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At least 541 records · Page 30

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NASA NTRS1991

Estimating slash pine biomass using radar backscatter

L-band HV multiple-incidence-angle aircraft synthetic aperture radar (SAR) data were analyzed in relation to average stand biomass, basal area, and tree height for 55 slash pine plantations located in northern Florida. This information was used to develop a system of equations to predict average stand biomass as a function of L-band (24.5-cm) radar backscatter. The system of equations developed in this study using three-stage least-squares and combinatorial screening accounted for 97 percent of the variability observed in average stand biomass per hectare. When applied to an independent data set, the biomass equations had an average bias of less than 1 percent with a standard error of approximately 3 percent. These results indicate that future Shuttle Imaging Radar Systems (e.g., SIR-C, which will have cross-polarized radar sensors) should be able to obtain better estimates of forest biomass than were obtained with previous satellite radar missions, which utilized only HH-polarized SAR data.

Hussin, Yousif Ali↗

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

More About Calibration Of Polarimetric SAR

Azimuthal symmetry is not assumed. Two sets of equations and algorithms for radiometric and polarimetric calibration of complex quadpolarization data gathered by synthetic-aperture radar (SAR) based partly on known scattering characteristics of artificial targets in scene, and partly on assumption that all other targets scatter reciprocally.

Klein, Jeffrey D.↗

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

Fast Vector-Quantizing Data Compressor

Proposed encoding digital electronic data-processing system compresses 7-Mb/s input stream of data into 1-Mb/s output stream. Intended to reduce flow of data from orbiting synthetic-aperture-radar (SAR) system to rate low enough for transmission to ground. Features include reliability, light weight, and low power. Proves advantageous in such terrestrial applications as compression of speech and of video signals.

Chang, Chi-Yung↗

NASA NTRS1991

Soil moisture measurements from airborne SAR

The preliminary results of algorithm development and testing for soil moisture retrieval at high incidence angles are reported. Based on first-order surface backscattering models, a physically based algorithm for retrieval of soil moisture was developed and evaluated using NASA/JPL aircraft synthetic aperture radar (SAR) data. It shows that the copolarization ratio is sensitive to soil moisture change but not to surface roughness at high incidence angles. This algorithm performed well at L-band and should be useful. This study suggests that incidence angles greater than 40 degrees are optimal for such monitoring.

Shi, Jiancheng↗

NASA NTRS1991

An experiment in remote manufacturing using the advanced communications technology satellite

The goal of the completed project was to develop an experiment in remote manufacturing that would use the capabilities of the ACTS satellite. A set of possible experiments that could be performed using the Advanced Communications Technology Satellite (ACTS), and which would perform remote manufacturing using a laser cutter and an integrated circuit testing machine are described in detail. The proposed design is shown to be a feasible solution to the offered problem and it takes into consideration the constraints that were placed on the experiment. In addition, we have developed two more experiments that are included in this report: backup of rural telecommunication networks, and remote use of Synthetic Aperture Radar (SAR) data analysis for on-site collection of glacier scattering data in the Antarctic.

Tsatsoulis, Costas↗

NASA NTRS1992

ERS-1 SAR ice routing of l'Astrolabe through the Northeast passage

The use of Synthetic Aperture Radar (SAR) data from the satellite ERS-1 to assist the French polar vessel 'L'Astrolabe' during its navigation through Artic sea ice in the Northeast Passage is reported. The ship spent one month on the voyage from Europe to Japan, and high resolution SAR images and ice maps based on SAR images from ERS-1 and Special Sensor Microwave/Imager were telefaxed to the ship using the Inmarsat system. The time delay from observation to the reception of SAR images aboard the ship varied from 6 hours to two days. The quality of these ice maps was compared with Russian ice maps and observations from the ship. The SAR imagery provided detailed information on ice floe distribution, ice concentration, ice types, open leads, and tracks in ice from icebreakers. The response from the Russian ice specialists on the quality of the SAR ice maps was very positive.

Johannessen, O. M.↗

NASA NTRS1992

Properties of radar backscatter of forests measured with a multifrequency polarimetric SAR

Fully polarimetric airborne synthetic aperture radar (AIRSAR) data, collected in Germany during the MAC Europe campaign, are calibrated using software packages developed at the Joint Research Center (JRC) in Italy for both L- and C-bands. During the period of the overflight dates, extensive ground truth was collected in order to describe the physical and statistical parameters of the canopy, the understory, and the soil. These parameters are compiled and converted into electromagnetic parameters suitable for input to the new polarimetric three-layer canopy model developed at the Wave Scattering Research Center (WSRC) at the University of Texas at Arlington. Comparisons between the theoretical predictions from the model and the calibrated data are carried out. Initial results reveal that the trend of the average phase difference can be predicted by the model, and that the backscattering ratio *shh/ svv is sensitive to the distribution of the primary branches.

Amar, F.↗

NASA NTRS1992

On the application of multifrequency polarimetric radar observations for sea-ice classification

The use of multifrequency polarimetric radar imagery to enhance the ability to separate different sea-ice types using single-frequency, single-polarization synthetic aperture radar (SAR) data is investigated. Backscatter characteristics of six radiometrically and polarimetrically distinct sea-ice types are selected in an unsupervised range-dependent analysis of multifrequency polarimetric SAR data using the maximum a posteriori (MAP) polarimetric classifier. Maximum ice discrimination is achieved with combined C- and L-band full polarimetry, and collocated passive microwave imagery suggests greater than 90 percent classification accuracy. C-band VV-pol alone achieves only 68 percent relative accuracy because it confuses multiyear and rough compressed first year ice. L-band, relative classification accuracy is 75 percent, 83 percent, and 85 percent, using HH-pol, HH- and VV-combined, or the full polarimetry, respectively. P-band is less accurate. Combinations of two frequencies at a single polarization show the greatest improvement over a single channel.

