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At least 253 records · Page 14

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NASA NTRS1992

Accounting For Gains And Orientations In Polarimetric SAR

Calibration method accounts for characteristics of real radar equipment invalidating standard 2 X 2 complex-amplitude R (receiving) and T (transmitting) matrices. Overall gain in each combination of transmitting and receiving channels assumed different even when only one transmitter and one receiver used. One characterizes departure of polarimetric Synthetic Aperture Radar (SAR) system from simple 2 X 2 model in terms of single parameter used to transform measurements into format compatible with simple 2 X 2 model. Data processed by applicable one of several prior methods based on simple model.

Freeman, Anthony↗

NASA NTRS1992

Polarimetric Radar Signatures Of Frozen And Thawed Forests

Report summarizes study of radiometrically and polarimetrically calibrated data from airborne synthetic-aperture-radar images of single-species forest stands in frozen and thawed conditions. Copolarization radar cross sections found as much as 6 dB less in frozen than in thawed condition. Effect attributed to fact that dielectric constants are greater in thawed condition. More-subtle differences determined by computing two features of statistics of Strokes matrices over resolution elements of each forest stand.

Kwok, Ronald↗

NASA NTRS1992

Iterative Bayesian Classification In Polarimetric SAR

In improved scheme for Bayesian classification of picture elements in polarimetric synthetic-aperture radar image of terrain, priori probability that given picture element belongs to given class, adjusted according to spatial variation of statistical properties of image data. Accuracy increases dramatically in first few iterations. Scheme involves sequence of classifications. In first, a priori probability that element belongs to class taken to be constant over the whole image. In subsequent classifications, adaptive a priori probabilities calculated for each picture element.

Van Zyl, Jakob J.↗

NASA NTRS1991

Analysis of polarimetric SAR signatures of vegetated areas

Several techniques to quantitatively analyze the information in the polarimetric signature are discussed, including: (1) a shape (texture) parameter; (2) fractional polarization; (3) the phase difference signature; and (4) the correlation coefficient. These techniques are applied to airborne synthetic aperture radar imagery collected over several different vegetation communities, including a mangrove swamp, a mixed-age loblolly pine forest, and a flooded bald cypress forest.

French, Nancy H. F.↗

NASA NTRS1991

Polarimetric radar measurements of a tropical rainforest

In Mar. 1990, the NASA/JPL DC-8 Airborne Synthetic Aperture Radar (AIRSAR) was flown over an area in northern Belize and the surrounding areas of Guatamala and Mexico. We have extracted the three-frequency polarimetric signatures of a variety of natural areas and have found that many appear to have a unique radar signature, if all polarizations and frequencies are examined.

Durden, S.↗

NASA NTRS1991

Performance of a polarimetric SAR calibration algorithm

Results of an investigation of the performance of a polarimetric SAR (synthetic aperture radar) calibration algorithm are presented. This calibration technique assumes that the co- and cross-polarized components of azimuthally symmetric natural targets are uncorrelated, and that these targets are reciprocal. Monte Carlo simulations were performed to evaluate its performance for a variety of system and surface types, in the presence of various noise levels. Some empirical limits are obtained on leakage between channels, correlation between HH and VV backscatter, ratio of cross-pol to co-pol backscatter, system noise level, size of training sample, and amount of correlation between cross-pol and co-pol, for which good results are obtained.

Klein, Jeffrey D.↗

NASA NTRS1991

Assessment of surface penetration with polarimetric radar

An airborne P-, L-, and C-band polarimetric radar dataset acquired over the Atchafalaya Bay study site was used to assess its surface penetration capabilities. The dataset was decompressed and reformatted to form a three-wavelength and three-polarization nine-channel dataset. All nine channels were filtered for speckle noise removal, using the 7-by-7 local-statistics moving-window filtering. Significant smoothing of data was obtained so that the data can be classified using the SRCH and M234 ELAS programs. Preliminary assessment of the PLC images indicated that the radar waves penetrated muddy water. Therefore the radar can measure the water depth and can be used to map the submerged sediments. A statistical analysis of the digital data provided insight on the depth of muddy water penetration.

Wu, Shih-Tseng↗

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.↗

NASA NTRS1993

Comparison Of Two Methods Of Calibrating Polarimetric SAR

Report presents comparative analysis of two approaches to calibration of synthetic-aperture radar (SAR). Performed in context of NASA/JPL SAR system mounted in DC-8 airplane, also applicable to any polarimetric SAR system of similar design. Demonstrates functional equivalence of two approaches to calibration. In one, known as Klein's approach, SAR data calibrated supplied in scattering-matrix format. Other named after van Zyl, data calibrated supplied in Stokes-matrix (compressed) format.

Freeman, Anthony↗

NASA NTRS1992

Birefringence-balanced polarimetric optical fiber sensor for high-temperature measurements

A birefringence-balanced polarimetric multimode fiber temperature sensor is proposed and demonstrated. Two single-crystal sapphire rods are incorporated into the sensor head. They are connected end to end in such a way that the slow axis of the first rod is aligned with the fast axis of the second rod, referred to as the referencing rod. Since the lengths of the two rods are chosen to be almost the same, the original birefringence of the first rod is balanced by that of the second rod. A light-emitting diode serves as the light source. This sensor has been experimentally demonstrated for high-temperature measurements as high as 1500 C. A sensitivity of 5 C has been obtained.

