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NASA NTRS1989

Magellan SAR processing algorithm and H/W design

The SAR (synthetic-aperture radar) data-processing algorithm to be used for the Magellan mission is described. Radar system design, SAR data characteristics, and hardware (H/W) constraints, which are critical to the processing algorithm design, are highlighted. Data flow and the H/W architecture are given to show the real-time data processing capability. Simulation results obtained from processing the synthetic point-target echos are presented to demonstrate the performance of the processing algorithm.

Chen, M.↗

NASA NTRS1989

Calibration of quadpolarization SAR data using backscatter statistics

A new technique is described for calibration of complex multipolarization SAR imagery. Scatterer reciprocity and lack of correlation between like- and cross-polarized radar echoes for natural targets are used to remove cross-polarized contamination in the radar data channels without the use of known ground targets. If known targets are available, all data channels can be calibrated relative to one another and absolutely as well. The method is verified with airborne SAR data.

Klein, Jeffrey D.↗

NASA NTRS1991

The Danish SAR system - Design and initial tests

In January 1986, the design of a high-resolution airborne C-band SAR started at the Electromagnetics Institute of the Technical University of Denmark. The initial system test flights took place in November and December 1989. The authors describe the design of the system, its implementation, and its performance. They show how digital technology has been utilized to realize a very flexible radar with variable resolution, swath-width, and imaging geometry. The motion-compensation algorithms implemented to obtain the high resolution and the special features built into the system to ensure proper internal calibration are outlined. The data processing system, developed for image generation and quality assurance, is sketched, with special emphasis on the flexibility of the system. Sample images and a preliminary performance evaluation are presented, demonstrating that the design goals have been met. The ongoing system upgrades and the planned scientific utilization of the C-band SAR are described.

Madsen, Soren N.↗

NASA NTRS1992

More-Precise Calibration Of Polarimetric SAR

Algorithm for calibration of polarimetric synthetic-aperture-radar (SAR) data in Stokes-matrix representation more nearly exact. Present algorithm resembles prior algorithm closely, except requires extraction of one additional parameter from high-resolution raw SAR data in scattering-matrix format before compression and transformation to Stokes-matrix format and slight change in subalgorithm compressing those data.

Freeman, Anthony↗

NASA NTRS1992

Onboard System Processes SAR Data

Aircraft Flight Correlator (AFC) computing system, mounted with AIRSAR synthetic-aperture-radar (SAR) system, supplements recording and postflight analysis, processing portion of data in real or nearly real time to provide imagery for rapid evaluation. Facilitates diagnosis of SAR equipment or adjustment of parameters of experiment. Operates in two modes: "quick-look" mode, data processed in 10 minutes into high-resolution image; and "real-time" mode, data processed in real time to reduced resolution. Also used as aid to navigation.

Carande, Richard E.↗

NASA NTRS1992

Bacteriorhodopsin Film For Processing SAR Signals

"Instant" photographic film based on semisynthetic retinal pigment bacteriorhodopsin proposed for optical processing of synthetic-aperture-radar (SAR) signals. Input image recorded on film by laser operating at writing wavelength of bacteriorhodopsin, and output image recorded on computer by standard frame-grabber. Because it requires no chemical development, enables processing in nearly real time. Fast response and high resolution well suited for application. Film reusable, with concomitant reduction in cost of SAR processing.

Yu, Jeffrey W.↗

NASA NTRS1992

Statistical Approach To Extraction Of Texture In SAR

Improved statistical method of extraction of textural features in synthetic-aperture-radar (SAR) images takes account of effects of scheme used to sample raw SAR data, system noise, resolution of radar equipment, and speckle. Treatment of speckle incorporated into overall statistical treatment of speckle, system noise, and natural variations in texture. One computes speckle auto-correlation function from system transfer function that expresses effect of radar aperature and incorporates range and azimuth resolutions.