Rignot, Eric↗

NASA NTRS1992

Alaska SAR processor implementation of E-ERS-1

The synthetic aperture radar (SAR) data processing algorithm used by the Alaska SAR Facility (ASF) for the European Space Agency's first Remote-Sensing Satellite (E-ERS-1) SAR data are examined. Preprocessing highlights two features: signal measurement, which includes signal-to-noise ratio, replica measurement, and noise measurement; and Doppler measurement, which includes clutter lock and autofocus. The custom pipeline architecture performs the main processing with controls at the input interface, range correlator, corner-turn memory, azimuth correlator, and multi-look memory. The control software employs a flexible control scheme. The Committee on Earth Observation Satellites (CEOS) format encapsulates the ASF products. System performance for SAR image processing of E-ERS-1 data is reviewed.

Cuddy, David↗

NASA NTRS1992

Phase difference statistics related to sensor and forest parameters

The information content of ordinary synthetic aperture radar (SAR) data is principally contained in the radiometric polarization channels, i.e., the four Ihh, Ivv, Ihv and Ivh backscattered intensities. In the case of clutter, polarimetric information is given by the four complex degrees of coherence, from which the mean polarization phase differences (PPD), correlation coefficients or degrees of polarization can be deduced. For radiometric features, the polarimetric parameters are corrupted by multiplicative speckle noise and by some sensor effects. The PPD distribution is related to the sensor, speckle and terrain properties. Experimental results are given for the variation of the terrain hh/vv mean phase difference and magnitude of the degree of coherence observed on bare soil and on different pine forest stands.

Lopes, A.↗

NASA NTRS1992

The effect of topography on radar scattering from vegetated areas

It is shown how radar scattering from vegetated areas is affected by the topography of the surface underneath the vegetation, and that by the use of a discrete scatterer model 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. It is shown that for a relatively small tilt in the ground surface the ground-trunk interaction term may be replaced by scattering from the branches alone as the dominant scattering mechanism. The effect of the topography is more pronounced for scattering by longer wavelengths. The implications for algorithms designed to infer forest woody biomass and soil and vegetation moisture using polarimetric synthetic aperture radar (SAR) data are discussed.

Van Zyl, Jakob J.↗

NASA NTRS1994

SAR Processing Based On Two-Dimensional Transfer Function

Exact transfer function, ETF, is two-dimensional transfer function that constitutes basis of improved frequency-domain-convolution algorithm for processing synthetic-aperture-radar, SAR data. ETF incorporates terms that account for Doppler effect of motion of radar relative to scanned ground area and for antenna squint angle. Algorithm based on ETF outperforms others.

Chang, Chi-Yung↗

NASA NTRS1993

Spatial patterns in backscatter strength across the Greenland Ice Sheet

The relationship between the physical properties of the Greenland ice sheet and Synthetic Aperture Radar (SAR) data collected from aircraft and from ERS-1 is addressed. Limited aircraft data are combined with a description of the glacier surface to predict qualitatively the spatial and seasonal variation in backscatter strength across the ice sheet. In particular the model predicts relatively low backscatter near the ice edge where scattering is dominated by rough surface effects. Backscatter increases through the lake zone as volume scattering becomes important. Strongest backscatter is found in the percolation facies where volume scatter from snow grains and volume scatter from large, buried ice bodies becomes important. Backscatter weakens in the interior ice sheet where fine grained snow is the only mechanism producing backscatter.

Jezek, K. C.↗

NASA NTRS1992

Relating multifrequency radar backscattering to forest biomass: Modeling and AIRSAR measurement

During the last several years, significant efforts in microwave remote sensing were devoted to relating forest parameters to radar backscattering coefficients. These and other studies showed that in most cases, the longer wavelength (i.e. P band) and cross-polarization (HV) backscattering had higher sensitivity and better correlation to forest biomass. This research examines this relationship in a northern forest area through both backscatter modeling and synthetic aperture radar (SAR) data analysis. The field measurements were used to estimate stand biomass from forest weight tables. The backscatter model described by Sun et al. was modified to simulate the backscattering coefficients with respect to stand biomass. The average number of trees per square meter or radar resolution cell, and the average tree height or diameter breast height (dbh) in the forest stand are the driving parameters of the model. The rest of the soil surface, orientation, and size distributions of leaves and branches, remain unchanged in the simulations.

Sun, Guo-Qing↗

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

Mission planning for Shuttle Imaging Radar-C (SIR-C) with a real-time interactive planning software

The Shuttle Imaging Radar-C (SIR-C) mission will operate from the payload bay of the space shuttle for 8 days, gathering Synthetic Aperture Radar (SAR) data over specific sites on the Earth. The short duration of the mission and the requirement for realtime planning offer challenges in mission planning and in the design of the Planning and Analysis Subsystem (PAS). The PAS generates shuttle ephemerides and mission planning data and provides an interactive real-time tool for quick mission replanning. It offers a multi-user and multiprocessing environment, and it is able to keep multiple versions of the mission timeline data while maintaining data integrity and security. Its flexible design allows one software to provide different menu options based on the user's operational function, and makes it easy to tailor the software for other Earth orbiting missions.

Potts, Su K.↗