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At least 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Comparison of modeled backscatter with SAR data at P-band

In recent years several analytical models were developed to predict microwave scattering by trees and forest canopies. These models contribute to the understanding of radar backscatter over forested regions to the extent that they capture the basic interactions between microwave radiation and tree canopies, understories, and ground layers as functions of incidence angle, wavelength, and polarization. The Santa Barbara microwave model backscatter model for woodland (i.e. with discontinuous tree canopies) combines a single-tree backscatter model and a gap probability model. Comparison of model predictions with synthetic aperture radar (SAR) data and L-band (lambda = 0.235 m) is promising, but much work is still needed to test the validity of model predictions at other wavelengths. The validity of the model predictions at P-band (lambda = 0.68 m) for woodland stands at our Mt. Shasta test site was tested.

Wang, Yong↗
NASA NTRS1992

Strategies for detection of floodplain inundation with multi-frequency polarimetric SAR

Mapping of floodplain inundation patterns is a key element in developing hydrological and biogeochemical models for large tropical river basins such as the Amazon. Knowledge of the time sequence of inundation is necessary to determine both water routing and biogenic gas fluxes. Synthetic Aperture Radar (SAR) is uniquely suited for this application because of its ability to penetrate cloud cover and, in many cases, to detect flooding beneath a forest or herbaceous canopy. A procedure for discriminating flooded forest, flooded herbaceous vegetation, and open water from other cover types for a coastal wetland site on the lower Altamaha floodplain, Georgia, emphasizing robust classifiers that are not site-specific is currently being developed.

Hess, Laura L.↗
NASA NTRS1992

Evaluation of polarimetric SAR parameters for soil moisture retrieval

Results of ongoing efforts to develop an algorithm for soil moisture retrieval from Synthetic Aperture Radar (SAR) imagery are reported. Estimates of soil moisture are of great importance in numerous environmental studies, including hydrology, meteorology, and agriculture. Previous studies using extensive scatterometer measurements have established the optimum parameters for moisture retrieval as C-band HH radar operating at incidence angles between 10 to 15 deg. However, these parameters were not tested or verified with imaging radar systems. The results from different investigators showed considerable variability in the relationship between soil moisture and radar backscattering. This variability suggests that those algorithms are site-specific. Furthermore, the small incidence angle requirement limits the spatial application, especially for airborne radar systems.

Shi, Jian-Cheng↗
NASA NTRS1992

Soil conservation applications with C-band SAR

Soil conservation programs are becoming more important as the growing human population exerts greater pressure on this non-renewable resource. Indeed, soil degradation affects approximately 10 percent of Canada's agricultural land with an estimated loss of 6,000 hectares of topsoil annually from Ontario farmland alone. Soil loss not only affects agricultural productivity but also decreases water quality and can lead to siltation problems. Thus, there is a growing demand for soil conservation programs and a need to develop an effective monitoring system. Topography and soil type information can easily be handled within a geographic information system (GIS). Information about vegetative cover type and surface roughness, which both experience considerable temporal change, can be obtained from remote sensing techniques. For further development of the technology to produce an operational soil conservation monitoring system, an experiment was conducted in Oxford County, Ontario which investigated the separability of fall surface cover type using C-band Synthetic Aperture Radar (SAR) data.

Brisco, B.↗
NASA NTRS1993

Techniques and applications of SAR interferometry for ERS-1

The ERS-1 Synthetic Aperture Radar (SAR) demonstrated that it is possible to measure high resolution topography over large areas using interferometry with repeat orbit data sets. Given that the ERS-1 orbit is known with high precision, an automatic system for generation of interferograms is presented. Least squares estimation using ground control points provides an accurate method for determining the precise interferometric baseline. The system parameters which affect the accuracy of the Digital Elevation Models (DEM's) are errors in the interferometric baseline, decorrelation caused by baseline separation, thermal noise, and surface change. An adaptive filter based on the local interferometric coherence was developed to improve phase unwrapping of the interferogram. Final accuracies of the DEM's generated for single scene pairs in Alaska (U.S.) and Bonn (Germany) are on the order of 5 to 10 m.

Werner, Charles L.↗
NASA NTRS1993

Alaska SAR Facility mass storage, current system

This paper examines the mass storage systems that are currently in place at the Alaska SAR Facility (SAF). The architecture of the facility will be presented including specifications of the mass storage media that are currently used and the performances that we have realized from the various media. The distribution formats and media are also discussed. Because the facility is expected to service future sensors, the new requirements and possible solutions to these requirements are also discussed.

