Jeffrey D. Klein

Calibration of complex polarimetric SAR imagery using backscatter correlations

A 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) are 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 can be calibrated relative to one another and radiometrically as well. The method is verified with simulation and application to airborne SAR data. >

Polarimetric radar measurements of a forested area near Mt. Shasta

The authors present the results of an experiment using the NASA/JPL DC-8 AIRSAR (aircraft synthetic-aperture radar) over a coniferous forest near Mt. Shasta (California) in 1989. Calibration devices were deployed in clearings and under the forest canopy and passes at 20 degrees , 40 degrees , and 55 degrees incidence angles were made with the AIRSAR. A total of eight images at differing incidence angles have been processed and calibrated. The multipolarization multifrequency data were examined, and it was found that the C-band cross section averaged over like and cross polarizations is the best parameter for distinguishing between two stands with differing forest biomass. The average cross section at P- and L-bands is useful only for smaller incidence angles. Parameters describing the polarization behavior of the scattering were primarily useful in identifying the dominant scattering mechanisms for forest backscatter. >

The NASA/JPL Multifrequency, Multipolarisation Airborne SAR System

The Jet Propulsion Laboratory has designed, built and tested a new suite of polarimetric synthetic aperture radars, operating at L-, C- and P-Band. The three radars have been designed to replace and upgrade the system that was destroyed in an accident in 1985. A series of ground and flight tests have been conducted out of Ames Research Center, Mountain View, California during JanuaryFebruary of 1988 and the radar has flown over the Goldstone Calibration site in a sequence of experiments designed to calibrate the system. The radar has also taken part in a series of science campaigns in Alaska, California, Arizona and the East Coast of the USA. This paper will describe this new imaging radar system for the benefit of the user community.

Calibration of NASA/JPL DC-8 Sar Data

The paper describes a number of improvements in calibration of NASA/JPL DC-8 SAR (synthetic aperture radar) data, intended to make calibrated data from the system available to the majority of the investigators. The improvements include a move to a better site for calibration of the system at the start of each campaign season, the release of software to allow users to calibrate their data, the supply of trihedral corner reflectors and instructions on how to deploy them, and the setting up of an archive of calibrated data. Analysis of the calibration performance of the DC-8 SAR over a number of sites during 1990 suggests that the system is sufficiently stable to allow calibration of the standard data products without the presence of calibration devices within the scene. The limiting factor on DC-8 SAR data calibration would now appear to be the knowledge of the altitude of the aircraft, which determines the relationship between the measured slant range coordinates and the antenna pattern in elevation.

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.

Radar measurement of L-band signal fluctuations caused by propagation through trees

Fluctuations of an L-band, horizontally polarized signal that was transmitted from the ground through a coniferous forest canopy to an airborne radar are examined. The azimuth synthetic aperture radar (SAR) impulse response in the presence of the measured magnitude fluctuations shows increased sidelobes over the case with no trees. Statistics of the observed fluctuations are similar to other observations. >

Measurement and simulation of signal fluctuations caused by propagation through trees

We present measured magnitude and phase fluctuations of UHF, L band, and C band signals that were transmitted from the ground through a forest canopy to an airborne radar. We find that the measured fluctuations are similar to those calculated by a simple Monte Carlo simulation. Both observed and calculated RMS fluctuations are typically several decibels in magnitude and tens of degrees in phase at all three frequencies.

A Comparison Of Three Sar Interference Filters

Man-made interference at P-band (450 MHz) and, to a lesser extent, L-band (1 GHz) occasionally cause SAR images at those wavelengths to be unusable. Here, we discuss three interference filters, and quantify their ability to remove the interference while leaving target signal data. The following three interference filters will be described and compared : 1) Adaptive frequency-domain spike filtering, 2) Adaptive frequency-domain interference determination and masking, and 3) Interferencetarget correlation masking. Using JPL AIRSAR data, we may evaluate the algorithms by applying them to three data sets. The first data set was collected over a site free of interference, the second data set was collected with the transmitter off when P-band interference was present, and the third data set was constructed by the coherent addition of the first data set with the second data set. The interference filters are then applied to the three data sets. The resultant compressed stokes matrix data may then be compared with the normally processed interference-free image in a quantitative sense. The algorithms may be evaluated by measuring the polarization signature, SNR, equivalent number of looks, and impulse response of the processed images.

Results of 1993 repeat-pass SAR interferometry experiments

Presents the results of a repeat-pass SAR interferometry experiment performed in June 1993 near Portage, Maine, USA. Differential GPS data accurate to /spl plusmn/10 cm were acquired to aid in motion compensation and geolocation of targets in the imagery. The experiment and data analysis are discussed, and results are shown.<<ETX>>

Design Considerations For An Advanced Multi-polarisation SAR

In this paper we discuss elements of the system design and verification of the NASA/JPL Airborne Imaging Radar (AIR) system. Issues of importance to multipolarization systems (e.g. mutual coherence and amplitude balance between channels) are emphasized. Methods of detecting and correcting channel imbalances are discussed, and AIR test results are presented.