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Geoscience and Remote Sensing Symposium, 1994. IGARSS '94. Surface and Atmospheric Remote Sensing: Technologies, Data Analysis and Interpretation., International

Date 8-12 Aug 1994

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Displaying Results 1 - 25 of 197
  • Tikhonov's method of the ground-based radiometric retrieval of the ozone profile

    Page(s): 1901 - 1903 vol.4
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    The incorrect problem of the ozone height profile retrieval by ground-based measurements of the brightness temperatures in ozone spectral lines has been considered elsewhere only by using recurrence numerical methods based on properly chosen height discretization. Such an approach is mathematically inconsistent and does not allow the true retrieval possibilities to be established. The method based on the Tikhonov's theory has been worked out in order to solve the problem and numerical simulation in the lines centred at 110.8 and 142.2 GHz. The influence of measurement errors, spectral band width, and channel number in the spectral band on the retrieval of the ozone profile peculiarities at different height levels is investigated View full abstract»

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  • The generation and propagation of internal wave forms in the Strait of Gibraltar studied by ERS-1 SAR imagery and a numerical model

    Page(s): 2023 - 2025 vol.4
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    The generation and propagation of internal waves in the Strait of Gibraltar has been studied by analyzing 131 ERS-1 SAR scenes from 78 satellite overflights over this area in the period from December 1991 to February 1994. From the analysis of the ERS-1 SAR images the authors obtain the following results: (1) roughness patterns over the Camarinal Sill are visible from 1h after low tide at Gibraltar until 6h after low tide, (2) sea surface manifestations of eastward propagating internal waves are observed at distances from 23 km to 160 km from the Camarinal Sill, (3) the mean propagation speed of these internal waves is 2.0 ms -1, and (4) the spatial separation between the first two internal waves in a wave train ranges from 1.1 km inside the strait to 10 km in the Alboran Sea. The roughness pattern inside the strait are explained by a one-dimensional numerical model based on the Boussinesq equations for two water layers of different densities. The non-hydrostatic primitive shallow water equations include horizontal diffusion, bottom and interfacial friction. The model allows mean flows in both layers and is driven by a tidal flow at the open boundary. The proposed model explains the observed temporal and spatial evolution of roughness patterns inside the Strait of Gibraltar as well as the east-west asymmetry of the internal wave field View full abstract»

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  • Determination of surface features on glaciers in Alaska from ERS-1 SAR observations

    Page(s): 2398 - 2400 vol.4
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    Satellite microwave remote sensing using the European Research Satellite 1 (ERS-1) synthetic aperture radar (SAR) observations enables glaciers to be monitored worldwide. To interpret the SAR observations in the context of climate change, the relationship between radar reflectivity and snow/ice conditions has been extensively studied. In addition, the local surface roughness (microtopography) affects the radar reflectivity. In this study, USGS air photos (1 m resolution) of Columbia and Bering glaciers are used as `ground truth' to show how surface roughness affects ERS-1 radar reflectivity on sub-resolution spatial scales from 1-30 m. As expected, radar reflectivity is found to increase with increasing surface roughness. Crevasse pattern visibility is strongly dependent on illumination direction in both air photos and ERS-1 data. Crevasse patterns are most visible on ERS-1 when the crevasses are aligned normal to the radar look direction. Therefore, ERS-1 glacier monitoring data is most easily interpreted when collected from a constant look direction. Topographic effects can then be removed from snow/ice state reflectivity differences that determine the position of the firn or equilibrium line. During periods of uniform surface conditions, changes in radar reflectivity may indicate changes in surface topography due to surging View full abstract»

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  • Application of multilayer feedforward neural networks to precipitation cell-top altitude estimation