Cuddy, David↗
NASA NTRS1995

Mapping Vegetative Ground Cover From Polarimetric SAR Data

Three-frequency quad-polarization data used to distinguish among different types of cover. MAPVEG computer program performs first-level classification of NASA/JPL AIRSAR polarimetric synthetic-aperture-radar (SAR) data into simple ground-cover types. Classification images generated used to separate vegetated from nonvegetated areas; useful in determining soil moisture in areas free of vegetation. Classification separates forests from surrounding vegetation, and used to identify clear-cut areas. Urban areas and potential marshlands examples of other identifiable classes. Written in FORTRAN 77.

Chapman, Bruce↗
NASA NTRS1995

Program Classifies Multiple-Frequency Polarimetric SAR Data

POLMAP computer program classifies multifrequency, polarimetric synthetic-aperture-radar (SAR) data into homogeneous classes of radar back-scatter. Software implements maximum-a-posteriori classification scheme. Performs by use of simulated-annealing procedure, takes much longer to compute than ICM solution, but it maximizes posteriori distribution of classes for whole scene. Input statistics of image classes must be created by some independent means, and supplied as input to POLMAP. Used as input to image processing application program. Written in FORTRAN 77.

Rignot, Eric↗
NASA NTRS1995

Ice Processes and Growth History on Arctic and Sub-Arctic Lakes Using ERS-1 SAR Data

A survey of ice growth and decay processes on a selection of shallow and deep sub-Arctic and Arctic lakes was conducted using radiometrically calibrated ERS-1 SAR images. Time series of radar backscatter data were compiled for selected sites on the lakes during the period ot ice cover (September to June) for the years 1991-1992 and 1992-1993. A variety of lake-ice processes could be observed, and significant changes in backscatter occurred from the time of initial ice formation in autumn until the onset of the spring thaw. Backscatter also varied according to the location and depth of the lakes. The spatial and temporal changes in backscatter were most constant and predictable at the shallow lakes on the North Slope of Alaska. As a consequence, they represent the most promising sites for long-term monitoring and the detection of changes related to global warming and its effects on the polar regions.

Morris, K.↗
NASA NTRS1996

Modeling Wetland Vegetation using Polarimetric SAR

A three-year project to study small-scale topographic changes and relict geomorphic features on barrier islands using synthetic aperture radar (SAR) is described. A study area on the Texas coast consisting of Galveston Island and Bolivar Peninsula was overflown by the NASA/JPL DC 8 AIRSAR in April 1995. Data was acquired in the fully polarimetric mode using C-, L-, and P-bands and in the TOPSAR configuration with C- and L-bands in interferometric mode. The study area will be overflown again in late spring 1996. The data will be registered to global positioning system (GPS) surveyed points to form high resolution digital elevation models (DEM) and then analyzed to investigate possible topographic changes.

Slatton, K. Clint↗
NASA NTRS1997

Detecting Small-Scale Topographic Changes and Relict Geomorphic Features on Barrier Islands Using SAR

The shapes and elevations of barrier islands may change dramatically over a short period of time during a storm. Coastal scientists and engineers, however, are currently unable to measure these changes occurring over an entire barrier island at once. This three-year project, which is funded by NASA and jointly conducted by the Bureau of Economic Geology and the Center for Space Research at The University of Texas at Austin, is designed to overcome this problem by developing the use of interferometry from airborne synthetic aperture radar (AIRSAR) to measure coastal topography and to detect storm-induced changes in topography. Surrogate measures of topography observed in multiband, fully polarimetric AIRSAR (This type of data are now referred to as POLSAR data.) are also being investigated. Digital elevation models (DEM) of Galveston Island and Bolivar Peninsula, Texas obtained with Topographic SAR (TOPSAR) are compared with measurements by Global Positioning System (GPS) ground surveys and electronic total station surveys. In addition to topographic mapping, this project is evaluating the use of POLSAR to detect old features such as storm scarps, storm channels, former tidal inlets, and beach ridges that have been obscured by vegetation, erosion, deposition, and artificial filling. We have also expanded the work from the original proposal to include the mapping of coastal wetland vegetation and depositional environments. Methods developed during this project will provide coastal geologists with an unprecedented tool for monitoring and understanding barrier island systems. This understanding will improve overall coastal management policies and will help reduce the effects of natural and man-induced coastal hazards. This report summarizes our accomplishments during the second year of the study. Also included is a discussion of our planned activities for year 3 and a revised budget.

Gibeaut, James C.↗
NASA NTRS1996

Application of SIR-C SAR to Hydrology

The progress, results and future plans regarding the following objectives are presented: (1) Determine and compare soil moisture patterns within one or more humid watersheds using SAR data, ground-based measurements, and hydrologic modeling; (2) Use radar data to characterize the hydrologic regime within a catchment and to identify the runoff producing characteristics of humid zone watersheds; and (3) Use radar data as the basis for scaling up from small scale, near-point process models to larger scale water balance models necessary to define and quantify the land phase of GCM's (Global Circulation Models).

