also observed. The lowest level of a newly identified, negative-parity band is proposed to be the ground state of the nucleus. A systematic delay of the high-spin proton crossing frequency with increasing quadrupole deformation from 162Hf to 172Hf was established. Extensive band searches failed to reveal a triaxial, strongly deformed structure in 163Hf similar to the one observed in several nuclei around A ˜165 .

Yadav, R. B.; Ma, W. C.; Marsh, J. C.; Ijaz, Q. A.; Janssens, R. V. F.; Carpenter, M. P.; Hoffman, C. R.; Lauritsen, T.; Zhu, S.; Kondev, F. G.; Gürdal, G.; Hagemann, G. B.; Hartley, D. J.; Riedinger, L. L.; Mukhopadhyay, S.

2014-11-01

404

Can HF heating generate ESF bubbles?  

NASA Astrophysics Data System (ADS)

The injection of powerful HF waves into the ionosphere can lead to strong electron heating followed by a pressure perturbation which can locally reduce the plasma density. In the postsunset equatorial ionosphere, density perturbations can provide the seed to generate equatorial spread F (ESF) bubbles. In this paper, a modified version of the SAMI3/ESF ionosphere code is used to model the density depletions created by HF heating and to determine if ESF bubbles can be artificially generated. It is found that HF heating primarily redistributes plasma along the geomagnetic field and does not significantly perturb the flux tube integrated conductivities. Thus, HF heating does not appear to be a viable method to seed or generate ESF bubbles.

Zawdie, K. A.; Huba, J. D.

2014-12-01

405

2-D inner-shelf current observations from a single VHF WEllen RAdar (WERA) station  

USGS Publications Warehouse

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.

Voulgaris, G.; Kumar, N.; Gurgel, K.-W.; Warner, J.C.; List, J.H.

2011-01-01

406

Weather Radar and Instrumentation: Laboratory Modules  

NSDL National Science Digital Library

These 16 radar education modules, developed for the Weather Radar and Instrumentation Curriculum at the University of Oklahoma, provide hands-on instruction for beginning, intermediate, or advanced students to learn about radar systems, especially weather radar. Topics include hardware, weather radar, adaptive systems, advanced hydrometeors, applications of weather radar, and atmospheric interpretations. The modules may be downloaded.

407

Fiber optic coherent laser radar 3d vision system  

SciTech Connect

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.

Sebastian, R.L.; Clark, R.B.; Simonson, D.L. [and others

1994-12-31

408

Compressive spectrum sensing of radar pulses based on photonic techniques.  

PubMed

We present a photonic-assisted compressive sampling (CS) system which can acquire about 106 radar pulses per second spanning from 500 MHz to 5 GHz with a 520-MHz analog-to-digital converter (ADC). A rectangular pulse, a linear frequency modulated (LFM) pulse and a pulse stream is respectively reconstructed faithfully through this system with a sliding window-based recovery algorithm, demonstrating the feasibility of the proposed photonic-assisted CS system in spectral estimation for radar pulses. PMID:25836488

Guo, Qiang; Liang, Yunhua; Chen, Minghua; Chen, Hongwei; Xie, Shizhong

2015-02-23

409

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

410

Synthetic Aperture Radar Simulation On Radar Terrain Clutter  

Microsoft Academic Search

The subject of this paper is related to a new method of Synthetic Aperture Radar (i.e., SAR) simulation on radar terrain clutter. Usually, images are simulated at pixel level after Doppler compression. In this case this study deals with the simulation of the raw signal at the output of the antenna i.e. for each pulse emitted by the radar during

ARMAND Pierre; VIDAL-MADJAR Daniel

1992-01-01

411

Imaging Radar in the Mojave Desert-Death Valley Region  

NASA Technical Reports Server (NTRS)

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 operated in this way, with horizontal resolution of about 5 m and vertical errors less than 2 m. The findings and developments of these earlier investigations are discussed.

Farr, Tom G.

