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1

Bistatic synthetic aperture radar  

Microsoft Academic Search

Synthetic aperture radar (SAR) is becoming increasingly important in many military ground surveillance and targeting roles because of its ability to operate in all weather, day and night, and to detect, classify and geolocate objects at long stand-off ranges. Bistatic SAR, where the transmitter and receiver are on separate platforms, is seen as a potential means of countering vulnerability. This

A. M. Horne; G. Yates

2002-01-01

2

Imaging synthetic aperture radar  

DOEpatents

A linear-FM SAR imaging radar method and apparatus to produce a real-time image by first arranging the returned signals into a plurality of subaperture arrays, the columns of each subaperture array having samples of dechirped baseband pulses, and further including a processing of each subaperture array to obtain coarse-resolution in azimuth, then fine-resolution in range, and lastly, to combine the processed subapertures to obtain the final fine-resolution in azimuth. Greater efficiency is achieved because both the transmitted signal and a local oscillator signal mixed with the returned signal can be varied on a pulse-to-pulse basis as a function of radar motion. Moreover, a novel circuit can adjust the sampling location and the A/D sample rate of the combined dechirped baseband signal which greatly reduces processing time and hardware. The processing steps include implementing a window function, stabilizing either a central reference point and/or all other points of a subaperture with respect to doppler frequency and/or range as a function of radar motion, sorting and compressing the signals using a standard fourier transforms. The stabilization of each processing part is accomplished with vector multiplication using waveforms generated as a function of radar motion wherein these waveforms may be synthesized in integrated circuits. Stabilization of range migration as a function of doppler frequency by simple vector multiplication is a particularly useful feature of the invention; as is stabilization of azimuth migration by correcting for spatially varying phase errors prior to the application of an autofocus process.

Burns, Bryan L. (Tijeras, NM); Cordaro, J. Thomas (Albuquerque, NM)

1997-01-01

3

Soviet oceanographic synthetic aperture radar (SAR) research  

Microsoft Academic Search

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

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

1991-01-01

4

Synthetic Aperture Radar Signals: Formulations and Approaches for Data Analysis.  

National Technical Information Service (NTIS)

This report discusses principles of synthetic aperture radar, properties of radar targets, characteristics of radar imagery, statistical analysis of radar imagery, and the application of modern data analysis.

A. B. Lucero P. Swerling L. Breiman

1975-01-01

5

Synthetic Aperture Helicopter Radar Experimental Evaluation Program.  

National Technical Information Service (NTIS)

The purpose of the program is to determine the resolution and MTI performance of a helicopter radar concept employing rotor tip mounted antennas and real-time digital synthetic aperture processing. The approach involves an experimental evaluation of the c...

N. F. Powell

1969-01-01

6

Synthetic Aperture Helicopter Radar Experimental Evaluation Program.  

National Technical Information Service (NTIS)

The document is the first Quarterly Report for the Synthetic Aperture Helicopter Radar Experimental Evaluation program; it covers work performed between 1 February and 30 April 1969. In scope the program is to determine the resolution and MTI performance ...

N. F. Powell

1969-01-01

7

Exploitation of synthetic aperture radar imagery  

Microsoft Academic Search

Synthetic aperture radars are now operational in both military and commercial applications. They provide detailed images of terrain, regardless of cloud cover and natural illumination, and in an electromagnetic spectrum not exploited by other high-resolution sensors. Because synthetic aperture radar is a microwave range-measuring sensor, the imagery is basically a two-dimensional record of the microwave backscattering strength of the terrain

L. C. Graham

1976-01-01

8

Performance of spaceborne bistatic synthetic aperture radar  

Microsoft Academic Search

This paper reports on a model developed for evaluating major system performance of a spaceborne bistatic synthetic aperture radar (SAR) for remote sensing applications. The procedure accounts for formation flying aspects. It is particularly aimed at comparison of monostatic and bistatic cases, and, as a test case, it is applied to study a novel configuration, based on a small satellite

ANTONIO MOCCIA; GIUSEPPE SALZILLO; MARCO D'ERRICO; GIANCARLO RUFINO; GIOVANNI ALBERTI

2005-01-01

9

Polarimetric SAR (Synthetic Aperture Radar) Antenna Characterization.  

National Technical Information Service (NTIS)

A procedure is described for obtaining the two-way polarimetric properties of a Synthetic aperture radar (SAR) antenna from one-way measurements in a compact antenna test range. The two-way properties are determined by involving reciprocity and computing ...

R. M. Barnes D. J. Blejer

1989-01-01

10

Synthetic Aperture Helicopter Radar Experimental Evaluation Program.  

National Technical Information Service (NTIS)

The object of the program is to determine the resolution and MTI performance of a helicopter radar concept employing rotor tip mounted antennas and real-time digital synthetic aperture processing. The present report describes and analyzes the results of s...

N. F. Powell

1969-01-01

11

Segmentation of polarimetric synthetic aperture radar data  

Microsoft Academic Search

A statistical image model is proposed for segmenting polarimetric synthetic aperture radar (SAR) data into regions of homogeneous and similar polarimetric backscatter characteristics. A model for the conditional distribution of the polarimetric complex data is combined with a Markov random field representation for the distribution of the region labels to obtain the posterior distribution. Optimal region labeling of the data

Eric J. M. Rignot; Rama Chellappa

1992-01-01

12

Wind energy mapping from synthetic aperture radar  

Microsoft Academic Search

Satellite based synthetic aperture radar (SAR) measurements from, e.g. ERS-1\\/ERS-2 can be used for wind energy mapping in coastal regions for wind mill siting. The SAR has clear advantages for high spatial resolution wind field mapping since it is independent of daylight and clouds. The spatial resolution of 30 m is sufficient as is the 100 km wide and several

Ola M. Johannessen; Heidi Espedal; E. Bjorgo

1999-01-01

13

Real-time beamforming synthetic aperture radar  

Microsoft Academic Search

This paper discusses the concept and design of a real-time Digital Beamforming Synthetic Aperture Radar (DBSAR) for airborne applications which can achieve fine spatial resolutions and wide swaths. The development of the DBSAR enhances important scientific measurements in Earth science, and serves as a prove-of-concept for planetary exploration missions. A unique aspect of DBSAR is that it achieves fine resolutions

Rafael Rincon; Peter Hildebrand; Lawrence Hilliard; Damon Bradley; Luko Krnan; Salman Sheikh; Jared Lucey

2006-01-01

14

Performance limits for Synthetic Aperture Radar.  

SciTech Connect

The performance of a Synthetic Aperture Radar (SAR) system depends on a variety of factors, many which are interdependent in some manner. It is often difficult to ''get your arms around'' the problem of ascertaining achievable performance limits, and yet those limits exist and are dictated by physics, no matter how bright the engineer tasked to generate a system design. This report identifies and explores those limits, and how they depend on hardware system parameters and environmental conditions. Ultimately, this leads to a characterization of parameters that offer optimum performance for the overall SAR system. For example, there are definite optimum frequency bands that depend on weather conditions and range, and minimum radar PRF for a fixed real antenna aperture dimension is independent of frequency. While the information herein is not new to the literature, its collection into a single report hopes to offer some value in reducing the ''seek time''.

Doerry, Armin Walter

2006-02-01

15

Aperture weighting technique for video synthetic aperture radar  

NASA Astrophysics Data System (ADS)

We present a technique for aperture weighting for use in video synthetic aperture radar (SAR). In video SAR the aperture required to achieve the desired cross range resolution typically exceeds the frame rate period. As a result, there can be a significant overlap in the collected phase history used to form consecutive images in the video. Video SAR algorithms seek to exploit this overlap to avoid unnecessary duplication of processing. When no aperture weighting or windowing is used one can simply form oversampled SAR images from the non-overlapping sub-apertures using coherent back projection (or other similar techniques). The resulting sub-aperture images may be coherently summed to produce a full resolution image. A simple approach to windowing for sidelobe control is to weight the sub-apertures during summation of the images. Our approach involves producing two or more weighted images for each sub-aperture which can be linearly combined to approximate any desired aperture weighting. In this method we achieve nearly the same sidelobe control as weighting the phase history data and forming a new image for each frame without losing the computation savings of the sub-aperture image combining approach.

Hawley, Robert W.; Garber, Wendy L.

2011-05-01

16

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

17

Synthetic aperture radar for disaster monitoring  

NASA Astrophysics Data System (ADS)

Synthetic Aperture Radar (SAR) is well known to afford imaging in darkness and through clouds, smoke, and other obscurants. As such, it is particularly useful for mapping and monitoring a variety of natural and man-made disasters. A portfolio of SAR image examples has been collected using General Atomics Aeronautical Systems, Inc.'s (GA-ASI's) Lynx® family of Ku-Band SAR systems, flown on both operational and test-bed aircraft. Images are provided that include scenes of flooding, ice jams in North Dakota, agricultural field fires in southern California, and ocean oil slicks from seeps off the coast of southern California.

Dunkel, R.; Saddler, R.; Doerry, A. W.

2011-05-01

18

Synthetic aperture radar processing with tiered subapertures  

SciTech Connect

Synthetic Aperture Radar (SAR) is used to form images that are maps of radar reflectivity of some scene of interest, from range soundings taken over some spatial aperture. Additionally, the range soundings are typically synthesized from a sampled frequency aperture. Efficient processing of the collected data necessitates using efficient digital signal processing techniques such as vector multiplies and fast implementations of the Discrete Fourier Transform. Inherent in image formation algorithms that use these is a trade-off between the size of the scene that can be acceptably imaged, and the resolution with which the image can be made. These limits arise from migration errors and spatially variant phase errors, and different algorithms mitigate these to varying degrees. Two fairly successful algorithms for airborne SARs are Polar Format processing, and Overlapped Subaperture (OSA) processing. This report introduces and summarizes the analysis of generalized Tiered Subaperture (TSA) techniques that are a superset of both Polar Format processing and OSA processing. It is shown how tiers of subapertures in both azimuth and range can effectively mitigate both migration errors and spatially variant phase errors to allow virtually arbitrary scene sizes, even in a dynamic motion environment.

Doerry, A.W. [Sandia National Labs., Albuquerque, NM (United States). Synthetic Aperture Radar Dept.

1994-06-01

19

Segmentation of polarimetric synthetic aperture radar data.  

PubMed

A statistical image model is proposed for segmenting polarimetric synthetic aperture radar (SAR) data into regions of homogeneous and similar polarimetric backscatter characteristics. A model for the conditional distribution of the polarimetric complex data is combined with a Markov random field representation for the distribution of the region labels to obtain the posterior distribution. Optimal region labeling of the data is then defined as maximizing the posterior distribution of the region labels given the polarimetric SAR complex data (maximum a posteriori (MAP) estimate). Two procedures for selecting the characteristics of the regions are then discussed. Results using real multilook polarimetric SAR complex data are given to illustrate the potential of the two selection procedures and evaluate the performance of the MAP segmentation technique. It is also shown that dual polarization SAR data can yield segmentation resultS similar to those obtained with fully polarimetric SAR data. PMID:18296163

Rignot, E; Chellappa, R

1992-01-01

20

Multistatic synthetic aperture radar image formation.  

PubMed

In this paper, we consider a multistatic synthetic aperture radar (SAR) imaging scenario where a swarm of airborne antennas, some of which are transmitting, receiving or both, are traversing arbitrary flight trajectories and transmitting arbitrary waveforms without any form of multiplexing. The received signal at each receiving antenna may be interfered by the scattered signal due to multiple transmitters and additive thermal noise at the receiver. In this scenario, standard bistatic SAR image reconstruction algorithms result in artifacts in reconstructed images due to these interferences. In this paper, we use microlocal analysis in a statistical setting to develop a filtered-backprojection (FBP) type analytic image formation method that suppresses artifacts due to interference while preserving the location and orientation of edges of the scene in the reconstructed image. Our FBP-type algorithm exploits the second-order statistics of the target and noise to suppress the artifacts due to interference in a mean-square sense. We present numerical simulations to demonstrate the performance of our multistatic SAR image formation algorithm with the FBP-type bistatic SAR image reconstruction algorithm. While we mainly focus on radar applications, our image formation method is also applicable to other problems arising in fields such as acoustic, geophysical and medical imaging. PMID:20051343

Krishnan, V; Swoboda, J; Yarman, C E; Yazici, B

2009-12-31

21

Low-cost airborne synthetic aperture radar  

NASA Astrophysics Data System (ADS)

This paper describes the rudiments of a design and implementation approach that will produce low-cost and quick turnaround airborne synthetic aperture radar (SAR) systems including designs for remotely piloted vehicles (RPVs). The concept is based on strict adherence to a discipline of simplicity in application boundary definition, the corresponding design that follows, extension of this core of simplicity through the build and test cycle and continuation of this theme when system modification and upgrades are considered. As this paper points out, the tenets for low-cost development of SAR systems are not new. Indeed, several such developments validate the guidelines advocated in this paper. The crux of this end-to-end development simplicity is to minimize the functions assigned to the on-board radar systems, transferring them to less expensive ground-based information processing assets that will perform motion compensation, image signal processing and target identification/classification. This cause limitations in the applications sheath of the airborne system, but in many cases this is an acceptable compromise.

McCandless, Samuel W.; Huxtable, Barton D.; Jackson, Christopher R.

1997-06-01

22

Difficulties in superresolving synthetic aperture radar images  

NASA Astrophysics Data System (ADS)

The ability to resolve Synthetic Aperture Radar (SAR) images to finer resolutions than the system bandwidths classically allow is a tantalizing prospect. Seemingly superresolution offers something for nothing, or at least something better than the system was designed for if only we process enough or right. Over the years this has proved to be a rather popular area of investigation, generating a wide variety of algorithms and corresponding claims of performance. Nevertheless, the literature on the fundamental underlying principles of superresolution as applied to SAR has been rather anemic. This paper addresses the following questions: What exactly is superresolution? and What is not really superresolution, but perhaps more aptly described as image enhancement? Is true superresolution possible? and to what degree? What constrains superresolution? and very importantly, How should we objectively test whether an image is in fact superresolved? Whereas superresolution concepts offer the potential of resolution beyond the classical limit, this great promise has not generally been realized. That is not to say that many reported algorithms have no useful effect on images. True superresolution is defined herein as the recovery of true scene spectrum, that allows more accurate scene rendering. The analytical basis for superresolution theory is outlined, and the application to SAR is then investigated as an operator inversion problem, which is generally ill posed. Noise inherent in radar data tends to severely inhibit significant enhancement of image resolution. A criterion for judging superresolution processing of an image is presented.

Doerry, Armin W.; Dickey, Fred M.; Romero, Louis A.; DeLaurentis, John M.

2002-08-01

23

Ionospheric Irregularities and Their Potential Impact on Synthetic Aperture Radars.  

National Technical Information Service (NTIS)

Accumulating data are making it increasingly evident that major plasma irregularities populate substantial portions of the ionosphere. In contrast with these findings, satellite-borne synthetic aperture radar (SAR) systems tacitly assume that the ionosphe...

E. P. Szuszczewicz M. Singh P. Rodriguez S. Mango

1983-01-01

24

Gabor Segmentation of High Resolution Synthetic Aperture Radar Imagery.  

National Technical Information Service (NTIS)

This thesis investigates the use of Gabor filters and a radial basis function (RBF) network for segmentation of high resolution (1 foot by 1 foot) synthetic aperture radar (SAR) imagery. Processing involved correlation between the SAR imagery and Gabor fu...

M. A. Hazlett

1991-01-01

25

Automated Terrain Classification Using Polarimetric Synthetic Aperture Radar  

Microsoft Academic Search

last 30 years, synthetic aperture radar (SAR) has been established as a primary remote imaging instrument for Earth resource monitoring, planetary exploration, and military applications. SAR is an active sensor, illuminating targets with electromagnetic waves that can penetrate through cloud coverage. Consequently, it has all-weather and day\\/night imaging capabilities. Polarimetric synthetic aperture radar (PolSAR), also known as quad-polarization SAR, measures

J. S. Lee; M. R. Grunes; E. Pottier

26

Capabilities of Bistatic Synthetic Aperture Radar for Covert Battlefield Surveillance.  

National Technical Information Service (NTIS)

The capabilities of bistatic synthetic aperture radar to provide rapid update rate, real-time covert radar surveillance to the military user are considered. The spatial resolution and sensitivity achievable from a tactical system using a small RPV-borne t...

C. D. Hall

1989-01-01

27

Reconnaissance with ultra wideband UHF synthetic aperture radar  

Microsoft Academic Search

The author addresses the problem of detecting and identifying stationary and moving targets with foliage penetrating UHF synthetic aperture radar (SAR). The role of a target's coherent SAR signature, which varies with the radar's frequency and aspect angle, in forming the Fourier space of the SAR signal is analyzed. The resultant relationship is the basis of an algorithm which, after

MEHRDAD SOUMEKH

1995-01-01

28

Ionospheric and tropospheric effects on synthetic aperture radar performance  

Microsoft Academic Search

Synthetic aperture radar (SAR) produces high-resolution images of the Earth's surface (and subsurface, under some conditions) by coherently processing the returns from a pulsed radar. It is an active sensor, hence is not dependent on natural illumination for its operation, and the comparative transparency of the atmosphere at centimetre wavelengths allows penetration of clouds and haze. SAR therefore offers considerable

S. Quegan; J. Lamont

1986-01-01

29

Autonomous system for initializing synthetic aperture radar seeker acquisition  

Microsoft Academic Search

A method is described of guiding a missile having an active seeker including a synthetic aperture radar operating in a squint mode to a target aircraft having a search radar therein the maximum range of active seeker acquisition being within said missile's maneuver capability to intercept, and the maximum range of active seeker acquisition not exceeding the capability of the

1993-01-01

30

Autofocusing of (inverse) synthetic aperture radar for motion compensation  

Microsoft Academic Search

Ground imaging from an airborne synthetic aperture radar (SAR) and conversely aircraft imaging from a ground based radar (ISAR) require the knowledge of the motion of the antenna relative to the target, with an accuracy of a fraction of the wavelength upon a time span of seconds. This information is not necessarily directly available from navigation\\/tracking data and must be

H. M. J. Cantalloube; C. E. Nahum

1996-01-01

31

Synthetic aperture radar imaging with motion estimation and autofocus  

NASA Astrophysics Data System (ADS)

We introduce from first principles a synthetic aperture radar (SAR) imaging and target motion estimation method that is combined with compensation for radar platform trajectory perturbations. The main steps of the method are (a) segmentation of the data into properly calibrated small apertures, (b) motion or platform trajectory perturbation estimation using the Wigner transform and the ambiguity function of the data in a complementary way and (c) combination of small aperture estimates and construction of high-resolution images over wide apertures. The analysis provides quantitative criteria for implementing the aperture segmentation and the parameter estimation process. X-band persistent surveillance SAR is a specific application that is covered by our analysis. Detailed numerical simulations illustrate the robust applicability of the theory and validate the theoretical resolution analysis.

Borcea, L.; Callaghan, T.; Papanicolaou, G.

2012-04-01

32

Capabilities of bistatic synthetic aperture radar for covert battlefield surveillance  

NASA Astrophysics Data System (ADS)

The capabilities of bistatic synthetic aperture radar to provide rapid update rate, real time covert radar surveillance to the military user are considered. The spatial resolution and sensitivity achievable from a tactical system using a small remotely piloted vehicle-borne transmitter and a static ground based receiver are discussed and the relative advantages of two distinct types of emission modulation are examined. Finally, a number of areas requiring further study are identified.

Hall, C. D.

1989-10-01

33

Bistatic Synthetic Aperture Radar Imaging for Arbitrary Flight Trajectories  

Microsoft Academic Search

In this paper, we present an analytic, filtered backprojection (FBP) type inversion method for bistatic synthetic aperture radar (BISAR). We consider a BISAR system where a scene of interest is illuminated by electromagnetic waves that are transmitted, at known times, from positions along an arbitrary, but known, flight trajectory and the scattered waves are measured from positions along a different

Can Evren Yarman; Birsen Yazici; Margaret Cheney

2008-01-01

34

Focusing bistatic synthetic aperture radar using dip move out  

Microsoft Academic Search

The appearance of new synthetic aperture radar (SAR) acquisition techniques based on opportunity sources enhances interest in bistatic geometries. In seismic data acquisition, each source is currently accompanied by up to 10 000 receivers, and in the last two decades, the bistatic geometry has been carefully studied by scores of authors. Rather then introducing new focusing techniques, within the first-order

D. D'Aria; A. Monti Guarnieri; F. Rocca

2004-01-01

35

Multi-static synthetic aperture radar image formation  

Microsoft Academic Search

In this paper, we consider a multi-static synthetic aperture radar (SAR) imaging scenario where a swarm of airborne antennas, some of which are transmitting, receiving or both, are traversing arbitrary flight trajectories and transmitting arbitrary waveforms without any form of multiplexing. The received signal at each receiving antenna may be interfered by the scattered signals from multiple transmitters and the

V. P. Krishnan; J. Swoboda; C. E. Yarman; B. Yazici

2009-01-01

36

Extension of Synthetic Aperture Radar Seeker Systems to Circular Trajectories  

Microsoft Academic Search

Standard Synthetic Aperture Radars (SAR) have provided high resolution ground maps for the last 20 years. However, they require a horizontal linear trajectory which is a serious limitation in many applications. This dissertation is concerned with the extension of SAR to nonlinear trajectories. The limitations of the standard SAR are due to range walk and doppler bias. These problems are

Jong Gyu Kim

1989-01-01

37

Clutter statistics along edge features in synthetic aperture radar imagery  

Microsoft Academic Search

The K-distribution model for clutter over distributed targets in Synthetic Aperture Radar (SAR) images is extended to include clutter along edges and thin linear targets. The physical mechanisms generating edge features are analyzed. Assuming a boxcar system response, the detected field from a resolution cell along an edge is shown to be expressible in terms of sums of random contributions

R. G. Caves; P. J. Harley; S. Quegan

1995-01-01

38

Internal Calibration Of The Radarsat Synthetic Aperture Radar  

Microsoft Academic Search

Accurate radiometric calibration is an essential part of any operational synthetic aperture radar (sAR) system. In a full calibration plan, internal calibration measurements of system variations are needed to update the external calibration operations using ground calibration sites. This paper describes the internal calibration hardware and operations that have been defined for the Radarsat SAR system. The operational flexibility that

Anthony P. Luscombe

1990-01-01

39

Synthetic aperture radar performance in detecting shallow buried targets  

NASA Astrophysics Data System (ADS)

A radar performance model is developed to analyze the capability of wide-band, high- resolution airborne synthetic aperture radar detection of shallow buried targets such as metallic M-20 mines and utility cables. Feasible target detection depths are estimated as functions of radar polarization, depression angle, and frequency in UHF and VHF bands. The performance model has incorporated wave propagation loss, due to wave attenuation inside the soil medium, wave reflection, and divergence at the air-ground interface, radar target cross section estimation via method of moments, radar interference, including both ambient man-made noise and empirical backscattered ground surface clutter, which is determined from existing clutter measurements for bare soil, rocks, and desert terrain.

Jao, Jen King; Lee, Check F.; Merchant, Barbara L.

1996-05-01

40

Space-surface bistatic synthetic aperture radar - prospective and problems  

Microsoft Academic Search

The paper introduced a feasibility analysis of a synthetic aperture radar (SAR) with novel architecture. Two essential peculiarities are discussed: the system configuration with a moving transmitter when the receiver is stationary and noncooperative transmitters utilization for the system. The system is named space-surface BSAR or S-SBSAR. The system analysis confirms its feasibility. S-S SAR could find numerous applications where

M. Cherniakov

2002-01-01

41

Beaconless search and rescue using polarimetric synthetic aperture radar  

Microsoft Academic Search

In developing a beaconless search and rescue capability to quickly locate small aircraft that have crashed in remote areas, NASA’s Search and Rescue (S&R) Program brings together advanced polarimetric synthetic aperture radar processing, field and laboratory tests, and state-of-the-art automated target detection algorithms. This paper provides the status of this program, which began with experiments conducted in concert with the

Samuel W. McCandless; Barton D. Huxtable; Arthur W. Mansfield; Ronald Wallace; Rudolph Larsen; Houra Rais

1996-01-01

42

Unexploded ordnance detection experiments using ultrawideband synthetic aperture radar  

Microsoft Academic Search

The Army Research Laboratory (ARL) has several technology development programs that are evaluating the use of ultra- wideband synthetic aperture radar (UWB SAR) to detect and locate targets that are subsurface or concealed by foliage. Under these programs, a 1-GHz-bandwidth, low-frequency, fully polarimetric UWB SAR instrumentation system was developed to collect the data needed to support foliage and ground- penetrating

Clyde C. Deluca; Vincent Marinelli; Marc Ressler; Tuan Ton

1998-01-01

43

Ionospheric effects on synthetic aperture radar at VHF  

SciTech Connect

Synthetic aperture radars (SAR) operated from airplanes have been used at VHF because of their enhanced foliage and ground penetration compared to radars operated at UHF. A satellite-borne VHF SAR would have considerable utility but in order to operate with high resolution it would have to use both a large relative bandwidth and a large aperture. The presence of the ionosphere in the propagation path of the radar will cause a deterioration of the imaging because of dispersion over the bandwidth and group path changes in the imaged area over the collection aperture. In this paper we present calculations of the effects of a deterministic ionosphere on SAR imaging for a radar operated with a 100 MHz bandwidth centered at 250 MHz and over an angular aperture of 23{degrees}. The ionosphere induces a point spread function with an approximate half-width of 150 m in the slant-range direction and of 25 m in the cross-range direction compared to the nominal resolution of 1.5 m in both directions.

Fitzgerald, T.J.

1997-02-01

44

Optimum frequency for subsurface-imaging synthetic-aperture radar  

SciTech Connect

A subsurface-imaging synthetic-aperture radar (SISAR) has potential for application in areas as diverse as non-proliferation programs for nuclear weapons to environmental monitoring. However, most conventional synthetic-aperture radars operate at higher microwave frequencies which do not significantly penetrate below the soil surface. This study attempts to provide a basis for determining optimum frequencies and frequency ranges which will allow synthetic-aperture imaging of buried targets. Since the radar return from a buried object must compete with the return from surface clutter, the signal-to-clutter ratio is an appropriate measure of performance for a SISAR. A parameter-based modeling approach is used to model the complex dielectric constant of the soil from measured data obtained from the literature. Theoretical random-surface scattering models, based on statistical solutions to Maxwell`s equations, are used to model the clutter. These models are combined to estimate the signal-to-clutter ratio for canonical targets buried in several soil configurations. Initial results indicate that the HF spectrum (3--30 MHz), although it could be used to detect certain targets under some conditions, has limited practical value for use with SISAR, while the upper vhf through uhf spectrum ({approximately}100 MHz--1 GHz) shows the most promise for a general purpose SISAR system. Recommendations are included for additional research.

Brock, B.C.; Patitz, W.E.

1993-05-01

45

Optimum frequency for subsurface-imaging synthetic-aperture radar  

SciTech Connect

A subsurface-imaging synthetic-aperture radar (SISAR) has potential for application in areas as diverse as non-proliferation programs for nuclear weapons to environmental monitoring. However, most conventional synthetic-aperture radars operate at higher microwave frequencies which do not significantly penetrate below the soil surface. This study attempts to provide a basis for determining optimum frequencies and frequency ranges which will allow synthetic-aperture imaging of buried targets. Since the radar return from a buried object must compete with the return from surface clutter, the signal-to-clutter ratio is an appropriate measure of performance for a SISAR. A parameter-based modeling approach is used to model the complex dielectric constant of the soil from measured data obtained from the literature. Theoretical random-surface scattering models, based on statistical solutions to Maxwell's equations, are used to model the clutter. These models are combined to estimate the signal-to-clutter ratio for canonical targets buried in several soil configurations. Initial results indicate that the HF spectrum (3--30 MHz), although it could be used to detect certain targets under some conditions, has limited practical value for use with SISAR, while the upper vhf through uhf spectrum ([approximately]100 MHz--1 GHz) shows the most promise for a general purpose SISAR system. Recommendations are included for additional research.

Brock, B.C.; Patitz, W.E.

1993-05-01

46

Time-frequency analysis of synthetic aperture radar signals  

SciTech Connect

Synthetic aperture radar (SAR) has become an important tool for remote sensing of the environment. SAR is a set of digital signal processing algorithms that are used to focus the signal returned to the radar because radar systems in themselves cannot produce the high resolution images required in remote sensing applications. To reconstruct an image, several parameters must be estimated and the quality of output image depends on the degree of accuracy of these parameters. In this thesis, we derive the fundamental SAR algorithms and concentrate on the estimation of one of its critical parameters. We show that the common technique for estimating this particular parameter can sometimes lead to erroneous results and reduced quality images. We also employ time-frequency analysis techniques to examine variations in the radar signals caused by platform motion and show how these results can be used to improve output image quality.

Johnston, B.

1996-08-01

47

Landmine detection using ground penetrating radar and polarimetric Synthetic Aperture Radar  

Microsoft Academic Search

In this paper, the data processing based on polarimetric features extraction from Synthetic Aperture Radar (SAR) processed data is discussed. For this purpose, fully polarimetric data were collected using the ultra-wideband Ground Penetrating Radar (GPR) and quad ridged horn antenna. The measurement of plastic landmine, metallic pipe and rocks buried in the sand was carried out so that three dimensional

Vaclav Kabourek; Petr Cerny; Milos Mazanek

2011-01-01

48

Ground Penetrating Radar Image Focusing using Frequency-Wavenumber based Synthetic Aperture Radar Technique  

Microsoft Academic Search

In the classical B-Scan ground penetrating radar (GPR), the collected data represented in the image domain, depict undesired hyperbolic effects and have low resolution features. In this work, we present frequency-wavenumber based Synthetic Aperture Radar (SAR) focusing technique to solve this problem. The formulation of algorithm is given and applied to both the simulation data obtained by a physical optics

Enes Yigit; Sevket Demirci; Caner Ozdemir

2007-01-01

49

Synthetic aperture radar imaging of a two-story building  

NASA Astrophysics Data System (ADS)

This paper investigates the expected performance of a ground-based, multi-story building imaging radar system through far-field and near-field computer models. We created a 3-D computer-aided design model of a complex two-story building, simulated the radar response from this complex structure for various geometries and applied synthetic aperture radar image formation algorithms consistent with the simulation scenarios. In this study, we employed the Finite Difference Time Domain method and the Xpatch software to compute the radar signatures. The numerical results give a better understanding of the phenomenology of the scattering and imaging processes and show that relying solely on the far-field scattering data at one elevation angle is not sufficient to obtain the multi-story building layout. Multiple elevation angle views are required in order to determine the location of imaged objects in the vertical direction. Xpatch simulation results in a near-field strip-map configuration suggest a way to achieve this goal within the constraints of a ground-based radar system.

Le, Calvin; Dogaru, Traian

2012-05-01

50

Signal based motion compensation for synthetic aperture radar  

SciTech Connect

The purpose of the Signal Based Motion Compensation (SBMC) for Synthetic Aperture Radar (SAR) effort is to develop a method to measure and compensate for both down range and cross range motion of the radar in order to provide high quality focused SAR imagery in the absence of precision measurements of the platform motion. Currently SAR systems require very precise navigation sensors for motion compensation. These sensors are very expensive and are often supplied in pairs for reliability. In the case of GPS they can be jammed, further degrading performance. This makes for a potentially very expensive and possibly vulnerable SAR system. SBMC can eliminate or reduce the need for these expensive navigation sensors thus reducing the cost of budget minded SAR systems. The results on this program demonstrated the capability of the SBMC approach.

John Kirk

1999-06-07

51

Bistatic synthetic aperture radar imaging for arbitrary flight trajectories.  

PubMed

In this paper, we present an analytic, filtered backprojection (FBP) type inversion method for bistatic synthetic aperture radar (BISAR). We consider a BISAR system where a scene of interest is illuminated by electromagnetic waves that are transmitted, at known times, from positions along an arbitrary, but known, flight trajectory and the scattered waves are measured from positions along a different flight trajectory which is also arbitrary, but known. We assume a single-scattering model for the radar data, and we assume that the ground topography is known but not necessarily flat. We use microlocal analysis to develop the FBP-type reconstruction method. We analyze the computational complexity of the numerical implementation of the method and present numerical simulations to demonstrate its performance. PMID:18229806

Yarman, Can Evren; Yazici, Birsen; Cheney, Margaret

2008-01-01

52

A high resolution 2D omnidirectional synthetic aperture radar scanner at K band  

Microsoft Academic Search

In this paper a K-band 360° 2D imaging radar utilizing a synthetic aperture scanning principle is introduced. A small omnidirectional antenna is mounted on a rotating platform to create a circular synthetic aperture. Based on a broadband holographic reconstruction principle a high resolution 360° 2D image is calculated after each turn of the platform. The size of the synthetic aperture

Faiza Ali; Alexander Urban; Martin Vossiek

2010-01-01

53

A comparison of spotlight synthetic aperture radar image formation techniques  

SciTech Connect

Spotlight synthetic aperture radar images can be formed from the complex phase history data using two main techniques: (1) polar-to-cartesian interpolation followed by two-dimensional inverse Fourier transform (2DFFT), and (2) convolution backprojection (CBP). CBP has been widely used to reconstruct medical images in computer aided tomography, and only recently has been applied to form synthetic aperture radar imagery. It is alleged that CBP yields higher quality images because (1) all the Fourier data are used and (2) the polar formatted data is used directly to form a 2D Cartesian image and therefore 2D interpolation is not required. This report compares the quality of images formed by CBP and several modified versions of the 2DFFT method. We show from an image quality point of view that CBP is equivalent to first windowing the phase history data and then interpolating to an exscribed rectangle. From a mathematical perspective, we should expect this conclusion since the same Fourier data are used to form the SAR image. We next address the issue of parallel implementation of each algorithm. We dispute previous claims that CBP is more readily parallelizable than the 2DFFT method. Our conclusions are supported by comparing execution times between massively parallel implementations of both algorithms, showing that both experience similar decreases in computation time, but that CBP takes significantly longer to form an image.

Knittle, C.D.; Doren, N.E.; Jakowatz, C.V.

1996-10-01

54

Compact, autonomous, multi-mission synthetic aperture radar  

NASA Astrophysics Data System (ADS)

The utilization of unmanned aerial systems (UASs) for intelligence, surveillance and reconnaissance (ISR) applications continues to increase and unmanned systems have become a critical asset in current and future battlespaces. With the development of medium-to-low altitude, rapidly deployable aircraft platforms, the ISR community has seen an increasing push to develop ISR sensors and systems with real-time mission support capabilities. This paper describes the design and development of the RASAR (Real-time, Autonomous, Synthetic Aperture Radar) sensor system and presents demonstration flight test results. RASAR is a modular, multi-band (L and X) synthetic aperture radar (SAR) imaging sensor designed for self-contained, autonomous, real-time operation with mission flexibility to support a wide range of ISR needs within the size, weight and power constraints of Group III UASs. SAR waveforms are generated through direct digital synthesis enabling arbitrary waveform notching to enable operations in cluttered RF environments. RASAR is capable of simultaneous dual-channel receive to enable polarization based target discrimination. The sensor command and control and real-time image formation processing are designed to enable integration of RASAR into larger, multi-intelligence system of systems. The multi-intelligence architecture and a demonstration of real-time autonomous cross-cueing of a separate optical sensor will be presented.

Walls, Thomas J.; Wilson, Michael L.; Madsen, David; Knight, Chad; Jensen, Mark D.; Partridge, Darin C.; Addario, Mike

2013-05-01

55

Three-dimensional synthetic aperture radar imaging of a fir tree: first results  

Microsoft Academic Search

A three-dimensional (3D) inverse synthetic aperture radar (ISAR) imaging experiment on a fir tree is described. Radar measurements on single trees under laboratory conditions can be performed in the scatterometric, with no aperture synthesis, and in the imaging (SAR) mode. Imaging an entire tree requires the use of a wideband radar and a two-dimensional (2D) aperture which may be synthetic

Joaquim Fortuny; A. J. Sieber

1999-01-01

56

Synthetic aperture radar and interferometry development at Sandia National Laboratories  

SciTech Connect

Environmental monitoring, earth-resource mapping, and military systems require broad-area imaging at high resolutions. Many times the imagery must be acquired in inclement weather or during night as well as day. Synthetic aperture radar (SAR) provides such a capability. SAR systems take advantage of the long-range propagation characteristics of radar signals and the complex information processing capability of modern digital electronics to provide high resolution imagery. SAR complements photographic and other optical imaging capabilities because of the minimum constrains on time-of-day and atmospheric conditions and because of the unique responses of terrain and cultural targets to radar frequencies. Interferometry is a method for generating a three-dimensional image of terrain. The height projection is obtained by acquiring two SAR images from two slightly differing locations. It is different from the common method of stereoscopic imaging for topography. The latter relies on differing geometric projections for triangulation to define the surface geometry whereas interferometry relies on differences in radar propagation times between the two SAR locations. This paper presents the capabilities of SAR, explains how SAR works, describes a few SAR applications, provides an overview of SAR development at Sandia, and briefly describes the motion compensation subsystem.

NONE

1993-04-01

57

Synthetic-Aperture Radar Based on Nonsinusoidal Functions: III-Beam- Forming by Means of the Doppler Effect  

Microsoft Academic Search

Synthetic-aperture radar based on nonsinusoidal functions was discussed in two previous papers [1]. The Doppler effect was not used to produce the synthetic aperture, even though the conventional synthetic-aperture radar would not work without it. This paper shows how the Doppler effect of a nonsinusoidal wave can be used to produce a synthetic aperture. The main result is that the

Henning Harmuth

1979-01-01

58

Use of Synthetic Aperture Radar in Cold Climate Flood Response  

NASA Astrophysics Data System (ADS)

The purpose of this study was to investigate the usefulness of Synthetic Aperture Radar (SAR) satellite images during a cold climate disaster response event. There were 15 European Space Agency (ESA) Advanced Synthetic Aperture Radar ASAR scenes, five Japan Aerospace Exploration Agency (JAXA) Phased Array type L-band Synthetic Aperture Radar (PALSAR) scenes, one RADARSAT2 scene, and numerous optical sensor data. These data were primarily used to indentify floodwater inundation polygons and flow vectors. However, in cold climate flooding, there are complicating factors such as frazil ice, ice jams, and snow-covered, frozen flood waters that are not present during warmer flooding events. The imagery was obtained through the International Charter "Space and Major Disasters.” The Charter aims at providing a unified system of space data acquisition and delivery to those affected by natural or man-made disasters through Authorized Users. Each member agency has committed resources to support the provisions of the Charter, and thus is helping to mitigate the effects of disasters on human life and property. On 25 March 2009, the Charter was activated in response to the flooding along the Red River of the North in the states of North Dakota and Minnesota of the United States. The delivery time of a single SAR scene from a Charter participant was less than 12 hours from the time of acquisition. This expedited service allowed additional time for creating image-based derivations, field checking and delivery to a decision maker or emergency responder. SAR-derived data sets include identification of river ice and saturated ground conditions. This data could be provided to experts in river ice engineering for use in the development of plans to reduce ice jamming, its effect on water levels and additional stresses on river infrastructure. During disaster response applications, SAR data was found to very useful in indentifying open water and the front of ice jams. Using a river mask from historical imagery, the SAR data helped to confirm if areas behind flood protection were, in fact, frozen flood water or snow-covered field. This analysis would benefit from future research efforts because optical sensor data is of little use in this application.

Yarbrough, L. D.

2009-12-01

59

Automatic aircraft landing using interferometric inverse synthetic aperture radar imaging.  

PubMed

This paper presents an interferometric processing of an aircraft's monostatic and bistatic inverse synthetic aperture radar (ISAR) signatures for automatic landing. The aircraft's squint angle in this ISAR imaging problem is near 90 degrees . We show that this extreme squint angle does not pose any problem for the ISAR Fourier-based (wavefront) reconstruction algorithm. In fact, the aircraft can be imaged accurately, and without any erroneous shifts in the cross-range domain, within the imposed theoretical resolution. Moreover, the algorithm is accurate enough such that one can utilize the phase of the ISAR monostatic and bistatic measurements for interferometric processing. The resultant interferometric ISAR image is used to detect undesirable rotations in the aircraft's orientation. PMID:18285222

Soumekh, M

1996-01-01

60

Moving receive beam method and apparatus for synthetic aperture radar  

DOEpatents

A method and apparatus for improving the performance of Synthetic Aperture Radar (SAR) systems by reducing the effect of "edge losses" associated with nonuniform receiver antenna gain. By moving the receiver antenna pattern in synchrony with the apparent motion of the transmitted pulse along the ground, the maximum available receiver antenna gain can be used at all times. Also, the receiver antenna gain for range-ambiguous return signals may be reduced, in some cases, by a large factor. The beam motion can be implemented by real-time adjustment of phase shifters in an electronically-steered phased-array antenna or by electronic switching of feed horns in a reflector antenna system.

Kare, Jordin T. (San Ramon, CA)

2001-01-01

61

The Rapid Terrain Visualization interferometric synthetic aperture radar sensor.  

SciTech Connect

The Rapid Terrain Visualization interferometric synthetic aperture radar was designed and built at Sandia National Laboratories as part of an Advanced Concept Technology Demonstration (ACTD) to 'demonstrate the technologies and infrastructure to meet the Army requirement for rapid generation of digital topographic data to support emerging crisis or contingencies.' This sensor is currently being operated by Sandia National Laboratories for the Joint Precision Strike Demonstration (JPSD) Project Office to provide highly accurate digital elevation models (DEMs) for military and civilian customers, both inside and outside of the United States. The sensor achieves better than DTED Level IV position accuracy in near real-time. The system is being flown on a deHavilland DHC-7 Army aircraft. This paper outlines some of the technologies used in the design of the system, discusses the performance, and will discuss operational issues. In addition, we will show results from recent flight tests, including high accuracy maps taken of the San Diego area.

Graham, Robert H.; Hensley, William Heydon, Jr.; Bickel, Douglas Lloyd

2003-07-01

62

Adaptive resource allocation for synthetic aperture radars under resource constraints  

NASA Astrophysics Data System (ADS)

In along-track synthetic aperture radar systems, measurements from multiple phase centers can be used to remove bright stationary clutter in order to detect and estimate moving targets in the scene. The effectiveness of this procedure can be improved by increasing the number of antennas in the system. However, due to computational and communication constraints, it may be prohibitive to use a large number of antennas. In this work, an efficient resource allocation policy is provided to exploit sparsity in the scene, namely that there are few targets relative to the size of the scene. It is shown that even with limited computational resources, one can have significant estimation and computational gains over non-adaptive strategies. Moreover, the performance of the adaptive strategy approaches that of an oracle policy as the number of the stages grows large.

Newstadt, Gregory E.; Zelnio, Edmund G.; Hero, Alfred O.

2013-05-01

63

Ionospheric irregularities and their potential impact on synthetic aperture radars  

NASA Astrophysics Data System (ADS)

Accumulating data are making it increasingly evident that major plasma irregularities populate substantial portions of the ionosphere. In contrast with these findings, satellite-borne synthetic aperture radar (SAR) systems tacitly assume that the ionosphere is uniformly layered and unchanging under the orbiting SAR. Analysis of plasma irregularity structures measured directly on the S3-4 satellite shows that this assumption is readily violated near the nighttime equator during the occurrence of spread F and at high-latitudes on a nearly 24-hour basis. The irregularities can be very intense, covering scale sizes from meters to hundreds of kilometers. Associated along-track phase path calculations point to a potentially serious problem in SAR imaging integrity in restricted ionospheric space-time domains.

Szuszczewicz, E. P.; Rodriguez, P.; Mango, S.; Singh, M.

1983-10-01

64

Bistatic synthetic-aperture radar imaging of rotating objects  

Microsoft Academic Search

The imaging properties of a focused radar aperture synthesized by object rotation are considered. The ring-shaped aperture synthesized by the object rotation can provide high-resolution two-dimensional imaging using only monochromatic irradiation. The case of monochromatic irradiation is extended to the polychromatic case and to equivalent bistatic geometries. These techniques offer practical methods for radar imaging of rotating objects with scattering

D. Mensa; G. Heidbreder

1982-01-01

65

Fourier-domain multichannel autofocus for synthetic aperture radar.  

PubMed

Synthetic aperture radar (SAR) imaging suffers from image focus degradation in the presence of phase errors in the received signal due to unknown platform motion or signal propagation delays. We present a new autofocus algorithm, termed Fourier-domain multichannel autofocus (FMCA), that is derived under a linear algebraic framework, allowing the SAR image to be focused in a noniterative fashion. Motivated by the mutichannel autofocus (MCA) approach, the proposed autofocus algorithm invokes the assumption of a low-return region, which generally is provided within the antenna sidelobes. Unlike MCA, FMCA works with the collected polar Fourier data directly and is capable of accommodating wide-angle monostatic SAR and bistatic SAR scenarios. Most previous SAR autofocus algorithms rely on the prior assumption that radar's range of look angles is small so that the phase errors can be modeled as varying along only one dimension in the collected Fourier data. And, in some cases, implicit assumptions are made regarding the SAR scene. Performance of such autofocus algorithms degrades if the assumptions are not satisfied. The proposed algorithm has the advantage that it does not require prior assumptions about the range of look angles, nor characteristics of the scene. PMID:21606028

Liu, Kuang-Hung; Munson, David C

2011-05-19

66

Synthetic-aperture radar imaging through dispersive media  

NASA Astrophysics Data System (ADS)

In this paper we develop a method for synthetic-aperture radar (SAR) imaging through a dispersive medium. We consider the case when the sensor and scatterers are embedded in a known homogeneous dispersive material, the scene to be imaged lies on a known surface and the radar antenna flight path is an arbitrary but known smooth curve. The scattering is modeled using a linearized (Born) scalar model. We assume that the measurements are polluted with additive noise. Furthermore, we assume that we have prior knowledge about the power-spectral densities of the scene and the noise. This leads us to formulate the problem in a statistical framework. We develop a filtered-back-projection imaging algorithm in which we choose the filter according to the statistical properties of the scene and noise. We present numerical simulations for a case where the scene consists of point-like scatterers located on the ground, and demonstrate how the ability to resolve the targets depends on a quantity which we call the noise-to-target ratio. In our simulations, the dispersive material is modeled with the Fung-Ulaby equations for leafy vegetation. However, the method is also applicable to other dielectric materials where the dispersion is considered relevant in the frequency range of the transmitted signals.

Varslot, Trond; Héctor Morales, J.; Cheney, Margaret

2010-02-01

67

Correlation of oceanographic signatures appearing in synthetic aperture radar and interferometric synthetic aperture radar imagery with in situ measurements  

NASA Astrophysics Data System (ADS)

Synthetic aperture radar (SAR) imagery collected over the continental shelf near Cape Hatteras, N. C., is analyzed in conjunction with shipboard hydrographic and current measurements. The SAR measurements were made over a 2-hour period on June 20, 1993, in both standard mapping mode and interferometric synthetic aperture radar (INSAR) mode from a NASA DC-8 aircraft as part of the High-Resolution Remote Sensing Experiment. In situ currents were measured using a surface-towed acoustic Doppler current profiler (ADCP). The measurements were made near the end of a period of Gulf Stream incursion onto the shelf as detected using a shore-based HF radar. Winds were southwesterly at 4-6 m s-1. Long, curvilinear SAR signatures, resembling earlier SEASAT observations made in the same area, are shown to correspond to narrow, shallow fronts separating water masses that increase in surface density with distance offshore. Across-front changes in surface current inferred from the INSAR data are consistent with 2-m-depth currents measured by the ADCP over scales of tens of meters. Thus frontal current gradients measured by INSAR reflect real changes in surface current and are not due to biases induced by changes in the surface-wave spectrum. This lends support to the detailed INSAR surface maps derived by Graber et al. [1996]. An east-west salinity front having the largest observed surface density and current gradient is corrugated on length scales up to the local Rossby radius of deformation and translates southward between successive images. In data from the longer radar wavelengths the salinity front appears as a dark band downwind of a bright signature, and this is interpreted as a region where Bragg-scale waves regenerate following their dissipation in the frontal region. In addition to the fronts the imagery shows closely spaced packets of southward propagating ocean internal waves occurring in the strongly stratified inshore water mass. This case study further serves to emphasize the potential of SAR imagery for study of a wide range of shelf processes.

Marmorino, G. O.; Thompson, D. R.; Graber, H. C.; Trump, C. L.

