Estimating Soil Moisture from a Varying Subsurface Profile
No abstract available
polarimetric backscattering↗
Engineering topics
Van Zyl, Jakob J.
Publications and source records attributed to Van Zyl, Jakob J..
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↗
Calibration Of NASA/JPL DC-8 SAR Data
Report describes recent improvements in calibration of data gathered by polarimetric synthetic-aperture-radar (SAR) system operated by NASA's Jet Propulsion Laboratory. Improvements are: relocation of calibration site; JPL POLCAL software; and ANTENCAL software. Presents analysis of calibration performance over number of sites during years 1989 and 1990.
Freeman, Anthony↗
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.↗
Registration Of SAR Images With Multisensor Images
Semiautomated technique intended primarily to facilitate registration of polarimetric synthetic-aperture-radar (SAR) images with other images of same or partly overlapping terrain while preserving polarization information conveyed by SAR data. Technique generally applicable in sense one or both of images to be registered with each other generated by polarimetric or nonpolarimetric SAR, infrared radiometry, conventional photography, or any other applicable sensing method.
Evans, Diane L.↗
The effect of topography on radar scattering from vegetated areas
This paper shows how the radar scattering from vegetated areas is affected by the topography of the surface underneath the vegetation. It is shown, using a discrete scatterer model, that the dominant scattering mechanism may change drastically when the ground surface is tilted relative to the horizontal. In the case of a horizontal ground surface, total scattering may be dominated by scattering off the tree trunks, followed by a reflection off the ground surface. For a relatively small tilt in the ground surface (about 2 deg from horizontal), the ground-trunk interaction term may be replaced by scattering from the branches alone as the dominant scattering mechanism. We also show that the effect of the topography is more pronounced for scattering by longer wavelengths, and discuss the implications on algorithms designed to infer forest woody biomass and soil and vegetation moisture using polarimetric SAR data. The effect of the topography on the scattering behavior from forested areas is illustrated with images acquired by the NASA/JPL three-frequency polarimetric SAR over the Black Forest in Germany.
Van Zyl, Jakob J.↗
Radar interferometry studies of the earth's topography
Digital elevation models (DEMs) which have been acquired using the TOPSAR interferometric radar sensor are directly applicable to geological and geophysical studies. Attention is presently given to three illustrative examples of the use of DEMs: the correction of remote-sensing observations for local slope and topographic effects, topographic expressions of erosion and uplift in alluvial fans, and volcanology. The greatest advantages of TOPSAR over conventional photogrammetry include rapidity of data collection, high spatial and vertical resolution, and the ability to obtain contiguous data independent of cloud cover.
Evans, Diane L.↗
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.↗
Detection of land degradation with polarimetric SAR
Multispectral radar polarimeter data were collected over the Manix Basin Area of the Mojave desert using an airborne SAR. An analysis of the data reveals unusual polarization responses which are attributed to the formation of wind ripples on the surfaces of fields that have been abandoned for more than 5 years. This hypothesis has been confirmed through field observations, and a second-order perturbation model is shown to effectively model the polarization responses. The results demonstrate the usefulness of remote sensing techniques for the study of land degradation at synoptic scales.
Ray, Terrill W.↗
Modeling Characteristics Of Surfaces For Radar Polarimetry
Paper reviews mathematical models of polarimetric radar backscattering characteristics of various types of terrain; forests, grasslands, and lava fields. Represents approach to imaging radar polarimetry in which one accumulates models predicting realistic polarization signatures and represent distinct scattering processes, without attempting full vector solutions of Maxwell's equations in all cases. Idea to develop ability to invert models to identify unknown terrain depicted in polarimetric radar images. Describes models, major scattering characteristics predicted by models, and interpretation of characteristics in terms of dominant scattering mechanisms. Models predict realistic polarization signatures.
Van Zyl, Jakob J.↗
Calibration of Stokes and scattering matrix format polarimetric SAR data
An equivalence is noted between the backscatter and the polarimetric radar system assumptions for the approaches given by Klein (1992) and van Zyl (1990). It is shown that, to first order in the radar system crosstalk, an exact solution to the Stokes matrix format data calibration problem exists, and that van Zyl's approach can give this first-order solution for appropriately symmetrized polarimetric radar data. If the data are suitably symmetrized, the van Zyl approach can be used to calibrate both scattering matrix and Stokes matrix format data.