2001-01-01

412

Microwave emissions from police radar  

E-print Network

The purpose of this study was to evaluate police officers exposures to microwaves emitted by traffic radar units at the ocular and testicular level. Additionally, comparisons were made of the radar manufacturers published maximum power density...

Fink, John Michael

1994-01-01

413

Systems and Methods for Radar Data Communication  

NASA Technical Reports Server (NTRS)

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.

Bunch, Brian (Inventor); Szeto, Roland (Inventor); Miller, Brad (Inventor)

2013-01-01

414

Radar data smoothing filter study  

NASA Technical Reports Server (NTRS)

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.

White, J. V.

1984-01-01

415

Amplitude calibration of spaceborne synthetic aperture radars  

NASA Astrophysics Data System (ADS)

Problems encountered during attempts to calibrate SAR imagery, recent successful experiments conducted with SEASAT SAR data, and a proposed program for the calibration and validation of the radar imagery from the forthcoming SIR-B SAR are discussed. The SEASAT SAR data for 10 passes over Death Valley, California, were processed with a modified digital correlator. The procedure included a preliminary screening of the data to check for raw data saturation, compensation of waveforms and estimation of the amplitude of the pilot tone. All data was normalized to this pilot tone signal to reduce the effects of variable gains in the data links and ground receivers. The digital correlation algorithm generated image data. Evaluation of 6 passes results in a maximum pass to pass gain variation of only 1.1 dB and a standard deviation amongst the passes of 0.35 dB. previously announced in STAR as N83-26215

Held, D. N.

416

Matched window processing for mitigating over-the-horizon radar spread Doppler clutter  

Microsoft Academic Search

Ionospheric motion causes spreading of surface clutter in Doppler space which fundamentally limits the detection performance of skywave HF over-the-horizon radars. This paper presents a technique which reduces the effect of so-called “coincident” spread Doppler clutter, i.e., that which results from surface scattering from within the same range resolution cell as the target. The method exploits the spatial correlation of

K. Harmanci; Jepey Krolik

1999-01-01

417

Collaborative experiments by Akebono satellite, Tromso ionospheric heater, and European incoherent scatter radar  

Microsoft Academic Search

Joint experiments using the Akebono satellite and the ionospheric heating facility and European incoherent scatter radar near Tromso were carried out in November 1990 and February 1991. In these experiments, Tromso HF transmissions were amplitude modulated at frequencies of 2.5 and 4.0 kHz. Signals radiated from the polar electrojet (PEJ) antenna in the heated ionosphere at these VLF frequencies were

I. Kimura; P. Stubbe; M. T. Rietveld; R. Barr; K. Ishida; Y. Kasahara; S. Yagitani; I. Nagano

1994-01-01

418

Stepped-frequency radar signal processing  

NASA Astrophysics Data System (ADS)

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.

Seyfried, Daniel; Schoebel, Joerg

2015-01-01

419

Threat radar system simulations  

NASA Astrophysics Data System (ADS)

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.

Miller, L.

420

Spaceborne Imaging Radar Symposium  

NASA Technical Reports Server (NTRS)

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.

Elachi, C.

1983-01-01

421

Radar Investigations of Asteroids  

NASA Technical Reports Server (NTRS)

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.

Ostro, S. J.

1984-01-01

422

Radar detection of phobos.  

PubMed

Radar echoes from the martian satellite Phobos provide information about that object's surface properties at scales near the 3.5-cm observing wavelength. Phobos appears less rough than the moon at centimeter-to-decimeter scales. The uppermost few decimeters of the satellite's regolith have a mean bulk density within 20% of 2.0 g cm(-3). The radar signature of Phobos (albedo, polarization ratio, and echo spectral shape) differs from signatures measured for small, Earth-approaching objects, but resembles those of large (>/=100-km), C-class, mainbelt asteroids. PMID:17847261

Ostro, S J; Jurgens, R F; Yeomans, D K; Standish, E M; Greiner, W

1989-03-24

423

Microwave radar oceanographic investigations  

NASA Technical Reports Server (NTRS)

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.