1997-08-01

68

Unexploded ordnance detection experiments using ultrawideband synthetic aperture radar  

NASA Astrophysics Data System (ADS)

The Army Research Laboratory (ARL) has several technology development programs that are evaluating the use of ultra- wideband synthetic aperture radar (UWB SAR) to detect and locate targets that are subsurface or concealed by foliage. Under these programs, a 1-GHz-bandwidth, low-frequency, fully polarimetric UWB SAR instrumentation system was developed to collect the data needed to support foliage and ground- penetrating radar studies. The radar was integrated onto a 150-ft-high mobile boomlift platform in 1995 and was thus named the BoomSAR. In 1997, under the sponsorship of the Strategic Environmental Research and Development Program (SERDP), ARL began a project focused on enhancing the detection and discrimination of unexploded ordnance (UXO). The program's technical approach is to collect high-quality, precision data to support phenomenological investigations of electromagnetic wave propagation through varying dielectric media, which in turn supports the development of algorithms for automatic target detection. For this project, a UXO test site was set up at the Steel Crater Test Area -- an existing test site that already contained subsurface mines, tactical vehicles, 55-gallon drums, storage containers, wires, pipes, and arms caches located at Yuma Proving Ground (YPG), Arizona. More than 600 additional pieces of inert UXO were added to the Steel Crater Test Area, including bombs (250, 500, 750, 1000, and 2000 lb), mortars (60 and 81 mm), artillery shells (105 and 155 mm), 2.75-in. rockets, submunitions (M42, BLU-63, M68, BLU-97, and M118), and mines (Gator, VS1.6, M12, PMN, and POM- Z). In the selection of UXO to be included at YPG, an emphasis was placed on the types of munitions that may be present at CONUS test and training ranges.

Deluca, Clyde C.; Marinelli, Vincent; Ressler, Marc; Ton, Tuan

1998-09-01

69

Metrology, attitude, and orbit determination for spaceborne interferometric synthetic aperture radar  

Microsoft Academic Search

The Shuttle Radar Topography Mission (SRTM), scheduled for an 11 day Space Shuttle flight in 1999, will use an Interferometric Synthetic Aperture Radar instrument to produce a near-global digital elevation map of the earth's land surface with 16 m absolute vertical height accuracy at 30 meter postings. SRTM will achieve the required interferometric baseline by extending a receive-only radar antenna

Riley M. Duren; Ed Wong; Bill Breckenridge; Scott Shaffer; Courtney Duncan; Eldred F. Tubbs; Phil M. Salomon

1998-01-01

70

Low-frequency ultra-wideband synthetic aperture radar 1995 BoomSAR tests  

Microsoft Academic Search

The Army Research Laboratory has been investigating the potential of ultra-wideband synthetic aperture radar (UWB SAR) technology to detect and classify targets embedded in foliage or in the ground. The UWB foliage penetration (FOPEN) radar program has been extended to include the evaluation of ground penetration (GPEN) radar technology. ARL is investigating these problems by collecting high quality, precision data

Lynn Happ; Karl A. Kappra; Marc A. Ressler; Jeffrey P. Sichina; Keith Sturgess; Francis Le

1996-01-01

71

Tropical Cyclone Winds Retrieved from Synthetic Aperture Radar  

NASA Astrophysics Data System (ADS)

Within this paper we will introduce and validate our methodologies to retrieve high-resolution wind fields from synthetic aperture radar (SAR) with particular focus on tropical cyclones. SAR wind directions are extracted from the orientation of wind induced streaks, which are visible in the SAR images and that in general are well aligned with the mean surface wind direction. Wind speeds are retrieved from the measured normalized radar cross section (NRCS) from the ocean surface under consideration on the SAR derived wind direction and imaging geometry. Depending on the frequency as well as the SAR polarization for transmit and receive different geophysical model functions (GMF) have to be considered. In case of SAR data acquired at C-band with co-polarization using vertical (V) polarization in transmit and receive we use the well-known C-band model CMOD5n. For horizontal polarization in transmit and receive (HH-polarization) the CMOD5n model is extended by a function that describes the ratio of V to H polarization. For images acquired at H-polarization for transmit and V-polarization for receive (cross pol) or vice versa, we have developed our own GMF. We have investigated a large data set of SAR data acquired under tropical cyclone conditions and compared our retrieved wind fields to scatterometer winds, GPS drope sonde surface wind vectors and SFMR wind speeds acquired during the storms. The results show the quality of the SAR-retrieved wind fields from co-pol and, in particular, cross-pol winds., The later have an rms error similar to the SFMR measurements, which up to date is one of the best accepted wind measurement sources for tropical cyclone winds.

Horstmann, Jochen; Wackerman, Chris; Foster, Ralph; Caruso, Michael; Graber, Hans

2013-04-01

72

Fourier domain interpolation techniques for synthetic aperture radar  

NASA Astrophysics Data System (ADS)

Spotlight-mode synthetic aperture radar (SAR) produces complex Fourier data points on a polar grid which is offset from dc in the frequency domain. To produce an image in the spatial domain, it is necessary to invert this sampled Fourier data prior to extracting magnitude information. However, the polar format of the data makes this difficult, since there is no known polar FFT. An alternative is to interpolate the complex polar data to a Cartesian grid and then perform the two-dimensional FFT. The magnitude of the resulting data array represents the magnitude of the complex ground reflectivity of the terrain under illumination. The interpolation process can be very computationally intense, with an order two to fifty times that of the FFT. Reducing the computation in the interpolation stage, while maintaining reconstruction quality is the focus of this work. Several 2D interpolation techniques are examined, including nearest neighbor, bilinear, inverse-distance to the nth power, weighted sinc, chirp z-transform, and the newest interpolation algorithm proposed for this problem: the cubic spline. It is found that separable interpolation schemes outperform the more commonly used nearest neighbor and inverse distance algorithms, and that the cubic spline is very competitive in the weighted since interpolator in computation requirements and reconstruction quality. The chirp z-transform is determined to be a good alternative to the classical interpolation-DFT approach.

Mather, B. C.

1986-08-01

73

Clutter discrimination in polarimetric and interferometric synthetic aperture radar imagery  

NASA Astrophysics Data System (ADS)

Many synthetic aperture radar (SAR) images contain extended regions of apparently homogeneous clutter arising from areas of vegetation or uniformly driven expanses of water. These regions may contain localized clutter variations resulting from the presence of features of ecological interest, such as changes in vegetation density due to environmental effects or damping of the sea surface by pollutants. Alternatively such clutter variations may be due to the signatures of partially concealed land-based or maritime military targets. It is thus of interest to develop techniques which can discriminate localized clutter features from the background clutter. Multiple-channel SAR systems can provide several images of a scene of this type which contain complementary sets of information. These can be combined to generate a single enhanced image of the scene in which it is possible to discriminate more effectively among the features it contains. In this paper a unified discussion of multi-channel enhancement techniques, which make use of varying degrees of knowledge regarding the statistical characteristics of the image features, is presented.

Blacknell, David; Tough, Robert J. A.

1997-02-01

74

Mapping Boreal Wetlands Using Spaceborne Synthetic Aperture Radar  

NASA Astrophysics Data System (ADS)

Carbon and methane emissions from wetlands and lakes can have a large impact on global climate. These ecosystems are dominant features in the northern high latitudes hence the importance of assessing their spatial and temporal extent to improve upon global net carbon exchange estimates. Spaceborne synthetic aperture radar (SAR) is an effective tool for this purpose since large inaccessible areas can be monitored on a temporal basis regardless of atmospheric conditions or solar illumination and it is sensitive to vegetation and standing water. We employ ERS (C-band, 100 m, VV-polarization) and JERS (L-band, 100 m, HH-polarization) in this study to map wetlands within boreal sub-regions. Large scale L-band SAR mosaics assembled over boreal regions are used with supplementary multi-temporal data for the analysis. Path to path and year to year radiometric differences due predominantly to seasonal changes were a source of confusion. Decision tree classification tools are used to alleviate this problem. Digital elevation models (where available) and derived slope aspect are used to better distinguish drainage patterns. Texture images are used to help differentiate different wetland classes (e.g. fens, bogs, swamps, marshes, and open water). Examples of validated test regions are presented. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology and the University of Washington under contract with the National Aeronautics and Space Administration.

Podest, E.; McDonald, K. C.; Bohn, T.; Lettenmaier, D.

2006-12-01

75

Moving target imaging using ultrawideband synthetic aperture radar  

NASA Astrophysics Data System (ADS)

Moving Target High Resolution Imaging of Foliage Penetrate Ultra-Wide Band Synthetic Aperture Radar (FOPEN UWB SAR) is of great significance for battlefield awareness of concealed target. Great range migration and strong clutter make moving target detection and imaging difficult, especially the Signal to Clutter Ration(SCR) some times is so low that the moving targets is invisible in FOPEN UWB SAR imagery. To improve SCR, the clean technique is used in range compressed data domain. The clean technique and data reconstruction help single channel of FOPEN UWB SAR suppress strong tree clutter and stationary target signal from region of interest. A new definition called General Key-Stone Transform is given, which can correct any order of range migration. FOPEN UWB SAR has long integrated time. The plane and target moving in long time lead to complex range migration. To obtain high resolution imagery of moving target, General Key-Stone transform are applied to remove the range migration and realize multiple moving target data segment. Both General Key-Stone Transform and Clean Technique are applied in real data processing of FOPEN UWB SAR. The result shows that multiple moving targets in the trees are clearly detected and high resolution imagery is formed.

Guo, Hanwei; Liang, Diannong; Wan, Yan; Huang, Xiaotao; Dong, Zhen

2003-09-01

76

Snow mapping in alpine regions with synthetic aperture radar  

SciTech Connect

For climatological and hydrological investigations, the areas covered by snow and glacial ice are important parameters. Active microwave sensors can discriminate snow from other surfaces in all weather conditions, and their spatial resolution is compatible with the topographic variation in alpine regions. Using data acquired with the NASA AIRSAR in the Oetztal Alps in 1989 and 1991, the authors examine the usage of synthetic aperture radar (SAR) to map snow- and glacier-covered areas. By comparing polarimetric SAR data to images from the Landsat Thematic Mapper obtained under clear conditions one week after the SAR flight, they find that SAR data at 5.3 GHz (C-band) can discriminate between areas covered by snow from those that are ice-free. However, they are less suited to discrimination of glacier ice from snow and rock. The overall pixel-by-pixel accuracies--74% from VV polarization alone with topographic information, 76% from polarimetric SAR without any topographic information, and 79% from polarimetric SAR with topographic information--are high enough to justify the use of SAR as the data source in areas that are too cloud-covered to obtain data from the Thematic Mapper. This is especially true for snow discrimination, where accuracies exceed 80%, because mapping of a transient snow cover during a cloudy melt season is often difficult with an optical sensor. The AIRSAR survey was carried out in summer during a heavy rainstorm, when the snow surfaces were unusually rough.

Shi, J.; Dozier, J. (Univ. of California, Santa Barbara, CA (United States)); Rott, H. (Univ. of Innsbruck (Austria). Inst. for Meteorology and Geophysics)

1994-01-01

77

Target characterization and matching in synthetic aperture radar imagery  

NASA Astrophysics Data System (ADS)

Synthetic Aperture Radar (SAR) target characterization is a challenging area of focus in the field of computer vision. Typical image processing techniques are not directly applicable to SAR imagery which lack the typical features present in visual images. This thesis begins by developing the necessary tools for analyzing SAR images. These include image registration with respect to various operating parameters and the modeling of noise. Multiple algorithms are presented for segmenting targets from surrounding clutter. These methods are statistical in nature which rely on Constant False Alarm Rate detection, or on a histogram based approach. An algorithm for the determination of target aspect is presented which exhibits robustness to significant errors in the target segmentation process. Feature extraction is then developed by the use of topographic features which are invariant to monotonic intensity transformations. These features are shown to be more stable than other features presented in the literature. Target classification is accomplished by formulating the matching of previously developed features in the framework of a nonlinear objective function. The optimization of this objective yields a recognition engine for the SAR automatic target recognition system which is robust to spurious, missing and migrated features. Experimental results are presented for simulated as well as real SAR imagery.

Meth, Reuven

78

Feature-based classification with application to synthetic aperture radar  

NASA Astrophysics Data System (ADS)

In this dissertation we present two feature-based pattern classifiers with application to synthetic aperture radar, a template-based geometric hashing classifier and a model-based Bayesian feature classifier. First, we develop a classifier that exploits geometric locations of SAR scattering centers. The classifier is an extension of a geometric hashing method for optical images. We synthesize a hash table that can be efficiently searched for matching patterns. The hashing classifier can be used as a final classifier, and also as an index stage to generate a hypothesis list for a final classifier. We present classification results using features extracted from X-band SAR images of four vehicles. Second, we present model-based Bayesian feature matchers using attributed scattering center features. The matcher attempts to find the Bayes optimal match between an extracted feature vector and a set of predicted feature vectors, and incorporates uncertainty in both predicted and extracted feature vectors. We implement the matcher, and conduct a number of classification performance estimation experiments on a ten class problem using measured X-band SAR images. We compare performance versus number of feature attributes, uncertainty on the attributes, and correlation on attribute uncertainty. We also consider classification performance as a function of resolution. Finally, we present an analytical performance model that predicts classification performance of the Bayes matcher under some simplifying assumptions.

Chiang, Hung-Chih

79

Statistical assessment of model fit for synthetic aperture radar data  

NASA Astrophysics Data System (ADS)

Parametric approaches to problems of inference from observed data often rely on assumed probabilistic models for the data which may be based on knowledge of the physics of the data acquisition. Given a rich enough collection of sample data, the validity of those assumed models can be assessed in a statistical hypothesis testing framework using any of a number of goodness-of-fit tests developed over the last hundred years for this purpose. Such assessments can be used both to compare alternate models for observed data and to help determine the conditions under which a given model breaks down. We apply three such methods, the (chi) 2 test of Karl Pearson, Kolmogorov's goodness-of-fit test, and the D'Agostino-Pearson test for normality, to quantify how well the data fit various models for synthetic aperture radar (SAR) images. The results of these tests are used to compare a conditionally Gaussian model for complex-valued SAR pixel values, a conditionally log-normal model for SAR pixel magnitudes, and a conditionally normal model for SAR pixel quarter-power values. Sample data for these tests are drawn from the publicly released MSTAR dataset.

DeVore, Michael D.; O'Sullivan, Joseph A.

2001-08-01

80

Detection of Ionospheric Structures with L-Band Synthetic Aperture Radars  

Microsoft Academic Search

Numerical simulations of low-latitude ionospheric instabilities show the formation of plasma density structures can be detected by synthetic aperture radar (SAR) radio signals. At L-band, the phase front distortions produced by propagation through plasma \\

Paul A. Bernhardt; Thomas L. Ainsworth; Keith M. Groves; Ted Beach; Ronald G. Caton; Charles S. Carrano; Christian M. Alcala; Dale D. Sponseller

2008-01-01

81

Three-dimensional ground penetrating radar imaging using synthetic aperture time-domain focusing.  

National Technical Information Service (NTIS)

This paper discusses a three-dimensional synthetic aperture imaging technique based on time-domain focusing of pulse-echo radar data. We describe the basic image formation process, important data processing issues, and compensation for planar variations i...

E. M. Johansson J. E. Mast

1994-01-01

82

Motion Compensation Requirements for a High Resolution Spotlight SAR (Synthetic Aperture Radar).  

National Technical Information Service (NTIS)

The Canadian Department of National Defense is developing a high resolution airborne spotlight synthetic aperture radar (SAR). To attain the high contrast, high resolution and low geometric distortion objectives of the project, it is essential that very a...

J. S. A. Hepburn G. E. Haslam D. F. Liang W. S. Widnall

1986-01-01

83

Imaging targets embedded in a lossy half space with Synthetic Aperture Radar.  

National Technical Information Service (NTIS)

This paper addresses theoretical aspects of forming images from an airborne Synthetic Aperture Radar (SAR) of targets buried below the earth's surface. Soil is generally a lossy, dispersive medium, with wide ranging variability in these attributes dependi...

A. W. Doerry B. Boverie B. C. Brock D. Cress

1994-01-01

84

Model-supported exploitation of synthetic aperture radar images  

NASA Astrophysics Data System (ADS)

We address the application of model-supported exploitation techniques to synthetic aperture radar (SAR) imagery. The emphasis is on monitoring SAR imagery using wide area 2D and/or 3D site models along with contextual information. We consider here the following tasks useful in monitoring: (a) site model construction using segmentation and labeling techniques, (b) target detection, (c) target classification and indexing, and (d) SAR image-site model registration. The 2-D wide area site models used here for SAR image exploitation differ from typical site models developed for RADIUS applications, in that they do not model specific facilities, but constitute wide area site models of cultural features such as urban clutter areas, roads, clearings, fields, etc. These models may be derived directly from existing site models, possibly constructed from electro-optical (EO) observations. When such models are not available, a set of segmentation and labeling techniques described here can be used for the construction of 2D site models. The use of models can potentially yield critical information which can disambiguate target signatures in SAR images. We address registration of SAR and EO images to a common site model. Specific derivations are given for the case of registration within the RCDE platform. We suggest a constant false alarm rate (CFAR) detection scheme and a topographic primal sketch (TPS) based classification scheme for monitoring target occurrences in SAR images. The TPS of an observed target is matched against candidate targets TPSs synthesized for the preferred target orientation, inferred from context (e.g. road or parking lot targets). Experimental results on real and synthetic SAR images are provided.

Chellappa, Rama; Kuttikkad, Shyam; Meth, Reuven; Burlina, Philippe; Shekhar, Chandra S.

1996-02-01

85

Overview of results of Spaceborne Imaging Radar-C, X-Band Synthetic Aperture Radar (SIR-C\\/X-SAR)  

Microsoft Academic Search

The Spaceborne Imaging Radar-C, X-Band Synthetic Aperture Radar (SIR-C\\/X-SAR) was launched on the Space Shuttle Endeavour for two ten day missions in the spring and fall of 1994. Radar data from these missions are being used to better understand the dynamic global environment. During each mission, radar images of over 300 sites around the Earth were obtained, returning over a

Ellen R. Stofan; Diane L. Evans; Christianna Schmullius; Benjamin Holt; Jeffrey J. Plaut; Jakob van Zyl; Stephen D. Wall

1995-01-01

86

Antenna beamwidth and beamshape control techniques for satellite-borne synthetic aperture radar systems  

Microsoft Academic Search

The paper discusses methods of beamwidth and beamshape control suitable for a satellite-borne synthetic aperture radar (SAR) sensor system. The results of a parametric analysis which relates satellite orbital attitude, depression angle, beam width, and swath width are summarized. Attention is given to beam shaping techniques and their application to aperture configurations of interest to generate desired radiation patterns. Baseline

R. A. Kallas

1979-01-01

87

Effect of Faraday rotation on L-band interferometric and polarimetric synthetic-aperture radar data  

Microsoft Academic Search

Electromagnetic waves traveling through the ionosphere undergo a Faraday rotation of the polarization vector, which modifies the polarization and phase characteristics of the electromagnetic signal. Using L-band (?=24 cm), polarimetric synthetic aperture radar (SAR) data from the shuttle imaging radar C (SIR-C) acquired in 1994, the author simulates the effect of a change in the Faraday rotation angle ? on

Eric J. M. Rignot

2000-01-01

88

The observation of ocean surface phenomena using imagery from the SEASAT synthetic aperture radar: An assessment  

Microsoft Academic Search

Over the period July 4 to October 10, 1978, the SEASAT synthetic aperture radar (SAR) gathered 23 cm wavelength radar images of some 108 km2 of the earth's surface, mainly of ocean areas, at 25-40 m resolution. Our assessment is in terms of oceanographic and ocean monitoring objectives and is directed toward discovering the proper role of SAR imagery in

John F. Vesecky; Robert H. Stewart

1982-01-01

89

High-Resolution Inverse Synthetic Aperture Radar Imaging Based on the Shooting and Bouncing Ray Method  

Microsoft Academic Search

This paper concerns the simulation of inverse synthetic aperture radar (ISAR) image for radar targets based on the shooting and bouncing ray (SBR) method. Contrary to the conventional approach where the ISAR image is obtained by inverse Fourier transforming to the scattering field, we adopt a newly-developed method [8], where the Fourier transformation has been merged into the SBR algorithm.

X. B. Wang; X. Y. Zhou; T. J. Cui; Y. B. Tao; H. Lin

2008-01-01

90

Model-Based Information Extraction From Synthetic Aperture Radar Signals  

NASA Astrophysics Data System (ADS)

Synthetic aperture radar (SAR) is a remote sensing technology for imaging areas of the earth's surface. SAR has been successfully used for monitoring characteristics of the natural environment such as land cover type and tree density. With the advent of higher resolution sensors, it is now theoretically possible to extract information about individual structures such as buildings from SAR imagery. This information could be used for disaster response and security-related intelligence. SAR has an advantage over other remote sensing technologies for these applications because SAR data can be collected during the night and in rainy or cloudy conditions. This research presents a model-based method for extracting information about a building -- its height and roof slope -- from a single SAR image. Other methods require multiple images or ancillary data from specialized sensors, making them less practical. The model-based method uses simulation to match a hypothesized building to an observed SAR image. The degree to which a simulation matches the observed data is measured by mutual information. The success of this method depends on the accuracy of the simulation and on the reliability of the mutual information similarity measure. Electromagnetic theory was applied to relate a building's physical characteristics to the features present in a SAR image. This understanding was used to quantify the precision of building information contained in SAR data, and to identify the inputs needed for accurate simulation. A new SAR simulation technique was developed to meet the accuracy and efficiency requirements of model-based information extraction. Mutual information, a concept from information theory, has become a standard for measuring the similarity between medical images. Its performance in the context of matching a simulation image to a SAR image was evaluated in this research, and it was found to perform well under certain conditions. The factors that affect its performance, and the model-based method overall, were found to include the size of the building and its orientation. Further refinements that expand the range of operational conditions for the method would lead to a practical tool for collecting information about buildings using SAR technology. This research was performed using SAR data from MIT-Lincoln Laboratory.

Matzner, Shari A.

91

Universal multifractal scaling of synthetic aperture radar images of sea-ice  

Microsoft Academic Search

Multifrequency, multipolarization imaging radar scattering coefficient data sets, acquired by synthetic aperture radar (SAR) over sea-ice, were studied in order to reveal their scale-invariant properties. Two distinct scenes were acquired at C-band (5.6 cm) and L-band (25 cm) wavelengths for three different linear polarizations (HH, VV, and HV). These sea-ice radar scattering coefficient fields were investigated by applying both Fourier

Tony Falco; Frkdkric Francis; Sham Lovejoy; Daniel Schertzer; Bryan Kerman; Mark Drinkwater

1996-01-01

92

Autofocus algorithm for synthetic aperture radar imaging with large curvilinear apertures  

NASA Astrophysics Data System (ADS)

An approach to autofocusing for large curved synthetic aperture radar (SAR) apertures is presented. Its essential feature is that phase corrections are being extracted not directly from SAR images, but rather from reconstructed SAR phase-history data representing windowed patches of the scene, of sizes sufficiently small to allow the linearization of the forward- and back-projection formulae. The algorithm processes data associated with each patch independently and in two steps. The first step employs a phase-gradient-type method in which phase correction compensating (possibly rapid) trajectory perturbations are estimated from the reconstructed phase history for the dominant scattering point on the patch. The second step uses phase-gradient-corrected data and extracts the absolute phase value, removing in this way phase ambiguities and reducing possible imperfections of the first stage, and providing the distances between the sensor and the scattering point with accuracy comparable to the wavelength. The features of the proposed autofocusing method are illustrated in its applications to intentionally corrupted small-scene 2006 Gotcha data. The examples include the extraction of absolute phases (ranges) for selected prominent point targets. They are then used to focus the scene and determine relative target-target distances.

Bleszynski, E.; Bleszynski, M.; Jaroszewicz, T.

2013-05-01

93

Synthetic aperture radar imaging using a unique approach to frequency-modulated continuous-wave radar design  

Microsoft Academic Search

Synthetic-aperture-radar (SAR) imaging is an expensive endeavor. It can be difficult for universities, small business, or individuals to experiment with SAR imaging and algorithm development on a low budget. For this reason, a uniquely inexpensive solution to frequency-modulated continuous-wave (FMCW) radar was developed and then utilized as an ultra-low-cost SAR imaging system. This unique approach to FMCW radar used a

G. L. Charvat; Leo C. Kempel

2006-01-01

94

Phase correction system for automatic focusing of synthetic aperture radar  

DOEpatents

A phase gradient autofocus system for use in synthetic aperture imaging accurately compensates for arbitrary phase errors in each imaged frame by locating highlighted areas and determining the phase disturbance or image spread associated with each of these highlight areas. An estimate of the image spread for each highlighted area in a line in the case of one dimensional processing or in a sector, in the case of two-dimensional processing, is determined. The phase error is determined using phase gradient processing. The phase error is then removed from the uncorrected image and the process is iteratively performed to substantially eliminate phase errors which can degrade the image.

Eichel, Paul H. (Albuquerque, NM); Ghiglia, Dennis C. (Placitas, NM); Jakowatz, Jr., Charles V. (Albuquerque, NM)

1990-01-01

95

On a Novel Approach Using MLCC and CFAR for the Improvement of Ship Detection by Synthetic Aperture Radar  

Microsoft Academic Search

Multilook cross correlation (MLCC) is a useful technique in extracting the images of ships embedded in heavy sea clutter by synthetic aperture radar (SAR). In the ship detection experiment in 2006 by Phased Array L-band Synthetic Aperture Radar (PALSAR) on board the Advanced Land Observing Satellite, we applied MLCC to PALSAR data in order to extract small fishing boats. The

Seong-In Hwang; Kazuo Ouchi

2010-01-01

96

Bistatic synthetic aperture radar inversion with application in dynamic object imaging  

Microsoft Academic Search

An inversion method is presented for bistatic synthetic aperture radar imaging. The method is based on a Fourier analysis (Doppler processing) of the bistatic synthesized array's data followed by a phase modulation analysis of the Doppler data. The approach incorporates the phase information of the wavefront curvature in the transmitted waves as well as the resultant echoed signals. The Doppler

Mehrdad Soumekh

1991-01-01

97

The Prediction of Geometric Distortions in Airborne Synthetic Aperture Radar Imagery from Autofocus Measurements  

Microsoft Academic Search

The synthetic aperture radar (SAR) is an imaging system that achieves high azimuthal resolution by tracking individual point scatterers using their phase histories, with the expected phase history of a particular point scatterer being derived from the assumed motion of the airborne SAR platform. Normally, it is assumed that the platform travels along a straight line path and that the

David Blacknell; Anthony Freeman; Richard White; James Wood

1987-01-01

98

Optimization of Soil Hydraulic Model Parameters Using Synthetic Aperture Radar Data: An Integrated Multidisciplinary Approach  

Microsoft Academic Search

It is widely recognized that synthetic aperture radar (SAR) data are a very valuable source of information for the modeling of the interactions between the land surface and the atmosphere. During the last couple of decades, most of the research on the use of SAR data in hydrologic applications has been focused on the retrieval of land and biogeophysical parameters

Valentijn R. N. Pauwels; Anna Balenzano; Giuseppe Satalino; Henning Skriver; Niko E. C. Verhoest; Francesco Mattia

2009-01-01

99

Real-Time Optical Processor for Synthetic Aperture Radar Image Formation.  

National Technical Information Service (NTIS)

An acousto-optic processor which forms synthetic aperture radar images in real-time is described. It employs a space and time integrating architecture to perform the required two dimensional matched filtering operation as a sequence of one dimensional pro...

K. T. Stalker P. A. Molley F. M. Dickey

1987-01-01

100

On the modified chirp z transform for synthetic aperture radar systems  

Microsoft Academic Search

A modified chirp z-transform (MCZT) algorithm which has been proposed by Lawton (1988) to replace the conventional polar format interpolation in synthetic aperture radar systems is discussed. The key assumption used in the MCZT approach is that the spatial-frequency samples can be obtained on a concentric squares (CS) grid. The CS grid is briefly reviewed. The conventional approach to processing

John W. Adams; Robert W. Bayma; Michael E. Lawrence; Leon Petrosian

1991-01-01

101

Research of the aeroplane intelligent localization methods based on Synthetic Aperture Radar imagery  

Microsoft Academic Search

Synthetic aperture radar (SAR) presents prominent advantages, such as working in all-time and all weather condition, which makes it locate the aeroplane more advantageous. First, the article discusses the effect on aircraft location caused by factors such as topographic relief while SAR imaging. Then, proposes a method that calculates the areoplane's spatial position based on the multi-angular cone model after

Shao Yongshe; Han Yang; Zhang Leiyu

2009-01-01

102

Feature-enhanced synthetic aperture radar image formation based on nonquadratic regularization  

Microsoft Academic Search

We develop a method for the formation of spotlight-mode synthetic aperture radar (SAR) images with enhanced features. The approach is based on a regularized reconstruction of the scattering field which combines a tomographic model of the SAR observation process with prior information regarding the nature of the features of interest. Compared to conventional SAR techniques, the method we propose produces

Müjdat Çetin; William Clement Karl

2001-01-01

103

Atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps  

Microsoft Academic Search

Interferogram images derived from repeat-pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor. Other tropospheric variations, such as pressure and temperature, also induce distortions, but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term. Spatial and temporal changes of 20% in

Howard A. Zebker; Paul A. Rosen; Scott Hensley

1997-01-01

104

Synthetic aperture radar raw data compression using wavelet packet transform and trellis coded quantization  

Microsoft Academic Search

Performing some form of compression on synthetic aperture radar (SAR) data is necessary and important to curtail the downlink capacity and on-board storage requirements of a SAR system. In this paper, we present a transform coding approach for compression of SAR raw data using wavelet packet transform. Trellis coded quantization (TCQ) techniques are used to quantize the transform coefficients. A

Gowtham A. Tammana; Yuan F. Zheng; Robert L. Ewing

2005-01-01

105

A Multiple Beam Synthetic Aperture Radar Design Concept for Geoscience Applications  

Microsoft Academic Search

The multiple beam synthetic aperture radar (SAR) has been presented as a superior alternative to conventional side-looking SAR designs for mapping earth resources from space. The multiple beam approach provides wide swath coverage at nearly constant incident angle while conserving peak power. These desirable system characteristics, however, are realized at the expense of additional signal processing. A design example illustrates

Buford R. Jean; John W. Rouse

1983-01-01

106

SlimSAR: A Small, Multi-Frequency, Synthetic Aperture Radar for UAS Operation.  

National Technical Information Service (NTIS)

The SlimSAR is a small, low-cost, Synthetic Aperture Radar (SAR) and represents a new advancement in high-performance SAR. ARTEMIS employed a unique design methodology that exploits previous developments in designing the Slim- SAR to be smaller, lighter, ...

A. Margulis E. Zaugg M. Edwards

2010-01-01

107

Focusing of Airborne Synthetic Aperture Radar Data From Highly Nonlinear Flight Tracks  

Microsoft Academic Search

Standard focusing of data from synthetic aperture radar (SAR) assumes a straight recording track of the sensor platform. Small nonlinearities of airborne platform tracks are corrected for during a motion-compensation step while maintaining the assumption of a linear flight path. This paper describes the processing of SAR data acquired from nonlinear tracks, typical of sensors mounted on small aircraft or

Othmar Frey; Christophe Magnard; Maurice Ruegg; Erich Meier

2009-01-01

108

Basics of Polar-Format algorithm for processing Synthetic Aperture Radar images.  

SciTech Connect

The purpose of this report is to provide a background to Synthetic Aperture Radar (SAR) image formation using the Polar Format (PFA) processing algorithm. This is meant to be an aid to those tasked to implement real-time image formation using the Polar Format processing algorithm.

Doerry, Armin Walter

2012-05-01

109

Integrated satellite interferometry: Tropospheric noise, GPS estimates and implications for interferometric synthetic aperture radar products  

Microsoft Academic Search

Interferometric synthetic aperture radar (INSAR), like other astronomic and space geodetic techniques, is limited by the spatially and temporally variable delay of electromagnetic waves propagating through the neutral atmosphere. Statistical analysis of these variations, from a wide variety of instruments, reveals a power law dependence on frequency that is characteristic of elementary (Kolmogorov) turbulence. A statistical model for a major

Simon Williams; Yehuda Bock; Peng Fang

1998-01-01

110

Ionospheric effects on synthetic aperture radar at 100 MHz to 2 GHz  

Microsoft Academic Search

Recently, there has been increasing interest in the use of spaceborne synthetic aperture radar (SAR) for measuring forest biomass. However, it is noted that conventional SAR using C-band or higher frequencies cannot penetrate into foliage, and therefore the biomass measurements require longer wavelengths, typically P-band (500 MHz). It is also known that the ionosphere is highly dispersive, causing group delay

Akira Ishimaru; Yasuo Kuga; Jun Liu; Yunjin Kim; Tony Freeman

1999-01-01

111

Synthetic aperture radar data visualization on the iPod Touch  

Microsoft Academic Search

A major area of focus for the Air Force is sensor performance in urban environments. Aircraft with multiple sensor modalities, such as Synthetic Aperture RADAR (SAR), Infrared (IR), and Electro-Optics (EO), are essential for intelligence, surveillance, and reconnaissance (ISR) of current and future urban battlefields. Although applications exist for visualization of these types of imagery, they usually require at least

Aaron Fouts; Rhonda Vickery; Uttam Majumder; Tracy Burchett; Troy Klein; Michael Minardi

2010-01-01

112

Spectral signal to clutter and thermal noise properties of ocean wave imaging synthetic aperture radars  

Microsoft Academic Search

The high wavenumber detection cut-off is determined above which the spectrum of ocean waves imaged by a synthetic aperture radar (SAR) is lost in the background noise spectrum consisting of the clutter noise associated with the Rayleigh statistics of the backscattering surface and the thermal noise originating in the SAR system itself. For given power, the maximum detection cut-off wavenumber

Werner Alpers; Klaus Hasselmann

1982-01-01

113

The effect of orbital motions on synthetic aperture radar imagery of ocean waves  

Microsoft Academic Search

The formation of wave-like patterns in synthetic aperture radar (SAR) images of the ocean surface caused by orbital motions is investigated. Furthermore, the degradation in azimuthal resolution due to these motions is calculated by applying a least square fit to the phase history. Formulas are given which describe the variation of intensity in azimuthal direction in the image plane as

WERNER R. ALPERS; C. Rufenach

1979-01-01

114

Imaging targets embedded in a lossy half space with synthetic aperture radar  

Microsoft Academic Search

This paper addresses theoretical aspects of forming images from an airborne synthetic aperture radar (SAR) of targets buried below the Earth's surface. Soil is generally a lossy, dispersive medium, with wide ranging variability in these attributes depending on soil type, moisture content, and a host of other physical properties. Focussing a SAR subsurface image presents new dimensions of complexity relative

A. W. Doerry; B. C. Brock; B. Boverie; D. Cress

1994-01-01

115

Synthetic aperture radar; Proceedings of the Meeting, Los Angeles, CA, Jan. 20, 21, 1992  

Microsoft Academic Search

Topics discussed include the Lincoln Laboratory millimeter-wave synthetic aperture radar imaging system; a SAR radiometric characterization; an optical processing method of ISAR data; height accuracy and SAR image layover; a modified spotlight mode for a MMW SAR; multiple image processing to enhance stationary target detection; image compression using wavelet-type transform along generalized scan; and constrained least squares digital filters for

Richard D. McCoy; Martin E. Tanenhaus

1992-01-01

116

Imaging Simulation of Bistatic Synthetic Aperture Radar and Its Polarimetric Analysis  

Microsoft Academic Search

Employing the 3-D mapping and projection algorithm (MPA), an imaging simulation of bistatic synthetic aperture radar (BISAR) observation over a complex scenario is developed. Based on the explicit expression of the point target response of stripmap BISAR imaging, raw data are efficiently generated from the scattering map precalculated by MPA. Some examples of BISAR image simulation are studied. The polarimetric

Feng Xu; Ya-Qiu Jin

2008-01-01

117

Wavefront curvature limitations and compensation to polar format processing for synthetic aperture radar images.  

SciTech Connect

Limitations on focused scene size for the Polar Format Algorithm (PFA) for Synthetic Aperture Radar (SAR) image formation are derived. A post processing filtering technique for compensating the spatially variant blurring in the image is examined. Modifications to this technique to enhance its robustness are proposed.

Doerry, Armin Walter

2006-01-01

118

Digital ASIC implementation of a video filter for synthetic aperture radar.  

National Technical Information Service (NTIS)

Two GaAs ASICs have been designed and implemented for a synthetic aperture radar which eliminate the dc bias in the sampled video data and increase the signal to noise ratio by summing the data across consecutive bursts. The High Pass Filter and Presummer...

B. L. Remund J. Chow J. Salinas

1991-01-01

119

Ocean wave extraction from RADARSAT synthetic aperture radar inter-look image cross-spectra  

Microsoft Academic Search

This study is concerned with the extraction of directional ocean wave spectra from synthetic aperture radar (SAR) image spectra. The statistical estimation problem underlying the wave-SAR inverse problem is examined in detail in order to properly quantify the wave information content of SAR. As a concrete focus, a data set is considered comprising six RADARSAT SAR images co-located with a

Michael Dowd; Paris W. Vachon; Fred W. Dobson; Richard B. Olsen

2001-01-01

120

Observation of Planetary Oceans with Fully Polarimetric Synthetic Aperture Radar (SAR)  

Microsoft Academic Search

Synthetic Aperture Radar (SAR) is one of the most cost effective and powerful all weather tools for observation of planetary surface without sun light. The SAR systems can observe planetary surfaces with the very high resolution and large spatial coverage. We have developed and improved the algorithms for extracting quantitative information on geophysical parameters using various types of SAR data

Wooil M. Moon

2008-01-01

121

Sub-canopy soil moisture inversion using repeat pass Shuttle Imaging Radar C polarimetric Synthetic Aperture Radar interferometric data  

Microsoft Academic Search

The advances in polarimetric synthetic aperture radar (SAR) interferometry techniques provide a promising way to extract sub-canopy surface parameters using processed SAR images. In this paper, we evaluate the fully maximum likelihood decomposition model of polarimetric SAR interferometry for sub-canopy soil moisture estimation. We further propose a methodology for sub-canopy soil estimation using repeat pass space-borne SIR-C (Shuttle Imaging Radar

Xinwu Li; Huadong Guo; Zhen Li; Huanyin Yue; Quan Chen

2009-01-01

122

Conventional and synthetic aperture processing for airborne ground-penetrating radar  

NASA Astrophysics Data System (ADS)

For the past four years Airborne Environmental Surveys, a division of Era Aviation, Inc., has used unique and patented airborne frequency modulated, continuous wave radars and processes for detection and mapping subsurface phenomena. Primary application has focused on the detection of manmade objects in landfills, hazardous waste sites (some of which contain unexploded ordnance), and subsurface plumes of refined free- floating hydrocarbons. Recently, MSB Technologies, Inc. has developed a form of synthetic aperture radar processing, called GPSAR, that is tailored especially for the AES radars. Used as an adjunct to more conventional airborne ground-penetrating radar data processing techniques, GPSAR takes advantage of the radars' coherent transmission and produces imagery that is better focused and more accurate in determining an object's range and true depth. This paper describes the iterative stages of data processing and analysis used with the radars and shows the added advantages that GPSAR processing offers.

Cameron, Robert M.; Simkins, William L.; Brown, Russell D.

1994-07-01

123

A digital ASIC implementation of a video filter for synthetic aperture radar  

SciTech Connect

Two GaAs ASICs have been designed and implemented for a synthetic aperture radar which eliminate the dc bias in the sampled video data and increase the signal to noise ratio by summing the data across consecutive bursts. The High Pass Filter and Presummer ASICs process data at a maximum sample rate of 170 MHz and 125 MHz respectively. The chips are fully ECL and TTL compatible. The high pass filter is packaged in GigaBit's standard 132-pin ceramic package, while the presummer is packaged in TriQuint's standard 196-pin ceramic package. The presummer has been successfully tested in a prototype synthetic aperture radar at Sandia National Laboratories. The high pass filter has been successfully tested in a high speed test fixture. These ASICs provide flexibility and low power consumption at data rates previously unattainable with comparable hardware. 1 refs., 4 figs.

Remund, B.L. (Sandia National Labs., Albuquerque, NM (United States)); Chow, J.; Salinas, J. (GigaBit Logic, Newbury Park, CA (United States))

1991-01-01

124

Synthetic aperture radar (SAR) image focus performance during maneuvers  

NASA Astrophysics Data System (ADS)

Focus of a SAR image during maneuvers requires accurate estimates of the aircraft velocity vector. Velocity errors particularly along the radar line of sight (LOS) to the SAR map center cause LOS acceleration errors during an aircraft maneuver. This LOS acceleration results in defocused SAR images. Sensitivity to acceleration errors is greatest when mapping at small squint angles with respect to the aircraft velocity vector, i.e., at small angles with respect to the aircraft fore-aft axis. This paper shows the expected SAR map focus performance during maneuvers as a function of velocity errors. Simulation results showing expected focus performance using current and advanced processing techniques with background radar Doppler updates and with the use of Global Positioning System (GPS) are presented. With GPS aiding, velocity accuracy is improved by a factor of ten. The simulation results are compared to the flight test results performed with the APG-76 radar using both a gimbaled and a strapdown one nautical mile per hour class Inertial Navigation System with and without GPS aiding. The AN/APG-76 is a SAR radar with simultaneous Ground Moving Target Indication and is designed for `near the nose' imaging during aircraft maneuvers.

Ibsen, Paul M.; Guarino, Robert

1996-06-01

125

Mission analysis and design of a bistatic synthetic aperture radar on board a small satellite  

Microsoft Academic Search

This paper is aimed at a feasibility study of a new space-based observation technique: bistatic synthetic aperture radar, e.g. an active microwave sensor operating with separated transmitting and receiving antennae. Assuming ESA ENVISAT ASAR as main mission, a small satellite (BISSAT) equipped with a receiving-only antenna and flying in formation with ENVISAT is studied in details. In addition to conventional

Antonio Moccia; Sergio Vetrella; Roberta Bertoni

2000-01-01

126

Wide-Bandwidth Continuous-Wave Monostatic\\/Bistatic Synthetic Aperture Radar Imaging  

Microsoft Academic Search

Monostatic and bistatic synthetic aperture radar (SAR) imaging systems with wide-bandwidth continuous-wave (WB-CW) sources have been utilized for military reconnaissance. The WB-CW sources are less susceptible than FM-CW sources to electronic counter measures (ECM). The main shortcoming of the WB-CW microwave illumination is that its resultant SAR echoed signal is not composed of distinct Doppler spreadings around specific tones; this

Mehrdad Soumekh

1998-01-01

127

Dominant wave directions and significant wave heights from synthetic aperture radar imagery of the ocean  

Microsoft Academic Search

Seattle Abstract. We show that quasi-linear theory accounts for dominant wave directions observed in synthetic aperture radar (SAR) imagery of the ocean for range-to-velocity (R\\/V) ratios up to 70 s. We also show that when used in combination with Alpers and Hasselmann's (1982) model of signal-to-noise ratios in SAR imagery, this theory yields significant wave heights in good agreement with

William J. Plant; L. M. Zurk

1997-01-01

128

Dominant wave directions and significant wave heights from synthetic aperture radar imagery of the ocean  

Microsoft Academic Search

We show that quasi-linear theory accounts for dominant wave directions observed in synthetic aperture radar (SAR) imagery of the ocean for range-to-velocity (R\\/V) ratios up to 70 s. We also show that when used in combination with Alpers and Hasselmann's [1982] model of signal-to-noise ratios in SAR imagery, this theory yields significant wave heights in good agreement with those actually

William J. Plant; L. M. Zurk

1997-01-01

129

Routine Ocean Monitoring With Synthetic Aperture Radar Imagery Obtained From the Alaska Satellite Facility  

Microsoft Academic Search

The Alaska Satellite Facility (ASF) has been processing synthetic aperture radar (SAR) data for research and for near-real-time applications demonstrations since shortly after the launch of the European Space Agency's ERS-1 satellite in 1991. The long coastline of Alaska, the vast extent of ocean adjacent to Alaska, a scarcity of in-situ observations, and the persistence of cloud cover all contribute

W. G. Pichel; P. Clemente-Colon; X. Li; K. Friedman; F. Monaldo; D. Thompson; C. Wackerman; C. Scott; C. Jackson; R. Beal; J. McGuire; J. Nicoll

2006-01-01

130

On the modifier chirp z transform for synthetic aperture radar systems  

Microsoft Academic Search

A modified chirp z-transform (MCZT) algorithm which has been proposed by W. Lawton (IEEE Trans. Acoust., Speech, Signal Processing, vol.ASSP-36, p.931-3, June 1988) to replace the conventional polar format interpolation in synthetic aperture radar (SAR) systems is discussed. The key assumption used in the MCZT approach is that the spatial-frequency samples can be obtained on a concentric squares (CS) grid.

John W. Adams; Robert W. Bayma; Michael E. Lawrence; Leon Petrosian

1991-01-01

131

On the modified chirp z transform for synthetic aperture radar systems  

NASA Astrophysics Data System (ADS)

A modified chirp z-transform (MCZT) algorithm which has been proposed by Lawton (1988) to replace the conventional polar format interpolation in synthetic aperture radar systems is discussed. The key assumption used in the MCZT approach is that the spatial-frequency samples can be obtained on a concentric squares (CS) grid. The CS grid is briefly reviewed. The conventional approach to processing CS grid data is described. The MCZT is discussed, and its disadvantages are emphasized.

Adams, John W.; Bayma, Robert W.; Lawrence, Michael E.; Petrosian, Leon

1991-04-01

132

Atmospheric Fronts along the East Coast of Taiwan Studied by ERS Synthetic Aperture Radar Images  

Microsoft Academic Search

The existence of quasi-stationary alongshore atmospheric fronts typically located 30-70 km off the east coast of Taiwan is demonstrated by analyzing synthetic aperture radar (SAR) images of the sea surface acquired by the European Remote Sensing Satellites ERS-1 and ERS-2. For the data interpretation, cloud images from the Japanese Geostationary Meteorological Satellite GMS-4 and the American Terra satellite, rain-rate maps

Werner Alpers; Jen-Ping Chen; I.-I. Lin; Chun-Chi Lien

2007-01-01

133

A Statistical Description of Polarimetric and Interferometric Synthetic Aperture Radar Data  

Microsoft Academic Search

This paper provides a nearly complete analysis of the key distributions encountered in single- and multi-look polarimetric synthetic aperture radar data under the bivariate Gaussian and K-distribution models. It contains new analytic results on the moments of the amplitude and phase difference in single look data and on the moments of the amplitude in multi-look data. As yet no analytic

R. J. A. Tough; D. Blacknell; S. Quegan

1995-01-01

134

Coseismic crustal deformations of 1994 Northridge, California, earthquake detected by interferometric JERS 1 synthetic aperture radar  

Microsoft Academic Search

Coseismic deformations of the January 17, 1994, Northridge, California earthquake are mapped using interferometric combination of synthetic aperture radar images acquired by the Japanese Earth Resource Satellite (JERS 1) on April 30, 1993, and June 14, 1994. We make an interferogram in a rectangular area with a size of 18.6 km (N-S) by 29.9 km (E-W). Although coherence is not

Makoto Murakami; Mikio Tobita; Satoshi Fujiwara; Takashi Saito; Hiroshi Masaharu

1996-01-01

135

Novel guided-wave electro-optic processor for synthetic aperture radar imaging  

Microsoft Academic Search

We present the theoretical investigation of a novel architecture of a LiNbO3 guided-wave optical processor suitable for real-time microwave imaging in on-board synthetic aperture radar (SAR) applications, using a moving platform on either an aircraft or a spacecraft. The new configuration, which is basically interferometric, includes four Mach-Zehnder modulators, each characterized by an additional aperiodic phase-reversal traveling wave modulator. The

Mario N. Armenise; Vittorio M. Passaro

1994-01-01

136

Real-time synthetic aperture radar (SAR) processing with a new subaperture approach  

Microsoft Academic Search

A time-domain subaperture approach that is suitable for real-time synthetic aperture radar (SAR) processing and that produces high-quality, full-resolution images is presented. The real-time subaperture algorithm is based on an approximation of the phase history correction in each subaperture with a simple linear correction, which can be carried out by an up\\/down-conversion of the received signal followed by a moving

A. Moreira

1992-01-01

137

Tutorial review of synthetic-aperture radar (SAR) with applications to imaging of the ocean surface  

Microsoft Academic Search

A synthetic aperture radar (SAR) can produce high-resolution two-dimensional images of mapped areas. The SAR comprises a pulsed transmitter, an antenna, and a phase-coherent receiver. The SAR is borne by a constant velocity vehicle such as an aircraft or satellite, with the antenna beam axis oriented obliquely to the velocity vector. The image plane is defined by the velocity vector

KIYO TOMIYASU

1978-01-01

138

Emerging Applications of Interferometric Synthetic Aperture Radar (InSAR) in Geomorphology and Hydrology  

Microsoft Academic Search

Interferometric synthetic aperture radar (InSAR) is a powerful geodetic tool used to construct digital elevation models of the earth’s topography and to image centimeter–scale displacements associated with crustal deformation and the flow of ice sheets. The past decade has seen significant improvements in our understanding of earthquakes, volcanoes, and glaciers as a direct result of this technology. Geomorphology and hydrology

Laurence C. Smith

2002-01-01

139

Airborne synthetic aperture radar observations of “spiral eddy” slick patterns in the Southern California Bight  

Microsoft Academic Search

Repeat sampling on hourly time scales using an airborne synthetic aperture radar (SAR) is used to investigate the occurrence and evolving characteristics of spiral-shaped slick patterns, commonly presumed to be indicators of submesoscale ocean eddies, in the area around Santa Catalina Island, California (?33.4°N, 118.4°W). Simultaneous SAR imagery and boat survey data are examined over two ?5 h long periods

George O. Marmorino; Benjamin Holt; M. Jeroen Molemaker; Paul M. DiGiacomo; Mark A. Sletten

2010-01-01

140

Characterization of atmospheric precipitation effects on spaceborne synthetic aperture radar response at X, Ku, Ka band  

Microsoft Academic Search

Space-borne X-band synthetic aperture radars (SARs) provide a unique opportunity to measure rainfall over land with unsurpassed spatial resolution of about few hundred meters. This work explores the potential of space-borne X-SARs to estimate rainfall over land from both a model and retrieval point of view. The main objective is to provide a framework for a physically-based inversion of SARs

Frank Silvio Marzano; Saverio Mori; Nazzareno Pierdicca; Luca Pulvirenti

141

Estimates of currents in the nearshore ocean region using interferometric Synthetic Aperture Radar  

SciTech Connect

The authors report on the application of Synthetic Aperture Radar (SAR) as a high resolution remote sensing monitor of surface currents in the shore region of the ocean. They adapt and interferometric technique, where two receivers, mounted fore and aft on the aircraft record the reflected signal. After appropriate processing the two signals are interferometrically combined, and one can extract actual velocity fields from the ocean surface being monitored. They present results on the longshore current velocity.