Engman, Edwin T.↗
NASA NTRS1997

Crustal deformation in southern California using SAR interferometry

The rate of slow deformation processes along faults activated during the Landers 1992 earthquake was investigated. The analysis was performed by combining pairs of ERS-1/2 synthetic aperture radar (SAR) of Southern California (U.S.). The interferograms revealed several centimeters of post-seismic rebound in step-overs of the 1992 break. The southern branches of the 1992 break experienced surface creep, producing sharp phase cuts in the interferometric maps. The same approach was used in the Los Angeles (CA) basin. The tectonic signal in the interferograms of the Los Angeles basin was intermingled with signals due to ground subsidence caused by oil and water withdrawal.

Peltzer, G.↗
NASA NTRS1996

Mapping of Glacial Motion and Surface Topography of Hielo Patagonico Norte, Chile, Using Satellite SAR L-band Interferometry Data

The first topographic and ice-motion maps of the northwestern flank of Hielo Patagonico Norte (HPN, northern Patagonia Icefield), in Chile, were produced using satellite synthetic-aperture interferometric radar data acquired by NASA's Spaceborne Imaging Radar C instrument in October 1994. The topographic map has a IO m vertical precision with a 30 m horizontal spacing, which should be sufficient to serve as a reference for monitoring future mass changes of the icefield. The ice-motion map is accurate to within 4 mm/ d (or 1/ ma). The radar-derived surface topography and ice velocity are used to estimate the ice discharge from the accumulation area of four outlet glaciers, and the calving flux and mass balance of Glaciar San Rafael. The results demonstrate the use of SAR interferometry for monitoring glaciological parameters on a spatial and temporal scale unattainable by any other means.

Rignot, Eric↗
NASA NTRS1999

Calculation and Error Analysis of a Digital Elevation Model of Hofsjokull, Iceland from SAR Interferometry

Two ascending European Space Agency (ESA) Earth Resources Satellites (ERS)-1/-2 tandem-mode, synthetic aperture radar (SAR) pairs are used to calculate the surface elevation of Hofsjokull, an ice cap in central Iceland. The motion component of the interferometric phase is calculated using the 30 arc-second resolution USGS GTOPO30 global digital elevation product and one of the ERS tandem pairs. The topography is then derived by subtracting the motion component from the other tandem pair. In order to assess the accuracy of the resultant digital elevation model (DEM), a geodetic airborne laser-altimetry swath is compared with the elevations derived from the interferometry. The DEM is also compared with elevations derived from a digitized topographic map of the ice cap from the University of Iceland Science Institute. Results show that low temporal correlation is a significant problem for the application of interferometry to small, low-elevation ice caps, even over a one-day repeat interval, and especially at the higher elevations. Results also show that an uncompensated error in the phase, ramping from northwest to southeast, present after tying the DEM to ground-control points, has resulted in a systematic error across the DEM.

Barton, Jonathan S.↗
NASA NTRS1997

Estimation of Bare Surface Soil Moisture and Surface Roughness Parameter Using L-Band SAR Image Data

An algorithm based on a fit of the single-scattering Integral Equation Method (IEM) was developed to provide estimation of soil moisture and surface roughness parameter (a combination of rms roughness height and surface power spectrum) from quasi-polarized synthetic aperture radar (SAR) measurements. This algorithm was applied to a series of measurements acquired at L-band (1.25 GHz) from both AIRSAR (Airborne Synthetic Aperture Radar operated by Jet Propulsion Laboratory) and SIR-C (Spaceborne Imaging Radar-C) over a well-managed watershed in southwest Oklahoma. It was found that the two co-polarized backscattering coefficients and their combinations would provide the best input to the algorithm for estimation of soil moisture and roughness parameter. Application of the inversion algorithm to the co-polarized measurements of both AIRSAR and SIR-C resulted in estimated values of soil moisture and roughness parameter for bare and short-vegetated fields that compared favorably with those sampled on the ground. The root-mean-square (rms) errors of the comparison were found to be 3.4% and 1.9 dB for soil moisture and surface roughness parameter, respectively.

Shi, Jian-Cheng↗
NASA NTRS1998

Relating Vegetation Aerodynamic Roughness Length to Interferometric SAR Measurements

In this paper, we investigate the feasibility of estimating aerodynamic roughness parameter from interferometric SAR (INSAR) measurements. The relation between the interferometric correlation and the rms height of the surface is presented analytically. Model simulations performed over realistic canopy parameters obtained from field measurements in boreal forest environment demonstrate the capability of the INSAR measurements for estimating and mapping surface roughness lengths over forests and/or other vegetation types. The procedure for estimating this parameter over boreal forests using the INSAR data is discussed and the possibility of extending the methodology over tropical forests is examined.

Saatchi, Sassan↗