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1

Automatic Target Classification Using HF Multifrequency Radars.  

National Technical Information Service (NTIS)

The classification of radar targets such as aircraft and ships using lower resonance-region radar returns has been of significant interest in recent years. The H.F. band is in the resonance region of such targets. The probability of misclassification depe...

J. Chen

1983-01-01

2

Small Boat HF Radar Cross Sections.  

National Technical Information Service (NTIS)

The HF radar cross section of three small ocean-going craft were measured in full scale with the SEA ECHO radar. The measurements were made over a wide band of frequencies. Care was taken in the calibration of the system to insure accurate absolute values...

R. W. Bogle D. B. Trizna

1976-01-01

3

Waveform analysis for HF ground wave radar  

Microsoft Academic Search

According to general radar designing principles, this paper discusses the concepts and pro- cessing techniques concerning the radar waveform analysis. For the need in developing HF ground wave system, as requested by a key oceanic project in the national 863 plans, basic theories and parameter de- sign techniques on Frequency Modulated Interrupted Continuous Wave (FMICW) have been studied. This study

Wu Shi-cai; Yang Zi-jie; Wen Bi-yang; Shi Zhen-hua; Tian Jian-sheng

2001-01-01

4

FMCW Radar Waveforms in the HF Band  

Microsoft Academic Search

The HF band is used for various communications and radar requirements. Australian users of the band are required to adhere to spectrum management recommendations set by the Australian ACMA based on regulations set by the International Telecommunications Union (ITU). Here we exam- ine the applicability of the ITU recommendations on Linear Frequency Modulated Continuous Waveforms (LFMCW) and amplitude modulated LFMCW

Mike D. E. Turley

5

Development of HF ocean radar in japan  

Microsoft Academic Search

The HF ocean radar was developed in Japan from 1987 by Okinawa Radio Observatory, Communications Research Laboratory. We measured ocean surface currents and developed the method to estimate wave spectra. The observations of ocean surface currents were conducted in various areas. The observation in the east of Okinawa, where mesoscale eddies are dominant, is presented. We can observe the convergent

Yukiharu Hisaki

2003-01-01

6

Target Classification and Remote Sensing of Ocean Current Shear Using a Dual-Use Multifrequency HF Radar  

Microsoft Academic Search

In this paper, we describe a high-frequency (HF) radar capable of multifrequency operation over the HF band for dual-use application to ship classification and mapping ocean current shear and vector winds. The radar is based on a digital transceiver peripheral component interconnect (PCI) card family that supports antenna arrays of four to 32 elements with a single computer, with larger

Dennis Trizna

2006-01-01

7

HF radar data assimilation in the Monterey Bay area  

Microsoft Academic Search

The utility of high-frequency (HF) radar data for improving numerical circulation model predictions is evaluated. Comparisons of the statistical properties of the (CODAR-type) HF radar data and the observed wind indicate a strong correlation between the dominant alongshore, upwelling-favoring wind-forcing and HF radar-derived surface currents along the central California coastline. Because inadequate knowledge of the wind stress is probably a

Jeffrey D. Paduan; Igor Shulman

2004-01-01

8

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

9

CFAR Target Detection Based on Gumbel Distribution for HF Radar  

Microsoft Academic Search

High frequency (HF) radars are capable to detect and track targets at extremely long ranges. But the signal environment that includes external noise, different kinds of clutter and interference will significantly limit the detection and system capability. This paper considers a new approach to solve the target detection problem in a complex HF radar signal environment. It uses conventional constant

A. L. Dzvonkovskaya; H. Rohling

2006-01-01

10

Target Detection with Adaptive Power Regression Thresholding for HF Radar  

Microsoft Academic Search

High frequency (HF) radars are capable to detect and track targets at extremely long ranges. But the signal environment that includes external noise, different kinds of clutter and interference will significantly limit the detection performance and system capability. This paper considers a new approach to solve the target detection problem in a complex HF radar signal environment. It uses a

A. L. Dzvonkovskaya; H. Rohling

2006-01-01

11

Radio Frequency Interference Suppression Techniques in FMCW Modulated HF Radars  

Microsoft Academic Search

High-frequency (HF) radars are operated in the 3-30 MHz frequency range and need to share the frequency bands with other radio services. Due to their over-the-horizon (OTH) capabilities, HF radars play an important role in remote sensing and surveillance. The propagation conditions of the electromagnetic wave depend on the earth's ionosphere and mailnly follow a daily cycle. Communication paths between

Klaus-Werner Gurgel; Y. Barbin; T. Schlick

2007-01-01

12

Digital LPI Radar Detector.  

National Technical Information Service (NTIS)

The function of a Low Probability of Intercept (LPI) radar is to prevent its interception by an Electronic Support (ES) receiver. This objective is generally achieved through the use of a radar waveform that is mismatched to those waveforms for which an E...

P. G. Ong H. K. Teng

2001-01-01

13

KONRAD: Wide band digital HF receiver  

NASA Astrophysics Data System (ADS)

Electronic support measures (ESM) and spread spectrum techniques, i.e. direct sequence (DS) or frequency hopping (FH), in the HF band require a high dynamic range as well as a large instantaneous bandwidth in the receiver. This report describes an experimental digital receiver utilizing digitally implemented quadrature splitting and baseband translation. It is shown that the use of digital quadrature splitting improves the image rejection and that oversampling and digital filtering improves the dynamic range. The receiver is built of standard components which give a beneficial cost/performance ratio. The focus is on the analog hardware of the experimental digital receiver named KONRAD. The report also serves as the manual for this receiver.

Oscarsson, F.

1994-01-01

14

Design and Implementation of DDC Based on Walsh Transform for HF Radar Receiver  

Microsoft Academic Search

This paper studies the design and multiplierless realization of a digital down converter (DDC) in a high frequency (HF) radar\\u000a receiver. The novel structure mainly consists of a fast Walsh transform (FWT) and an inverse fast Walsh transform (IFWT),\\u000a both of which can be implemented using only addition and subtraction. Because the transform kernels of the FWT and the IFWT

Liyun Bai; Biyang Wen; Jing Yang

2006-01-01

15

On the accuracy of HF radar surface current measurements: Intercomparisons with ship-based sensors  

Microsoft Academic Search

High-frequency (HF) radar systems can provide periodic, two-dimensional, vector current estimates over an area approaching 1000 km . As the use of these HF systems has gained wider acceptance, a number of attempts have been made to estimate the accuracy of such systems. However, comparisons of HF radar current estimates with in situ sensors are difficult to interpret since HF

R. D. Chapman; L. K. Shay; H. C. Graber; J. B. Edson; A. Karachintsev; C. L. Trump; D. B. Ross

1997-01-01

16

Customizable Digital Receivers for Radar  

NASA Technical Reports Server (NTRS)

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

Moller, Delwyn; Heavey, Brandon; Sadowy, Gregory

2008-01-01

17

First HF radar measurements of summer mesopause echoes at SURA  

Microsoft Academic Search

HF sounding of the mesosphere was first carried out at SURA in summer 1994 at frequencies in the range 8–9 MHz using one of the sub-arrays of the SURA heating facility. The observations had a range resolution of 3 km. Almost all measurements indicated the presence of strong radar returns from altitudes between 83 and 90 km with features very

A. N. Karashtin; Yu. V. Shlyugaev; V. I. Abramov; I. V. Berezin; V. V. Bychkov; E. B. Eryshev; G. P. Komrakov

1997-01-01

18

HF radar measurements in Liverpool Bay, Irish Sea  

Microsoft Academic Search

A phased array HF radar systems transmitting at 13 MHz with sites at Form by Point, north of the Mersey outflow, and on the North Wales coast near Abergele has been operational since August 2005. Data on a 4 km grid are recorded every 20 minutes, with hourly data telemetered to the Proud man Oceanographic Laboratory by telephone land line.

M. J. Howarth; R. J. Player; J. Wolf; L. A. Siddons

2007-01-01

19

Digital modules for phased array radar  

Microsoft Academic Search

The architecture for a digital transmit\\/receive module for phased array radars is described. The module is a true digital component: control and data inputs and outputs are sequences of numbers. Direct digital synthesis for frequency generation and a digital receiver provide the core of the digital module, and these two items are discussed separately. A wide range of system performance

A. Garrod

1996-01-01

20

Digital modules for phased array radar  

Microsoft Academic Search

The architecture for a digital transmit\\/receive module for phased array radars is described. The module is a true digital component: control and data inputs and outputs are sequences of numbers. Direct digital synthesis for frequency generation and a digital receiver provide the core of the digital module, and these two items are discussed separately. A wide range of system performance

Adrian Garrod

1995-01-01

21

Wave Measurements with Multi-frequency Hf Radar in the East China Sea  

Microsoft Academic Search

Waves, winds and currents can be extracted from the Doppler power Spectra of HF Radar. Worldwide research has been done for this purpose during the last 4 decades. A new multi-frequency HF (MHF) radar is applied to enrich this study in a ten-day experiment completed in the East China Sea. The new MHF radar is designed to simultaneously work at

Z. Chen; C. Zhao; Y. Jiang; W. Hu

2011-01-01

22

Improved Reliability Prediction for HF (High Frequency) Digital Voice Transmission.  

National Technical Information Service (NTIS)

A method for predicting the performance of High Frequency (HF) digital voice transmission is described. The method takes into account the effects of multipath propagation and signal processing techniques which exploit the multipath to achieve improved per...

A. Malaga

1989-01-01

23

Nightside studies of coherent HF Radar spectral width behaviour  

NASA Astrophysics Data System (ADS)

A previous case study found a relationship between high spectral width measured by the CUTLASS Finland HF radar and elevated electron temperatures observed by the EISCAT and ESR incoherent scatter radars in the post-midnight sector of magnetic local time. This paper expands that work by briefly re-examining that interval and looking in depth at two further case studies. In all three cases a region of high HF spectral width (>200 ms-1) exists poleward of a region of low HF spectral width (<200 ms-1). Each case, however, occurs under quite different geomagnetic conditions. The original case study occurred during an interval with no observed electrojet activity, the second study during a transition from quiet to active conditions with a clear band of ion frictional heating indicating the location of the flow reversal boundary, and the third during an isolated sub-storm. These case studies indicate that the relationship between elevated electron temperature and high HF radar spectral width appears on closed field lines after 03:00 magnetic local time (MLT) on the nightside. It is not clear whether the same relationship would hold on open field lines, since our analysis of this relationship is restricted in latitude. We find two important properties of high spectral width data on the nightside. Firstly the high spectral width values occur on both open and closed field lines, and secondly that the power spectra which exhibit high widths are both single-peak and multiple-peak. In general the regions of high spectral width (>200 ms-1) have more multiple-peak spectra than the regions of low spectral widths whilst still maintaining a majority of single-peak spectra. We also find that the region of ion frictional heating is collocated with many multiple-peak HF spectra. Several mechanisms for the generation of high spectral width have been proposed which would produce multiple-peak spectra, these are discussed in relation to the data presented here. Since the regions of high spectral width are observed both on closed and open field lines the use of the boundary between low and high spectral width as an ionospheric proxy for the open/closed field line boundary is not a simple matter, if indeed it is possible at all.

Woodfield, E. E.; Davies, J. A.; Lester, M.; Yeoman, T. K.; Eglitis, P.; Lockwood, M.

2002-09-01

24

Temporal and spatial resolution of HF ocean radars  

NASA Astrophysics Data System (ADS)

The spatial and temporal resolutions of the two main types of HF radar are compared, with reference to the phasedarray and the crossed-loop direction-finding systems which make up the Australian Coastal Ocean radar Network. Both genres use a swept frequency "chirp" modulation to define the range of a pixel being observed but the method for determining the azimuth direction of the pixel is a strong point of differentiation. The phased-array systems produce independent maps of surface currents in about 1/7 of the time for the crossed-loop systems because of contrasting noise performance of the antennas. The use of beam-forming analysis in the phased-arrays is shown to give spatial resolutions, for vector currents, of about 10 km close to the shore, and 25 km at ranges of 150 km. The corresponding vector current spatial resolutions for the crossed-loop systems are 40 km and 60 km respectively.

Heron, Malcom L.; Atwater, Daniel P.

2013-03-01

25

New antenna layout for a SuperDARN HF radar  

NASA Astrophysics Data System (ADS)

A new antenna layout for a Super Dual Auroral Radar Network (SuperDARN) HF radar has been developed. The new layout utilizes two auxiliary arrays; one behind and one in front of the main array, rather than the single auxiliary array that existing radars use. The rear auxiliary array consists of three antennas providing beam-steering capability while the front auxiliary array consists of a single antenna. This layout is expected to greatly improve the calculation of elevation angle of arrival. Simulations presented show the advantages and disadvantages of using twin-terminated folded dipole (TTFD) antennas and log-periodic dipole arrays in standard and modified SuperDARN array configurations. TTFD antennas are shown to have superior front-to-back ratio and beam-steering capability but suffer from shadowing effects due to the presence of corner reflectors. Impedance-matching techniques used in SuperDARN radars are discussed, and the results of a new matching method, exhibiting a superior voltage standing-wave ratio over the SuperDARN frequency band, are presented. Shadowing of the main array by the front auxiliary array is investigated, and it is shown that the impact of the front array on the main array gain pattern is significantly less for the case of a single front antenna than for a four-antenna front array. Radar phase calibration techniques are discussed, and it is proposed that the additional single-antenna front array be used for system-wide radar phase calibration. An algorithm for the determination of elevation angle of arrival using the new layout is also given.

Custovic, Edhem; McDonald, Andrew J.; Whittington, James; Elton, Darrell; Kane, Thomas A.; Devlin, John C.

2013-11-01

26

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

27

Large-scale imaging of high-latitude convection with Super Dual Auroral Radar Network HF radar observations  

Microsoft Academic Search

The HF radars of the Super Dual Auroral Radar Network (SuperDARN) provide measurements of the E x B drift of ionospheric plasma over extended regions of the high- latitude ionosphere. With the recent augmentation of the northern hemisphere component to six radars, a sizable fraction of the entire convection zone (approximately one-third) can be imaged nearly instantaneously (-2 min). To

J. M. Ruohoniemi; K. B. Baker

1998-01-01

28

Ship detection with high-resolution HF skywave radar  

NASA Astrophysics Data System (ADS)

This paper presents an overview of ship detection by high-frequency (HF) skywave backscatter over-the-horizon radar (OTHR). Ships have been detected at ranges of 2000 km or more by OTHR that uses sufficient resolution in the radar spatial and Doppler frequency domains. The HF sea-echo Doppler spectrum limits the target signal-to-clutter ratio (SCR), as a function of the ocean wave-height distribution, wind direction, radio frequency, and ship target radial velocity. Maximum sea-clutter spectrum purity, and hence larger SCR, is achieved with the use of stable single-mode ionospheric propagation. Real-time measurement and interpretation of ionospheric propagation features therefore must guide the choice of OTHR operating frequency. Experimental data recorded at the ONR/SRI Wide Aperture Research Facility (WARF) bistatic OTHR in central California demonstrate reliable ship detection in the Northeast Pacific Ocean. WARF transmits 1-MW average effective radiated power, using a linear frequency-modulated continuous-wave (FMCW) waveform, and receives with a 2.55-km broadside array of vertical monopole element pairs. Swept bandwidths as high as 200 kHz have been used. Sufficient spectral resolution is achieved with a coherent integration time (CIT) of 12.8 s. Longer CIT, and autoregressive (AR) spectral analysis techniques such as Marple's algorithm, have been used to improve Doppler resolution.

Barnum, J. R.

1986-04-01

29

HF radar observations of ionospheric backscatter during geomagnetically quiet periods  

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

30

Measurements of near surface ocean currents using HF radar  

NASA Astrophysics Data System (ADS)

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

Laws, Kenneth Evans

31

The Space-Based Calibration of Optical Systems and HF Radars Using the Precision Expandable Radar Calibration Sphere  

Microsoft Academic Search

The Precision Expandable Radar Calibration Sphere (PERCS) is designed to provide a relatively simple target in space that can be used to determine the operational parameters of both ground Imaging systems and HF radars. PERCS is a 10 meter diameter wire frame in low earth orbit with corner cube reflectors placed at 60 or more vertices around the wire frame.

P. Bernhardt

2007-01-01

32

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, T.; Nishitani, N.; Kawamura, S.; Murayama, Y.

2013-12-01

33

Results from UHF and HF radar studies of ionospheric interaction experiments at HAARP  

NASA Astrophysics Data System (ADS)

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 radar facility MUIR has recently become operational on the HAARP site Complementary to these radar probe diagnostics are new stimulated electromagnetic emissions SEE receivers which record the electromagnetic emissions that propagate to the ground Radio-induced aurora are monitored We report on series of experiments performed at HAARP which employ all of the new radar optical and SEE diagnostics Employing HF pump pulses of varying lengths from milliseconds to tens of seconds we are able to reproduce analyze and compare prompt temporal and spectral signatures of Strong Langmuir Turbulence SLT measured by the HAARP MUIR UHF radar The HF radar measures the evolution of irregularities which may be compared with features in the UHF backscatter These results are compared to measurements of SLT previously performed at other HF heating facilities

Sheerin, J.; Bristow, W.; Watkins, B.; Oyama, S.; Heinselman, C.

34

Low-Profile Multifrequency HF Antenna Design for Coastal Radar Applications  

Microsoft Academic Search

A novel design for an electrically small high-frequency (HF) antenna suitable for coastal radar applications is presented. The principle design objectives were to develop an HF antenna resonant at multiple frequencies that is also compact and easily transportable for deployment to coastal sites and on floating platforms. The compact antenna achieves practical performance values for radiation resistance, bandwidth, and gain

James Baker; Hyoung-Sun Youn; Nuri Celik; Magdy F. Iskander

2010-01-01

35

Meridian-scanning photometer, coherent HF radar, and magnetometer observations of the cusp: a case study  

Microsoft Academic Search

The dynamics of the cusp region and post- noon sector for an interval of predominantly IMF By, Bz < 0 nT are studied with the CUTLASS Finland coherent HF radar, a meridian-scanning photometer located at Ny Alesund, Svalbard, and a meridional network of magnetometers. The scanning mode of the radar is such that one beam is sampled every 14 s,

S. E. Milan; M. Lester; S. W. H. Cowley; J. Moen; P. E. Sandholt; C. J. Owen

1999-01-01

36

Digital filters for synthetic aperture radar  

NASA Astrophysics Data System (ADS)

An organized approach is discussed for designing a set of optimal digital filters that can accommodate a wide range of synthetic-aperture radar (SAR) geometries. The basic SAR signal processing functions are reviewed since they are the basis for the filter design problems. Special digital filter optimality criteria are described that are tailored to the SAR environment. The results from recent filter design publications related to these critria are summarized and examples are included to demonstrate the effectiveness of this approach to designing filters for SAR processors.

Adams, J. W.; Medlin, G. W.; Bayma, R. W.

37

Seasonal variation of HF radar F region echo occurrence in the midnight sector  

Microsoft Academic Search

Long-term data (1996–2001) for a number of Super Dual Auroral Radar Network (SuperDARN) HF radars in both the Northern and Southern Hemispheres are used to study the midnight F region echo occurrence. We confirm the previously reported increase of echo occurrence toward the solar cycle maximum for all radars considered and a clear winter maximum for some of them. The

A. V. Koustov; G. J. Sofko; D. André; D. W. Danskin; L. V. Benkevitch

2004-01-01

38

Seasonal variation of HF radar F region echo occurrence in the midnight sector  

Microsoft Academic Search

Long-term data (1996-2001) for a number of Super Dual Auroral Radar Network (SuperDARN) HF radars in both the Northern and Southern Hemispheres are used to study the midnight F region echo occurrence. We confirm the previously reported increase of echo occurrence toward the solar cycle maximum for all radars considered and a clear winter maximum for some of them. The

A. V. Koustov; G. J. Sofko; D. André; D. W. Danskin; L. V. Benkevitch

2004-01-01

39

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 surfacewave radars can make these measurements out to approximately 100 km from the rdar, coverage out to 3000 km can be obtained with skywave radars that illuminate the sea via a single inospheric reflection. To

Joseph W. Maresca; T. M. Georges

1980-01-01

40

Digital evaluation of SEASAT-SAR radar image data  

Microsoft Academic Search

The use of spaceborne digital radar image data for small scale topographic and thematic mapping was studied. The information content of digital L-band radar data were analyzed; various evaluation methods of digital image processing for filtering, edge detection, and statistical analysis were employed and tested with regard to their applicability. The tests reveal which surface types and structures can be

Berthold Pfeiffer

1988-01-01

41

Hybrid Optical/Digital Processor for Radar Imaging.  

National Technical Information Service (NTIS)

Essex is developing a prototype hybrid optical/digital processor for radar image formation using wideband arbitrary waveforms. The processor is called the Advanced Optical Processor (AOP) and is a hybrid acousto- optic/digital processor that generates hig...

K. Frampton P. Stover

2003-01-01

42

Weighting in digital synthetic aperture radar processing  

NASA Technical Reports Server (NTRS)

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

Dicenzo, A.

1979-01-01

43

APQ-102 imaging radar digital image quality study  

NASA Astrophysics Data System (ADS)

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

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

1982-11-01

44

Assessment of the impact of HF radar current measurements on hydrodynamical model forecasts in the German Bight  

Microsoft Academic Search

The impact of high frequency (HF) radar measurements in the German Bight is investigated using a statistical assessment approach as well as an assimilation method. Within the project COSYNA (Coastal Observation SYstem for Northern and Arctic seas) three HF radar stations located in Wangerooge, Büsum, and Sylt will provide continuous surface current measurements. The presented study is about first steps

Johannes Schulz-Stellenfleth; Emil Stanev; Friedwart Ziemer; Klaus-Werner Gurgel

2010-01-01

45

Digital signal processing for target detection in FMCW radar  

Microsoft Academic Search

The paper describes a method of digital signal processing for extracting and isolating targets in the return signal of an FMCW radar. Digital filtering of the frequency spectrum of the return signal is followed by nonlinear optimization to detect the presence of multiple targets amid clutter. Results using a practical radar show that the method gives enhanced detection of weak

A. E. Carr; L. G. Cuthbert; A. D. Olver

1981-01-01

46

Digital signal processing for target detection in FMCW radar  

NASA Astrophysics Data System (ADS)

The paper describes a method of digital signal processing for extracting and isolating targets in the return signal of an FMCW radar. Digital filtering of the frequency spectrum of the return signal is followed by nonlinear optimization to detect the presence of multiple targets amid clutter. Results using a practical radar show that the method gives enhanced detection of weak return signals.

Carr, A. E.; Cuthbert, L. G.; Olver, A. D.

1981-10-01

47

Observations of Pi2 pulsations by the Wallops HF radar in association with substorm expansion  

Microsoft Academic Search

We report the first sub-auroral Pi2 pulsations observations by a SuperDARN type HF radar. The Wallops radar LOS measurements obtained at ionospheric altitudes, ?56° magnetic latitude, 23 hour magnetic local time, are shown to be highly correlated with ground magnetic field perturbations obtained at Ottawa. The period of the Pi2 pulsations is 118 s and the m-number is ?2.3. The

J. W. Gjerloev; R. A. Greenwald; C. L. Waters; K. Takahashi; D. Sibeck; K. Oksavik; R. Barnes; J. Baker; J. M. Ruohoniemi

2007-01-01

48

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

49

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

50

Compact Digital Receiver Development for Radar Based Remote Sensing  

Microsoft Academic Search

This paper is the first of a series of publications that discusses the design and implementation of an inexpensive, nearly all-digital FPGA-based radar receiver which can be used in a variety of applications including single\\/dual-polarization weather radar, sidelobe cancellation, a subarray module for a digital beam-forming phased-array radar, and other applications where a compact, low-power, low-cost receiver is needed. The

M. Yearyl; R. Kelleyl; J. Meierl; S. Ongl; R. Palmer

2008-01-01

51

Optimization of boundary conditions of a North Western Mediterranean coastal zone using HF radar measurements  

NASA Astrophysics Data System (ADS)

Correction of open boundary conditions (OBC) is attempted to improve surface velocity fields by assimilating HF radar velocities in a North Western Mediterranean (NWM) coastal model nested in a large scale operational model (Mercator Ocean system PSY2) providing IC (Initial Conditions) and OBC. A method based on HF radar velocities assimilation using an Ensemble Kalman Filter (EnKF) to derive the optimal wind forcing had already been validated. The objective of this work is to implement this method to the OBC correction. An ensemble simulation of the NWM sea model is carried out under different OBC to estimate model error covariance and covariance between surface currents and OBC. We evaluate the ability to correct the baroclinic oceanic forcings and to improve the surface current using a distant HF radar system. First, the method is assessed using twin experiments and a NWM sea model based on a Regional Ocean Model System (ROMS) configuration at 1/12°. Next, the method is applied to a high resolution (1/64°) NEMO-based model using a HF radar system operating in the Cote d'Azur. The method evaluation is done in both the eulerian and the lagrangian framework, based on a comprehensive data set (surface radial currents, surface drifter trajectories) obtained during the TOSCA (MedProgram) campaign. TOSCA project intends to optimize the response to marine accidents (oil spill, search and rescue) in Mediterranean sea, and the radar data assimilation may represent a great advantage to describe with more accuracy surface currents. Keywords : HF radar, data assimilation, ensemble simulation, surface meso-scale process, North Western Mediterranean sea, coastal modelling.

Marmain, Julien; Molcard, Anne; Forget, Philippe; Barth, Alexander

2013-04-01

52

Spatial temporal and frequency methods to mitigate interference in HF surface wave radar  

Microsoft Academic Search

In this paper, the spatial, temporal and frequency techniques to suppress interference in HF surface wave radar are presented. By exploiting the characteristics of the co-channel interference and deliberately selecting the secondary data, the proposed methods can effectively suppress both stationary and non-stationary interference. For most practical applications, the proposed interference suppression techniques can be combined to improve the interference

Su Hong-tao; An Zhi-juan; Bao Zheng; Zhang Shou-hong

2006-01-01

53

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

Microsoft Academic Search

Surface currents measured by HF Doppler radar as part of a study of the Chesapeake Bay outflow plume are examined using a 'real-vector' empirical orthogonal function (EOF) analysis (Kaihatu et al., 1998). Based on about 23 days of nearly continuous data, the analysis shows that the first three EOF modes, judged to be the only significant modes, account for 76%

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

1999-01-01

54

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

Microsoft Academic Search

Surface currents measured by HF Doppler radar as part of a study of the Chesapeake Bay outflow plume are examined using a ‘real-vector’ empirical orthogonal function (EOF) analysis (Kaihatu et al., 1998). Based on about 23 days of nearly continuous data, the analysis shows that the first three EOF modes, judged to be the only significant modes, account for 76%

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

1999-01-01

55

Spatial Relationships Between HF Radar Aurora Optical Aurora and Electron Precipitation.  

National Technical Information Service (NTIS)

HF backscatter data were obtained at College, Alaska, during 16 passes of satellite-borne particle-detectors near the College meridian. On the nightside of the Earth the gross position and the occurrence of precipitating auroral electrons and radar aurora...

H. F. Bates R. D. Sharp A. E. Belon J. S. Boyd

1968-01-01

56

HF Radar Measurements of Surface Currents at the Georgia Coast, 9 to 11 May 1978.  