Shemer, L.; Markman, D. (Tel-Aviv Univ., Ramat-Aviv (Israel)); Marom, M.

1993-04-15

142

Strapdown inertial measurement units for motion compensation for synthetic aperture radars  

Microsoft Academic Search

It is shown that synthetic-aperture radar (SAR) motion can be compensated by using an antenna-mounted strapdown inertial measurement unit (IMU) as the motion sensing system, but sensor and system errors affect SAR image quality. A strapdown IMU consists of three accelerator channels and three gyro channels. Strapdown IMU errors include gyro-scale and accelerometer-scale factor and bias errors, velocity error, platform

Thomas A. Kennedy

1988-01-01

143

Performance of Stereoradargrammetric Methods Applied to Spaceborne Monostatic–Bistatic Synthetic Aperture Radar  

Microsoft Academic Search

This paper aims to investigate the performance of stereoradargrammetric methods applied to spaceborne monostatic-bistatic synthetic aperture radar (SAR) data for digital elevation model (DEM) generation. Stereoradargrammetric techniques for robust DEM generation were successfully experienced on monostatic repeat-pass SIR-A, SIR-B, SIR-C\\/X-SAR, ERS1\\/2, JERS-1, and Radarsat data. However, novel configurations achievable by modern spacecraft flying in formation will allow for the attainment

Alfredo Renga; Antonio Moccia

2009-01-01

144

Access to Synthetic Aperture Radar Data from the Alaska Satellite Facility  

Microsoft Academic Search

The Alaska Satellite Facility (ASF) currently downlinks, archives, processes and distributes Synthetic Aperture Radar (SAR) data for several international satellites. The SAR data are available to NASA-approved researchers and U.S. government agencies. A straightforward proposal process provides easy access to large quantities of worldwide RADARSAT-1 and JERS-1 data, as well as ERS-1 and ERS-2 data for Alaska and Antarctica. This

V. G. Wolf; M. Harbin; R. Sanches

2006-01-01

145

X-SAR: The X-band synthetic aperture radar on board the Space Shuttle  

NASA Astrophysics Data System (ADS)

The X-band synthetic aperture radar (X-SAR) is the German/Italian contribution to the NASA/JPL Shuttle Radar Lab missions as part of the preparation for the Earth Observation System (EOS) program. The Shuttle Radar Lab is a combination of several radars: an L-band (1.2 GHz) and a C-band (5.3 GHz) multipolarization SAR known as SIR-C (Shuttle Imaging Radar); and an X-band (9.6 GHz) vertically polarized SAR which will be operated synchronously over the same target areas to deliver calibrated multifrequency and multipolarization SAR data at multiple incidence angles from space. A joint German/Italian project office at DARA (German Space Agency) is responsible for the management of the X-SAR project. The space hardware has been developed and manufactured under industrial contract by Dornier and Alenia Spazio. Besides supporting all the technical and scientific tasks, DLR, in cooperation with ASI (Agencia Spaziale Italiano) is responsible for mission operation, calibration, and high precision SAR processing. In addition, DLR developed an airborne X-band SAR to support the experimenters with campaigns to prepare for the missions. The main advantage of adding a shorter wavelength (3 cm) radar to the SIR-C radars is the X-band radar's weaker penetration into vegetation and soil and its high sensitivity to surface roughness and associated phenomena. The performance of each of the three radars is comparable with respect to radiometric and geometric resolution.

Werner, Marian U.

1993-05-01

146

Moving target detection in foliage using along track monopulse synthetic aperture radar imaging.  

PubMed

This paper presents a method for detecting moving targets embedded in foliage from the monostatic and bistatic synthetic aperture radar (SAR) data obtained via two airborne radars. The two radars, which are mounted on the same aircraft, have different coordinates in the along track (cross-range) domain. However, unlike the interferometric SAR systems used for topographic mapping, the two radars possess a common range and altitude (i.e., slant range). The resultant monopulse SAR images are used to construct difference and interferometric images for moving target detection. It is shown that the signatures of the stationary targets are weakened in these images. Methods for estimating a moving target's motion parameters are discussed. Results for an ultrawideband UHF SAR system are presented. PMID:18283004

Soumekh, M

1997-01-01

147

A model for forming airborne synthetic aperture radar images of underground targets  

SciTech Connect

Synthetic Aperture Radar (SAR) from an airborne platform has been proposed for imaging targets beneath the earth`s surface. The propagation of the radar`s energy within the ground, however, is much different than in the earth`s atmosphere. The result is signal refraction, echo delay, propagation losses, dispersion, and volumetric scattering. These all combine to make SAR image formation from an airborne platform much more challenging than a surface imaging counterpart. This report treats the ground as a lossy dispersive half-space, and presents a model for the radar echo based on measurable parameters. The model is then used to explore various imaging schemes, and image properties. Dynamic range is discussed, as is the impact of loss on dynamic range. Modified window functions are proposed to mitigate effects of sidelobes of shallow targets overwhelming deeper targets.

Doerry, A.W.

1994-01-01

148

Interferometric Synthetic Aperture Radar Studies of Alaska Volcanoes  

Microsoft Academic Search

position and attitude of satellites is required to remove the effect caused by the differences in the satellite orbits of the two passes. The topographic effects in the interferogram can be removed by producing a synthetic interferogram based on an accurate digital elevation model (DEM) and subtracting it from the interferogram to be studied (2,3). This results in a deformation

Zhong Lu; Charles Wicks; John Power; Daniel Dzurisin; Wayne Thatcher; Timothy Masterlark; Cascades USGS

2009-01-01

149

Synthetic Aperture Radar: The NCCS Enables Search and Rescue  

NASA Astrophysics Data System (ADS)

For as long as planes have gone down, dedicated men and women have used ever-improving technologies to aid their search for survivors. Nearly 2,000 general aviation crashes occur each year in U.S.-and many, like the Montana incident, occur without witnesses. On average, every day in the U.S. one airplane is reported missing. The Air Force Rescue Coordination Center (AFRCC) organizes search missions for about 100 aircraft each year. Some of these are not found before the searches called off, and are discovered only by chance long after the crash. In some cases, the crash site is never found. NASA Search and Rescue Mission is using NCCS rescues to develop tools for processing radar data that can help these effort

2002-07-01

150

A system for the real time exploitation of digital synthetic aperture radar data  

NASA Astrophysics Data System (ADS)

The Advanced Building Block for Large Area Exploitation (ABLE) is a system designed to demonstrate the feasibility of doing real time synthetic aperture radar exploitation. ABLE has four subsystems, which have the following functions: (1) reception and processing of the phase histories to produce an image; (2) automatic change detection; (3) two-stage exploitation function proper; and (4) production and management of cues, as well as the ancillary management necessary for efficient exploitation. ABLE's major components consist of the Synthetic Aperture Precision Processor High Reliability (SAPPHIRE) digital correlator, the automatic change detection subsystem, the exploitation subsystem, and the exploitation management system. Factors influencing the system engineering are discussed, and the resulting design features are described.

Withman, R. L.

151

On the Soil Roughness Parameterization Problem in Soil Moisture Retrieval of Bare Surfaces from Synthetic Aperture Radar  

Microsoft Academic Search

Synthetic Aperture Radar has shown its large potent ial for retrieving soil moisture maps at regional scales. However, since th e backscattered signal is determined by several surface characteristics, the retrieval of s oil moisture is an ill-posed problem when using single configuration imagery. Unless accurate surface roughness parameter values are available, retrieving soil moisture from radar back scatter usually

Niko E. C Verhoest; Hans Lievens; Wolfgang Wagner; Jesús Álvarez-Mozos; M. Susan Moran; Francesco Mattia

2008-01-01

152

Ionospheric effects on a wide-bandwidth, polarimetric, space-based, synthetic-aperture radar  

SciTech Connect

The earth`s ionosphere consists of an ionized plasma which will interact with any electromagnetic wave propagating through it. The interaction is particularly strong at vhf and uhf frequencies but decreases for higher microwave frequencies. These interaction effects and their relationship to the operation of a wide-bandwidth, synthetic-aperture, space-based radar are examined. Emphasis is placed on the dispersion effects and the polarimetric effects. Results show that high-resolution (wide-bandwidth) and high-quality coherent polarimetrics will be very difficult to achieve below 1 GHz.

Brock, B.C.

1993-01-01

153

Ionospheric effects on a wide-bandwidth, polarimetric, space-based, synthetic-aperture radar  

SciTech Connect

The earth's ionosphere consists of an ionized plasma which will interact with any electromagnetic wave propagating through it. The interaction is particularly strong at vhf and uhf frequencies but decreases for higher microwave frequencies. These interaction effects and their relationship to the operation of a wide-bandwidth, synthetic-aperture, space-based radar are examined. Emphasis is placed on the dispersion effects and the polarimetric effects. Results show that high-resolution (wide-bandwidth) and high-quality coherent polarimetrics will be very difficult to achieve below 1 GHz.

Brock, B.C.

1993-01-01

154

Target classification in synthetic aperture radar using map-seeking circuit technology  

NASA Astrophysics Data System (ADS)

Conventional target recognition approaches for SAR include template matching and feature-based classification. However, unlike visual imagery, Synthetic Aperture Radar (SAR) presents a unique challenge in that many attributes, such as scattering centers, are extremely pose dependent and wink in and out with even minor viewing geometry changes. This work implements a highly efficient biologically-inspired 3D template-based approach, the Map Seeking Circuit (MSC) algorithm, for target recognition in SAR. Instead of exhaustively searching a high dimensional state space, the MSC algorithm efficiently searches a superposition hypersurface to estimate target location and 3D pose. Results are shown from applying the algorithm to real SAR datasets.

Peterson, Cameron K.; Murphy, Patricia; Rodriguez, Pedro

2011-05-01

155

Three-dimensional ground penetrating radar imaging using synthetic aperture time-domain focusing  

SciTech Connect

This paper discusses a three-dimensional synthetic aperture imaging technique based on time-domain focusing of pulse-echo radar data. We describe the basic image formation process, important data processing issues, and compensation for planar variations in the media. We present a high-resolution volumetric image reconstruction of a concrete test slab and show that we are able to identify steel reinforcing bars in the image. We conclude with a brief comparison of this imaging method with a technique based on diffraction tomography.

Johansson, E.M.; Mast, J.E.

1994-08-01

156

Three-dimensional ground-penetrating radar imaging using synthetic aperture time-domain focusing  

NASA Astrophysics Data System (ADS)

This paper discusses a three-dimensional synthetic aperture imaging technique based on time- domain focusing of pulse-echo radar data. We describe the basic image formation process, important data processing issues, and compensation for planar variations in the media. We present a high-resolution volumetric image reconstruction of a concrete test slab and show that we are able to identify steel reinforcing bars in the image. We conclude with a brief comparison of this imaging method with a technique based on diffraction tomography.

Johansson, Erik M.; Mast, Jeffrey E.

1994-09-01

157

Wind wave directions determined form synthetic aperture radar imagery and from a tower in Lake Michigan  

NASA Astrophysics Data System (ADS)

Directional wave spectra calculated from digitized synthetic aperture radar (SAR) images of waves on Lake Michigan are compared to a wave directional spectrum determined from measurements taken at a tower and to a one-dimensional spectrum determined from a Waverider buoy. The comparison is within one frequency band for peak energy frequency and within 20° for direction, but the SAR image intensity spectrum does not have the same shape as a wave height spectrum. Wave refraction directions observed in the SAR spectra are within 10° of classical wave refraction calculations.

Schwab, David J.; Schuchman, Robert A.; Liu, Paul C.

1981-03-01

158

Correction of motion measurement errors beyond the range resolution of a synthetic aperture radar  

DOEpatents

Motion measurement errors that extend beyond the range resolution of a synthetic aperture radar (SAR) can be corrected by effectively decreasing the range resolution of the SAR in order to permit measurement of the error. Range profiles can be compared across the slow-time dimension of the input data in order to estimate the error. Once the error has been determined, appropriate frequency and phase correction can be applied to the uncompressed input data, after which range and azimuth compression can be performed to produce a desired SAR image.

Doerry, Armin W. (Albuquerque, NM); Heard, Freddie E. (Albuquerque, NM); Cordaro, J. Thomas (Albuquerque, NM)

2008-06-24

159

Direction synthesis in DOA estimation for monostatic multiple input multiple output (MIMO) radar based on synthetic impulse and aperture radar (SIAR) and its performance analysis  

Microsoft Academic Search

A new direction synthetic method for monostatic multiple input multiple output (MIMO) radar is presented based on synthetic\\u000a impulse and aperture radar (SIAR) system. Concerned with the monostatic MIMO radar which simultaneously emits orthogonal signals\\u000a with multi-carrier-frequency and possesses sparsely distributed transmitting and receiving arrays with respective location,\\u000a as well as the situation for the presence of multipath propagation in

GuangHui Zhao; BaiXiao Chen; ShouPing Zhu

2008-01-01

160

Method for the processing of the reception signal of a deramp type synthetic aperture radar  

US Patent & Trademark Office Database

A Deramp type radar used in synthetic aperture radar for radar imaging transmits coherently repeated linear frequency-modulated pulses and carries out a sort of pulse compression in reception by demodulation of the echo signals received by means of a frequency ramp that reproduces all or part of a transmitted pulse, and by a Fourier transform performed in range. The application to a Deramp type radar signal of a standard SAR processing is disturbed by the fact that, in this signal, the effectively demodulated part of an echo signal due to a target has a position with respect to this echo signal and a duration that are variable as a function of the distance from the target to the radar. The proposed method makes it possible to eliminate this disturbance by means of a particular choice of a common temporal support used for the demodulation of the signals of all the targets of the useful swath and a phase correction applied to the level of the pulse response of the image focusing filter of the SAR processing. Secondarily, a second phase correction can be applied to the complex reflection coefficients obtained for the dots of the image at the end of the SAR processing.

2000-06-06

161

The tomographic formulation of spotlight mode synthetic aperture radar extended to three dimensional targets  

SciTech Connect

In this paper we take a new look at the tomographic formulation of spotlight mode synthetic aperture radar (SAR), so as to include the case of targets having three-dimensional structure. This bridges the work of David C. Munson and his colleagues, who first described SAR in terms of two-dimensional tomography, with Jack Walker`s original derivation of spotlight mode SAR imaging via Doppler analysis. The main result is to demonstrate that the demodulated radar return data from a spotlight mode collection represent a certain set of samples of the three-dimensional Fourier transform of the target reflectivity function, and to do so using tomographic principles instead of traditional Doppler arguments. We then show that the tomographic approach is useful in interpreting the two-dimensional SAR image of a three-dimensional scene. In particular, the well-known SAR imaging phenomenon commonly referred to as layover is easily explained in terms of tomographic projection. 4 refs.

Jakowatz, C.V. Jr.; Thompson, P.A.

1992-06-01

162

The tomographic formulation of spotlight mode synthetic aperture radar extended to three dimensional targets  

SciTech Connect

In this paper we take a new look at the tomographic formulation of spotlight mode synthetic aperture radar (SAR), so as to include the case of targets having three-dimensional structure. This bridges the work of David C. Munson and his colleagues, who first described SAR in terms of two-dimensional tomography, with Jack Walker's original derivation of spotlight mode SAR imaging via Doppler analysis. The main result is to demonstrate that the demodulated radar return data from a spotlight mode collection represent a certain set of samples of the three-dimensional Fourier transform of the target reflectivity function, and to do so using tomographic principles instead of traditional Doppler arguments. We then show that the tomographic approach is useful in interpreting the two-dimensional SAR image of a three-dimensional scene. In particular, the well-known SAR imaging phenomenon commonly referred to as layover is easily explained in terms of tomographic projection. 4 refs.

Jakowatz, C.V. Jr.; Thompson, P.A.

1992-01-01

163

Processing of wide-angle synthetic aperture radar signals for target detection  

NASA Astrophysics Data System (ADS)

This study investigated methods of targets detection using Wide-Angle Synthetic Aperture Radar (WASAR). WASAR uses multiple aspect angle Synthetic Aperture Radar (SAR) images of the same scene. The SAR images were generated using a pre-release software package from package from Loral Corporation. The software was able to generate 512 by 512 pixel SAR images that contained various vegetation return which for our purposes we classified as clutter. Within this clutter, targets (M35 trucks) could be placed at random location and orientations. The software also had the capability of generating fully-polarimetic WASAR images with multiple depression angles. This data was then processed and various detection algorithms tested to exploit the amount and diversity of information available from the multiple images. SAR images are generally known to contain large amounts of data, and WASAR images contain even more due to the multiple images. Various pre-processing filters were analyzed for detection optimization. These filters included: polarimetric averaging, polarimetric span, polarimetric optimal weighting, and polarimetric whitening filters. Simple classical detection (thresholding) algorithms were evaluated using these preprocessed data sets. The use of WASAR imagery improved detection by allowing thresholds to be set higher than for simple SAR thereby avoiding false alarms yet still allowing detection of the known targets.

Knurr, Kurt W.

1993-12-01

164

Invariant triangle-based stationary oil platform detection from multitemporal synthetic aperture radar data  

NASA Astrophysics Data System (ADS)

An automatic algorithm for stationary oil platform detection from multitemporal synthetic aperture radar data is proposed. The proposed algorithm consists of the following two parts. (1) A two-parameter constant false-alarm rate (CFAR) algorithm is used to extract targets from the Environment Satellite (ENVISAT) advanced synthetic aperture radar (ASAR), in which the focus is to determine the appropriate parameters of CFAR, thus ensuring as few as possible false-alarm targets when sea-surface targets are effectively extracted. (2) A simple point cluster matching pattern is proposed based on an invariant triangle rule, by which targets extracted from multitemporal ENVISAT ASAR images are automatically matched for detection of stationary targets (e.g., oil platforms). This invariant triangle rule is that any three moving targets have an extremely low probability of maintaining a relative position in multitemporal images, whereas stationary targets can always maintain a fixed relative position. Even under high noise, this invariant triangle rule can be used to realize the target data matching with high robustness. The experiment shows that the false-alarm rate and the missing rate are relatively low when all the targets are detected. The proposed invariant-triangle-based point cluster matching pattern can conduct effective detection and monitoring of stationary oil platforms.

Cheng, Liang; Yang, Kang; Tong, Lihua; Liu, Yongxue; Li, Manchun

2013-01-01

165

Aboveground biomass estimation of tropical forest from Envisat advanced synthetic aperture radar data using modeling approach  

NASA Astrophysics Data System (ADS)

Retrieval of the aboveground forest biomass (AGB), especially in high biomass forests (>100 t/ha), remains a challenging task for the researchers worldwide. The retrieval of AGB over a tropical forest area in India using Envisat advanced synthetic aperture radar C-band backscatter, interferometric synthetic aperture radar (InSAR) coherence and semi-empirical models viz., water cloud model (WCM) and interferometric water cloud model (IWCM), is studied. In process, the model parameters, i.e., backscatter from vegetation and ground, two-way tree transmissivity, and coherence from vegetation and ground were retrieved. The model training procedure to retrieve the model parameters consisted of an iterative regression of WCM and IWCM. High AGB accuracy (R2=0.73) with low root mean square error (RMSE=53.76 t/ha) was achieved through multidate weighted averaging using RMSE-based weighting coefficients and WCM. Multidate data and InSAR coherence images showed better results (R2=0.90, RMSE=35.92 t/ha) compared to individual coherence images. The InSAR coherence was found to be better for AGB retrieval than SAR backscatter as the former did not saturate for high AGB values.

Kumar, Shashi; Pandey, Uttara; Kushwaha, Satya P.; Chatterjee, Rajat S.; Bijker, Wietske

2012-01-01

166

Factors governing selection of operating frequency for subsurface-imaging synthetic-aperture radar  

NASA Astrophysics Data System (ADS)

A subsurface-imaging synthetic-aperture radar (SISAR) has potential for application in areas as diverse as non- proliferation programs for nuclear weapons to environmental monitoring. However, subsurface imaging is complicated by propagation loss in the soil and surface-clutter response. Both the loss and surface-clutter response depend on the operating frequency. This paper examines several factors which provide a basis for determining optimum frequencies and frequency ranges which will allow synthetic-aperture imaging of buried targets. No distinction can be made between objects at different heights when viewed with a conventional imaging radar (which uses a 1D synthetic aperture), and the return from a buried object must compete with the return from the surface clutter. Thus, the signal-to-clutter ratio is an appropriate measure of performance for a SISAR. A parameter-based modeling approach is used to model the compelx dielectric constant of the soil from measured data obtained from the literature. Theoretical random-surface scattering models, based on statistical solutions to Maxwell's equations, are used to model the clutter. These models are combined to estimate the signal-to-clutter ratio for canonical targets buried in several soil configurations. Results indicate that the HF spectrum (3-30 MHz), although it could be used to detect certain targets under some conditions, has limited practical value for use with SISAR, while the upper VHF through UHF spectrum ($AP100 MHz - 1 GHz) shows the most promise for a general purpose SISAR system. Recommendations are included for additional research.

Brock, Billy C.; Patitz, Ward E.

1994-07-01

167

Factors governing selection of operating frequency for subsurface- imaging synthetic-aperture radar  

SciTech Connect

A subsurface-imaging synthetic-aperture radar (SISAR) has potential for application in areas as diverse as non-proliferation programs for nuclear weapons to environmental monitoring. However, subsurface imaging is complicated by propagation loss in the soil and surface-clutter response. Both the loss and surface-clutter response depend on the operating frequency. This paper examines several factors which provide a basis for determining optimum frequencies and frequency ranges which will allow synthetic-aperture imaging of buried targets. No distinction can be made between objects at different heights when viewed with a conventional imaging radar (which uses a one-dimensional synthetic aperture), and the return from a buried object must compete with the return from the surface clutter. Thus, the signal-to-clutter ratio is an appropriate measure of performance for a SISAR. A parameter-based modeling approach is used to model the complex dielectric constant of the soil from measured data obtained from the literature. Theoretical random-surface scattering models, based on statistical solutions to Maxwell`s equations, are used to model the clutter. These models are combined to estimate the signal-to-clutter ratio for canonical targets buried in several soil configurations. Results indicate that the HF spectrum (3--30), although it could be used to detect certain targets under some conditions, has limited practical value for use with SISAR, while the upper VIHF through UHF spectrum ({approximately}100 MHz - 1 GHz) shows the most promise for a general purpose SISAR system. Recommendations are included for additional research.

Brock, B.C.; Patitz, W.E.

1993-12-31

168

Upper ocean fine-scale features in synthetic aperture radar imagery. Part II: Numerical modeling  

NASA Astrophysics Data System (ADS)

We have been able to reproduce synthetic aperture radar (SAR) signatures of freshwater plumes and sharp frontal interfaces interacting with wind stress, as well as internal waves by combining hydrodynamic simulations with a radar imaging algorithm. The numerical simulations were performed using a non-hydrostatic model, the computational fluid dynamics (CFD) software ANSYS Fluent. We modeled the dynamics of freshwater plumes and their interaction with ambient stratification in the upper ocean as well as with wind stress. We then combined the results from the CFD model with a radar imaging algorithm to simulate the sea surface signature in SAR images. As the plume propagates into a stratified environment, a resonant interaction between the density-driven current and the ambient stratification can lead to internal waves and a fragmentation of the freshwater plume. This fragmentation can be seen as a banding pattern in the simulated radar image of the sea surface. In addition, wind stress leads to directional anisotropy of fine-scale sea surface signatures with respect to the wind direction. The numerical results are consistent with observations of freshwater plumes in the Western Equatorial Pacific during TOGA COARE and observations in the Straits of Florida reported in a companion paper (Soloviev et al., 2011). Internal waves can lead to a signal in the measured electromagnetic field in the ocean. As part of this work, we have also simulated electromagnetic signatures of freshwater plumes and internal waves in the total magnetic field, which potentially provides a link between SAR signatures of transient ocean dynamics and magnetic field fluctuations in the ocean. The novel approach of combining a CFD model with a radar imaging algorithm to investigate the dynamics of small-scale oceanic features and their sea surface signatures in SAR images can be useful for the study and interpretation of a range of near-surface processes, among them freshwater plumes and sharp frontal interfaces, as well as magnetic signatures of oceanic processes.

Matt, S.; Fujimura, A.; Soloviev, A.

2011-12-01

169

Flexible end-to-end system design for synthetic aperture radar applications  

NASA Astrophysics Data System (ADS)

This paper presents ARTEMIS, Inc.'s approach to development of end-to-end synthetic aperture radar systems for multiple applications and platforms. The flexible design of the radar and the image processing tools facilitates their inclusion in a variety of application-specific end-to-end systems. Any given application comes with certain requirements that must be met in order to achieve success. A concept of operation is defined which states how the technology is used to meet the requirements of the application. This drives the design decisions. Key to adapting our system to multiple applications is the flexible SlimSAR radar system, which is programmable on-the-fly to meet the imaging requirements of a wide range of altitudes, swath-widths, and platform velocities. The processing software can be used for real-time imagery production or post-flight processing. The ground station is adaptable, and the radar controls can be run by an operator on the ground, on-board the aircraft, or even automated as part of the aircraft autopilot controls. System integration takes the whole operation into account, seeking to flawlessly work with data links and on-board data storage, aircraft and payload control systems, mission planning, and image processing and exploitation. Examples of applications are presented including using a small unmanned aircraft at low altitude with a line of sight data link, a long-endurance UAV maritime surveillance mission with on-board processing, and a manned ground moving target indicator application with the radar using multiple receive channels.

Zaugg, Evan C.; Edwards, Matthew C.; Bradley, Joshua P.

2012-05-01

170

A new look at spotlight mode synthetic aperture radar as tomography: imaging 3-D targets.  

PubMed

A new 3D tomographic formulation of spotlight mode synthetic aperture radar (SAR) is developed. This extends the pioneering work of Munson et al. (1983), who first formally described SAR in terms of tomography but who made the simplifying assumption that the target scene was 2D. The present authors treat the more general and practical case in which the radar target reflectivities comprise a 3D function. The main goal is to demonstrate that the demodulated radar return data from a spotlight mode collection represent a certain set of samples of the 3D Fourier transform of the target reflectivity function and to do so using a tomographic paradigm instead of traditional range-Doppler analysis. They also show that the tomographic approach is useful in interpreting the reconstructed 2D SAR image corresponding to a 3D scene. Specifically, the well-known SAR phenomenon of layover is easily explained in terms of tomographic projections and is shown to be analogous to the projection effect in conventional optical imaging. PMID:18290021

Jakowatz, C V; Thompson, P A

1995-01-01

171

Investigation of ground target detection methods in fully polarimetric wide angle synthetic aperture radar images  

NASA Astrophysics Data System (ADS)

Target detection is a high priority of the Air Force for the purpose of reconnaissance and bombardment. This research investigates and develops methods to distinguish ground targets from clutter (i.e. foliage, landscape etc.) in Wide Angle Synthetic Aperture Radar (WASAR) images. WASAR uses multiple aspect angle SAR images of the same target scene. The WASAR data was generated from a pre-release software package (XPATCH-ES) provided by the sponsor (WL-AARA). A statistical analysis and feature extraction is performed on the XPATCH-ES data. Polarimetric and wide angle covariance matrices are estimated and analyzed. From an analysis of the wide angle covariance matrix it is shown that natural clutter has in general a uniform radar return for changing aspect angles, whereas the radar return for a target varies. Based on this analysis, two new wide angle algorithms, the WASAR Whitening Filter and the Adaptive WASAR Whitening Filter (AWWF) are developed. The target detection performance of polarimetric and multi aspect angle image combining algorithms are quantified using Receiver Operating Characteristic curves and target to clutter ratios. It is shown that wide angle processing provides superior target detection performance over polarimetric processing. Combinations of wide angle and polarimetric algorithms were used to achieve a 13.7 dB processing gain in target to clutter ratio when compared to unprocessed images of the target scene. This represents a significant improvement in target detection capabilities.

Laggan, Wayne B.

1995-03-01

172

Models for synthetic aperture radar imaging of the Ocean: A comparison  

NASA Astrophysics Data System (ADS)

Theoretical comparisons are made of different models for synthetic aperture radar (SAR) imaging of ocean waves. The velocity bunching model, distributed surface model, Lyzenga model, Canadian Center for Remote Sensing/Radarsat (CCRS/RADARSAT) model, and the Ocean Research and Engineering (ORE) model are compared analytically with respect to their description of the SAR imaging process and the radar backscatter process. The study concentrates on the temporal description of the backscatter process and its impact on SAR imaging of the ocean. Sample simulations are conducted so as to quantify some of the similarities and differences of the aforementioned models. Other SAR imaging models are discussed, as they pertain to the comparisons noted above. The analytical and numerical simulations show that the Lyzenga model, the CCRS/RADARSAT, model and the ORE model are similar for most commonly occurring sea states. The velocity bunching model is similar to these models when the SAR integration time is small, but it tends to deviate for long integration times. The distributed surface model is shown to describe the imaging process adequately when the radar backscatter is highly correlated in space and time.

Kasilingam, Dayalan P.; Shemdin, Omar H.

1990-09-01

173

Universal multifractal scaling of synthetic aperture radar images of sea-ice  

SciTech Connect

Multifrequency, multipolarization imaging radar scattering coefficient data sets, acquired by synthetic aperture radar (SAR) over sea-ice, were studied in order to reveal their scale-invariant properties. Two distinct scenes were acquired at C-band (5.6 cm) and L-band (25 cm) wavelengths for three different linear polarizations (HH, VV, and HV). These sea-ice radar scattering coefficient fields were investigated by applying both Fourier and multifractal analysis techniques. The (multi) scaling of the data is clearly exhibited in both scenes for all three polarizations at L-band and for the HV polarization at C-band. The fields presenting this symmetry were found to be well described by universal multifractals. The corresponding parameters {alpha}, C{sub 1}, and H were determined for all these fields and were found to vary little with only the parameter H (characterizing the degree of nonconservation) displaying some systematic sensitivity to polarization. The values found for the universal multifractal parameters are {alpha} {approx} 1.85 {+-} 0.05, C{sub 1} {approx} 0.0086 {+-} 0.0041, and H {approx} {minus}0.15 {+-} 0.05.

Falco, T.; Francis, F.; Lovejoy, S. [McGill Univ., Montreal, Quebec (Canada). Physics Dept.; Schertzer, D. [Univ. Pierre et Marie Curie, Paris (France). Lab. de Meteorologie Dynamique; Kerman, B. [Atmospheric Environment Service, Burlington, Ontario (Canada); Drinkwater, M. [Jet Propulsion Lab., Pasadena, CA (United States)

1996-07-01

174

Mesoscale Near-Surface Wind Speed Variability Mapping with Synthetic Aperture Radar  

PubMed Central

Operationally-significant wind speed variability is often observed within synthetic aperture radar-derived wind speed (SDWS) images of the sea surface. This paper is meant as a first step towards automated distinguishing of meteorological phenomena responsible for such variability. In doing so, the research presented in this paper tests feature extraction and pixel aggregation techniques focused on mesoscale variability of SDWS. A sample of twenty eight SDWS images possessing varying degrees of near-surface wind speed variability were selected to serve as case studies. Gaussian high- and low-pass, local entropy, and local standard deviation filters performed well for the feature extraction portion of the research while principle component analysis of the filtered data performed well for the pixel aggregation. The findings suggest recommendations for future research.

Young, George; Sikora, Todd; Winstead, Nathaniel

2008-01-01

175

On the focusing issue of synthetic aperture radar imaging of ocean waves  

SciTech Connect

It is now widely accepted that the imaging of ocean surface waves by synthetic aperture radar (SAR) can be adequately described by velocity bunching theory in conjunction with the two-scale wave model. However, it has been conjectured that this theory is incapable of explaining why, under certain conditions, the image contrast of airborne SAR imagery of ocean waves can be enhanced by defocusing the SAR processor. It this were true it would raise serious doubts about the validity of the velocity bunching theory to describe the SAR imaging of ocean waves. In this paper the velocity bunching theory is defended. It is shown that image contrast enhancement by defocusing can also be obtained by this theory, which does not require the introduction of the phase or group velocity of the long ocean waves as a basic element of the SAR imaging theory.

Bruning, C. (Max-Planck-Inst. fuer Meterologie, Bundesstrasse 55, D-2000 Hamburg 13 (DE)); Alpers, W.R. (Univ. Hamburg, Inst. fuer Meereskunde, Troplowitzstrasse 7, D-2000 Hamburg 54 (DE)); Schroter, J.G. (Alfred-Wegener-Inst. fuer Polar-und Meeresforschung, D-2850 Bremerhaven (DE))

1991-01-01

176

A two-level image pair simulator for interferometric synthetic aperture radar  

NASA Astrophysics Data System (ADS)

This paper presents a novel simulator to obtain single-look complex (SLC) image pair from the distributed target for interferometric synthetic aperture radar (InSAR). From conventional works, two simulation levels are derived: one is raw signal level (RSL) which means using raw signal to obtain SLC image pairs, the other is SLC image level (SIL) which means obtaining the SLC image pairs directly from existing SAR images. Conventional simulators only work on one simulation level, use complicated backscattering models, have high computational load on RSL and mismatch the real data on SIL. The novel simulator can robustly work on both RSL and SIL. It not only simplified the backscattering model, but also reduces the computational load on RSL. Moreover, the novel simulator creatively uses complex backscattering coefficient (CBC) pair to generate SLC image pair on SIL, which makes the result more accurately match real data. Finally, the improvements of this novel simulator are demonstrated by experimental results.

Chen, Wenxun; Xiang, Zheng; Liu, Xingzhao; Zhu, Mengmeng

2008-10-01

177

A multiscale approach to a synthetic aperture radar in dispersive random media  

NASA Astrophysics Data System (ADS)

We consider synthetic aperture radar (SAR) image formation in the situation when the propagation medium is random and dispersive. The propagation model is the Klein-Gordon equation with a random index of refraction and a random dispersive term. We show via a multiscale analysis how medium heterogeneities and dispersion affect the image. In fact, in a situation with a strong source chirp signal, the main effect of the medium heterogeneities is to introduce random phase distortions in the SAR data. We carry out a novel scaling analysis that gives a precise characterization of this canonical phase perturbation and how it affects image resolution and stability. The main effect of the phase perturbation is to reduce the azimuthal resolution and the signal-to-noise ratio and we quantify this performance degradation.

Garnier, Josselin; Sølna, Knut

2013-05-01

178

General adaptive-neighborhood technique for improving synthetic aperture radar interferometric coherence estimation.  

PubMed

A new method for filtering the coherence map issued from synthetic aperture radar (SAR) interferometric data is presented. For each pixel of the interferogram, an adaptive neighborhood is determined by a region-growing technique driven by the information provided by the amplitude images. Then pixels in the derived adaptive neighborhood are complex averaged to yield the filtered value of the coherence, after a phase-compensation step is performed. An extension of the algorithm is proposed for polarimetric interferometric SAR images. The proposed method has been applied to both European Remote Sensing (ERS) satellite SAR images and airborne high-resolution polarimetric interferometric SAR images. Both subjective and objective performance analysis, including coherence edge detection, shows that the proposed method provides better results than the standard phase-compensated fixed multilook filter and the Lee adaptive coherence filter. PMID:15330474

Vasile, Gabriel; Trouvé, Emmanuel; Ciuc, Mihai; Buzuloiu, Vasile

2004-08-01

179

Coherence estimation in synthetic aperture radar data based on speckle noise modeling.  

PubMed

In the past we proposed a multidimensional speckle noise model to which we now include systematic phase variation effects. This extension makes it possible to define what is believed to be a novel coherence model able to identify the different sources of bias when coherence is estimated on multidimensional synthetic radar aperture (SAR) data. On the one hand, low coherence biases are basically due to the complex additive speckle noise component of the Hermitian product of two SAR images. On the other hand, the availability of the coherence model permits us to quantify the bias due to topography when multilook filtering is considered, permitting us to establish the conditions upon which information may be estimated independently of topography. Based on the coherence model, two coherence estimation approaches, aiming to reduce the different biases, are proposed. Results with simulated and experimental polarimetric and interferometric SAR data illustrate and validate both, the coherence model and the coherence estimation algorithms. PMID:17230249

López-Martínez, Carlos; Pottier, Eric

2007-02-01

180

The Use of Multiple-Polarization Data in Foliage Penetrating (FOPEN) Synthetic Aperture Radar (SAR) Applications  

SciTech Connect

Foliage penetrating (FOPEN) synthetic aperture radar (SAR) systems are capable of producing images of targets concealed under a foliage canopy. The quality and interpretability of these images, however, is generally limited by dense foliage clutter and by fundamental foliage-induced image degradation. Use of a polarimetric SAR to provide multiple polarization channels can mitigate these effects by offering target and scene information beyond that provided by a single-polarization SAR. This paper presents the results of a literature survey to investigate the use of multiple-polarization data in conjunction with FOPEN SAR applications. The effects of foliage propagation on SAR image quality are briefly summarized. Various approaches to multiple-polarization-based FOPEN target detection are described. Although literature concerning FOPEN target recognition is scarce, the use of multiple-polarization data for in-the-clear target recognition is described. The applicability of various target detection and recognition applications for use with concealed target SAR (CTSAR) imagery is considered.

RICHARDS,JOHN A.

2002-07-01

181

Regional Mapping of the Offshore Wind Resource: Towards a Significant Contribution From SpaceBorne Synthetic Aperture Radars  

Microsoft Academic Search

This paper reviews and discusses the benefits of synthetic aperture radar (SAR) satellite imagery for regional mapping of the offshore wind resources, mostly in comparison to the more standard approach of numerical mesoscale and\\/or microscale models. Remote sensing measurements can be used as a complementary approach to numerical models, as well as a semi-autonomous approach to assess offshore and coastal

Philippe Beaucage; Monique Bernier; GaËtan Lafrance; Julien Choisnard

2008-01-01

182

Volcano-wide fringes in ERS synthetic aperture radar interferograms of Etna (1992-1998): Deformation or tropospheric effect?  

Microsoft Academic Search

Mount Etna (3300 m) is the volcano that has been first and most studied by differential synthetic aperture radar. Previous papers gave evidence for a large-scale deformation of the entire edifice consistent with unrest episodes but with a poor fit with classical elastic models. Also, atmospheric effects on mountainous areas are known to be very significant. Accordingly, interferograms may reflect

François Beauducel; Pierre Briole; Jean-Luc Froger

2000-01-01

183

Coseismic deformation of the 2001 Mw = 7.8 Kokoxili earthquake in Tibet, measured by synthetic aperture radar interferometry  

Microsoft Academic Search

The 14 November 2001, Mw = 7.8, Kokoxili earthquake ruptured more than 400 km of the westernmost stretch of the left-lateral Kunlun fault in northern Tibet. Interferometric synthetic aperture radar data from descending orbits, along four adjacent tracks covering almost the entire rupture, and 1-m pixel Ikonos satellite images are used to map the rupture geometry and the surface displacements

C. Lasserre; G. Peltzer; F. Crampé; Y. Klinger; J. Van der Woerd; P. Tapponnier

2005-01-01

184

Focus of attention for millimeter and ultra wideband synthetic aperture radar imagery  

NASA Astrophysics Data System (ADS)

The major goal of this research is to develop efficient detectors for Synthetic Aperture Radar (SAR) images, exploiting the reflectivity characteristics of targets in different radar types. Target detection is a signal processing problem whereby one attempts to detect a stationary target embedded in background clutter while minimizing the false alarm probability. In radar signal processing, the better resolution provided by the Millimeter Wave (MMW) SAR enhances the detectability of small targets. As radar technology evolves, the newly developed Ultra Wideband (UWB) SAR provides better penetration capabilities to locate concealed targets in foliage. In this thesis we demonstrate that local intensity kernel tests can be formulated based on the generalized likelihood ratio test (GLRT), while preserving constant false alarm rate (CFAR) characteristics. Both the widely used two-parameter CFAR and the g -CFAR can be viewed as special cases of the local intensity tests with different intensity kernels. It is demonstrated that the first-order Gamma kernel is a good approximation for the principal eigenvector of the projected radial intensity of targets, which provides the optimal matching intensity kernel. This also explains the better performance of the g -CFAR detector over the two parameter CFAR detector. We also developed different CFAR subspace detectors for UWB images, utilizing a Laguerre function subspace. The driven response produced by natural clutter degrades the performance of these subspace detectors. In addition to the driven response, the distinguishing feature of metallic targets in UWB is the resonance response. Therefore, we further propose a two-stage detection scheme: g -CFAR detector followed by the quadratic Laguerre discriminator (QLD). We evaluate every detector and discriminator using ROC curves in a large area (about 2 km2) of imagery. The combined g -CFAR and quadratic Laguerre discriminator improve the simple Laguerre subspace detector more than one hundred fold for a perfect detection rate (Pd = 1).

Yen, Li-Kang

185

A High Resolution, Light-Weight, Synthetic Aperture Radar for UAV Application  

SciTech Connect

(U) Sandia National Laboratories in collaboration with General Atomics (GA) has designed and built a high resolution, light-weight, Ku-band Synthetic Aperture Radar (SAR) known as "Lynx". Although Lynx can be operated on a wide variety of manned and unmanned platforms, its design is optimized for use on medium altitude Unmanned Aerial Vehicles (UAVS). In particular, it can be operated on the Predator, I-GNAT, and Prowler II platforms manufactured by GA. (U) The radar production weight is less than 120 lb and operates within a 3 GHz band from 15.2 GHz to 18.2 GHz with a peak output power of 320 W. Operating range is resolution and mode dependent but can exceed 45 km in adverse weather (4 mm/hr rain). Lynx has operator selectable resolution and is capable of 0.1 m resolution in spotlight mode and 0.3 m resolution in stripmap mode, over substantial depression angles (5 to 60 deg) and squint angles (broadside ±45 deg). Real-time Motion Compensation is implemented to allow high-quality image formation even during vehicle turns and other maneuvers.

Doerry, A.W.; Hensley, W.H.; Stence, J.; Tsunoda, S.I. Pace, F.; Walker, B,C.; Woodring, M.

1999-05-27

186

Developing a small multi frequency synthetic aperture radar for UAS operation: the SlimSAR  

NASA Astrophysics Data System (ADS)

The SlimSAR is a small, low-cost, Synthetic Aperture Radar (SAR) and represents a new advancement in high-performance SAR. ARTEMIS employed a unique design methodology in designing the SlimSAR that exploits previous developments. The system is designed to be smaller, lighter, and more flexible while consuming less power than typical SAR systems. The system consists of an L-band core and frequency block converters and is very suitable for use on a number of small UAS's. Both linear-frequency-modulated continuous-wave (LFM-CW) and pulsed modes have been tested. The LFM-CW operation achieves high signal-to-noise ratio while transmitting with less peak power than a comparable pulsed system. The flexible control software allows us to change the radar parameters in flight. The system has a built-in high quality GPS/IMU motion measurement solution and can also be packaged with a small data link and a gimbal for high frequency antennas. Multi-frequency SAR provides day and night imaging through smoke, dust, rain, and clouds with the advantages of additional capabilities at different frequencies (i.e. dry ground and foliage penetration at low frequencies, and change detection at high frequencies.)

Zaugg, Evan; Edwards, Matthew; Margulis, Alex

2010-04-01

187

A method for retrieving the directional ocean wave spectra from synthetic aperture radar image  

NASA Astrophysics Data System (ADS)

Directional ocean wave spectra can describe the energy distribution of ocean wave and play an important role in oceanography. Synthetic aperture radar (SAR) can measure wave spectra based on a nonlinear mapping model between the image spectra (or cross spectra) and wave spectra. Due to the complexity of variable estimation and wave number cut off in azimuth direction in the mapping process, some scientists have been endeavoring to improve the retrieval of wave spectra. The paper proposes a method for the retrieval, which don't depend on any external information except wind direction. It separates into two parts. In part 1, the spectra for real image or the cross spectra for complex image are calculated. And the modulation transfer function (MTF) is estimated including real aperture radar (RAR) MTF and velocity bunching. Then the wave spectra are retrieved by direct dividing based on the quasi-linear relation. The 180° ambiguity is removed from the imaginary part of cross spectra or the wind direction. The significant wave height (Hs), peak wave wavelength (L) and peak wave direction (D) are extracted from the retrieval. If the angle between the D and the azimuth direction is higher than 45°, the retrieval is finished. If the angle is lower than 45°, we go on retrieving. In part 2, the first guess spectra are needed to compensate the lost wave information, which can be parametrically constructed based on the retrieved wave spectra in part 1. Finally the wave spectra are iteratively retrieved from the first guess spectra based on the nonlinear relation. The Envisat ASAR images are used to validate the method. In case 1, the RMSE between this method and SARTool on D, L, Hs is 7.6°, 19.7 m, 0.18 m respectively. In case 2, the RMSE between this method and Jason-1 on Hs is 0.5 m.

Ren, Lin; Yang, Jingsong; Chen, Peng

2012-09-01

188

Automatic classification of targets in synthetic aperture radar imagery using topographic features  

NASA Astrophysics Data System (ADS)

Automatic classification of target in synthetic aperture radar (SAR) imagery is performed using topographic features. Targets are segmented from wide area imagery using a constant false alarm rate (CFAR) detector. Individual target areas are classified using the topographical primal sketch which assigns each pixel a label that is invariant under monotonic gray tone transformations. A local surface fit is used to estimate the underlying function oat each target pixel. Pixels are classified based on the zero crossings of the first directional derivatives and the extrema of second directional derivatives. These topographic labels along with the quantitative values of second directional derivative extrema and gradient are used in target matching schemes. Multiple matching schemes are investigated including correlation and graph matching schemes that incorporate distance between features as well as similarity measures. Cost functions are tailored to the topographic features inherent in SAR imagery. Trade offs between the different matching schemes are addressed with respect to robustness and computational complexity. Classification is performed using one foot and one meter imagery obtained from XPATCH simulations and the MSTAR synthetic dataset.