    Page(s): 1870 - 1872 vol.4
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    The use of passive 118-GHz O2 observations of rain cells for precipitation cell-top altitude estimation is demonstrated using a multilayer feedforward neural network retrieval system. Data was derived from a collection of 118-GHz rain cell observations along with estimates of the cell-top altitude obtained by optical stereoscopy. The observations were made using the millimeter wave temperature sounder (MTS) scanning spectrometer aboard the NASA ER-2 research aircraft during the Genesis of Atlantic Lows Experiment (GALE) and the Cooperative Huntsville Meteorological Experiment (COHMEX), 1986. The neural network estimator applied to MTS spectral differences between clouds and nearby clear air yielded an RMS discrepancy of 1.77 km for a combined cumulus, mature and dissipating cell set and 1.50 km for the cumulus-only set. A slight improvement in RMS discrepancy to 1.48 km was achieved by including additional MTS information on the absolute atmospheric temperature profile. Comparison of these results with a nonlinear statistical estimator shows that superior results can be obtained with the neural network retrieval system. The neural network estimator was then used to create imagery of cell-top altitudes estimated from 118-GHz CAMEX spectral imagery gathered from September through October, 1993 View full abstract»

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  • Estimation of penetration depth in a random medium using frequency decorrelation of the backscattered field

    Page(s): 2492 - 2493 vol.4
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    Frequency decorrelation of co-polarized and cross-polarized fields backscattered from a random medium is shown to be sensitive to the penetration depth and the physical parameters of the medium. The backscatter decorrelation bandwidth is shown to be inversely proportional to the penetration depth. Measurements conducted on snow under wet and dry conditions using 35 and 94 GHz scatterometers showed the sensitivity of the backscatter decorrelation bandwidth to snow wetness, particularly at 94 GHz. The backscatter decorrelation bandwidth can be used to estimate the penetration depth and water content in snow and soil media View full abstract»

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  • Small slope approximation for microwave polarimetric observation of the sea surface

    Page(s): 2421 - 2423 vol.4
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    The thermal microwave emission of the sea surface is determined mainly by the resonant ripples at near-nadir angles of observation (Irisov et al., 1987). Their amplitudes and directions of propagation are closely related to the local wind speed and direction. The anisotropy of the surface gravitational-capillary waves leads to a polarization dependence, which can be used for the remote sensing of the near-surface wind. The small-slope approximation is developed to calculate the brightness temperature of the rough ocean surface, taking into account the whole sea spectrum. The estimation of the higher order terms is made. The possibility of scanning for full polarization measurements is considered View full abstract»

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  • An inverse technique for obtaining cirrus cloud microphysical parameters using combined radar and lidar backscatter measurements

    Page(s): 1904 - 1906 vol.4
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    A technique utilizing NOAA's ground-based infrared lidar and millimeter radar measurements to infer range-resolved cirrus cloud microphysical parameters is presented. An example of cloud properties retrieved from lidar and radar backscatter data obtained during a recent cloud field experiment is shown to illustrate this retrieval technique View full abstract»

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  • ERS-1 SAR images of atmospheric gravity waves

    Page(s): 2026 - 2028 vol.4
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    ERS-1 synthetic aperture radar (SAR) images of atmospheric gravity waves are discussed. One case study is presented in detail, in which it is shown that the intense long wavelength phenomenon observed in the SAR image is an atmospheric gravity wave generated by the passage of a warm front. Atmospheric soundings and a 2-layer model indicate that the wave phenomenon could have been supported by the observed temperature inversion layer and accompanying wind shear View full abstract»

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  • Simulation of a polarimetric random noise/spread spectrum radar for subsurface probing applications

    Page(s): 2494 - 2498 vol.4
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    A novel polarimetric ultra-wideband radar system operating in the 1-2 GHz frequency range for subsurface probing applications is currently under development at the University of Nebraska. Spread spectrum and random noise signals are being explored as possible modulation waveforms. Detection and localization of buried objects is accomplished by correlating the reflected waveform with a time-delayed replica of the transmitted waveform. Broadband dual-polarized log-periodic antennas are used for transmission and reception. A unique signal processing scheme is used to obtain the target's polarimetric amplitude and phase response by frequency translation of the ultra-wideband signal by a coherent 160 MHz phase-locked source. In addition, the radar system features high depth resolution, low bandwidth-duration product, as well as simplified signal processing. In this paper, the results of computer simulations of the radar system performance covering a wide range of modulation waveforms, soil moisture conditions, depth/orientation/type of buried objects are described and compared. The simulation studies confirm the ability of the proposed radar system to image and identify various types of buried objects View full abstract»