National Technical Information Service (NTIS)

Described is a field experiment in which surface currents were measured by HF radar situated on the Georgia coast. The study area includes the waters of the Savannah River Delta, Wassaw Sound, and the adjacent inner continental shelf. Presented herein are...

M. M. Janopaul B. L. Weber

1980-01-01

57

Analysis of radar images by means of digital terrain models  

NASA Technical Reports Server (NTRS)

It is pointed out that the importance of digital terrain models in the processing, analysis, and interpretation of remote sensing data is increasing. In investigations related to the study of radar images, digital terrain models can have a particular significance, because radar reflection is a function of the terrain characteristics. A procedure for the analysis and interpretation of radar images is discussed. The procedure is based on a utilization of computer simulation which makes it possible to produce simulated radar images on the basis of a digital terrain model. The simulated radar images are used for the geometric and radiometric rectification of real radar images. A description of the employed procedures is provided, and the obtained results are discussed, taking into account a test area in Northern California.

Domik, G.; Leberl, F.; Kobrick, M.

1984-01-01

58

The Space-Based Calibration of Optical Systems and HF Radars Using the Precision Expandable Radar Calibration Sphere  

NASA Astrophysics Data System (ADS)

The Precision Expandable Radar Calibration Sphere (PERCS) is designed to provide a relatively simple target in space that can be used to determine the operational parameters of both ground Imaging systems and HF radars. PERCS is a 10 meter diameter wire frame in low earth orbit with corner cube reflectors placed at 60 or more vertices around the wire frame. For optical system calibration, PERCS will provide precisely spaced reflection points on the vertices of a large polyhedron. For HF radar calibration, PERCS will have a known radar cross section that is independent of observation direction within 0.5 dB. Laser satellite tracking will provide accurate orbital position and velocity of PERCS. The PERCS will orbit at 600 km altitude in a high inclination. Because of the wire frame construction, atmospheric drag will be low and the large spherical structure is expected to be available for more than five years. The PERCS satellite will be launched in a stowed configuration that has less than one meter in diameter. After launch, the PERCS will expand to a diameter of almost 10 meters. Hoberman Sphere technology will be used to produce a stable wire-frame to act as a radar scatter target. The sphere is based on a truncated icosahedron commonly known in chemistry as a "buckyball". The 60 vertices (V60) are hinged to be joined to 90 rigid segments. Each segment is hinged so that the PERCS can be folded into a compact package for launch.

Bernhardt, P.

59

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

60

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

61

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

62

HF Over-the-Horizon Radar System Performance Analysis.  

National Technical Information Service (NTIS)

The basic concept of the structure and properties of the ionosphere are discussed to explain how the performance of the over-the-horizon radar (OTHR) system is affected. An overview of the OTHR system characteristics and performance are presented along wi...

B. Liu

2007-01-01

63

Minimizing interference in automotive radar using digital beamforming  

NASA Astrophysics Data System (ADS)

Millimetre wave radar is an essential part of automotive safety functions. A high interference tolerance, especially with other radar sensors, is vital. This paper gives an overview of the motivation, the boundary conditions and related activities in the MOSARIM project funded by the European Union and concerned with interference mitigation in automotive radars. Current and planned activities considering Digital Beamforming (DBF) as a method for interference mitigation are presented.

Fischer, C.; Goppelt, M.; Blöcher, H.-L.; Dickmann, J.

2011-07-01

64

Digital signal processing in FMCW radar marine tank gauging system  

Microsoft Academic Search

A marine tank gauging system based on the FMCW radar is introduced. The range measurement principle of this system is presented. The digital signal processing procedure based on the FFT is described. The experimental results are also reported

Qi GuoQing

1996-01-01

65

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

66

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

67

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

68

Applying digital VLSI technology to radar signal processing  

Microsoft Academic Search

In spite of great advances in radar signal processing related to technological progress, the present digital signal processing (DSP) capability, still falls well short of what could be specified by a radar designer. It is, therefore, necessary to pay attention to the special characteristics of VLSI circuits in order to be able to exploit silicon as fully as possible as

J. B. G. Roberts; P. Simpson; B. C. Merrifield

1986-01-01

69

Elevation angle-of-arrival determination for a standard and a modified superDARN HF radar layout  

NASA Astrophysics Data System (ADS)

Calculations have been developed for the determination of elevation angle of arrival for a modified Super Dual Auroral Radar Network (SuperDARN) HF radar antenna layout consisting of dual auxiliary interferometer arrays: one behind and one in front of the main array. These calculations show that such a layout removes the 2? ambiguity or angle-of-arrival aliasing effect observed in existing SuperDARN HF radars. Ray tracing and simulation results are presented which show that there is significant potential for aliasing with existing SuperDARN radars and the standard interferometer algorithm under routine operating conditions.

McDonald, Andrew J.; Whittington, James; Larquier, Sebastien; Custovic, Edhem; Kane, Thomas A.; Devlin, John C.

2013-11-01

70

Digital processing system of the radar echo-signals  

NASA Astrophysics Data System (ADS)

A PC-based system for the digital processing of radar echo signals is described. The proposed system, involving user-level interactive RSAS, is implemented on a PC-based digital processing system compatible with the IBM-XT. Both hardware and software features are considered.

Giryn, Andrzej

71

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

72

Evaluation of the attenuation provided by a radar absorbing material (RAM) coating on an HF wire rope antenna  

Microsoft Academic Search

A shipboard electromagnetic interference (EMI) problem is considered. The use of radar absorbent material (RAM) to reduce unintentional X-band (8-12 GHz) radar reflections from HF wire rope antennas is analyzed. An exact series solution for a lossy-coated circular cylinder was developed and used to determine the effectiveness of the various RAM coatings

Griffin K. Gothard; Broun Hall

1991-01-01

73

Estimation and Verification of Vessel Radar-Cross-Sections for HF Surface Wave Radar.  

National Technical Information Service (NTIS)

The radar cross sections (RCS) of both small and large ships for High Frequency Surface Wave Radar (HFSWR) were studied by using Numerical Electromagnetics Code 4 and by using measurements from a HFSWR system at Cape Race, Newfoundland, Canada. The result...

H. Wilson H. Leong

2005-01-01

74

Height dependence of the observed spectrum of radar backscatter from HF-induced ionospheric Langmuir turbulence  

SciTech Connect

Observations of the spectrum of 430-MHz radar backscatter from HF-induced Langmuir turbulence with height discrimination are described. During very stable ionospheric conditions under which the height of the below-threshold backscatter spectrum had changed by less than 300 m during a 7-min period, a 20-s-long temporary increase in the HF power from 3 MW ERP to 38 MW equivalent radiated HF power resulted in subsequent strong above-threshold spectra extending to heights up to 1200 m greater than the height of the below-threshold spectrum for more than a minute. The generation of irregularities in the plasma density during the 20 s of enhanced HF power is suggested as a possible cause of this persistence of strong above-threshold spectra at greater heights. The initial temporal evolution of the backscatter spectrum from Langmuir turbulence after the start of HF transmissions was observed for different heights. The observational results are compared with the predictions of existing theories of Langmuir turbulence.

Fejer, J.A. (Univ. of California, San Diego, La Jolla (United States)); Sulzer, M.P. (National Astronomy and Ionosphere Center, Arecibo (Puerto Rico)); Djuth, F.T. (Geospace Research, Los Angeles, CA (United States))

1991-09-01

75

Real-Time Digital Signal Processing of Phased Array Radars  

Microsoft Academic Search

With the advance of hardware and software technology, modern phased array radars are now built with commercial-off-the-shelf (COTS) components, and it opens up a new era in real-time resource scheduling of digital signal processing. This paper targets the essential issues in building a component-oriented signal processor (SP), which is one of the two major modules in modern phased array radars.

Chin-fu Kuo; Tei-wei Kuo; Cheng Chang

2003-01-01

76

Digital active-aperture phased-array radar  

Microsoft Academic Search

A digital active-aperture architecture for phased-array radars has been proposed by NRL to improve performance and reduce the life-cycle cost of future USA Navy radars. Considering various approaches, NRL has been procuring and testing various component alternatives and is implementing the design described above in order to demonstrate this technology. The simulations, analysis, and laboratory measurements that have been performed

B. H. Cantrell; J. W. De Graaf; L. M. Leibowitz

2000-01-01

77

UHF and HF Radar Studies of Langmuir Turbulence Experiments at HAARP  

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

78

UHF and HF Radar Studies of Langmuir Turbulence Experiments at HAARP  

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

79

UHF and HF Radar Studies of Langmuir Turbulence Experiments at HAARP  

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

80

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

81

The Dynamic Reconnection-Driven Polar Cap as seen by HF Radar (PolarDARN)  

NASA Astrophysics Data System (ADS)

The SuperDARN HF radar pair (called PolarDARN) at Rankin Inlet (73.2° AACGM LAT) and Inuvik (71.2° AACGM LAT) is now fully operational (Rankin, May 2006 and Inuvik, Nov. 2007). For the first time, detailed two-dimensional radar convection maps of the polar cap region and poleward portion of the auroral oval are available with a one-minute time resolution. These radar images show clearly the signature of reconnection in the proximity of the ionospheric mapping of the OCFLB (open-closed field line boundary). Near magnetic noon (midnight), high-speed flows into (out of) the polar cap, away from (toward) the radars, are seen regularly, presumably mapping the fast outflows from the dayside and nightside reconnection regions. The convection maps reveal a very dynamic polar cap, with substantial changes in the convection pattern from one minute to the next. Examples of the reconnection-driven convection are presented, for By-dominant conditions and for both Bz+ and Bz- IMF conditions. The noon region for Bz+ conditions appears to be the counterpart of the auroral proton spot seen clearly with the IMAGE FUV instrument (Frey et al., JGR, 107, A7, 2002; Fusilier et al., JGR, 107, A7, 2002; Frey et al., Nature, 426, 533, 2003; Phan et al., GRL, 30, 10, 2003).

Sofko, G. J.; St. Maurice, J.; Koustov, A. V.; McWilliams, K.; Hussey, G.; Watanabe, M.; Yan, X.; Choudhary, R.; Andre, D.; Wiid, J.

2007-12-01

82

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

83

The relationship of HF radar backscatter to the accumulation of open magnetic flux prior to substorm onset  

NASA Astrophysics Data System (ADS)

We identify a characteristic signature observed in Halley HF radar data during the substorm growth phase and investigate its relationship to magnetotail evolution leading up to substorm onset. The signature is a super-diurnal equator-ward propagation of the equatorward edge of the HF radar backscatter returns. It is found to be characteristic of a particular class of substorms, those which are the first to occur following quiet magnetospheric and ionospheric conditions. By using solar wind data, we estimate the reconnection electric field at the magnetopause for four such events. An empirical relationship is found to exist between the time integral of this electric field and the latitude of the HF radar backscatter. Relating this solely to the addition of open magnetic flux to the polar cap, we would estimate the length of the dayside reconnection X line to be 12 RE. It is likely that additional factors affect this empirical relationship.

Lewis, R. V.; Freeman, M. P.; Reeves, G. D.

1998-11-01

84

Digital Processing of Meteorological Radar Signals.  

National Technical Information Service (NTIS)

The paper describes a signal processing technique which reduces the variance to an acceptale level for quantitative measurements using the log power output from the radar as the variable. The decrease in variance is a function of the number of samples tak...

D. Sirmans

1972-01-01

85

Giant ionospheric disturbances observed with the SuperDARN Hokkaido HF radar and GPS network after the 2011 Tohoku earthquake  

NASA Astrophysics Data System (ADS)

Giant ionospheric disturbances induced by the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0) on 11 March 2011 are studied by using data from the SuperDARN Hokkaido HF radar and GPS receiver network (GEONET) in Japan. The HF radar observations revealed strong disturbances to the north of Hokkaido that propagated northward at velocities of 6.7-1.8 km/s triggered by northward-propagating seismic surface waves. An induction magnetometer in Hokkaido recorded part of the seismic wave propagation from the epicenter. After the passage of the 6.7-1.8 km/s waves the radar observed northward-propagating disturbances (343-136 m/s) due to atmospheric gravity waves (AGW) perhaps excited near the epicenter. Interestingly, the radar first detected peculiar disturbances with periods of about 2-4 min caused by the acoustic resonance. GEONET, which covers the area on the south of the radar field of view, provided total electron content (TEC) data. Comparisons between radar and TEC observations indicate the following: (1) 6.7-1.8 km/s waves observed with the radar do not always have counterparts in TEC. (2) Acoustic waves of 1.3-0.7 km/s identified in TEC are not observed with the radar. (3) Disturbances caused by both AGW and acoustic resonance are simultaneously discernible in both TEC and radar data.

Ogawa, T.; Nishitani, N.; Tsugawa, T.; Shiokawa, K.

2012-12-01

86

Digital Signal Processor for Doppler Radar Sensing of Vital Signs.  

National Technical Information Service (NTIS)

A digital signal processor for Doppler radar sensing of vital signs is described. A voltage waveform signal containing respiration and heartbeat signatures is low-pass filtered (0.7 Hz) for the respiration and band-pass filtered (1.0 - 3.0 Hz) for the hea...

B. Lohman O. Boric-Lubecke V. M. Lubecke P. W. Ong M. M. Sondhi

2001-01-01

87

Assessment of the impact of HF radar current measurements on hydrodynamical model forecasts in the German Bight  

NASA Astrophysics Data System (ADS)

The impact of high frequency (HF) radar measurements in the German Bight is investigated using a statistical assessment approach as well as an assimilation method. Within the project COSYNA (Coastal Observation SYstem for Northern and Arctic seas) three HF radar stations located in Wangerooge, Büsum, and Sylt will provide continuous surface current measurements. The presented study is about first steps towards the use of these data in an assimilation system to improve forecasts with a three dimensional hydrodynamical model. To get a first idea about the impact of radar measurements, an optimal linear estimator is used to re-construct the complete surface current field from HF radar observations taking into account both the prior current distribution and radar measurement errors. The prior current distribution is estimated using a three dimensional hydrodynamical primitive equation model with 1 km resolution. The performance of the HF radar observations is quantified in terms of the re-construction quality. Different combinations of radar stations are investigated using synthetic observations. In particular the impact of the additional two-dimensional information obtained with two stations instead of one station is illustrated. The direct use of radial current components for the re-construction is compared to the use of surface current vectors derived from the combination of two or three radar stations. Apart from the capability of the HF radar observations to provide estimates of the current field at the time of the observations, the potential of the measurements to provide forecasts is investigated with the linear re-construction approach as well. Furthermore the linear approach is used to re-construct the surface elevation rate of change making use of the continuity equation. An assimilation method based on the ensemble Kalman filter is used for a first impact assessment of HF radar measurements within a forecast system. Synthetic measurements with different characteristics, e.g., different combinations of radar stations, different measurement errors, are investigated. Twin runs are performed to compare forecasts with different configurations of the assimilation system, e.g., different assimilation intervals or different numbers of ensemble members. First available measurements of the radial surface current component obtained by the Wangerooge station are analyzed. Both the horizontal current field structure and the temporal evolution of the current field are compared to the numerical model with a focus on the M2 tidal signal. The analysis will also provide a statistics on the frequency of missing values, which is important for the assimilation of the data.

Schulz-Stellenfleth, Johannes; Stanev, Emil; Ziemer, Friedwart; Gurgel, Klaus-Werner

2010-05-01

88

Mapping surface currents from HF radar radial velocity measurements using optimal interpolation  

NASA Astrophysics Data System (ADS)

An optimal interpolation (OI) method to compute surface vector current fields from radial velocity measurements derived from high-frequency (HF) radars is presented. The method assumes a smooth spatial covariance relationship between neighboring vector currents, in contrast to the more commonly used un-weighted least-squares fitting (UWLS) method, which assumes a constant vector velocity within a defined search radius. This OI method can directly compute any quantities linearly related to the radial velocities, such as vector currents and dynamic quantities (divergence and vorticity) as well as the uncertainties of those respective fields. The OI method is found to be more stable than the UWLS method and reduces spurious vector solutions near the baselines between HF radar installations. The OI method produces a covariance of the uncertainty of the estimated vector current fields. Three nondimensional uncertainty indices are introduced to characterize the uncertainty of the vector current at a point, representing an ellipse with directional characteristics. The vector current estimation using the OI method eliminates the need for multiple mapping steps and optimally fills intermittent coverage gaps. The effects of angular interpolation of radial velocities, a commonly used step in the preprocessing of radial velocity data prior to vector current computation in the UWLS method, are presented.

Kim, Sung Yong; Terrill, Eric J.; Cornuelle, Bruce D.

2008-10-01

89

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

NASA Astrophysics Data System (ADS)

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

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

2008-05-01

90

Morning sector drift-bounce resonance driven ULF waves observed in artificially-induced HF radar backscatter  

NASA Astrophysics Data System (ADS)

HF radar backscatter, which has been artificially-induced by a high power RF facility such as the EISCAT heater at Tromsø, has provided coherent radar ionospheric electric field data of unprecedented temporal resolution and accuracy. Here such data are used to investigate ULF wave processes observed by both the CUTLASS HF radars and the EISCAT UHF radar. Data from the SP-UK-OUCH experiment have revealed small-scale (high azimuthal wave number, m -45) waves, predominantly in the morning sector, thought to be brought about by the drift-bounce resonance processes. Conjugate observations from the Polar CAM-MICE instrument indicate the presence of a non-Maxwellian ion distribution function. Further statistical analysis has been undertaken, using the Polar TIMAS instrument, to reveal the prevalence and magnitude of the non-Maxwellian energetic particle populations thought to be responsible for generating these wave types.

Baddeley, L. J.; Yeoman, T. K.; Wright, D. M.; Davies, J. A.; Trattner, K. J.; Roeder, J. L.

2002-09-01

91

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

92

Evaluation of an HF-radar ship detection and tracking algorithm by comparison to AIS and SAR data  

Microsoft Academic Search

Since several years, High Frequency (HF) Over-The-Horizon (OTH) radar is used to measure oce?anographie parameters, such as currents, waves, and wind direction over large areas up to 200 km off the coast. Cost effective low power systems transmitting less than 50 Watts have been developed, e.g. the WERA (WEUen RAdar), and are now commercially available. Besides their applications in oceanography

Klaus-Werner Gurgel; Thomas Schlick; Jochen Horstmann; Salvatore Maresca

2010-01-01

93

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

94

Digital filter design for radar image formation  

NASA Technical Reports Server (NTRS)

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.

1989-01-01

95

Estimation of Ocean Current Velocity in Coastal Area Using Radarsat-1 SAR Images and HF-Radar Data  

Microsoft Academic Search

This paper presents the results of the surface current velocity estimation using 6 Radarsat-1 SAR images and high frequency (HF) radar data acquired in west coastal area near Incheon, Korea. We extracted the surface velocity from SAR images based on the Doppler shift approach in which the azimuth frequency shift is related to the motion of surface target in the

Moon-Kyung Kang; Hoonyol Lee; Chan-Su Yang; Wang-Jung Yoon

2008-01-01

96

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. ...

97

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...

98

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

99

Observations of double-peaked E region coherent spectra with the CUTLASS Finland HF radar  

NASA Astrophysics Data System (ADS)

Cooperative UK Twin Located Auroral Sounding System Finland HF radar observations of E region coherent spectra are presented for several events. The Burg spectrum method is applied to study microstructure of the spectra. It is discovered that many spectra are two-peaked, and quite often there is a systematic pattern in their occurrence; the double-peak echoes are typically observed at intermediate and far ranges of the E region echo band and at ranges farther than the power maximum in the range profile. The typical separation between the peaks is about 150 m/s and hardly changes with the azimuth of observations. Velocities of two components in a double-peak spectrum are typically larger and smaller than the velocity of the unresolved spectrum and single-peaked velocity of echoes at shorter ranges. It is hypothesized that the two components of the echoes occur because of signal reception from the top and bottom of the electrojet layer.

Danskin, D. W.; Koustov, A. V.; Makarevitch, R. A.; Lester, M.

2004-04-01

100

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

101

An update on multi-channel digital receiver development for the phased array radar at the National Weather Radar Testbed  

Microsoft Academic Search

This paper describes the beginning states of a new project that will digitize radar signals coming from eight channels on the phased array antenna at the National Weather Radar Testbed (NWRT) in Norman, Oklahoma. At the current time, a single-channel digital receiver is operational to mimic the current capability. The multi-channel digital data will foster a new generation of adaptive\\/fast

M. Yeary; J. Crain; A. Zahrai; R. Palmer; M. Xue; T.-Y. Yu; G. Zhang; Y. Zhang; R. Doviak; Q. Xu; P. Chilson

2009-01-01

102

Smoothing and Differentiation of the Output of a Doppler Radar by a Digital Spectralanalytic Method.  

National Technical Information Service (NTIS)

A digital method for smoothing and differentiating the output of a Doppler radar is presented. The raw output of the radar is transformed into the frequency domain. Then the appropriate filtering and differentiation operations are performed followed by an...

F. P. Devries

1972-01-01

103

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

104

Subinertial and seasonal variations in the Soya Warm Current revealed by HF ocean radars, coastal tide gauges, and bottom-mounted ADCP  

Microsoft Academic Search

Subinertial and seasonal variations in the Soya Warm Current (SWC) are investigated using data obtained by high frequency\\u000a (HF) ocean radars, coastal tide gauges, and a bottom-mounted acoustic Doppler current profiler (ADCP). The HF radars clearly\\u000a captured the seasonal variations in the surface current fields of the SWC. Almost the same seasonal cycle was repeated in\\u000a the period from August

Naoto Ebuchi; Yasushi Fukamachi; Kay I. Ohshima; Masaaki Wakatsuchi

2009-01-01

105

Global digital topography mapping using a scanning radar altimeter  

NASA Technical Reports Server (NTRS)

The conceptual design of a Scanning Radar Altimeter system capable of collecting less than 300-m spatial and less than 3-m height resolution digital topography data for the entire globe, from an orbital platform, is presented. A 37-GHz frequency SRA system is used to achieve the requisite resolution while reducing antenna length in the along-track dimension. Near-global coverage in a short time period is obtained by scanning the antenna beam cross-track, in a swath of about 100 km. Attention is given to the algorithm that will be used to retrieve pixel height from the return waveform.

Elachi, C.; Im, K. E.; Li, F.; Rodriguez, E.

1987-01-01

106

Validation of Orthorectified Interferometric Radar Imagery and Digital Elevation Models  

NASA Technical Reports Server (NTRS)

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

Smith Charles M.

2004-01-01

107

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

NASA Astrophysics Data System (ADS)

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

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

1980-09-01

108

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

109

High Frequency (HF) Upgrade Study for the Canadian Regional Operations Control Center (ROCC) AWACS Digital Information Link (RADIL) Project.  

National Technical Information Service (NTIS)

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 g...

K. Wickwire

1995-01-01

110

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

111

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

112

Comparison between real drifter's trajectories and simulated trajectories using HF radar data, in the Bay of Biscay  

NASA Astrophysics Data System (ADS)

A High Frequency (HF) radar network is operational since the beginning of 2009 for the oceanic region of the Basque Country, Spain (south-eastern part of the 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 emitting at 40 kHz broadband and 4.5 MHz frequency and covering a 150 km range with 5 km radial and 5° angular resolutions. Hourly space- and time-covering measurements are contributing considerably to the study of surface current patterns and the main physical processes in the area. Additional applications relate, for example, to security of navigation, maritime rescue, validation and improvement of numerical models and trajectories prediction. Since 2009, different drifters have been deployed in the study area. Since the radar has been proved to reproduce the time evolution of the currents through comparison with moored buoys with a reasonable accuracy, the aim of this work is to evaluate the capabilities of the system to reproduce the trajectories of a set of drifters available in the study area. To make trajectory simulations, we will use HF radar total velocities, surface velocities obtained from EOF (Empirical Orthogonal Function) analysis of the whole radar data set, forecast velocities for 48 hours and also OMA (Open-Boundary Modal Analysis) derived current velocities.

Solabarrieta, Lohitzune; Cook, Michael; Paduan, Jeffrey; Sergey, Frolov; Rubio, Anna; Fontán, Almudena; Castanedo, Sonia; Gonzalez, Manuel; Medina, Raúl; Fernández, Vicente; Charria, Guillaume

2013-04-01

113

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

Microsoft Academic Search

The ionosphere at high latitudes is the site of important effects in space weather. These include strong electrical currents that may disrupt power systems through induced currents and density irregularities that can degrade HF and satellite communication links. With the impetus provided by the National Space Weather Program, the radars of the Super Dual Auroral Radar Network have been applied

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

2001-01-01

114

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

115

Digital elevation models of the Moon from Earth-based radar interferometry  

Microsoft Academic Search

Three-dimensional (3D) maps of the nearside and polar regions of the Moon can be obtained with an Earth-based radar interferometer. This paper describes the theoretical background, experimental setup, and processing techniques for a sequence of observations performed with the Goldstone Solar System Radar in 1997. These data provide radar imagery and digital elevation models of the polar areas and other

Jean-Luc Margot; Donald B. Campbell; Raymond F. Jurgens; Martin A. Slade

2000-01-01

116

FPGA based IF digital receiver for the PARSAX - Polarimetric agile radar  

Microsoft Academic Search

An FPGA-based digital receiver has been developed to perform real-time processing for the PARSAX radar. It is a fully polarimetric FMCW radar with dual-orthogonal sounding signals, which has the possibility to measure all elements of the radar targets polarization scattering matrix simultaneously, in one sweep. This paper presents the design principles including the range profile interpretation, optimal parameters selection and

Zongbo Wang; Oleg A. Krasnov; Leo P. Ligthart; F. van der Zwan

2010-01-01

117

Digital filtering, calibration and correlation analysis of radar-echoes from the tropo- and stratosphere  

Microsoft Academic Search

VHF-radars have been successfully used for remote sensing of the lower and middle atmosphere. The received radar-echoes are digitized and these raw data are processed in several sequential steps. By digitally filtering the raw data which is equivalent to a compression or a coherent integration, the amount of data is reduced and at the same time the signal-to-noise ratio is

R. Ruester; R. F. Woodman

1978-01-01

118

Digital Data Acquisition for Laser Radar for Vibration Analysis.  

National Technical Information Service (NTIS)

Laser radar for vibration analysis represents a military application to develop a target identification system in the future. The problem addressed is how to analyze the vibrations of a target illuminated by the laser radar to achieve a positive identific...

F. G. Montes

1998-01-01

119

Toward bay\\/harbor circulation model improvement incorporating HF radar data based on SeaSonde deployments on San Fransisco Bay  

Microsoft Academic Search

Two High-Resolution SeaSonde HF radars were deployed on San Francisco Bay during summer 1999. Normal total vector map coverage was produced in the common overlap area east of Tiburon, North of Golden Gate. The authors focus on the important Golden-Gate region with the highest flows, which was seen only by the radar on Treasure Island. This is a case where

D. Barrick; R. Cheng; N. Garfield; J. Paduan; P. Lilleboe; J. Gartner; L. Pederson

2000-01-01

120

Suppression of power line harmonic interference in HF surface-wave radar  

Microsoft Academic Search

Experimental data of the Cape Bonavista High-Frequency Surface-Wave Radar (HFSWR) Facility was contaminated by power line harmonics. The harmonics modulate the radar signal (mainly sea clutter) and replicate it into the Doppler spectrum. The spectral replicas distort the noise and sea clutter statistics in the signal. It is necessary to suppress them before the statistics can be obtained. A new

Hank Leong

1992-01-01

121

Radar Studies of the Solar Corona: A Review of Experiments Using HF wavelengths.  