Rignot, Eric J.↗

NASA NTRS1991

Snow and glacier mapping with polarimetric SAR

The objective of this study was to examine the capability of mapping snow and glaciers in alpine regions using synthetic aperture radar (SAR) imagery when topographic information is not available. The topographic effects on the received power for a resolution cell can be explained by the change in illumination area and incidence angle in a slant-rante representation of SAR imagery. The specific polarization signatures and phase difference between HH and VV components are relatively independent of the illuminated are, and the incidence angle has only a small effect on these parameters. They provide a suitable measurement data set for snow and glacier mapping in a high-relief area. The results show that the C-band images of the enhancement factor, the phase difference between HH and VV scattering components, and the normalized cross product of VV scattering elements provide the capability to discriminate among snow with different wetnesses, glaciers, and rocky regions.

Shi, Jiancheng↗

NASA NTRS1991

Phi-s correlation and dynamic time warping - Two methods for tracking ice floes in SAR images

The authors present two algorithms for performing shape matching on ice floe boundaries in SAR (synthetic aperture radar) images. These algorithms quickly produce a set of ice motion and rotation vectors that can be used to guide a pixel value correlator. The algorithms match a shape descriptor known as the Phi-s curve. The first algorithm uses normalized correlation to match the Phi-s curves, while the second uses dynamic programming to compute an elastic match that better accommodates ice floe deformation. Some empirical data on the performance of the algorithms on Seasat SAR images are presented.

Mcconnell, Ross↗

NASA NTRS1992

Design, test, and applications of the Alaska SAR Facility

The key science requirements, the overall design, and the innovative testing approaches that have been used to ensure the functionality of the Alaska SAR Facility (ASF) are described. The facility is to play an important role in the remote sensing applications of Arctic oceanography, geology, glaciology, hydrology, and ecosystem processes. Attention is given to the ASF's three major components: the Receiving Ground Station, the SAR Processing System, and the Archive and Operations System. The ASF hardware configuration and software support, through extensive design and implementaton reviews, were shown to satisfy the initial memorandum of agreement first initiated by NASA for the establishment of a receiving ground station and image processing facility at the University of Alaska Fairbanks, and also to satisfy the science objectives formulated by the prelaunch Science Working team. The testing strategy and techniques used in the implementation of the ASF to assure functionality is outlined. The test structures, approach, and environment are considered.

Berwin, R. W.↗

NASA NTRS1992

Multi-spectral analysis of ice sheets using co-registered SAR and TM imagery

Landsat Thematic Mapper and airborne Synthetic Aperture Radar (SAR) imagery acquired over an area of south-western Greenland are coregistered and analyzed. Significant corrections to the SAR data were required to account for range-darkening, non-square pixel dimensions, speckle, and relief distortion. In one area, exposed rock was available for use as co-registration control, while in another area it was absent and supraglacial lakes and streams were used. The coregistered scenes highlight many differences between the optical and radar signatures of ice sheets.

Vornberger, P. L.↗

NASA NTRS1992

Bayesian classification of polarimetric SAR images using adaptive a priori probabilities

The problem of classifying earth terrain by observed polarimetric scattering properties is tackled with an iterative Bayesian scheme using a priori probabilities adaptively. The first classification is based on the use of fixed and not necessarily equal a priori probabilities, and successive iterations change the a priori probabilities adaptively. The approach is applied to an SAR image in which a single water body covers 10 percent of the image area. The classification accuracy for ocean, urban, vegetated, and total area increase, and the percentage of reclassified pixels decreases greatly as the iteration number increases. The iterative scheme is found to improve the a posteriori classification accuracy of maximum likelihood classifiers by iteratively using the local homogeneity in polarimetric SAR images. A few iterations can improve the classification accuracy significantly without sacrificing key high-frequency detail or edges in the image.