Meth, Reuven; Chellappa, Rama

1996-06-01

189

Algoritimos E Metodologia de Processamento Para Sintese de Imagens de Radar de Abertura Sintetica (SAR) (Algorithms and Methods for Processing Synthetic Aperture Radar (SAR) Images).  

National Technical Information Service (NTIS)

The Synthetic Aperture Radar (SAR) concepts is presented in this work, and describes a digital processing method to SAR system. The Doppler model is used to derive algorithms to the SAR processing. Matched Filters are used to range and azimuth compression...

J. C. Mura

1991-01-01

190

Comparison of Simulated and Measured Synthetic Aperture Radar Image Spectra with Buoy-Derived Ocean Wave Spectra During the Shuttle Imaging Radar B Mission  

Microsoft Academic Search

During the SIR-B mission over the North Sea, two successful synthetic aperture radar (SAR) data takes with simultaneous buoy measurements of ocean wave spectra have been obtained on October 6 and 8, 1984. On October 6, the SAR imaging of ocean waves was predicted as strongly nonlinear and on October 8 as almost linear. The SIR-B experiment confirmed the theoretical

Werner Alpers; Claus Bruening; Karl Richter

1986-01-01

191

Monitoring Changes in Aboveground Biomass in Loblolly Pine Forests Using Multichannel Synthetic Aperture Radar Data  

NASA Astrophysics Data System (ADS)

A study was conducted to evaluate using synthetic aperture radar (SAR) for estimating aboveground biomass in loblolly pine (Pinus taeda L.) forests. The data set for this experiment was a multiple-frequency (C-, L- and P-band), polarimetric SAR data set collected by the NASA/JPL AIRSAR System over the Duke University Research Forest located near Durham, North Carolina. In addition to the SAR data set, a set of ground measurements were collected to describe the tree geometry and biomass characteristics from 59 different stands consisting principally of loblolly pine within the Duke Forest. The aboveground, dry weight woody biomass in these test stands ranges from < 1 to >50 kg-m^2. The first analysis performed on this data set was to produce algorithms to estimate both dry and wet weight biomasses for each of the test stands, and to distribute this biomass amongst various tree components (e.g., boles, branches, and needles/leaves) as well as the different layers within the tree canopy (e.g., canopy, subcanopy and understory) in order to better relate biomass to the radar backscattering measurements. This was accomplished by development of allometric equations to estimate biomass for individual trees, from which stand estimates on an aerial basis were derived. The biomass estimates were then statistically correlated with radar backscatter (sigma ^circ) measurements derived from the SAR data set. It was found that sigma^ circ at a variety of radar frequencies (P, L, and C-bands) and linear-polarization combinations (HH, HV, and VV) were significantly correlated (at a level of significance of p = 0.001) to either individual biomass components (e.g., bole biomass, branch biomass, needle/leaf biomass, etc.) or multiple combinations of these components. While the correlations were significant at all linear polarizations at L- and P-bands, they were only significant in the cross -polarized channel at C-band. Finally, a two-step method was developed to estimate aboveground biomass from multichannel SAR data. The error estimate (coefficient of variation) for the various biomass components ranged between 16% and 27%. It is concluded that the pine stand biomasses (dry weight) for which these algorithms are valid range between 15 and 40 kg-m ^{2}.

Kasischke, Eric Stewart

192

Imaging mesoscale upper ocean dynamics using synthetic aperture radar and optical data  

NASA Astrophysics Data System (ADS)

A synergetic approach for quantitative analysis of high-resolution ocean synthetic aperture radar (SAR) and imaging spectrometer data, including the infrared (IR) channels, is suggested. This approach first clearly demonstrates that sea surface roughness anomalies derived from Sun glitter imagery compare very well to SAR roughness anomalies. As further revealed using these fine-resolution (˜1 km) observations, the derived roughness anomaly fields are spatially correlated with sharp gradients of the sea surface temperature (SST) field. To quantitatively interpret SAR and optical (in visible and IR ranges) images, equations are derived to relate the "surface roughness" signatures to the upper ocean flow characteristics. As developed, a direct link between surface observations and divergence of the sea surface current field is anticipated. From these satellite observations, intense cross-frontal dynamics and vertical motions are then found to occur near sharp horizontal gradients of the SST field. As a plausible mechanism, it is suggested that interactions of the wind-driven upper layer with the quasi-geostrophic current field (via Ekman advective and mixing mechanisms) result in the generation of secondary ageostrophic circulation, producing convergence and divergence of the surface currents. The proposed synergetic approach combining SST, Sun glitter brightness, and radar backscatter anomalies, possibly augmented by other satellite data (e.g., altimetry, scatterometry, ocean color), can thus provide consistent and quantitative determination of the location and intensity of the surface current convergence/divergence (upwelling/downwelling). This, in turn, establishes an important step toward advances in the quantitative interpretation of the upper ocean dynamics from their two-dimensional satellite surface expressions.

Kudryavtsev, Vladimir; Myasoedov, Alexander; Chapron, Bertrand; Johannessen, Johnny A.; Collard, Fabrice

2012-04-01

193

Foldbelt exploration with synthetic aperture radar (SAR) in Papua New Guinea  

SciTech Connect

Synthetic aperture radar (SAR) is being successfully used within the southern fold and thrust belt of Papua New Guinea to map surface structure and stratigraphy and to help plan a hydrocarbon exploration program. The airborne SAR imagery, along with other surface data, is used as a primary exploration tool because acquisition of acceptable seismic data is extremely costly due to extensive outcrops of Tertiary Darai Limestone which develops rugged karst topography. Most anticlines in the licenses are capped with this deeply karstified limestone. The region is ideally suited to geologic analysis using remote sensing technology. The area is seldom cloud free and is covered with tropical rain forest, and geologic field studies are limited. The widespread karst terrain is exceedingly dangerous, if not impossible, to traverse on the ground. SAR is used to guide ongoing field work, modeling of subsurface structure, and selection of well locations. SAR provides their explorationists with an excellent data base because (1) structure is enhanced with low illumination, (2) resolution is 6 x 12 m, (3) digital reprocessing is possible, (4) clouds are penetrated by the SAR, and (5) the survey was designed for stereoscopic photogeology. Landsat images and vertical aerial photographs complement SAR but provide subdued structural information because of minimal shadowing (due to high sun angles) and the jungle cover. SAR imagery reveals large-scale mass wasting that has led to a reevaluation of previously acquired field data. Lithologies can be recognized by textural and tonal changes on the SAR images despite near-continuous canopy of jungle. Reprocessing and contrast stretching of the digital radar imagery provide additional geologic information.

Ellis, J.M.; Pruett, F.D.

1987-05-01

194

On the detection of crevasses in glacial ice with synthetic-aperture radar.  

SciTech Connect

The intent of this study is to provide an analysis of the scattering from a crevasse in Antarctic ice, utilizing a physics-based model for the scattering process. Of primary interest is a crevasse covered with a snow bridge, which makes the crevasse undetectable in visible-light images. It is demonstrated that a crevasse covered with a snow bridge can be visible in synthetic-aperture-radar (SAR) images. The model of the crevasse and snow bridge incorporates a complex dielectric permittivity model for dry snow and ice that takes into account the density profile of the glacier. The surface structure is based on a fractal model that can produce sastrugi-like features found on the surface of Antarctic glaciers. Simulated phase histories, computed with the Shooting and Bouncing Ray (SBR) method, are processed into SAR images. The viability of the SBR method for predicting scattering from a crevasse covered with a snow bridge is demonstrated. Some suggestions for improving the model are given.

Brock, Billy C.

2010-02-01

195

A fast level set method for synthetic aperture radar ocean image segmentation.  

PubMed

Segmentation of high noise imagery like Synthetic Aperture Radar (SAR) images is still one of the most challenging tasks in image processing. While level set, a novel approach based on the analysis of the motion of an interface, can be used to address this challenge, the cell-based iterations may make the process of image segmentation remarkably slow, especially for large-size images. For this reason fast level set algorithms such as narrow band and fast marching have been attempted. Built upon these, this paper presents an improved fast level set method for SAR ocean image segmentation. This competent method is dependent on both the intensity driven speed and curvature flow that result in a stable and smooth boundary. Notably, it is optimized to track moving interfaces for keeping up with the point-wise boundary propagation using a single list and a method of fast up-wind scheme iteration. The list facilitates efficient insertion and deletion of pixels on the propagation front. Meanwhile, the local up-wind scheme is used to update the motion of the curvature front instead of solving partial differential equations. Experiments have been carried out on extraction of surface slick features from ERS-2 SAR images to substantiate the efficacy of the proposed fast level set method. PMID:22399940

Huang, Xiaoxia; Huang, Bo; Li, Hongga

2009-02-03

196

Segmenting Shadows from synthetic aperture radar imagery using edge-enhanced region growing  

NASA Astrophysics Data System (ADS)

An enhanced region-growing approach for segmenting regions is introduced. A region-growing algorithm is merged with stopping criteria based on a robust noise-tolerant edge-detection routine. The region-grow algorithm is then used to segment the shadow region in a Synthetic Aperture Radar (SAR) image. This approach recognizes that SAR phenomenology causes speckle in imagery even to the shadow area due to energy injected from the surrounding clutter and target. The speckled image makes determination of edges a difficult task even for the human observer. This paper outlines the edge-enhanced region grow approach and compares the results to three other segmentation approaches including the region-grow only approach, an automated-threshold approach based on a priori knowledge of the SAR target information, and the manual segmentation approach. The comparison is shown using a tri-metric inter- algorithmic approach. The metrics used to evaluate the segmentation include percent-pixels same (PPS), the partial- directed hausdorff (PDH) metric, and a shape-based metric based on the complex inner product (CIP). Experimental results indicate that the enhanced region-growing technique is a reasonable segmentation for the SAR target image chips obtained from the Moving and Stationary Target Acquisition and Recognition (MSTAR) program.

Power, Gregory J.; Wilson, Kelce S.

2000-11-01

197

Operational and research use of spaceborne synthetic aperture radar at NOAA/NESDIS  

NASA Astrophysics Data System (ADS)

RADARSAT-1 synthetic aperture radar (SAR) satellite data acquired under a U.S-Canada agreement have proven very beneficial to National Oceanic and Atmospheric Administration (NOAA) National Environmental Satellite, Data, and Information Service (NESDIS) and to the National Ice Center (NIC) - a multi-agency operational center representing the Department of Defense (Navy), the Department of Commerce (NOAA), and the Department of Transportation (Coast Guard) - in support of a variety of environmental research and monitoring activities. RADARSAT-1 SAR imagery is the main data stream used by NIC to produce sea ice analysis products operationally. A project to demonstrate additional near real-time SAR applications in Alaska began in the fall of 1999. The Alaska SAR Demonstration (AKDEMO) has provided and infrastructure to validate and test prototype SAR products that respond to critical needs in the region not satisfied with other observational data available. Other projects supported by RADARSAT-1 SAR data include the StormWatch Project lead by The Johns Hopkins University Applied Physics Laboratory; the HurricaneWatch Project conducted in partnership with the Canada Centre for Remote Sensing (CCRS), the Canadian Space Agency (CSA), and the NOAA Atlantic Oceanographic and Metoeorological Laboratory (AOML); as well as several coastal dynamics, pollution and flooding monitoring and research activities. A review and highlights of our SAR experience along with future plans to utilize operationally data from newly available and future satellite missions are presented in this paper.

Clemente-Colón, P.; Pichel, W. G.; Friedman, K. S.; Li, X.; Arabini, E.; Tseng, W.; Bertoia, C. A.; Monaldo, F. M.; Wackerman, C. C.

2003-04-01

198

Synthetic aperture radar data visualization on the iPod Touch  

NASA Astrophysics Data System (ADS)

A major area of focus for the Air Force is sensor performance in urban environments. Aircraft with multiple sensor modalities, such as Synthetic Aperture RADAR (SAR), Infrared (IR), and Electro-Optics (EO), are essential for intelligence, surveillance, and reconnaissance (ISR) of current and future urban battlefields. Although applications exist for visualization of these types of imagery, they usually require at least a laptop computer and internet connection. Field operatives need to be able to access georeferenced information about imagery as part of a Geographic Information System (GIS) on mobile devices. The iPod/iPhone has a 640x480 resolution multi-touch display, making it an excellent device for interacting with georeferenced imagery. We created an iPhone application that loads SAR imagery and allows the user to interact with it. The user multi-touch interface provides pan and zoom capabilities as well as options to change parameters relating to the query. We describe how operatives in the field can use this application to investigate SAR and GIS related problems on the iPhone mobile device, which otherwise would require a computer and Internet connection.

Fouts, Aaron; Vickery, Rhonda; Majumder, Uttam; Burchett, Tracy; Klein, Troy; Minardi, Michael

2010-04-01

199

Ground moving target indication and parameters estimation using a dual-frequency synthetic aperture radar  

NASA Astrophysics Data System (ADS)

A new scheme is presented to estimate the range and azimuth velocity components of a detected moving target by using a dual-frequency synthetic aperture radar (SAR). It consists of a moving target detector, a range velocity estimator, and an azimuth velocity estimator. In this scheme, two original SAR images are achieved from the returns first, and then processed by a symmetric defocusing filter pair (SDFP) to produce two defocused images. By comparing the sharpness of the two defocused images, the moving targets are indicated and isolated form each original SAR image. For a selected moving target, its range velocity component is estimated by using a Doppler ambiguity solver and a stepped approximation-and-comparison algorithm. After range velocity compensated, the target in the patch is concentrated in less range bins, and its azimuth velocity component is estimated by using an SDFP bank. Finally, the moving target is refocused and its azimuth displacement caused by range velocity component is corrected. The effectiveness of the proposed scheme is confirmed by the experiments with the field and simulated data.

Lv, Gaohuan; Wang, Junfeng; Liu, Xingzhao; Wang, Kaizhi

2012-12-01

200

Penetration depth of interferometric synthetic-aperture radar signals in snow and ice  

NASA Astrophysics Data System (ADS)

Digital elevation models of glaciated terrain produced by the NASA/Jet Propulsion Laboratory (JPL) airborne interferometric synthetic-aperture radar (InSAR) instrument in Greenland and Alaska at the C- (5.6 cm wavelength) and L-band (24-cm) frequencies were compared with surface elevation measured from airborne laser altimetry to estimate the phase center of the interferometric depth, or penetration depth, ?p. On cold polar firn at Greenland summit, ?p = 9±2m at C- and 14±4m at L-band. On the exposed ice surface of Jakobshavn Isbrae, west Greenland, ?p = 1±2 m at C- and 3±3 m at L-band except on smooth, marginal ice where ?p=15±5 m. On colder marginal ice of northeast Greenland, ?p reaches 60 to 120 m at L-band. On the temperate ice of Brady Glacier, Alaska, ?p is 4±2 m at C-and 12±6 m at L-band, with little dependence on snow/ice conditions. The implications of the results on the scientific use of InSAR data over snow/ice terrain is discussed.

Rignot, Eric; Echelmeyer, Keith; Krabill, William

201

Seasonal subsidence and rebound in Las Vegas Valley, Nevada, observed by synthetic aperture radar interferometry  

USGS Publications Warehouse

Analyses of areal variations in the subsidence and rebound occurring over stressed aquifer systems, in conjunction with measurements of the hydraulic head fluctuations causing these displacements, can yield valuable information about the compressibility and storage properties of the aquifer system. Historically, stress-strain relationships have been derived from paired extensometer/piezometer installations, which provide only point source data. Because of the general unavailability of spatially detailed deformation data, areal stress-strain relations and their variability are not commonly considered in constraining conceptual and numerical models of aquifer systems. Interferometric synthetic aperture radar (InSAR) techniques can map ground displacements at a spatial scale of tens of meters over 100 km wide swaths. InSAR has been used previously to characterize larger magnitude, generally permanent aquifer system compaction and land subsidence at yearly and longer timescales, caused by sustained drawdown of ground-water levels that produces intergranular stresses consistently greater than the maximum historical stress. We present InSAR measurements of the typically small-magnitude, generally recoverable deformations of the Las Vegas Valley aquifer system occurring at seasonal timescales. From these we derive estimates of the elastic storage coefficient for the aquifer system at several locations in Las Vegas Valley. These high-resolution measurements offer great potential for future investigations into the mechanics of aquifer systems and the spatial heterogeneity of aquifer system structure and material properties as well as for monitoring ongoing aquifer system compaction and land subsidence.

Hoffmann, J.; Zebker, H. A.; Galloway, D. L.; Amelung, F.

2001-01-01

202

A Fast Level Set Method for Synthetic Aperture Radar Ocean Image Segmentation  

PubMed Central

Segmentation of high noise imagery like Synthetic Aperture Radar (SAR) images is still one of the most challenging tasks in image processing. While level set, a novel approach based on the analysis of the motion of an interface, can be used to address this challenge, the cell-based iterations may make the process of image segmentation remarkably slow, especially for large-size images. For this reason fast level set algorithms such as narrow band and fast marching have been attempted. Built upon these, this paper presents an improved fast level set method for SAR ocean image segmentation. This competent method is dependent on both the intensity driven speed and curvature flow that result in a stable and smooth boundary. Notably, it is optimized to track moving interfaces for keeping up with the point-wise boundary propagation using a single list and a method of fast up-wind scheme iteration. The list facilitates efficient insertion and deletion of pixels on the propagation front. Meanwhile, the local up-wind scheme is used to update the motion of the curvature front instead of solving partial differential equations. Experiments have been carried out on extraction of surface slick features from ERS-2 SAR images to substantiate the efficacy of the proposed fast level set method.

Huang, Xiaoxia; Huang, Bo; Li, Hongga

2009-01-01

203

Reduction of ionospheric distortions for spaceborne synthetic aperture radar with the help of image registration  

NASA Astrophysics Data System (ADS)

We propose a robust technique for reducing the ionospheric distortions in spaceborne synthetic aperture radar (SAR) images. It is based on probing the terrain on two distinct carrier frequencies. Compared to our previous work on the subject (Smith and Tsynkov 2011 SIAM J. Imaging Sciences 4 501-42), the increase in robustness is achieved by applying an area-based image registration algorithm to the two images obtained on two frequencies. This enables an accurate evaluation of the shift between the two images, which, in turn, translates into an accurate estimate of the total electron content and its along-track gradient in the ionosphere. These estimates allow one to correct the matched filter and thus improve the quality of the image. Moreover, for the analysis of SAR resolution in the current paper we take into account the Ohm conductivity in the ionosphere (in addition to its temporal dispersion), and also consider the true Kolmogorov spectrum of the ionospheric turbulence, as opposed to its approximate representation that we have used previously.

Gilman, Mikhail; Smith, Erick; Tsynkov, Semyon

2013-05-01

204

Remote sensing of ocean waves by along-track interferometric synthetic aperture radar  

NASA Astrophysics Data System (ADS)

A new wave retrieval method for the Along-Track Interferometric Synthetic Aperture Radar (AT-InSAR) phase image is presented. The new algorithm, named parametric retrieval algorithm (PRA), uses the full nonlinear mapping relations. It differs from previous retrieval algorithms in that it does not require a priori information about the sea state or the wind vector from scatterometer data. Instead, it combines the observed AT-InSAR phase spectrum and assumed wind vector to estimate the wind sea spectrum. The method has been validated using several C-band and X-band HH-polarized AT-InSAR observations collocated with spectral buoy measurements. In this paper, X-band and C-band HH-polarized AT-InSAR phase images of ocean waves are first used to study AT-InSAR wave imaging fidelity. The resulting phase spectra are quantitatively compared with forward-mapped in situ directional wave spectra collocated with the AT-InSAR observations. Subsequently, we combine the parametric retrieval algorithm (PRA) with X-band and C-band HH-polarized AT-InSAR phase images to retrieve ocean wave spectra. The results show that the ocean wavelengths, wave directions, and significant wave heights estimated from the retrieved ocean wave spectra are in agreement with the buoy measurements.

Zhang, Biao; Perrie, Will; He, Yijun

2009-10-01

205

Automated global water mapping based on wide-swath orbital synthetic aperture radar  

NASA Astrophysics Data System (ADS)

This paper presents an automated technique, embedded in an online service, which ingests orbital synthetic aperture radar (SAR) imagery and outputs surface water maps in near real time and on a global scale. The service anticipates future open data dissemination of water extent information using the European Space Agency's Sentinel-1 data. The classification methods used are innovative but practical and different per 1 × 1 degree tile. For each tile, a probability distribution function of a pixel, being covered with water or being dry is established based on a long SAR training dataset. These probability distributions are conditional on the backscatter and the incidence angle. In classification mode the probability of water coverage is calculated, conditional on the current backscatter - incidence angle combination. The overlap between the probability distributions of a pixel being wet or dry is used as a proxy for the quality of our classification. The service has multiple uses, e.g. for water body dynamics in times of drought or for urgent inundation extent determination during floods. The service generates data systematically: it is not an on-demand service activated only for emergency response, but instead is always up-to-date and available. We demonstrate its use in flood situations using Envisat ASAR information during the 2011 Thailand floods. A first merge with a NASA near real time water product based on MODIS optical satellite imagery shows excellent agreement between these independent satellite-based water products.

Westerhoff, R. S.; Kleuskens, M. P. H.; Winsemius, H. C.; Huizinga, H. J.; Brakenridge, G. R.

2012-06-01

206

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

Microsoft Academic Search

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

Christopher G. Cochrane; Richard C. Ghail

2006-01-01

207

Multi-aspect detection of surface and shallow-buried unexploded ordnance via ultra-wideband synthetic aperture radar  

Microsoft Academic Search

An ultra-wideband (UWB) synthetic aperture radar (SAR) system is investigated for the detection of former bombing ranges, littered by unexploded ordnance (UXO). The objective is detection of a high enough percentage of surface and shallow-buried UXO, with a low enough false-alarm rate, such that a former range can be detected. The physics of UWB SAR scattering is exploited in the

Yanting Dong; Paul R. Runkle; Lawrence Carin; Raju Damarla; Anders Sullivan; Marc A. Ressler; Jeffrey Sichina

2001-01-01

208

A New Methodology for Synthetic Aperture Radar (SAR) Raw Data Compression Based on Wavelet Transform and Neural Networks  

Microsoft Academic Search

\\u000a Synthetic Aperture Radar (SAR) raw data are characterized by a high entropy content. As a result, conventional SAR compression\\u000a techniques (such as block adaptive quantization and its variants) do not provide fully satisfactory performances. In this\\u000a paper, a novel methodology for SAR raw data compression is presented, based on discrete wavelet transform (DWT). The correlation\\u000a between the DWT coefficients of

Giacomo Capizzi; Salvatore Coco; Antonio Laudani; Giuseppe Pappalardo

2004-01-01

209

Interferometric synthetic aperture radar study of Okmok volcano, Alaska, 1992–2003: Magma supply dynamics and postemplacement lava flow deformation  

Microsoft Academic Search

Okmok volcano, located in the central Aleutian arc, Alaska, is a dominantly basaltic complex topped with a 10-km-wide caldera that formed circa 2.05 ka. Okmok erupted several times during the 20th century, most recently in 1997; eruptions in 1945, 1958, and 1997 produced lava flows within the caldera. We used 80 interferometric synthetic aperture radar (InSAR) images (interferograms) to study

Zhong Lu; Timothy Masterlark; Daniel Dzurisin

2005-01-01

210

Interferometric synthetic aperture radar study of Okmok volcano, Alaska, 1992-2003: Magma supply dynamics and postemplacement lava flow deformation  

Microsoft Academic Search

Okmok volcano, located in the central Aleutian arc, Alaska, is a dominantly basaltic complex topped with a 10-km-wide caldera that formed circa 2.05 ka. Okmok erupted several times during the 20th century, most recently in 1997; eruptions in 1945, 1958, and 1997 produced lava flows within the caldera. We used 80 interferometric synthetic aperture radar (InSAR) images (interferograms) to study

Zhong Lu; Timothy Masterlark; Daniel Dzurisin

2005-01-01

211

A geosynchronous synthetic aperture radar; for tectonic mapping, disaster management and measurements of vegetation and soil moisture  

Microsoft Academic Search

A geosynchronous synthetic aperture radar (SAR) with an orbit inclination of 50-65° can provide daily coverage of all of North and South America. Longitudinally, the width of the mapped area would be on the order of ±50° at the Equator, somewhat more at the most northern\\/southern latitudes. Within the area mapped, very good temporal coverage can be obtained-up to several

S. N. Madsen; Wendy Edelstein; Leo D. DiDomenico; John LaBrecque

2001-01-01

212

Application of selective linear predictive coding (SLPC) in enhancing cross-range resolution of Inverse Synthetic Aperture Radar (ISAR)  

NASA Astrophysics Data System (ADS)

High range resolution X-band Inverse Synthetic Aperture Radar (ISAR) using stepped frequency waveforms is described. Target images are produced by performing inverse Fourier transform in range dimension and linear predictive coding in the cross-range dimension. Enhancement in cross-range resolution is produced by applying selective linear predictive coding (SLPC) technique. The signal processing technique is tested using simulated point targets, data from ship targets and a motor vehicle.

Nandagopal, D.; Longstaff, D.; Nash, G.; Heibronn, D. J.; Haywood, B.

1989-12-01

213

Synthetic Aperture Image Holography.  

National Technical Information Service (NTIS)

The paper describes the underwater imaging method of 'Synthetic Aperture Image Holography' which has real-time imaging capability. The method utilizes image holography and computer synthetic aperture techniques. The imaging system consists of the acoustic...

T. Sato J. S. Jaffe

1985-01-01

214

Transient ultra wide band measurement applications: radar cross section, synthetic aperture radar, electromagnetic compatibility  

Microsoft Academic Search

The Electronic Armament Centre (CELAR: Centre d'Electronique de L'Armement) and the Research Institute of Microwave and Optical Communications (IRCOM: Institut de Recherches en Communications Optiques et Micro-ondes) has evaluated the use of ultra-wide-band (UWB) short pulse measurement facilities to characterize target electromagnetic signatures. A first device is capable of determining the radar cross section (RCS) within a 200 MHz to

J. Andrieu; C. Dubois; M. Lalande; V. Bertrand; P. Delmote; B. Beillard; E. Martinod; B. Jecko; R. Guilleret; F. Monnier; M. Legoff

2003-01-01

215

Application of SEASAT-1 Synthetic Aperture Radar (SAR) Data to Enhance and Detect Geological Lineaments and to Assist Landsat Landcover Classification Mapping.  

National Technical Information Service (NTIS)

Digital SEASAT-1 synthetic aperture radar (SAR) data were used to enhance linear features to extract geologically significant lineaments in the Appalachian region. Comparison of Lineaments thus mapped with an existing lineament map based on LANDSAT MSS im...

R. Sekhon

1981-01-01

216

On the extraction of directional sea-wave spectra from synthetic- aperture radar-signal arrays without matched filtering.  

USGS Publications Warehouse

An economical method of digitally extracting sea-wave spectra from synthetic-aperture radar-signal records, which can be performed routinely in real or near-real time with the reception of telemetry from Seasat satellites, would be of value to a variety of scientific disciplines. This paper explores techniques for such data extraction and concludes that the mere fact that the desired result is devoid of phase information does not, of itself, lead to a simplification in data processing because of the nature of the modulation performed on the radar pulse by the backscattering surface. -from Author

Wildey, R. L.

1980-01-01

217

Automatic target recognition (ATR) performance on wavelet-compressed synthetic aperture radar (SAR) imagery  

NASA Astrophysics Data System (ADS)

With the large amount of image data that can be produced in real-time by new synthetic aperture radar (SAR) platforms, such as Global Hawk, compression techniques will be needed for both transmission and storage of this data. Also to keep image analysts (IA's) from being overwhelmed, high-speed automatic target cueing and/or recognition (ATC, ATR) systems will be needed to help exploit this large amount of data in real-time. Past SAR image compression studies have used subjective visual ratings and/or statistical measures such as mean-squared-error (MSE) to compare compression performance. Statistical metrics are much more appealing than unreproducible biased visual interpretations. However, the use of statistical metrics, such as MSE, has practical limitations on SAR imagery due to the high frequency speckle noise that is characteristic. In this case, the MSE metric is dominated by how well the noise speckle is preserved -- a statistic that is of no consequence. Since the large amount of data that dictates the need for compression also dictates the need for ATR, a meaningful statistic would be ATR performance. This ATR performance metric would emphasize how well pixels on target are preserved. Therefore, we have investigated ATR performance using a wavelet compression technique, since this technique has achieved very high compression on other types of imagery. We have used the Rice University Computational Mathematics Laboratory's wavelet compression algorithm in conjunction with a 'synthetic discriminant function' (SDF) based ATR algorithm. The SDF technique was developed at Carnegie Mellon University and successfully applied to SAR imagery by the Northrop Grumman Science & Technology Center. This combination allows ATR performance to be parameterized as a function of compression rate. The SAR data used for this research was taken from the public-released MSTAR target and clutter data set. We show results for both target detection and target identification versus false alarms for varying compression rates.

Hoffelder, Michael; Tian, Jun

2000-08-01

218

Synthetic Aperture Sonar.  

National Technical Information Service (NTIS)

The report discusses synthetic-aperture imagery applied to the Seabed Treaty verification problem. It presents the basic theory of the synthetic-aperture side-looking sonar and shows the transition region from real to synthetic aperture in terms of resolu...

J. N. Bucknam A. M. Chwastyk H. D. Black F. C. Paddison

1971-01-01

219

Observations and modeling of the current deformation in Afar using Synthetic Aperture Radar Interferometry  

NASA Astrophysics Data System (ADS)

The Afar system is a unique place on Earth where a triple rift junction may be emerging. As the three rifts separating Arabia, Nubia and Somalia plates have not achieved a complete connection at present, I observe a 200 km wide area of complex surface deformation. A variety of extensional structures including a network of faults, fissures, dikes, and volcanic centers are collectively accommodating far field movement of the surrounding plates. Understanding the nature and distribution of the deformation over this vast region is critical since here I observe the transition between established oceanic ridges (the Red Sea and the Aden-Goubbet ridges) and continental deformation. In this study I use the technique of Synthetic Aperture Radar Interferometry (InSAR) to analyze radar data of the Afar region, and to construct a 10 yr timeline of surface displacement over a 200 km by 400 km area. By combining data acquired from ascending and descending passes I construct a two-dimensional velocity maps of the region. The maps show localized extensional deformation across the Asal-Ghoubbet rift segment accommodating the diverging motion of the Arabia-Somalia plates, as well as regional uplift asymmetrically distributed north and south of the Asal Rift area. The vertical velocity map in the rift indicates subsidence of the rift floor with respect to the rift shoulders, accommodated by fault creep. To interpret the observed velocity across the Asal rift I develop a 2-dimensional and a 3-dimensional dislocation model using a combination of dikes, sill and faults embedded in an elastic half space. The forward modeling allows me to place the overall geometry of sub-surface structures and estimate rates of dike and sill inflation, and fault movement. Then I construct a 3-dimensional model to perform a least-squares inversion of the radar-derived velocity maps. The results show an inflating body centered under the Fieale volcano expanding at a rate of 2 106 m3/yr. Faults bordering the rift show both down-dip and opening motion especially at their base where they connect with the inflating body. These findings suggest that the faults react passively to the pressurized magmatic system at depth, and contribute to plate accretion by taking up the injected material in the shallow part of the crust. The sustained process I currently witness in the Asal rift might be characteristic of the 'inter-crisis' state of a magmatic rift system where pressurized fluids accumulate at relatively shallow depth, eventually leading to lateral dike injection as during the seismo-magmatic crisis of 1978.

Tomic, Jelena

220

An improved algorithm for the retrieval of ocean wave spectra from synthetic aperture radar image spectra  

NASA Astrophysics Data System (ADS)

An earlier algorithm for retrieving two-dimensional wave spectra from synthetic aperture radar (SAR) image spectra is improved by using a modified cost function and introducing an additional iteration loop in which the first-guess input spectrum is systematically updated. For this purpose a spectral partitioning scheme is applied in which the spectrum is decomposed into a finite number of distinct wave systems. At each iteration step, the individual wave systems of the partitioned nth-guess wave spectrum are adjusted to agree in mean energy, frequency, and direction with the corresponding mean values of the associated wave systems of the SAR-inverted wave spectrum. The algorithm retrieves smooth wave spectra, avoiding the discontinuities which tended to arise in the previous algorithm in the transition region near the azimuthal wavenumber cutoff of the SAR image spectrum. The azimuthal cutoff of the SAR spectrum is also reproduced more accurately. The greatest improvement of the new retrieval algorithm is obtained when the discrepancies between the initial first-guess wave spectrum and the observed SAR spectrum are large. In this case the additional updating loop for the input spectrum enables the retrieved spectrum to adjust such that the simulated SAR spectrum matches more closely the observed SAR spectrum. The overall correlation of a large set of simulated SAR spectra with the measured SAR spectra is found to be significantly higher than with the previous algorithm, indicating that the algorithm not only overcomes isolated shortcomings of the earlier algorithm but also yields retrieved wave spectra which are generally more consistent with the input SAR data. An additional practical advantage of the new algorithm is that it returns spectral partioning parameters which can be used in SAR wave data assimilation schemes.

Hasselmann, S.; Brüning, C.; Hasselmann, K.; Heimbach, P.

1996-07-01

221

High-resolution mapping of Bora winds in the northern Adriatic Sea using synthetic aperture radar  

NASA Astrophysics Data System (ADS)

The Adriatic Sea is regularly subjected to strong Bora wind events from the northeast during winter. The events have a strong effect on the oceanography in the Adriatic, driving basin-scale gyres that determine the transport of biogeochemical material and extracting large amounts of heat. The Bora is known to have multiple surface wind jets linked to the surrounding orography and have been the focus of many studies, but it has not been possible to describe the detailed spatial structure of these jets by in situ observations. Using high-resolution spaceborne RADARSAT-1 synthetic aperture radar (SAR) images collected during an active Bora period (23 January-16 February 2003), we created a series of high-resolution (300 m) maps of the wind field. The obtained winds show reasonable agreement with several in situ wind observations, with an RMS wind speed error of 3.6 m/s, slightly higher than the 2-3 m/s errors reported in previous studies. These SAR images reveal the spatial structure of the Bora wind in unprecedented detail, showing several new features. In the Senj region of Croatia, several images show rhythmic structure with wavelengths of 2-3 km that may reflect Bora pulsation seen at fixed locations by previous investigators. Along the Italian coast, several images show a wide (20-30 km) band of northwesterly winds that abruptly change to the northeasterly Bora winds further offshore. Meteorological model results suggest that these northwesterly winds are consistent with those of a barrier jet forming along the Italian Apennine mountain chain.

Signell, Richard P.; Chiggiato, Jacopo; Horstmann, Jochen; Doyle, James D.; Pullen, Julie; Askari, Farid

2010-04-01

222

Modeling Water Flow in the Everglades Wetlands Using Interferometric Synthetic Aperture Radar (InSAR)Observations  

NASA Astrophysics Data System (ADS)

New space-based Interferometric Synthetic Aperture Radar (InSAR) observations of the Everglades wetlands provide high spatial resolution maps of water level changes that are essential for improved modeling efforts of surface water sheetflow. In this study, we model the Everglades' Water Conservation Area 1 (WCA-1), which is used to restore, protect, and preserve water resources and wildlife in southern Florida. We use a 2-D surface flow finite element model that considers the vegetation cover as a spatially roughness variable, topography data and influence of peripheral canals. The model provides the water elevation and velocity field throughout the conservation areas, based on rainfall record, discharge inputs and outflows through managed hydraulic structures. Our study focuses on two InSAR observed water level change patterns in WCA-1 acquired during two seasons and different weather conditions. The first pattern describes water level changes in the spring of 1998, showing a radial change caused mainly due to flow along the peripheral canals. The second pattern describes longitudinal change occurring in the fall of 2004, in the peak of hurricanes season, which caused abrupt flow income into the conservation areas. In order to improve the model results, we use a two-step procedure to calculate the vegetation roughness coefficient, which varies both in space and time. The first step includes a Supervised Image Analysis classification of WCA-1 according to remotely sensed determined vegetation maps. The estimated values are assigned to the model for the initial run. In the second step, we use an iterative procedure adjusting the vegetation roughness coefficients until the modeled water level changes agree with the InSAR observations. This technique of coupling high spatial resolution InSAR images with numerical modeling allows improved predictive abilities in the WCA under different weather scenarios, thus helping water resources managers and operators in their decision making.

Garcia-Martinez, R.; Miralles-Wilhelm, F.; Wdowinski, S.

2005-05-01

223

Vegetation profiles in tropical forests from multibaseline interferometric synthetic aperture radar, field, and lidar measurements  

NASA Astrophysics Data System (ADS)

This paper addresses the estimation of vertical vegetation density profiles from multibaseline interferometric synthetic aperture radar (InSAR) data from the AirSAR aircraft at C band over primary, secondary, and abandoned-pasture stands at La Selva Biological Station, Costa Rica in 2004. Profiles were also estimated from field data taken in 2006 and lidar data taken with the LVIS, 25 m spot instrument in 2005. After motivating the study of tropical forest profiles based on their role in the global carbon cycle, ecosystem state, and biodiversity, this paper describes the InSAR, field, and lidar data acquisitions and analyses. Beyond qualitative agreement between profiles from the 3 measurement techniques, results show that InSAR and lidar profile-averaged mean height have RMS scatters about field-measured means of 3.4 m and 3.2 m, 16% and 15% of the average mean height, respectively. InSAR and lidar standard deviations of the vegetation distribution have RMS scatters about the field standard deviations of 1.9 m and 1.5 m, or 27% and 21%, respectively. Dominant errors in the profile-averaged mean height for each measurement technique were modeled. InSAR inaccuracies, dominated by ambiguities in finding the ground altitude and coherence calibration, together account for about 3 m of InSAR error in the mean height. The dominant, modeled error for the field measurements was the inaccuracy in modeling the trees as uniformly filled volumes of leaf area, inducing field errors in mean height of about 3 m. The dominant, modeled lidar error, also due to finding the ground, was 2 m.

Treuhaft, R. N.; Chapman, B. D.; Dos Santos, J. R.; GonçAlves, F. G.; Dutra, L. V.; GraçA, P. M. L. A.; Drake, J. B.

2009-12-01

224

Quantifying methane ebullition in thermokarst lakes with space borne synthetic aperture radar (SAR)  

NASA Astrophysics Data System (ADS)

Northern high latitude wetlands and thermokarst lakes in permafrost regions have been identified as strong sources for methane (CH4), a powerful greenhouse gas. Quantifying the spatial distribution and magnitude of CH4 sources in these regions has become increasingly important in the current scenario of global warming and amidst concerns of partial release of the large permafrost soil carbon pool through thawing by thermokarst lakes. Ebullition (bubbling) is an important mode of CH4 emission from thermokarst lakes to the atmosphere. However, due to its sporadic behavior, large uncertainties remain in estimating the magnitude of ebullition emissions from lakes. Synthetic Aperture Radar (SAR) remote sensing of lake ice is a potentially valuable tool to constrain bottom-up estimates of lake ebullition in regions where lake ice forms. Here we explored various SAR imaging parameters as they correlate to field measurements of CH4 ebullition bubbles in the ice of ten thermokarst lakes on the northern Seward Peninsula, Alaska. We found that ebullition bubbles trapped in frozen lakes were strongly correlated with L-band single polarized horizontal (HH) SAR (R2 = 0.70, P = 0.002) and with the 'roughness' component of a classic Pauli decomposition of PALSAR L-band quad-polarized signal (R2 = 0.77, P = 0.001). We found no such correlation with ERS-2 C-band single polarized vertical (VV) SAR. We present the results of our single-pol and quad-pol SAR geospatial analysis, a discussion of probable scattering mechanisms of ebullition bubbles in frozen thermokarst lakes and our recommendation for the optimal season for SAR observation. Our results indicate that calibrated L-band SAR could be a valuable tool for estimating methane ebullition in lakes on a regional scale by evaluating the backscatter intensity from early winter lake ice.

Engram, M. J.; Walter Anthony, K.; Meyer, F. J.; Grosse, G.

2011-12-01

225

Monitoring flooding and vegetation on seasonally inundated floodplains with multifrequency polarimetric synthetic aperture radar  

NASA Astrophysics Data System (ADS)

The ability of synthetic aperture radar to detect flooding and vegetation structure was evaluated for three seasonally inundated floodplain sites supporting a broad variety of wetland and upland vegetation types: two reaches of the Solimoes floodplain in the central Amazon, and the Magela Creek floodplain in Northern Territory, Australia. For each site, C- and L-band polarimetric Shuttle Imaging Radar-C (SIR-C) data was obtained at both high- and low-water stages. Inundation status and vegetation structure were documented simultaneous with the SIR-C acquisitions using low-altitude videography and ground measurements. SIR-C images were classified into cover states defined by vegetation physiognomy and presence of standing water, using a decision-tree model with backscattering coefficients at HH, VV, and HV polarizations as input variables. Classification accuracy was assessed using user's accuracy, producer's accuracy, and kappa coefficient for a test population of pixels. At all sites, both C- and L-band were necessary to accurately classify cover types with two dates. HH polarization was most. useful for distinguishing flooded from non-flooded vegetation (C-HH for macrophyte versus pasture, L-HH for flooded versus non-flooded forest), and cross-polarized L-band data provided the best separation between woody and non-woody vegetation. Increases in L-HH backscattering due to flooding were on the order of 3--4 dB for closed-canopy varzea and igapo forest, and 4--7 dB, for open Melaleuca woodland. The broad range of physiognomies and stand structures found in both herbaceous and woody wetland communities, combined with the variation in the amount of emergent canopy caused by water level fluctuations and phenologic changes, resulted in a large range in backscattering characteristics of wetland communities both within and between sites. High accuracies cannot be achieved for these communities using single-date, single-band, single-polarization data, particularly in the case of distinguishing flooded macrophyte from non-flooded forest vegetation. However, the large changes in backscattering caused by flooding make it possible to achieve good accuracies (>85%) using multi-temporal data. Where river stage records are available, SAR-based maps of inundation status on a series of dates can be linked to long-term stage data to define wetland habitat types based on flooding regime and low-water vegetation cover.

Hess, Laura Lorraine

226

Coastal oceanography applications of spaceborne synthetic aperture radar (SAR) in the Middle Atlantic Bight (MAB)  

NASA Astrophysics Data System (ADS)

This study provides basic interpretative tools necessary to understand spaceborne synthetic aperture radar (SAR) observations of ocean surface signatures in the Middle Atlantic Bight (MAB). The research focuses on SAR imaged features related to dynamical processes over the continental shelf and near-shelf region. Particular attention is given to signatures acquired during summer upwelling. Other processes and features addressed include the detection of coastal plumes and fronts, oceanic internal waves, bathymetric features, as well as ocean surface atmospheric signatures prevalent in SAR imagery. The ability of SAR to detect upwelling conditions and track their evolution in the MAB is demonstrated. The connection between localized low backscatter and seasonal upwelling in the coastal zone is established for the first time using spaceborne SAR together with supporting in situ and satellite thermal and ocean color data. Reduced backscatter over areas of active upwelling is attributed to a combination of factors including water viscosity, atmospheric stability, and the presence of biogenic slicks. Low backscatter patterns imaged by SAR are found to match upwelling patterns in satellite sea surface temperature (SST) observations. The abundance of slick filaments within upwelling areas is frequently indicated by SAR and supports satellite ocean color observations of enhanced biological activity resulting from upwelling-enhanced nutrient availability. Backscatter sensitivity to SST under slick-free conditions is investigated. A coefficient of thermal stability is defined using a simplified thermal front model. The coefficient parameterizes the change in backscatter as a function of boundary layer stability and wind speed. Its dependence on wind speed and on the atmospheric diabatic state is found to be similar to that of the drag coefficient. Values for the coefficient of thermal stability are also in general agreement with previous results based on tower radar observations. The ability of SAR sea surface roughness observations to capture outflow patterns from multiple estuarine sources along the MAB coast is documented. In particular, the spaceborne imaging of a Delaware Bay twin-front plume is shown and its recurrent nature confirmed. Spaceborne SAR imaging of estuarine outflow patterns is found to be consistent with available airborne data and historical in situ salinity observations.

Clemente-Colon, Pablo

2002-09-01

227

Waves in frazil and pancake ice and their detection in Seasat synthetic aperture radar imagery  

NASA Astrophysics Data System (ADS)

A theoretical model of waves propagating into an ice cover composed of frazil and pancake ice is developed and compared with measurements of wavelength and direction derived from synthetic aperture radar (SAR) imagery obtained from Seasat in October 1978. The theoretical model is based on the concept that ice of these types, which consists of small crystals or cakes, has only a mass-loading effect on the water surface. We derive the dispersion relation for phase and group velocities, finding that there is an upper frequency limit for propagation into the ice. From the reflection coefficient at the ice edge we derive the wave radiation pressure exerted on the ice, showing that it will cause a slick of frazil ice backed by thicker floes to become more dense or thick with increasing penetration. The implications for radar scattering enabling detection on SAR are that the Bragg resonant wavelength corresponds to waves above the frequency limit for propagation, so that a frazil slick appears dark on an SAR image. When the frazil ice becomes transformed into pancake ice, through slick compression or other means, the raised edges of the pancakes cause the ice to appear bright despite the fact that there are no waves present at the Bragg wavelength. These results are applied to a Seasat SAR image obtained from the Chukchi Sea. The appearance of the ice in the image corresponds to what we expect for frazil ice gradually transforming itself into pancake ice, backed by thicker floes. We derive directional wave number spectra outside and inside the ice cover by digital Fourier analysis of image subscenes, and we find that the change of wavelength and angle of refraction of the dominant wave entering the ice field are both characteristic of the dispersion relation derived theoretically. Mean ice thicknesses extracted from the theory correspond to thicknesses expected for such slicks. The technique offers a possible means of extracting the thickness of fields of frazil and pancake ice from SAR imagery; this may be of considerable utility when ERS 1 SAR is used to study the advancing winter ice edge in the Antarctic, which consists of vast areas of these ice types.

Wadhams, Peter; Holt, Benjamin

1991-05-01

228

Differential Synthetic Aperture Radar Interferometry in monitoring large landslide (La Frasse, Switzerland)  

NASA Astrophysics Data System (ADS)

Spaceborne Differential Interferometric Synthetic Aperture Radar (DInSAR) is able to detect quasi vertical movements covering very large areas in a continuous way; it can be considered as an efficient tool to detect and monitor slope instabilities. The La Frasse landslide is located in the Canton of Vaud (Switzerland). It has a length of 2 km, a width of 500 m and its sliding surface is located at a depth of 60 to 100 m. With high velocities (presently at 40 cm/y in the active lower part), La Frasse landslide is in highly hazardous area according to the Swiss legislation. According to Varnes classification, it is a complex slide composed of tertiary flysch material and flowing over on flysch and limestone bedrock. The landscape is occupied by forests, pastures, some habitations and two main roads to touristic areas. The foot of the landslide is continuously eroded by the river "Grande-Eau". First of all, two interferometric pairs are constructed with data provided by the satellite Alos. The big wavelength (24 cm) of ALOS' PALSAR sensor gives good results in the foot of the landslide, where the movements are highest. Afterwards, fifty-three interferometric pairs are constructed with twenty-two images acquired with the European satellite Envisat. With the shorter wavelength (5.6 cm) of the Envisat's ASAR sensor, but the higher number of interferograms, the analysis provides the mean velocities of landslide's scaterrers by using the Small Baseline Subset (SBAS) methodology. The DInSAR results were compared to ground displacements measured every 2h by an optical total station (Robovec™ System). The results of this study are coherent with the amplitude of the deformations monitored by Robovec™. Moreover, the computation of the mean velocities shows that today, total displacements are measured in the active lower part of the landslide; the data complete Robovec™ results. But the accuracy of the measured displacements and the number of scatterers could be improved by synthetizing the topographic phase from an aerial laser scanning DEM instead of the STRM DEM. The number of scatterers can also be increased by installing corner reflectors in the fastest-moving area of the landslide. At present, a draining gallery is being constructed under the active part of the landslide. As soon as the construction is finished, it would be interesting to measure displacements by SBAS to control the efficiency of the gallery.

Michoud, C.; Rune Lauknes, T.; Pedrazzini, A.; Jaboyedoff, M.; Tapia, R.; Steinmann, G.