National Technical Information Service (NTIS)

The use of high frequency (9 to 40 MHz), high power radars to study the solar corona has a remarkable history. Solar radar experiments were proposed and started at the beginning of the modern era of space physics research. Early in the 1960's the El Campo...

P. Rodriguez

1999-01-01

122

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

123

The Signal Digital Processing in the Millimeter Band FMCW Radar  

Microsoft Academic Search

The frequency-modulated continuous wave-radars - (FMCW-radars) are widely applied in the car road safety systems, the aircraft altimeters, the fusion plasma microwave diagnostics and in other ranging systems of different usage. The most optimal choice in terms of the \\

A. V. Varavin; G. P. Ermak; A. S. Vasilev; I. V. Popov

2007-01-01

124

Simultaneous PMC and PMSE observations with a ground-basedlidar and SuperDARN HF radar over Syowa Station, Antarctica  

NASA Astrophysics Data System (ADS)

A Rayleigh-Raman lidar system had been installed by the 52nd JapaneseAntarctic Research Expedition on February, 2011 at Syowa Station Antarctica(69.0°S, 39.5°E). Polar Mesospheric Cloud (PMC) was detected by the lidar at22:30UT (+3hr for LT) on Feb 4th, 2011, the first day of a routineoperation. This event is the first time to detect PMC over Syowa Station bya lidar. In the same night, SuperDARN HF radar with oblique incidence beamsalso detected Polar Mesosphere Summer Echoes (PMSEs) during 21:30UT to23:00UT. Although these signals were detected at different times andlocations, PMC motion estimated using horizontal wind velocities obtained bya collocated MF radar strongly suggests that they have a common origin (i.e.ice particle). We consider that this event occurred in the end of PMCactivity period at Syowa Station in the austral summer season (2010-2011),since the lidar did not detected any PMC signals on other days in February,2011. This is consistent with satellite-born PMC observations by AIM/CIPSand atmospheric temperature observations by AURA/MLS instruments.

Suzuki, Hidehiko; Nakamura, Takuji; Tsutsumi, Masaki; Kawahara, Takuya D.; Ogawa, Tadahiko; Tomikawa, Yoshihiro; Ejiri, Mitsumu K.; Sessai Yukimatu, Akira; Abo, Makoto

2012-07-01

125

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

126

Digital beamforming developments for the joint NASA\\/Air Force Space Based Radar  

Microsoft Academic Search

The Space Based Radar (SBR) program includes a joint technology demonstration between NASA and the Air Force to design a low-earth orbiting, 2×50 m L-band (1.26 GHz) radar system for Earth science and intelligence-related observations. A key subsystem aboard SBR is the electronically-steerable digital beamformer (DBF) network that interfaces between 32 smaller subantenna panels in the array and the on-board

Mark A. Fischman; Charles Le

2004-01-01

127

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

Microsoft Academic Search

The space based radar (SBR) program includes a joint technology demonstration between NASA and the Air Force to design a low-earth orbiting, 2×50 m L-band (1.26 GHz) radar system for both Earth science and intelligence-related observations. A key subsystem aboard SBR is the electronically-steerable digital beamformer (DBF) network that interfaces between 32 smaller sub-antenna panels in the array and the

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

2004-01-01

128

Temporal impulsive noise excision in the range-Doppler map of HF radar  

Microsoft Academic Search

In this paper we present an effective scheme to excise impulsive noise pixels from a range-Doppler image or map. The temporal impulses in High Frequency Ocean Surveillance radar (HFOSR) Doppler spectrum image arise due to local lightning discharges or man-made sources. Previous work focused on locating the noise position (detection) and applying a simple blanking technique, thereby burying targets in

Xiaoli Lu; R. Lynn Kirlin; Jian Wang

2003-01-01

129

Objectively mapping HF radar-derived surface current data using measured and idealized data covariance matrices  

Microsoft Academic Search

Surface currents measured by high-frequency radars are objectively mapped using covariance matrices computed from hourly surface current vectors spanning two years. Since retrievals of surface radial velocities are inherently gappy in space and time, the irregular density of surface current data leads to negative eigenvalues in the sample covariance matrix. The number and the magnitude of the negative eigenvalues depend

Sung Yong Kim; Eric Terrill; Bruce Cornuelle

2007-01-01

130

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

131

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

132

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

133

A STATUS REPORT ON THE RF AND DIGITAL COMPONENTS OF THE MULTICHANNEL RECEIVER DEVELOPMENT AT THE NATIONAL WEATHER RADAR TESTBED  

Microsoft Academic Search

This paper describes the status of a project that will simultaneously digitize the radar signals coming from eight channels on the phased array antenna at the Na- tional Weather Radar Testbed (NWRT) in Norman, Ok- lahoma. At the current time, a single-channel digital receiver is operational on this S-band radar to mimic the current WSR-88D capability. The multi-channel dig- ital

M. Yeary; J. Crain; A. Zahrai; R. Kelley; J. Meier; Y. Zhang; I. Ivic; C. Curtis; R. Palmer; T.-Y. Yu; G. Zhang; R. Doviak; P. Chilson; M. Xue; Q. Xu

134

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

135

Simultaneous PMC and PMSE observations with a ground-based lidar and SuperDARN HF radar at Syowa Station, Antarctica  

NASA Astrophysics Data System (ADS)

A Rayleigh-Raman lidar system was installed in January 2011 at Syowa Station, Antarctica (69.0° S, 39.6° E). Polar mesospheric clouds (PMCs) were detected by lidar at around 22:30 UTC (LT -3 h) on 4 February 2011, which was the first day of observation. This was the first detection of PMCs over Syowa Station by lidar. On the same day, a Super Dual Auroral Radar Network (SuperDARN) HF radar with oblique-incidence beams detected polar mesospheric summer echoes (PMSE) between 21:30 and 23:00 UTC. This event is regarded as the last PMC activity around Syowa Station during the austral summer season (2010-2011), since no other PMC signals were detected by lidar in February 2011. This is consistent with results of PMC and mesopause temperature observations by satellite-born instruments of AIM (Aeronomy of Ice in the Mesosphere)/CIPS (Cloud Imaging and Particle Size) and AURA/MLS (Microwave Limb Sounder) and horizontal wind measurements taken by a separate MF radar. Doppler velocity of PMSE observed by the HF radar showed motion toward Syowa Station (westward). This westward motion is consistent with the wind velocities obtained by the MF radar. However, the PMSE region showed horizontal motion from a north-to-south direction during the PMC event. This event indicates that the apparent horizontal motion of the PMSE region can deviate from neutral wind directions and observed Doppler velocities.

Suzuki, H.; Nakamura, T.; Ejiri, M. K.; Ogawa, T.; Tsutsumi, M.; Abo, M.; Kawahara, T. D.; Tomikawa, Y.; Yukimatu, A. S.; Sato, N.

2013-10-01

136

Quantization noise in digital signal processing by harmonic analysis in a synthetic-aperture radar  

Microsoft Academic Search

The paper derives and analyzes expressions for assessing the effect of quantization noise arising in digital signal processing by harmonic analysis in a synthetic-aperture radar on the output signal for an arbitrary weight function in an FFT processor. The output signal-to-noise ratio is shown to depend on the FFT base size, the digit-representation length in the processing system, and the

N. A. Sazonov

1985-01-01

137

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

NASA Astrophysics Data System (ADS)

The rapid expansion of urbanization along the world's coastal areas requires a more comprehensive and accurate understanding of the coastal ocean. Over the past several decades, numerical ocean circulation models have tried to provide such insight, based on our developing understanding of physical ocean processes. The systematic establishment of coastal ocean observation systems adopting cutting-edge technology, such as high frequency (HF) radar, satellite sensing, and gliders, has put such ocean model predictions to the test, by providing comprehensive observational datasets for the validation of numerical model forecasts. The New York Harbor Observing and Prediction System (NYHOPS) is a comprehensive system for understanding coastal ocean processes on the continental shelf waters of New York and New Jersey. To increase confidence in the system's ocean circulation predictions in that area, a detailed validation exercise was carried out using HF radar and Lagrangian drifter-derived surface currents from three drifters obtained between March and October 2010. During that period, the root mean square (RMS) differences of both the east-west and north-south currents between NYHOPS and HF radar were approximately 15 cm s-1. Harmonic analysis of NYHOPS and HF radar surface currents shows similar tidal ellipse parameters for the dominant M2 tide, with a mean difference of 2.4 cm s-1 in the semi-major axis and 1.4 cm s-1 in the semi-minor axis and 3° in orientation and 10° in phase. Surface currents derived independently from drifters along their trajectories showed that NYHOPS and HF radar yielded similarly accurate results. RMS errors when compared to currents derived along the trajectory of the three drifters were approximately 10 cm s-1. Overall, the analysis suggests that NYHOPS and HF radar had similar skill in estimating the currents over the continental shelf waters of the Middle Atlantic Bight during this time period. An ensemble-based set of particle tracking simulations using one drifter which was tracked for 11 days showed that the ensemble mean separation generally increases with time in a linear fashion. The separation distance is not dominated by high frequency or short spatial scale wavelengths suggesting that both the NYHOPS and HF radar currents are representing tidal and inertial time scales correctly and resolving some of the smaller scale eddies. The growing ensemble mean separation distance is dominated by errors in the mean flow causing the drifters to slowly diverge from their observed positions. The separation distance for both HF radar and NYHOPS stays below 30 km after 5 days, and the two technologies have similar tracking skill at the 95 % level. For comparison, the ensemble mean distance of a drifter from its initial release location (persistence assumption) is estimated to be greater than 70 km in 5 days.

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

2012-08-01

138

Optimum digital recursive filters for step scan phased array radars  

Microsoft Academic Search

A design method for recursive filters with optimum clutter rejection is presented. The designed filters are suitable for MTI (moving target indication) systems in step scan phased array radars. The designed filters are optimized for a given clutter power spectrum and a finite number of samples without initialization. The performance of the designed filters was studied by considering their clutter

Hussian Al-Ahmad; Gordon B. Lockhart

1991-01-01

139

A digital ASIC for synthesizing false target radar images  

Microsoft Academic Search

Modern, wideband, inverse synthetic aperture radar (ISAR) is capable of generating images of targets, rendering traditional false target decoy methods obsolete. The paper describes an application specific integrated circuit (ASIC) capable of generating false target decoy images for countering imaging ISARs. The application and operation of the ASIC in an electronic attack system is also discussed. The fully programmable chip

Douglas J. Fouts; P. E. Pace; C. Karow; S. R. T. Ekestorm

2002-01-01

140

Geometric rectification of radar imagery using digital elevation models  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

141

The use of digital modulation signals in radar system for detection of nonlinear scatterers  

Microsoft Academic Search

This paper deals with initial application of digital modulation techniques in the radar systems utilizing non-linear junction detection (NLJD) principle. Various types of devices, such as handheld detectors for searching of hidden listening devices, have previously been developed and are commercially available. However, these devices transmit single frequency harmonic waveform which in general limits efficiency of energy transmission to nonlinear

Vladimir Polacek; Radomir Pavlik

2011-01-01

142

An advanced digital signal processor for the HRR polarimetric MMW active guidance radar  

Microsoft Academic Search

Polarimetric CFAR detection procedures are first outlined. An advanced digital signal processor used for MMW polarimetric HRR active precision guiding radar is configured that involves a preamplifier and filter, a spectral analyzer and a DSP-based polarimetric detector\\/discriminator to seek and track ground targets in surface clutter. A fuzzy relative optimal state (FROS) of a processor is conceptualized concerning the compromise

Yong Rin; Benchao Sie; Lui Yongtan

1993-01-01

143

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

144

Simulation of constituent transport using a reduced 3D constituent transport model (CTM) driven by HF Radar: Model application and error analysis  

Microsoft Academic Search

Data-driven constituent transport models (CTM), which take surface current measurements from High Frequency (HF) Radar as input can be applied within the context of real-time environmental monitoring, oceanographic assessment, response to episodic events, as well as search and rescue in surface waters.This paper discusses a numerical method that allows for the evaluation of diffusion coefficients in anisotropic flow fields from

Temitope O. Ojo; James S. Bonner; Cheryl A. Page

2007-01-01

145

Ship detection in heavy sea clutter echoes and man-made radio noise environment for an on-shore HF ground wave frequency agile radar  

Microsoft Academic Search

The spectral characteristics of sea clutter echoes and man-made noise disturbance in the HF band are analyzed. A new spectral method for ship detection in heavy sea clutter and man-made noise environment by an onshore ground wave radar is introduced. A T-R cell averaging detector with the assistance of a spectrum monitoring system operates on a frequency agile mode, and

Xiaolin Qiao; Yongtan Liu

1990-01-01

146

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

147

A technique for accurately determining the cusp-region polar cap boundary using SuperDARN HF radar measurements  

NASA Astrophysics Data System (ADS)

Accurately measuring the location and motion of the polar cap boundary (PCB) in the high-latitude ionosphere can be crucial for studies concerned with the dynamics of the polar cap, e.g. the measurement of reconnection rates. The Doppler spectral width characteristics of backscatter received by the SuperDARN HF radars have been previously used for locating and tracking the PCB in the cusp region. The boundary is generally observed in meridional beams of the SuperDARN radars and appears as a distinct change between low spectral width values observed equatorward of the cusp region, and high, but variable spectral width values observed within the cusp region. To identify the spectral width boundary (SWB) between these two regions, a simple algorithm employing a spectral width threshold has often been applied to the data. However, there is not, as yet, a standard algorithm, or spectral width threshold, which is universally applied. Nor has there been any rigorous assessment of the accuracy of this method of boundary determination. This study applies a series of threshold algorithms to a simulated cusp-region spectral width data set, to assess the accuracy of different algorithms. This shows that simple threshold algorithms correctly identify the boundary location in, at the most, 50% of the cases and that the average boundary error is at least ~ 1 2 range gates (~ 1° latitude). It transpires that spatial and temporal smoothing of the spectral width data (e.g. by median filtering), before application of a threshold algorithm can increase the boundary determination accuracy to over 95% and the average boundary error to much less than a range gate. However, this is sometimes at the cost of temporal resolution in the motion of the boundary location. The algorithms are also applied to a year’s worth of spectral width data from the cusp ionosphere, measured by the Halley SuperDARN radar in Antarctica. This analysis highlights the increased accuracy of the enhanced boundary determination algorithm in the cusp region. Away from the cusp, the resulting SWB locations are often dependent on the choice of threshold. This suggests that there is not a sharp latitudinal SWB in regions of the dayside ionosphere away from the cusp, but that there is a shallower latitudinal gradient in spectral width near the boundary location.

Chisham, G.; Freeman, M. P.

2003-04-01

148

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

NASA Astrophysics Data System (ADS)

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

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

2004-02-01

149

Surface current variability and wind influence in the northeastern Adriatic Sea as observed from high-frequency (HF) radar measurements  

NASA Astrophysics Data System (ADS)

A network of HF radars operated in the northeastern Adriatic Sea in the period September 2007 to August 2008. Surface currents were collected with the purpose of studying the temporal and spatial modes of surface circulation in the area. Their dependence on local wind forcing was investigated using wind records from coastal stations and the mesoscale meteorological model ALADIN/HR. EOF decomposition, spectral and tidal analyses, and time-lagged correlation extracted the dominant features in the area and their time scales. The time-averaged flow presented a cyclonic circulation pattern with relatively weak currents and standard deviations comparable to average values. Three dominant current patterns were extracted by the EOF analysis, which accounted for about 70% of total variance. In the region, wind was the major source of current variability over a wide portion of frequencies, whereas tidal forcing was weak and limited to the semidiurnal and diurnal frequencies, representing 10%-20% of the total variance. The response to wind forcing was immediate with veering angles consistent with Ekman dynamics in the majority of the area. Coherence analyses revealed strong correlation within the sub-tidal and diurnal bands, the latter related to diurnal sea-breezes variability. The seasonal variability of the inertial motions was also observed in the area.

Cosoli, Simone; Ga?i?, Miroslav; Mazzoldi, Andrea

2012-02-01

150

Evolution of negative SI-induced ionospheric flows observed by SuperDARN King Salmon HF radar  

NASA Astrophysics Data System (ADS)

The spatial evolution of vortex-like flow structures induced by a negative sudden impulse (SI-) is studied on the basis of SuperDARN King Salmon HF radar (KSR) with other ground and satellite data. A large dip in the solar wind density induced a fairly large SI- with a SYM-H amplitude of ˜40 nT. The SI-induced ionospheric flow signatures in the evening sector (MLT ˜ 19 h) were observed by KSR as a westward flow associated with the preliminary impulse (PI) followed by a more intense eastward flow with the main impulse (MI) in the sub-auroral region of the magnetic latitude ˜60-70 deg, consistent with the local ground magnetic field observations. Following the first PI-MI flow sequence, KSR saw a second and possibly third sequence of flow variation which were much smaller in flow amplitude than the first pair but showed qualitatively very similar flow variations and latitudinal/longitudinal propagation characteristics. These observations can be interpreted as aftershocks of the first PI-MI; the same sequence of vortices and field-aligned currents were generated and then drifted anti-sunward with the same mechanism, namely the pumping motion of the dayside magnetosphere. These results are qualitatively consistent with predictions suggested by recent numerical simulations.

Hori, T.; Shinbori, A.; Nishitani, N.; Kikuchi, T.; Fujita, S.; Nagatsuma, T.; Troshichev, O.; Yumoto, K.; Moiseyev, A.; Seki, K.

2012-12-01

151

Digital image processing techniques applied to the radar detection problem  

Microsoft Academic Search

The author investigates the utility of applying to the radar detection problem several nonlinear filtering structures that have been shown to be useful in image processing. In particular, a CFAR-(constant-false-alarm-rate-)like window processing technique is described. After describing the form of this processing window and pointing out the similarities between it and both conventional CFAR and median filtering windows, the author

C. R. Guarino

1991-01-01

152

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

153

Travelling Ionospheric Disturbances Generated by High Power HF SURA Facility: the Results from Kharkiv Incoherent Scatter Radar  

NASA Astrophysics Data System (ADS)

The results of ionospheric disturbances observation which accompanied periodic near-Earth plasma heating by high-power HF SURA facility radiation were presented. The experiments to modify the ionosphere were conducted on September 20 - 23, 2010 between 12:50 and 17:40 UT. The temporal and height variations of electron density obtained by Kharkiv incoherent scatter radar were analyzed. The main feature of the present study was that the diagnostic instrument was located 1000 km away from the SURA facility. The ionospheric modifications were detected to significantly change the spectral content of wave disturbances in the electron density. The wave disturbance with a period of near 30 min that corresponds to facility cyclic operation (the heating of 20 min and the pause of 10 min) and with relative amplitude of 0.08 - 0.10 was at the heights of 200 - 300 km. Its time delay was of 60 - 90 min between the first heating start and wave observation. It is important that such disturbance was observed in all time intervals when the ionosphere was heated by high power HF radio waves. The apparent velocity of this wave disturbance was about 190 - 280 m/s, assuming that it was generated by the first heating switch-on. Since the ionosphere is inertial (and hence integrating) medium, it can be assumed that ionospheric disturbance generation occurred after second or third heating switch-on. The apparent wave velocity was then in the range of 280 - 560 m/s. Internal gravity waves and traveling ionospheric disturbances are known to have such horizontal velocities. Thus, the effect observed over Kharkiv may be explained by the generation and/or amplification of traveling ionospheric disturbances. This inferred wave pattern was in good agreement with theoretical estimates. The interaction of subsystems in the Earth - the atmosphere - the ionosphere - the magnetosphere system may possibly contribute to this observable effect. The observed wave disturbances may also be generated by solar terminator moving. Long-term, regular measurements are needed to more accurately separate the effects of ionosphere heating from those of terminator moving.

Chernogor, L.; Domnin, I.; Panasenko, S.; Uryadov, V.

2012-04-01

154

A survey of analog-to-digital converter technology for radar applications  

NASA Astrophysics Data System (ADS)

The first section of this report discusses sample and hold devices (SHD) which are required prior to the analog to digital converter (ADC) in most radar applications. The SHDs discussed had acquisition times of 10 microsecs or less. plots of SHD droop rate and aperture uncertainty versus acquisition time are presented. The next section contains details on a variety of commercial off the shelf ADCs that have sampling rates greater than 100 KHz. They are compared by resolution, sampling rate, packaging, logic family, size, cost, power requirements, and temperature stability. Finally, brief descriptions of ADCs in development are discussed, and a resolution versus sampling rate comparison of noncommercial ADCs being manufactured by radar houses and their suppliers is presented. The performance envelopes of the commercial and noncommercial ADCs are then overlayed on the estimated 1988 Radar and ELINT resolution and sampling rate requirements.

Jones, B. E.

1982-03-01

155

A digital signal processing system for coherent laser radar  

NASA Technical Reports Server (NTRS)

A data processing system for use with continuous-wave lidar is described in terms of its configuration and performance during the second survey mission of NASA'a Global Backscatter Experiment. The system is designed to estimate a complete lidar spectrum in real time, record the data from two lidars, and monitor variables related to the lidar operating environment. The PC-based system includes a transient capture board, a digital-signal processing (DSP) board, and a low-speed data-acquisition board. Both unprocessed and processed lidar spectrum data are monitored in real time, and the results are compared to those of a previous non-DSP-based system. Because the DSP-based system is digital it is slower than the surface-acoustic-wave signal processor and collects 2500 spectra/s. However, the DSP-based system provides complete data sets at two wavelengths from the continuous-wave lidars.

Hampton, Diana M.; Jones, William D.; Rothermel, Jeffry

1991-01-01

156

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

157

Real-Time Digital Signal Processing of Component-Oriented Phased Array Radars  

Microsoft Academic Search

With the advance of hardware and software technology, modern phased array radars are now built with commercial off-the-shelf (COTS) components, and it opens up a new era in real-time resource scheduling of digital signal processing. This paper targets the essential issues in building a component-oriented signal processor (SP), which is one of the two major modules in modern phased array

Chin-fu Kuo; Tei-wei Kuo; Cheng Changt

2000-01-01

158

Global digital topography mapping with a synthetic aperture scanning radar altimeter  

NASA Technical Reports Server (NTRS)

Global digital topography data of the land surface is of importance in a variety of geoscientific and application disciplines. Such a database, with a spatial resolution of 150 to 500 m and height accuracy of 5 m or better can be acquired from an orbiting platform using a synthetic aperture scanning radar altimeter. Near-global coverage can be achieved within 14 days from an orbiting platform in a polar or near-polar orbit.

Elachi, C.; Im, K. E.; Rodriguez, E.

1990-01-01

159

Analysis of a generalized coding\\/decoding method using FIR digital filters for radar waveform design  

Microsoft Academic Search

Previous results dealing with radar systems utilizing complementary coded pulse compression waveforms are extended. The objective is to show how the generation and compression of such codes can be based on a specific single-input\\/multiple-output FIR (finite-impulsive-response) digital filter structure. Driving this filter with a unit pulse yields all members of a complementary code set sequence simultaneously. A decoder is then

Daniel B. Koch

1990-01-01

160

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

161

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

Code of Federal Regulations, 2010 CFR

...may require that the digital spectral power density (and total power) be lower by several dB than is currently used for either DSB or SSB emissions. (c) Emission characteristics â(1) Bandwidth and center frequency. A full digitally...

2009-10-01

162

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

163

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

164

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

165

A digital implementation of a radar coherent-on-receive system  

NASA Astrophysics Data System (ADS)

A digital coherent-on receive subsystem was designed, built, and tested in order to provide coherent-on receive operation for pulsed radar systems employing incoherent magnetron transmitters. The design used two finite impulse response filters, which extracted the coherent phase from the return signal by performing a matched filter operation between the transmit and receive signals. The phase locking characteristics of this subsystem were evaluated using a magnetron transmitter, and its performance was compared with that of a conventional coherent oscillator (COHO) which was tested in a similar fashion. Results indicate that in a nonchirped environment, the performance of the digital technique is comparable to that obtained with the COHO, while the possibility of it displaying superior performance in a highly chirped scenario exists.

Fernando, M. C.

1989-09-01

166

Multiple-site investigation of the properties of an HF radio channel and the ionosphere using Digital Radio Mondiale broadcasting  

NASA Astrophysics Data System (ADS)

The Digital Radio Mondiale (DRM), one of the new digital radio broadcasting standards, has been designed to overcome typical short wave radio channel difficulties, such as the multipath propagation and fast temporal changes of the received signal level, both related to the properties of the ionosphere along the path of propagation. In particular, some of the RF carriers used in the applied COFDM transmission technique serve to estimate the current state of the radio channel to enable the proper demodulation of the received signal.We have been detecting such RF carriers on select frequency channels (standard DRM broadcast) using a network of recording stations located in different parts of Poland in order to collect data on the HF radio channel. We have been also evaluating the usefulness of this procedure in providing information on the current state of the ionosphere in the refraction region between the transmitter and receivers. When the DRM system becomes more widespread, this method can supplement data that comes from the ionosondes, since it does not require much financial resources and the receivers can be easily scattered over a large area. This paper presents a set of experimental data and its analysis.

Mlynarczyk, Janusz; Koperski, Piotr; Kulak, Andrzej

2012-01-01

167

Radar  

Microsoft Academic Search

Over 1,000,000 km2 of the equatorial surface of Mars west of the Arsia Mons volcano displays no 3.5-cm radar echo to the very low level of the radar system noise for the Very Large Array; the area displaying this unique property has been terms \\

James R. Zimbelman; Kenneth S. Edgett

1994-01-01

168

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

NASA Astrophysics Data System (ADS)

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

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

2001-12-01

169

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

170

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

171

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

172

Analysis and characterization of the vertical accuracy of digital elevation models from the Shuttle Radar Topography Mission  

Microsoft Academic Search

The first near-global high-resolution digital elevation model (DEM) of the Earth has recently been released following the successful Shuttle Radar Topography Mission (SRTM) of 2000. This data set will have applications in a wide range of fields and will be especially valuable in the Earth sciences. Prior to widespread dissemination and use, it is important to acquire knowledge regarding the

Giacomo Falorni; Vanessa Teles; Enrique R. Vivoni; Rafael L. Bras; Kevin S. Amaratunga

2005-01-01

173

A simple method for optimizing radar absorbent material coatings on HF rope antennas for the increased attenuation of unwanted reflections  

Microsoft Academic Search

The research presented here examines the maximum attenuation available from concentric layers of radar absorbing materials (RAM) surrounding an infinitely long perfect electrically conducting circular cylinder. The electrical phenomenology of normally incident transverse magnetic (TM) and transverse electrical (TE) waves associated with backscattered and bistatic behavior is investigated for a frequency range up to 25 GHz. Some of the more

George W. Jarriel; Lloyd S. Riggs; Michael E. Baginski

1997-01-01

174

Application of Wigner Distribution for the Detection of Accelerating Low-Altitude Aircraft using HF Surface-Wave Radar.  

National Technical Information Service (NTIS)

Real radar data has been analysed using the Fourier transform method and the type-III Wigner distribution. The results show that whenever the target was detectable by the Fourier transform method, the target was detectable also by the smoothed type-III Wi...