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  • Development of a high resolution ice echo sounder for Arctic ice sheet

    Page(s): 2401 - 2402 vol.4
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    An ice core experiment conducted jointly by Japan and Canada was initiated in the Arctic region three years ago. It is now planned to drill the ice cap in the Canadian Arctic which would yield ice samples that have been in existence for hundreds of years. To start this study, ion concentrations, micro particles chemistry and the electrical properties of the ice and melt water having been measured to reconstruct paleoclimate/environment in the Arctic region. In order to support this program, a new type of echo sounder has been developed by Communications Research Laboratory (CRL). It has a capability of detecting the structure of ice beneath a surface with high resolution View full abstract»

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  • Simulation study of a microwave radiometric temperature profiler for the Antarctic atmosphere

    Page(s): 2436 - 2438 vol.4
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    Describes a simulation study carried out by applying the radiative transfer equation to a data base of radiosoundings released from the Dumont d'Urville station, located in the proximity of the Eastern coasts of Antarctica. This study was conducted for defining the specifications of the radiometric channels and for assessing an inversion algorithm for temperature profile retrieval, suitable for the foreseen operational mode of a continuously working ground based microwave radiometer observing the Antarctic atmosphere View full abstract»

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  • Two-dimensional simulations of SAR imagery of ocean waves

    Page(s): 2029 - 2031 vol.4
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    The authors have carried out two-dimensional simulations of synthetic aperture radar (SAR) imagery of ocean waves and compared these simulations with actual images obtained during the SAXON-FPN experiment. They have simulated the imagery using measured imaging parameters and three variations of SAR imaging theory which make progressively more simplifying assumptions: time-dependent, velocity-bunching, and quasi-linear. They find that under most standard SAR imaging conditions, time-dependent and velocity-bunching models are indistinguishable. However, for long integration times the velocity bunching simulations show a smearing of the spectral peak. This effect is intensified for large R/V ratios (where R is the average range distance and V is the platform velocity). The quasi-linear formulation assumes linear imaging and fails for large R/V ratios to reproduce the low frequency behavior observed in actual imagery, due to the non-linear effects. The advantage of the more simple formulations is, of course, shorter computing time. They find that time-dependent modelling takes about 100 times longer than velocity-bunching and closer to 300 times longer than quasi-linear modelling to produce results View full abstract»

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  • Design of a Ka band polarimetric radiometer

    Page(s): 2419 - 2420 vol.4
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    In order to develop the capability of conducting more efficient research flights, the University of Massachusetts secured funding from the U.S. Navy to develop a Ka band polarimetric radiometer for future airborne surveys. The design, which is discussed, uses concepts developed as part of the ESTAR thinned array radiometer project, which uses correlation techniques to image terrain at L-Band. This paper discusses the design of the authors' polarimeter and the development status. The authors also discuss other potential applications other than the measurement of wind direction View full abstract»

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  • Interpretation of parametric maps obtained by means of “blue to green ratio” over coastal waters

    Page(s): 2106 - 2108 vol.4
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    This paper deals with the effects of dissolved organic matter on the “blue to green ratio” used for pigment estimation in oceanography. A model of ocean colour by Sathyendranath et al. (1989), with slight modifications, was used to compute mean reflectance values in the blue and green channels of a radiometer. A statistical analysis was performed to find the best correlation between the logarithms of “blue to green ratio” and the logarithms of marine parameter concentrations. The results suggest that the maps retrieved by means of “blue to green ratio” should be interpreted in terms of a new parameter, that is a cumulative-concentration of pigments and dissolved organic matter View full abstract»

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  • Coastline detection from SAR images