2009-04-01

229

High-resolution synthetic aperture radar experiments for ATR development and performance prediction  

NASA Astrophysics Data System (ADS)

Commercial availability of very high-resolution synthetic aperture radar (SAR) imagery will enable development of automatic target recognition (ATR) algorithms to exploit its rich information content. This availability also permits exploration of both empirical and first principles approaches for predicting ATR performance. This paper describes a recent collection of high resolution SAR imagery. It details the operating conditions represented by the data and provides recommended experiments designed to challenge ATR algorithms and performance prediction. This set of information, along with the imagery, is contained in a Problem Set that will be made available to the community. The imagery is from a Deputy Under Secretary of Defense (DUSD) for Science and Technology (S&T) sponsored collection using the Sandia National Laboratory and General Atomics Lynx Sensor. The Lynx is now available as a commercial off-the-shelf (COTS) sensor. It was designed for use in medium-altitude UAVs and manned platforms. It operates at Ku-band frequency in stripmap, spotlight, and ground moving target indicator modes. Imagery in this collection was collected at 4' resolution and was then also reprocessed to 1' resolution. The collection included several military vehicles with significant variation in target, sensor, and background conditions. Defined experiments in the Problem Set present ATR algorithm development challenges by defining development (training) sets with limited representation of operating conditions and test sets that explore the algorithm's ability to extend to more complex operating conditions. These challenges are critical to military employment of ATR because the real world contains much more variability than it will be possible to explicitly address in an algorithm. For example, neither the storage nor the search through an exhaustive bay of templates is achievable for any realistic application. Thus, advanced developments that allow robust performance in denied conditions will accelerate the transition of ATR to the field. Additional experiments in the Problem Set present challenges in ATR performance prediction. Here, the development imagery provides empirical data to support development of prediction approaches. Test imagery provides an opportunity to validate the prediction technique's ability to, for example, interpolate or extrapolate performance.

Westerkamp, Lori A.; Morrison, S. A.; Wild, Thomas J.; Mossing, John C.

2002-08-01

230

Novel guided-wave electro-optic processor for synthetic aperture radar imaging  

NASA Astrophysics Data System (ADS)

We present the theoretical investigation of a novel architecture of a LiNbO3 guided-wave optical processor suitable for real-time microwave imaging in on-board synthetic aperture radar (SAR) applications, using a moving platform on either an aircraft or a spacecraft. The new configuration, which is basically interferometric, includes four Mach-Zehnder modulators, each characterized by an additional aperiodic phase-reversal traveling wave modulator. The electrode configuration is appropriately designed to reproduce the product of the base-band SAR received echoes and two reference signals and, then, to perform both the range and azimuth compression. The two product signals are separately time integrated by two fast photodetectors. The sampled signals coming out of the detectors include both the required product signals and intermodulation products and are electronically filtered for reproducing the correct product with no amplitude distortion. At this stage, the signals are multiplexed and registered on a 2D buffer to reproduce the final correlation functions for the range and azimuth directions. Because of the serial multiplication between the received echoes and reference signals, the circuit can operate with very long data streams. Our proposed processor can reproduce the images coming from ground features using a conventional chirp pulse SAR system with the antenna beam looking at 90 deg from the direction of platform motion. The circuit can operate at a free-space wavelength of 1.3 micrometers with a radiofrequency of 410 MHz, a response time/bandwidth ratio of approximately equals 10-5 microsecond(s) /MHz, a linear dynamic range of approximately equals 50 dB, and an SNR approximately equals 8 dB, assuming chirp pulses as reference signals. The circuit performance is evaluated by considering lithium niobate as the substrate material and two different waveguide fabrication techniques: titanium indiffusion (Ti:LiNbO3) and proton exchange with annealing (APE:LiNbO3). The best results in terms of linear dynamic range and optical losses are obtained by the titanium indiffused channel waveguides. We calculated in any fabrication condition a swath range resolution of d(sigma) approximately equals 10 m in airborne simulation and about 60 m in the satellite simulation, whereas the azimuth resolution is about d(rho) equals 1.5 and 6 m, respectively. Significant improvements in terms of SNR (90%) and SAR resolution (50%) are obtained by using binary pseudorandom sequences as reference signals, i.e., approximately equals 15 dB, (Delta) (sigma) equals 2 and < 58 m, (Delta) (rho) approximately equals 1.5 and 6 m, respectively.

Armenise, Mario N.; Passaro, Vittorio M.

1994-06-01

231

Quiet-zone evaluation using a spherical synthetic-aperture radar  

Microsoft Academic Search

A compact range, for example, will never produce a perfect plane wave in the target zone. Knowledge of the actual incident field is essential for assessing and\\/or improving the measurement quality. We use quiet-zone illumination data to produce a synthetic-aperture image of a microwave measurement range, allowing isolation and physical removal of unwanted signal sources. We discuss results concerning resolution,

R. C. Wittman; Donald N. Black

1997-01-01

232

Mapping tropical forest cover and deforestation using synthetic aperture radar (SAR) images  

Microsoft Academic Search

The changes in forest cover in many parts of the world lead to increase the accumulation of atmospheric carbon and thus accelerate\\u000a the process of global warming. Optical remote sensing has been used to map and quantify deforestation but its application\\u000a is limited because of the presence of cloud coverage on the images. Recent availability of several space-borne synthetic aperture

M. Mahmudur Rahman; Josaphat Tetuko Sri Sumantyo

2010-01-01

233

Realce de Texturas Em Imagens de Radar de Abertura Sintetica (SAR) Por Filtros de Reducao Speckle (Texture Enhancement of Synthetic Aperture Radar (SAR) Images with Speckle Noise Reduction Filters).  

National Technical Information Service (NTIS)

Synthetic aperture radar images are becoming an increasingly important remote sensing data source because of their acquisition characteristics such as weather independence and soil humidity relationship. Unfortunately, they are disturbed by the so called ...

L. V. Dutra N. D. D. Mascarenhas

1991-01-01

234

An Integrated Navigation System using GPS Carrier Phase for Real-Time Airborne Synthetic Aperture Radar (SAR)  

SciTech Connect

A Synthetic Aperture Radar (SAR) requires accu- rate measurement of the motion of the imaging plat- form to produce well-focused images with minimal absolute position error. The motion measurement (MoMeas) system consists of a inertial measurement unit (IMU) and a P-code GPS receiver that outputs corrected ephemeris, L1 & L2 pseudoranges, and L1 & L2 carrier phase measurements. The unknown initial carrier phase biases to the GPS satellites are modeled as states in an extended Kalman filter and the resulting integrated navigation solution has po- sition errors that change slowly with time. Position error drifts less than 1- cm/sec have been measured from the SAR imagery for various length apertures.

Fellerhoff, J. Rick; Kim, Theodore J.; Kohler, Stewart M.

1999-06-24

235

Monitoring deformation at the Geysers Geothermal Field, California using C-band and X-band interferometric synthetic aperture radar  

NASA Astrophysics Data System (ADS)

We resolve deformation at The Geysers Geothermal Field using two distinct sets of interferometric synthetic aperture radar (InSAR) data. The first set of observations utilize archived European Space Agency C-band synthetic aperture radar data from 1992 through 1999 to image the long-term and large-scale subsidence at The Geysers. The peak range velocity of approximately 50 mm/year agrees with previous estimates from leveling and global positioning system observations. Data from a second set of measurements, acquired by TerraSAR-X satellites, extend from May 2011 until April 2012 and overlap the C-band data spatially but not temporally. These X-band data, analyzed using a combined permanent and distributed scatterer algorithm, provide a higher density of scatterers (1122 per square kilometer) than do the C-band data (12 per square kilometer). The TerraSAR-X observations resolve 1 to 2 cm of deformation due to water injection into a Northwest Geysers enhanced geothermal system well, initiated on October 2011. The temporal variation of the deformation is compatible with estimates from coupled numerical modeling.

Vasco, D. W.; Rutqvist, Jonny; Ferretti, Alessandro; Rucci, Alessio; Bellotti, Fernando; Dobson, Patrick; Oldenburg, Curtis; Garcia, Julio; Walters, Mark; Hartline, Craig

2013-06-01

236

Observation of Planetary Oceans with Fully Polarimetric Synthetic Aperture Radar (SAR)  

NASA Astrophysics Data System (ADS)

Synthetic Aperture Radar (SAR) is one of the most cost effective and powerful all weather tools for observation of planetary surface without sun light. The SAR systems can observe planetary surfaces with the very high resolution and large spatial coverage. We have developed and improved the algorithms for extracting quantitative information on geophysical parameters using various types of SAR data available on Earth's surface, both space-borne SAR (ERS-1/2, RADARSAT, and ENVISAT ASAR) and airborne SAR (NASA(JPL) AIRSAR). SAR is the only system that can provide a synoptic view of find wind fields near the coastal area on Earth. Many SAR images including RADARSAT and ENVISAT ASAR's alternating polarization mode and wide swath mode were to investigate the ability of retrieving sea surface wind field and the results are quite accurate and operationally acceptable. We installed corner reflectors on the nearby beach to calibrate the SAR data, and we obtained in-situ measurements from the several coast-based automatic weather systems and ocean buoys. Using the simultaneously acquired polarization ENVISAT ASAR data (HH and VV), the most appropriate polarization ratio was evaluated and applied for improving the wind retrieval model. In addition, the best combinations depending on given sea states and incidence angle ranges were investigated. The characteristics of short-period and long-period (near-inertial) internal waves are also investigated with several space-borne SAR systems. The possibility of inferring characteristics of the interior ocean dynamics from the SAR image associated with internal solitary waves was tested using a hydrodynamic interaction model (action balance equation) and a radar backscattering model (two-scale tilted Bragg model). These models were used iteratively to fit the observed SAR data to the simulated SAR. The estimated results were compared with in-situ measurements. The typical scales and the spatial and temporal characteristics of internal waves observed in the western part of the East Sea test area were also estimated from more than 140 SAR images. On the other hand, very long wave patterns (13-10 km) were observed in two successively acquired ENVISAT ASAR images and interpreted as near-inertial internal waves based on the hydrographic data. The Along Track Interferometric SAR (ATI-SAR), utilizing two SAR antennas separated along the platform flight direction and combined interferometrically, was also tested and validated to derive ocean surface current and wave information. The phase of ATI-SAR is related to the line-of-sight velocity of the water scatterers. The surface current extraction from the ATI-SAR velocity is still an open question, because the Doppler shift is not simply proportional to the component of the mean surface current. It also includes other types of contributions associated with the phase velocity of the Bragg waves and orbital motions of all ocean waves that are longer than Bragg waves. For accurate current estimation, a new and practically useful method was developed using simultaneously measured L- and C-band ATI-SAR data. The influence of Bragg resonant waves and long ocean wave motions on the ATI-SAR velocity according to the radar-frequency was analyzed and effectively eliminated. The method was applied to NASA(JPL) L- and C-band ATI-SAR measurements. The resulting ocean surface current vectors were compared with in situ measurements collected by an RCM (Recording Current Meter). Furthermore, ocean surface wave information was extracted from the ATI-SAR data using a quasi-linear transform. The limitations of the transform were also discussed. The basic principles and the results of these multi-disciplinary observation approaches on the Earth's ocean may be extended to investigate other terrestrial planetary surface observation in the solar system. With recent launching of several fully polarimetric SAR systems such as ALOS, TerraSAR-X and RADARSAT-2, we now have the real opportunities, which we can further extend our application capabilities on Earth to other terrestr

Moon, Wooil M.

237

Three-dimensional subsurface imaging synthetic aperture radar (3D SISAR). Final report, September 22, 1993--September 22, 1996  

SciTech Connect

The concept developed under this applied research and development contract is a novel Ground Penetrating Radar system capable of remotely detecting, analyzing, and mapping buried waste containers from a mobile platform. From the testing and analysis performed to date, the 3-D SISAR has achieved the detection, accurate location, and three-dimensional imaging of buried test objects from a stand-off geometry. Tests have demonstrated that underground objects have been located to within 0.1 meter of their actual position. This work validates that the key elements of the approach are performing as anticipated. The stand-off synthetic aperture radar (SAR) methodology has been demonstrated to be a feasible approach as a remote sensing technique. The radar sensor constructed under this project is providing adequate quality data for imaging, and the matched filters have been demonstrated to provide enhanced target detection. Additional work is on-going in the area of underground propagation and scattering phenomena to provide enhanced depth performance, as the current imaging results have been limited to a few feet of depth underground.

NONE

1998-12-31

238

Application of synthetic aperture radar (SAR) imagery to volcano mapping in the humid tropics: a case study in East Java, Indonesia  

Microsoft Academic Search

Volcanoes in humid tropical environments are frequently cloud covered, typically densely vegetated and rapidly eroded. These\\u000a factors complicate field and laboratory studies and even the basic identification of potentially active volcanoes. Numerous\\u000a previous studies have highlighted the potential value of radar remote sensing for volcanology in equatorial regions. Here,\\u000a cloud- and vegetation-penetrating LHH-band (??24?cm) synthetic aperture radar (SAR) data from

Simon A. Carn

1999-01-01

239

Motion compensation of short-range, wide-beam synthetic aperture radar  

NASA Astrophysics Data System (ADS)

Up to now, SAR systems are a well known possibility for long-range detection. Applying them for short-range applications with wide-beam antennas, of course, does not increase the resolution but the probability to detect hidden targets with an anisotropic radar cross section significantly in comparison to other detection systems. Working with an appropriate wavelength even improves the possiblity to look through natural cover like grass. An application is detecting fawn while pasture mowing. The main issue in such applications is the antenna's motion in range direction as it is carried by cars or traction engines. If motion is not compensated, the phase cannot be reconstructed correctly, the resolution gets poorer and, in worst case, the target even disappears. Conventional methods for motion compensation either fail for wide beam antennas, since for contributions of wide angles the phase reconstruction is incorrect, or is not applicable for realtime data processing, because the processing time due to interpolation or similar steps is very high. We present a method of image reconstruction regarding motion of the antenna as well as wide beamwidth. This method is analyzed concerning processing time in comparison to the conventional image reconstruction. In our system we use a combination of algorithms. There is shown a comparison for different algorithms dependent of the antenna's motion and aperture angle.

Reichthalhammer, T.; Biebl, E.

2011-07-01

240

Reservoir monitoring and characterization using satellite geodetic data: Interferometric Synthetic Aperture Radar observations from the Krechba field, Algeria  

SciTech Connect

Deformation in the material overlying an active reservoir is used to monitor pressure change at depth. A sequence of pressure field estimates, eleven in all, allow us to construct a measure of diffusive travel time throughout the reservoir. The dense distribution of travel time values means that we can construct an exactly linear inverse problem for reservoir flow properties. Application to Interferometric Synthetic Aperture Radar (InSAR) data gathered over a CO{sub 2} injection in Algeria reveals pressure propagation along two northwest trending corridors. An inversion of the travel times indicates the existence of two northwest-trending high permeability zones. The high permeability features trend in the same direction as the regional fault and fracture zones. Model parameter resolution estimates indicate that the features are well resolved.

Vasco, D.W.; Ferretti, Alessandro; Novali, Fabrizio

2008-05-01

241

Automatic target classification of man-made objects in synthetic aperture radar images using Gabor wavelet and neural network  

NASA Astrophysics Data System (ADS)

Processing of synthetic aperture radar (SAR) images has led to the development of automatic target classification approaches. These approaches help to classify individual and mass military ground vehicles. This work aims to develop an automatic target classification technique to classify military targets like truck/tank/armored car/cannon/bulldozer. The proposed method consists of three stages via preprocessing, feature extraction, and neural network (NN). The first stage removes speckle noise in a SAR image by the identified frost filter and enhances the image by histogram equalization. The second stage uses a Gabor wavelet to extract the image features. The third stage classifies the target by an NN classifier using image features. The proposed work performs better than its counterparts, like K-nearest neighbor (KNN). The proposed work performs better on databases like moving and stationary target acquisition and recognition against the earlier methods by KNN.

Vasuki, Perumal; Roomi, S. Mohamed Mansoor

2013-01-01

242

On the retrieval of significant wave heights from spaceborne Synthetic Aperture Radar (ERS-SAR) using the Max-Planck Institut (MPI) algorithm  

Microsoft Academic Search

Synthetic Aperture Radar (SAR) onboard satellites is the only source of directional wave spectra with con- tinuous and global coverage. Millions of SAR Wave Mode (SWM) imagettes have been acquired since the launch in the early 1990's of the first European Remote Sensing Satellite ERS-1 and its successors ERS-2 and ENVISAT, which has opened up many possibilities specially for wave

Nelson Violante-Carvalho

2005-01-01

243

A study of P-band synthetic aperture radar applicability and performance for Mars exploration: Imaging subsurface geology and detecting shallow moisture  

Microsoft Academic Search

Over the past decade, orbital images of the Martian surface revealed key evidence about the history of the planet environment (craters, faults, paleo-lakes, and rivers), partially hidden under a widespread layer of aeolian deposits. Furthermore, several recent observations and studies support the hypothesis that water could be found in the shallow subsurface of Mars. Low-frequency synthetic aperture radar (SAR) has

Philippe Paillou; Yannick Lasne; Essam Heggy; Jean-Marie Malézieux; Gilles Ruffié

2006-01-01

244

Hunt for forgotten warplanes: a unique application for the Goddard Space Flight Center Search and Rescue Synthetic Aperture Radar (SAR2) program  

Microsoft Academic Search

The principal purpose of the Beaconless Search and Rescue program at Goddard Space Flight Center (GSFC) is to utilize synthetic aperture radar (SAR) for the efficient and rapid location of recent small aircraft crashes. An additional side benefit might prove to be the detection and discovery of long lost or forgotten historic aircraft that have now become of immense value

Gerald Yagen; Christopher R. Jackson

1998-01-01

245

Use of Synthetic Aperture Radar (SAR) for geologic reconnaissance in Arctic regions: An example from the Arctic National Wildlife Refuge, Alaska  

Microsoft Academic Search

Satellite-based synthetic aperture radar (SAR) can provide an additional remote-sensing tool for regional geologic studies in arctic regions. Although SAR data do not yield direct information on rock type and do not replace traditional optical data, SAR data can provide useful geologic information in arctic regions where the stratigraphic column includes a wide range of lithologies, and bedrock exposures have

C. L. Hanks; R. M. Guritz

1997-01-01

246

Experiences in Implementing an Expert System Supported Man-Machine-Interface for the Configuration of the Intelligent SAR (Synthetic Aperture Radar) Processor.  

National Technical Information Service (NTIS)

In view of ERS-1 and X-SAR, DFVLR is establishing a high throughput Processing and Archiving Facility (PAF) for high precision synthetic aperture radar (SAR) products. Concerning the requirements throughput and product quality, it was realized that the SA...

W. Noack A. Popella R. Konjack

1989-01-01

247

Usefulness of synthetic aperture radar (SAR) interferometry for digital elevation model (DEM) generation and estimation of land surface displacement in Jharia coal field area  

Microsoft Academic Search

Land surface displacement is a phenomenon of ground movement, which may occur due to various reasons including unplanned mining. The quantification of land surface displacement through conventional field surveys is based on sparingly distributed point data, which may be insufficient for many applications. A detailed spatial and temporal monitoring of land surface displacements through remote sensing-based synthetic aperture radar (SAR)

Atanu Bhattacharya; Manoj K. Arora; Mukat L. Sharma

2011-01-01

248

Usefulness of synthetic aperture radar (SAR) interferometry for digital elevation model (DEM) generation and estimation of land surface displacement in Jharia coal field area  

Microsoft Academic Search

Land surface displacement is a phenomenon of ground movement, which may occur due to various reasons including unplanned mining. The quantification of land surface displacement through conventional field surveys is based on sparingly distributed point data, which may be insufficient for many applications. A detailed spatial and temporal monitoring of land surface displacements through remote sensing-based synthetic aperture radar (SAR)

Atanu Bhattacharya; Manoj K. Arora; Mukat L. Sharma

2012-01-01

249

Southern San Andreas-San Jacinto fault system slip rates estimated from earthquake cycle models constrained by GPS and interferometric synthetic aperture radar observations  

Microsoft Academic Search

We use ground geodetic and interferometric synthetic aperture radar satellite observations across the southern San Andreas (SAF)-San Jacinto (SJF) fault systems to constrain their slip rates and the viscosity structure of the lower crust and upper mantle on the basis of periodic earthquake cycle, Maxwell viscoelastic, finite element models. Key questions for this system are the SAF and SJF slip

Paul Lundgren; Eric A. Hetland; Zhen Liu; Eric J. Fielding

2009-01-01

250

The Galápagos Islands seen from space: the contribution of Synthetic Aperture Radar Interferometry (InSAR) to volcano monitoring  

NASA Astrophysics Data System (ADS)

Although the Galápagos volcanoes are some of the most active volcanoes on Earth, because of their geographic isolation and the difficult working conditions they have been virtually unmonitored by geodetic methods until the last 18 years. The use of detailed Interferometric Synthetic Aperture Radar (InSAR) measurements of the surface deformation provides a unique opportunity to study magmatic processes in such a location. The phase difference (interferogram) of SAR images pairs for the same area acquired at different times, provides measurements of the ground deformation along the radar line-of-sight (LOS) with centimeter to millimeter accuracy. We use SAR data acquired over the Galápagos by the European Space Agency satellites ERS-1, ERS-2, ENVISAT and by the Canadian Space Agency satellite Radarsat-1, between 1992 and 2010. In order to obtain the temporal evolution of ground deformation at each volcano, we use the selected dataset and we apply the Small Baseline Subset (SBAS) method. We present SBAS displacement time-series for Wolf, Darwin, Fernandina, Alcedo, Sierra Negra and Cerro Azul, showing that all the six volcanoes that forms Fernandina and Isabela Islands have been actively deforming during the last eighteen years. We also identify and constrain some of the sources that generate the observed surface deformation by performing non-linear inversions in a homogeneous, isotropic, elastic half-space. With the frequent acquisitions of the ENVISAT satellite, we are able to study the evolution of the latest eruptions at Cerro Azul in 2008 and at Fernandina in 2009.

Osmanoglu, B.; Baker, S.; Bagnardi, M.; Amelung, F.

2010-12-01

251

Investigating ground deformation and subsidence in northern Metro Manila, Philippines using Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR)  

NASA Astrophysics Data System (ADS)

The extent of ground deformation and subsidence in northern Metro Manila was examined using Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) technique. Using the Stanford Method for Persistent Scatterers/Multi-Temporal InSAR (StaMPS/MTI) software, we processed 21 descending ENVISAT radar imageries taken from 2003 to 2006. The processed interferograms show high coherence due to the high density of PS points in the region of interest. The PSInSAR processing reveals several areas in northern Metro Manila, specifically in Caloocan, Malabon, Navotas and Valenzuela-collectively known as CAMANAVA-that exhibit deformation characteristics similar to that of ground subsidence. Results show that the areas manifesting apparent subsidence are moving with a maximum rate of 4.38 cm/year relative to the satellite. This is consistent with the geodetic surveying results from 1979 to 2009 showing subsidence of approximately 1 meter or 3.33 cm/year per year. Government data also identify these areas as among those with the highest rates of groundwater extraction in Metro Manila, suggesting the possibility of anthropogenic activities as the major cause of subsidence. With this study, we hope to get a better understanding of the nature of subsidence affecting parts of northern Metro Manila. Doing so would help mitigate the effects of potential flood disasters.

Eco, R. C.; Lagmay, A. A.; Bato, M. P.

2011-12-01

252

Imaging algorithms for a strip-map synthetic aperture sonar: minimizing the effects of aperture errors and aperture undersampling  

Microsoft Academic Search

Imaging the sea floor using high-precision synthetic aperture sonar (SAS) techniques is at the stage where the efficiency and the robustness of the various imaging algorithms are of concern. There have been several block processing algorithms developed for relatively narrow-band-, narrow swath-, and narrow beamwidth synthetic aperture systems mainly for use by the synthetic aperture radar (SAR) community. These algorithms

Peter T. Gough; David W. Hawkins

1997-01-01

253

Bistatic synthetic aperture radar with non-cooperative LEOS based transmitter  

Microsoft Academic Search

The authors consider Low Earth Orbited Satellite (LEOS) systems for personal communications. Their rather high power spectral density near the Earth surface could be used for aircraft detection. Bistatic radars that utilize communication signal transmitting from LEOS could operate in a passive mode. Moreover, the targets will be characterized by their bistatic radar cross-section (RCS) that could be 20 to

C. Mikhail; K. Kurt; N. David

2000-01-01

254

Delineation of inundated area and vegetation along the Amazon floodplain with the SIR-C synthetic aperture radar  

SciTech Connect

Floodplain inundation and vegetation along the Negro and Amazon rivers near Manaus, Brazil were accurately delineated using multi-frequency, polarimetric synthetic aperture radar (SAR) data from the April and October 1994 SIR-C missions. A decision-tree model was used to formulate rules for a supervised classification into five categories: water, clearing (pasture), aquatic macrophyte (floating meadow), nonflooded forest, and flooded forest. Classified images were produced and tested within three days of SIR-C data acquisition. Both C-band (5.7 cm) and L-band (24 cm) wavelengths were necessary to distinguish the cover types. HH polarization was most useful for distinguishing flooded from nonflooded vegetation (C-HH for macrophyte versus pasture, and L-HH for flooded versus nonflooded forest), and cross-polarized L-band data provided the best separation between woody and nonwoody vegetation. Between the April and October missions, the Amazon River level fell about 3.6 m and the portion of the study area covered by flooded forest decreased from 23% to 12%. This study demonstrates the ability of multifrequency SAR to quantify in near realtime the extent of inundation on forested floodplains, and its potential application for timely monitoring of flood events.

Hess, L.L.; Melack, J.M.; Filoso, S. [Univ. of California, Santa Barbara, CA (United States); Wang, Y. [Univ. of California, Santa Barbara, CA (United States). Inst. for Computational Earth System Science]|[East Carolina Univ., Greenville, NC (United States). Dept. of Geography

1995-07-01

255

Coastal flood inundation monitoring with Satellite C-band and L-band Synthetic Aperture Radar data  

USGS Publications Warehouse

Satellite Synthetic Aperture Radar (SAR) was evaluated as a method to operationally monitor the occurrence and distribution of storm- and tidal-related flooding of spatially extensive coastal marshes within the north-central Gulf of Mexico. Maps representing the occurrence of marsh surface inundation were created from available Advanced Land Observation Satellite (ALOS) Phased Array type L-Band SAR (PALSAR) (L-band) (21 scenes with HH polarizations in Wide Beam [100 m]) data and Environmental Satellite (ENVISAT) Advanced SAR (ASAR) (C-band) data (24 scenes with VV and HH polarizations in Wide Swath [150 m]) during 2006-2009 covering 500 km of the Louisiana coastal zone. Mapping was primarily based on a decrease in backscatter between reference and target scenes, and as an extension of previous studies, the flood inundation mapping performance was assessed by the degree of correspondence between inundation mapping and inland water levels. Both PALSAR- and ASAR-based mapping at times were based on suboptimal reference scenes; however, ASAR performance seemed more sensitive to reference-scene quality and other types of scene variability. Related to water depth, PALSAR and ASAR mapping accuracies tended to be lower when water depths were shallow and increased as water levels decreased below or increased above the ground surface, but this pattern was more pronounced with ASAR. Overall, PALSAR-based inundation accuracies averaged 84% (n = 160), while ASAR-based mapping accuracies averaged 62% (n = 245).

Ramsey, Elijah, III; Rangoonwala, Amina; Bannister, Terri

2013-01-01

256

Integration of speckle de-noising and image segmentation using Synthetic Aperture Radar image for flood extent extraction  

NASA Astrophysics Data System (ADS)

Flood is one of the detrimental hydro-meteorological threats to mankind. This compels very efficient flood assessment models. In this paper, we propose remote sensing based flood assessment using Synthetic Aperture Radar (SAR) image because of its imperviousness to unfavourable weather conditions. However, they suffer from the speckle noise. Hence, the processing of SAR image is applied in two stages: speckle removal filters and image segmentation methods for flood mapping. The speckle noise has been reduced with the help of Lee, Frost and Gamma MAP filters. A performance comparison of these speckle removal filters is presented. From the results obtained, we deduce that the Gamma MAP is reliable. The selected Gamma MAP filtered image is segmented using Gray Level Co-occurrence Matrix (GLCM) and Mean Shift Segmentation (MSS). The GLCM is a texture analysis method that separates the image pixels into water and non-water groups based on their spectral feature whereas MSS is a gradient ascent method, here segmentation is carried out using spectral and spatial information. As test case, Kosi river flood is considered in our study. From the segmentation result of both these methods are comprehensively analysed and concluded that the MSS is efficient for flood mapping.

Senthilnath, J.; Shenoy, H. Vikram; Rajendra, Ritwik; Omkar, S. N.; Mani, V.; Diwakar, P. G.

2013-06-01

257

A parametric scheme for the retrieval of two-dimensional ocean wave spectra from synthetic aperture radar look cross spectra  

NASA Astrophysics Data System (ADS)

A parametric inversion scheme for the retrieval of two-dimensional (2-D) ocean wave spectra from look cross spectra acquired by spaceborne synthetic aperture radar (SAR) is presented. The scheme uses SAR observations to adjust numerical wave model spectra. The Partition Rescaling and Shift Algorithm (PARSA) is based on a maximum a posteriori approach in which an optimal estimate of a 2-D wave spectrum is calculated given a measured SAR look cross spectrum (SLCS) and additional prior knowledge. The method is based on explicit models for measurement errors as well as on uncertainties in the SAR imaging model and the model wave spectra used as prior information. Parameters of the SAR imaging model are estimated as part of the retrieval. Uncertainties in the prior wave spectrum are expressed in terms of transformation variables, which are defined for each wave system in the spectrum, describing rotations and rescaling of wave numbers and energy as well as changes of directional spreading. Technically, the PARSA wave spectra retrieval is based on the minimization of a cost function. A Levenberg-Marquardt method is used to find a numerical solution. The scheme is tested using both simulated SLCS and ERS-2 SAR data. It is demonstrated that the algorithm makes use of the phase information contained in SLCS, which is of particular importance for multimodal sea states. Statistics are presented for a global data set of 11,000 ERS-2 SAR wave mode SLCS acquired in southern winter 1996.

Schulz-Stellenfleth, J.; Lehner, S.; Hoja, D.

2005-05-01

258

Small-scale deformations associated with the 1992 Landers, California, earthquake mapped by synthetic aperture radar interferometry phase gradients  

NASA Astrophysics Data System (ADS)

The Landers earthquake (Mw 7.3) occurred on June 28, 1992, and ruptured nearly 100 km of previously mapped and unmapped faults in the Mojave Desert. We use synthetic aperture radar interferometry (InSAR) to examine the cumulative surface deformation between April 24 and August 7, 1992, in a 100 × 100 km region surrounding the northern portion of the earthquake rupture. Also, we introduce a technique for manipulating SAR interferograms to extract short-wavelength displacement information. This technique involves computation and subsequent combination of interferometric phase gradient maps. The InSAR results show significant deformation signatures associated with faults, fractures, dry lake beds, and mountainous regions within 75-100 km of the main rupture. Using the phase gradient method, we are able to extract small-scale deformation patterns near the main rupture. Many of the preexisting, mapped faults within 50 km of the main rupture experienced triggered slip; these include the Old Woman, Lenwood, Johnson Valley, West Calico, and Calico Faults. The InSAR results also indicate right-lateral offsets along secondary fractures trending N-NE within the left-lateral zone of shear between the main rupture and the Johnson Valley Fault. Additionally, there are interesting interferogram fringe signatures surrounding Troy Dry Lake and Coyote Dry Lake that are related to deformation of dry lake beds.

Price, Evelyn J.; Sandwell, David T.

1998-11-01

259

Patterns of irrigated rice growth and malaria vector breeding in Mali using multi-temporal ERS-2 synthetic aperture radar  

PubMed Central

We explored the use of the European Remote Sensing Satellite 2 Synthetic Aperture Radar (ERS-2 SAR) to trace the development of rice plants in an irrigated area near Niono, Mali and relate that to the density of anopheline mosquitoes, especially An. gambiae. This is important because such mosquitoes are the major vectors of malaria in sub-Saharan Africa, and their development is often coupled to the cycle of rice development. We collected larval samples, mapped rice fields using GPS and recorded rice growth stages simultaneously with eight ERS-2 SAR acquisitions. We were able to discriminate among rice growth stages using ERS-2 SAR backscatter data, especially among the early stages of rice growth, which produce the largest numbers of larvae. We could also distinguish between basins that produced high and low numbers of anophelines within the stage of peak production. After the peak, larval numbers dropped as rice plants grew taller and thicker, reducing the amount of light reaching the water surface. ERS-2 SAR backscatter increased concomitantly. Our data support the belief that ERS-2 SAR data may be helpful for mapping the spatial patterns of rice growth, distinguishing different agricultural practices, and monitoring the abundance of vectors in nearby villages.

Diuk-Wasser, M. A.; Dolo, G.; Bagayoko, M.; Sogoba, N.; Toure, M. B.; Moghaddam, M.; Manoukis, N.; Rian, S.; Traore, S. F.; Taylor, C. E.

2007-01-01

260

SEASAT Synthetic Aperture Radar (SAR) Response to Lowland Vegetation Types in Eastern Maryland and Virginia  

Microsoft Academic Search

Examination of SEASAT SAR images of eastern Maryland and Virginia reveals botanical distinctions between vegetated lowland areas and adjacent upland areas. Radar returns from the lowland areas can be either brighter or darker than returns from the upland forests. Scattering models and scatterometer measurements predict an increase of 6 dB in backscatter from vegetation over standing water. This agrees with

M. Dennis Krohn; N. M. Milton; Donald B. Segal

1983-01-01

261

Digital Realtime SAR (Synthetic Aperture Radar) Processor for C- and X-Band Applications.  

National Technical Information Service (NTIS)

A flexible hardware concept to handle high speed image processing tasks is applied to a real time SAR-processor covering C-band ERS-1 as well as X-band radar data. The SPECAN-algorithm used in the processor breadboard, the basic hardware processing module...

R. Schotter

1986-01-01

262

Fast algorithm for a near-field synthetic aperture radar processor  

Microsoft Academic Search

A radar image can be formed by coherently integrating the backscattered fields over the measured frequency band and cross-range scan. This coherent integration can be seen as a convolution of the measured data and a focusing function, which only depends on the geometry of the measurement. Thus, by applying fast Fourier transform (FFT) techniques and computing a product in the

Joaquim Fortuny; Alois J. Sieber

1994-01-01

263

Annual validation of significant wave heights of ERS-1 synthetic aperture radar wave mode spectra using TOPEX\\/Poseidon and ERS-1 altimeter data  

Microsoft Academic Search

Significant wave heights retrieved globally during 1994 from low bit rate imagette spectra of the synthetic aperture radar (SAR) operating in the intermittent wave mode (SWM) onboard the first European Remote Sensing (ERS-1) satellite (Hsswm) are validated using independent, buoy-validated satellite altimeter data from TOPEX\\/Poseidon (Hstop) and ERS-1 (Hsers). Hsswm is retrieved using the extended inversion algorithm of the fully

Eva Bauer; Patrick Heimbach

1999-01-01

264

Ground deformation due to tectonic, hydrothermal, gravity, hydrogeological, and anthropic processes in the Campania Region (Southern Italy) from Permanent Scatterers Synthetic Aperture Radar Interferometry  

Microsoft Academic Search

We apply the Permanent Scatterers Synthetic Aperture Radar Interferometry (PS-InSAR) technique to the Campania Region (Southern Italy), which includes the Southern Apennines chain and Plio-Quaternary structural depressions, with the aim to detect ground displacements at a regional scale. The study area, which extends for 13,600 km2, is characterized by intense urbanization, active volcanoes (Phlegraean Fields, Vesuvius and Ischia), seismogenic structures, landslides,

G. Vilardo; G. Ventura; C. Terranova; F. Matano; S. Nardò

2009-01-01

265

First-year sea ice spring melt transitions in the Canadian Arctic Archipelago from time-series synthetic aperture radar data, 1992–2002  

Microsoft Academic Search

This paper synthesizes 10-years' worth of interannual time-series space-borne ERS-1 and RADARSAT-1 synthetic aperture radar (SAR) data collected coincident with daily measurement of snow-covered, land-fast first-year sea ice (FYI) geophysical and surface radiation data collected from the Seasonal Sea Ice Monitoring and Modeling Site, Collaborative-Interdisciplinary Cryospheric Experiment and 1998 North Water Polynya study over the period 1992 to 2002. The

J. J. Yackel; D. G. Barber; T. N. Papakyriakou; C. Breneman

2007-01-01

266

Assessment of ERS synthetic aperture radar wave spectra retrieved from the Max-Planck-Institut (MPI) scheme through intercomparisons of 1 year of directional buoy measurements  

Microsoft Academic Search

One year of directional buoy measurements comprising the period from May 1994 to April 1995 acquired in deep ocean waters by an offshore heave-pitch-roll buoy are used for the assessment of the directional wave spectra retrieved from synthetic aperture radar (SAR) images using the Max-Planck-Institut (MPI) scheme. SAR is the only sensor so far deployed from satellites that can provide

N. Violante-Carvalho; I. S. Robinson; J. Schulz-Stellenfleth

2005-01-01

267

Millimeter wave and synthetic aperture radar; Proceedings of the Meeting, Orlando, FL, Mar. 27, 28, 1989  

NASA Astrophysics Data System (ADS)

The present conference on mm-wave and SAR architectures and algorithms for both signal processing/calibration and image processing/exploitation discusses the use of the chirp z-transform for radar image formation, digital interpolations for polar-format processing, polarimetric calibrations using distributed clutter, imaging in multidimensions and monopulse processing and practice, vector quantization for SAR data-rate reduction, and digital filter design for radar image formation. Also discussed are a shadow-tracking algorithm for moving-target detection, Doppler-rate filtering for the detection of moving targets with SAR, mm-wave planar integrated waveguide transceivers, an advanced microwave precipitation radiometer, and a Kelvin-wake image artifact for SAR.

Huddleston, G. K.; Tanenhaus, Martin; Williams, Brian P.

268

Interferometric Baseline Performance Estimations for Multistatic Synthetic Aperture Radar Configurations Derived from GRACE GPS Observations  

Microsoft Academic Search

Recent studies have demonstrated the usefulness of global positioning system (GPS) receivers for relative positioning of formation-flying satellites using dual-frequency carrier-phase observations. The accurate determination of distances or baselines between satellites flying in formation can provide significant benefits to a wide area of geodetic studies. For spaceborne radar interferometry in particular, such measurements will improve the accuracy of interferometric products

A. O. Kohlhase; R. Kroes; S. D’Amico

2006-01-01

269

Iterative sidelobe reduction in transmission-constrained, stepped frequency, synthetic aperture radar  

NASA Astrophysics Data System (ADS)

Researchers at the Army Research Laboratory (ARL) have recently developed an iterative technique for improving image quality in ultrawideband (UWB) radar systems. This technique, dubbed "recursive sidelobe minimization" (RSM), has been applied extensively to data sets in which no constraints have been placed on the amount of transmitted bandwidth. That is, no frequency notching was required prior to transmission of the waveform. In this paper we describe an extension of the earlier RSM technique designed to reduce the artifacts introduced by frequency notching. We include results obtained applying the technique to both simulated and measured data.

Ranney, Kenneth; Nguyen, Lam; Sichina, Jeffrey

2010-04-01

270

Interferometric synthetic aperture radar (InSAR) for fine-resolution basal ice sheet imaging  

NASA Astrophysics Data System (ADS)

This dissertation work was to examine the feasibility of InSAR through the ice sheets to create a fine resolution basal topography map and extraction of basal composition. InSAR was shown to be possible through the ice sheet, using data collected by the MCRDS radar around the NEEM drill site. Reflectivity maps were generated leading to the possibility of extracting useful basal composition data. Extraction of basal composition information was examined including estimating the roughness of basal topography and removing the effects of local slope.

Blake, William Arthur

271

Synthetic aperture radar imaging of the sea surface during the PROMESS experiment  

NASA Astrophysics Data System (ADS)

The PROMESS experiment carried out wind and wave measurements on the sea surface with radars operating in the C-band, as with the Active Microwave Instrument aboard ERS-1. A good range of wave heights (ranging from 1 to 7 m) and wind speeds were encountered. The SAR 580 performed measurements with different azimuth angles in C and X-bands simultaneously. Images were obtained from a digital processor and from an optical one. The two sets of images were processed with Fourier and speckle removal technics. The wave length and direction of the long waves is determined with good accuracy. One day featured two wave systems at the same time with different wave lengths and directions. The two systems are well separated and measured by the SAR. The shape of the equivalent monodirectional wave spectrum obtained is very close to the one measured by the waverider.

Piau, P.; Gray, L.

1985-06-01

272

High-resolution rainfall signatures on X-band Synthetic Aperture Radar imagery: model analysis and experimental validation  

NASA Astrophysics Data System (ADS)

Climate modelers need global precipitation measurements because the released latent heat distribution has a profound effect on the performance of such models. Precipitation measurements are also required to facilitate water management strategies by hydrologists, and managers of transportation, agricultural and flood relief agencies. Although precipitation measurements are widely available in technologically advanced countries, the measurement of precipitation over oceans, mountainous terrain and less developed regions leaves much to be desired. Since the 1980s much of our understanding of global precipitation has been provided by space-borne passive microwave radiometers and a combination of microwave and infrared passive measurements. Unfortunately space-borne microwave radiometers, even in combination with infrared sensors, have had limited success in retrieving precipitation over land because they rely heavily on the scattering properties of ice in the upper regions of precipitating clouds. Those scattering properties may be poorly related to surface rainfall rates. This limitation can be overcome over land by space-based radars operating at X or Ku band. The Ku band Precipitation Radar (PR) aboard the Tropical Rainfall Measurement Mission (TRMM) program has provided unique precipitation measurements over land. Mountainous terrain has presented challenges to both ground and space-based radars. Radar reflectivity measurements from PR are routinely removed within about 1 to 2 kilometers from mountainous surfaces to avoid ground clutter. If significant shallow precipitation or rain cells smaller than the 4 km horizontal resolution occur along mountain slopes, then such precipitation may be missed by PR. The measurement of light, small rain cells may also be impaired by the signal-to-noise ratio floor of the PR. A new opportunity to measure precipitation from space may be afforded by the forthcoming availability of several X-band Synthetic Aperture Radars (X-SARs). The TerraSAR-X (TSX) was launched on June 15, 2007 by the Deutsches Zentrum f. Luft u. Raumfahrt (DLR) and another X-SAR will be launched by 2009. The Constellation of Small Satellites for Mediterranean basin Observations (COSMO-SkyMed, CSK) will be launched by the Agenzia Spaziale Italiana (ASI) within 2009. The first of four of these satellites was launched by ASI on June 7, 2007. The Israeli Defense Ministry plans to launch yet another X-band SAR, the TecSAR SAR Technology Demonstration Satellite, later in 2009. Space-borne X-SARs are generally not designed for atmospheric observation. SARs are often considered "all weather" sensors. However, there is relevant theoretical and experimental evidence that X-band radar may be significantly affected by precipitation occurrence within the synthetically scanned area [9]-[13]. As a matter of fact, PR was designed at Ku band which is only 4 GHz away from X band. Several authors showed that X-SARs are more sensitive to rainfall effects than SARs operating at longer wavelengths, such as L and C bands [10]-[13]. For example, this was demonstrated by the Shuttle Missions STS-59 and 68 of 1994 and the STS-99 Shuttle Radar Topography Mission (SRTM) of 2000 carrying the first X-SAR along with L and C band SARs. Rainfall reflectivity at X-band may be enhanced by about 12 dB and the attenuation increased by about 4 dB when compared to C-band reflectivity and attenuation. The potential of X-SAR for precipitation retrieval is intriguing. They will probably be able to measure rainfall over land with greater sensitivity than from radiometers. The high spatial resolution (less than 100 m) of X-SARs can provide new insights into the structure of precipitating clouds with respect to PR and its future upgrades. X-SAR platforms could also significantly enhance the planned constellation of satellites carrying microwave radiometers and radars that will be part of the foreseen Global Precipitation Measurements (GPM) mission. These X-SAR satellites, then, may make a valuable contribution to our understanding of the hydrological

Marzano, F. S.; Mori, S.; Mugnai, A.; Weinman, J. A.

2009-04-01

273

Present day velocity field in Central Nevada Seismic Belt observed by Interferometric synthetic aperture radar  

NASA Astrophysics Data System (ADS)

We present the contemporary velocity field in the western Basin and Range province observed by satellite radar interferometry. A recent study in the Central Nevada Seismic Belt (CNSB) reported a broad area of uplift (~ 2-3 mm/yr) explained by postseismic mantle relaxation after a sequence of four earthquakes (M ~ 7) that occurred in the first half of the 20th century. To investigate the contemporary crustal deformation at the CNSB we use SAR imagery that covers a swath nearly 600 km long (six conventional SAR frames) acquired by the European Remote Sensing Satellites ERS-1 and ERS-2 between 1992 and 2009, and Envisat between 2004 and 2010. Time-Series results from Envisat suggest that the uplift velocity decreased for the last 7 years, which is consistent with models of postseismic relaxation. We also produce line of sight (LOS) velocity fields for different time periods (1992 - 2000, 1999 - 2009 and 1992 - 2009) by averaging independent interferograms with small perpendicular baselines (< 150 m). Additionally we identify high rates of deformation at Long Valley Caldera, land subsidence due to water pumping on mines and agricultural exploitation areas, and ground deformation associated with moderate earthquakes. We also present results of orbital error correction using continuous GPS data during the time-series inversion.

Greene, F.; Amelung, F.; Wdowinski, S.

2010-12-01

274

Airborne Synthetic Aperture Radar Study of Soil Moisture at Mars Analogs  

NASA Astrophysics Data System (ADS)

Hypotheses involving water have been proposed for Martian surface processes such as gullies, duracrust cementation and dark slope streaks. Future SAR missions capable of detecting soil moisture could test these hypotheses, but standard soil moisture retrieval techniques for SAR data such as the Integral Equation Method (IEM) are not applicable to Mars due to the current lack of high resolution surface roughness data. Another approach would be to conduct repeat passes, where surface roughness is assumed to be constant and changes in backscatter are related to changes in soil moisture. This study was undertaken to determine optimal parameters for detecting soil moisture at Mars analog sites. Quad-polarized C, L and P band AIRSAR data at 11m slant resolution were collected at four sites: a fluvial plain near Cameron, AZ; artificial recharge basins near Tucson, AZ and gullies in San Juan Mountains, CO and Death Valley, CA. Soil moisture was measured at a range of depths (0-40cm) with gravimetric sampling and over a large spatial extent with Time Domain Reflectometry (TDR). For a homogenous unvegetated sand bar at Cameron, a significant correlation (< 0.025 level of significance in a t-distribution test) was found for L-VV and L-TP with soil moisture at 0 cm depth, C-HV had a weaker correlation (< 0.05 level of significance) to 0 cm moisture on both the sand bar and the unvegetated surface of a recharge basin. The lack of response to deeper moisture in this study cannot discount the potential for detecting deeper moisture on Mars if the radar wavelength is long enough to penetrate a desiccated upper layer. Further analysis of the gully sites and TDR data will also be presented.

Doggett, T.; Greeley, R.; Baker, V.; Chien, S.; Davies, A.; Dohm, J.; Ferre, T.; Hinnel, A.; Rucker, D.; Williams, K.