T. Thayaparan A. Yasotharan

2002-01-01

175

Digital signal processing and numerical analysis for radar in geophysical applications  

NASA Astrophysics Data System (ADS)

Numerical solutions for signal processing are described in this work as a contribution to study of echo detection methods for ionospheric sounder design. The ionospheric sounder is a high frequency radar for geophysical applications. The main detection approach has been done by implementing the spread-spectrum techniques using coding methods to improve the radar's range resolution by transmitting low power. Digital signal processing has been performed and the numerical methods were checked. An algorithm was proposed and its computational complexity was calculated.The proposed detection process combines two channels correlations with the local code and calculates threshold (Vt) by statistical evaluation of the background noise to design a detection algorithm. The noisy signals treatment was performed depending on the threshold and echo amplitude. In each case, the detection was improved by using coherent integration. Synthetic signals, close loop and actual echoes, obtained from the Advanced Ionospheric Sounder (AIS-INGV) at Rome Ionospheric Observatory, were used to verify the process.The results showed that, even in highly noisy environments, the echo detection is possible.Given that these are preliminary results, further studies considering data sets corresponding to other geophysical conditions are needed.

Molina, María G.; Cabrera, M. A.; Ezquer, R. G.; Fernandez, P. M.; Zuccheretti, E.

2013-05-01

176

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

177

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

178

Analog radar signal design and digital signal processing a Heisenberg nilpotent Lie group approach  

NASA Astrophysics Data System (ADS)

Introductory discussion of radar principles Analog radar signal design The radar synthesis problem The radar invariant problem The compact Heisenberg nilmanifold A geometric approach to cardinal spline interpolation Finite phase space, and finite Fourier transform The phase discontinuity of Fourier optics Conclusions References

Schempp, Walter

179

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

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

180

Modelling of the electromagnetic scattering by sea surfaces at grazing incidence. Application to HF surface wave radars  

NASA Astrophysics Data System (ADS)

The object of the study is to model the electromagnetic scattering by time-evolving sea surfaces illuminated by high frequency surface wave radars. A common way to simulate this case is to consider the scattering at grazing incidence. Recent studies have focused on so-called exact methods. As such methods are very time and memory consuming, it becomes important to implement techniques to reduce the calculation costs. Another important issue is to better understand the interactions between the electromagnetic waves and moving sea surfaces. We present in this article our simulator main characteristics and a comparison between simulated data and measurements.

Demarty, Yaël; Thirion-Lefevre, Laetitia; Gobin, Vincent

2010-01-01

181

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

182

Frequency diversity wideband digital receiver and signal processor for solid-state dual-polarimetric weather radars  

NASA Astrophysics Data System (ADS)

The recent spate in the use of solid-state transmitters for weather radar systems has unexceptionably revolutionized the research in meteorology. The solid-state transmitters allow transmission of low peak powers without losing the radar range resolution by allowing the use of pulse compression waveforms. In this research, a novel frequency-diversity wideband waveform is proposed and realized to extenuate the low sensitivity of solid-state radars and mitigate the blind range problem tied with the longer pulse compression waveforms. The latest developments in the computing landscape have permitted the design of wideband digital receivers which can process this novel waveform on Field Programmable Gate Array (FPGA) chips. In terms of signal processing, wideband systems are generally characterized by the fact that the bandwidth of the signal of interest is comparable to the sampled bandwidth; that is, a band of frequencies must be selected and filtered out from a comparable spectral window in which the signal might occur. The development of such a wideband digital receiver opens a window for exciting research opportunities for improved estimation of precipitation measurements for higher frequency systems such as X, Ku and Ka bands, satellite-borne radars and other solid-state ground-based radars. This research describes various unique challenges associated with the design of a multi-channel wideband receiver. The receiver consists of twelve channels which simultaneously downconvert and filter the digitized intermediate-frequency (IF) signal for radar data processing. The product processing for the multi-channel digital receiver mandates a software and network architecture which provides for generating and archiving a single meteorological product profile culled from multi-pulse profiles at an increased data date. The multi-channel digital receiver also continuously samples the transmit pulse for calibration of radar receiver gain and transmit power. The multi-channel digital receiver has been successfully deployed as a key component in the recently developed National Aeronautical and Space Administration (NASA) Global Precipitation Measurement (GPM) Dual-Frequency Dual-Polarization Doppler Radar (D3R). The D3R is the principal ground validation instrument for the precipitation measurements of the Dual Precipitation Radar (DPR) onboard the GPM Core Observatory satellite scheduled for launch in 2014. The D3R system employs two broadly separated frequencies at Ku- and Ka-bands that together make measurements for precipitation types which need higher sensitivity such as light rain, drizzle and snow. This research describes unique design space to configure the digital receiver for D3R at several processing levels. At length, this research presents analysis and results obtained by employing the multi-carrier waveforms for D3R during the 2012 GPM Cold-Season Precipitation Experiment (GCPEx) campaign in Canada.

Mishra, Kumar Vijay

183

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

NASA Technical Reports Server (NTRS)

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

Imhoff, Marc Lee; Gesch, Dean B.

1990-01-01

184

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

SciTech Connect

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

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

1991-01-01

185

An 8-bit 2.5 gigasample A\\/D converter multichip module for all-digital radar receiver for AN\\/APS 145 radar on Navy E2-C Airborne Early Warning Aircraft  

Microsoft Academic Search

This paper will discuss multichip module (MCM) technology as it is applied to a prototype high performance direct digitizing channelized radar receiver system under development for the Navy's E2-C Airborne Early Warning Aircraft, which encompasses both analog signals at UHF frequencies and multi-gigahertz digital signals. Critical issues which arise in the design of such a system will be discussed, including

Rick L. Thompson; Michael J. Degerstrom; Wayne L. Walters; Mark E. Vickberg; Paul J. Riemer; Eric L. H. Amundsen; Barry K. Gilbert

1997-01-01

186

Noise Radar for range\\/Doppler processing and digital beamforming using low-bit ADC  

Microsoft Academic Search

Pulse compression radar is used in a great number of radar applications. Excellent range resolution and high resistance to electronic countermeasures (ECM) can be achieved by long wideband modulated pulses, which spread out the transmitted energy in frequency and time. By using random noise as the waveform, the range ambiguity can be suppressed as well. In this paper, noise radar

Sune R. J. Axelsson

2003-01-01

187

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

NASA Astrophysics Data System (ADS)

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

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

188

Experimental investigations of digital signal processing techniques in an FMCW radar for naval application  

Microsoft Academic Search

Recently we have observed increased interest in frequency modulated continuous wave (FMCW) radars, mainly because of their low probability of intercept (LPI) properties. In such radars the information on range of targets appears in the frequency domain and it is obtained on the basis of spectrum analysis carried out for a so called beat signal. The beat signal is a

A. Grzywacz

2002-01-01

189

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

190

First observations of ionospheric irregularities and flows over the south geomagnetic pole from the SuperDARN HF radar at McMurdo Station, Antarctica  

Microsoft Academic Search

In February 2010 a new SuperDARN radar began operation at McMurdo Station, Antarctica. The radar's orientation places the south geomagnetic pole near the center of the field of view at about 1200 km range. The radar is the highest latitude radar of the SuperDARN network, both geographically and geomagnetically, and the observations have a different character than those of the

W. A. Bristow; R. T. Parris; J. Spaleta

2010-01-01

191

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

192

First observations of ionospheric irregularities and flows over the south geomagnetic pole from the SuperDARN HF radar at McMurdo Station, Antarctica  

NASA Astrophysics Data System (ADS)

In February 2010 a new SuperDARN radar began operation at McMurdo Station, Antarctica. The radar’s orientation places the south geomagnetic pole near the center of the field of view at about 1200 km range. The radar is the highest latitude radar of the SuperDARN network, both geographically and geomagnetically, and the observations have a different character than those of the auroral zone radars. One particular feature of note is the high incidence of observed backscatter. When ionospheric altitudes are above the solar shadow height the incidence of observation is greater than 80% for a large portion of the radar field of view. This is indicative of the near constant presence of field-aligned density irregularities in the polar cap. This paper presents statistics of the observations along with estimates of the convection velocity maps. Prevailing IMF and solar wind velocity were taken from the Omni database and compared to the observed flows.

Bristow, W. A.; Parris, R. T.; Spaleta, J.

2010-12-01

193

A Four-Channel 94GHz SiGe-Based Digital Beamforming FMCW Radar  

Microsoft Academic Search

This paper presents a multi-channel frequency-modulated continuous-wave (FMCW) radar sensor operating in the frequency range from 91 to 97 GHz. The millimeter-wave radar sensor utilizes an SiGe chipset comprising a single signal-generation chip and multiple monostatic transceiver (TRX) chips, which are based on a 200-GHz $f_{\\\\rm T}$ HBT technology. The front end is built on an RF soft substrate in

Martin Jahn; Reinhard Feger; Christoph Wagner; Ziqiang Tong; Andreas Stelzer

2012-01-01

194

Comparison of antenna dispersion and digital signal processing effects in ultrawideband Ground Penetrating Radar systems  

NASA Astrophysics Data System (ADS)

In Ground Penetrating Radar it is of great interest to have a pulse width as narrow as possible to achieve best resolution capability. However, ultrawideband antennas may cause distortion to the radar signal due to dispersion, which is dependent on the frequency and bandwidth, as well as the direction of radiation. As dispersion causes an increase of the peak's width, the resolution capability is degraded.

Seyfried, Daniel; Brueckner, Sebastian; Schoebel, Joerg

2014-02-01

195

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

196

The Sensitivity of a Volcanic Flow Model to Digital Elevation Models From Diverse Sources: Digitized Map Contours and Airborne Interferometric Radar  

NASA Astrophysics Data System (ADS)

A growing trend in the field of volcanic hazard assessment is the use of computer models of a variety of flows to predict potential areas of devastation. The accuracy of these computer models depends on two factors, the nature and veracity of the flow model itself, and the accuracy of the topographic data set over which it is run. All digital elevation models (DEMs) contain innate errors. The nature of these depends on the accuracy of the original measurements of the terrain, and on the method used to build the DEM. We investigate the effect that these errors have on the performance of a simple volcanic flow model designed to delineate areas at risk from lahar inundation. The volcanic flow model was run over two DEMs of southern Ruapehu volcano derived from (1) digitized 1:50,000 topographic maps, and (2) airborne C-band synthetic aperture radar interferometry obtained using the NASA AIRSAR system. On steep slopes (exceeding 4 degrees), drainage channels are more likely to be incised deeply, and flow paths predicted by the model are generally in agreement for both DEMs despite the differing nature of the source data. Over shallow slopes (approx. 4 degrees and less), where channels are less deep and are more likely to meander, problems were encountered with flow path prediction in both DEMs due to interpolation errors and forestry. The predicted lateral and longitudinal extent of deposit inundation was also sensitive to the type of DEM used, most likely in response to the differing degrees of surface texture preserved in the DEMs. A technique to refine contour-derived DEMs and reduce the error in predicted flow paths was tested to improve the reliability of the modeled flow path predictions. The suitability of forthcoming topographic measurements acquired by a single-pass space-borne instrument, the NASA Shuttle Radar Topography Mission (SRTM) are also tested.

Stevens, N. F.; Manville, V.; Heron, D. W.

2001-12-01

197

A digital signal processor for Doppler radar sensing of vital signs  

Microsoft Academic Search

A signal processor for the determination of respiration and heart rates in Doppler radar measurements is described. The processor can reliably calculate both rates for a subject at distances as large as 2 m. The rate determination is based on autocorrelation and uses several enhancement techniques, including a center clipper. Several representative results are included to show the future potential

B. Lohman; O. Boric-Lubecke; V. M. Lubecke; P. W. Ong; M. M. Sondhi

2002-01-01

198

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

199

A general statistical instrument theory of atmospheric and ionospheric radars  

SciTech Connect

Some basic functional relationships between the statistics of the signals received in a radar and the statistics of the density fluctuations of a scattering medium are derived. They vary in their degree of generality, but they are all very general in scope. They include monostatic and bistatic radars scattering from either atmospheric, ionospheric, or meteorological media. They are valid for refractive and slightly dispersive media, so they can also be used for HF ionospheric radars. They include the effects of filtering, including receiver filtering, pulse compression coding and decoding schemes, and coherent integration, or any alternative linear digital filtering scheme. Functional relationships to include cross-correlation schemes, such as Faraday rotation experiments and interferometers, are included. Some simplified expressions are derived for frequently encountered situations, where different approximations can be made. These simplified expressions cover a large number of radar techniques currently in use for atmospheric and ionospheric applications.

Woodman, R.F. (Instituto Geofisico del Peru, Lima (Peru))

1991-05-01

200

Using X-band weather radar measurements to monitor the integrity of digital elevation models for synthetic vision systems  

NASA Astrophysics Data System (ADS)

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. Futher, 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 real-time 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 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, Steven D.; Uijt de Haag, Maarten; Sayre, Jonathon

2003-09-01

201

Aspect angle dependence of HF enhanced incoherent backscatter  

Microsoft Academic Search

An HF ionospheric interaction experiment was performed in November and December of 1997 using the EISCAT HF transmitter and 931 and 224 MHz incoherent scatter radars, all co-located near Tromsø, Norway. During this experiment the pointing of the UHF radar was varied in a predetermined and repeating cycle between elevation angles of 90 and 77.2 degrees south, that is, between

B. Isham; M. T. Rietveld; T. Hagfors; C. La Hoz; E. Mishin; W. Kofman; T. B. Leyser; A. P. van Eyken

1999-01-01

202

Complementary Code and Digital Filtering for Detection of Weak VHF Radar Signals from the Mesosphere  

Microsoft Academic Search

Measurements of the structure and the dynamics of the middle atmosphere with a fine height resolution have been carried out using the SOUSY-VHF-Radar (SOUSY = SOUnding SYstem), operated by the Max-Planck-Institute for Aeronomy in the Harz mountains in Germany. Since the echoes from the middle atmosphere are coherent within a time scale of the order of a second, the received

Gerhard Schmidt; Rudiger Ruster; Peter Czechowsky

1979-01-01

203

Comparison of Satellite Radar Altimeter Derived Heights with Global Digital Terrain Model Heights.  

National Technical Information Service (NTIS)

A study of the use of SEASAT and Geosat altimeter data for global height determination is reported. Currently available Global Digital Elevation Models (GDEMs) are of limited spatial resolution and accuracy, while satellite altimetry offers the prospects ...

J. K. Ridley P. A. M. Berry C. M. Birkett C. G. Rapley

1992-01-01

204

Comparing Digital Flood Insurance Rate Maps (DFIRMs) to Interferometric Synthetic Aperture Radar (IFSAR) Products.  

National Technical Information Service (NTIS)

As part of the Federal Emergency Management Agency (FEMA) Map Modernization program, Flood Insurance Rate Maps (FIRMs) are converted from hard copy products to Digital Flood Insurance Rate Maps (DFIRMs). The next generation of DFIRMs will have more data a...

J. J. Damron

2000-01-01

205

HF Laser.  

National Technical Information Service (NTIS)

A review is made of the research and development of the HF chemical laser and related work. Many gaseous compounds are used as laser media successfully; reaction kinetics and technological problems are described. The hybrid chemical laser of HF-CO sub 2 s...

K. Suzuki M . Iwasaki

1977-01-01

206

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

207

High-Resolution Digital Mapping of Soil Surface Water Content at the Field Scale Using Ground Penetrating Radar  

NASA Astrophysics Data System (ADS)

Measuring soil surface water content spatial variability is essential for many environmental and agricultural researches and engineering applications, as this variable controls important key processes of the hydrological cycle such as infiltration, runoff, evaporation, and energy exchanges between the earth and the atmosphere. In particular, the characterization of spatial patterns and heterogeneities over a continuous range of scales is presently subject to intensive research for developing, calibrating and testing distributed hydrological models, with, e.g., the installation of field- to watershed-scale observatories. In that respect, ground penetrating radar (GPR) appears to be a promising tool for real-time, high resolution digital soil mapping at the field scale. Yet existing GPR techniques for quantitative soil characterization still suffer from a series of limitations, mainly arising from the strong simplifying assumptions that are commonly made with respect to electromagnetic wave propagation phenomena. We have developed a new GPR methodology based on full-waveform forward and inverse modelling, that inherently maximizes radar information retrieval capabilities thanks to an accurate electromagnetic model and system calibration procedure. The radar system consists of a vector network analyzer combined with an off- ground, zero-offset, ultra-wideband horn antenna, thereby setting up a stepped-frequency continuous-wave (SFCW) GPR. A full-waveform model describes accurately the radar signal by accounting for (1) all antenna effects and antenna-soil interactions through a linear system of frequency dependent, complex transfer functions, and (2) wave propagation in three-dimensional multilayered media through a Green's function as exact solution of Maxwell's equations. A fast procedure was developed to evaluate the involved spatial Green's function from its spectral counterpart, whose integral is singular. The soil electromagnetic properties and their vertical distribution are estimated by inverse modeling using various iterative optimization strategies, depending on the model complexity. The method presents especially considerable advantages compared to the current surface characterization techniques using GPR, namely, the ground wave and common reflection methods. The proposed methodology was successfully validated for a series of model configurations of increasing complexity. For the particular case of soil surface water content retrieval, we especially addressed the impact of shallow soil layering on the inverse estimates in case it is or not accounted for in the inverse model configuration. The results show that thin layers should not be neglected, especially when high contrasts between soil layers are encountered. The method is now routinely used for real-time, automated mapping of soil surface water content in the field. GPR-derived maps are compared to ground-truth measurements and satellite radar data products. Stochastic approaches are used for assessing the uncertainty on the inverse estimates. The proposed method constitutes in particular a robust alternative to other GPR approaches for shallow soil characterization.

Minet, J.; Lambot, S.; Slob, E.; Vereecken, H.; Vanclooster, M.

2009-05-01

208

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

Microsoft Academic Search

Various digital enhancement techniques for SAR are compared using SIR-B and Seasat images of the Canadian Shield. The three best methods for enhancing geological structure were found to be: (1) a simple linear contrast stretch; (2) a mean or median low-pass filter to reduce speckle prior to edge enhancement or a K nearest-neighbor average to cosmetically reduce speckle; and (3)

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

1988-01-01

209

Monitoring of Ground Movement and Generation of Digital Elevation Models Using Interferometric Synthetic Aperture Radar (InSAR) Data  

NASA Astrophysics Data System (ADS)

Interferometric synthetic aperture radar (InSAR) has the potential for measuring deformation of the earth's surface with very high accuracy and for the development of digital elevation models. Both capabilities are of high relevance for ground movement assessment. In addition, when archived raw data is available (post 1992), recent historic movement may be quantifiable. InSAR utilizes satellite-based data acquired at two different times along orbits of a similar trajectory to detect changes in the ground surface elevation. This technique can be used to monitor ground movement for rectangular areas as large as 100 kilometers on a side. Knowledge of topography, geology, trends and mechanics of existing ground movement is required for successful interpretation of InSAR data. The detection of ground surface deformation in terrain of high slope relief terrain is difficult. For ground deformation mapping by means of InSAR it is necessary to separate the motion-related and the topographic phase contributions. This is achieved by using a low resolution digital elevation model (DEM) during the processing of InSAR data. The application of InSAR technology to mining areas provides monitoring of not only the active mine areas but also the adjacent regions that has been affected by mining. Thus InSAR technique proves to be an essential ground monitoring methods in future for mining areas. The results from the InSAR analysis are compared with data from a ground-based monitoring system comprised of measured survey prisms for an open pit mine in Canada. InSAR analysis provided the location of the stable site for relocating the crusher which was affected by movement of pit slope. The presentation will show the application of InSAR technology to various mines in USA and Canada. Besides subsidence evaluation, InSAR data is also used to generate digital elevation models (DEM) and digital terrain models (DTM). The DEM and DTM derived from InSAR data for a mine in Canada is compared with the survey and LIDAR data to demonstrate the applicability of InSAR data to model surface topography.

Panda, B. B.

2013-12-01

210

Multidimensional radar picture  

NASA Astrophysics Data System (ADS)

In marine navigation systems, the three-dimensional (3D) visualization is often and often used. Echosonders and sonars working in hydroacustic systems can present pictures in three dimensions. Currently, vector maps also offer 3D presentation. This presentation is used in aviation and underwater navigation. In the nearest future three-dimensional presentation may be obligatory presentation in displays of navigation systems. A part of these systems work with radar and communicates with it transmitting data in a digital form. 3D presentation of radar picture require a new technology to develop. In the first step it is necessary to compile digital form of radar signal. The modern navigation radar do not present data in three-dimensional form. Progress in technology of digital signal processing make it possible to create multidimensional radar pictures. For instance, the RSC (Radar Scan Converter) - digital radar picture recording and transforming tool can be used to create new picture online. Using RSC and techniques of modern computer graphics multidimensional radar pictures can be generated. The radar pictures mentioned should be readable for ECDIS. The paper presents a method for generating multidimensional radar picture from original signal coming from radar receiver.

Waz, Mariusz

2010-05-01

211

An 8Bit 2-gigasample\\/second A\\/D converter multichip module for digital receiver demonstration on Navy AN\\/APS145 E2-C Airborne Early Warning Aircraft radar  

Microsoft Academic Search

This paper will discuss multichip module technology as it is applied to a prototype high performance direct digitizing channelized radar receiver system under development for the Navy's E2-C Airborne Early Warning Aircraft, which encompasses both analog signals at UHF frequencies and multigigahertz digital signals. Critical issues which arise in the design of such a system will be discussed, including thermal

R. L. Thompson; M. J. Degerstrom; W. L. Walters; M. E. Vickberg; P. J. Riemer; L. H. Amundsen; B. K. Gilbert

1998-01-01

212

First observations of ionospheric irregularities and flows over the south geomagnetic pole from the Super Dual Auroral Radar Network (SuperDARN) HF radar at McMurdo Station, Antarctica  

NASA Astrophysics Data System (ADS)

Observations from the first 100 days of operation of the Super Dual Auroral Radar Network (SuperDARN) radar at McMurdo Station, Antarctica are presented. The observations are examined for incidence of ionospheric scatter, which is higher than has been found at the auroral zone radars of the SuperDARN network. During some hours of each day, the probability of observing ionospheric scatter exceeded 90%. In the later portion of the period examined, there was a period of time each day during which the scatter incidence dropped significantly. Incidence was as examined versus solar illumination of the ionosphere, and it was found that the decreases coincided with periods when the ionosphere was in darkness. From this, it is concluded that propagation effects were the reason for the decreases. Plasma velocity observations from the period are also presented and compared with the prevailing interplanetary magnetic field (IMF). The observations were averaged over the central polar cap (? > 85°) and were selected for intervals when the radar line of sight was nearly parallel to the Earth-Sun (E-S) line or perpendicular (E-S-perp) to it. A linear relationship was found between the IMF z component and the E-S velocity and similar relationship between the E-S-perp velocity and the IMF y component. There was a significant spread of velocities about the best fit lines. The IMF and average velocity time series were cross-correlated for a number of intervals, and it was found that the average correlation was about 50%, though during some intervals, the correlation exceeds 80%. No explanation is given for the variance of the correlation.

Bristow, W. A.; Spaleta, J.; Parris, R. T.

2011-12-01

213

The MST radar technique  

NASA Technical Reports Server (NTRS)

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

Roettger, J.

1984-01-01

214

Superconductor Digital-RF Receiver Systems  

NASA Astrophysics Data System (ADS)

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

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

215

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

216

Decoders for MST radars  

NASA Technical Reports Server (NTRS)

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

Woodman, R. F.

1983-01-01

217

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

218

Target identification from radar signatures  

Microsoft Academic Search

Modern high resolution radar techniques and real time digital signal processing advances indicate the feasibility of extracting characteristic features of aircraft targets from their radar signatures. Two basic approaches have been suggested. The low frequency approach utilizes harmonically related radar frequencies with wavelengths comparable to the target dimensions. The microwave approach utilizes spread spectrum techniques to achieve high range resolution.

R. Strattan

1978-01-01

219

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

220

Spectral estimation for clutter processing in digital radars by Dimension-Adaptive Particle Swarm Optimization (DA-PSO)  

Microsoft Academic Search

Power spectrum estimation from radar data is essential for target detection. For instance, microburst causes detrimental effects on airplane performance, and hence its detection is critical. We compare auto-regression (AR), Periodogram, Kaiser windowed Periodogram, and multiple-signal-classification (MUSIC) methods for microburst clutter spectrum estimation. Given a long train of returned signal, we are able to segment the signal to obtain multiple

Lisa Ann Osadciw; Yanjun Yan

2009-01-01

221

Water slope and discharge in the Amazon River estimated using the shuttle radar topography mission digital elevation model  

Microsoft Academic Search

We find that the standard deviation, hence error, of the water surface elevation data from the Shuttle Radar Topography Mission (SRTM) is 5.51 m for basin-wide, regional and local Amazon mainstem reaches. This error implies a minimum reach length of 733km in order to calculate a reliable water-surface slope. Resulting slopes are 1.92 +\\/- 0.19 cm\\/km for Manacapuru, 2.86 +\\/-

Gina LeFavour; Doug Alsdorf

2005-01-01

222

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

223

Radar principles  

Microsoft Academic Search

The basic operating principles, design, and applications of radars are discussed in an introductory text intended for first-year graduate students. Topics addressed include radar measurements, radar target cross sections, radar detection, ground effects, matched filters, ambiguity functions, coded radar signals, and radar measurement accuracy. Consideration is given to processing coherent pulse trains, moving-target indicators, CFAR, SAR, and monopulse antenna tracking.

Nadav Levanon

1988-01-01

224

Solid state transmitters for modern radar applications  

NASA Astrophysics Data System (ADS)

To exemplify the advancing state-of-the-art in radar SS transmitters, this paper describes in some detail three major systems covering a broad range of frequencies: HF, UHF and L-band, which utilize SS transmitters. At HF a 200 kW CW transmitter is described which is applicable in an over-the-horizon radar application; at UHF the Pave Paws (AN/FPS-115) long-range phased array radar transmitter (over 0.5 megawatt PK power per face) is presented; and finally at L-band an 80 kW pulsed transmitter for shipboard and ATC surveillance applications is described.

Hoft, Donald J.; Agi, Fuat

225

Bandwidth occupancy profile of mid-Atlantic HF band users  

NASA Astrophysics Data System (ADS)

Emerging technologies that use spread spectrum and frequency hopping signals may enable more efficient use of the high-frequency (HF) band. High-powered HF radar is an example of this technology where channels are used that appear to be unoccupied and the frequency hopping signal of the HF radar has been remarkably free from interfering with conventional spectrum occupants. Considering future application of HF systems of this type, it is of interest to examine the availability of free channels in the frequency range between 3 and 30 MHz for bandwidth (BW) availability and time duration. This paper discusses the characteristics of channels that are available for use in the HF spectrum based on spectrum measurements by the Navy's Relocatable Over-the-Horizon Radar (ROTHR) located in the southeast section of Virginia. In particular, the ROTHR data being analyzed are from the spectrum monitor (SM). The SM is a subsystem of the ROTHR which measures the power level in 3-kHz intervals for frequencies between 5 and 28 MHz, the radar's operating frequency range. Measurements of the HF spectrum were analyzed for the fall and winter seasons at the radar's location. The analysis consisted of estimating the number of clear channels of various widths in selected megahertz bands over the ROTHR's operating frequency range. Characteristics of available channels are presented in various graphical forms which include clear channel availability, probability of at least one clear channel of a specified width, and duration of clear channels as a function of frequency. The Weibull distribution is proposed as an analytical model for investigating channel duration. Analysis results indicate which portion of the HF spectrum is most likely to have available bandwidths and what their expected durations are as a function of season and time of day.