    Page(s): 2134 - 2136 vol.4
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    Coastline detection from synthetic aperture radar (SAR) images is in the category of edge or boundary detection. But the lack of contrast between the ocean and nearby land areas makes the ordinary edge detection methods inferior. Ocean areas in SAR images, however, are much more homogeneous in grey levels than land areas and features reflecting the “roughness” of an image can be very useful for sea-land separation. This paper tests several features. Experiment results show that the best result is given by the absolute deviation from the mean extracted using a 7×7 scanning window and that a reasonable sea-land separation can be obtained from it with the help of Gibbs distribution. But misclassification occurs if a land area is homogeneous enough or a sea area is also “rough”. This is manifested in the segmentation image as surplus small “lakes” and “islands” which are eliminated if their area is below the user-specified threshold. Another problem is the blurring effect of the window operation. The consequence is found to be an over-segmentation of the land areas and so deblurring is done through an even contraction of the land areas. The detected coastlines are found, when overlaid on the original image, to coincide quite well with the true situation View full abstract»

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  • SAR image filtering with the ICM algorithm

    Page(s): 2185 - 2187 vol.4
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    The ICM (iterated conditional modes) algorithm is an iterative proposal for the improvement of maximum likelihood segmentation. It is based upon the modelling of the a priori distribution for the classes with a multiclass Potts-Strauss Markov random field (MRF) framework. In this work, a new speckle filtering procedure is proposed, based on the ICM algorithm. This is done by increasing the number of classes on the a priori distribution, considering from 16 up to 256 levels. The model for the SAR image filtering procedure includes a multiplicative noise, described by the Rayleigh distribution, under the conditions of one look and linear detection. The ICM algorithm also uses a parameter estimation technique for the underlying MRF distribution, under the pseudolikelihood framework. These estimators are obtained in a computationally feasible form. The presented results are compared with those obtained by the well-known Nagao-Matsuyama filter, which was proposed as an edge preserving filter. The ICM speckle noise filter gave substantially superior visual results on a real SAR image over all the number of considered classes, at the price of an increased computational effort, when more than sixteen classes (grey levels) are considered View full abstract»

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  • Ingara: the Australian Airborne Imaging Radar System

    Page(s): 2240 - 2242 vol.4
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    The Ingara Australian Airborne Imaging Radar System, formerly called AuSAR, is a low cost airborne imaging radar technology demonstrator currently under development at the Defence Science and Technology Organisation in Adelaide, Australia. The aims of Ingara are to evaluate airborne multimode radar technology, such as synthetic aperture radar and moving target indicator, for the Australian Defence Forces and to provide the scientific and remote sensing community access to an in-country imaging radar sensor for assessment. The Ingara system first flew in March 1993 and in June 1993 was commissioned in its base form. It currently undergoing further development and evaluation until the end of 1995 View full abstract»

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  • A new approach to quantifying abundances of materials in multispectral images

    Page(s): 2372 - 2374 vol.4
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    The authors tested a new technique for mapping abundances of materials using multispectral images which they call Foreground-Background Analysis (FBA). The method maximizes the contrast between sets of foreground and background spectra while simultaneously minimizing the variability within these sets. Spectral variability introduces errors in the fractions (abundance) of endmembers when simple mixture models (2-5 endmembers) are applied to complex natural surfaces. FBA was tested using CCD-camera measurements of known materials in the laboratory and included variations in illumination geometry. Lower abundance uncertainties were obtained using FBA than with simple mixture models View full abstract»

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  • Stereo passive remote sensing of aerosol transport and diffusion