Jackson, F. C.

1988-01-01

424

Investigation of the differences in stability of the OCxxxHF and COxxxHF complexes  

SciTech Connect

The structure and energetics of the isomeric H-bonded complexes OCxxxHF and COxxxHF have been investigated by ab initio molecular orbital theory and by natural bond orbital analysis. Only with the inclusion of electron correlation is a significant preference for the experimentally observed OCxxxHF isomer found. The large effect of correlation upon the relative stability of the two isomers is apparently entirely an electrostatic effect caused by the correlation-induced sign reversal of the dipole moment of CO. Nevertheless, a molecular multipole expansion is found inadequate to account for the principal features of these H-bonded complexes and their relative stability. Contrary to a recent study, we find that ''charge transfer'' effects are highly significant contributions to the binding in these complexes. The differences in stability of OCxxxHF and COxxxHF are attributed primarily to differences in the interaction of carbon and oxygen lone pairs of CO donating into the unfilled antibond on HF, i.e., to differences in n/sub C/..-->..sigma/sub HF/( and n/sub O/..-->..sigma/sub HF/( matrix elements.

Curtiss, L.A.; Pochatko, D.J.; Reed, A.E.; Weinhold, F.

1985-03-15

425

HF Accelerated Electron Fluxes, Spectra, and Ionization  

NASA Astrophysics Data System (ADS)

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 to derive more accurate HF electron flux spectra.

Carlson, Herbert C.; Jensen, Joseph B.

2014-12-01

426

Highly deformed Bands in {sup 175}Hf  

SciTech Connect

Two high-spin regularly spaced rotational bands with large dynamical moments of inertia have been identified in {sup 175}Hf with the Gammasphere spectrometer. These new bands are very similar to the previously identified triaxial superdeformed bands in the hafnium nuclei. However, the new bands in {sup 175}Hf have been linked into the known level scheme and thereby provide the first firm spin assignments for these structures in this region. In order to understand the new bands, theoretical calculations have been performed based on the ULTIMATE CRANKER code. The new bands in {sup 175}Hf are deduced to be built upon highly deformed structures. No experimental evidence for triaxiality was established and this work suggests that the structure of the so-called 'triaxial' superdeformed bands in the Hf nuclei may be quite different from those identified in the lighter mass Lu nuclei. Since the two highly deformed bands in {sup 175}Hf are associated with different deformations, this work also identifies the role of the intruder orbits in polarizing the nuclear shape.

Scholes, D.T.; Cullen, D.M. [Schuster Laboratory, University of Manchester, Manchester M13 9PL (United Kingdom); Kondev, F.G. [Nuclear Engineering, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Janssens, R.V.F.; Carpenter, M.P.; Abu Saleem, K.; Ahmad, I.; Heinz, A.; Khoo, T.L.; Lauritsen, T.; Lister, C.J.; Moore, E.F.; Seweryniak, D.; Wiedenhoever, I. [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Hartley, D.J.; Djongolov, M.K.; Balabanski, D.L.; Danchev, M.; Goon, J.; Riedinger, L.L. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States)] [and others

2004-11-01

427

The Shuttle Imaging Radar B (SIR-B) experiment report  

NASA Technical Reports Server (NTRS)

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.

Cimino, Jo Bea; Holt, Benjamin; Richardson, Annie

1988-01-01

428

A study on Ganymede's surface topography: Perspectives for radar sounding  

NASA Astrophysics Data System (ADS)

Radar sounding of Jovian icy satellites has great potential to address specific science questions such as the presence of subsurface liquid water. Radargrams acquired over Mars polar caps allow observing clear echoes up to kilometers depth. However, Jovian icy satellites display dramatically different surface topographies. In order to assess possible issues arising from such surface topographies on radar sounding, we performed a study on different DEMs (Digital Elevation Models) obtained on Ganymede. Topographic data are derived using stereo and photoclinometric analysis of Galileo and Voyager images at resolutions of 16-629 m. Main results are presented in this paper. Overall we found that Ganymede's surface is quite rough, with mean slopes at 630 m scale varying from 3.5° to 8°, smoothest terrains being found within sulcii. This will be a major challenge for the design of radar sounders and parameters should be chosen accordingly in order to correctly sound this planetary body. Previous studies have shown similar concern for Europa.