McNeal, G. D.

1997-09-01

226

Hf Adaptive Modem Air-to-Ground Test.  

National Technical Information Service (NTIS)

This report presents the accumulation of experimental data, computational processing, and engineering analysis of one-way HF digital data transmitted form an aircraft to a ground station. The aircraft traveled from Riverside, California to Honolulu, Hawai...

P. A. Vena

1967-01-01

227

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

228

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

229

The Hf–Au system  

Microsoft Academic Search

The Hf–Au system has been reinvestigated by means of differential thermal analysis, X-ray diffraction and electron probe microanalysis. The existence of the seven intermetallic phases, previously reported, Hf2Au, HfAu, Hf7Au10, HfAu2, HfAu3, HfAu4 and HfAu5 was confirmed. We specify here their type of formation. For the equiatomic compound, we have shown the presence of a martensitic transformation and of allotropic

M Lomello-Tafin; Ph Galez; P Feschotte; J. L Jorda

2000-01-01

230

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  

NASA Astrophysics Data System (ADS)

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 flight safety. Error models were generated and verified with flight-test data. High-fidelity simulation was used to investigate vertical accuracy improvement. Improvement was found to be 1.2 meters, a reduction of 28.6% in the vertical error. Flight testing was performed to assess the feasibility of enhanced flight safety. Reasons for enhanced flight safety are twofold: (1) the ad-hoc integration of terrain elevation data into the cockpit conceivably may create scenarios which lead to accidents because the cockpit display is quite realistic, and (2) reduction of controlled flight into terrain (CFIT). The radar altimeter is the principle sensor used to compare navigation outputs with publicly available DTED. Results show that it is feasible to define an operationally useful probability of agreement, Pa, among KGPS, DTED and the radar altimeter, by using a mean-square-difference test statistic. This probability of agreement can be used to warn the pilot if the terrain depiction does not agree with the navigation solution provided by KGPS, thus enhancing flight safety.

Gray, Robert Anthony

231

RCS of ships and aircraft at HF frequencies  

NASA Astrophysics Data System (ADS)

Coastal radar operating at high frequency (HF) has the potential of monitoring iceberg movement and ship and aircraft traffic over a wide area of ocean. The HF radar cross-section of an aircraft-like scatterer of simple geometry is investigated. At these frequencies, the aircraft size is comparable to the wavelength. The aircraft radar cross-section (RCS) is obtained both by computation and by direct measurement. It is demonstrated that at low frequencies in the HF range, the dorsal fin is the dominant scatterer, but at high HF the fuselage can scatter more strongly than the dorsal fin. Aircraft often carry wire antennas for HF communication, and it is shown that such wires can dramatically alter the RCS of the aircraft near the resonant frequencies of the wire. The RCS of a ship modelled as a parallelepiped with mast is 20-30 decibels larger than that of an aircraft, and is dominated at low HF by the contribution of the mast.

Trueman, C. W.; Kubina, S. J.; Mishra, S. R.; Larose, C.

232

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

233

Forward modeling of ground-penetrating radar data using digitized outcrop images and multiple scenarios of water saturation  

NASA Astrophysics Data System (ADS)

Simple petrophysical models and a sedimentologically interpreted outcrop photograph corresponding to the plane of a ground-penetrating radar (GPR) survey are combined to create models for the simulation of GPR. This makes possible the comparison of GPR field data, synthetic GPR sections, and a lithology image. On the basis of this comparison the usefulness of the method for identifying hydrologically significant lithofacies and the sensitivity of the results to different subsurface conditions may be investigated. In particular, GPR simulations are performed for an outcrop model at three states of water saturation: uniformly drained (uniform residual saturation), nonuniformly saturated, and fully saturated. As predicted by reflection coefficient calculations, comparison among the synthetic simulations highlights the importance of the existing pore water distribution in determining the "visibility" of lithologic elements in GPR sections. Comparisons of the synthetic GPR sections with the field data show overall agreement, though the occurrence of various observed reflections depends on the presence and distribution of pore water. Conclusions are also drawn about extending outcrop analog-derived results to investigations of real (fully saturated) aquifers.

Kowalsky, M. B.; Dietrich, P.; Teutsch, G.; Rubin, Y.

2001-06-01

234

Bistatic coherent radar receiving system  

NASA Astrophysics Data System (ADS)

A coherent-on-receive MTI radar receiver system for use with cooperative or non-cooperative radar transmitters of either the coherent or noncoherent, simple magnatron type and scanning antennas is discussed. The receiver includes coherent digital signal processing with provision for normalizing or compensating phase variations in the transmitter carrier pulses.

Yamano, L. C.

1984-10-01

235

Bistatic coherent radar receiving system  

Microsoft Academic Search

A coherent-on-receive MTI radar receiver system for use with cooperative or non-cooperative radar transmitters of either the coherent or noncoherent, simple magnatron type and scanning antennas is discussed. The receiver includes coherent digital signal processing with provision for normalizing or compensating phase variations in the transmitter carrier pulses.

L. C. Yamano

1984-01-01

236

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

237

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

238

Radar principles  

NASA Astrophysics Data System (ADS)

The basic operating principles, design, and applications of radars are discussed in an introductory text intended for first-year graduate students. Topics addressed include radar measurements, radar target cross sections, radar detection, ground effects, matched filters, ambiguity functions, coded radar signals, and radar measurement accuracy. Consideration is given to processing coherent pulse trains, moving-target indicators, CFAR, SAR, and monopulse antenna tracking. Extensive diagrams and graphs are provided.

Levanon, Nadav

239

Impact of extremely high speed logic technology on radar performance  

Microsoft Academic Search

Limitations related to the utilization of digital procedures in radar systems are connected with the difference between the throughput rates of the digital devices and the required throughput rate for broadband, multiple-range-gated radar signals. The present investigation is concerned with the feasibility of innovative uses of extremely high speed integrated circuits in radar. The probable technologies for high speed electronics

E. K. Reedy; R. B. Efurd; M. N. Yoder

1982-01-01

240

Multifrequency Doppler Radar Observations of Electron Gyroharmonic Effects during Electromagnetic Pumping of the Ionosphere  

Microsoft Academic Search

Experimental results of multifrequency HF Doppler radar studies during electromagnetic pumping of the ionosphere from the ground are reported. The Doppler shifts of the radar waves after turn-on of the vertically injected HF pump wave depend on the pump frequency and exhibit, at relatively large reflection altitudes, opposite signs for pump frequencies above or below an electron gyroharmonic. The results

S. Grach; G. Komrakov; M. Yurishchev; B. Thide; T. Leyser; T. Carozzi

1997-01-01

241

An overview of high-latitude hf induced aurora from EISCAT  

NASA Astrophysics Data System (ADS)

The EISCAT HF facility is capable of transmitting over 200 MW into the ionosphere below 5.423 MHz using the low-gain antenna array. Over 1000 MW above 5.423 MHz is available using the high-gain antenna array. During O-mode pumping in the hours after sunset, F-region electrons can be accelerated sufficiently to excite the oxygen atoms and nitrogen molecules, resulting in observable optical emissions at 844.6 (O), 630 (O1D), 557.7 (O1S) and 427.8 (N2) nm above EISCAT. Initial success came in February 1999 with optical recordings by ALIS (Auroral Large Imaging System) from various Swedish locations south of EISCAT and DASI (Digital All-Sky Imager) from Skibotn, Norway, 50 km south-east of EISCAT. Several observations have features unique to high latitudes. Novel discoveries include: (1) Very large electron temperature enhancements of a few 1000 K, which maximise along the magnetic field line direction (2) Ion temperature enhancements of a few 100 K accompanied by large ion outflows, (3) The optical emission usually appears near the magnetic field line direction regardless of the HF transmitter beam pointing direction, (4) The optical emission appears below the HF pump reflection altitude as well as the upper-hybrid resonance height, (5) The optical emission and HF coherent radar backscatter disappears when pumping on the 3rd, 4th or 5th gyro-harmonic frequency, (6) The first artificial optical observations at 844.6 (O) and 427.8 (N2) nm and (7) Annular optical structures, which subsequently collapse into blobs.

Kosch, M.; Gustavsson, B.; Rietveld, M.

242

Quantifying the Differences in Low Probability of Intercept Radar Waveforms Using Quadrature Mirror Filtering.  

National Technical Information Service (NTIS)

Low Probability of Intercept (LPI) radars are a class of radar systems that possess certain performance characteristics causing them to be nearly undetectable by most modern digital intercept receivers, Consequently, LPI radar systems can operate undetect...

P. Jarpa

2002-01-01

243

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

244

Crop Classification with a Landsat\\/Radar Sensor Combination  

Microsoft Academic Search

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

Robert Y. Li; Fawwaz T. Ulaby; Ronald J. Eyton

1980-01-01

245

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

246

Superconductor Digital Electronics: -- Current Status, Future Prospects  

NASA Astrophysics Data System (ADS)

Two major applications of superconductor electronics: communications and supercomputing will be presented. These areas hold a significant promise of a large impact on electronics state-of-the-art for the defense and commercial markets stemming from the fundamental advantages of superconductivity: simultaneous high speed and low power, lossless interconnect, natural quantization, and high sensitivity. The availability of relatively small cryocoolers lowered the foremost market barrier for cryogenically-cooled superconductor electronic systems. These fundamental advantages enabled a novel Digital-RF architecture - a disruptive technological approach changing wireless communications, radar, and surveillance system architectures dramatically. Practical results were achieved for Digital-RF systems in which wide-band, multi-band radio frequency signals are directly digitized and digital domain is expanded throughout the entire system. Digital-RF systems combine digital and mixed signal integrated circuits based on Rapid Single Flux Quantum (RSFQ) technology, superconductor analog filter circuits, and semiconductor post-processing circuits. The demonstrated cryocooled Digital-RF systems are the world's first and fastest directly digitizing receivers operating with live satellite signals, enabling multi-net data links, and performing signal acquisition from HF to L-band with 30 GHz clock frequencies. In supercomputing, superconductivity leads to the highest energy efficiencies per operation. Superconductor technology based on manipulation and ballistic transfer of magnetic flux quanta provides a superior low-power alternative to CMOS and other charge-transfer based device technologies. The fundamental energy consumption in SFQ circuits defined by flux quanta energy 2x10-19 J. Recently, a novel energy-efficient zero-static-power SFQ technology, eSFQ/ERSFQ was invented, which retains all advantages of standard RSFQ circuits: high-speed, dc power, internal memory. The voltage bias regulation, determined by SFQ clock, enables the zero-power at zero-activity regimes, indispensable for sensor and quantum bit readout.

Mukhanov, Oleg

2011-03-01

247

Monitoring the F-region peak electron density using HF backscatter interferometry  

NASA Astrophysics Data System (ADS)

High frequency (HF, 10-20 MHz) radars routinely utilize Bragg scatter from plasma fluctuations to monitor ionospheric turbulence. While the propagation of the probing HF radio waves is also strongly affected by the regular structure of the ionosphere, this information is rarely extracted from the data. In the present work we present and test a new technique for estimating the F-region peak electron densities, NmF2, using information about the vertical refraction of HF backscatter echoes that is readily available in the Super Dual Auroral Radar Network (SuperDARN) data set.

Ponomarenko, P. V.; Koustov, A. V.; St.-Maurice, J.-P.; Wiid, J.

2011-11-01

248

24 GHz radar front-end for FMCW and spread spectrum radar applications  

Microsoft Academic Search

Two configurations of radar front-end with a multi-chip assembly for automotive applications have been studied and presented. One configuration is suitable for both FMCW radar and spread spectrum radar with the replacement of a base-band module that could be realized by a digital synthesizer; the concept \\

Zhaolong Li; Ke Wu

2006-01-01

249

HF Wideband Modem.  

National Technical Information Service (NTIS)

This was an engineering effort to design, simulate, implement and test two HF modems capable of sustaining data rates of 4800 b/s or greater over standard 3 KHz HF channels. The first twelve months of effort encompassed propagation analysis, modulation wa...

V. Ellins P. H. Anderson M. N. Sandler

1982-01-01

250

A comparison of velocity measurements from the CUTLASS Finland radar and the EISCAT UHF system  

Microsoft Academic Search

The CUTLASS Finland radar, which com- prises an integral part of the SuperDARN system of HF coherent radars, provides near continuous observations of high-latitude plasma irregularities within a field-of- view which extends over some four million square kilometres. Within the Finland radar field-of-view lie both the EISCAT mainland and EISCAT Svalbard incoherent scatter radar facilities. Since the CUTLASS Finland radar

J. A. Davies; M. Lester; S. E. Milan; T. K. Yeoman

1999-01-01

251

HF pump-induced E-region irregularities: is there a gyro-harmonic frequency dependence ?  

NASA Astrophysics Data System (ADS)

E-region irregularities of 1-m scale length can be produced by high power O-mode HF transmissions, as shown by observations using the STARE (Scandinavian Twin Auroral Radar Experiment) 140 MHz coherent radars. The current understanding of the generation of these density irregularities by HF-heating lies within the frame-work of excitation of the thermal resonance instability at the upper hybrid level, like the irregularities generated in F region. In the F region the production of such decameter-scale irregularities shows a minimum when the HF pump frequency is close to a harmonic of the electron gyro-frequency. The natural question arises whether this is also true for the meter-scale irregularities in the E region. To answer this, HF-pumping experiments have been performed while monitoring the backscatter intensity from the Malvik (Norway) radar in near real-time. Results from these experiments will be presented.

Rietveld, M. T.; Nielsen, E.; Bruns, M.; Schmidt, W.

252

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

253

Radar frequency radiation  

NASA Astrophysics Data System (ADS)

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

Malowicki, E.

1981-11-01

254

Simultaneous measurements of HF-enhanced plasma waves and artificial field-aligned irregularities at Arecibo  

SciTech Connect

Two radar systems with beams intersecting in the HF-modified F region were used to simultaneously measure HF-enhanced plasma lines (HFPLs) and artificial geomagnetic field-aligned irregularities (AFAIs). The Arecibo 430-MHz radar was used for the HFPL observations, and a portable 49.92-MHz backscatter radar was deployed on the island of Guadeloupe to monitor the AFAIs. The experiment was desgined to examine the degree to which HF-induced plasma turbulence influences the development of AFAIs. When the HF beam is stepped up in power, sustained HFPLs and AFAIs are first observed at the same HF power level, indicating that ponderomotively driven instabilities may be involved in the early time development of AFAIs. As the HF power is increased, the HFPL backscatter power begins to saturate at {approximately}70 MW effective radiated power (ERP). However, the backscatter from AFAIs is linearly dependent on HF power, even at the highest (120 MW ERP) HF power levels available at Arecibo. This suggests that additional processes may contribute to the development of AFAIs. For example, ponderomotively driven instabilities may give rise to weak geomagnetic field-aligned irregularities that are subsequently driven unstable by processes excited near the upper hybrid resonance. It is also likely that AFAIs greatly impact the development of HF-induced plasma turbulence at late times (>1 s) following HF turn-on. Once the ionosphere is preconditioned by high-power HF modifications, AFAIs and HFPLs can be simultaneously sustained at a much lower HF power level than that needed to originally excite them. The nature of the preconditioning process is currently not well understood. New theoretical initiatives are clearly needed to guide future experimental activity in this area.

Noble, S.T. (Rice Univ., Houston, TX (USA)); Djuth, F.T. (Aerospace Corp., Los Angeles, CA (USA))

1990-09-01

255

Improved techniques for monitoring the HF spectrum  

NASA Astrophysics Data System (ADS)

A critical review of contemporary papers on modulation recognition, signal separation, and Single Station Location (SSL) is described in the context of High-Frequency (HF) radio-communications. High-frequency communications is undergoing resurgence despite advances in long-range satellite communication systems. Defense agencies are using the HF spectrum for backup communications as well as for spectrum surveillance applications. Spectrum management organizations are monitoring the HF spectrum to control and enforce licensing. This type of activity usually requires a system that is able to determine the location of a source of transmissions, separate valid signals from interferers and noise, and characterize signals-of-interest (SOI). The immediate aim is to show that commercial-off-the-shelf (COTS) equipment can be used to locate HF transmission sources, enhance SOIs and reject interference, and recognize signal types. The described work on single-station-location (SSL), signal separation, and modulation recognition is contributing to these goals. This paper describes the overall objectives and some of the disadvantages and benefits of various schemes for single-station-location (SSL), signal separation, and modulation recognition. It also proposes new approaches that may relieve shortcomings of existing methods -- including selection of benchmarks or modulations for various transmission scenarios and propagation modes, and use of multiple digital receivers or compression techniques to improve modulation recognition, signal separation, and location of HF emitters.

Giesbrecht, James E.; Clarke, Russell; Abbott, Derek

2004-03-01

256

Hf Adaptive Modem Test.  

National Technical Information Service (NTIS)

This report presents an accumulation of experimental data from which was determined the relative performance of several modem modes for various HF channel conditions. In addition to these results, thresholds are defined for each channel condition which sp...

P. A. Vena

1967-01-01

257

HF modulated ionospheric currents  

NASA Astrophysics Data System (ADS)

The HAARP HF facility is used to modulate the components of the auroral electrojet that flow in the D-region of the ionosphere, creating ELF/VLF radiation which is then measured at a receiver co-located with the HAARP HF antenna. An HF heating model is coupled to a full wave plasma interaction FDTD code to determine the ELF/VLF response of the ionospheric plasma to the modulated HF stimulation. The predicted FDTD fields on the ground are found to be in remarkable agreement with those measured at a receiver co-located with HAARP. The FDTD code also predicts an upwardly propagating whistler mode that is tightly bound to the magnetic field lines.

Payne, J. A.; Inan, U. S.; Foust, F. R.; Chevalier, T. W.; Bell, T. F.

2007-12-01

258

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.

0002-11-30

259

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

260

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

261

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

262

Wireless Networks for Beamforming in Distributed Phased Array Radar.  

National Technical Information Service (NTIS)

The Wirelessly Networked Aperstructure Digital Phased Array Radar (WNADPAR) applies three relatively new concepts: Opportunistic, Aperstructure, and Wirelessly Networked Digital Architecture concepts. Using this approach almost the full length of the ship...

J. S. Noris

2007-01-01

263

Velocity Compensation in Stepped Frequency Radar.  

National Technical Information Service (NTIS)

As compared to the commonly used constant frequency radar waveforms, the stepped-frequency waveform can achieve high range resolution while still retaining the advantages of lower instantaneous receiver bandwidth and lower analog-to-digital sampling rate....

Y. B. Ma

1995-01-01

264

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

265

Transmitter Noise Cancellation in Monostatic FMCW Radar  

Microsoft Academic Search

Digital leakage cancellation realizes noise cancellation at RF frequency, in addition to suppress leakage signal in FMCW monostatic radar. Noise cancellation mechanism is analyzed with autocorrelation function of noise. The measurement results in Ka band radar test are provided and show the effectiveness

Kaihui LinandYuanxun; Yuanxun Ethan Wang

2006-01-01

266

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

267

Satellite radar interferometry - Two-dimensional phase unwrapping  

Microsoft Academic Search

Interferometric synthetic aperture radar observations provide a means for obtaining high-resolution digital topographic maps from measurements of amplitude and phase of two complex radar images. The phase of the radar echoes may only be measured modulo 2 pi; however, the whole phase at each point in the image is needed to obtain elevations. An approach to 'unwrapping' the 2 pi

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

1988-01-01

268

The ambiguity function of the step frequency radar signal processor  

Microsoft Academic Search

In step frequency radar, the frequency of each pulse is increased in steps to achieve large effective bandwidth sequentially instead of instantaneously and thus easing the requirements on the analog to digital converter (ADC) and other hardware. This paper discusses the step frequency radar and its associated signal processing, and it investigates this type of radar with the ambiguity function.

G. S. Gill; Jen-Chih Huang

1996-01-01

269

Radar - Principles, technology, applications  

NASA Astrophysics Data System (ADS)

An overview of modern radar is presented. The topics addressed include: functions and parameters of the radar system, the radar equation, targets and interfering signals, target echo information extraction, tracking radar, radar transmitters and microwave components, radar antennas, receivers and displays, radar signal processing, high resolution radar.

Edde, Byron

270

Radar observables  

NASA Astrophysics Data System (ADS)

A comprehensive account is given of missile design considerations relevant to the prediction, control, and measurement of airframe radar cross sections (RCSs), with a view to the minimization of missile observability. RCS reduction may proceed through airframe shaping to deflect incident radar emissions, as well as through the use of radar-absorbing surface materials and the devision of active radar signal-cancellation methods; some combination of these is often required, due to the deficiencies of any one method. The interaction of all RCS-reduction methods with airframe aerodynamic-design criteria are stressed.

Knott, Eugene F.

271

OFDM LDPC performance comparison on an HF multipath fading channel  

NASA Astrophysics Data System (ADS)

High Frequency (HF) radio communication channels provide unique challenges to digital communication systems. Typical HF communication systems propagate electromagnetic energy in the 2-30MHz radio spectrum using the earth's ionosphere and surface as both refractors and reflectors for non line of sight communications. Constantly changing ionosphere conditions result in multipath and severe fading channel characteristics. Through numerical simulation, short block length block length (9e+3) Low Density Parity Check (LDPC) forward error correction codes used in conjunction with Orthogonal Frequency Division Multiplexing (OFDM) will be shown to provide excellent communication performance across the HF channel. Average bit error rate performance results will be shown for a 2ms, 1Hz and 2Hz Watterson HF channel model for both regular and irregular LDPC parity check matrices. Some results will also be shown for imperfect channel estimation and its effects upon the performance of the LDPC decoder.

Kellerman, Fred C.

2008-05-01

272

Radar Astronomy.  

National Technical Information Service (NTIS)

A general review of radar astronomy is given. Typical radar systems are described and results cited. Methods of determining elements of orbits and rotation rates of planets are discussed. A proposed test of the Einstein theory of general relativity is des...

G. H. Pettengill I. I. Shapiro

1965-01-01

273

Radar astronomy  

Microsoft Academic Search

Radar Astronomy is a new and growing branch of Astronomy. Although it seems that radio echo studies must be confined to the solar system, they can play an important part in developing our understanding of the Sun and the planets. At the present time these objects are barely detectable by radar techniques and much of the work has been concerned

J. V. Evans

1960-01-01

274

HF-Pump-induced parametric instabilities in the auroral E-region  

Microsoft Academic Search

In November 1999 the EISCAT high-power, high-frequency (HF) facility located near Tromsø, Norway, was used to create artificial plasma turbulence in the ionosphere. During the experiment the EISCAT 224 MHz radar and sometimes the 931 MHz radar were used to obtain measurements of incoherent scatter ion and plasma lines, and artificially enhanced spectra of E-region plasma waves were measured for

M. T. Rietveld; B. Isham; T. Grydeland; C. La Hoz; T. B. Leyser; F. Honary; H. Ueda; M. Kosch; T. Hagfors

2002-01-01

275

Use of the Hualien, Taiwan, dynasonde for surveillance of HF environmental radio and positioning of transmitting stations  

NASA Astrophysics Data System (ADS)

Since 2010, a 2nd generation NOAA HF radars, also referred as dynasonde, has been built at Hualien (23.89 N, 121.55 E), Taiwan. The Hualien dynasonde has a new design of ionospheric radar of fully digitizing the complex signal records and using multiple parallel receiver channels for simultaneous measurements of signals from multiple spaced receiving antennas. The Hualien dynasonde utilizes interferometric sounding pulse patterns and a receiving antenna array (including eight receivers connected to different spaced dipole antennas) to receive not only ionospherical echoes but also environmental radio signals. We have applied the Hermite normal form method to solve the phase-measurement aliasing and least squares problem and improve measurements of radio angles of arrival (AOA). The further ray-tracing experiments can be used for the study of radio wave propagation in the ionosphere. In this study we present a numerical and step by step ray-tracing method on a phenomenological ionospheric electron density model, the TaiWan Ionospheric Model (TWIM), which is constructed from the FormoSat3 / Constellation Observing System for Meteorology, Ionosphere and Climate (FS3/COSMIC) ionospheric radio occultation data and global ionosonde foF2 data. The three-dimensional TWIM consists of vertically-fitted ?-Chapman-type layers, with distinct F2, F1, E, and D layers, for which the layer parameters such as peak density, peak density height, and scale height are represented by surface spherical harmonics. This way the continuity of Ne and its derivatives is maintained. The methodology is successfully applied to a practical HF transmitter for oblique incidence ray tracing. Then, the AOA data will be used for backward ray tracing in the TWIM model and be used to determine ground-based transmitting station position.

Tsai, L.-C.; Chen, G. H.; Tian, M. H.; Zhang, Y.

2012-04-01

276

Synthesis and structural investigation of the compounds containing HF anions: Ca(HF), BaF(HF)(PF) and PbF(HF)(PF)  

Microsoft Academic Search

Three new compounds Ca(HF), BaF(HF)(PF) and PbF(HF)(PF) were obtained in the system metal(II) fluoride and anhydrous HF (aHF) acidified with excessive PF. The obtained polymeric solids are slightly soluble in aHF and they crystallize out of their aHF solutions. Ca(HF) was prepared by simply dissolving CaF in a neutral aHF. It represents the second known compound with homoleptic HF environment

Tina Bunic; Melita Tramsek; Evgeny Goreshnik; Boris Zemva

2008-01-01

277

Analysis of Low Probability of Intercept (LPI) Radar Signals Using Cyclostationary Processing.  

National Technical Information Service (NTIS)

LPI radar is a class of radar systems that possess certain performance characteristics that make them nearly undetectable by today's digital intercept receivers, This presents a significant tactical problem in the battle space To detect these types of rad...

A. F. Lime

2002-01-01

278

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

NASA Astrophysics Data System (ADS)

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

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

279

A MIMO FMCW radar approach to HFSWR  

NASA Astrophysics Data System (ADS)

In this paper we propose one possible approach how to apply the concept of multiple-input multiple-output (MIMO) to monostatic Frequency Modulated Continuous Wave (FMCW) High-Frequency Surface Wave Radar (HFSWR) in a maritime environment. Common tasks for a HFSWR are sea-state monitoring and ship detection, where our focus is on ship detection. A limiting factor in HFSWR is the available bandwidth, which is inversely proportional to the range resolution capability of the radar and typical below 100 kHz. The question is how to extend or combine a conventional single-input multiple-output (SIMO) FMCW phased-array type radar with stretch processing and the colocated MIMO concept to "reuse" the very limited HF radar band resources. Another important question to answer is how MIMO FMCW waveforms can be separated at the receiver.

Hinz, J. O.; Zölzer, U.

2011-07-01

280

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

281

FPGA implementation of a software-defined radar processor  

NASA Astrophysics Data System (ADS)

A unified digital pulse compression processor is introduced as a radar-application-specific-processor (RASP) architecture for the next generation of adaptive radar. Based on traditional pulse compression matched filter and correlation receiver, the processor integrates specific designs to handle waveform diversities, which includes random noise waveforms, as well as digital transceiver self-reconfiguration for adaptive radars. Initial prototype of this processor is implemented with the latest Xilinx FPGA device and tested with an RF spaceborne radar transceiver testbed. Initial validation results show the effectiveness of real-time processing and engineering concepts.