    Page(s): 1907 - 1910 vol.4
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    Atmospheric aerosol transport and diffusion in the planetary boundary layer is characterized by high spatial and temporal variability. Point and single line of sight sensors provide insufficient information necessary for detailed evaluation of aerosol transport and diffusion models, for detecting the trajectory of hazardous material releases, or measurement of environmental pollution. A stereo passive remote sensing system providing detailed smoke screen transport and diffusion measurements during U.S. Army field tests offers extensive aerosol transport and diffusion measurement capability. The system uses digital image processing of thermal image data to provide a pixel by pixel two-dimensional map (perpendicular to the observers line of sight) of transmission or path integrated concentration. The ambient (natural) background scene in the imager field of view is the radiometric source against which transmission measurements are made. Additionally, the system uses sets of multispectral imagers in stereo pairs to obtain generalized three dimensional descriptions of smoke screen transport and diffusion. These data are used to compute the path taken by the centroid of the smoke screen and overall cloud dimensions as a function of time. Time resolution for the system is 10 Hz. The ability of the system to provide three dimensional aerosol transport and diffusion data and path integrated aerosol concentration maps with sufficient sensitivity to evaluate transport and diffusion models in detail, and to detect hazardous material trajectories and environmental pollution is demonstrated analytically and experimentally View full abstract»

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  • Multitemporal classification of Texas AVHRR imagery using harmonic components

    Page(s): 2528 - 2530 vol.4
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    Multitemporal approaches using sequential data acquired over multiple years are essential for satisfactory discrimination between many land cover classes whose signatures exhibit seasonal trends. The seasonal variability can represented by a harmonic model which is characterized by three components: frequency, phase and amplitude. The trigonometric components of the harmonic function inherently contain temporal information about changes of land use. Using the estimates which are obtained from sequential images through spectral analysis, seasonal periodicity can be incorporated into multitemporal classification. The Normalized Difference Vegetation Index (NDVI) was computed for two-day composites of the Advanced Very High Resolution Radiometer (AVHRR) imagery over Texas from 1991 to 1992. Vegetation types were then classified both with the estimated harmonic components and the average NDVI using an unsupervised segmentation approach based on a hierarchical clustering algorithm that incorporates spatial textural information. Results are compared to output from the classification of a typical image observed in each season during the two year period View full abstract»

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  • Field-of-view calibration of the Microwave Limb Sounder on the Upper Atmosphere Research Satellite

    Page(s): 2224 - 2227 vol.4
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    Describes the field-of-view (FOV) calibration of the Microwave Limb Sounder (MLS) on board NASA's Upper Atmosphere Research Satellite (UARS). Calibration data are derived from measurements and analytical models, combined with in flight data. Particular emphasis is given to pointing calibration and estimation of far sidelobe levels and radiance offsets, using both the Moon and the residual signals when the FOV is pointed high above Earth's atmosphere View full abstract»

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  • Seasonal changes observed in AVIRIS images of Jasper Ridge, California

    Page(s): 2360 - 2362 vol.4
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    The authors examined three 1992 Airborne Visible Infrared Imaging Spectrometer (AVIRIS) images of Jasper Ridge Biological Preserve (JRBP) for spectral changes associated with community type and for phenological patterns over the growing season. The images were obtained on June 2, September 4, and October 6, 1992 and were calibrated to surface reflectance. Images were analyzed with spectral mixture analysis using library endmembers representing green foliage, non-photosynthetic vegetation, and soils characteristic of the site. The images were co-registered in a Geographic Information System (GIS), along with a digital elevation model (DEM) of the Menlo Park 7.5 min. Quandrangle obtained from US Geological Service and a field-based vegetation map provided by the JRBP. Vegetation endmember fractions were used to define vegetation communities and compared to the field-based vegetation map. Because there the terrain did not have steep north and south facing slopes, adding a DEM to the analysis did not increase accuracy of the classification. Vegetation fractions can be related to patterns expected for wetlands and grasslands, and for evergreen and deciduous shrub and tree communities. After vegetation boundaries were defined using the field-based map, the authors extracted the mean vegetation spectrum and standard deviation of the spectrum for each vegetation type. Changes in AVIRIS spectra over the season were compared among communities and these spectra were compared to field-based reflectance and biochemistry measurements of foliage that were representative of each community over the same seasonal period View full abstract»

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  • On-line complex permittivity measurements for ground penetrating radar