Berquin, Y.; Kofman, W.; Herique, A.; Alberti, G.; Beck, P.

2013-03-01

429

Doppler radar echoes of lightning and precipitation at vertical incidence  

NASA Technical Reports Server (NTRS)

Digital time series data at 16 heights within two storms were collected at vertical incidence with a 10-cm Doppler radar. On several occasions during data collection, lightning echoes were observed as increased reflectivity on an oscilloscope display. Simultaneously, lightning signals from nearby electric field change antennas were recorded on an analog recorder together with the radar echoes. Reflectivity, mean velocity, and Doppler spectra were examined by means of time series analysis for times during and after lightning discharges. Spectra from locations where lightning occurred show peaks, due to the motion of the lightning channel at the air speed. These peaks are considerably narrower than the ones due to precipitation. Besides indicating the vertical air velocity that can then be used to estimate hydrometeor-size distribution, the lightning spectra provide a convenient means to estimate the radar cross section of the channel. Subsequent to one discharge, we deduce that a rapid change in the orientation of hydrometeors occurred within the resolution volume.

Zrnic, D. S.; Rust, W. D.; Taylor, W. L.

1982-01-01

430

Description, characteristics and testing of the NASA airborne radar  

NASA Technical Reports Server (NTRS)

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.

Jones, W. R.; Altiz, O.; Schaffner, P.; Schrader, J. H.; Blume, H. J. C.

1991-01-01

431

Development of land based radar polarimeter processor system  

NASA Technical Reports Server (NTRS)

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.

Kronke, C. W.; Blanchard, A. J.

1983-01-01

432

Preliminary science results from the Shuttle Imaging Radar-B  

NASA Technical Reports Server (NTRS)

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.

Ruzek, M.

1985-01-01

433

Multiline radar scan  

NASA Technical Reports Server (NTRS)

Scanning scheme is more efficient than conventional scanning. Originally designed for optical radar in space vehicles, scheme may also find uses in site-surveillance security systems and in other industrial applications. It should be particularly useful when system must run on battery energy, as would be case in power outages.

Levinson, S.

1977-01-01

434

Airborne firefinder radar concept  

Microsoft Academic Search

An airborne firefinder radar (AFFR) is suggested for an upgraded version of the forthcoming Global Hawk Unmanned Aerial Vehicle (UAV). The AFFR could detect an artillery shell within 1 second of firing and, within a few seconds, determine its trajectory origin location (position of the gun) to a circular error probable (CEP) of less than 50 meters. The AFFR could

R. J. Sullivan; J. F. Nicoll; J. M. Ralston

1998-01-01

435

Impulse radar studfinder  

DOEpatents

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.

McEwan, Thomas E. (Livermore, CA)

1995-01-01

436

Impulse radar studfinder  

DOEpatents

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.

McEwan, T.E.

1995-10-10

437

High resolution radar imaging  

NASA Astrophysics Data System (ADS)