Van Zyl, J. J.↗

NASA NTRS1991

Multi-frequency, multi-polarization SAR and radiometer sea ice classification

Microwave remotely sensed data were acquired simultaneously in March 1988 over Beaufort, Chukchi, and Bering Sea ice using the JPL multifrequency, polarimetric synthetic aperture radar (SAR), and multifrequency dual-polarization GSFC radiometer. The experiment was conducted as a series of coordinated underflights of the DMSP SSM/I satellite radiometer to validate ice products derived from its radiance values. Concurrent flights by an NRL P-3 aircraft enabled overlapping high-resolution, single-frequency images to be acquired over the same surfaces using a Ka-band scanning microwave radiometer. Precise coregistration to an accuracy of 100 m, +/- 25 m enables comparison of temporally and spatially coincident active and passive microwave datasets. Three-channel polarimetric SAR data are compared with dual-polarized radiometer data at several SSM/I frequencies, showing backscatter signatures to be highly correlated with radiometric temperatures. Further comparisons are used to evaluate ice concentration retrievals and to show how multiparameter datasets can be used to resolve ambiguities present in identifying certain sea ice forms with a single microwave instrument.

Drinkwater, Mark R.↗

NASA NTRS1991

Unsupervised segmentation of polarimetric SAR data using the covariance matrix

An unsupervised selection of polarimetric features useful for the segmentation and analysis of polarimetric synthetic aperture radar (SAR) data is presented. The technique is based on multidimensional clustering of the parameters composing the polarimetric covariance matrix of the data. Clustering is performed on the logarithm of these quantities. Once the polarimetric cluster centers have been determined, segmentation of the polarimetric data into regions is performed using a maximum likelihood polarimetric classifier. Segmentation maps are further improved using a Markov random field to describe the statistics of the regions and computing the maximum of the product of the local conditional densities. Examples with real polarimetric SAR imagery are given to illustrate the potential of this method.

Rignot, Eric↗

NASA NTRS1992

Real-time processor for the Danish airborne SAR

A real-time processor for the Danish high-resolution SAR is presented in terms of its functional performance, algorithm, architecture, and implementation. The real-time processor is mainly intended to assist the operator in using the SAR system, but since the processor has been designed to produce high-quality images, it is expected to make off-line processing superfluous in many cases. The range-Doppler algorithm is adopted and supplemented with an extensive motion compensation, considering the special conditions related to the real-time strip mapping of large scenes. The processor is a pipeline of about 20 elements interconnected by a dedicated data path and a control bus. Only three different types of elements are involved: a programmable signal processing element, a multipurpose memory element, and a multipurpose interface element. The prototypes of these three elements have been tested with satisfactory results.

Dall, J.↗

NASA NTRS1992

Calibration of complex polarimetric SAR imagery using backscatter correlations

A new technique for calibration of multipolarization synthetic aperture radar (SAR) imagery is described. If scatterer reciprocity and lack of correlation between co- and cross-polarized radar echoes (for azimuthally symmetric distributed targets) is assumed, the effects of signal leakage between the radar data channels can be removed without the use of known ground targets. If known targets are available, all data channels may be calibrated relative to one another and radiometrically as well. The method is verified with simulations and application to airborne SAR data.

Klein, Jeffrey D.↗

NASA NTRS1992

Preliminary analysis of ERS-1 SAR for forest ecosystem studies

An image obtained by the C-band VV-polarized ERS-1 SAR is examined with respect to potential land applications. A scene obtained near noon on August 15, 1991, along the U.S.-Canadian border near Sault Ste. Marie is calibrated relative to an array of trihedral corner reflectors and active radar calibrators distributed across the swath. Extensive contemporaneous ground observations of forest stands are used to predict the radar backscattering coefficient sigma at the time of the SAR overpass using a first-order vector radiative transfer model. These predictions generally agree with the calibrated ERS-1 data to within 1 dB. It is demonstrated that the dynamic range of sigma is sufficient to perform limited discrimination of various forest and grassland communities even for a single-date observation. Furthermore, retrieval of near-surface soil moisture is feasible for grass-covered soils when plant biomass is less than 1 tonne/ha.

Dobson, M. G.↗

NASA NTRS1993

Classification Of Terrain In Polarimetric SAR Images

Two algorithms processing polarimetric synthetic-aperture-radar data found effective in assigning various parts of SAR images to classes representing different types of terrain. Partially automate interpretation of SAR imagery, reducing amount of photointerpretation needed and putting whole interpretation process on more quantitative and systematic basis. First algorithm implements Bayesian classification scheme "supervised" by use of training data. Second algorithm implements classification procedure unsupervised.

Van Zyl, Jakob J.↗