2004-05-01

275

Synthetic aperture active sonar imaging  

Microsoft Academic Search

The main problems involved in synthetic aperture sonar imaging are medium instability, slow mapping rate, and platform motion. Proposed solutions to these problems are reviewed, and a new technique for synthetic aperture sonar imaging is presented which allows a fast mapping rate and improved motion compensation. This technique involves using multiple receivers to form a complex-valued preliminary image for each

Bretton L. Douglas; Hua Lee

1992-01-01

276

Remote sensing of a dynamic sub-arctic peatland reservoir using optical and synthetic aperture radar data  

NASA Astrophysics Data System (ADS)

Stephens Lake, Manitoba is an example of a peatland reservoir that has undergone physical changes related to mineral erosion and peatland disintegration processes since its initial impoundment. In this thesis I focused on the processes of peatland upheaval, transport, and disintegration as the primary drivers of dynamic change within the reservoir. The changes related to these processes are most frequent after initial reservoir impoundment and decline over time. They continue to occur over 35 years after initial flooding. I developed a remote sensing approach that employs both optical and microwave sensors for discriminating land (Le. floating peatlands, forested land, and barren land) from open water within the reservoir. High spatial resolution visible and near-infrared (VNIR) optical data obtained from the QuickBird satellite, and synthetic aperture radar (SAR) microwave data obtained from the RADARSAT-1 satellite were implemented. The approach was facilitated with a Geographic Information System (GIS) based validation map for the extraction of optical and SAR pixel data. Each sensor's extracted data set was first analyzed separately using univariate and multivariate statistical methods to determine the discriminant ability of each sensor. The initial analyses were followed by an integrated sensor approach; the development of an image classification model; and a change detection analysis. Results showed excellent (> 95%) classification accuracy using QuickBird satellite image data. Discrimination and classification of studied land cover classes using SAR image texture data resulted in lower overall classification accuracies (˜ 60%). SAR data classification accuracy improved to > 90% when classifying only land and water, demonstrating SAR's utility as a land and water mapping tool. An integrated sensor data approach showed no considerable improvement over the use of optical satellite image data alone. An image classification model was developed that could be used to map both detailed land cover classes and the land and water interface within the reservoir. Change detection analysis over a seven year period indicated that physical changes related to mineral erosion, peatland upheaval, transport, and disintegration, and operational water level variation continue to take place in the reservoir some 35 years after initial flooding. This thesis demonstrates the ability of optical and SAR satellite image remote sensing data sets to be used in an operational context for the routine discrimination of the land and water boundaries within a dynamic peatland reservoir. Future monitoring programs would benefit most from a complementary image acquisition program in which SAR images, known for their acquisition reliability under cloud cover, are acquired along with optical images given their ability to discriminate land cover classes in greater detail.

Larter, Jarod Lee

277

Development of a GPS-aided motion measurement, pointing, and stabilization system for a Synthetic Aperture Radar. [Global Positioning System (GPS)  

SciTech Connect

An advanced Synthetic Aperture Radar Motion Compensation System has been developed by Sandia National Laboratories (SNL). The system includes a miniaturized high accuracy ring laser gyro inertial measurement unit, a three axis gimbal pointing and stabilization assembly, a differential Global Positioning System (GPS) navigation aiding system, and a pilot guidance system. The system provides several improvements over previous SNL motion compensation systems and is capable of antenna stabilization to less than 0.01 degrees RMS and absolute position measurement to less than 5.0 meters RMS. These accuracies have been demonstrated in recent flight testing aboard a DHC-6-300 Twin Otter'' aircraft.

Fellerhoff, J.R.; Kohler, S.M.

1991-01-01

278

Comparing range data across the slow-time dimension to correct motion measurement errors beyond the range resolution of a synthetic aperture radar  

DOEpatents

Motion measurement errors that extend beyond the range resolution of a synthetic aperture radar (SAR) can be corrected by effectively decreasing the range resolution of the SAR in order to permit measurement of the error. Range profiles can be compared across the slow-time dimension of the input data in order to estimate the error. Once the error has been determined, appropriate frequency and phase correction can be applied to the uncompressed input data, after which range and azimuth compression can be performed to produce a desired SAR image.

Doerry, Armin W. (Albuquerque, NM); Heard, Freddie E. (Albuquerque, NM); Cordaro, J. Thomas (Albuquerque, NM)

2010-08-17

279

Estimating lava volume by precision combination of multiple baseline spaceborne and airborne interferometric synthetic aperture radar: The 1997 eruption of Okmok Volcano, Alaska  

USGS Publications Warehouse

Interferometric synthetic aperture radar (InSAR) techniques are used to calculate the volume of extrusion at Okmok volcano, Alaska by constructing precise digital elevation models (DEMs) that represent volcano topography before and after the 1997 eruption. The posteruption DEM is generated using airborne topographic synthetic aperture radar (TOPSAR) data where a three-dimensional affine transformation is used to account for the misalignments between different DEM patches. The preeruption DEM is produced using repeat-pass European Remote Sensing satellite data; multiple interferograms are combined to reduce errors due to atmospheric variations, and deformation rates are estimated independently and removed from the interferograms used for DEM generation. The extrusive flow volume associated with the 1997 eruption of Okmok volcano is 0.154 ?? 0.025 km3. The thickest portion is approximately 50 m, although field measurements of the flow margin's height do not exceed 20 m. The in situ measurements at lava edges are not representative of the total thickness, and precise DEM data are absolutely essential to calculate eruption volume based on lava thickness estimations. This study is an example that demonstrates how InSAR will play a significant role in studying volcanoes in remote areas.

Lu, Z.; Fielding, E.; Patrick, M. R.; Trautwein, C. M.

2003-01-01

280

Coherence-based land cover classification in forested areas of Chattisgarh, Central India, using environmental satellite--advanced synthetic aperture radar data  

NASA Astrophysics Data System (ADS)

In the present work, the potential of synthetic aperture radar (SAR) interferometric coherence in land cover classification is studied over forested areas of Bilaspur, Chattisgarh, India using Environmental Satellite--Advanced Synthetic Aperture Radar (ENVISAT-ASAR) C-band data. Single look complex (SLC) interferometric pair ASAR data of 24th September 2006 (SLC-1) and 29th October 2006 (SLC-2) covering the study area were acquired and processed to generate backscatter and interferometric coherence images. A false colored composite of coherence, backscatter difference, and mean backscatter was generated and subjected to maximum likelihood classification to delineate major land cover classes of the study area viz., water, barren, agriculture, moist deciduous forest, and sal mixed forests. Accuracy assessment of the classified map is carried out using kappa statistics. Results of the study suggested potential use of ENVISAT-ASAR C-band data in land cover classification of the study area with an overall classification accuracy of 82.5%, average producer's accuracy of 83.69%, and average user's accuracy of 81%. The present study gives a unique scope of SAR data application in land cover classification over the tropical deciduous forest systems of India, which is still waiting for its indigenous SAR system.

Nizalapur, Vyjayanthi; Madugundu, Rangaswamy; Jha, Chandra Shekhar

2011-01-01

281

Impulse response of alternative synthetic apertures for subsurface detection  

NASA Astrophysics Data System (ADS)

Many researchers and system developers have proposed exploiting synthetic aperture processing to enhance the spatial resolution of subsurface radar imaging for mine and UXO detection. In this paper, we examine the 3D spatial impulse response associated with alternative geometries for synthetic aperture data collection. Several alternative radar geometries have been chosen for examination corresponding to both forward-looking as well as down- looking configurations.

Ralston, James M.

2000-08-01

282

Theoretical analysis of the effect of forest structure on synthetic aperture radar backscatter and the remote sensing of biomass  

NASA Astrophysics Data System (ADS)

The study reported used the Michigan Microwave Canopy Scattering model (MIMICS) and forest canopy biometric data from tropical and subtropical broadleaf forests to simulate a series of forest stands having equivalent above ground biomass while still exhibiting substantial structural differences. The potential effect that extreme structural differences might have on the biomass signal and saturation threshold was assessed, using the surface aperture radar (SAR) response to these structures. A forest canopy structural descriptor derived from the vegetation surface area to volume ratio appears to explain the differences in the SAR backscatter that were observed. In many vegetation stands, structural consolidation is directly related to an increase in biomass during the 'thinning phase' of forest succession. This structural effect may explain the good relationship between SAR backscatter and biomass in these cases.

Imhoff, Marc L.

1995-03-01

283

Synthetic aperture sonar image statistics  

Microsoft Academic Search

Synthetic Aperture Sonar (SAS) systems are capable of producing photograph quality seafloor imagery using a lower frequency than other systems of comparable resolution. However, as with other high-resolution sonar systems, SAS imagery is often characterized by heavy-tailed amplitude distributions which may adversely affect target detection systems. The constant cross-range resolution with respect to range that results from the synthetic aperture

Shawn F. Johnson

2009-01-01

284

Use of Synthetic Aperture Radar (SAR) for geologic reconnaissance in Arctic regions: An example from the Arctic National Wildlife Refuge, Alaska  

SciTech Connect

Satellite-based synthetic aperture radar (SAR) can provide an additional remote-sensing tool for regional geologic studies in arctic regions. Although SAR data do not yield direct information on rock type and do not replace traditional optical data, SAR data can provide useful geologic information in arctic regions where the stratigraphic column includes a wide range of lithologies, and bedrock exposures have been reduced to rubble by frost action. For example, in ERS-1 SAR data from the Arctic National Wildlife Refuge (ANWR) of the northeastern Brooks Range, Alaska, carbonate and clastic rocks can give remarkably different radar responses on minimally reprocessed SAR data. The different radar response of different lithologies can specifically the size and angularity of scree in talus slopes. Additional postacquisition processing can both remove many of the negative terrain effects common in SAR data and enhance contrasts in bedrock lithology. Because of this ability to discriminate between gross lithologic packages, the ERS-1 SAR data can be used to provide a regional view of ANWR and a detailed look at specific areas. A mosaic of ERS-1 SAR data from all of ANWR provides a synoptic view of the regional structural framework, such as the anticlinoria of northern ANWR and the different allochthonous units of central and southern ANWR. Higher resolution ERS-1 SAR data of the Porcupine Lake area can be used to examine specific structural and stratigraphic problems associated with several major structural boundaries.

Hanks, C.L.; Guritz, R.M. [Univ. of Alaska, Fairbanks, AK (United States)

1997-01-01

285

Hunt for forgotten warplanes: a unique application for the Goddard Space Flight Center Search and Rescue Synthetic Aperture Radar (SAR2) program  

NASA Astrophysics Data System (ADS)

The principal purpose of the Beaconless Search and Rescue program at Goddard Space Flight Center (GSFC) is to utilize synthetic aperture radar (SAR) for the efficient and rapid location of recent small aircraft crashes. An additional side benefit might prove to be the detection and discovery of long lost or forgotten historic aircraft that have now become of immense value for museum display or among wealthy collectors. As the GSFC SAR2 program matures and its achievements in SAR target detection become more widely available, they will be of use to amateur and professional airplane hunters. We recommend that such ancillary benefits be kept in mind during the continued development and testing of such equipment, which would be of benefit to all future generations concerning the history of aviation. We welcome and encourage all participants to notify organizations such as ours of the discovery of any historic aircraft wreckage or intact abandoned old aircraft throughout the world.

Yagen, Gerald; Jackson, Christopher R.

1998-09-01

286

Synthetic Aperture Imaging of Surface Laid Targets by Sound  

NASA Astrophysics Data System (ADS)

This paper discusses the design and implementation of a synthetic aperture acoustic imaging system for investigating solid objects in an outdoor environment. Measurement results are reported for a setup consisting of a rail-mounted transceiver, digital data acquisition and control system, and local storage with data post processing capabilities. This imaging system works much like typical sonar and RF synthetic aperture radar technologies but operates above ground and uses acoustic waves in air for its interrogation.

Vignola, Joseph F.; Judge, John A.; Good, Chelsea E.; Bishop, Steven S.; Gugino, Peter M.; Soumekh, Mehrdad

2012-06-01

287

Terahertz interferometric synthetic aperture tomography for confocal imaging systems.  

PubMed

Terahertz (THz) interferometric synthetic aperture tomography (TISAT) for confocal imaging within extended objects is demonstrated by combining attributes of synthetic aperture radar and optical coherence tomography. Algorithms recently devised for interferometric synthetic aperture microscopy are adapted to account for the diffraction-and defocusing-induced spatially varying THz beam width characteristic of narrow depth of focus, high-resolution confocal imaging. A frequency-swept two-dimensional TISAT confocal imaging instrument rapidly achieves in-focus, diffraction-limited resolution over a depth 12 times larger than the instrument's depth of focus in a manner that may be easily extended to three dimensions and greater depths. PMID:22513671

Heimbeck, M S; Marks, D L; Brady, D; Everitt, H O

2012-04-15

288

Randomly iterated search and statistical competency as powerful inversion tools for deformation source modeling: Application to volcano interferometric synthetic aperture radar data  

NASA Astrophysics Data System (ADS)

Modern geodetic techniques provide valuable and near real-time observations of volcanic activity. Characterizing the source of deformation based on these observations has become of major importance in related monitoring efforts. We investigate two random search approaches, simulated annealing (SA) and genetic algorithm (GA), and utilize them in an iterated manner. The iterated approach helps to prevent GA in general and SA in particular from getting trapped in local minima, and it also increases redundancy for exploring the search space. We apply a statistical competency test for estimating the confidence interval of the inversion source parameters, considering their internal interaction through the model, the effect of the model deficiency, and the observational error. Here, we present and test this new randomly iterated search and statistical competency (RISC) optimization method together with GA and SA for the modeling of data associated with volcanic deformations. Following synthetic and sensitivity tests, we apply the improved inversion techniques to two episodes of activity in the Campi Flegrei volcanic region in Italy, observed by the interferometric synthetic aperture radar technique. Inversion of these data allows derivation of deformation source parameters and their associated quality so that we can compare the two inversion methods. The RISC approach was found to be an efficient method in terms of computation time and search results and may be applied to other optimization problems in volcanic and tectonic environments.

Shirzaei, M.; Walter, T. R.

2009-10-01

289

Experimental results of synthetic aperture microwave radiometer  

Microsoft Academic Search

Introduces briefly the principles of the interferometric synthetic aperture, a system design of a C-band microwave interferometric synthetic aperture radiometer and its experimental results. This system has a 6-element thinned array with 11 analog complex correlators to obtain the 11 visibility functions, which result in 22 digitally synthesized spatial resolution cells. The synthetic aperture radiometer has a spatial resolution as

Zhang Shengwei; Ji Wu; Jing Li; Shifeng Zheng; Jingshan Jiang

2002-01-01

290

The effects of snow on landmarks in K/sub u/ band SAR (Synthetic Aperture Radar) images  

SciTech Connect

This report documents research into the effects of snow on candidate landmarks for the TFS radar. It includes a discussion of a simple snow model, relevant backscatter data from previous ground based collections, predictions of the effects of snow coverage based on this data, a discussion of the snow data collection with the TFS radar, and an analysis of the results of that collection. All SAR images are for a K/sub u/ band radar, with HH polarization, and a 30/degree/ depression angle. The images have three meter resolution and a one kilometer swath. SAR images were collected of both rural and urban landmarks. 5 refs., 7 figs., 19 tabs.

Murrary, M.

1989-04-01

291

Three-dimensional surface displacement of the 2008 May 12 Sichuan earthquake (China) derived from Synthetic Aperture Radar: evidence for rupture on a blind thrust  

NASA Astrophysics Data System (ADS)

The Sichuan earthquake, Mw 7.9, struck the Longmen Shan (LMS) range front, China, on 2008 May 12, affecting an area of moderate historical seismicity where little active shortening has been previously reported. Recent studies based on space geodesy have succeeded in retrieving the far field surface displacements caused by the earthquake, but the near field (+/-25km from the faults) coseismic surface displacement is still poorly constrained. Thus, shallow fault geometry and shallow coseismic slip are still poorly resolved. Here, for the first time for this earthquake, we combine C and L-band Synthetic Aperture Radar offsets data from ascending and descending tracks to invert for the 3-D surface displacement in the near coseismic field of the Sichuan earthquake. Our data, coupled with a simple elastic dislocation model, provide new results strongly suggesting the presence of a blind thrust striking along the range front and being active at depth during the earthquake. The presence of a rupture on a blind thrust brings new evidence for an out-of-sequence thrusting event and new elements for interpreting the tectonic strain partitioning in the LMS, which has important implications both for seismic hazard assessment and long-term evolution of the mountain belt.

de Michele, Marcello; Raucoules, Daniel; de Sigoyer, Julia; Pubellier, Manuel; Chamot-Rooke, Nicolas

2010-12-01

292

Monitoring Hydrocarbons Transfer in the Gulf of Mexico with Synthetic Aperture Radar; Radarsat-1, Envisat, ERS-1, ERS-2 and JERS-1.  

NASA Astrophysics Data System (ADS)

The Gulf of Mexico contains hundreds of active hydrocarbons seeps. Seepage in the Northern and Southern Gulf of Mexico tend to `leak' through conduits generated by salt techtonism and related processes. Hydrocarbons are then transported to the sea surface in oily bubbles, once on the surface the oil spreads into layers approximately .1µm thick, detectable by Synthetic Aperture Radar (SAR) instruments onboard spacecrafts like Radarsat, Envisat, Ers-1, Ers-2 and Jers-1. Since 1992, SAR coverage have been collected over the Gulf of Mexico. In total more than 4000 orbital passes over the Gulf of Mexico generated more than 30,000 images that can be used to examine natural hydrocarbon seepage in this region. Much of these data have been archived by the Alaska Satellite Facility through data sharing agreements with NASA and with satellite operators. We have completed a spatial, temporal and SAR Mode classification of the entire SAR coverage. This catalog can be used to plan studies of natural variation in hydrocarbon seepage and to delineate coverage in areas of special interest. The complete catalog is being made available online to facilitate collaborative research in this field.

Garcia-Pineda, O. G.; Zimmer, B.; Mestas-Nunez, A.; MacDonald, I. R.

2007-05-01

293

Transient rift opening in response to multiple dike injections in the Manda Hararo rift (Afar, Ethiopia) imaged by time-dependent elastic inversion of interferometric synthetic aperture radar data  

Microsoft Academic Search

Interferometric synthetic aperture radar (InSAR) data spanning the time intervals separating thirteen dike intrusions in the Manda Hararo–Dabbahu rift (Afar, Ethiopia) from 2005 to 2009 show that transient deformation occurs in the inter-diking period. This deformation can be explained by the presence of seven inflating or deflating pressure sources. By combining the data acquired on four different InSAR tracks, through

R. Grandin; A. Socquet; M.-P. Doin; E. Jacques; J.-B. de Chabalier; G. C. P. Kingl

2010-01-01

294

Broadband synthetic aperture geoacoustic inversion.  

PubMed

A typical geoacoustic inversion procedure involves powerful source transmissions received on a large-aperture receiver array. A more practical approach is to use a single moving source and/or receiver in a low signal to noise ratio (SNR) setting. This paper uses single-receiver, broadband, frequency coherent matched-field inversion and exploits coherently repeated transmissions to improve estimation of the geoacoustic parameters. The long observation time creates a synthetic aperture due to relative source-receiver motion. This approach is illustrated by studying the transmission of multiple linear frequency modulated (LFM) pulses which results in a multi-tonal comb spectrum that is Doppler sensitive. To correlate well with the measured field across a receiver trajectory and to incorporate transmission from a source trajectory, waveguide Doppler and normal mode theory is applied. The method is demonstrated with low SNR, 100-900?Hz LFM pulse data from the Shallow Water 2006 experiment. PMID:23862809

Tan, Bien Aik; Gerstoft, Peter; Yardim, Caglar; Hodgkiss, William S

2013-07-01

295

Results from the DARPA and ONR synthetic aperture sonar programs  

Microsoft Academic Search

SAR processing has revolutionized radar imaging over the past 35 years. SAR techniques are now being applied employed in sonar processing; the enabling technologies being adaptive focusing techniques imported from the SAR world. Synthetic aperture sonar (SAS) produces acoustic images with high resolution that is independent of range. Moreover, within the limits of diffraction, that resolution is also independent of

Ralph E. Chatham; Matthew A. Nelson; Enson Chang

2000-01-01

296

Synthetic aperture sonar image statistics  

NASA Astrophysics Data System (ADS)

Synthetic Aperture Sonar (SAS) systems are capable of producing photograph quality seafloor imagery using a lower frequency than other systems of comparable resolution. However, as with other high-resolution sonar systems, SAS imagery is often characterized by heavy-tailed amplitude distributions which may adversely affect target detection systems. The constant cross-range resolution with respect to range that results from the synthetic aperture formation process provides a unique opportunity to improve our understanding of system and environment interactions, which is essential for accurate performance prediction. This research focused on the impact of multipath contamination and the impact of resolution on image statistics, accomplished through analyses of data collected during at-sea experiments, analytical modeling, and development of numerical simulations. Multipath contamination was shown to have an appreciable impact on image statistics at ranges greater than the water depth and when the levels of the contributing multipath are within 10 dB of the direct path, reducing the image amplitude distribution tails while also degrading image clarity. Image statistics were shown to depend strongly upon both system resolution and orientation to seafloor features such as sand ripples. This work contributes to improving detection systems by aiding understanding of the influences of background (i.e. non-target) image statistics.

Johnson, Shawn F.

297

Relationships between autofocus methods for SAR and self-survey techniques for SONAR. [Synthetic Aperture Radar (SAR)  

SciTech Connect

Autofocus methods in SAR and self-survey techniques in SONAR have a common mathematical basis in that they both involve estimation and correction of phase errors introduced by sensor position uncertainties. Time delay estimation and correlation methods have been shown to be effective in solving the self-survey problem for towed SONAR arrays. Since it can be shown that platform motion errors introduce similar time-delay estimation problems in SAR imaging, the question arises as to whether such techniques could be effectively employed for autofocus of SAR imagery. With a simple mathematical model for motion errors in SAR, we will show why such correlation/time-delay techniques are not nearly as effective as established SAR autofocus algorithms such as phase gradient autofocus or sub-aperture based methods. This analysis forms an important bridge between signal processing methodologies for SAR and SONAR. 5 refs., 4 figs.

Wahl, D.E.; Jakowatz, C.V. Jr.; Ghiglia, D.C.; Eichel, P.H.

1991-01-01

298

Theory for synthetic aperture radar imaging of the ocean surface - With application to the Tower Ocean Wave and Radar Dependence experiment on focus, resolution, and wave height spectra  

NASA Astrophysics Data System (ADS)

A one-dimensional model for simulating azimuthal SAR imaging of the ocean surface is developed which can admit both the 'distributed surface' and 'velocity bunching' approaches. Computer simulations demonstrate that the time-dependent modulation patterns due to the radar cross section variation and the velocity bunching effects provide optimum focusing around half the phase velocity of the long wave. The results indicate that in the Tower Ocean Wave and Radar Dependence experiment, SAR imaging at L band is approximately linear.

Kasilingam, Dayalan P.; Shemdin, Omar H.

1988-11-01

299

Southern San Andreas-San Jacinto fault system slip rates estimated from earthquake cycle models constrained by GPS and interferometric synthetic aperture radar observations  

NASA Astrophysics Data System (ADS)

We use ground geodetic and interferometric synthetic aperture radar satellite observations across the southern San Andreas (SAF)-San Jacinto (SJF) fault systems to constrain their slip rates and the viscosity structure of the lower crust and upper mantle on the basis of periodic earthquake cycle, Maxwell viscoelastic, finite element models. Key questions for this system are the SAF and SJF slip rates, the slip partitioning between the two main branches of the SJF, and the dip of the SAF. The best-fitting models generally have a high-viscosity lower crust (? = 1021 Pa s) overlying a lower-viscosity upper mantle (? = 1019 Pa s). We find considerable trade-offs between the relative time into the current earthquake cycle of the San Jacinto fault and the upper mantle viscosity. With reasonable assumptions for the relative time in the earthquake cycle, the partition of slip is fairly robust at around 24-26 mm/a for the San Jacinto fault system and 16-18 mm/a for the San Andreas fault. Models for two subprofiles across the SAF-SJF systems suggest that slip may transfer from the western (Coyote Creek) branch to the eastern (Clark-Superstition hills) branch of the SJF from NW to SE. Across the entire system our best-fitting model gives slip rates of 2 ± 3, 12 ± 9, 12 ± 9, and 17 ± 3 mm/a for the Elsinore, Coyote Creek, Clark, and San Andreas faults, respectively, where the large uncertainties in the slip rates for the SJF branches reflect the large uncertainty in the slip rate partitioning within the SJF system.

Lundgren, Paul; Hetland, Eric A.; Liu, Zhen; Fielding, Eric J.

2009-02-01

300

Sensitivity analysis of C- and Ku-band synthetic aperture radar data to soil moisture content in a semiarid region  

NASA Astrophysics Data System (ADS)

In this study, the sensitivity of the C-band (5.3 GHz) with a 23sp° incidence angle and the Ku-band (14.85 GHz) with 35sp° ,\\ 55sp° , and 75sp° incidence angles to surface soil moisture content from a semiarid region were evaluated. To obtain an improved soil moisture estimation, a practical technique to reduce the influence of soil roughness and vegetation in the SAR data was developed in a study area located in the Walnut Gulch Experimental Watershed, a representative site of shrub- and grass-dominated rangelands of the southwestern part of the United States. To correct for soil roughness effects, the C-band radar backscattering coefficients sigmasp° from a wet season image were subtracted from sigmasp° derived from a dry season image. The assumption was that, in semiarid regions, the SAR data from the dry season was dependent only on the soil roughness effects. To correct for vegetation effects, an empirical relation between sigmasp° and leaf area index was used, the latter derived from Landsat Thematic Mapper data. The results showed that when both soil roughness and vegetation effects were corrected for, the sensitivity of sigmasp° to soil moisture improved substantially. The sensitivity of sigmasp° to soil moisture was also evaluated in agricultural fields with bare soil and periodic roughness components (planting row and furrow structures). Four types of SAR system configurations were analyzed: C-band with a 23sp° incidence angle and Ku-band with 35sp° ,\\ 55sp° , and 75sp° incidence angles. The test sites were located at the University of Arizona's Maricopa Agricultural Center, south of Phoenix, Arizona. The results showed that the sensitivity of sigmasp° to soil moisture was strongly dependent upon the field conditions. The SAR signal was nearly insensitive to soil moisture for furrowed fields (furrow spacing ˜95 cm; amplitude ˜22 cm), but for fields with planting row structures (row spacing ˜24 cm; amplitude ˜2 cm), the SAR data was sensitive to soil moisture, particularly with the C-band at a 23sp° incidence angle and the Ku-band with a 35sp° incidence angle, regardless of the row direction.

Sano, Edson Eyji

301

Robust synthetic aperture processing in oceanic fluctuations  

Microsoft Academic Search

The previous synthetic aperture techniques have been investigated to increase signal gain, improve angular resolution and peak-to-sidelobe level ratios for towed line array sonar systems. However, the synthetic aperture method in this paper is performed for conformal array systems by mapping real elements on an axis to control like a linear array. The proposed method for the conformal array performs

Jun Hwan Kim; Ki Man Kim; Won Tcheon Oh; Kyoung Cheol Doh

2000-01-01

302

Geological Applications of Multipolarization SAR *Synthetic Aperature Radar) Data.  

National Technical Information Service (NTIS)

Spaceborne Synthetic Aperture Radar (SAR) data acquired by SEASAT and the Shuttle Imaging Radar (SIR-A/B) operating at L-band with HH polarization were found to be useful in conjunction with other sensors for lithologic discrimination in arid environments...

D. L. Evans

1986-01-01

303

Inverse-synthetic-aperture imaging of trees over a ground plane  

SciTech Connect

Recent data collections with the Sandia VHF-UHF synthetic-aperture radar have yielded surprising results; trees appear brighter in the images than expected! In an effort to understand this phenomenon, various small trees have been measured on the Sandia folded compact range with the inverse-synthetic-aperture imaging system. A compilation of these measurements is contained in this report.

Zittel, D.H.; Brock, B.C.; Littlejohn, J.H.; Patitz, W.E.

1995-11-01

304

A vertical beamforming design approach for increased area coverage rate for synthetic aperture sonar  

Microsoft Academic Search

The authors present a design approach for increasing the area coverage rate for a bottom mapping synthetic aperture sonar (SAS). The approach uses dual acoustic data channels which are established by vertical beamforming from a single phase-shifted transducer array. An SAR (synthetic aperture radar) image quality criterion known as the ambiguity ratio, which affects image contrasts, is applied to the

James C. Nelander; Arthur Craig Kenton; James A. Wright

1989-01-01

305

Investigation of land subsidence in the Houston-Galveston region of Texas by using the Global Positioning System and interferometric synthetic aperture radar, 1993-2000  

USGS Publications Warehouse

Since the early 1900s, groundwater has been the primary source of municipal, industrial, and agricultural water supplies for the Houston-Galveston region, Texas. The region's combination of hydrogeology and nearly century-long use of groundwater has resulted in one of the largest areas of subsidence in the United States; by 1979, as much as 3 meters (m) of subsidence had occurred, and approximately 8,300 square kilometers of land had subsided more than 0.3 m. The U.S. Geological Survey, in cooperation with the Harris-Galveston Subsidence District, used interferometric synthetic aperture radar (InSAR) data obtained for four overlapping scenes from European remote sensing satellites ERS-1 and ERS-2 to analyze land subsidence in the Houston-Galveston region of Texas. The InSAR data were processed into 27 interferograms that delineate and quantify land-subsidence patterns and magnitudes. Contemporaneous data from the Global Positioning System (GPS) were reprocessed by the National Geodetic Survey and analyzed to support, verify, and provide temporal resolution to the InSAR investigation. The interferograms show that the area of historical subsidence in downtown Houston along the Houston Ship Channel has stabilized and that recent subsidence occurs farther west and north of Galveston Bay. Three areas of recent subsidence were delineated along a broad arcuate (bowshaped) feature from Spring, Tex., southwest to Cypress, Tex., and south to Sugar Land, Tex., with subsidence rates ranging from 15 millimeters per year (mm/yr) to greater than 60 mm/yr. Multiyear interferograms near Seabrook, Tex., within the historical subsidence area and nearby Galveston Bay, show several fringes of subsidence (approximately 85 millimeters from January 1996 to December 1997) in the area; however it is difficult to determine the subsidence magnitude near Seabrook because many of the InSAR fringes were truncated or ill-defined. Horizontal and vertical GPS data throughout the area support the InSAR measured subsidence rates and extent. The subsidence rates for a few GPS stations northwest of Houston began to decrease in 2007, which may indicate that subsidence may be decreasing in these areas.

Bawden, Gerald W.; Johnson, Michaela R.; Kasmarek, Mark C.; Brandt, Justin; Middleton, Clifton S.

2012-01-01

306

Detection and measurement of land subsidence using interferometric synthetic aperture radar and Global Positioning System, San Bernardino County, Mojave Desert, California  

USGS Publications Warehouse

Land subsidence associated with ground-water-level declines has been recognized as a potential problem in parts of the Mojave Desert, California. Ground water has been the primary source of domestic, agricultural, and municipal water supplies in the desert since the early 1900s. Pumping of ground water from the Mojave River and Morongo ground-water basins in the southwestern Mojave Desert resulted in water-level declines of more than 30 meters (100 feet) between the 1950s and the 1990s. A Global Positioning System (GPS) survey of a geodetic network was used to determine the location, extent, and magnitude of vertical land-surface changes in Lucerne Valley in the Morongo ground-water basin. The GPS survey was conducted in 1998 to estimate historical elevation changes by comparing GPS-derived elevations with historical elevations (which were available for some of the monuments in the network as early as 1944) and to establish baseline values that can be used for comparisons with future GPS surveys. The GPS measurements indicated that about 600 millimeters (2 feet) [plus or minus 1,500 millimeters (5 feet)] of subsidence occurred at three of the monuments between 1969 and 1998 but that very little to no vertical change in position occurred at seven other monuments in the network. Water levels in the area of subsidence in Lucerne Valley declined about 15 meters (50 feet) during 1970-98. Interferometric synthetic aperture radar (InSAR) methods were used to characterize vertical land-surface changes in the Mojave River and Morongo ground-water basins during various intervals of time between 1992 and 1999. Interferograms, InSAR-generated displacement maps, show that subsidence ranging from 45 to 90 mm (0.15 to 0.3 ft) occurred in four areas of these two ground-water basins--the El Mirage, Lockhart-Harper Lake (dry), Newberry Springs, and Lucerne Valley areas. Some of the InSAR measurements were affected by the earthquakes at Landers and Hector Mine, California, and by atmospheric artifacts. Water-level data were examined for areas undergoing vertical land-surface changes to determine whether the vertical land-surface changes may be related to aquifer-system compaction caused by ground-water-level changes. Temporally relevant water-level data were sparse for some areas, particularly the El Mirage and Lockhart-Harper Lake (dry) areas. Water levels in wells proximate to the subsiding areas generally declined between 1992 and 1999; water levels in some wells proximate to the subsiding areas experienced seasonal periods of declines and recoveries.

Sneed, Michelle; Ikehara, Marti E.; Stork, Sylvia V.; Amelung, Falk; Galloway, Devin L.

2003-01-01

307

Interferometric synthetic aperture radar observation of vertical land displacement in the vicinity of the All-American Canal at the United States and Mexico border  

NASA Astrophysics Data System (ADS)

Interferometric Synthetic Aperture Radar (InSAR) provided a synoptic view of the status of groundwater levels in the vicinity of the All-American Canal (AAC) by measuring vertical land displacements. The European Remote Sensing satellite SAR images were used to produce surface deformation maps. The full time period (1992-2000) was divided to two shorter periods (early and late) (1992-97 and 1996-2000). For low coherence areas such as agricultural fields in the Mexicali Valley, Persistent Scatterers InSAR (PSInSAR) was used to detect any deformation signals. The surface deformation maps from InSAR indicated that there were insignificant vertical land displacements in the vicinity of the AAC. However, the surrounding areas of the East Mesa Geothermal Field (EMGF) were subsiding over the full observation period (-38 mm/year). The maximum subsidence rate at the EMGF was reduced by 21% between the early (-43 mm/year) and late (-34 mm/year) periods. The AAC was within the edges of the spatial extent of the EMGF subsidence, especially during the early period, which was associated with a high averaged net geothermal production. The maximum subsidence on the East Highline Canal was -9.5 +/- 0.5 cm and -2.4 +/- 0.8 cm for the early and late periods, respectively. Results from PSInSAR in Mexicali City and the Mexicali Valley showed insignificant displacements. This lack of deformation indicated that there was no measurable surface deformation in the areas, but validation data were not available. The most interesting phenomenon is the high density of persistent scatterers in the areas between the Andrade Mesa and the Mexicali Valley, and the Sand Hills dunes. Forward modeling was conducted to characterize the reservoir zone of the EMGF based on the InSAR displacement over the full time period. Inputs to the model were the maximum subsidence (-3.8 cm) and depth of the reservoir, the radius of the reservoir and Poisson's ratio. An interactive approach was conducted to find the radius of the reservoir and Poisson's ratio. The radius of the EMGF reservoir is between 1,900 m and 2,000 m with Poisson's ratios between 0.180 and 0.205 at a deforming depth of 800 m.

Han, Joo-Yup

308

Determination of Classification Accuracy for Land Use/cover Types Using Landsat-Tm Spot-Mss and Multipolarized and Multi-Channel Synthetic Aperture Radar  

NASA Astrophysics Data System (ADS)

The primary objective of this study was to determine the degree to which modern SAR systems can be used to obtain information about the Earth's vegetative resources. Information obtainable from microwave synthetic aperture radar (SAR) data was compared with that obtainable from LANDSAT-TM and SPOT data. Three hypotheses were tested: (a) Classification of land cover/use from SAR data can be accomplished on a pixel-by-pixel basis with the same overall accuracy as from LANDSAT-TM and SPOT data. (b) Classification accuracy for individual land cover/use classes will differ between sensors. (c) Combining information derived from optical and SAR data into an integrated monitoring system will improve overall and individual land cover/use class accuracies. The study was conducted with three data sets for the Sleeping Bear Dunes test site in the northwestern part of Michigan's lower peninsula, including an October 1982 LANDSAT-TM scene, a June 1989 SPOT scene and C-, L- and P-Band radar data from the Jet Propulsion Laboratory AIRSAR. Reference data were derived from the Michigan Resource Information System (MIRIS) and available color infrared aerial photos. Classification and rectification of data sets were done using ERDAS Image Processing Programs. Classification algorithms included Maximum Likelihood, Mahalanobis Distance, Minimum Spectral Distance, ISODATA, Parallelepiped, and Sequential Cluster Analysis. Classified images were rectified as necessary so that all were at the same scale and oriented north-up. Results were analyzed with contingency tables and percent correctly classified (PCC) and Cohen's Kappa (CK) as accuracy indices using CSLANT and ImagePro programs developed for this study. Accuracy analyses were based upon a 1.4 by 6.5 km area with its long axis east-west. Reference data for this subscene total 55,770 15 by 15 m pixels with sixteen cover types, including seven level III forest classes, three level III urban classes, two level II range classes, two water classes, one wetland class and one agriculture class. An initial analysis was made without correcting the 1978 MIRIS reference data to the different dates of the TM, SPOT and SAR data sets. In this analysis, highest overall classification accuracy (PCC) was 87% with the TM data set, with both SPOT and C-Band SAR at 85%, a difference statistically significant at the 0.05 level. When the reference data were corrected for land cover change between 1978 and 1991, classification accuracy with the C-Band SAR data increased to 87%. Classification accuracy differed from sensor to sensor for individual land cover classes, Combining sensors into hypothetical multi-sensor systems resulted in higher accuracies than for any single sensor. Combining LANDSAT -TM and C-Band SAR yielded an overall classification accuracy (PCC) of 92%. The results of this study indicate that C-Band SAR data provide an acceptable substitute for LANDSAT-TM or SPOT data when land cover information is desired of areas where cloud cover obscures the terrain. Even better results can be obtained by integrating TM and C-Band SAR data into a multi-sensor system.

Dondurur, Mehmet

309

GNSS-based passive radar sensing using hybrid-aperture system  

NASA Astrophysics Data System (ADS)

A hybrid-aperture radar system is being developed for passive, GNSS-based sensing and imaging missions. Different from previous work, the real aperture (RA) array has excellent cross-range resolution and electronic scanning capability, and synthetic aperture processing is applied for the dimension along the UAV/aircraft flight path. The hybrid aperture thus provides real-time, combined sensing capability and multiple functions. Multi-level signal synchronization and tracking is used to ensure the signal phase coherency and integrity. The advantages of covert radar sensing and reduced onboard computing complexity of this sensor are being demonstrated through experiments.

Silver, Randy; Zhang, Yan Rockee; Suarez, Hernan; Pan, Yu; Huang, Yih-Ru

2013-05-01

310

Detection and Measurement of Land Subsidence Using Global Positioning System and Interferometric Synthetic Aperture Radar, Coachella Valley, California, 1998-2000  

USGS Publications Warehouse

Land subsidence associated with ground-water-level declines has been recognized as a potential problem in Coachella Valley, California. Since the early 1920s, ground water has been a major source of agricultural, municipal, and domestic supply in the valley. Pumping of ground water resulted in water-level declines as large as 15 meters (50 feet) through the late 1940s. In 1949, the importation of Colorado River water to the lower Coachella Valley began, resulting in a reduction in ground-water pumping and a recovery of water levels during the 1950s through the 1970s. Since the late 1970s, demand for water in the valley has exceeded deliveries of imported surface water, resulting in increased pumping and associated ground-water-level declines and, consequently, an increase in the potential for land subsidence caused by aquifer-system compaction. The location, extent, and magnitude of the vertical land-surface changes in Coachella Valley between 1998 and 2000 were determined using Global Positioning System (GPS) and interferometric synthetic aperture radar (InSAR) methods. GPS measurements made at 15 geodetic monuments in the lower Coachella Valley indicate that -34 to +60 millimeters ? 45 millimeters (-0.11 to +0.20 foot ? 0.15 foot) of vertical change in the land surface occurred during the 2-year period. Changes at three of the monuments exceeded the maximum uncertainty of ? 45 millimeters (? 0.15 foot) at the 95-percent confidence level, which indicates that small amounts of uplift occurred at these monuments between October 1998 and August 2000. Water-level measurements made at wells near the three uplifted monuments during this 2-year period indicate that the water levels fluctuate seasonally; water-level measurements made at these wells in September 1998 and September 2000 indicate that the water levels rose slightly near two monuments and declined slightly near the third. The relation between the seasonally fluctuating, but fairly stable, water levels between September 1998 and September 2000 and the slight uplift at the monuments may indicate that the water levels are fluctuating in the elastic range of stress and that the preconsolidation stress of the aquifer system was not exceeded during the 2-year period. Results of the InSAR measurements made between June 17, 1998, and October 4, 2000, indicate that land subsidence, ranging from about 40 to 80 millimeters (0.13 to 0.26 foot), occurred in three areas of the Coachella Valley; near Palm Desert, Indian Wells, and La Quinta. Measurements made between June 17, 1998, and June 2, 1999, indicate that about 15 millimeters (0.05 foot) occurred southeast of Lake Cahuilla. All the subsiding areas coincide with or are near areas where ground-water levels declined between 1998 and 2000; some water levels in 2000 were at the lowest levels in their recorded histories. The coincident areas of subsidence and declining water levels suggest that aquifer-system compaction may be causing subsidence. If the stresses imposed by the historically lowest water levels exceeded the preconsolidation stress, the aquifer-system compaction and associated land subsidence may be permanent. Although the localized character of the subsidence signals look typical of the type of subsidence characteristically caused by localized pumping, the subsidence also may be related to tectonic activity in the valley.

Sneed, Michelle; Stork, Sylvia V.; Ikehara, Marti E.

2002-01-01

311

Natural and Unnatural Oil Layers on the Surface of the Gulf of Mexico Detected and Quantified in Synthetic Aperture RADAR Images with Texture Classifying Neural Network Algorithms  

NASA Astrophysics Data System (ADS)

Effervescent hydrocarbons rise naturally from hydrocarbon seeps in the Gulf of Mexico and reach the ocean surface. This oil forms thin (~0.1 ?m) layers that enhance specular reflectivity and have been widely used to quantify the abundance and distribution of natural seeps using synthetic aperture radar (SAR). An analogous process occurred at a vastly greater scale for oil and gas discharged from BP's Macondo well blowout. SAR data allow direct comparison of the areas of the ocean surface covered by oil from natural sources and the discharge. We used a texture classifying neural network algorithm to quantify the areas of naturally occurring oil-covered water in 176 SAR image collections from the Gulf of Mexico obtained between May 1997 and November 2007, prior to the blowout. Separately we also analyzed 36 SAR images collections obtained between 26 April and 30 July, 2010 while the discharged oil was visible in the Gulf of Mexico. For the naturally occurring oil, we removed pollution events and transient oceanographic effects by including only the reflectance anomalies that that recurred in the same locality over multiple images. We measured the area of oil layers in a grid of 10x10 km cells covering the entire Gulf of Mexico. Floating oil layers were observed in only a fraction of the total Gulf area amounting to 1.22x10^5 km^2. In a bootstrap sample of 2000 replications, the combined average area of these layers was 7.80x10^2 km^2 (sd 86.03). For a regional comparison, we divided the Gulf of Mexico into four quadrates along 90° W longitude, and 25° N latitude. The NE quadrate, where the BP discharge occurred, received on average 7.0% of the total natural seepage in the Gulf of Mexico (5.24 x10^2 km^2, sd 21.99); the NW quadrate received on average 68.0% of this total (5.30 x10^2 km^2, sd 69.67). The BP blowout occurred in the NE quadrate of the Gulf of Mexico; discharged oil that reached the surface drifted over a large area north of 25° N. Performing a similar estimate using 5x5 km grid cells, we observed discharged oil over an area of 1.20x10^5 km^2; 91% of this area was east of 90° W. The average area oil covered water observed in the SAR images was 4.41x104^ km^2, 98% of which was observed in the eastern Gulf. Numerical oil spill model experiments are used to clarify the distinction between the area impacted by the BP oil spill and the surface slicks due to known natural seeps. Natural oil seepage has been cited as a background source of hydrocarbon contamination in the Gulf of Mexico. Our direct comparison shows that during the blowout, the discharged oil impacted an average area two orders of magnitude greater than the entire Gulf total and three orders of magnitude greater than the usual dose received in the northeastern region. Because the layers of discharged oil were often many times thicker than natural seep oil, additional scale factors are required to show the true difference in doses. These differences should be weighed when evaluating the relative impact of natural and unnatural oil in a large marine ecosystem.

MacDonald, I. R.; Garcia-Pineda, O. G.; Morey, S. L.; Huffer, F.

2011-12-01

312

Axial superresolution by synthetic aperture generation  

NASA Astrophysics Data System (ADS)

The use of tilted illumination onto the input object in combination with time multiplexing is a useful technique to overcome the Abbe diffraction limit in imaging systems. It is based on the generation of an expanded synthetic aperture that improves the cutoff frequency (and thus the resolution limit) of the imaging system. In this paper we present an experimental validation of the fact that the generation of a synthetic aperture improves not only the lateral resolution but also the axial one. Thus, it is possible to achieve higher optical sectioning of three-dimensional (3D) objects than that defined by the theoretical resolution limit imposed by diffraction. Experimental results are provided for two different cases: a synthetic object (micrometer slide) imaged by a 0.14 numerical aperture (NA) microscope lens, and a biosample (swine sperm cells) imaged by a 0.42 NA objective.

Micó, V.; García, J.; Zalevsky, Z.

2008-12-01

313

Detection and measurement of land subsidence using Global Positioning System and interferometric synthetic aperture radar, Coachella Valley, California, 1996-98  

USGS Publications Warehouse

Land subsidence associated with ground-water-level declines has been recognized as a potential problem in Coachella Valley, California. Since the early 1920s, ground water has been a major source of agricultural, municipal, and domestic supply in the valley, resulting in water-level declines as large as 15 meters (50 feet) through the late 1940s. In 1949, the importation of Colorado River water to the lower Coachella Valley began, resulting in a reduction in ground-water pumping and a recovery of water levels from the 1950s through the 1970s. Since the late 1970s, the demand for water in the valley has exceeded the deliveries of imported surface water, again resulting in increased pumping and ground-water-level declines. The magnitude and temporal occurrence of land subsidence in the lower Coachella Valley are not well known; data are sparse and accuracy varies. Also, the area is tectonically active and has subsided during the past several million years, which further complicates interpretations of the data. Land-surface-elevation data have been collected by many agencies using various methods and different geographic scales; because of this, the -150 millimeters (-0.5 foot) of subsidence determined for the southern parts of the valley for 1930-96 may have a possible error of plus or minus (?)90 millimeters (?0.3 foot). The location, extent, and magnitude of vertical land-surface changes from 1996 to 1998 were determined using Global Positioning System (GPS) and interferometric synthetic aperture radar (InSAR) methods. GPS measurements for 14 monuments in the lower Coachella Valley indicate that the vertical land-surface changes from 1996 to 1998 ranged from -13 to -67 millimeters ? 40 millimeters (-0.04 to -0.22 foot ?0.13 foot). Changes at seven of the monuments exceeded the measurement error of ?40 millimeters (?0.13 foot), which indicates that small amounts of land subsidence occurred at these monuments between 1996 and 1998. Some of the water levels measured in wells near several of these monuments during 1996-98 were the lowest water levels in the recorded histories of the wells. The possible relation between the stresses caused by historically low water levels and the measured vertical changes in land surface suggests that the preconsolidation stress of the aquifer system may have been exceeded during this period and that subsidence may be permanent. Comparisons of several paired monuments and wells indicated that the relation between short-term ground-water-level changes and vertical changes in land surface in the lower Coachella Valley is not clearly defined. Results of InSAR measurements made between 1996 and 1998 indicate that vertical changes in land surface, ranging from about -20 to -70 millimeters ? 5-10 millimeters (-0.07 to -0.23 foot ? 0.02-0.03 foot), occurred in three areas of the Coachella Valley--near Palm Desert, Indian Wells, and Lake Cahuilla. The areas of subsidence near Palm Desert and Indian Wells coincide with areas of substantial ground-water production during 1996-98. The Coachella Valley Water District reported that they had no ground-water production wells in the Lake Cahuilla area but that there may be private production wells in the area. Production from these wells or possibly tectonic activity may be contributing to or causing the subsidence. The geodetic network used for the GPS measurements described in this report covers the area from the Salton Sea on the south to just northwest of Indio. The maps processed using InSAR overlap the part of the geodetic network west of Coachella and north of Lake Cahuilla, and include the Palm Desert area. Both methods of measuring vertical land-surface changes, GPS and InSAR, were used to characterize vertical land-surface changes from the Palm Desert area to the Salton Sea. Because InSAR produces more spatially detailed data over large areas, it generally was useful where vertical land-surface changes were previously unrecognized, such as the

Sneed, Michelle; Ikehara, Marti E.; Galloway, D. L.; Amelung, Falk

2001-01-01

314

Results of synthetic aperture sonar experiments  

Microsoft Academic Search

Results are presented from synthetic aperture sonar (SAS) experiments with three different test systems: one oriented toward mine detection; one toward buried UXO detection; and one toward buried cable detection. The first two systems share hydrophone arrays of 32-10-cm long elements. Results are presented that demonstrate key features of SAS images: azimuth resolution independent of range, grating lobe suppression by

M. Neudorfer; J. Kosalos; R. Bonneau

2000-01-01

315

An implementation of synthetic aperture focusing technique in frequency domain.  