The goal of this project is to formulate and investigate new approaches for forming images of radar targets from spotlight-mode, delay-doppler measurements. These measurements could be acquired with a high-resolution radar-imaging system operating with an optical-or radio-frequency carrier. Two approaches are under study. The first is motivated by an image-reconstruction algorithm used in radionuclide imaging called the confidence-weighted algorithm; here, we will refer to this approach as the chirp-rate modulation approach. The second approach is based on more fundamental principles which starts with a mathematical model that accurately describes the physics of an imaging radar-system and then uses statistical-estimation theory with this model to derive processing algorithms; we will refer to this as the estimation-theory approach. Progress during this reporting period has been made on: (1) extending the estimation-theory approach to include a constraint on input signal-to-noise ratio; (2) extending the estimation-theory approach to include a sieve constraint for stabilizing image estimates, (3) extending the estimation-theory approach to include a specular or glint component in the radar-echo data; (4) analyzing the performance of the estimation-theory approach through computer simulations; and (5) modifying the chirp-rate modulation approach through the introduction of the Wigner-Ville distribution. A patent was awarded associated with the chirp-rate modulation approach.

Snyder, Donald L.

1988-11-01

438

Compressed Synthetic Aperture Radar  

Microsoft Academic Search

In this paper, we introduce a new synthetic aperture radar (SAR) imaging modality which can provide a high-resolution map of the spatial distribution of targets and terrain using a significantly reduced number of needed transmitted and\\/or received electromagnetic waveforms. This new imaging scheme, requires no new hardware components and allows the aperture to be compressed. It also presents many new

Vishal M. Patel; Glenn R. Easley; Dennis M. Healy; Jr.

2010-01-01

439

Stepped frequency ground penetrating radar  

DOEpatents

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.

Vadnais, Kenneth G. (Ojai, CA); Bashforth, Michael B. (Buellton, CA); Lewallen, Tricia S. (Ventura, CA); Nammath, Sharyn R. (Santa Barbara, CA)

1994-01-01

440

Digital materials for digital fabrication  

E-print Network

This thesis introduces digital materials by analogy with digital computation and digital communications. Traditional fabrication techniques include pick-and-place, roll-to-roll, molding, patterning and more. Current research ...

Popescu, George A

2007-01-01

441

Use of weather radar for flood forecasting in the Sieve River Basin: A sensitivity analysis  

Microsoft Academic Search

Weather radar, in combination with a distributed rainfall-runoff model, promises to significantly improve real-time flood forecasting. This paper investigates the value of radar-derived precipitation in forecasting streamflow in the Sieve River basin, near Florence, Italy. The basin is modeled with a distributed rainfall-runoff model that exploits topographic information available from digital elevation maps. The sensitivity of the flood forecast to

Marcos L. Pessoa; Rafael L. Bras; Earle R. Williams

1993-01-01

442

Discrimination of geologic units in Death Valley using dual frequency and polarization imaging radar data  

Microsoft Academic Search

Simultaneous analysis of dual frequency and dual polarization radar imagery of a portion of Death Valley, California has yielded a nearly complete discrimination of surficial geologic units. Radar imagery in like polarized L-band (i.e., 25 cm wavelength), crosspolarized L-band and like polarized X-band (i.e., 3 cm wavelength) were digitally combined and ratioed to enhance the variation in the backscatter cross-section

M. Daily; C. Elachi; T. Farr; G. Schaber

1978-01-01

443

Signal-to-Noise Ratio in Doppler Radar System for Heart and Respiratory Rate Measurements  

Microsoft Academic Search

A CMOS Doppler radar sensor has been developed and used to measure motion due to heart and respiration. The quadrature direct-conversion radar transceiver has been fully integrated in 0.25-mum CMOS, the baseband analog signal conditioning has been developed on a printed circuit board, and digital signal processing has been performed in Matlab. The theoretical signal-to-noise ratio (SNR) is derived based

Amy D. Droitcour; Olga Boric-Lubecke; Gregory T. A. Kovacs

2009-01-01

444

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

445

Surface current patterns in the northern Adriatic extracted from high-frequency radar data using self-organizing map analysis  

NASA Astrophysics Data System (ADS)

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.