Suarez, Hernan; Zhang, Yan Rockee

2013-05-01

282

Over-the-Horizon Radar Multipath and Multisensor Track Fusion Algorithm Development.  

National Technical Information Service (NTIS)

Over-the horizon radar (OTHR) and microwave radar networks can together generate track data over a wide surveillance region. However the data is often subject to ambiguity and uncertainty due to the complexities of the HF signal propagation environment, w...

P. W. Sarunic K. A. White M. G. Rutten

2001-01-01

283

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

NASA Astrophysics Data System (ADS)

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 backscatter are: SLT spectra including the outshifted plasma line or free-mode, appearance of a short timescale ponderomotive overshoot effect, collapse, cascade and co-existing spectra, control of artificial field-aligned irregularities (AFAI), the aspect angle dependence of the plasma line spectra, and suprathermal electrons. Mapping the intensity of SLT versus pointing angle, we have discovered a number of regions of strong interaction displaced from the primary HF interaction region. Stimulated electromagnetic emission (SEE) measurements complement radar measurements. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.

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

2010-11-01

284

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

285

Generating nonlinear FM chirp radar signals by multiple integrations  

DOEpatents

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) [Albuquerque, NM

2011-02-01

286

Low power High Frequency Surface Wave Radar application for ship detection and tracking  

Microsoft Academic Search

High-frequency (HF) radars are operated in the 3-30 MHz frequency band and are known to cover ranges up to some thousand kilometers. Sky wave over-the-horizon radars (OTHR) utilize reflection by the ionosphere, but they require a transmit power up to 100 kilowatts. Especially for oceanographic applications, low power high frequency surface wave radar (HFSWR) systems have been developed, which use

Anna Dzvonkovskaya; Klaus-Werner Gurgel; Hermann Rohling; Thomas Schlick

2008-01-01

287

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

288

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

289

Model for artificial ionospheric duct formation due to HF heating  

NASA Astrophysics Data System (ADS)

Strong electron heating by the injection of highly powerful HF waves can lead to the formation of ionospheric plasma density perturbations that stretch along the magnetic field lines. Those density perturbations can serve as ducts for guiding natural and artificial ELF/VLF waves. This paper presents a theoretical model of duct formation due to HF heating of the ionosphere. The model is based on the modified SAMI2 code, and is validated by comparison with two well documented experiments. One experiment, conducted at the SURA heating facility, used the low orbit satellite DEMETER as a diagnostic tool to measure the electron and ion temperature and density along the overflying satellite orbit close to the magnetic zenith of the HF-heater. The second experiment, conducted at the EISCAT HF facility and diagnosed by the EISCAT Incoherent Scatter Radar, measured the vertical profiles of the electron and ion temperature between 150-600 km. The model agrees well with the observations, and provides a new understanding of the processes during ionospheric modification.

Milikh, G. M.; Demekhov, A. G.; Papadopoulos, K.; Vartanyan, A.; Huba, J. D.; Joyce, G.

2010-04-01

290

Acoustic Radar Employing Particle Velocity Sensors  

Microsoft Academic Search

\\u000a A concept, practical realization and applications of a passive acoustic radar for automatic localization and tracking of sound\\u000a sources were presented in the paper. The device consists of the new kind of multichannel miniature sound intensity sensors\\u000a and a group of digital signal processing algorithms. Contrary to active radars, it does not emit a scanning beam but after\\u000a receiving surroundings

Józef Kotus; Andrzej Czy?ewski

291

Aspect angle dependency of the HF modification measured with MUIR at HAARP  

NASA Astrophysics Data System (ADS)

In this paper we present results of height-resolved observations of F-region Langmuir turbulence measured with MUIR (Modular UHF Ionospheric Radar; 446 MHz) at HAARP (High frequency Active Auroral Research Program) in Alaska, USA. The scientific objective of this paper is to study aspect angle dependency of the HF modification. The best way to achieve the objective is the simultaneous multi-position measurement with the incoherent- scatter (IS) radar. However, general IS radars take, at least, a few seconds to change the radar beam position. MUIR is the best diagnostic tool for this study because it can change the beam direction every IPP (interpulse period) with the phased array system. We conducted two experiments at HAARP; 26 March 2006 and 31 July 2007. For the March 2006 experiment, three MUIR beam positions were selected: geographical vertical, up B (elevation angle = 75 degree), and midway between the two (elevation angle = 82 degree). This experiment was arranged for studying the aspect angle dependency of Langmuir oscillations associated with low HF duty cycle (1%: on/off = 0.1s / 9.9s). The radar-backscatter spectra with 10-ms time resolution were deduced at individual radar-beam positions. For the July 2007 experiment, nine MUIR beam positions around the up B position were selected under relatively high HF duty cycle (50%: on/off = 3min/3min). The presentation will report aspect angle dependencies of (1) the Langmuir oscillation development in the first 100 ms after HF turn-on using data taken during the March 2006 experiment and (2) persistency of the Langmuir oscillation using data taken during the August 2007 experiment.

Oyama, S.; Watkins, B. J.

2007-12-01

292

Performance assessment of HF-radar ship detection  

Microsoft Academic Search

Recently, significant efforts have gone into developing more reliable Integrated Mar- itime Surveillance (IMS) systems. The main purpose of these systems is to detect and track, and identify and classify cooperative and non-cooperative targets crossing maritime national bound- aries. In such a context, each kind of sensor (i.e. shipborne or airborne, on-shore or off-shore) has its own tasks. Great attention

Salvatore Maresca; Jochen Horstmann; Raffaele Grasso; Matthew Coffin; Klaus-Werner Gurgel; Thomas Schlick

2011-01-01

293

HF radar based current observation system in the German Bight  

Microsoft Academic Search

In the South-Eastern part of the North Sea, known as the German Bight, the Helmholz-Zentrum Geesthacht (HZG, former GKSS Research Center) is currently realizing the experimental observation Network COSYNA for: Coastal Observing System for Northern and Arctic Seas. The observation area underlies extensive industrial use like oil and gas production, wind farming, transportation of all kind of goods, fishery, tourism

Jorg Seemann; Friedwart Ziemer; Marius Cysewski; Stylianos Flampouris; Klaus-Werner Gurgel; Thomas Schlick

2011-01-01

294

Survey of Digital Beam Forming Techniques and Current Technology.  

National Technical Information Service (NTIS)

Digital beamforming provides key advantages over analog beamforming in radar applications where proper response to multiple jammers in a rapidly changing environment is required. Ths survey reviews these advantages and various digital methods for attainin...

J. E. McCord

1988-01-01

295

Assessing 4D-VAR for dynamical mapping of coastal high-frequency radar in San Diego  

Microsoft Academic Search

The problem of dynamically mapping high-frequency (HF) radar radial velocity observations is investigated using a three-dimensional hydrodynamic model of the San Diego coastal region and an adjoint-based assimilation method. The HF radar provides near-real-time radial velocities from three sites covering the region offshore of San Diego Bay. The hydrodynamical model is the Massachusetts Institute of Technology general circulation model (MITgcm)

I. Hoteit; B. Cornuelle; S. Y. Kim; G. Forget; A. Köhl; E. Terrill

2009-01-01

296

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

297

The Shuttle Radar Topography Mission  

NASA Technical Reports Server (NTRS)

On February 22, 2000 Space Shuttle Endeavour landed at Kennedy Space Center, completing the highly successful 11-day flight of the Shuttle Radar Topography Mission (SRTM). Onboard were over 300 high-density tapes containing data for the highest resolution, most complete digital topographic map of Earth ever made. SRTM is a cooperative project between NASA and the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense. The mission was designed to use a single-pass radar interferometer to produce a digital elevation model (DEM) of the Earth's land surface between about 60 deg north and 56 deg south latitude. When completed, the DEM will have 30 m pixel spacing and about 15 m vertical accuracy. Two orthorectified image mosaics (one from the ascending passes with illumination from the southeast and one from descending passes with illumination from the southwest) will also be produced.

Farr, Tom G.; Kobrick, Mike

2000-01-01

298

Highly Integrated Radar Sensor-on-Chip  

NASA Astrophysics Data System (ADS)

A highly integrated 24 GHz radar sensor is presented, based on a Radio Frequency Integrated Circuit (RFIC) which was specifically developed for a Frequency Modulated Shift Keying (FMSK) based Radar system design. Antenna, waveform, the Radio Frequency (RF) and Digital Signal Processor (DSP) module, the software design, cost and performance aspects will be described. The significant technical and economical advantages of the implemented Silicon-Germanium (SiGe) Bipolar CMOS (BiCMOS) transceiver are demonstrated. Some automotive and other applications based on this technology and new radar system design will be explained.

Mende, Ralph

2012-05-01

299

Ice sheet studies using synthetic aperture radar  

NASA Technical Reports Server (NTRS)

The objective was to demonstrate the utility of synthetic aperture radar in ice sheet studies. The major advantage of SAR imagery over visible imagery is the all-weather capability of radar and the ability to specify look angle. Available digital SAR imagery over ice sheets was collected and examined both qualitatively and quantitatively using corroborative data, such as LANDSAT imagery, to confirm feature identification and interpretations. A simple scattering model will be developed to assess the relative importance of surface topography, composition, and subsurface layering to the intensity of radar backscatter. Recommendations of system parameters will be made for optimal SAR operation over ice sheets.

Bindschadler, R.

1988-01-01

300

Radar target signature program performance specification  

NASA Astrophysics Data System (ADS)

This report is a Program Performance Specification (PPS) for a digital computer program that calculates the radar signatures of ships. The PPS will be used to guide the program through three development phases and acceptance testing. The primary objectives of the program are accuracy, flexibility of application, ease of modeling, and portability. The ship is modeled by identifying and defining all the geometrical shapes which cause radar scattering and coherently adding the signals from all the appropriate ones. The program will handle far-field, near-field, and bistatic geometries, antenna patterns, radar absorbing material, and high range resolution effects.

Toothman, H. L.

1981-06-01

301

Analysis of synthetic aperture radar imagery  

NASA Technical Reports Server (NTRS)

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

Blanchard, B. J. (principal investigator)

1976-01-01

302

Radar Antenna.  

National Technical Information Service (NTIS)

An antenna is described for range-gated, pulse doppler, radar systems. The antenna includes first and second, shortened, half-wave dipoles and first and second reflecting screens. One dipole is fed through a fixed 22 1/2 degree phase-shift network while t...

O. E. Rittenback

1978-01-01

303

Radar Roadmap.  

National Technical Information Service (NTIS)

Instrumentation radar has played a very significant role in testing and training for more than 50 years. Along with optics, it has been a major supplier of time space position information (TSPI). With the advent of the Global Positioning System (GPS), the...

1998-01-01

304

Radar nomenclature  

Microsoft Academic Search

Like much of the equipment used by the armed forces, both civil and military radar systems may be allocated an identification resolved from a synonym, mnemonic, project name, number, application notation, or specialised nomenclature and sometimes may even be based upon the whims of an intelligence reporting service. Of these, mnemonics are very popular; whilst of designation systems used by

J. C. Wise

2004-01-01

305

FPGA based Ultra-Wideband pseudo-noise radar  

Microsoft Academic Search

A high accuracy experimental platform for Ultra Wide Band (UWB) PN radar performance evaluation has been created. This PN radar platform could be used for the applications such as unmanned- aerial-vehicle anti-collision and short-range distance measurement etc (3). It includes compact size X-band radar transceiver, baseband signal processing in FPGA, high speed analog to digital converter (ADC), and Matlab tools.

Amutha Jayakumar; Asha Durafe

2011-01-01

306

The development of DBF phased array radar system  

Microsoft Academic Search

This paper presents the basic concept and implementation of an 8 element DBF (digital beamforming) phased array radar. The real transmitting patterns with various frequencies, weights and nullings are shown. The receiving pattern is also given

Wang Yan; Wu Manqing; Jin Xueming; Lu Jiaguo

2001-01-01

307

Combined Linear and Nonlinear Radar: Waveform Generation and Capture.  

National Technical Information Service (NTIS)

A combined-radar transceiver is constructed which enables target ranging in both linear and nonlinear (harmonic) receive modes. The transceiver is constructed using an arbitrary waveform generator as the signal source, a high-speed digitizing oscilloscope...

G. J. Mazzaro K. D. Sherbondy

2013-01-01

308

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 ...

309

Scalable overtone HF chemical laser  

SciTech Connect

A method of producing essentially coherent electromagnetic emissions with high efficiency from excited HF molecules at overtone frequencies is described comprising the steps of: thermally dissociating a molecular gas containing fluorine to produce F atoms; reacting the F atoms with a gas containing hydrogen to produce excited HF molecules; preferentially depleting ..delta..v=2 overtone vibrational transitions of the excited HF molecules to produce the electromagnetic emissions at overtone frequencies such that the electromagnetic emissions from the ..delta..v=2 overtone vibrational transitions have an output power which is a significant percentage of the output power obtainable from ..delta..v=1 fundamental vibrational transitions of excited HF molecules so that the electromagnetic emissions produced by the ..delta..v=2 overtone vibrational transitions can be efficiently scaled to high output powers.

Jeffers, W.O.

1988-07-26

310

Detection and diagnosis of radar modeling errors using covariance consistency  

Microsoft Academic Search

Often, detection-based tracking algorithms are developed without much regard for the effects of either the radar's analog signal processing or its digital signal-processing algorithms. In this paper, we combine the effects of the radar's signal processing and tracking algorithms to assess the combined effect on covariance consistency of various algorithms. To do this, we first define the terms detection, detection

Andy H. Register; Mahendra Mallik; W. Dale Blair; Chris Burton; Paul Burns

2009-01-01

311

vsb-RADAR - A 35 GHz Doppler Radar For Velocity Distance And Acceleration Measurements On Railbound Vehicles  

Microsoft Academic Search

Certain problems associated with conventional vehicular speed sensing such as wheel slip or wheel lock can be avoided by employing a microwave sensing technique. A 35 GHz doppler-radar has been developed to measure velocity, distance and acceleration of railbound vehicles. This radar, the vsb-RADAR, employs a Gunn-Device, a wave-guide slot antenna and a digital signal processor to provide the measuring

Bertram Keller; Holger Meinel; Bernhard Rembold

1978-01-01

312

Half life of 175Hf.  

PubMed

This work measured the half life of radioisotope (175)Hf, which was produced by neutron activation method at the ZF-300-II Intense Neutron Generator in Lanzhou University. The half life of (175)Hf, measured by ?-ray spectrometry using a well calibrated GEM-60P coaxial High Purity Germanium (HPGe) detector, has been found to be 70.65±0.19 days. The present result agrees with the literature data well, while the accuracy was improved. PMID:22871434

Fang, Kaihong; Wang, Dawei; Yang, Shaobo; Zhao, Jiangtao; Peng, Haibo; Wang, Qiang; Wang, Tieshan

2012-10-01

313

Equatorial radar system  

Microsoft Academic Search

A large clear air radar with the sensitivity of an incoherent scatter radar for observing the whole equatorial atmosphere up to 1000 km altitude is now being designed in Japan. The radar, called the Equatorial Radar, will be built in Pontianak, Kalimantan Island, Indonesia (0.03 N, 109.3 E). The system is a 47 MHz monostatic Doppler radar with an active

S. Rukao; T. Tsuda; T. Sato; S. Kato

1989-01-01

314

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

315

ANDVT MINTERM [digital radiocommunication  

Microsoft Academic Search

The ANDVT MINTERM (advanced narrowband digital voice manpack terminal) provides secure half-duplex voice, data, and remote keying capabilities for transmission over HF, UHF, VHF, and wireline facilities. These features are provided in a small, low-power, lightweight, rugged package. The MINTERM secure voice utilizes the LPC 10 (linear prediction coding) vocoder to compress the sampled voice signal to 2400 bit\\/s. The

D. M. Caprioni; P. A. Muscianesi

1991-01-01

316

Modulation recognition for HF signals  

NASA Astrophysics Data System (ADS)

High-frequency (HF) communications is undergoing resurgence despite advances in long-range satellite communication systems. Defense agencies are using the HF spectrum for backup communications as well as for spectrum surveillance applications. Spectrum management organizations are monitoring the HF spectrum to control and enforce licensing. These activities usually require systems capable of determining the location of a source of transmissions, separating valid signals from interference and noise, and recognizing signal modulation. Our ultimate aim is to develop robust modulation recognition algorithms for real HF signals, that is, signals propagating by multiple ionospheric modes. One aspect of modulation recognition is the extraction of signal identifying features. The most common features for modulation recognition are instantaneous phase, amplitude, and frequency. However, this paper focuses on two feature parameters: coherence and entropy. Signal entropy and the coherence function show potential for robust recognition of HF modulation types in the presence of HF noise and multi-path. Specifically, it is shown that the methods of calculation of coherence and entropy are important and that appropriate calculations ensure stability in the parameters. For the first time a new metric, called Coherence-Median Difference (CMD), is introduced that provides a measure of the dominance of coherence at specific frequencies to coherence at all other frequencies in a particular bandwidth.

Giesbrecht, James E.; Clarke, Russell; Abbott, Derek

2005-02-01

317

A Band FMCW Radar Front-End With Adaptive Leakage Cancellation  

Microsoft Academic Search

Monostatic frequency modulation continuous wave radars that use one antenna to simultaneously transmit and receive can result in compact and lightweight synthetic aperture radar systems. One of the greatest challenges in designing a continuous-wave monostatic radar is realizing enough isolation between the transmitter and the receiver. A novel real-time digital signal processing scheme is proposed to cancel the transmitter leakage

Kaihui Lin; Yuanxun Ethan Wang; Cheng-Keng Pao; Yi-Chi Shih

2006-01-01

318

Imaging a BQM-74E Target Drone Using Coherent Radar Cross Section Measurements  

Microsoft Academic Search

ince the early 1980s and the advent of the modern computer, digital radar imaging has developed into a mature field. In this article, the specific problem of imaging a rotating target with a stationary radar is reviewed and built upon. The relative motion between the rotating target and the stationary radar can be used to create a circular synthetic aperture

Allen J. Bric

1997-01-01

319

Sampling rate influence on detection performance of CFAR algorithms implemented in radar extractor  

Microsoft Academic Search

A radar extractor based on a two-processor digital signal-processing (DSP) card implemented in a standard personal computer (PC) has been developed. A constant false alarm rate (CFAR) processor is applied as a part of radar extractor algorithms. Some particular problems related to the CFAR automatic detection of radar signals are investigated, from theoretical and practical point of view, and given

Miroslav M. Petrovic; Dragan D. Dimitrijevic; Aleksandar T. Kostic

2001-01-01

320

Low-cost radar surveillance of inland waterways for homeland security applications  

Microsoft Academic Search

Low-cost radar systems have been developed for homeland security missions. These detect and track small maneuvering craft in the water. The systems consist of a conventional marine radar, a capture card that digitizes the radar signals, and a computer that processes them. We have an experimental system that can monitor western Lake Ontario. It runs in real time, with operator

P. Weber; A. Premji; T. J. Nohara; C. Krasnor

2004-01-01

321

High Resolution Radar Signal Processor for Isar and Automatic Target Recognition  

Microsoft Academic Search

This paper describes a radar signal processor architecture suitable for implementing monopulse high resolution radar (HRR). A coherent transmitter and receiver radar is used to transmit and process waveforms with long pulse widths and high-bandwidth properties. The received signals are YQ demodulated, sampled and processed using a digital filter matched to the transmitted waveform. The output of the processor is

L. J. Sciaccat; R. J. Evans

1996-01-01

322

Signal Processing for Passive Radar Using OFDM Waveforms  

Microsoft Academic Search

Passive radar is a concept where illuminators of opportunity are used in a multistatic radar setup. New digital signals, like digital audio\\/video broadcast (DAB\\/DVB), are excellent candidates for this scheme, as they are widely available, can be easily decoded to acquire the noise-free signal, and employ orthogonal frequency division multiplex (OFDM). Multicarrier transmission schemes like OFDM use block channel equalization

Christian R. Berger; Bruno Demissie; Jörg Heckenbach; Peter Willett; Shengli Zhou

2010-01-01

323

Radar image processing module development program, phase 3  

NASA Technical Reports Server (NTRS)

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

1977-01-01

324

Radar echo processing with partitioned de-ramp  

SciTech Connect

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

325

TRMM radar  

NASA Astrophysics Data System (ADS)

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

Okamoto, Kenichi

1993-05-01

326

TRMM radar  

NASA Technical Reports Server (NTRS)

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

Okamoto, Kenichi

1993-01-01

327

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

328

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

329

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

NASA Astrophysics Data System (ADS)

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

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

2008-06-01

330

Planetary Radar Studies.  

National Technical Information Service (NTIS)

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 an...

T. W. Thompson J. A. Cutts

1981-01-01

331

A simple digital TDPAC spectrometer  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

332

Vegetation height estimation from Shuttle Radar Topography Mission and National Elevation Datasets  

Microsoft Academic Search

A study was conducted to determine the feasibility of obtaining estimates of vegetation canopy height from digital elevation data collected during the 2000 Shuttle Radar Topography Mission (SRTM). The SRTM sensor mapped 80% of the Earth's land mass with a C-band Interferometric Synthetic Aperture Radar (InSAR) instrument, producing the most complete digital surface map of Earth. Due to the relatively

Josef Kellndorfer; Wayne Walker; Leland Pierce; Craig Dobson; Jo Ann Fites; Carolyn Hunsaker; John Vona; Michael Clutter

2004-01-01

333

NASA experimental airborne doppler radar and real time processor for wind shear detection  

NASA Technical Reports Server (NTRS)

The topics are presented in viewgraph form and include the following: experimental radar system capabilities; an experimental radar system block diagram; wind shear radar signal and data processor (WRSDP); WRSDP hardware architecture; WRSDP system design goals; DSP software development tools; OS-9 software development tools; WRSDP digital signal processing; WRSDP display operational modes; WRSDP division of functions; structure of WRSDP signal and data processing algorithms; and the wind shear radar flight experiment.

Schaffner, Philip H.; Richards, Mark A.; Jones, William R.; Crittenden, Lucille H.

1992-01-01

334

Ionospheric electron heating, optical emissions, and striations induced by powerful HF radio waves at high latitudes: Aspect angle dependence  

Microsoft Academic Search

In recent years, large electron temperature increases of 300% (3000 K above background) caused by powerful HF-radio wave injection have been observed during nighttime using the EISCAT incoherent scatter radar near Tromsø in northern Norway. In a case study we examine the spatial structure of the modified region. The electron heating is accompanied by ion heating of about 100 degrees

M. T. Rietveld; M. J. Kosch; N. F. Blagoveshchenskaya; V. A. Kornienko; T. B. Leyser; T. K. Yeoman

2003-01-01

335

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

336

The SIR-C/X-SAR synthetic aperture radar system  

NASA Technical Reports Server (NTRS)

SIR-C/X-SAR, a three-frequency radar to be flown on the Space Shuttle in September 1993, is described. The SIR-C system is a two-frequency radar operating at 1250 MHz (L-band) and 5300 MHz (C-band), and is designed to get four-polarization radar imagery at multiple surface angles. The X-SAR system is an X-band imaging radar operating at 9600 MHz. The discussion covers the mission concept; system design; hardware; RF electronics; digital electronics; command, timing, and telemetry; and testing.

Jordan, Rolando L.; Huneycutt, Bryan L.; Werner, Marian

1991-01-01

337

Wavelet based hierarchical coding scheme for radar image compression  

NASA Astrophysics Data System (ADS)

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

Sheng, Wen; Jiao, Xiaoli; He, Jifeng

2007-11-01

338

Auxiliary signal processing system for a multiparameter radar  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

339

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

340

Radar target signature program performance specification  

Microsoft Academic Search

This report is a Program Performance Specification (PPS) for a digital computer program that calculates the radar signatures of ships. The PPS will be used to guide the program through three development phases and acceptance testing. The primary objectives of the program are accuracy, flexibility of application, ease of modeling, and portability. The ship is modeled by identifying and defining

H. L. Toothman

1981-01-01

341

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

342

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

343

Soviet oceanographic synthetic aperture radar (SAR) research  

SciTech Connect

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

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

1991-01-01

344

Radar sounder performances for ESA JUICE mission  

NASA Astrophysics Data System (ADS)

The Jupiter Icy moons Explorer (JUICE) is the first Large-class mission chosen as part of ESA's Cosmic Vision 2015-2025 program. The mission will study Jovian icy moons Ganymede and Europa as potential habitats for life, addressing two key themes of Cosmic Vision namely the conditions for planet formation and the emergence of life, and the Solar System interactions. The radar sounder instrument on this mission will have great potential to address specific science questions such as the presence of subsurface liquid water and ice shell geophysical structures. One major constraint for radar sounding is the roughness of the planetary surface. The work presented will focus on the characterization of Ganymede's surface topography to better understand its surface properties from a radar point of view. These results should help to put constraints on the design of JUICE's radar sounder. We use topographic data derived from the Voyager and Galileo missions images to try to characterize the surface structure and to quantify its geometry (in terms of slopes and RMS heights mainly). This study will help us evaluating the radar budget in a statistical approach. In addition, deterministic simulations of surface radar echoes conducted on synthetic surfaces -extrapolated from Digital Elevation Models- will be presented to better assess radar sounding performances.

Berquin, Y. P.; Kofman, W. W.; Heggy, E.; Hérique, A.

2012-12-01

345

Observation and theory of the radar aurora  

SciTech Connect

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

Sahr, J.D.

1990-01-01

346

Equatorial Radar System.  

National Technical Information Service (NTIS)

A large clear air radar with the sensitivity of an incoherent scatter radar for observing the whole equatorial atmosphere up to 1000 km altitude is now being designed in Japan. The radar, called the Equatorial Radar, will be built in Pontianak, Kalimantan...

S. Rukao T. Tsuda T. Sato S. Kato

1989-01-01

347

Wind shear radar simulation  

NASA Technical Reports Server (NTRS)

Viewgraphs used in a presentation on wind shear radar simulation are given. Information on a microburst model of radar reflectivity and wind velocity, radar pulse output, the calculation of radar return, microburst power spectrum, and simulation plans are given. A question and answer session is transcribed.

Britt, Charles L.

1988-01-01

348

Radar cross section  

Microsoft Academic Search

The technological evolution in signal processing that has been made in last decades led to improvements in radar performances. Increasing the radar range by improving its sensitivity has been made by the designers of aircraft and other military systems to try to decrease the radar cross section of these types of equipment. The radar cross section is a matter of

L. Nicolaescu; Teofil Oroian

2001-01-01

349

Surface circulation in the Gulf of Trieste (northern Adriatic Sea) from radar, model, and ADCP comparisons  

NASA Astrophysics Data System (ADS)

High resolution high frequency (HF) radar observations of surface currents in the Gulf of Trieste (GoT) are presented and compared to moored subsurface current measurements and to high-resolution simulations from the Northern Adriatic Princeton Ocean Model (NAPOM) oceanographic model. Dominant circulation modes of the GoT were resolved and numerical model capabilities in reconstructing them were assessed. The time frame covers March 2011 through October 2012. NAPOM reconstructs the dominant surface circulation features observed by the radar, such as the general basin-wide cyclonic circulation scheme and the coastal jet outflowing the GoT, but is in general less energetic than radar currents. Comparisons between radar, ADCP, and model currents suggest that the model underestimates originate within the low-frequency, diurnal, semidiurnal, and inertial bands, and that both radar and model currents do not reproduce the diurnal tidal ellipse structure observed by the moored current meter. However, radar-model results for the semidiurnal tides are spatially consistent. Using empirical orthogonal function (EOF) decomposition, the coherent spatial scales and corresponding temporal scales were extracted. Findings suggest that HF radar current observations complement model simulations in regions of enhanced topographic variability where variance of model currents at the surface is distorted by the effects of the sigma layer grid. On the contrary, model results complement radar observations in areas with poor radar coverage, and furthermore provide spatial and temporal continuity of ocean state forecasts.