PubMed

A new implementation of a synthetic aperture focusing technique (SAFT) based on concepts used in synthetic aperture radar and sonar is presented in the paper. The algorithm, based on the convolution model of the imaging system developed in frequency domain, accounts for the beam pattern of the finite-sized transducer used in the synthetic aperture. The 2D fast Fourier transform (FFT) is used for the calculation of a 2D spectrum of the ultrasonic data. The spectrum is then interpolated to convert the polar coordinate system used for the acquisition of ultrasonic signals to the rectangular coordinates used for the presentation of imaging results. After compensating the transducer lobe amplitude profile using a Wiener filter, the transformed spectrum is subjected to the 2D inverse Fourier transform to get the time-domain image again. The algorithm is computationally attractive due to the use of 2D FFT. The performance of the proposed frequency-domain algorithm and the classical time-domain SAFT are compared in the paper using simulated and real ultrasonic data. PMID:17718329

Stepinski, Tadeusz

2007-07-01

316

Radar aperture synthesis observations of asteroids  

NASA Astrophysics Data System (ADS)

We report of Goldstone-VLA, radar aperture-synthesis observations of the mainbelt asteroids 324 Bamberga and 7 Iris and the near-Earth asteroids 1991 EE and 4179 Toutatis. Simultaneous resolution of echoes in both angle and Doppler frequency provide new constraints on the mainbelt asteroids' pole directions: Bamberga's spin vector is within 40 deg of the south ecliptic pole, and the twofold ambiguity in Iris' pole direction (P. Magnusson, 1989) is resolved in favor of the ecliptic coordinates lambda = 15 deg, beta = +25 deg. For Bamberga, monostatic and bistatic radar echoes and VLA thermal-emission measurements, also reported here, are consistent with radiometric estimates of Bamberga's size and with the hypothesis that the asteroid is overlain by a regolith having a porosity of approximately 50%. Our near-Earth asteroid measurements required the development of new on-line VLA software that allows imaging of objects that are in the telescope's `near field.' This software has been successfully tested on Toutatis at a distance of 0.06 AU and will be essential for VLA observations of Earth-approaching comets.

de Pater, Imke; Palmer, Patrick; Mitchell, David L.; Ostro, Steven J.; Yeomens, Donald K.; Snyder, Lewis E.

1994-10-01

317

High-resolution DOA estimation from synthetic aperture beamforming  

Microsoft Academic Search

We have introduced a new direction of arrival algorithm that synthetically extends the spatial aperture (synthetic aperture conventional beamformer, SA-CBF) that couples the resolution capability of the MUSIC algorithm and the robustness of the conventional Bartlett beamformer. The synthetic aperture is created bv using a 2D data extrapolation technique from 2D linear prediction algorithm whose number of parameters were selected

Claudio S. Marino; P. M. Chau

2005-01-01

318

Statistics of synthetic aperture sonar images  

Microsoft Academic Search

We have examined certain statistical aspects of seabed images formed by wideband synthetic aperture sonar. In particular, we have formed high-quality data-adaptive non-parametric kernel estimates from the envelope images. In most cases, the estimated tails of the distribution appear to be substantially heavier than those of the Rayleigh-distribution. Parametric approaches, e.g., fits of the data to a Rayleigh mixture, suggest

Alfred Hanssen; Jonas Kongsli; Roy E. Hansen; Sean Chapman

2003-01-01

319

Seabed segmentation in synthetic aperture sonar images  

NASA Astrophysics Data System (ADS)

A synthetic aperture sonar (SAS) image segmentation algorithm using features from a parameterized intensity image autocorrelation function (ACF) is presented. A modification over previous parameterized ACF models that better characterizes periodic or rippled seabed textures is presented and discussed. An unsupervised multiclass k-means segmentation algorithm is proposed and tested against a set of labeled SAS images. Segmentation results using the various models are compared against sand, rock, and rippled seabed environments.

Cobb, J. Tory; Principe, Jose

2011-05-01

320

Synthetic Aperture Fourier Holographic Optical Microscopy  

NASA Astrophysics Data System (ADS)

We report a new synthetic aperture optical microscopy in which high-resolution, wide-field amplitude and phase images are synthesized from a set of Fourier holograms. Each hologram records a region of the complex two-dimensional spatial frequency spectrum of an object, determined by the illumination field’s spatial and spectral properties and the collection angle and solid angle. We demonstrate synthetic microscopic imaging in which spatial frequencies that are well outside the modulation transfer function of the collection optical system are recorded while maintaining the long working distance and wide field of view.

Alexandrov, Sergey A.; Hillman, Timothy R.; Gutzler, Thomas; Sampson, David D.

2006-10-01

321

Constraining the slip distribution and fault geometry of the Mw 7.9, 3 November 2002, Denali fault earthquake with Interferometric Synthetic Aperture Radar and Global Positioning System data  

USGS Publications Warehouse

The Mw 7.9, Denali fault earthquake (DFE) is the largest continental strike-slip earthquake to occur since the development of Interferometric Synthetic Aperture Radar (InSAR). We use five interferograms, constructed using radar images from the Canadian Radarsat-1 satellite, to map the surface deformation at the western end of the fault rupture. Additional geodetic data are provided by displacements observed at 40 campaign and continuous Global Positioning System (GPS) sites. We use the data to determine the geometry of the Susitna Glacier fault, thrusting on which initiated the DFE, and to determine a slip model for the entire event that is consistent with both the InSAR and GPS data. We find there was an average of 7.3 ?? 0.4 m slip on the Susitna Glacier fault, between 1 and 9.5 km depth on a 29 km long fault that dips north at 41 ?? 0.7?? and has a surface projection close to the mapped rupture. On the Denali fault, a simple model with large slip patches finds a maximum of 8.7 ?? 0.7 m of slip between the surface and 14.3 ?? 0.2 km depth. A more complex distributed slip model finds a peak of 12.5 ?? 0.8 m in the upper 4 km, significantly higher than the observed surface slip. We estimate a geodetic moment of 670 ?? 10 ?? 10 18 N m (Mw 7.9), consistent with seismic estimates. Lack of preseismic data resulted in an absence of InSAR coverage for the eastern half of the DFE rupture. A dedicated geodetic InSAR mission could obviate coverage problems in the future.

Wright, T. J.; Lu, Z.; Wicks, C.

2004-01-01

322

The prediction and validation of spatial variation of storm tide height along the coastline of North Somerset, U.K. during extreme events typical of coastal flooding using Synthetic Aperture Radar.  

NASA Astrophysics Data System (ADS)

Inundation modellers are faced with the problem of determining coastal flood risk in a future climate in order to aid planners, policy makers and engineers. Current research suggests a major source of uncertainty is the water-level height along the coastline which is used to force 2D inundation models of the region studied. Recent research has indicated that the spatial variation of the water-level during a storm (storm tide) has a predictable spatial relationship based upon historical storm events, however, this new proposed method needs to be validated. Detailed observations of a storm tide along a coastline are very rare, but it is believed that Synthetic Aperture Radar (SAR) can be employed with the "water-line method" to provide this detailed dataset of observed water heights. This project is accessing the degree to which current space-borne SAR imagery can be used to determine detailed water-level heights along a coastline during an extreme water-level event typical of a coastal flood, and then employing this dataset to validate a new spatial storm tide variation prediction method. Future inundation risk models may benefit from this research with an improved and more accurate forcing condition, but also oceanographers and coastal scientists can employ the SAR imagery-derived water level approach developed within this work to aid storm surge and coastal inundation research.

Lewis, Matt; Schumann, Guy; Horsburgh, Kevin; Bates, Paul

2010-05-01

323

Web Application System with Synthetic Aperture Rader Image Processing for Education  

Microsoft Academic Search

Remotely sensed images observed by synthetic aperture radar (SAR) become to be more significant for a variety of purposes. It is necessary to process and focus SAR images at a user's side for required precision. This paper presents a concept, a system structure, and an implementation method for a web application system with a SAR image processing for education. The

Yuuhei Teramoto; Yosuke Ito; Kenji Abe

2009-01-01

324

Aperture Synthesis Imaging at the EISCAT Svalbard radar  

NASA Astrophysics Data System (ADS)

The EISCAT incoherent radar on Svalbard has two dishes. In addition to this two dishes three smaller passive array antennas were built to attempt to implement radar aperture synthesis imaging. Limited to measurements of coherent backscatter the primary science goal of this new receiver system is to study so called naturally enhanced ion acoustic lines. In order to compare radar aperture synthesis images with optical data phase calibration of the interferometer system is needed. We present the phase calibration of the Svalbard interferometer system including the passive array antennas. The calibration was done using optical signatures of satellite transits and the coherent backscatter of the satellites. The optical signature provide accurate position of the satellites. Furthermore we will present sudo-3D aperture synthesis radar images from first observations of satellites conducted with this system.

Schlatter, N. M.; Goodbody, B. C.; Grydeland, T.; Ivchenko, N.; Gustavsson, B.; Belyey, V.; Lanchester, B. S.

2012-04-01

325

Synthetic Aperture Microwave Imaging on MAST  

NASA Astrophysics Data System (ADS)

A novel microwave imaging device, the Synthetic Aperture Microwave Imaging (SAMI) radiometer has been designed and built to obtain the first fully 3D images of microwave mode conversion in the edge of tokamak plasmas to facilitate high time resolution measurements of the edge current density. The imaging technique has been adapted from radio astronomy and Earth remote sensing, but with high time resolution (˜5?s) due to the exceptionally bright source. This diagnostic has no optical components, instead using frequency down converting electronics and a digitiser. All image reconstructions are then done in post-processing. First data for SAMI has been obtained at the time of abstract submission and is currently under analysis. Preliminary results will be presented and discussed.

Freethy, Simon; Huang, Billy; Shevchenko, Vladimir; Vann, Roddy

2011-11-01

326

Use of Synthetic Aperture Radar (SAR) to Identify and Characterize Overwintering Areas of Fish in Ice-Covered Arctic RIvers: A Demonstration with Broad Whitefish and their Habitats in the Sagavanirktok River, Alaska  

SciTech Connect

In northern climates, locating overwintering fish can be very challenging due to thick ice cover. Areas near the coast of the Beaufort Sea provide valuable overwintering habitat for both resident and anadromous fish species; identifying and understanding their use of overwintering areas is of special interest. Synthetic aperture radar (SAR) imagery from two spaceborne satellites was examined as an alternative to radiotelemetry for identifying anadromous fish overwintering. The presence of water and ice were sampled at 162 sites and fish were sampled at 16 of these sites. From SAR imagery alone, we successfully identified large pools inhabited by overwintering fish in the ice-covered Sagavanirktok River. In addition, the imagery was able to identify all of the larger pools (mean minimum length of 138m (range 15-470 m; SD=131)) of water located by field sampling. The effectiveness of SAR to identify these pools varied from 31% to 100%, depending on imagery polarization, the incidence angle range, and the orbit. Horizontal transmit–vertical receive (HV) polarization appeared best. The accuracy of SAR was also assessed at a finer pixel-by-pixel (30-m x30-m) scale. The best correspondence at this finer scale was obtained with an image having HV polarization. The levels of agreement ranged from 54% to 69%. The presence of broad whitefish (the only anadromous species present) was associated with salinity and pool size (estimated with SAR imagery); fish were more likely to be found in larger pools with low salinity. This research illustrates that SAR imaging has great potential for identifying under-ice overwintering areas of riverine fish. These techniques should allow managers to identify critical overwintering areas with relatively more ease and lower cost than traditional techniques.

Brown, Richard S.; Duguay, Claude R.; Mueller, Robert P.; Moulton, Larry; Doucette, Peter J.; Tagestad, Jerry D.

2010-12-01

327

Large Aperture Multi-Dimensional Laser Radar Testbed.  

National Technical Information Service (NTIS)

A 39 cm aperture multi-dimensional laser radar has been built and made operational. This sensor acquires pixel registered range, Doppler, 3-5 micrometer passive, and visible passive data. Range is digitized at 200 MHz for .75 m range resolution. Doppler i...

D. U. Fluckiger M. P. Boldue L. A. Prior

1988-01-01

328

Development of the synthetic aperture microwave radiometer, ESTAR  

Microsoft Academic Search

Ten years ago, the synthetic aperture radiometer (ESTAR) published its first image. Since then, ESTAR has successfully demonstrated the potential of aperture synthesis for microwave remote sensing. This paper summarizes the status of the instrument and presents a modern image for comparison with the “initial results” published ten years ago

D. M. Le Vine; C. T. Swift; M. Haken

2001-01-01

329

Synthetic aperture technique for twin-line array  

Microsoft Academic Search

We propose a synthetic aperture technique for a twin-line array. The towed line array system has been investigated in underwater environments to improve the signal-to-noise ratio and angular resolution. But to achieve that, it required a long aperture size. It caused physical problems-fluctuations, sensor positioning, towing array etc. It has a left-right ambiguity at the receiver between the opposite angles.

In-Sik Yang; Seung-Yong Yang; Ki-Man Kim

2001-01-01

330

Target Identification Using Radar Imagery and Moment Methods.  

National Technical Information Service (NTIS)

In the past, most radar target recognition techniques have concentrated on the use of one-dimensionsal target signatures. However, the development of the Synthetic Aperture Radar (SAR) and the recent development of the Inverse Synthetic Aperture (ISAR) te...

G. A. Ioannidis

1980-01-01

331

Image simulator for one-dimensional synthetic aperture microwave radiometer  

Microsoft Academic Search

Calibration for a one-dimensional synthetic aperture microwave radiometer is critical. Phase and amplitude calibration of the visibility samples must be carried out to compensate for system bias before measurement. This bias mainly comes from the un-uniform characteristics and the couplings between the receiving channels. To take into account this problem, a numerical image retrieving method is considered using an intermediate

Wu Qiong; Liu Hao; Wu Ji

2004-01-01

332

Synthetic transmit aperture imaging using orthogonal Golay coded excitation  

Microsoft Academic Search

The frame rate in medical ultrasound imaging may be increased significantly by reducing the number of transmits per image frame. Cooley et al. (1994) and Lockwood et al. (1995) have described synthetic transmit aperture (STA) systems where each frame is imaged using data obtained from a small number of point sources fired in succession. These systems have potential for very

Richard Y. Chiao; Lewis J. Thomas

2000-01-01

333

Reduction of the Reconstruction Bias in Synthetic Aperture Imaging Radiometry  

Microsoft Academic Search

Synthetic Aperture Imaging Radiometers (SAIR) are powerful instruments for high-resolution observation of planetary surfaces at low microwave frequencies. This article is concerned with the reconstruction of radiometric brightness temperature maps from SAIR interferometric measurements. Even in the absence of modeling errors and radiometric noise, a systematic error, or bias, has been observed in the reconstructed maps. The origin of this

Eric ANTERRIEU

2006-01-01

334

A Rectangular Array for Motion Induced Synthetic Aperture Radiometer  

Microsoft Academic Search

In this paper, high spatial resolution imaging of a motion induced synthetic aperture radiometer with sparse rectangular array is presented. The imaging process is described including an observation scenario and image formation. The equivalent array factor and instantaneous spatial frequency coverage are presented to demonstrate the performance. Additionally, the differences between the proposed system and previous studies are discussed.

Hyuk Park; Sung-Hyun Kim; Ho-Jin Lee; Nam-Won Moon; Yong-Hoon Kim

2008-01-01

335

High fidelity synthetic aperture sonar products for target analysis  

Microsoft Academic Search

Synthetic aperture sonar (SAS) can produce images with centimetre-level resolution and area coverage of better than one square kilometer per hour. This makes SAS an ideal sensor for detection and classification of small targets over large areas. Fully automated target analysis allows improved autonomy when using autonomous underwater vehicles (AUVs) and saves a tedious manual analysis in post-mission analysis. Recognition

Roy E Hansen; Hayden J Callow; T. O. Saebo; Per Espen Hagen; Bjørnar Langli

2008-01-01

336

Synthetic Aperture Sonar Imaging of Simple Finite Targets.  

National Technical Information Service (NTIS)

During the Sediment Acoustics Experiment 2004 (SAX04), a synthetic aperture sonar (SAS) was used to detect simple targets that were either proud or buried below a water-sediment interface, where the nominal grazing angle of incidence from the SAS to the p...

E. I. Thorsos K. L. Williams S. G. Kargl

2011-01-01

337

A Technique for Interferometric Synthetic Aperture Sonar Image Processing  

Microsoft Academic Search

Interferometric Synthetic Aperture Sonar provides a means of obtaining high resolution three-dimensional i mages of objects on the sea floor. This paper describes a technique for forming images using interferometric sonar data. The technique is novel in the way it combines image co-registration and height estimation. Results of applying the technique to real sonar data are given.

S M Banks; H D Griffiths; T J Sutton

338

A New Synthetic Aperture Sonar Processing Method Using Coherence Analysis  

Microsoft Academic Search

This paper introduces two methods that use a co- herence analysis framework to generate synthetic aperture sonar (SAS)-like images that display acoustic color (AC) information useful for the classification of buried and\\/or proud underwater objects. The first method is applicable to sonar backscatter collected with multiple hydrophones and involves forming two channels using the data of two hydrophone subarrays at

Neil Wachowski; Mahmood R. Azimi-Sadjadi

2011-01-01

339

An experimental study on synthetic aperture sonar for perturbed array  

Microsoft Academic Search

Synthetic Aperture Sonar is a technique of extending physically limited length of an array through signal processing. SAS method is often used to enhance bearing resolution of a system. Previous techniques assume most of array shapes as linear, so when towed array shapes are distorted, this can create a deviation from actual situation. In this paper, we estimated perturbed array

Hyun-Woo Kang; Hee-Young Park; Dae-Hee Youn; Chungyong Lee; Ki-Man Kim; Won-Tchon Oh

2004-01-01

340

Improved image reconstruction techniques for synthetic aperture radiometers  

Microsoft Academic Search

Ripple in excess of that attributable to Gibb's phenomenon has been identified in brightness temperature images created from data collected by synthetic aperture radiometers used for Earth remote sensing. The cause of the excess ripple is identified, and methods for reducing its effect on image quality are proposed

Mark A. Goodberlet

2000-01-01

341

Optimum synthetic-aperture imaging of extended astronomical objects.  

PubMed

In optical aperture-synthesis imaging of stellar objects, different beam combination strategies are used and proposed. Coaxial Michelson interferometers are very common and a homothetic multiaxial interferometer is recently realized in the Large Binocular Telescope. Laboratory experiments have demonstrated the working principles of two new approaches: densified pupil imaging and wide field-of-view (FOV) coaxial imaging using a staircase-shaped mirror. We develop a common mathematical formulation for direct comparison of the resolution and noise sensitivity of these four telescope configurations for combining beams from multiple apertures for interferometric synthetic aperture, wide-FOV imaging. Singular value decomposition techniques are used to compare the techniques and observe their distinct signal-to-noise ratio behaviors. We conclude that for a certain chosen stellar object, clear differences in performance of the imagers are identifiable. PMID:17361290

van der Avoort, Casper; Pereira, Silvania F; Braat, Joseph J M; den Herder, Jan-Willem

2007-04-01

342

Reconstructing 3-D Ship Motion for Synthetic Aperture Sonar Processing  

NASA Astrophysics Data System (ADS)

We are investigating the feasibility of coherent ping-to-ping processing of multibeam sonar data for high-resolution mapping and change detection in the deep ocean. Theoretical calculations suggest that standard multibeam resolution can be improved from 100 m to ~10 m through coherent summation of pings similar to synthetic aperture radar image formation. A requirement for coherent summation of pings is to correct the phase of the return echoes to an accuracy of ~3 cm at a sampling rate of ~10 Hz. In September of 2003, we conducted a seagoing experiment aboard R/V Revelle to test these ideas. Three geodetic-quality GPS receivers were deployed to recover 3-D ship motion to an accuracy of +- 3cm at a 1 Hz sampling rate [Chadwell and Bock, GRL, 2001]. Additionally, inertial navigation data (INS) from fiber-optic gyroscopes and pendulum-type accelerometers were collected at a 10 Hz rate. Independent measurements of ship orientation (yaw, pitch, and roll) from the GPS and INS show agreement to an RMS accuracy of better than 0.1 degree. Because inertial navigation hardware is susceptible to drift, these measurements were combined with the GPS to achieve both high accuracy and high sampling rate. To preserve the short-timescale accuracy of the INS and the long-timescale accuracy of the GPS measurements, time-filtered differences between the GPS and INS were subtracted from the INS integrated linear velocities. An optimal filter length of 25 s was chosen to force the RMS difference between the GPS and the integrated INS to be on the order of the accuracy of the GPS measurements. This analysis provides an upper bound on 3-D ship motion accuracy. Additionally, errors in the attitude can translate to the projections of motion for individual hydrophones. With lever arms on the order of 5m, these errors will likely be ~1mm. Based on these analyses, we expect to achieve the 3-cm accuracy requirement. Using full-resolution hydrophone data collected by a SIMRAD EM/120 echo sounder we are applying the 6 components of ship motion to correct the phase center of each hydrophone. Successive pings will be analyzed for phase coherence.

Thomsen, D. R.; Chadwell, C. D.; Sandwell, D.

2004-12-01

343

Synthetic aperture acoustic imaging of canonical targets with a 2-15 kHz linear FM chirp  

NASA Astrophysics Data System (ADS)

Synthetic aperture image reconstruction applied to outdoor acoustic recordings is presented. Acoustic imaging is an alternate method having several military relevant advantages such as being immune to RF jamming, superior spatial resolution, capable of standoff side and forward-looking scanning, and relatively low cost, weight and size when compared to 0.5 - 3 GHz ground penetrating radar technologies. Synthetic aperture acoustic imaging is similar to synthetic aperture radar, but more akin to synthetic aperture sonar technologies owing to the nature of longitudinal or compressive wave propagation in the surrounding acoustic medium. The system's transceiver is a quasi mono-static microphone and audio speaker pair mounted on a rail 5meters in length. Received data sampling rate is 80 kHz with a 2- 15 kHz Linear Frequency Modulated (LFM) chirp, with a pulse repetition frequency (PRF) of 10 Hz and an inter-pulse period (IPP) of 50 milliseconds. Targets are positioned within the acoustic scene at slant range of two to ten meters on grass, dirt or gravel surfaces, and with and without intervening metallic chain link fencing. Acoustic image reconstruction results in means for literal interpretation and quantifiable analyses. A rudimentary technique characterizes acoustic scatter at the ground surfaces. Targets within the acoustic scene are first digitally spotlighted and further processed, providing frequency and aspect angle dependent signature information.

Vignola, Joseph F.; Judge, John A.; Good, Chelsea E.; Bishop, Steven S.; Gugino, Peter M.; Soumekh, Mehrdad

2011-05-01

344

THE EFFECT OF SOUND VELOCITY VARIATIONS ON SYNTHETIC APERTURE SONAR  

Microsoft Academic Search

Near-field acoustic imaging requires that the geometry and the sound velocity between observation system (sonar) and scene (seafloor) to be known. An incorrect sound velocity leads to degradation imagery and poor image quality. In synthetic aperture sonar (SAS) imaging, the scene is almost always in the near-field. This means accurate estimation of sound-velocity is vitally important for high-quality imagery. We

Roy Edgar Hansen; Hayden John Callow; Torstein Olsmo Sæbø

345

DETECTION RATE STATISTICS IN SYNTHETIC APERTURE SONAR IMAGES  

Microsoft Academic Search

Synthetic aperture sonar (SAS) has proved to be successful for mine hunting and is now robust for generating high-resolution images over wide swath. The subsequent step in the processing is detection, discriminating between mine-like and non-mine-like objects, which is designed to minimise the number of missed mines so that the system can manage the detection rate. Statistical analysis using SAS

Johannes Groen; Enrique Coiras; David Williams

346

Dual-transponder Precision Navigation System for Synthetic Aperture Sonar  

Microsoft Academic Search

The technical details of a dual-transponder, long-baseline positioning system to mea- sure the sway of a free towed Synthetic Aperture Sonar (SAS) are presented. The sway is measured with respect to freely deployed, battery powered, transponders which sit stationary on the seabed connected via cables to floating buoys housing high-accuracy GPS timing receivers. A T\\/R switch allows a single hydrophone

E N Pilbrow; M P Hayes; P T Gough

2002-01-01

347

High-rate synthetic aperture communications in shallow water.  

PubMed

Time reversal communication exploits spatial diversity to achieve spatial and temporal focusing in complex ocean environments. Spatial diversity can be provided easily by a vertical array in a waveguide. Alternatively, spatial diversity can be obtained from a virtual horizontal array generated by two elements, a transmitter and a receiver, due to relative motion between them, referred to as a synthetic aperture. This paper presents coherent synthetic aperture communication results from at-sea experiments conducted in two different frequency bands: (1) 2-4 kHz and (2) 8-20 kHz. Case (1) employs binary-phase shift-keying modulation, while case (2) involves up to eight-phase shift keying modulation with a data rate of 30 kbits/s divided by the number of transmissions (diversity) to be accumulated. The receiver utilizes time reversal diversity combining followed by a single channel equalizer, with frequent channel updates to accommodate the time-varying channel due to coupling of space and time in the presence of motion. Two to five consecutive transmissions from a source moving at 4 kts over 3-6 km range in shallow water are combined successfully after Doppler compensation, confirming the feasibility of coherent synthetic aperture communications using time reversal. PMID:20000919

Song, H C; Hodgkiss, W S; Kuperman, W A; Akal, T; Stevenson, M

2009-12-01

348

Investigating the Application of Synthetic Aperture Altimetry over oceans, coastal and inland waters.  

NASA Astrophysics Data System (ADS)

The application of Synthetic Aperture Radar (SAR) techniques to classical radar altimetry promises significant improvements to measurements made over land, oceans and ice. CryoSat-2, to be launched towards the end of 2009, will be the first to operate an altimeter with a SAR mode. Although it was designed with ice applications as the prime objective, these data will also be of great interest to the hydrosphere and oceanography communities, since they also have the potential to support significant progress in coastal monitoring, ocean floor topography, gravity field and inland water monitoring. Thus the SAMOSA project, funded by the European Space Agency and led by SatOC (UK), was initiated to provide a thorough scientific assessment of this technology and to quantify the improvement that may be expected in measurements over water surfaces offered by SAR altimetry, as compared to conventional altimetry. The SAMOSA study combined theoretical developments with the analysis of computer simulations of SAR altimeter data over oceanic, coastal and inland water features. The theoretical work included the development of a new theoretical model for the SAR altimeter mode processed echoes over water. This model was then used to develop and test a re-tracker specifically designed for SAR mode data For the computer simulations, the CryoSat mission performance simulator (CRYMPS) was used. This simulator, developed by Mullard Space Science Laboratories (UK) specifically for Cryosat, simulates the products for the three available Cryosat-2 altimeter modes: Synthetic Aperture Radar, Interferometric Synthetic Aperture Radar and Low Rate Mode (equivalent to a conventional altimeter). The project team generated a number of digital elevation and backscatter models, representing short sections of representative oceanic, coastal and inland water "scenarios", and used these to investigate the modelled response of the SAR mode altimeter. For this presentation we present an overview of the results of the project, including - The results of computer simulations to investigate the SAR altimeter response to oceanic features such as fronts, slicks and variable wave fields. - An investigation into how SAR altimeter data can help improve recovery of short spatial scale geophysical signals over the ocean (bathymetry, marine gravity field) - The development and testing of a new echo model and associated re-tracker adapted to the specific nature of SAR altimetry echoes. - An investigation of the modelled performance of the SAR altimeter over coastal and complex inland water features. We offer some recommendations for further theoretical and experimental investigations, and some suggestions on processing approaches for CRYOSAT-2 data to support the improved retrieval of data over ocean, coastal and inland water surfaces.

Cotton, D.; Benveniste, J.; Andersen, O.; Berry, P.; Cipollini, P.; Gommenginger, C.; Martin-Puig, C.; Raney, K.

2009-04-01

349

Synthetic-aperture sonar imaging with a multiple-element receiver array  

Microsoft Academic Search

The application of synthetic aperture techniques in sonar imaging of the ocean floor has been limited by sonar platform instability. The authors present a robust algorithm for motion estimation and compensation to perform synthetic aperture image formation. First, the algorithm uses the acoustic returns from a receiver array to form a complex-valued physical-aperture image for each transmit burst. Perturbations of

Brett L. Douglas; Hua Lee

1993-01-01

350

Synthetic aperture imaging using sources with finite aperture: deconvolution of the spatial impulse response.  

PubMed

A method for ultrasonic synthetic aperture imaging using finite-sized transducers is introduced that is based on a compact, linear, discrete model of the ultrasonic measurement system developed using matrix formalism. Using this model a time-domain algorithm for deconvolution of the transducer's spatial impulse responses (SIRs) is developed that is based on a minimum mean square error (MMSE) criterion. The algorithm takes the form of a spatiotemporal filter that compensates for the SIRs associated with a finite-sized transducer at every point of the processed image. A major advantage of the proposed method is that it can be used for any transducer, provided that its associated SIRs are known. This is in contrast to the synthetic aperture focusing technique (SAFT), which treats the transducer as a point source. The performance of the method is evaluated with simulations and experiments, performed in water using a linear phased array. The results obtained using the proposed method are compared to those obtained with a classical time-domain SAFT algorithm. For a finite aperture source, it is clearly shown that the resolution obtained using the proposed method is superior to that obtained using the SAFT algorithm. PMID:12880037

Lingvall, Fredrik; Olofsson, Tomas; Stepinski, Tadeusz

2003-07-01

351

Imaging with Concave Large-Aperture Therapeutic Ultrasound Arrays Using Conventional Synthetic-Aperture Beamforming  

PubMed Central

Several dual-mode ultrasound array (DMUA) systems are being investigated for potential use in image-guided surgery. In therapeutic mode, DMUAs generate pulsed or continuous-wave (CW) high-intensity focused ultrasound (HIFU) beams capable of generating localized therapeutic effects within the focal volume. In imaging mode, pulse-echo data can be collected from the DMUA elements to obtain B-mode images or other forms of feedback on the state of the target tissue before, during, and after the application of the therapeutic HIFU beam. Therapeutic and technological constraints give rise to special characteristics of therapeutic arrays. Specifically, DMUAs have concave apertures with low f-number values and are typically coarsely sampled using directive elements. These characteristics necessitate pre- and post-beamforming signal processing of echo data to improve the spatial and contrast resolution and maximize the image uniformity within the imaging field of view (IxFOV). We have recently developed and experimentally validated beamforming algorithms for concave large-aperture DMUAs with directive elements. Experimental validation was performed using a 1 MHz, 64-element, concave spherical aperture with 100 mm radius of curvature. The aperture was sampled in the lateral direction using elongated elements 1??×33.3? with 1.333??? center-to-center spacing (? is the wavelength). This resulted in f-number values of 0.8 and 2 in the azimuth and elevation directions, respectively. In this paper, we present a new DMUA design approach based on different sampling of the shared concave aperture to improve image quality while maintaining therapeutic performance. A pulse-wave (PW) simulation model using a modified version of the Field II program is used in this study. The model is used in generating pulse-echo data for synthetic-aperture (SA) beamforming for forming images of a variety of targets, e.g., wire arrays and speckle-generating cyst phantoms. To provide validation for the simulation model and illustrate the improvements in image quality, we show SA images of similar targets using pulse-echo data acquired experimentally using our existing 64-element prototype. The PW simulation model is used to investigate the effect of transducer bandwidth as well as finer sampling of the concave DMUA aperture on the image quality. The results show that modest increases in the sampling density and transducer bandwidth result in significant improvement in spatial and contrast resolutions in addition to extending the DMUA IxFOV.

Wan, Yayun; Ebbini, Emad S.

2009-01-01

352

Imaging with concave large-aperture therapeutic ultrasound arrays using conventional synthetic-aperture beamforming.  

PubMed

Several dual-mode ultrasound array (DMUA) systems are being investigated for potential use in image- guided surgery. In therapeutic mode, DMUAs generate pulsed or continuous-wave (CW) high-intensity focused ultrasound (HIFU) beams capable of generating localized therapeutic effects within the focal volume. In imaging mode, pulse-echo data can be collected from the DMUA elements to obtain B-mode images or other forms of feedback on the state of the target tissue before, during, and after the application of the therapeutic HIFU beam. Therapeutic and technological constraints give rise to special characteristics of therapeutic arrays. Specifically, DMUAs have concave apertures with low f-number values and are typically coarsely sampled using directive elements. These characteristics necessitate pre- and post-beamforming signal processing of echo data to improve the spatial and contrast resolution and maximize the image uniformity within the imaging field of view (IxFOV). We have recently developed and experimentally validated beamforming algorithms for concave large-aperture DMUAs with directive elements. Experimental validation was performed using a 1 MHz, 64-element, concave spherical aperture with 100 mm radius of curvature. The aperture was sampled in the lateral direction using elongated elements 1-lambda x 33.3-lambda with 1.333-lambda center-to-center spacing (lambda is the wavelength). This resulted in f-number values of 0.8 and 2 in the azimuth and elevation directions, respectively. In this paper, we present a new DMUA design approach based on different sampling of the shared concave aperture to improve image quality while maintaining therapeutic performance. A pulse-wave (PW) simulation model using a modified version of the Field II program is used in this study. The model is used in generating pulse-echo data for synthetic-aperture (SA) beamforming for forming images of a variety of targets, e.g., wire arrays and speckle-generating cyst phantoms. To provide validation for the simulation model and illustrate the improvements in image quality, we show SA images of similar targets using pulse-echo data acquired experimentally using our existing 64-element prototype. The PW simulation model is used to investigate the effect of transducer bandwidth as well as finer sampling of the concave DMUA aperture on the image quality. The results show that modest increases in the sampling density and transducer bandwidth result in significant improvement in spatial and contrast resolutions in addition to extending the DMUA IxFOV. PMID:18986915

Wan, Yayun; Ebbini, Emad S

2008-08-01

353

A real aperture radar for low resolution mapping at low costs  

Microsoft Academic Search

This paper briefly describes the results obtained in the course of the trade-off analysis activity of low cost scatterometers based on real aperture measurement. This has been carried out at Alenia Aerospazio-Space Division in the frame of internal research activities and of the European Space Agency (ESA) “Modest Resolution Radar for Radar\\/Radiometer Applications” contract. The idea of low resolution radar

F. Impagnatiello; G. Angino; G. Leggeri

1997-01-01

354

Passive synthetic aperture processing as a Kalman filter problem  

SciTech Connect

Passive synthetic aperture processing of a towed array is basically the coherent processing of the array data over a given length of time which, based on the speed of tow, translates into an equivalent increase in aperture length, and therefore a concomitant increase in spatial gain. The Kalman filter formalism is particularly suited to this task for four reasons. First, it coherently updates the measurements based on a comparison of their predicted values, based on a signal model, and subsequent measurements taken at a later time, in a recursive manner. Second, it allows in principle any signal model, i.e., not simply plane waves. Third, it generates a minimum variance estimate not only on the desired bearings, but any desired (observable) model parameters. Finally, it avoids the explicit construct of a beamformer, thus permitting the precision of the estimates to have no lower limit (such as the spatial bin size of a beamformer) other than the minimum variance obtainable under the given signal to noise conditions. Samples of multiple bearing estimations based on synthetic data will be shown. Also, a general formalism will be presented that allows direct estimation and update of certain signal model parameters.

Sullivan, E.J. (Naval Undersea Warfare Ctr., Newport, RI 02841 (United States)); Candy, J.V. (Lawrence Livermore Natl. Lab., Univ. of California, Livermore, CA 94550 (United States))

1994-05-01

355

See Through the Static: 3D Synthetic Aperture PIV  

NASA Astrophysics Data System (ADS)

A new method for resolving three-dimensional (3D) fluid velocity fields using a technique called synthetic aperture particle image velocimetry (PIV) is presented. The method makes use of the lightfield imaging and synthetic aperture refocusing techniques that are emerging in the imaging community. Images are captured using an array of cameras positioned on one plane such that the fields of view of the cameras overlap and images can be easily recombined in software using a warp-shift-average algorithm to digitally refocus on different planes. The result is sharply focused particles in the plane of interest, whereas particles out-of-plane appear blurred. The 3D intensity field of particle-laden flows can be reconstructed by refocusing throughout the entire volume and filtering out the blurred particles. 3DPIV techniques can then be applied to these intensity fields to extract velocity data. This technique shows the potential of enabling larger volumes to be resolved with more particles, yielding higher spatial resolution than existing methods. A simulated vortex ring flow field demonstrates the capability of the technique for resolving vector fields in 3D.

Belden, Jesse; Truscott, Tadd T.; Techet, Alexandra H.

2009-11-01

356

Phase error correction for synthetic-aperture phased-array imaging systems  

NASA Astrophysics Data System (ADS)

If one replaces the ordinary single receiver of a synthetic- aperture radar (SAR) with a linear array of receivers underneath the wings of an aircraft, one obtains a 3D signal history (to spatial dimensions plus the frequency dimension) that allows the computation of a 3D image (angle-angle- range) of a scene. Because of the limited extent of the wingspan, the cross-track resolution is limited, driving one to use high frequencies, such as 94 GHz, having a wavelength of 3.2 mm. At such short wavelengths, the motion of the wings during the synthetic-aperture integration time will cause large phase errors that will severely blur the image. This paper describes an approach to measuring and correcting these and other phase errors. The approach involves having three transmitters, each at a slightly different monotone frequency. Relative to the first receiver, the second is displaced along the direction of the array of receivers and the third is displaced perpendicular to that direction. The array of receivers can separate the three corresponding signals reflected form the ground from one another. We will show mathematical analysis that allows us to determine the phase errors at each receiver form these three signals. It is required either that the three transmitters experience the same phase errors (so they should be rigidly mounted together) or that the phase errors at the three transmitters are measured. No measurement of phase errors on the receivers is required.

Fienup, James R.

2000-11-01

357

High-speed synthetic aperture microscopy for live cell imaging  

PubMed Central

We present a high-speed synthetic aperture microscopy for quantitative phase imaging of live biological cells. We measure 361 complex amplitude images of an object with various directions of illumination covering an NA of 0.8 in less than one-thirteenth of a second and then combine the images with a phase-referencing method to create a synthesized phase image. Because of the increased depth selectivity, artifacts from diffraction that are typically present in coherent imaging are significantly suppressed, and lateral resolution of phase imaging is improved. We use the instrument to demonstrate high-quality phase imaging of live cells, both static and dynamic, and thickness measurements of a nanoscale cholesterol helical ribbon.

Kim, Moonseok; Choi, Youngwoon; Fang-Yen, Christopher; Sung, Yongjin; Dasari, Ramachandra R.; Feld, Michael S.; Choi, Wonshik

2011-01-01

358

A Cascade Algorithm for Estimating and Compensating Motion Error for Synthetic Aperture Sonar Imaging  

Microsoft Academic Search

This paper presents a three-level cascade algorithm for estimating and compensating platform motion errors during synthetic aperture sonar imaging. By using a multiple element receiving array, physical aperture images can be produced from each transmit burst. With proper spatial sampling, there is sufficient redundancy in successive physical aperture images to extract motion parameters that can be applied to the image

John M. Silkaitis; Brett L. Douglas; Hua Lee

1994-01-01

359

Real-time synthetic aperture sonar imaging using a parallel architecture  

Microsoft Academic Search

This paper describes a parallel architecture that has been developed to perform real-time synthetic aperture sonar imaging as part of the Acoustical Imaging Development (ACID) project. The project has successfully developed a synthetic aperture sonar system for producing high resolution images of the sea floor and that has been tested during a series of sea trials in May 1993 off

Vijay Singh Riyait; Michael Andrew Lawlor; Alan E. Adams; Oliver R. Hinton; Bayan S. Sharif

1995-01-01

360

Synthetic-aperture sonar imaging: system analysis, image formation, and motion compensation  

Microsoft Academic Search

This paper presents an overview of various components of the development and implementation of synthetic aperture sonar systems for high-resolution underwater imaging: including data acquisition systems, physical aperture image formation, and motion estimation and compensation for synthetic-aperture image formation. The description of the data acquisition systems includes multiple element arrays, insonification waveforms, formation of illumination beam patterns, and array-element calibration

John M. Silkaitis; Bretton L. Douglas; Hua Lee

1995-01-01

361

High-resolution imaging with a real-time synthetic aperture ultrasound system: a phantom study  

NASA Astrophysics Data System (ADS)

It is difficult for ultrasound to image small targets such as breast microcalcifications. Synthetic aperture ultrasound imaging has recently developed as a promising tool to improve the capabilities of medical ultrasound. We use two different tissueequivalent phantoms to study the imaging capabilities of a real-time synthetic aperture ultrasound system for imaging small targets. The InnerVision ultrasound system DAS009 is an investigational system for real-time synthetic aperture ultrasound imaging. We use the system to image the two phantoms, and compare the images with those obtained from clinical scanners Acuson Sequoia 512 and Siemens S2000. Our results show that synthetic aperture ultrasound imaging produces images with higher resolution and less image artifacts than Acuson Sequoia 512 and Siemens S2000. In addition, we study the effects of sound speed on synthetic aperture ultrasound imaging and demonstrate that an accurate sound speed is very important for imaging small targets.

Huang, Lianjie; Labyed, Yassin; Simonetti, Francesco; Williamson, Michael; Rosenberg, Robert; Heintz, Philip; Sandoval, Daniel

2011-03-01

362

Application of a matched filter approach for finite aperture transducers for the synthetic aperture imaging of defects  

Microsoft Academic Search

The suitability of the synthetic aperture imaging of defects using a matched filter approach on finite aperture transducers was investigated. The first part of the study involved the use a finite-difference time-domain (FDTD) algorithm to simulate the phased array ultrasonic wave propagation in an aluminum block and its interaction with side-drilled hole-like defects. B-scans were generated using the FDTD method

L. Satyanarayan; Ajith Muralidharan; Chittivenkata Krishnamurthy; Krishnan Balasubramaniam

2010-01-01

363

Improved terahertz imaging with a sparse synthetic aperture array  

NASA Astrophysics Data System (ADS)

Sparse arrays are highly attractive for implementing two-dimensional arrays, but come at the cost of degraded image quality. We demonstrate significantly improved performance by exploiting the coherent ultrawideband nature of singlecycle THz pulses. We compute two weighting factors to each time-delayed signal before final summation to form the reconstructed image. The first factor employs cross-correlation analysis to measure the degree of walk-off between timedelayed signals of neighboring elements. The second factor measures the spatial coherence of the time-delayed delayed signals. Synthetic aperture imaging experiments are performed with a THz time-domain system employing a mechanically scanned single transceiver element. Cross-sectional imaging of wire targets is performed with a onedimensional sparse array with an inter-element spacing of 1.36 mm (over four ? at 1 THz). The proposed image reconstruction technique improves image contrast by 15 dB, which is impressive considering the relatively few elements in the array. En-face imaging of a razor blade is also demonstrated with a 56 x 56 element two-dimensional array, showing reduced image artifacts with adaptive reconstruction. These encouraging results suggest that the proposed image reconstruction technique can be highly beneficial to the development of large area two-dimensional THz arrays.

Zhang, Zhuopeng; Buma, Takashi

2010-02-01

364

Analysis of vibration influence on Synthetic Aperture Lidar imaging  

NASA Astrophysics Data System (ADS)

Based on the theory of the coherent detection of laser, a signal model of Synthetic Aperture Lidar is set up. As the wavelength of laser light from the SAL is shorter than that of microwave from the SAR about several times, considering the parts of Taylor Series must be enough, compute and analysis the influence of vibration error on the phase of SAL echo signal. In order to validate the signal model and the theory computation, numerical simulation on a strip-mode is carried out. On the reference of the national military standard for environment, in the condition of the frequency below 500MHz, simulate and show the influence of the vibration parameters such as amplitude, frequency or initial phase on the SAL imaging, and the image with the vibration of ideal point target is given. The simulation results show that the influence of vibration on the azimuth resolution is severity, but that on the range resolution is trivial, this is by the reason of the period of vibration is different from the period of laser pulse, and in one laser pulse period, the vibration is considered immovability, therefore the influence on the range compress is nonentity, and the range resolution is steady. In addition, simulate the condition of the same amplitude and frequency but different initial phase, find that the influence of different initial phase on SAL imaging is different and serious, as the initial phase is stochastic, the influence of vibration on SAL imaging is erratically.

Lv, Xu-Guang; Hao, Shi-Qi; Leng, Jiao-Feng

2011-11-01

365

Space-based moving target positioning using radar with a switched aperture antenna  

Microsoft Academic Search

Ground moving target indication (GMTI) by space based radar can effectively only be performed with a multi- aperture \\/ multi-channel system or a satellite cluster [1]. To keep weight, power consumption, data rate and costs low, the technique of switching subapertures from pulse to pulse has been proposed. While the detection performance using STAP (space-time adaptive processing) has been analysed

Joachim H. G. Ender; Christoph H. Gierull; Delphine Cerutti-Maori

2007-01-01

366

On radar polarimetry in FM-CW radar  

Microsoft Academic Search

This paper attempts to apply the principle of radar polarimetry to wideband synthetic aperture FM-CW radar and presents a basic polarimetric detection result of a linear target in a laboratory measurement. Although the principle of radar polarimetry has well been established for the completely polarized wave and for the monostatic case, it still needs to be extended to wideband radar

Y. Yamaguchi; T. Nishikawa; W.-M. Boerner; M. Sengoku; Hyo Joon Eom

1993-01-01

367

Low cost realization of space-borne synthectic aperture radar - MicroSAR  

NASA Astrophysics Data System (ADS)

Spaceborne Earth Observation data has been used for decades in the areas of meteorology and optical imaging. The systems and satellites have, in the main, been owned and operated by a few government institutions and agencies. More recently industrial organizations in North America have joined the list. Few of these, however, include Synthetic Aperture Radar (SAR)., although the additional utility in terms of all weather, 24 hour measurement capability over the Earth's surface is well recognized. Three major factors explain this:1) Relationships between the SAR measurements of radar backscatter and images to the specific information needs have not been seen as sufficiently well understood or robust2) Availability of suitable sources, at the relevant performance and data quality have been inadequate to provide service assurance that is necessary to sustain commercial businesses3) Costs associated with building, launching and operating spaceborne SAR have not been low enough as to achieve an acceptable return of investment. A significant amount of research and development has been undertaken throughout the World to establish reliable and robust algorithms for information extraction from SAR data. Much of this work has been carried out utilizing airborne systems over localized and carefully controlled regions. In addition, an increasing number of pilot services have been offered by geo-information providers. This has allowed customer confidence to grow. With the status of spaceborne SAR being effectively in the development phase, commercial funding has been scarce, and there has been need to rely on government and institutional budgets. Today the increasing maturity of the technology of SAR and its applications is beginning to attract the commercial sector. This is the funding necessary to realize sufficient assets to be able to provide a robust supply of SAR data to the geo-information providers and subsequently a reliable service to customers. Reducing the costs associated with implementing spaceborne SAR systems is an aspect of work that has been addressed over the past decade by the main S RA system expert companies. As the experimental systems have been realized and understood, so there has been a move to transfer these systems from the research and scientific domains into operational and commercial implementations. The end of the cold war, combined with the ever increasingly competitive telecommunications market, have assisted in driving down the launch costs, a significant cost element in any space system budget. To take maximum benefit from this it is still necessary to be able to make light weight satellites, in the region of 450 Kgs or less. Typically SAR satellites have been in the neighbourhood of 1.5 to 2.5 Tonnes. In order to achieve the low cost systems, not only the satellite mass needs to be tackled but also several other factors:- Design complexity- Production costs- Performance- Calibration and verification A novel approach has been established to address all of these factors. Developments are already in progress to prove the approach and that the low costs are achievable. This is called MicroSAR. This paper starts with an overview of the market status. A description of the MicroSAR system, its developments, calibration philosophy, trade-offs carried out, its performance envelope and an outline of the steps taken to achieve a low cost Synthetic Aperture Radar system are then presented.

Carter, D.; Hall, C.