Mihanovi?, Hrvoje; Cosoli, Simone; Vilibi?, Ivica; Ivankovi?, Damir; Dadi?, Vlado; Ga?I?, Miroslav

2011-08-01

446

On the spatial distribution of decameter?scale subauroral ionospheric irregularities observed by SuperDARN radars  

NASA Astrophysics Data System (ADS)

The midlatitude Super Dual Auroral Radar Network (SuperDARN) radars regularly observe nighttime low?velocity Sub?Auroral Ionospheric Scatter (SAIS) from decameter?scale ionospheric density irregularities during quiet geomagnetic conditions. To establish the origin of the density irregularities responsible for low?velocity SAIS, it is necessary to distinguish between the effects of high frequency (HF) propagation and irregularity occurrence itself on the observed backscatter distribution. We compare range, azimuth, and elevation data from the Blackstone SuperDARN radar with modeling results from ray tracing coupled with the International Reference Ionosphere assuming a uniform irregularity distribution. The observed and modeled distributions are shown to be very similar. The spatial distribution of backscattering is consistent with the requirement that HF rays propagate nearly perpendicular to the geomagnetic field lines (aspect angle ?1°). For the first time, the irregularities responsible for low?velocity SAIS are determined to extend between 200 and 300 km altitude, validating previous assumptions that low?velocity SAIS is an F?region phenomenon. We find that the limited spatial extent of this category of ionospheric backscatter within SuperDARN radars' fields?of?view is a consequence of HF propagation effects and the finite vertical extent of the scattering irregularities. We conclude that the density irregularities responsible for low?velocity SAIS are widely distributed horizontally within the midlatitude ionosphere but are confined to the bottom?side F?region.

Larquier, S.; Ponomarenko, P.; Ribeiro, A. J.; Ruohoniemi, J. M.; Baker, J. B. H.; Sterne, K. T.; Lester, M.

2013-08-01

447

GeoSAR: A Radar Terrain Mapping System for the New Millennium  

NASA Technical Reports Server (NTRS)

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.

Thompson, Thomas; vanZyl, Jakob; Hensley, Scott; Reis, James; Munjy, Riadh; Burton, John; Yoha, Robert

2000-01-01

448

The ADMX-HF (High Frequency) Experiment  

NASA Astrophysics Data System (ADS)

For many years, the Axion Dark Matter eXperiment (ADMX) has searched for dark-matter axions by their resonant conversion to photons in a high-Q microwave cavity embedded in a strong magnetic field; to date focusing on the ˜1 GHz range, or ma˜ few micro-eV. A second platform, ADMX-HF is now being constructed at Yale University which will focus on technology development and a first look at data in the ˜10 GHz range. Consisting of a 9T superconducting magnet (40 cm long x 14 cm diameter), a dilution refrigerator and a quantum-limited receiver based on Josephson Parametric Amplifiers (JPA) ADMX-HF is projected to achieve sensitivity within the axion model band, despite its smaller volume than ADMX. ADMX-HF is a collaboration of Yale, JILA/Colorado, UC Berkeley and LLNL, and by agreement will create a unified data set with ADMX.

Lehnert, K. W.

2013-04-01

449

Space Radar Image of Oetzal, Austria  

NASA Technical Reports Server (NTRS)

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 site is covered by glaciers. Corner reflectors are set up for calibration. Five corner reflectors can be seen on the Gepatschferner and two can be seen on the Vernagtferner. 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. X-SAR was developed by the Dornier and Alenia Spazio companies for the German space agency, Deutsche Agentur fuer Raumfahrtangelegenheiten (DARA), and the Italian space agency, Agenzia Spaziale Italiana (ASI), with the Deutsche Forschungsanstalt fuer Luft und Raumfahrt e.V.(DLR), the major partner in science, operations and data processing of X-SAR.