Freeman, Anthony↗
Another Technique For Calibration Of Polarimetric Radar
Inexpensive technique involves four-stage procedure where different aspects of radar system calibrated at each stage. Provides calibration of relative phase, crosstalk, relative amplitude, and absolute amplitude. Only artificial target(s) required is at least one trihedral corner reflector. Advantage of four-step calibration procedure is that one does not have to perform entire procedure if one does not need full calibration.
Van Zyl, Jakob J.↗
Estimates of surface roughness derived from synthetic aperture radar (SAR) data
Radar remote sensing data provide a unique perspective of the earth's crust and the processes that have influenced its evolution. Physically based models are required, however, to relate the geophysical quantities being measured by the radar sensor to useful geologic information. In this study, synthetic aperture radar (SAR) data over the Cima volcanic field in the Mojave Desert of California are quantitatively connected with microtopography through inversion of a radar backscatter model. Changes in surface roughness inferred from the derived microtopography are modeled and found to be consistent with aeolian mantling as surfaces age. Estimated rates of aeolian deposition for the Cima area are compared to the Lunar Crater volcanic field in Nevada. Rates of deposition appear to be higher at Cima volcanic field, most likely because of its proximity to Soda Lake, the main source of the aeolian material.
Evans, Diane L.↗
Algorithms For Compression Of Polarimetric-Radar Image Data
Two sets of algorithms provide moderate improvements in compression and decompression of scattering-matrix data from polarimetric imaging radar system. Algorithms operate on original single-look scattering matrices, do not symmetrize scattering matrices and, preserve asymmetrical data on background-noise and equipment effects.
Van Zyl, Jakob J.↗
Monsoon '90 - Preliminary SAR results
Multifrequency polarimetric synthetic aperture radar (SAR) images of the Walnut Gulch watershed near Tombstone, Arizona were acquired on 28 Mar. 1990 and on 1 Aug. 1990. Trihedral corner reflectors were deployed prior to both overflights to allow calibration of the two SAR data sets. During both overflights, gravimetric soil moisture and dielectric constant measurements were made. Detailed vegetation height, density, and water content measurements were made as part of the Monsoon 1990 Experiment. Preliminary results based on analysis of the multitemporal polarimetric SAR data are presented. Only the C-band data (5.7-cm wavelength) radar images show significant difference between Mar. and Aug., with the strongest difference observed in the HV images. Based on the radar data analysis and the in situ measurements, we conclude that these differences are mainly due to changes in the vegetation and not due to the soil moisture changes.
Dubois, Pascale C.↗
Relative phase calibration of the NASA/DC-8 three-frequency polarimetric SAR system
Relative phase calibration of radar polarimetry data may be achieved by utilizing the phase information of the receiver calibration tone and knowledge of the antenna path differences among channels measured upon installation of the radar polarimeter. This calibration method does not require any assumptions on the scattering behavior of the scene. This method of phase calibration may be verified by examining the polarization signatures of calibration instruments such as the trihedral corner reflectors.
Lou, Yunling↗
Development of soil moisture retrieval algorithm for L-band SAR measurements
A study of algorithm development and testing for soil moisture retrieval for bare fields using L-band synthetic aperture radar (SAR) imagery is reported. First-order surface scattering models predict that the copolarization ratio is sensitive to soil moisture but not to surface roughness. All possible ratios of the co-polarization signals and their linear combinations are evaluated. The best sensitivity to soil moisture is achieved from measurements as predicted by the first-order surface scattering model. The effects of system noise and volume scattering of soil are evaluated. To minimize the effect of the volume scattering, an algorithm which includes both the surface and volume scattering has been developed and tested using Jet Propulsion Laboratory Airborne SAR (JPL AIRSAR) data. The results show that the estimation of soil moisture can be improved after removing the system noise and including the volume scattering effect at large incidence angles.
Shi, Jiancheng↗
Polarization signatures for abandoned agricultural fields in the Manix Basin area of the Mojave Desert - Can polarimetric SAR detect desertification?
Radar backscatter from abandoned circular alfalfa fields in the Manix Basin area of the Mojave desert shows systematic changes with length of abandonment. The obliteration of circular planting rows by surface processes could account for the disappearance of bright spokes, which seem to be reflection patterns from remnants of the planting rows, with increasing length of abandonment. An observed shift in the location of the maximum L-band copolarization return away from VV, as well as an increase in surface roughness, both occurring with increasing age of abandonment, seems to be attributable to the formation of wind ripples on the relatively vegetationless fields.
Ray, Terrill W.↗