Wang, Anbo↗

NASA NTRS1991

Quantitative investigations of geologic surfaces utilizing airborne visible/infrared imaging spectrometer (AVIRIS) and polarimetric radar (AIRSAR) data for Death Valley, California

Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and polarimetric radar (AIRSAR) data were collected over Death Valley, California, USA, in September 1989. These two data sets were used to quantitatively characterize both the mineralogy and surface structure of the valley floor. Field mapping and characterization of the salt flats across the valley identified 16 separate units. The AVIRIS data were calibrated using the 'empirical line' method, and spectra extracted for the 16 units. A water vapor map was generated from the AVIRIS data and showed spatial variations in its distribution due to evaporation of surface water. Unmixing of the 16 spectral units produced maps of endmember abundance.

Kierein-Young, Kathryn S.↗

NASA NTRS1992

Performance characterization of polarimetric active radar calibrators and a new single antenna design

Three aspects of a polarimetric active radar calibrator (PARC) are treated: (1) experimental measurements of the magnitudes and phases of the scattering-matrix elements of a pair of PARCs operating at 1.25 and 5.3 GHz; (2) the design, construction, and performance evaluation of a PARC; and (3) the extension of the single-target-calibration technique (STCT) to a PARC. STCT has heretofore been limited to the use of reciprocal passive calibration devices, such as spheres and trihedral corner reflectors.

Sarabandi, Kamal↗

NASA NTRS1992

Terrain effects on backscattering coefficients derived from multifrequency, polarimetric SAR data

A set of multidate, multilook angle polarimetric SAR data, acquired in Pennsylvania during July 1990 was recorded to determine the effect of local incidence angle. Cosine-based and polynomial models are found to be equally good for correcting SAR data for local incidence angle effects. A modified approach, considering the correction factor as additive rather than multiplicative, gave better results. The standard error in the estimation of soil moisture improves from 8.1 to 5.8 after applying corrections to incidence angle effects.

Rao, K. S.↗

NASA NTRS1992

Polarimetric signatures of a coniferous forest canopy based on vector radiative transfer theory

Complete polarization signatures of a coniferous forest canopy are studied by the iterative solution of the vector radiative transfer equations up to the second order. The forest canopy constituents (leaves, branches, stems, and trunk) are embedded in a multi-layered medium over a rough interface. The branches, stems and trunk scatterers are modeled as finite randomly oriented cylinders. The leaves are modeled as randomly oriented needles. For a plane wave exciting the canopy, the average Mueller matrix is formulated in terms of the iterative solution of the radiative transfer solution and used to determine the linearly polarized backscattering coefficients, the co-polarized and cross-polarized power returns, and the phase difference statistics. Numerical results are presented to investigate the effect of transmitting and receiving antenna configurations on the polarimetric signature of a pine forest. Comparison is made with measurements.

Karam, M. A.↗

NASA NTRS1992

Polarimetric and multifrequency SAR signatures of wet snow

C-, L-, and P-band polarimetric signatures of wet snow surfaces have been analyzed, based on airborne synthetic aperture radar (AIRSAR) surveys of an Alpine test site. The importance of surface roughness is evident in the C- and L-band signatures, whereas the diffuse scattering contribution by internal inhomogeneities in the snowpack increases from the C- to the P-band at incidence angles below 50 deg due to increasing penetration.

Rott, Helmut↗

NASA NTRS1994

Software For Calibration Of Polarimetric SAR Data

POLCAL (Polarimetric Radar Calibration) software tool intended to assist in calibration of synthetic-aperture radar (SAR) systems. In particular, calibrates Stokes-matrix-format data produced as standard product by NASA/Jet Propulsion Laboratory (JPL) airborne imaging synthetic aperture radar (AIRSAR). Version 4.0 of POLCAL is upgrade of version 2.0. New options include automatic absolute calibration of 89/90 data, distributed-target analysis, calibration of nearby scenes with corner reflectors, altitude or roll-angle corrections, and calibration of errors introduced by known topography. Reduces crosstalk and corrects phase calibration without use of ground calibration equipment. Written in FORTRAN 77.

Van Zyl, Jakob↗

NASA NTRS1994

Segmentation Of Polarimetric SAR Data

Report presents one in continuing series of studies of segmentation of polarimetric synthetic-aperture-radar, SAR, image data into regions. Studies directed toward refinement of method of automated analysis of SAR data.

Rignot, Eric J. M.↗

NASA NTRS1993

Dust in the Martian atmosphere: Polarimetric sensing

Telescopic optical polarimetry over the planet Mars enables us to detect and localize scatterers in the Martian atmosphere. Polarization discriminates between crystal clouds and dust particles. For dust grains, sizes can be derived. There is an increase in size from very small grains forming the permanent dust haze to sub-micrometer size grains for the local dust veils and the several micrometer size pieces found in the dust storm clouds. From all these polarimetric results, an overview emerges about the behavior of dust particles in the Martian atmosphere.

Dollfus, A.↗