368

Synthetic interferometer radar for topographic mapping  

Microsoft Academic Search

The production of topographic maps requires two kinds of information. First, the detail to be placed on the map sheet must be identified. Second, the positions of the various objects and features must be measured in three dimensions. Current airborne radar technology provides the means to satisfy both of these requirements in adverse weather and at any time, day or

L. C. Graham

1974-01-01

369

Quantitative phase microscopy and synthetic aperture tomography of live cells  

NASA Astrophysics Data System (ADS)

For more than a decade MIT's George R. Harrison Spectroscopy Laboratory has been developing quantitative phase microscopy (QPM) for biological study. Measurements of a point field were made in the mid 90s, then extended to the full 2D field, and recently, to 3D by using tomography. In the first part of this thesis improvements in the techniques of Fourier Phase Microscopy (FPM) and Hilbert Phase Microscopy (HPM) and their applications to characterize cells and tissues are reported. Tomographic phase microscopy (TPM) provides quantitative information and highly detailed structural information about a live cell, but in its current form it can only examine one cell at a time. Many biological applications including statistical analysis of a large collection of cells such as flow cytometry need a tomography technique that can measure many cells at a time. For the second part of this thesis we have developed a new tomography technique that can measure many cells continuously. In this study we demonstrate the new technique by translating a live cell across a focused beam. This beam is composed of many angular plane waves, and by applying a so-called synthetic aperture algorithm we retrieve individual wave components of the focused beam. We demonstrate for the first time that we can retrieve the field of the focused beam and synthesize any arbitrary angular plane wave. We then construct a 3D map of the variations of the refractive index in a live cell from a series of these synthesized angular plane waves. This new technique is the first step needed to analyze cells flowing through a beam to provide a high-throughput 3D refractive index tomograms that can be used as a new kind of statistical optical assay of living cells.

Lue, Niyom

370

Temporal domain processing for a synthetic aperture array  

Microsoft Academic Search

A method for the synthesis of an aperture with improved bearing resolution and signal gain is described. The proposed method temporally synthesizes data from an overlap correlator, which is obtained by aperture domain averaging of phase differences. Previous studies, such as extended towed array measurements (ETAM), had a restriction in that the overlapped hydrophones between successive measurements of a towed

Seungil Kim; Dae Hee Youn; Chungyong Lee

2002-01-01

371

Synthetic aperture technique applied to a multi-beam echo sounder  

Microsoft Academic Search

We are developing a synthetic aperture technique using a Sea Beam 2000 multi-beam echo sounder to observe subsea crustal movements for earthquake studies. Augmented by the Kinematic GPS and a motion sensor, the synthetic aperture technique was successfully applied to the Sea Beam 2000 with a 12 kHz frequency acoustic signal. The 4.3-meter long projector produces a transmission fan beam

Akira Asada; Tetsuichiro Yabuki

2001-01-01

372

Ice Ridge Observations by Means of SAR (Synthetic Aperture Radar).  

National Technical Information Service (NTIS)

A SAR-model for a sea ice ridge is suggested and conclusions drawn, for example with regard to look angle and incidence angle dependence. Although ice ridges show up most clearly at large angles of incidence it is suggested that important information abou...

J. Askne R. Johansson

1988-01-01

373

Signal processing of FMCW Synthetic Aperture Radar data  

Microsoft Academic Search

In the field of airborne earth observation there is special attention to compact, cost effective, high resolution imaging sensors. Such sensors are foreseen to play an important role in small-scale remote sensing applications, such as the monitoring of dikes, watercourses, or highways. Furthermore, such sensors are of military interest; reconnaissance tasks could be performed with small unmanned aerial vehicles (UAVs),

A. Meta

2006-01-01

374

Magellan ephemeris improvement using synthetic aperture radar landmark measurements  

Microsoft Academic Search

A technique is described for measuring the positions of landmarks in multiple SAR images of the surface of Venus taken aboard the Magellan spacecraft. These measurements are then used to improve the spacecraft orbit estimate. The Venus-fixed coordinates of the landmarks are also estimated, as are the low-order coefficients of the gravitational field. Sample results are shown for five-orbit and

Paul W. Chodas; Tseng-Chan Wang; William L. Sjogren; John E. Ekelund

1992-01-01

375

Three-dimensional subsurface imaging synthetic aperture radar  

SciTech Connect

Inadequate resources, aggravated by the limited capabilities of existing site characterization technologies, require that new systems be developed to effectively aid site cleanup. The quantity, condition, and the precise location of buried waste storage containers is often unknown, and is always difficult to assess. Significant safety hazards may also be present at these sites. Therefore, new non-invasive detection techniques are needed that will be cost effective, user friendly, and have a growth path toward a system capable of accessing remote terrain. These detection methods must be economical to use and be capable of exploring large land areas quickly with minimal personnel risk. They should provide the precision for identifying the size, depth, type, and possibly the condition of the waste containers.

Wuenschel, E.

1995-12-31

376

Wind vector retrieval using ERS-1 synthetic aperture radar imagery  

Microsoft Academic Search

An automated algorithm intended for operational use is developed and tested for estimating wind speed and direction using ERS-1 SAR imagery. The wind direction comes from the orientation of low frequency, linear signatures in the SAR imagery that the authors believe are manifestations of roll vortices within the planetary boundary layer. The wind direction thus has inherently a 180° ambiguity

Christopher C. Wackerman; Clifford L. Rufenach; Robert A. Shuchman; Johnny A. Johannessen; Kenneth L. Davidson

1996-01-01

377

Quantitative statistical assessment of conditional models for synthetic aperture radar  

Microsoft Academic Search

Many applications of object recognition in the presence of pose uncertainty rely on statistical models-conditioned on pose-for observations. The image statistics of three-dimensional (3-D) objects are often assumed to belong to a family of distributions with unknown model parameters that vary with one or more continuous-valued pose parameters. Many methods for statistical model assessment, for example the tests of Kolmogorov-Smirnov

Michael D. Devore; Joseph A. O'sullivan

2004-01-01

378

Target classification using SAR (Synthetic Aperture Radar) polarimetric data  

Microsoft Academic Search

The polarimetric behavior of canonicals within single resolution cells is investigated. The aim of this investigation is to ascertain whether the contents of a resolution cell can be determined by examination of the polarimetric data. The canonicals addressed are the dihedral and the flatplate, although the associated theory and software is readily applicable to other primitives. The main software package

Alan P. Callaghan

1989-01-01

379

Synthetic aperture radar automatic target recognition using adaptive boosting  

NASA Astrophysics Data System (ADS)

We propose a novel automatic target recognition (ATR) system for classification of three types of ground vehicles in the MSTAR public release database. First, each image chip is pre-processed by extracting fine and raw feature sets, where raw features compensate for the target pose estimation error that corrupts fine image features. Then, the chips are classified by using the adaptive boosting (AdaBoost) algorithm with the radial basis function (RBF) net as the base learner. Since the RBF net is a binary classifier, we decompose our multiclass problem into a set of binary ones through the error-correcting output codes (ECOC) method, specifying a dictionary of code words for the set of three possible classes. AdaBoost combines the classification results of the RBF net for each binary problem into a code word, which is then "decoded" as one of the code words (i.e., ground-vehicle classes) in the specified dictionary. Along with classification, within the AdaBoost framework, we also conduct efficient fusion of the fine and raw image-feature vectors. The results of large-scale experiments demonstrate that our ATR scheme outperforms the state-of-the-art systems reported in the literature.

Sun, Yijun; Liu, Zhipeng; Todorovic, Sinisa; Li, Jian

2005-05-01

380

Multistatic synthetic aperture imaging of aircraft using reflected television signals  

NASA Astrophysics Data System (ADS)

We investigate passive radar imaging of aircraft using reflected TV signals. Such passive multistatic ``radar'' has been developed to detect and track aircraft with good accuracy. The additional capability of image formation would help to identify targets. The Fourier space sampling provided by passive radar is nonuniform. For a given aircraft flight path, different receiver locations give rise to different sampling patterns. We simulate multistatic radar returns using Fast Illinois Solver Code (FISC) and show that a good sampling pattern can be used to form a recognizable target image using direct Fourier reconstruction. However, a bad sampling pattern can make it impossible to form a useful image. In the Gaithersburg, MD area, we can select a good receiver location using 21 or fewer channels, which provides good enough Fourier-space coverage to form a useful aircraft image.

Wu, Yong; Munson, David C.

2001-08-01

381

Synthetic aperture technique applied to a multi-beam echo sounder  

NASA Astrophysics Data System (ADS)

We are developing a synthetic aperture technique using a Sea Beam 2000 multi-beam echo sounder to observe subsea crustal movements for earthquake studies. Augmented by the Kinematic GPS and a motion sensor, the synthetic aperture technique was successfully applied to the Sea Beam 2000 with a 12 kHz frequency acoustic signal. The 4.3-meter long projector produces a transmission fan beam in alongtrack beamwidth of 2 degrees, but a synthesis of the data achieved about 37 m aperture length, equivalent to a 0.3 degrees alongtrack beamwidth. Bathymetry measurements at the water depth of 900 m obtained through the synthetic aperture processing show considerable improvement of the signal-to-noise ratio and reveal detailed features of the seafloor.

Asada, A.; Yabuki, T.

2001-04-01

382

Application of a matched filter approach for finite aperture transducers for the synthetic aperture imaging of defects.  

PubMed

The suitability of the synthetic aperture imaging of defects using a matched filter approach on finite aperture transducers was investigated. The first part of the study involved the use a finite-difference time-domain (FDTD) algorithm to simulate the phased array ultrasonic wave propagation in an aluminum block and its interaction with side-drilled hole-like defects. B-scans were generated using the FDTD method for three active aperture transducer configurations of the phased array (a) single element and (b) 16-element linear scan mode, and (c) 16-element steering mode. A matched filter algorithm (MFA) was developed using the delay laws and the spatial impulse response of a finite size rectangular phased array transducer. The conventional synthetic aperture focusing technique (SAFT) algorithm and the MFA were independently applied on the FDTD signals simulated with the probe operating at a center frequency of 5 MHz and the processed B-scans were compared. The second part of the study investigated the capability of the MFA approach to improve the SNR. Gaussian white noise was added to the FDTD generated defect signals. The noisy B-scans were then processed using the SAFT and the MFA and the improvements in the SNR were estimated. The third part of the study investigated the application of the MFA to image and size surface-crack-like defects in pipe specimens obtained using a 45 degrees steered beam from a phased array probe. These studies confirm that MFA is an alternative to SAFT with little additional computational burden. It can also be applied blindly, like SAFT, to effect synthetic focusing with distinct advantages in treating finite transducer effects, and in handling steered beam inspections. Finally, limitations of the MFA in dealing with larger-sized transducers are discussed. PMID:20529712

Satyanarayan, L; Muralidharan, Ajith; Krishnamurthy, Chittivenkata; Balasubramaniam, Krishnan

2010-06-01

383

Improvement of synthetic aperture techniques by means of the coarray analysis  

NASA Astrophysics Data System (ADS)

In the field of ultrasonic imaging, the synthetic aperture techniques are well known due to their ability for obtain images using fewer resources. Initially, these techniques were developed to reduce the cost and complexity of phased array instrumentation. Although these drawbacks have already been overcome, the interest on the synthetic aperture systems has not decayed. The reasons of that are the high image quality achieved with these techniques (images dynamically focused both in emission and reception), and the fact that they are an excellent solution for the design of new high performance instrumentation with a low volume and power consumption, easily integrable in autonomous and embedded systems. Using the coarray as a model of the pulse-echo systems, the present work analyzes experimentally the main synthetic aperture strategies appeared until now, introducing two new proposals (2R-SAFT and nR-SAFT) that allow to improve the quality of the images without increase the hardware complexity of the system.

Martín-Arguedas, C. J.; Martínez-Graullera, O.; Romero-Laorden, D.; Pérez-López, M.; Gómez-Ullate, L.

2012-05-01

384

Unusual Radar Echoes from the Greenland Ice Sheet.  

National Technical Information Service (NTIS)

In June 1991, the NASA/Jet Propulsion Laboratory airborne synthetic-aperture radar (AIRSAR) instrument collected the first calibrated data set of multifrequency, polarimetric, radar observations of the Greenland ice sheet. At the time of the AIRSAR overfl...

E. J. Rignot J. J. Vanzyl S. J. Ostro K. C. Jezek

1993-01-01

385

The Venus Radar Mapper mission  

Microsoft Academic Search

The Venus Radar Mapper (VRM) mission is sponsored by NASA to put a single spacecraft in orbit around Venus to map the surface using a synthetic aperture mapping radar. This paper describes the VRM mission at its present state of design. The science objectives and project constraints are described. Key features of the spacecraft system and radar system are discussed.

E. Cutting; J. H. Kwok; S. N. Mohan

1984-01-01

386

A radar tour of Venus  

Microsoft Academic Search

The surface of Venus is briefly characterized in a summary of results obtained by the Soviet Venera 15 and 16 8-cm synthetic-aperture radars, IR radiometers, and radar altimeters. A series of radar images, mainly from Kotelnikov et al. (1984), are presented and discussed, and the descent vehicles to be released by the two Vega spacecraft as they pass Venus in

J. K. Beatty

1985-01-01

387

Large-scale temporal and spatial imaging of soil brightness temperature with an L-band synthetic aperture microwave radiometer  

Microsoft Academic Search

The Microwave Remote Sensing Lab (MIRSL) at the University of Massachusetts has developed a second-generation L-band synthetic aperture microwave radiometer referred to as the Electronically Steered Thinned Array Radiometer, or ESTAR, which measures soil moisture or ocean salinity from an airborne platform. This dissertation reviews the basics of synthetic aperture microwave radiometry, then details recent modifications to the ESTAR instrument,

John D. Isham

1999-01-01

388

Synthetic aperture sonar for seabed imaging: relative merits of narrow-band and wide-band approached  

Microsoft Academic Search

The advantages of using wideband sonar systems in underwater acoustical imaging by means of synthetic aperture (side-looking) sonars are described and illustrated through simulation examples. The simulations are conducted for two cases of sonar platform motion: perfect trajectory and disturbed trajectory. Several schemes used for wideband synthetic aperture processing are investigated and their relative merits (resolution and complexity) in the

Jacques Chatillon; Marie-Edith Bouhier; Manell E. Zakharia

1992-01-01

389

On the Reduction of the Reconstruction Bias in Synthetic Aperture Imaging Radiometry  

Microsoft Academic Search

Synthetic aperture imaging radiometers (SAIRs) are powerful instruments for high-resolution observation of planetary surfaces at low microwave frequencies. This paper is concerned with the reconstruction of radiometric brightness temperature maps from SAIR interferometric measurements. Even in the absence of modeling errors and radiometric noise, a systematic error, or bias, has been observed in the reconstructed maps. The origin of this

Eric Anterrieu

2007-01-01

390

On the Reduction of the Reconstruction Bias in Synthetic Aperture Imaging Radiometry (Corrected)?  

Microsoft Academic Search

Synthetic aperture imaging radiometers (SAIRs) are powerful instruments for high-resolution observation of planetary surfaces at low microwave frequencies. This paper is concerned with the reconstruction of radiometric brightness temperature maps from SAIR interferometric measurements. Even in the absence of modeling errors and radiometric noise, a systematic error, or bias, has been observed in the reconstructed maps. The origin of this

Eric Anterrieu

2007-01-01

391

A new system for real-time synthetic aperture ultrasonic imaging  

Microsoft Academic Search

The authors devised a way to generate in real time a cross-sectional image of an object with uniformly high resolution based on the synthetic aperture focusing technique (SAFT). A computer simulation was conducted to study the effects of essential parameters on the resulting images. An imaging system was built that produces a cross-sectional image composed of an assembly of line

Yoshihiko Ozaki; Hiroaki Sumitani; Toshimasa Tomoda; Mitsuo Tanaka

1988-01-01

392

Complex spectral Fourier-domain imaging method for Synthetic Aperture Microwave Radiometer  

Microsoft Academic Search

Conventional microwave radiometer belongs to spatial-domain imaging system to detect area thermal source and it acquires radiometric signal from the object source point and point. Synthetic Aperture Microwave Radiometer belongs to staring imaging system. It applies Fourier-domain technique to obtain source's microwave spectrum called visibility and thus make scanning process not necessary. This novel imaging method can save much consuming

Qiong Wu; Ji Wu

2010-01-01

393

Relative Height Estimation by Cross-Correlating Ground-Range Synthetic Aperture Sonar Images  

Microsoft Academic Search

The relative height of the seafloor can be estimated by using two vertically displaced receivers. In this paper, we propose techniques to improve the accuracy of the estimated height. Our results are based on the use of synthetic aperture sonar (SAS) imaging, which implies coherent addition of complex images acquired from a moving platform. The SAS processing improves the along-track

T. O. Saebo; Roy Edgar Hansen; Alfred Hanssen

2007-01-01

394

Statistical autofocus of synthetic aperture sonar images using image contrast optimisation  

Microsoft Academic Search

We present results of a technique for autofocus of stripmap synthetic aperture sonar (SAS) imagery. The technique of contrast optimisation is posed in a general Bayesian framework. The algorithm uses standard optimisation techniques on towfish motion parameters to minimise a cost function. The cost function consists of an image contrast measure, approximating the image likelihood, and a path likelihood measure,

S. A. Fortune; M. P. Hayes; P. T. Gough

2001-01-01

395

Scalar image processing filters for speckle reduction on synthetic aperture sonar images  

Microsoft Academic Search

High resolution images provided by synthetic aperture sonar (SAS) sensors are of great interest, especially for the detection, location and classification of mines lying on the sea bed. But these data obtained by an active imagery system are highly corrupted by a noise called the speckle. To reduce this noise and suppress the spurious reflections it generates on the images,

Jocelyn Chanussot; F. Maussang; A. Hetet

2002-01-01

396

Active Sonar Beacons to aid Synthetic Aperture Sonar Autofocussing: Beacon-Controller Design and Performance  

Microsoft Academic Search

This paper presents the design and performance of a microprocessor based beacon- controller. It has been developed as part of a new method to determine the path of a free-towed Synthetic Aperture Sonar (SAS) by autofocussing images of active bea- cons. The beacons are deployed on the seabed in the target area to listen for and transmit acoustic signals. The

E N Pilbrow; M P Hayes

397

Three-dimensional differential interference contrast microscopy using synthetic aperture imaging  

PubMed Central

Abstract. We implement differential interference contrast (DIC) microscopy using high-speed synthetic aperture imaging that expands the passband of coherent imaging by a factor of 2.2. For an aperture synthesized coherent image, we apply for the numerical post-processing and obtain a high-contrast DIC image for arbitrary shearing direction and bias retardation. In addition, we obtain images at different depths without a scanning objective lens by numerically propagating the acquired coherent images. Our method achieves high-resolution and high-contrast 3-D DIC imaging of live biological cells. The proposed method will be useful for monitoring 3-D dynamics of intracellular particles.

Kim, Moonseok; Choi, Youngwoon; Fang-Yen, Christopher; Sung, Yongjin; Kim, Kwanhyung; Dasari, Ramachandra R.; Feld, Michael S.; Choi, Wonshik

2012-01-01

398

Performance analysis of the weighted window CFAR algorithms [radar signal processing  

Microsoft Academic Search

With the deterioration of radar operation environment and the enhancement of menace to radar, the task of radar target detection becomes more complicated. Such as the detection of airplane, ship or cruise missile in over the horizon radar (OTHR), and the detection of moving targets in synthetic aperture radar (SAR). Therefore, it is necessary to make a further study of

Meng Xiangwei; Guan Jian; He You

2003-01-01

399

An automatic method for assembling a large synthetic aperture digital hologram.  

PubMed

A major issue so far for digital holography is the low spatial resolution generally achieved. The numerical aperture is limited by the area of currently available detectors, such as CCD sensors, which is significantly lower than that of a holographic plate. This is an even more severe constraint when IR sensors such as microbolometers are taken into account. In order to increase the numerical aperture of such systems, we developed an automatic technique which is capable of recording several holograms and of stitching them together, obtaining a digital hologram with a synthetic but larger numerical aperture. In this way we show that more detail can be resolved and a wider parallax angle can be achieved. The method is demonstrated for visible as well IR digital holography, recording and displaying large size objects. PMID:22418289

Pelagotti, A; Paturzo, M; Locatelli, M; Geltrude, A; Meucci, R; Finizio, A; Ferraro, P

2012-02-27

400

A synthetic aperture imaging ladar demonstrator with Ø300mm antenna and changeable footprint  

NASA Astrophysics Data System (ADS)

A demonstrator of synthetic aperture imaging ladar (SAIL) is constructed with the maximum aperture Ø300mm of antenna telescope. This demonstrator can be set with a rectangular aperture to produce a rectangular footprint suitable for scanning format with a high resolution and a wide strip. Particularly, the demonstrator is designed not only for the farfield application but also for the verifying and testing in the near-field in the laboratory space. And a 90 degree optical hybrid is used to mitigate the external phase errors caused by turbulence and vibration along line of sight direction and the internal phase errors caused by local fiber delay line. This paper gives the details of the systematic design, and the progresses of the experiment at a target distance around 130m.

Zhou, Yu; Zhi, Yanan; Yan, Aimin; Xu, Nan; Wang, Lijuan; Wu, Yapeng; Luan, Zhu; Sun, Jianfeng; Liu, Liren

2010-08-01

401

Optical imaging process based on two-dimensional Fourier transform for synthetic aperture imaging ladar  

NASA Astrophysics Data System (ADS)

The synthetic aperture imaging ladar (SAIL) systems typically generate large amounts of data difficult to compress with digital method. This paper presents an optical SAIL processor based on compensation of quadratic phase of echo in azimuth direction and two dimensional Fourier transform. The optical processor mainly consists of one phase-only liquid crystal spatial modulator(LCSLM) to load the phase data of target echo and one cylindrical lens to compensate the quadratic phase and one spherical lens to fulfill the task of two dimensional Fourier transform. We show the imaging processing result of practical target echo obtained by a synthetic aperture imaging ladar demonstrator. The optical processor is compact and lightweight and could provide inherent parallel and the speed-of-light computing capability, it has a promising application future especially in onboard and satellite borne SAIL systems.

Sun, Zhiwei; Zhi, Ya'nan; Liu, Liren; Sun, Jianfeng; Zhou, Yu; Hou, Peipei

2013-09-01

402

The optical synthetic aperture image restoration based on the improved maximum-likelihood algorithm  

NASA Astrophysics Data System (ADS)

Optical synthetic aperture imaging (OSAI) can be envisaged in the future for improving the image resolution from high altitude orbits. Several future projects are based on optical synthetic aperture for science or earth observation. Comparing with equivalent monolithic telescopes, however, the partly filled aperture of OSAI induces the attenuation of the modulation transfer function of the system. Consequently, images acquired by OSAI instrument have to be post-processed to restore ones equivalent in resolution to that of a single filled aperture. The maximum-likelihood (ML) algorithm proposed by Benvenuto performed better than traditional Wiener filter did, but it didn't work stably and the point spread function (PSF), was assumed to be known and unchanged in iterative restoration. In fact, the PSF is unknown in most cases, and its estimation was expected to be updated alternatively in optimization. Facing these limitations of this method, an improved ML (IML) reconstruction algorithm was proposed in this paper, which incorporated PSF estimation by means of parameter identification into ML, and updated the PSF successively during iteration. Accordingly, the IML algorithm converged stably and reached better results. Experiment results showed that the proposed algorithm performed much better than ML did in peak signal to noise ratio, mean square error and the average contrast evaluation indexes.

Geng, Zexun; Xu, Qing; Zhang, Baoming; Gong, Zhihui

2012-09-01

403

The design and development of a geostationary synthetic thinned aperture radiometer  

Microsoft Academic Search

The Precipitation and All-Weather Temperature and Humidity (PATH) mission outlined in the National Research Council decadal survey for launch in 2016--2020 recommends a microwave array spectrometer as the instrument payload. A design for the Geostationary Synthetic Thinned Aperture Radiometer (GeoSTAR) is presented that fulfils all but one of the mission requirements---integration time---and options are available to meet this requirement. A

Boon Hwang Lim

2009-01-01

404

Implementation of adaptive and synthetic-aperture processing schemes in integrated active-passive sonar systems  

Microsoft Academic Search

Progress in the implementation of state-of-the-art signal processing schemes in sonar systems is limited mainly by the moderate advance made in sonar computing architectures and the lack of operational evaluation of the advanced processing schemes. Until recently, matrix-based processing techniques, such as adaptive and synthetic-aperture processing, could not be efficiently implemented in the current type of sonar systems, even though

STERGIOS STERGIOPOULOS

1998-01-01

405

Calculation of the spatial resolution of a synthetic aperture microwave radiometer  

Microsoft Academic Search

The synthetic aperture microwave radiometer (SAMR) has been proved to be an interesting system for the remote sensing of the\\u000a earth from space with a high spatial resolution. This paper presents the formulas for computing the spatial resolution of\\u000a the SAMR. Some practical examples are also presented, and it is proved that the spatial resolution becomes more inferior with\\u000a the

Lu Jun; Zhang Zuyin

1995-01-01

406

Perspectives on Worldwide Spaceborne Radar Programs  

Microsoft Academic Search

Radar technology and techniques were originally developed for land-based, maritime, and airborne applications. Spaceborne radar systems development began in the 1960s in the USSR for military purposes, and in the 1970s in the United States for civilian scientific purposes. NASA launched the SeaSAT satellite in 1978, carrying a synthetic aperture radar, a radar altimeter, a radar scatterometer, and a radiometer,

P. A. Rosen; G. M. Buccolo

2007-01-01

407

The evolution of the SEASAT imaging radar  

Microsoft Academic Search

The paper describes the design parameters and development of a synthetic aperture radar for use on the SEASAT spacecraft. This imaging radar is designed to operate at altitudes of 800 km with an orbital inclination of 108 deg, a nominal resolution of 25 m, and a swath width of 100 km. The design evolved from planetary imaging radar studies conducted

W. E. Brown Jr.

1975-01-01

408

Region-Enhanced Passive Radar Imaging  

Microsoft Academic Search

Abstract We adapt and apply a recently-developed region-enhanced synthetic aperture radar (SAR) image reconstruction technique to the problem of passive radar imaging. One goal in passive radar imaging is to form images of aircraft using signals transmitted by commercial radio and television stations that are reflected from the objects of interest. This involves reconstructing an image from sparse samples of

Mujdat Cetin; Aaron D. Lanterman

2004-01-01

409

Assessment of radial image distortion and spherical aberration on 3D synthetic aperture PIV measurements  

NASA Astrophysics Data System (ADS)

This paper presents a study of the effects of radial image distortion and spherical aberration on reconstruction quality of synthetic aperture particle image velocimetry (SAPIV). A simulated SAPIV system is used to image a synthetic particle volume. An idealized pinhole camera model is used for image formation with distortion and spherical aberration being added on with a polynomial model and a Fourier waveform model, respectively. Images from a simulated 5 × 5 camera array are taken, distorted or aberrated, realigned and averaged to form synthetic aperture images at a set of depths within the seeded volume. These images are thresholded to recover three-dimensional (3D) particle locations and a reconstructed 3D intensity field is formed. This reconstructed field is then evaluated according to intensity data and a signal-to-noise ratio (SNR) as well as standard and rank correlation metrics. Results show that even small amounts of image distortion and spherical aberration can lead to lower correlation values, degradation of the SNR and information loss. Use of rank correlation increases the ability to match elements between the synthetic and reconstructed volumes relative to standard correlation.

Kubaczyk, Daniel M.; Techet, Alexandra H.; Hart, Douglas P.

2013-10-01

410

Compilation System for Venus Radar Mission (Magellan).  

National Technical Information Service (NTIS)

A synthetic aperture radar (SAR) compilation system was developed for extraction of topographic information of Venus from stereoradar imagery to be obtained from the Magellan mission. The system was developed for an AS-11AM analytical stereoplotter. Exten...

S. S. C. Wu F. J. Schafer A. Howington

1987-01-01

411

Decorrelation in interferometric radar echoes  

Microsoft Academic Search

A radar interferometric technique for topographic mapping of surfaces, implemented utilizing a single synthetic aperture radar (SAR) system in a nearly repeating orbit, is discussed. The authors characterize the various sources contributing to the echo correlation statistics, and isolate the term which most closely describes surficial change. They then examine the application of this approach to topographic mapping of vegetated

Howard A. Zebker; John Villasensor

1992-01-01

412

Imaging Radars for Geoscience Use  

Microsoft Academic Search

Properties of a side-looking airborne radar (SLAR) designed for geoscience rather than military use are presented. The speckled nature of usual single-frequency radar images may be reduced by averaging in azimuth and by averaging in range or transmitting excess range bandwidth. With synthetic aperture systems, averaging is possible in both range and azimuth, but only range averaging (excess bandwidth) is

R. K. Moore; G. C. Thomann

1971-01-01

413

The effects of piston error on image quality of synthetical aperture optical imaging system  

NASA Astrophysics Data System (ADS)

The relationship between image quality and piston errors of synthetical aperture optical imaging system has been studied. An active segmented cophasing imaging system and its Zemax simulation model were set up. Diversity piston errors were introduced and the corresponding MTF were calculated with the Zemax simulation model. Simulation experiments have been carried out with the cophasing imaging system, and the results are coincident with the simulated results. The results show that image quality changes with the increase of the piston error periodically if the piston error is smaller than the coherent length of the light source, and the image quality becomes the worst if the piston error is an odd multiple of ?.

Zhang, Jun; Zhao, Weirui; Yang, Feng; Zhang, Lifang

2012-11-01

414

Inverse synthetic aperture ladar: a high-fidelity modeling and simulation tool  

NASA Astrophysics Data System (ADS)

A wave-optics model is developed which allows simulation of an Inverse Synthetic Aperture LADAR (ISAL) imaging system. This end-to-end tool models the complex interactions of Linear Frequency Modulated (LFM) chirped pulses, object/beam interactions including object articulation, speckle phenomenology, heterodyne detection with noise, atmospheric turbulence, and laser-guide star adaptive optics. Detected signal outputs are simulated and processed to explore system design trades and to test and compare image processing algorithms. Model verification results will be presented as well as reconstructed images.

Pellizzari, Casey; Spencer, Mark; Steinhoff, Nicholas; Belsher, John; Tyler, Glenn; Williams, Skip; Williams, Stacie

2013-09-01

415

Layers of different thicknesses in mineral oil spills detected by grey level textures of real aperture radar images  

Microsoft Academic Search

An analysis of the colour coded reflectivity level (grey level) textures of real aperture radar (RAR) imagery, which were obtained over a monomolecular sea slick, a medium fuel oil spill and a chocolate mousse oil spill, suggests that thick and thin parts within a mineral oil spill can be quickly detected. This offers an additional independent all-weather and day-and-night approach

Heinrich Hünerfuss; Werner Alpers; Franz Witte

1989-01-01

416

Sound Field Directivity Correction in Synthetic Aperture Algorithm for Medical Ultrasound  

NASA Astrophysics Data System (ADS)

The paper presents modified multi-element synthetic transmit aperture (MSTA) method for ultrasound imaging with RF echoes correction taking into account the influence of the element directivity, which property becomes significant as the element width becomes commensurable with the wavelength corresponding to the nominal frequency of the transmit signal. The angular dependence of the radiation efficiency of the transmit-receive aperture is approximated by a far-field radiation pattern resulting from the exact solution of the corresponding mixed boundary-value problem for periodic baffle system. The directivity is calculated at the nominal frequency of the excitation signal and is incorporated into the conventional MSTA algorithm. Numerical experiments performed in MATLAB® environment using data simulated by FIELD II program as well as measurement data acquired using the Ultrasonix SonixTOUCH Research system are shown. The comparison of the results obtain by the modified and conventional MSTA methods is given which reveals significant improvement of the image quality, especially in the area neighboring to the transducer's aperture, and increase of the visualization depth at the same time.

Tasinkevych, Yuriy; Klimonda, Ziemowit; Lewandowski, Marcin; Nowicki, Andrzej

417

Three-dimensional target features extraction in curvilinear SAR with aperture errors  

Microsoft Academic Search

In curvilinear synthetic aperture radar (SAR), it is difficult to compensate the curvilinear aperture errors. The algorithm proposed in this paper, based on the phase compensation technique in inverse SAR (ISAR), compensates the aperture errors by using the range and phase information in the reference bins. Consequently, the scatterers' three-dimensional (3-D) features are extracted from the compensated data. Simulation results

Zhigang Su; Yingning Peng; Xiutan Wang

2005-01-01

418

GeoSTAR: a synthetic aperture microwave sounder for geostationary missions  

NASA Astrophysics Data System (ADS)

The Geostationary Synthetic Thinned Aperture Radiometer (GeoSTAR) is a new microwave atmospheric sounder under development. It will bring capabilities similar to those now available on low-earth orbiting environmental satellites to geostationary orbit - where such capabilities have not been available. GeoSTAR will synthesize the multi-meter aperture needed to achieve the required spatial resolution, which will overcome the obstacle that has prevented a GEO microwave sounder from being implemented until now. The synthetic aperture approach has until recently not been feasible, due to the high power needed to operate the on-board high-speed massively parallel processing system required for 2D-synthesis, as well as a number of system and calibration obstacles. The development effort under way at JPL, with important contributions from the Goddard Space Flight Center and the University of Michigan, is intended to demonstrate the measurement concept and retire much of the technology risk. To that purpose a small ground based demo version of GeoSTAR is being constructed, which will be used to characterize system performance and test various calibration methods. This prototype development, which is being sponsored by NASA through its Instrument Incubator Program, will be completed in 2005. A GeoSTAR space mission can then be initiated. In parallel with the technology development, mission architecture studies are also under way in collaboration with the NOAA Office of System Development. In particular, the feasibility of incorporating GeoSTAR on the next generation of the geostationary weather satellites, GOES-R, is being closely examined. That would fill a long standing gap in the national weather monitoring capabilities.

Lambrigtsen, Bjorn H.; Wilson, William J.; Tanner, Alan B.; Kangaslahti, Pekka

2005-01-01

419

Radar Images of the Earth: Volcanoes  

NSDL National Science Digital Library

This site features links to thirty-five NASA radar images of the world's volcanoes, including brief descriptions of the respective processes and settings involved. The images were created with the Spaceborne Imaging Radar-C and X-Band Synthetic Aperture Radar (SIR-C/X-SAR) as part of NASA's Mission to Planet Earth. The radar illuminates Earth with microwaves allowing detailed observations at any time, regardless of weather or sunlight conditions.

420

Radar Images of the Earth: Oceans  

NSDL National Science Digital Library

This site features links to seven NASA radar images of the world's oceans, including brief descriptions of the respective processes and settings. The images were created with the Spaceborne Imaging Radar-C and X-Band Synthetic Aperture Radar (SIR-C/X-SAR) as part of NASA's Mission to Planet Earth. The radar illuminates Earth with microwaves allowing detailed observations at any time, regardless of weather or sunlight conditions.

421

Radar Images of the Earth: Cities  

NSDL National Science Digital Library

This site features links to more than fifty NASA radar images of the world's cities, including brief descriptions of the respective processes and settings involved. The images were created with the Spaceborne Imaging Radar-C and X-Band Synthetic Aperture Radar (SIR-C/X-SAR) as part of NASA's Mission to Planet Earth. The radar illuminates Earth with microwaves allowing detailed observations at any time, regardless of weather or sunlight conditions.

422

Space Radar Images of the Earth: Archaeology  

NSDL National Science Digital Library

This site features links to twelve NASA radar images of the world's famous archaeology sites, including brief descriptions of the respective processes and settings involved. The images were created with the Spaceborne Imaging Radar-C and X-Band Synthetic Aperture Radar (SIR-C/X-SAR) as part of NASA's Mission to Planet Earth. The radar illuminates Earth with microwaves allowing detailed observations at any time, regardless of weather or sunlight conditions.

423

Radar Images of the Earth: Interferometry  

NSDL National Science Digital Library

This site features links to nineteen NASA radar images using interferometry to enhance details or measure changes in elevation. The image pages contain brief descriptions of the respective processes and settings. They were created with the Spaceborne Imaging Radar-C and X-Band Synthetic Aperture Radar (SIR-C/X-SAR) as part of NASA's Mission to Planet Earth. The radar illuminates Earth with microwaves allowing detailed observations at any time, regardless of weather or sunlight conditions.

424

Models of radar imaging of the ocean surface waves  

Microsoft Academic Search

A number of models which would explain ocean wave imagery taken with a synthetic aperture imaging radar are analyzed analytically and numerically. Actual radar imagery is used to support some conclusions. The models considered correspond to three sources of radar backscatter cross section modulation:tilt modulation, roughness variation, and the wave orbital velocity. The effect of the temporal changes of the

CHARLES ELACHI

1977-01-01

425

Polarimetric SAR calibration experiment using active radar calibrators  

Microsoft Academic Search

Active radar calibrators are used to derive both the amplitude and phase characteristics of a multichannel polarimetric synthetic aperture radar (SAR) from the complex image data. Results are presented from an experiment carried out using the NASA\\/JPL DC-8 aircraft SAR over a calibration site at Goldstone, California. As part of the experiment, polarimetric active radar calibrators (PARCs) with adjustable polarization

Anthony Freeman; Yuhsyen Shen; C. L. Werner

1990-01-01

426

Gaussian Markov random field modeling of textures in high-frequency synthetic aperture sonar images  

NASA Astrophysics Data System (ADS)

This paper describes our attempts to model sea bottom textures in high-frequency synthetic aperture sonar imagery using a Gaussian Markov random field. A least-squares estimation technique is first used to estimate the model parameters of the down-sampled grey-scale sonar images. To qualitatively measure estimation results, a fast sampling algorithm is then used to synthesize the sea bottom textures of a fourth-order Gaussian Markov random field which is then compared with the original sonar image. A total of four types of sea floor texture are used in the case study. Results show that the 4th order GMRF model mimics patchy sandy textures and sand ripple, but does not reproduce more complex textures exhibited by coral and rock formations.

Foo, Simon Y.; Cobb, James T.; Stack, Jason R.

2008-05-01

427

The impact of aberrations on object reconstruction with interferometric synthetic aperture microscopy  

NASA Astrophysics Data System (ADS)

Interferometric synthetic aperture microscopy (ISAM) reconstructs the scattering potential of a sample with spatially invariant resolution, based on the incident beam profile, the beam scan pattern, the physical model of light sample interaction, and subsequent light collection by the system. In practice, aberrations may influence the beam profile, particularly at higher NA, when ISAM is expected to provide maximum benefit over optical coherence microscopy. Thus it is of interest to determine the effects of aberrations on ISAM reconstructions. In this paper we present the forward model incorporating the effects of aberrations, which forms the basis for aberration correction in ISAM. Simulations and experimental results show that when operating far from focus, modest amounts of spherical aberration can introduce artifacts to the point-spread function, even at relatively low NA ~ 0.1-0.2. Further work will investigate computational methods to correct the effects of aberrations, i.e. to perform virtual adaptive optics.

Adie, Steven G.; Graf, Benedikt W.; Ahmad, Adeel; Darbarsyah, Budiman; Boppart, Stephen A.; Carney, P. Scott

2011-02-01

428

Unsupervised domain transfer of latent Dirichlet allocation derived representations from synthetic aperture sonar imagery  

NASA Astrophysics Data System (ADS)

Identifying the important discriminating information demonstrated by objects in SAS imagery is important for automatic target recognition. We present a method for determining which information is important using a generative model for documents, introduced by Blei, Ng, and Jordan3 in which each document is generated by choosing a distribution over topics and then choosing each word in the document from a topic selected according to this distribution. We use this algorithm to analyze synthetic aperture sonar data by using Bayesian model selection to establish the number of topics. We show that the extracted topics capture meaningful structure in the SAS data, consistent with the class designations provided, and demonstrate the transfer of this knowledge across sensor domains.

Isaacs, Jason C.

2013-06-01

429

Synthetic Aperture Focusing Technique for the Ultrasonic Evaluation of Friction Stir Welds  

NASA Astrophysics Data System (ADS)

An ultrasonic technique using numerical focusing and processing is presented in this paper for the detection of different types of flaws in friction stir welds (FSW). The data is acquired using immersion ultrasonic technique or laser ultrasonics, while the Synthetic Aperture Focusing Technique (SAFT) is used for numerical focusing. Measurements on the top and far sides of the weld for both lap and butt joints of thin aluminum sheets are investigated. Discontinuities such as wormholes, hooking, lack of penetration and voids are found to be easily detected. The limit of detectability and a comparison with mechanical properties are discussed. Also, the detection of joint line remnants or kissing bonds due to entrapped oxide layers seems possible in lap joint structures using high frequency laser-ultrasonics.

Lévesque, D.; Dubourg, L.; Mandache, C.; Kruger, S. E.; Lord, M.; Merati, A.; Jahazi, M.; Monchalin, J.-P.

2008-02-01

430

A new system for real-time synthetic aperture ultrasonic imaging.  

PubMed

The authors devised a way to generate in real time a cross-sectional image of an object with uniformly high resolution based on the synthetic aperture focusing technique (SAFT). A computer simulation was conducted to study the effects of essential parameters on the resulting images. An imaging system was built that produces a cross-sectional image composed of an assembly of line images of depth direction, i.e. processed A-scan images, and displays a scroll picture on a CRT (cathode ray tube) with no interruption regardless of the object size. It takes only 3 ms from the start of transmission of the ultrasonic wave to the completion of a line image reconstruction, and the framed image on a CRT is updated at the TV rate of 1/30 s. Imaging experiments were conducted using the system, and its expected performance was demonstrated. PMID:18290220

Ozaki, Y; Sumitani, H; Tomoda, T; Tanaka, M

1988-01-01

431

A new system for real-time synthetic aperture ultrasonic imaging  

NASA Astrophysics Data System (ADS)

The authors devised a way to generate in real time a cross-sectional image of an object with uniformly high resolution based on the synthetic aperture focusing technique (SAFT). A computer simulation was conducted to study the effects of essential parameters on the resulting images. An imaging system was built that produces a cross-sectional image composed of an assembly of line images of depth direction, i.e., processed A-scan images, and displays a scroll picture on a CRT (cathode ray tube) with no interruption regardless of the object size. It takes only 3 ms from the start of transmission of the ultrasonic wave to the completion of a line image reconstrution, and the framed image on a CRT is updated at the TV rate of 1/30 s. Imaging experiments were conducted using the system, and its expected performance was demonstrated.

Ozaki, Yoshihiko; Sumitani, Hiroaki; Tomoda, Toshimasa; Tanaka, Mitsuo

1988-11-01

432

The design and development of a geostationary synthetic thinned aperture radiometer  

NASA Astrophysics Data System (ADS)

The Precipitation and All-Weather Temperature and Humidity (PATH) mission outlined in the National Research Council decadal survey for launch in 2016--2020 recommends a microwave array spectrometer as the instrument payload. A design for the Geostationary Synthetic Thinned Aperture Radiometer (GeoSTAR) is presented that fulfils all but one of the mission requirements---integration time---and options are available to meet this requirement. A technological roadmap exists for the development of the key hardware components to minimize size and power requirements, especially with respect to the receiver and digital correlator design. The fabrication of the instrument demonstrator, GeoSTAR-D, contributed significantly to the hardware development (receivers, antennas, correlators) and provided a test-bed to verify the theoretical understanding of a two-dimensional Synthetic Thinned Aperture Radiometry (STAR). Measurements in the anechoic chamber provided a boresight phase calibration and verified that the antenna patterns closely matched the theoretical model. Field deployment of the instrument with an engineered Earth disk target allowed for generation of GEO like measurements and calibration validation. A theoretical based image retrieval algorithm was implemented and combined with various models to account for the sky aliases and minimize the target discontinuities. Images generated after sky alias removal and Gibbs mitigation had residual errors of less than 2%. A high resolution Earth disk model is generated from existing publically available datasets, appropriate geophysical parameter models and a full radiative transfer model. The model allows for the generation of un-physically realizable scenes to determine the impact of individual geophysical parameters on the observed brightness temperature. The realistic brightness temperature images are then evaluated with a GeoSTAR-like instrument simulator to investigate the effectiveness of apodization, spatial frequency information content and various processing algorithms. At the temperature sounding channels, sufficient contrast is available even at the largest baselines. The recommended retrieval algorithm performs well even when based on imperfect input models.

Lim, Boon Hwang

433

Adaptive Filtering of Radar Images for Autofocus Applications.  

National Technical Information Service (NTIS)

Autofocus techniques are being designed at the Jet Propulsion Laboratory to automatically choose the filter parameters (i.e., the focus) for the digital synthetic aperture radar correlator; currently, processing relies upon interaction with a human operat...

J. A. Stiles V. S. Frost J. S. Gardner D. R. Eland K. S. Shanmugam

1981-01-01

434

Application of the differential evolution algorithm to the optimization of two-dimensional synthetic aperture microwave radiometer circle array  

Microsoft Academic Search

A new optimization technique based on the differential evolution algorithm is presented for the design of two-dimensional synthetic aperture microwave radiometer circle array. The object function is designed by minimizing redundant array and maximizing the distance between spatial frequency coverage samples and the optimal results of 16~32 elements circle array are obtained. Compare with simulated annealing algorithm and symmetrical distribution

Kun Chao; Zhenwei Zhao; Zhensen Wu; Rui Lang

2010-01-01

435

Passive Synthetic Aperture Sonar techniques in combination with tow ship noise canceling: application to a triplet towed array  

Microsoft Academic Search

An important issue in research on passive ASW operations is improvement in signal-to-noise ratio (SNR) and bearing resolution for targets emitting low frequency signals. One of the techniques believed to improve these characteristics is Synthetic Aperture Sonar (SAS). The method is based on the artificial enlargement of a sonar array by coherently integrating acoustic snapshots at different antenna positions. This

M. E. G. D. Colin; J. Groen

2002-01-01

436

Efficient synthetic refocusing method from multiple coded aperture images for 3D user interaction  

NASA Astrophysics Data System (ADS)

In this paper, we propose an efficient synthetic refocusing method from multiple coded aperture images for 3D user interaction. The proposed method is applied to a flat panel display with a sensor panel which forms lens-less multi-view cameras. To capture the scene in front of the display, the modified uniformly redundant arrays (MURA) patterns are displayed on the LCD screen without the backlight. Through the imaging patterns on the LCD screen, MURA coded images are captured in the sensor panel. Instead of decoding all coded images to synthetically generate a refocused image, the proposed method only decodes one coded image corresponding to the refocusing image at a certain distance after circularly shifting and averaging all coded images. Further, based on the proposed refocusing method, the depth of an object in front of the display is estimated by finding the most focused image for each pixel through a stack of the refocused images at different depth levels. Experimental results show that the proposed method captures an object in front of the display, generates refocused images at different depth levels, and accurately determines the depth of an object including real human hands near the display

Suh, Sungjoo; Choi, Changkyu; Park, Dusik; Kim, Changyeong

2013-02-01

437

The Venus Radar Mapper (VRM) mission  

Microsoft Academic Search

The Venus Radar Mapper (VRM) mission is sponsored by NASA to put a single spacecraft in orbit around Venus to map the surface of Venus using a synthetic aperture mapping radar. The spacecraft is scheduled to be launched in April 1988 using a Shuttle-Centaur G combination. The spacecraft arrives at Venus in late July 1988 and begins its mapping mission

E. Cutting; J. H. Kwok; S. N. Mohan

1984-01-01

438

Venus Radar Mapper orbit accuracy analysis  

Microsoft Academic Search

Spacecraft orbital accuracies during the mapping phase of the Venus Radar Mapper Mission are the subject of this paper. The analysis presented describes the navigational strategy for the prime mission in support of mapping the planet Venus using a spacecraft deployed Synthetic Aperture Radar. Achievable orbital accuracies are shown to be limited by accuracy of interferometric data to be used.

S. N. Mohan; P. B. Esposito

1984-01-01

439

A spaceborne ground penetrating radar: MIMOSA  

Microsoft Academic Search

The MIMOSA radar is a spaceborne unfocused nadir looking synthetic aperture P-Band radar designed to penetrate the Earth superficial layers and proposed in the frame of the Earth Explorer Opportunity Missions (ESA). This paper reviews all the mission aspects. The scientific objectives are presented: 3D mapping of Antarctic ice sheet, biomass monitoring, and prospective objectives. The instrument concept is developed.

A. Herique; W. Kofman; P. Bauer; F. Remy; L. Phalippou

1999-01-01

440

A fully polarimetric borehole radar based numerical modelling: Fully polarimetric response to synthetic fractures and \\  

Microsoft Academic Search

A fully polarimetric borehole radar system with four combinations of dipole and cylindrical slot antennas was developed to acquire fully polarimetric data sets in drilled boreholes. To better under the fully polarimetric response