Cosoli, Simone; Li?er, Matjaž; Vodopivec, Martin; Mala?i?, Vlado

2013-11-01

350

Digital Optical Circuit Technology  

NASA Technical Reports Server (NTRS)

The Proceedings for the 48th Meeting of the AGARD Avionics Panel contain the 18 papers presented a Technical Evaluation Report, and discussions that followed the presentations of papers. Seven papers were presented in the session devoted to optical bistability. Optical logic was addressed by three papers. The session on sources, modulators and demodulators presented three papers. Five papers were given in the final session on all optical systems. The purpose of this Specialists' Meeting was to present the research and development status of digital optical circuit technology and to examine its relevance in the broad context of digital processing, communication, radar, avionics and flight control systems implementation.

Dove, B. L. (editor)

1985-01-01

351

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

352

Study of Synthetic Aperture Radar (SAR) imagery characteristics  

NASA Technical Reports Server (NTRS)

Sources of geometric and radiometric fidelity errors in AN/APQ-102A radar imagery are discussed, along with a digital computer program to correct the distortions. The major effort, a computer program which will process digitalized recorded AN/APQ-102A phase histories into imagery, is described. All computer programs are listed.

1975-01-01

353

Ein Beitrag zur Struktur hochschmelzender Hafnium-Phasen: HfC-UC, Hf 2 Si, HfSi und Hf 5 Si 3 (C)  

Microsoft Academic Search

UC und HfC lösen sich bei 2000°C bereits nach 2 Stdn. in merklichem Maße. Ein homogener Übergang wird jedoch bei den gewählten Bedingungen nicht erreicht. Hf2Si und HfSi kristallisieren wie die entsprechenden Zr-Silizide im CuAl2-bzw. FeB-Typ. Hf5Si3, durch Kohlenstoff bzw. Bor stabilisiert, hat D88-Struktur.

H. Nowotny; E. Laube; R. Kieffer; F. Benesovsky

1958-01-01

354

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

355

High Frequency (HF) Automatic Link Establishment (ALE) Transition Plan.  

National Technical Information Service (NTIS)

The High Frequency (HF) Automatic Link Establishment (ALE) Transition Plan describes an evolutionary HF ALE technology transition process that points toward HF 2000, a modern, automated, HF communications system that manages resources to optimize data thr...

1995-01-01

356

Description and demonstration of the new Middle and Upper atmosphere Radar imaging system: 1-D, 2-D, and 3-D imaging of troposphere and stratosphere  

Microsoft Academic Search

The Middle and Upper atmosphere Radar (MUR) was upgraded in March 2004 for radar imaging capability with 5 frequencies across a 1 MHz bandwidth and 25 digital receivers. Although digitization introduces problems of its own, the uniformity of digitization is a great benefit over the analogue system in place before. This increased reliability will help make the new system an

G. Hassenpflug; M. Yamamoto; H. Luce; S. Fukao

2008-01-01

357

Radar detection using Siegel distance between autoregressive processes, application to HF and X-band radar  

Microsoft Academic Search

In this paper, we present an original generalization of the CFAR technique . The technique of CFAR consists in testing two alternative assumptions ldquopresence of targetrdquo versus ldquoabsence of targetrdquo in a distance-azimuth cell called ldquocell under testrdquo. In the case where the noise is Gaussian and additive, one can show that the CFAR is equivalent to withdraw from the

J. Lapuyade-Lahorgue; F. Barbaresco

2008-01-01

358

ENDO atmospheric EXO atmospheric radar modeling. Radar cross section modeling, appendix L  

Microsoft Academic Search

This effort is concerned with the development and inplementation of a set of digital computer programs that will augment the RADC digital computer radar simulation model procured under Contract F30602-72-C0393 (01707201). The computer programs shall consist of a sequence of subroutines that correspond to separate functions such as a chaff model, target model, propagation effects, and clutter model. The original

R. J. Hancock; F. H. Cleveland

1976-01-01

359

Observation and theory of the radar aurora  

NASA Astrophysics Data System (ADS)

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

Sahr, John David

360

Observation and Theory of the Radar Aurora  

NASA Astrophysics Data System (ADS)

Plasma density irregularities occurring near the Aurora Borealis cause scattering of HF, VHF, and UHF radio waves. The scattering is so strong that a small radar, such a the Cornell University Portable Radar Interferometer (CUPRI), can easily detect this "radar aurora." Analysis of the resulting radar signal provides great detail about the spatial and temporal characteristics of these auroral E region irregularities. We present observations of the radar aurora from recent campaigns in northern Sweden. After reviewing the basic theory and observations of auroral electrojet irregularities, we introduce a simple nonlinear fluid theory of electrojet ion-acoustic waves, and reduce it to a form of the "three-wave interaction" equations. This theory provides a simple mechanism for excitation of linearly stable waves at large aspect and flow angles, as well as a prediction of the power spectra that a coherent scatter radar should observe. In addition, this theory may be able account for "type 3" waves without resorting to ion gyro modes, such as the electrostatic ion-cyclotron wave. During the course of our research we have generated a simple new radar transmitting mode and signal processing algorithm which very simply solves a frequency aliasing problem that often occurs in CUPRI auroral radar studies when a single-pulse spectral mode is used. Several new radar data analysis routines have been developed, including principally the "cross-beam image" and scatter plots of the second versus first moments of the power spectrum of the irregularities. Analysis of vertical interferometer data shows that "type 3" waves originate at ordinary electrojet altitudes, not in the upper E region, from which we conclude that the electrostatic ion-cyclotron mode does not generate "type 3" waves. The measured height of type 3 waves and other spectral analyses provide support for our pure ion -acoustic theory of type 3 waves. In closing, we offer suggestions for hardware improvements to the CUPRI radar, new experiments to test new and existing theories, as well as specific paths for further theoretical exploration.

Sahr, John David

1990-01-01

361

Geostatistical analysis of ground-penetrating radar data: A means of describing spatial variation in the subsurface  

Microsoft Academic Search

We have investigated the use of ground-penetrating radar (GPR) as a means of characterizing the heterogeneity of the subsurface. Radar data were collected at several sites in southwestern British Columbia underlain by glaciodeltaic sediments. A cliff face study was conducted in which geostatistical analysis of a digitized photograph of the face and the radar image of the face showed excellent

Jane Rea; Rosemary Knight

1998-01-01

362

Fifty years of radar  

NASA Astrophysics Data System (ADS)

A development history of radar technology is presented, with attention to the driving of radar system design advances by the emergence of such weapon systems as long range aircraft and cruise missiles in World War II and the range of current applications for state-of-the-art radar techniques. The applications noted encompass over-the-horizon backscatter radars for aircraft detection at 500-1800 nmi ranges, ultralow sidelobe antenna military radars, a long range, frequency scanning three-dimensional S-band radar, a shipborne phased array radar for the collection of exoatmospheric and endoatmospheric data on ballistic missile reentry vehicles, multimission/multimode X-band fighter aircraft radars, and phased array air defense radars.

Skolnik, M. I.

1985-02-01

363

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

364

The PACES digital engagement model  

Microsoft Academic Search

This paper describes the Passive and Active Countermeasures Evaluation Simulation (PACES). PACES is best characterized as an engineering level digital engagement model used to study the effectiveness of electronic countermeasures and aircraft maneuvers against threat radar and missile systems. A typical scenario consists of one or two maneuvering aircraft deploying electronic countermeasures (ECM) against a single threat system. PACES includes

E. L. Gau

1997-01-01

365

Analysis of a digital RF memory in a signal-delay application  

SciTech Connect

Laboratory simulation of the approach of a radar fuze towards a target is an important factor in our ability to accurately measure the radar`s performance. This simulation is achieved, in part, by dynamically delaying and attenuating the radar`s transmitted pulse and sending the result back to the radar`s receiver. Historically, the device used to perform the dynamic delay has been a limiting factor in the evaluation of a radar`s performance and characteristics. A new device has been proposed that appears to have more capability than previous dynamic delay devices. This device is the digital RF memory. This report presents the results of an analysis of a digital RF memory used in a signal-delay application. 2 refs.

Jelinek, D.A.

1992-03-01

366

Noncircular waveforms exploitation for Radar Signal processing: Survey and study for agile radar waveform  

Microsoft Academic Search

With new generation of Active Digital Radar Antenna, there is a renewal of waveform generation and processing approaches, and new strategies can be explored to optimize waveform design and waveform analysis and to benefit of all potential waveform diversity. Among these strategies, building and exploitation of the Noncircularity of waveforms is a promising issue. Up to the middle of the

F. Barbaresco; P. Chevalier

2009-01-01

367

Simulations and measurements of a radar cross section of a Boeing 747-200 in the 20-60 MHz frequency band  

Microsoft Academic Search

HF and VHF low frequency bands provide a promising way to perform radar target recognition. At these frequencies, Radar Cross Section (RCS) behavior is not well known because the scattered field is due to a complex phenomenon where the interactions between the different parts of the structure have a significant contribution, which makes the prediction difficult. A wire model of

A. David; C. Brousseau; A. Bourdillon

2003-01-01

368

Simulations and measurements of a radar cross section of a Boeing 747-200 in the 20–60 MHz frequency band  

Microsoft Academic Search

HF and VHF low frequency bands provide a promising way to perform radar target recognition. At these frequencies, Radar Cross Section (RCS) behavior is not well known because the scattered field is due to a complex phenomenon where the interactions between the different parts of the structure have a significant contribution, which makes the prediction difficult. A wire model of

A. David; C. Brousseau; A. Bourdillon

2003-01-01

369

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

370

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

371

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

372

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

373

Radar images analysis for scattering surfaces characterization  

NASA Astrophysics Data System (ADS)

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

Piazza, Enrico

1998-10-01

374

Hf isotope compositions of komatiites  

Microsoft Academic Search

Many of the oldest ?3.5 Ga komatiites have low Al2O3\\/TiO2 and depleted HREE, features that are attributed to garnet fractionation at some stage during their formation. It is not known, however, whether this fractionation took place at the time of melting, or well before, perhaps during the crystallization of an early magma ocean. We report here the Hf isotope compositions

Janne Blichert-Toft; Nicholas T. Arndt

1999-01-01

375

Synthesis and structural investigation of the compounds containing HF 2 ? anions: Ca(HF 2) 2, Ba 4F 4(HF 2)(PF 6) 3 and Pb 2F 2(HF 2)(PF 6)  

Microsoft Academic Search

Three new compounds Ca(HF2)2, Ba4F4(HF2)(PF6)3 and Pb2F2(HF2)(PF6) were obtained in the system metal(II) fluoride and anhydrous HF (aHF) acidified with excessive PF5. The obtained polymeric solids are slightly soluble in aHF and they crystallize out of their aHF solutions. Ca(HF2)2 was prepared by simply dissolving CaF2 in a neutral aHF. It represents the second known compound with homoleptic HF environment

Tina Buni?; Melita Tramšek; Evgeny Goreshnik; Boris Žemva

2008-01-01

376

Synthesis and structural investigation of the compounds containing HF2- anions: Ca(HF2)2, Ba4F4(HF2)(PF6)3 and Pb2F2(HF2)(PF6)  

Microsoft Academic Search

Three new compounds Ca(HF2)2, Ba4F4(HF2)(PF6)3 and Pb2F2(HF2)(PF6) were obtained in the system metal(II) fluoride and anhydrous HF (aHF) acidified with excessive PF5. The obtained polymeric solids are slightly soluble in aHF and they crystallize out of their aHF solutions. Ca(HF2)2 was prepared by simply dissolving CaF2 in a neutral aHF. It represents the second known compound with homoleptic HF environment

Tina Bunic; Melita Tramsek; Evgeny Goreshnik; Boris Zemva

2008-01-01

377

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

378

Analysis of a digital chirp synthesizer  

SciTech Connect

Definite advantages are gained by using a chirp (linear-FM) waveform for radar pulse compression. Digital generation of this waveform provides programmability, predictability, and repeatability. Of the digital implementations considered, the digital chirp synthesizer is shown to have the most flexibility and is more readily miniaturized than the arbitrary waveform generator design. Elements and features of the digital chirp synthesizer are examined and design considerations are presented. A TTL breadboard circuit that was built demonstrates the soundness of the fundamental design of the digital chirp synthesizer concept. 10 refs., 18 figs., 10 tabs.

Allen, C.T.

1988-08-01

379

Radar, Target and Ranging.  

National Technical Information Service (NTIS)

This Test Operations Procedure (TOP) provides conventional test methods employing conventional test instrumentation for testing conventional radars. Single tests and subtests designed to test radar components, transmitters, receivers, antennas, etc., and ...

1984-01-01

380

Radar Absorbing Material Design.  

National Technical Information Service (NTIS)

Low observable platforms have extremely low radar cross section specifications that cannot be achieved by shaping alone. The application of radar absorbing material is necessary, in which case the appropriate constitutive parameters and thickness must be ...

C. K. Yuzcelik

2003-01-01

381

Satellite radar interferometry - Two-dimensional phase unwrapping  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

382

Equatorial radar system  

Microsoft Academic Search

A large clear air radar with the sensitivity of an incoherent scatter radar for observing the whole equatorial atmosphere up to 1000 km altitude is now being designed in Japan. The radar will be built in Pontianak, West Kalimantan, Indonesia (0.03 deg N, 109.29 deg E). The system is a 47-MHz monostatic Doppler radar with an active phased array configuration

Shoichiro Fukao; Toshitaka Tsuda; Toru Sato; Susumu Kato

1990-01-01

383

Radar observations of asteroids  

NASA Technical Reports Server (NTRS)

The type of information that can be obtained from radar observations of asteroids includes sizes, shapes, spin vectors, and such surface characteristics as the decimeter-scale morphology, topographic relief, regolith porosity, and metal concentration. This paper describes the two radar facilities active in asteroid studies (the Arecibo Observatory in Puerto Rico and the Goldstone Radar in California) and techniques used in radar observations of asteroids. Results available for main-belt and near-earth asteroids are discussed.

Ostro, Steven J.

1989-01-01

384

Fifty years of radar  

Microsoft Academic Search

A development history of radar technology is presented, with attention to the driving of radar system design advances by the emergence of such weapon systems as long range aircraft and cruise missiles in World War II and the range of current applications for state-of-the-art radar techniques. The applications noted encompass over-the-horizon backscatter radars for aircraft detection at 500-1800 nmi ranges,

M. I. Skolnik

1985-01-01

385

Harmonic Radar Literature Harmonisk Radar - en Litteraturstudie.  

National Technical Information Service (NTIS)

A harmonic radar sends on a given frequency f sub o and receives on another frequency usually 3 f sub o. The overtone is generated on joints between the metal parts of the radar target. The generated high harmonic frequency is very weak, which is why this...

B. Jansson

1980-01-01

386

Harmonic radar literature  

Microsoft Academic Search

A harmonic radar sends on a given frequency f sub o and receives on another frequency usually 3 f sub o. The overtone is generated on joints between the metal parts of the radar target. The generated high harmonic frequency is very weak, which is why this radar has an extremely low range of detection. Natural objects in the target

B. Jansson

1980-01-01

387

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

388

Radar cross section measurements  

Microsoft Academic Search

The present status of radar cross section (RCS) measurements is addressed. The fundamental considerations and definitions associated with RCS measurements are reviewed, including radar waveform, polarization requirements, far-field requirements, and target dimensional scaling. Different types of measurement facilities are examined, including their range geometries, target support systems, calibration standards, and facility evaluation. Instrumentation radar requirements and designs are reviewed, and

Robert B. Dybdal

1987-01-01

389

Automatic Radar Waveform Recognition  

Microsoft Academic Search

In this paper, a system for automatically recognizing radar waveforms is introduced. This type of techniques are needed in various spectrum management, surveillance and cognitive radio or radar applications. The intercepted radar signal is classified to eight classes based on the pulse compression waveform: linear frequency modulation (LFM), discrete frequency codes (Costas codes), binary phase, and Frank, P1, P2, P3,

Jarmo Lundn; Visa Koivunen

2007-01-01

390

Controlling radar signature  

Microsoft Academic Search

Low observable technologies for military and tactical aircraft are reviewed including signature-reduction techniques and signal detection\\/jamming. Among the applications considered are low-signature sensors and the reduction of radar cross section in conjunction with radar-absorbing structures and materials. Technologies for reducing radar cross section are shown to present significant technological challenges, although they afford enhanced aircraft survivability.

Foulke

1992-01-01

391

A transceiver module of the Mu radar  

NASA Technical Reports Server (NTRS)

The transceiver (TR) module of a middle and upper atmospheric radar is described. The TR module used in the radar is mainly composed of two units: a mixer (MIX unit) and a power amplifier (PA unit). The former generates the RF wave for transmission and converts the received echo to the IF signal. A 41.5-MHz local signal fed to mixers passes through a digitally controlled 8-bit phase shifter which can change its value up to 1,000 times in a second, so that the MU radar has the ability to steer its antenna direction quickly and flexibly. The MIX unit also contains a buffer amplifier and a gate for the transmitting signal and preamplifier for the received one whose noise figure is less than 5 dB. The PA unit amplifies the RF signal supplied from the MIX unit up to 63.7 dBm (2350 W), and feeds it to the crossed Yagi antenna.

Kato, S.; Ogawa, T.; Tsuda, T.; Sato, T.; Kimura, I.; Fukao, S.

1983-01-01

392

Radar image analysis utilizing junctive image metamorphosis  

NASA Astrophysics Data System (ADS)

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

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

1998-09-01

393

Magellan: Radar performance and data products  

USGS Publications Warehouse

The Magellan Venus orbiter carries only one scientific instrument: a 12.6-centimeter-wavelength radar system shared among three data-taking modes. The syntheticaperture mode images radar echoes from the Venus surface at a resolution of between 120 and 300 meters, depending on spacecraft altitude. In the altimetric mode, relative height measurement accuracies may approach 5 meters, depending on the terrain's roughness, although orbital uncertainties place a floor of about 50 meters on the absolute uncertainty. In areas of extremely rough topography, accuracy is limited by the inherent line-of-sight radar resolution of about 88 meters. The maximum elevation observed to date, corresponding to a planetary radius of 6062 kilometers, lies within Maxwell Mons. When used as a thermal emission radiometer, the system can determine surface emissivities to an absolute accuracy of about 0.02. Mosaicked and archival digital data products will be released in compact disk (CDROM) format.

Pettengill, G. H.; Ford, P. G.; Johnson, W. T. K.; Raney, R. K.; Soderblom, L. A.

1991-01-01

394

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

395

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))

1992-01-01

396

Volume-imaging UHF radar measurement of atmospheric turbulence  

Microsoft Academic Search

The Turbulent Eddy Profiler (TEP) is a volume-imaging 915 MHz radar designed for atmospheric boundary layer turbulence studies. TEP is a pulsed, phased-array radar using digital beamforming techniques to provide four-dimensional images of refractive index fluctuations and wind vectors on grid scales comparable to those of large-eddy simulations. During October 1999, TEP was deployed during the Cooperative Atmospheric Surface Exchange

Jie Li; Francisco J. Lopez-Dekker; Turker Ince; S. J. Frasier

2000-01-01

397

Arrival Angles of Mid-latitude Mesospheric Hf Echoes  

NASA Astrophysics Data System (ADS)

Mesospheric HF sounding is performed at SURA facility of Radiophisical Research Institute since 1994 using HF SURA radar operated in 4.5­9.3 MHz frequency range. Together with measurements of amplitudes and Doppler velocities of mesospheric echoes their arrival angles were measured as well using spaced along magnetic merid- ian sub-arrays of SURA facility antenna array. Distribution of arrival angles is dif- ferent for different types of echoes. Below approximately 80 km where echoes are observed sporadically it is narrow with angular width of about 1­2 degrees usually centered at vertical direction. Sometimes declination to several degrees from vertical occured while angular distribution remains narrow. Echoes from meteor tracks are also narrow with the same angular width often showing dependence of arrival angle on altitude. Most permanent and intense echoes are observed from mesopause region and usually show different angular distribution. It is much wider, up to more than 10 degrees, and has fast (few seconds) temporal variations. This feature can be explained supposing turbulent scattering as a nature of echoes from those altitudes when sev- eral sources of scattered signal of comparable amplitudes are distributed across the antenna main lobe. Another evidence of turbulent scattering is a weak correlation of signal amplitudes received by spaced antennas. Described work was supported by RFBR through the Grant 99­05­64483.

Karashtin, A. N.; Shlyugaev, Yu. V.; Bychkov, V. V.; Komrakov, G. P.; Malikeev, A. L.

398

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

399

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

400

Surface current observations using high frequency radar and its assimilation into the New York Harbor Observing and Prediction System  

NASA Astrophysics Data System (ADS)

A surface current observation system based on high-frequency (HF) radar (CODAR) has been constructed for Raritan Bay, NJ; and the New York Bight (NYB) Apex. The availability of surface current data measured using HF radar in real-time over a synoptic scale makes it appropriate for data assimilation (DA). The present work is an attempt to validate HF radar data in the NYB Apex and to develop a practical, but still nearly optimal, method to assimilate HF radar data into an estuarine and coastal ocean circulation model in a tidally-dominated region of NY/NJ Harbor Estuary and the NYB Apex. This model, forced by an extensive real-time observational network, is called the New York Harbor Observing and Prediction System (NYHOPS). A nudging or Newtonian damping scheme is developed to assimilate HF radar data. A nudging parameter is introduced into the equations of motion which affects the model dynamics. The data is imparted to neighboring (three-dimensional) grid points via model dynamics. The effectiveness of HF radar DA is studied by computing the DA skill based on mean square error. A positive DA skill (0 -- 100%) represents an improvement in the model performance by HF radar DA. The HF radar data validation study showed a reasonable comparison between HF radar surface currents and near-surface in-situ currents obtained from one out of the two moorings. HF radar DA experiments focused on both the hindcasting as well as forecast capabilities of the NYHOPS model with respect to three regions; inner-shelf region (0 -- 30 m), mid-shelf (30 -- 90m), and outer-shelf (90 -- 120 m). For the inner-NJ shelf region, based on NYHOPS model hindcasts, a 40 day long DA study using HF radar data in Raritan Bay and the NYB Apex region yielded a DA skill of +22% for near-surface currents (with respect to mooring data), and +53% and +38% for near-surface temperature and salinity (with respect to Glider/fixed sensor data). Based on NYHOPS model forecasts, for the inner-NJ shelf region, another 120 days long DA study using HF radar data in the NYB region yielded a DA skill of +11% for near-surface currents (with respect to mooring data), and +10% and +16% for near-surface temperature and salinity (with respect to Glider/fixed sensor data). The DA skill for temperature and salinity is higher in the inner-NJ shelf (0 -- 30m) region and decreases steadily towards mid-NJ shelf (30 -- 90m) and outer-NJ shelf (90 -- 120m) regions. The nudging scheme is found to be robust and efficient for the NYHOPS model with minimum computational burden.

Gopalakrishnan, Ganesh

401

Sub-Surface Radar for the EJSM mission: discussion on environmental noise limiting performance  

NASA Astrophysics Data System (ADS)

The Europa Jupiter System Mission (EJSM) is one of the major European Space Agency (ESA) missions in the Solar System currently under study. It is aimed at exploring Jupiter and its icy moon Ganymede. The Sub-Surface Radar (SSR) instrument is a radar sounder system at low frequency (HF/VHF band) designed to penetrate the surface of Ganymede icy moon of Jupiter for performing a subsurface analysis with a relatively high range resolution. The paper addresses the main sources of environmental noises that can limit the overall performance of the radar: the presence of a relevant Jupiter radio emission and the clutter caused by characteristics of planet's surface.

Alberti, G.; Berquin, Y.; Cecconi, B.; Bruzzone, L.; Kofman, W.; Herique, A.; Schenk, P.; Mattei, S.

2011-10-01

402

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

403

Radar image preprocessing. [of SEASAT-A SAR data  

NASA Technical Reports Server (NTRS)

Standard image processing techniques are not applicable to radar images because of the coherent nature of the sensor. Therefore there is a need to develop preprocessing techniques for radar images which will then allow these standard methods to be applied. A random field model for radar image data is developed. This model describes the image data as the result of a multiplicative-convolved process. Standard techniques, those based on additive noise and homomorphic processing are not directly applicable to this class of sensor data. Therefore, a minimum mean square error (MMSE) filter was designed to treat this class of sensor data. The resulting filter was implemented in an adaptive format to account for changes in local statistics and edges. A radar image processing technique which provides the MMSE estimate inside homogeneous areas and tends to preserve edge structure was the result of this study. Digitally correlated Seasat-A synthetic aperture radar (SAR) imagery was used to test the technique.

Frost, V. S.; Stiles, J. A.; Holtzman, J. C.; Held, D. N.

1980-01-01

404

Methane hydrates and their HF doped analogues  

NASA Astrophysics Data System (ADS)

A computational study is carried out to simulate methane hydrates as well as to know the effect of HF doping on their stability and structure. By using ab initio molecular dynamics simulation interaction of methane with HF doped clathrate hydrates is studied. The total energy profiles present insights into the stability and structure of methane hydrates. The HF doping increases the stability of the methane hydrates without any distortion of the cage when methane is encapsulated in 512 cages.

Mondal, Sukanta; Giri, Santanab; Chattaraj, Pratim Kumar

2013-07-01

405

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

2007-08-16

406

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

407

Music-Enhanced CFAR for High Frequency Over-the-Horizon Radar  

Microsoft Academic Search

To increase the number of location options for an HF surface-wave radar (HFSWR) there is significant interest in reducing the physical size of the receive array. Reducing the aperture results in a degradation of both sensitivity and azimuth information. Azimuth accuracy may be retained by the use of high-resolution methods (such as MUSIC) that have a significantly smaller beamwidth than

J. Wang; R. J. Riddolls; A. M. Ponsford

2007-01-01

408

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

409

Digital wires  

Microsoft Academic Search

We study hardware implementations of cellular automata as reliable, adjustable, and secure commication lines. We discuss energy efficient digital wires on a nano-scale, all-optical digital wires, and digital wires as power lines and present performance data of a prototype digital wire, a six cells wide and ten cells long Boolean network. We show that digital wires have the following advantages:

Alfred Hübler

2009-01-01

410

High Performance Waveform Generator Design for Full-Coherent Millimeter-Wave Radar  

Microsoft Academic Search

Millimeter-wave radar has attracted much attention as a replacement of some infrared or laser systems currently in use. In this paper, an approach of developing high performance waveform for full-coherent millimeter-wave radar is proposed. With good frequency configuration and optimal utilization of DDS (direct digital synthesizer), PLL (phase locked loop) and FPGA (field programming gate array), the developed radar waveform

Jingye Cait; Yishi Yang; Yuanwang Yang; Lianfu Liu; Xueyong Zhu

2007-01-01

411

Nearshore Processes, Currents and Directional Wave Spectra Monitoring Using Coherent and Non-coherent Imaging Radars  

Microsoft Academic Search

Two new radar systems have been developed for real-time measurement of near-shore processes, and results are presented for measurements of ocean wave spectra, near-shore sand bar structure, and ocean currents. The first is a non-coherent radar based on a modified version of the Sitex radar family, with a data acquisition system designed around an ISR digital receiver card. The card

D. Trizna; K. Hathaway

2007-01-01

412

Rendezvous radar for the orbital maneuvering vehicle  

NASA Technical Reports Server (NTRS)

This paper describes the development of the Rendezvous Radar Set (RRS) for the Orbital Maneuvering Vehicle (OMV) for the National Aeronautics and Space Administration (NASA). The RRS was to be used to locate, and then provide vectoring information to, target satellites (or Shuttle or Space Station) to aid the OMV in making a minimum-fuel-consumption approach and rendezvous. The RRS design is that of an X-Band, all solid-state, monopulse tracking, frequency hopping, pulse-Doppler radar system. The development of the radar was terminated when the OMV prime contract to TRW was terminated by NASA. At the time of the termination, the development was in the circuit design stage. The system design was virtually completed, the PDR had been held. The RRS design was based on Motorola's experiences, both in the design and production of radar systems for the US Army and in the design and production of hi-rel communications systems for NASA space programs. Experience in these fields was combined with the latest digital signal processor and micro-processor technology to design a light-weight, low-power, spaceborne radar. The antenna and antenna positioner (gimbals) technology developed for the RRS is now being used in the satellite-to-satellite communication link design for Motorola's Iridium telecommunications system.