1994-01-01

450

Implementing digital terrain data in knowledge-aided space-time adaptive processing  

Microsoft Academic Search

Many practical problems arise when implementing digital terrain data in airborne knowledge-aided (KA) space-time adaptive processing (STAP). This paper addresses these issues and presents solutions with numerical implementations. In particular, using digital land classification data and digital elevation data, techniques are developed for registering these data with radar return signals, correcting for Doppler and spatial misalignments, adjusting for antenna gain,

CHRISTOPHER T. CAPRARO; GERARD T. CAPRARO; Ivan Bradaric; DONALD D. WEINER; MICHAEL C. WICKS; WILLIAM J. BALDYGO

2006-01-01

451

FMCW radar for the sense function of sense and avoid systems onboard UAVs  

NASA Astrophysics Data System (ADS)

Rockwell Collins France (RCF) radar department is currently developing, in close collaboration with TNO in The Hague, The Netherlands, a Frequency Modulated Continuous Wave (FMCW) radar sensor dedicated to Obstacle Warning function and potentially to air traffic detection. The sensor combines flood light illumination and digital beam forming to accommodate demanding detection and coverage requirements. Performances have been evaluated in flight tests and results prove that such a radar sensor is a good candidate for the Sense Function of Sense and Avoid Systems onboard UAV.

Itcia, Eric; Wasselin, Jean-Philippe; Mazuel, Sébastien; Otten, Matern; Huizing, Albert

2013-10-01

452

Alterations of Visual Reaction Time and Short Term Memory in Military Radar Personnel  

PubMed Central

Background Radar transmitters emit high-power radiofrequency radiation by creation of a high-voltage and high-frequency alternating electrical current. Methods: Health effects of occupational exposure to military radar were investigated. Visual reaction time was recorded with a simple blind computer-assisted-visual reaction time test. To assess the short-term memory, modified Wechsler Memory Scale test was performed. Results: The mean +/- SD reaction time in radar works (N=100) and the control group (N=57) were 238.58 +/? 23.47 milliseconds and 291.86 +/? 28.26 milliseconds (P<0.0001), respectively. The scores of forward digit span in radar works and the control group were 3.56 +/? 0.77 and 4.29 +/? 1.06 (P<0.0001), while the scores of backward digit span in radar works and the control group were 2.70 +/? 0.69 and 3.62 +/? 0.95 (P<0.0001). The scores of word recognition in radar works and the control group were 3.37 +/? 1.13 and 5.86 +/? 1.11 (P<0.0001). Finally, the scores of paired words in radar works and the control group were 13.56 +/? 1.78 and 15.21 +/? 2.20 (P<0.0001). It can be concluded that occupational exposures to radar radiations decreases reaction time, which may lead to a better response to different hazards. Conclusion: To the best of our knowledge, this is the first study to show that occupational exposure to radar microwave radiation leads to decreased reaction time and the lower performance of short-term memory. Altogether, these results indicate that occupational exposure to radar microwave radiations may be linked to some non-detrimental and detrimental health effects. PMID:23785684

MORTAZAVI, Seyed Mohammad Javad; TAEB, Shahram; DEHGHAN, Naser

2013-01-01

453

Survey of ULF wave signatures seen in the Tasman International Geospace Environment Radars data  

NASA Astrophysics Data System (ADS)

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.

Norouzi-Sedeh, L.; Waters, C. L.; Menk, F. W.

2015-02-01

454

Monsoon flood boundary delineation and damage assessment using space borne imaging radar and Landsat data  

NASA Technical Reports Server (NTRS)

Space-borne synthetic aperture radar (SAR) data acquired by the Shuttle Imaging Radar-B (SIR-B) Program and Landsat Multispectral Scanner Subsystem (MSS) Data from Landsat 4 were used to map flood boundaries for the assessment of flood damage in the Peoples Republic of Bangladesh. The cloud penetrating capabilities of the L-band radar provided a clear picture of the hydrologic conditions of the surface during a period of inclement weather at the end of the wet phase of the 1984 monsoon. The radar image data were digitally processed to geometrically rectify the pixel geometry and were filtered to subdue radar image speckle effects. Contrast enhancement techniques and density slicing were used to create discrete land-cover categories corresponding to surface conditions present at the time of the Shuttle