Locke, John W.; Olds, Keith; Parks, Howard

1991-01-01

413

Digital Libraries.  

ERIC Educational Resources Information Center

Provides an overview of digital libraries research, practice, and literature. Highlights include new technologies; redefining roles; historical background; trends; creating digital content, including conversion; metadata; organizing digital resources; services; access; information retrieval; searching; natural language processing; visualization;…

Fox, Edward A.; Urs, Shalini R.

2002-01-01

414

Real-time DSP for reflected power cancellation in FMCW radars  

Microsoft Academic Search

A novel real-time DSP scheme is proposed for leakage cancellation in monostatic frequency modulated continuous wave (FMCW) radars. With the digital implementation, the proposed scheme shows a much more precise control of the leakage cancellation, compared to conventional analog implementation. Other advantages also include that the DC offset existing in analog mixers, affecting the cancellation performance, are eliminated. A radar

Kaihui Lin; Yuanxun Ethan Wang

2004-01-01

415

FPGA based signal processing module design and implementation for FMCW vehicle radar systems  

Microsoft Academic Search

In this paper, we design the signal processing module based on FPGA for vehicle FMCW radar systems. We employ the detection algorithms based on two-step FFT (Fast Fourier Transform) using the several fast ramps in order to resolve radar range-velocity ambiguities. We implement the detection algorithms including the first FFT, DBF (Digital Beam Forming), the second FFT, and CFAR (Constant

Eugin Hyun; Sang-Dong Kim; Yeong-Hwan Ju; Jong-Hun Lee; Eung-Noh You; Jeong-Ho Park; Dong-Jin Yeom; Sang-Hyun Park; Seung-Gak Kim

2011-01-01

416

FPGA controlled DDS based frequency sweep generation of high linearity for FMCW radar systems  

Microsoft Academic Search

Two significant requirements in an FMCW radar system are linearity and low phase noise. Especially in range detection applications the achievable accuracy directly depends on the linearity of the modulated radar signal. In general PLL based systems with digital generated reference signals are used to meet this requirement. In this paper an FPGA controlled DDS based signal generator for highly

Serdal Ayhan; Viet Vu-Duy; Philipp Pahl; Steffen Scherr; Michael Hubner; Jurgen Becker; Thomas Zwick

2012-01-01

417

Research of CMLD-CFAR Detecting Algorithm in Radar Reconnaissance Receiver  

Microsoft Academic Search

In radar signal reconnaissance digital receiver based on DFT (Discrete Fourier Transform), automatic CFAR (Constant False Alarm Rate) detection in frequency domain is necessary in processing of peak-seek algorithm. A CMLD-CFAR (Censored Mean Level Detector CFAR) algorithm in frequency domain is presented. By researching the threshold generating algorithm of pulse radar signalspsila spectrum under clutter background, a threshold generating algorithm

Shuhua Wei; Xiaojun Wang

2009-01-01

418

Application of Radar Signal Processing System Based on DSP in the VTS  

Microsoft Academic Search

Radar signal processing system is an important part of vessel traffic services. In order to overcome the shortcomings of traditional analog video system, this paper proposes a design solution for digital radar signal processing system based on DSP and a new method that is a constant false alarm rate algorithm based on wavelet transform. This method can suppress the interference

Shuang Xu; Jiyin Zhao; Jidong Suo

2009-01-01

419

Radar processing of 2n-1 and 2n PRN coded waveforms  

Microsoft Academic Search

The processing of waveforms that are not LFM requires that the bandwidth of the signal be considered. Pseudo-random noise coded waveforms are now being used by cellular telephones and are being considered for use in radar systems. With the prevalence of digital signal processing (DSP) hardware, it is appears that the radar community has accepted that DSP equipment can process

M. J. Dorsett

2000-01-01

420

A New Implementation of the Mellin Transform and its Application to Radar Classification of Ships  

Microsoft Academic Search

A modified Mellin transform for digital implementation is developed and applied to range radar profiles of naval vessels. The scale invariance property of the Mellin transform provides a means for extracting features from the profiles which are insensitive to the aspect angle of the radar. Past implementations of the Mellin transform based on the FFT have required exponential sampling, interpolation,

Philip E. Zwicke; Imre Kiss

1983-01-01

421

Uninterrupted power supply with intermediate HF circuit  

Microsoft Academic Search

Contents This work presents an uninterrupted monophase power supply with IGBT transistors and HF intermediate circuit. Two three-phase UPS circuits with intermediate HF circuit are also presented, based on the suggested control method. All the suggested versions are characterized by small dimensions and a high fundamental content (0,995) of the alternating output voltages.

D. Alexa; M. Florea

1992-01-01

422

HF radiation emitted by chaotic leader processes  

NASA Astrophysics Data System (ADS)

This paper presents direct measurements of narrowband 10 MHz HF radiation from so-called “chaotic leaders” associated with subsequent return strokes. Although the term is controversial and poorly defined, we find that more than 30% of subsequent strokes in close lightning flashes contain electric field characteristics that are best described as “chaotic”. In earlier studies, return strokes have consistently been observed to be the strongest sources of HF radiation, but the results for leader processes are less consistent. We also observe return strokes to be the main HF emitter, and the leaders before the first return stroke in a flash sequence also emit HF though somewhat less intensely. The leaders preceding subsequent strokes typically emit little or no HF radiation, whether they are dart or dart-stepped leaders. However, it was observed that the presence of a chaotic component increases the leader HF intensity dramatically Defining the HF intensity unequivocally can be problematic for processes like chaotic leaders which have a combination of continuous and impulsive phenomena. Two time-domain methods were used to measure the HF intensity, the peak energy and the RMS energy. In the frequency domain these correspond to the energy spectral density (ESD) and power spectral density (PSD), respectively. It was found that the methods are not necessarily compatible. Thus, it is suggested that to clarify future work, leader processes should be characterized by the PSD rather than the ESD.

Mäkelä, J. S.; Edirisinghe, M.; Fernando, M.; Montaño, R.; Cooray, V.

2007-04-01

423

182Hf, a new isotope for AMS  

NASA Astrophysics Data System (ADS)

The neutron-rich isotope 182Hf with its half-life of 9+/-2 million years was alive in the early solar system and has been used to study the early development of the Earth and the Moon through isotopic anomalies of its stable decay product 182W. In addition, 182Hf may also complement a few other radionuclides in the million-year half-life range to trace relatively recent stellar events with high neutron fluxes in the vicinity of the Earth. This may be accomplished by finding measurable traces of live 182Hf in suitable terrestrial archives. With accelerator mass spectrometry (AMS) it should be possible to detect minute amounts of 182Hf. We will show that the main interference for the detection, the stable isobar 182W, can be significantly reduced by using HfF5- ions. The AMS detection method of 182Hf and first results from Hf control rods of a recently retired research reactor are presented, which encourage us to search for naturally produced traces of 182Hf on Earth.

Vockenhuber, Christof; Bichler, Max; Golser, Robin; Kutschera, Walter; Priller, Alfred; Steier, Peter; Winkler, Stephan

2004-08-01

424

HF conductivity of parametrically unstable magnetized plasma  

Microsoft Academic Search

Summary form only given. The anomalous absorption of high-frequency (HF) pump wave in a nonequilibrium magnetized plasma was studied early on the basis of the kinetic theory of fluctuations. The frequency bands in which the effective HF power dissipation mechanisms exist in a thermonuclear and space plasmas are the lower hybrid (LH) and upper hybrid (UH) regions. In this report

V. G. Panchenko; V. N. Pavlenko

2002-01-01

425

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

NASA Astrophysics Data System (ADS)

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 'damage' is done by the bottomside spread F.

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

426

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

427

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

428

Dependence of spectral width of polar cap HF echoes upon electric field  

NASA Astrophysics Data System (ADS)

The EISCAT Svalbard Radar (ESR) monitors plasma parameters in the ionospheric region that is frequently located near the polar cap boundary. The SuperDARN radar at Hankasalmi, Finland detects coherent echoes from this region and these echoes typically show increased spectral width. We consider data of joint ESR and SuperDARN observations to show that the spectral width of HF echoes tends to increase with the electric field. This relationship is explained in terms of non-linear evolution of the ExB gradient drift instability with energy cascade from hundred of meters wavelengths to meter wavelengths. We assume that non-linearly generated, relatively strong decameter waves (seen by the Hankasalmi radar) decay through three-wave interaction with shorter wavelengths and estimate that the decameter waves/irregularities decay time is determined by the parameters of the shorter wavelength structures. We associate the decameter wave decay time with the correlation time, and thus the spectral width, of HF echoes.

Koustov, A. V.; Shalimov, S.; Kozlovsky, A.

2010-12-01

429

Dependence of spectral width of ionospheric F region HF echoes on electric field  

NASA Astrophysics Data System (ADS)

The EISCAT Svalbard radar (ESR) monitors plasma parameters in the ionospheric region that is frequently located near the polar cap boundary. The SuperDARN radar at Hankasalmi, Finland, detects coherent echoes from this region, and these echoes typically show increased spectral width. We consider data of joint ESR and SuperDARN observations to show that the spectral width of HF echoes tends to increase with the ionospheric electric field. This relationship is explained in terms of nonlinear evolution of the E × B gradient drift instability with energy cascade from hundreds of meter wavelengths to meter wavelengths. We assume that decameter waves (seen by the Hankasalmi radar) with relatively large amplitude decay through a three-wave interaction with shorter wavelengths and estimate that the decay time of the decameter waves/irregularities is determined by the parameters of the shorter-wavelength structures. We associate the decameter wave decay time with the correlation time, and thus the spectral width, of HF echoes.

Kozlovsky, A.; Shalimov, S.; Koustov, A. V.; Lukianova, R.; Turunen, T.

2011-07-01

430

Apollo experience report: Lunar module landing radar and rendezvous radar  

NASA Technical Reports Server (NTRS)

A developmental history of the Apollo lunar module landing and rendezvous radar subsystems is presented. The Apollo radar subsystems are discussed from initial concept planning to flight configuration testing. The major radar subsystem accomplishments and problems are discussed.

Rozas, P.; Cunningham, A. R.

1972-01-01

431

Lincoln Laboratory millimeter-wave synthetic aperture radar imaging system  

NASA Astrophysics Data System (ADS)

The Lincoln Laboratory millimeter-wave synthetic aperture radar (SAR) imaging system is part of a DARPA-funded program that was established at Lincoln Laboratory to investigate the detection and classification of stationary targets using ultra-high resolution, fully polarimetric SAR and real aperture radar (RAR) data. The system consists of an airborne radar that operates at 33.56 GHz. The raw radar data are recorded on high density digital tapes that are sent to the Radar Data Analysis Center, which is located at Lincoln Laboratory in Lexington, Mass. This center processes the data to create calibrated SAR and RAR images. The Radar Data Analysis Center consists of a number of major data processing elements: an image formation processor, an archival storage and retrieval system, and a cluster of computer systems used for data analysis. In order to accomplish the goals of the DARPA program, it is essential that the radar data be very carefully calibrated. The calibration process consists of three major steps: (1) an internally generated calibration pulse is inserted into the radar receiver at the front end; (2) calibration targets (dihedrals and trihedrals) deployed on the ground are measured by the radar from the air and; (3) special calibration processing software uses the measurements from (1) and (2) to achieve polarimetric calibration. This paper describes the airborne radar, the ground processing facility, and the calibration process. Recent SAR images, generated from airborne measurements, of ground clutter and selected urban areas are presented. The images were generated using the polarimetric whitening filter (PWF), a novel processing technique developed at Lincoln Laboratory. The PWF process exploits the polarimetric measurement capability of the radar to create imagery that is nearly optical in quality.

Henry, John C.; Murphy, Thomas J.; Carusone, Kathleen M.

1992-05-01

432

1989 IEEE National Radar Conference, 4th, Dallas, TX, Mar. 29, 30, 1989, Proceedings  

NASA Astrophysics Data System (ADS)

Papers on topics related to radar systems and subsystems are presented, including an ultrareliable radar, system optimization for radar surveillance from space, multirole survivable radar balancing threats, terrain following radars, adaptive optimum attitude extrapolator for precise antenna pointing control, bistatic radar noncooperative illuminator synchronization, supperresolution and ISAR imaging, analog-to-digital converter effects on airborne radar, and biphase codes with minimum peak sidelobes. Other topics include long-term noncoherent integration across resolvable sea clutter areas, false alarm control using ambiguous velocity, track quality estimation for multiple target tracking radars, synthesis of phased array far-field patterns, and the effect of interchannel mismatches upon adaptive array cancellation. Additional subjects include wideband phase steered array, an improved bandwidth microstrip antenna design for airborne phased arrays, the Naval Space Surveillance System solid state transmitter, synacit classification of radar measurements, a statistical radar clutter classifier, L-band radar fading statistics vs resolution, radar characterization of ship wake signatures and ambient ocean clutter features, and polarimetric signatures of artificial sea ice.

433

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

434

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

435

A comparison of velocity measurements from the CUTLASS Finland radar and the EISCAT UHF system  

NASA Astrophysics Data System (ADS)

The CUTLASS Finland radar, which comprises an integral part of the SuperDARN system of HF coherent radars, provides near continuous observations of high-latitude plasma irregularities within a field-of-view which extends over some four million square kilometres. Within the Finland radar field-of-view lie both the EISCAT mainland and EISCAT Svalbard incoherent scatter radar facilities. Since the CUTLASS Finland radar commenced operation, in February 1995, the mainland EISCAT UHF radar has been run in common programme 1 and 2 modes for a total duration exceeding 1000 h. Simultaneous and spatially coincident returns from these two radars over this period provide the basis for a comparison of irregularity drift velocity and F-region ion velocity. Initial comparison is limited to velocities from four intervals of simultaneous radar returns; intervals are selected such that they exhibit a variety of velocity signatures including that characteristic of the convection reversal and a rapidly fluctuating velocity feature. Subsequent comparison is on a statistical basis. The velocities measured by the two systems demonstrate reasonable correspondence over the velocity regime encountered during the simultaneous occurrence of coherent and incoherent scatter; differences between the EISCAT UHF measurements of F-region ion drift and the irregularity drift velocities from the Finland radar are explained in terms of a number of contributing factors including contamination of the latter by E-region echoes, a factor which is investigated further, and the potentially deleterious effect of discrepant volume and time sampling intervals.

Davies, J. A.; Lester, M.; Milan, S. E.; Yeoman, T. K.

1999-07-01

436

Multifunction laser radar: II  

NASA Astrophysics Data System (ADS)

Laser radar systems are required for various military applications including obstacle detection, target recognition, and terrain mapping. Each application requires different system parameters such as pulse energy, repetition rate, and field of view. This paper is the second in a series of papers describing the progress toward a multifunction laser radar system under construction for the Cooperative Eyesafe Laser Radar Program (CELRAP) of the U.S. Army CECOM Night Vision and Electronic Sensors Directorate.

Hutchinson, James A.; Trussell, Charlie W.; Allik, Toomas H.; Hamlin, Scott J.; McCarthy, John C.; Jack, Michael D.

2000-09-01

437

Description and availability of airborne Doppler radar data  

NASA Astrophysics Data System (ADS)

An airborne, forward-looking, pulse, Doppler radar has been developed in conjunction with the joint FAA/NASA Wind Shear Program. This radar represents a first in an emerging technology. The radar was developed to assess the applicability of an airborne radar to detect low altitude hazardous wind shears for civil aviation applications. Such a radar must be capable of looking down into the ground clutter environment and extracting wind estimates from relatively low reflectivity weather targets. These weather targets often have reflectivities several orders of magnitude lower than the surrounding ground clutter. The NASA radar design incorporates numerous technological and engineering achievements in order to accomplish this task. The basic R/T unit evolved from a standard Collins 708 weather radar, which supports specific pulse widths of 1-7 microns and Pulse Repetition Frequencies (PRF) of less than 1-10 kHz. It was modified to allow for the output of the first IF signal, which fed a NASA developed receiver/detector subsystem. The NASA receiver incorporated a distributed, high-speed digital attenuator, producing a range bin to range bin automatic gain control system with 65 dB of dynamic range. Using group speed information supplied by the aircraft's navigation system, the radar signal is frequency demodulated back to base band (zero Doppler relative to stationary ground). The In-phase & Quadrature-phase (I/Q) components of the measured voltage signal are then digitized by a 12-bit A-D converter (producing an additional 36 dB of dynamic range). The raw I/Q signal for each range bin is then recorded (along with the current radar & aircraft state parameters) by a high-speed Kodak tape recorder.

Harrah, S. D.; Bracalente, E. M.; Schaffner, P. R.; Baxa, E. G.

438

Description and availability of airborne Doppler radar data  

NASA Technical Reports Server (NTRS)

An airborne, forward-looking, pulse, Doppler radar has been developed in conjunction with the joint FAA/NASA Wind Shear Program. This radar represents a first in an emerging technology. The radar was developed to assess the applicability of an airborne radar to detect low altitude hazardous wind shears for civil aviation applications. Such a radar must be capable of looking down into the ground clutter environment and extracting wind estimates from relatively low reflectivity weather targets. These weather targets often have reflectivities several orders of magnitude lower than the surrounding ground clutter. The NASA radar design incorporates numerous technological and engineering achievements in order to accomplish this task. The basic R/T unit evolved from a standard Collins 708 weather radar, which supports specific pulse widths of 1-7 microns and Pulse Repetition Frequencies (PRF) of less than 1-10 kHz. It was modified to allow for the output of the first IF signal, which fed a NASA developed receiver/detector subsystem. The NASA receiver incorporated a distributed, high-speed digital attenuator, producing a range bin to range bin automatic gain control system with 65 dB of dynamic range. Using group speed information supplied by the aircraft's navigation system, the radar signal is frequency demodulated back to base band (zero Doppler relative to stationary ground). The In-phase & Quadrature-phase (I/Q) components of the measured voltage signal are then digitized by a 12-bit A-D converter (producing an additional 36 dB of dynamic range). The raw I/Q signal for each range bin is then recorded (along with the current radar & aircraft state parameters) by a high-speed Kodak tape recorder.

Harrah, S. D.; Bracalente, E. M.; Schaffner, P. R.; Baxa, E. G.

1993-01-01

439

Radar Imaging and Feature Extraction.  

National Technical Information Service (NTIS)

Advanced spectral estimation methods are presented for radar imaging and target feature extraction. We study problems involved in inverse synthetic aperture radar (ISAR) autofocus and imaging, synthetic aperture radar (SAR) autofocus and motion compensati...

J. Li

1999-01-01

440

Stepped Frequency Imaging Radar Simulation.  

National Technical Information Service (NTIS)

In this thesis, a technique involving Stepped Frequency and Inverse Synthetic Aperture Radar (ISAR) processing have been employed to develop two- dimensional radar images of an aircraft target. Radar returns from prominent scatterers of various parts of t...

K. L. Mun

2000-01-01

441

Review of Radar Absorbing Materials.  

National Technical Information Service (NTIS)

Radar is a sensitive detection tool and since its development, methods for reducing microwave reflections have been explored. Radar absorbers can be classified as impedance matching or resonant absorbers. Radar absorbing materials are made from resistive ...

P. Saville

2005-01-01

442

Landform Identification: Lunar Radar Images.  

National Technical Information Service (NTIS)

Three sets of polarized radar-echo images of the Moon were examined to establish the relation between radar resolution and landform-identification resolution. After comparison with lunar maps and photographs, real and apparent landforms on the radar image...

H. J. Moore T. W. Thompson

1987-01-01

443

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

444

Equatorial radar system  

NASA Astrophysics Data System (ADS)

A large clear air radar with the sensitivity of an incoherent scatter radar for observing the whole equatorial atmosphere up to 1000 km altitude is now being designed in Japan. The radar, called the Equatorial Radar, will be built in Pontianak, Kalimantan Island, Indonesia (0.03 N, 109.3 E). The system is a 47 MHz monostatic Doppler radar with an active phased array configuration similar to that of the MU radar in Japan, which has been in successful operation since 1983. It will have a PA product of more than 5 x 10(9) sq. Wm (P = average transmitter power, A = effective antenna aperture) with sensitivity more than 10 times that of the MU radar. This system configuration enables pulse-to-pulse beam steering within 25 deg from the zenith. As is the case of the MU radar, a variety of sophisticated operations will be made feasible under the supervision of the radar controller. A brief description of the system configuration is presented.

Rukao, S.; Tsuda, T.; Sato, T.; Kato, S.

1989-04-01

445

Equatorial radar system  

NASA Technical Reports Server (NTRS)

A large clear air radar with the sensitivity of an incoherent scatter radar for observing the whole equatorial atmosphere up to 1000 km altitude is now being designed in Japan. The radar, called the Equatorial Radar, will be built in Pontianak, Kalimantan Island, Indonesia (0.03 N, 109.3 E). The system is a 47 MHz monostatic Doppler radar with an active phased array configuration similar to that of the MU radar in Japan, which has been in successful operation since 1983. It will have a PA product of more than 5 x 10(9) sq. Wm (P = average transmitter power, A = effective antenna aperture) with sensitivity more than 10 times that of the MU radar. This system configuration enables pulse-to-pulse beam steering within 25 deg from the zenith. As is the case of the MU radar, a variety of sophisticated operations will be made feasible under the supervision of the radar controller. A brief description of the system configuration is presented.

Rukao, S.; Tsuda, T.; Sato, T.; Kato, S.

1989-01-01

446

Harmonic radar literature  

NASA Astrophysics Data System (ADS)

A harmonic radar sends on a given frequency f sub o and receives on another frequency usually 3 f sub o. The overtone is generated on joints between the metal parts of the radar target. The generated high harmonic frequency is very weak, which is why this radar has an extremely low range of detection. Natural objects in the target area do not disturb the high frequency harmonics. The radar becomes clutter free. The principals of generating high frequency harmonics cover tunneling, semiconductor and microwave effects. Signal generation is most powerful when f sub o is between 100 and 1000 MHz.

Jansson, B.

1980-07-01

447

Creation of artificial ionospheric layers using high-power HF waves  

NASA Astrophysics Data System (ADS)

We report the first evidence of artificial ionospheric plasmas reaching sufficient density to sustain interaction with a high-power HF pump beam produced by the 3.6 MW High-Frequency Active Auroral Program (HAARP) transmitter in Gakona, Alaska. The HF-driven ionization process is initiated near the 2nd electron gyroharmonic at 220 km altitude in the ionospheric F region. Once the artificial plasma reaches sufficient density to support interaction with the transmitter beam it rapidly descends as an ionization wave to 150 km altitude. Although these initial artificial layers appear to be dynamic and highly structured, this new ability to produce significant artificial plasma in the upper atmosphere opens the door to a new regime in ionospheric radio wave propagation where transmitter-produced plasmas dominate over the natural ionospheric plasma and may eventually be employed as active components of communications, radar, and other systems.

Pedersen, Todd; Mishin, Evgeny; Kendall, Elizabeth; Mills, Travis; Carlson, H. C.; Snyder, A. L.; Gustavsson, Bjorn

448

Creation of artificial ionospheric layers using high-power HF waves  

NASA Astrophysics Data System (ADS)

We report the first evidence of artificial ionospheric plasmas reaching sufficient density to sustain interaction with a high-power HF pump beam produced by the 3.6 MW High-Frequency Active Auroral Program (HAARP) transmitter in Gakona, Alaska. The HF-driven ionization process is initiated near the 2nd electron gyroharmonic at 220 km altitude in the ionospheric F region. Once the artificial plasma reaches sufficient density to support interaction with the transmitter beam it rapidly descends as an ionization wave to ˜150 km altitude. Although these initial artificial layers appear to be dynamic and highly structured, this new ability to produce significant artificial plasma in the upper atmosphere opens the door to a new regime in ionospheric radio wave propagation where transmitter-produced plasmas dominate over the natural ionospheric plasma and may eventually be employed as active components of communications, radar, and other systems.

Pedersen, T.; Gustavsson, B.; Mishin, E.; Kendall, E.; Mills, T.; Carlson, H. C.; Snyder, A. L.

2010-01-01

449

The EcoSAR P-band Synthetic Aperture Radar  

Microsoft Academic Search

The EcoSAR instrument is a new concept in Synthetic Aperture Radar for the polarimetric and interferometric measure- ments of biomass and ecosystem structure. EcoSAR will employ a digital beamforming architecture, a highly capable digital wave- form generator and receiver system, and ad- vanced dual-polarization array antennas with an interferometric baseline of 25 m on the NASA P3 aircraft.

Rafael F. Rincon; Temilola Fatoyinbo; Guoqing Sun; K. Jon Ranson; Martin Perrine; Manohar Deshapnde; Quenton Bonds

2011-01-01

450

Aviation Digital Data Service (ADDS)  

NSDL National Science Digital Library

The Aviation Digital Data Service (ADDS) makes available to the aviation community digital and graphical analyses, forecasts and observations of meteorological variables in the United States. Analyses, forecasts, and observations are available for turbulence, icing, convection, wind speed, and temperature. You can even select the altitude of interest. Satellite and radar images are also available. Java tools to help with the analysis of the maps provided are available for download. Developed as the data distribution component of the Aviation Gridded Forecast System (AGFS), ADDS is a joint effort of NOAA Forecast Systems Laboratory (FSL), NCAR Research Applications Program (RAP), and the National Centers for Environmental Prediction (NCEP) Aviation Weather Center (AWC).

451

DPLL in Cooperated with PI Controller for HF-Inverter Control System  

Microsoft Academic Search

This paper presents a HF (high frequency)-inverter using a digital phase-locked loop (DPLL) technique in cooperated with PI controller to ensure its output power factor up to unity and operating frequency tracking the load-resonant frequency rapidly and precisely. In the dynamic condition, when the error between the frequencies of the operation and load resonance of the proposed inverter and its

Jing Hui; Xiaohui Zang; Fengjiu Zhang; Jinfei Shen

2006-01-01

452

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 Envis