    Page(s): 2513 - 2515 vol.4
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    One of the major problems for a subsurface radar to predict is the true target distance and maximum likely penetration depth in the media under investigation. These radar parameters can be determined from the complex permittivity of the media. Since the permittivity of the surface under examination is usually unknown, most subsurface radars are calibrated in time units only: actual subsurface distances have to be inferred from other knowledge of the soil/rock. This paper presents a technique to provide on-line, complex permittivity measurements for the ground penetrating radar, to help predict these important distance parameters. The system consists of an electrically short monopole antenna backed by a ground plane; the input impedance of the antenna is a function of the complex permittivity of the surrounding media. Using a model for the complex input impedance of the antenna, the electrical properties of the media can be determined. To test the performance of the system, measurements were taken to determine the electrical properties of air, salt water and pure water, since these properties are known accurately via Debye's formula. Measurements of the complex permittivity of sand as a function of frequency and water content, as well as the permittivity of the saline solutions are presented. This system was then integrated into a stepped frequency continuous wave ground penetrating radar. Tests using targets buried at known depths in a large sand box were used to verify the performance of the system and its limitations. Results of field trials are presented View full abstract»

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  • A comparison of several algorithms for on-board SAR raw data reduction

    Page(s): 2197 - 2199 vol.4
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    This paper shows a comparison of different SAR (synthetic aperture radar) raw data reduction algorithms as applied to E-SAR data (experimental airborne SAR) and spaceborne ERS1 data. The Block Adaptive Quantizer (BAQ) and a Fuzzy Block Adaptive Quantizer (FBAQ) were selected and analysed. In addition, different algorithms based on a BAQ, the Discrete Cosine Block Adaptive Quantizer (DCT-BAQ), the Walsh-Hadamard Block Adaptive Quantizer (WHT-BAQ) and the Block Adaptive Vector Quantizer (BAVQ) mere examined. Signal-to-distortion noise ratios (SDNR) of 11.69 dB (BAQ), 8.00 dB (FBAQ), 2.09 dB (DCT-BAQ and) and 11.94 dB (BAVQ) for E-SAR data and 8.77 dB (BAQ), 5.17 dB (DCT-BAQ) and 9.56 dB (BAVQ) for ERS1 data for a data rate of 2 bits/sample were achieved with a reduction factor of about 3 for the E-SAR data and 2.5 for ERS1 data View full abstract»

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  • Performance verification of spectral and panchromatic modules of the MOMS-02 sensor flown aboard STS-55/D2-mission

    Page(s): 2301 - 2304 vol.4
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    A second generation instrument of the MOMS (Modular Optoelectronic Multispectral/Stereo Scanner) was flown in the frame of the German D2 mission aboard Space Shuttle flight STS-55. The newly designed sensor provides multispectral coverage in 4 bands including the visible and near-infrared range. In addition, MOMS-02 is equipped with a three line along track stereo device recording for/aft and nadir panchromatic data. During the mission (April to May 1993) approximately 7 mio. km2 of data have been recorded in 7 different modes from a mean altitude of 296 km resulting in a GIFOV of 4.5×4.5 m2 in the nadir panchromatic and 13.5×13.5 m2 in the panchromatic for/aft and multispectral bands. MOMS-02 data of distinct test-sites, recorded at different conditions have been investigated on its quantitative and qualitative performance. Different algorithms are used for estimating entropy, signal to noise ratio, point spread function and interband correlation. The results are related to complementary LANDSAT TM and SPOT HRV data sets. The first impression of the raw data was quite positive as compared to the data of the pilot system MOMS-01. Recognizable image distortions could be related to electronic malfunctions and/or to lack of power, shielding and thermal (heating-up) influences. These problems are identified and will he solved for future missions by change of electronic parts and supply of a sufficient thermal environment. The entropy, SNR and PSF performances an comparable to the operational sensors. However, MOMS band 3 is slightly weaker in its performance especially in the SNR. The reason for this was found in electronic malfunctions and may also be related to the band width design that is about 10 nm narrower than the nominal (originally defined) one. Results of the correlation analysis confirm the new arrangement of the band centers and widths. An improvement in spectral dynamic of about 10-15% versus a broad banded design could be estimated View full abstract»

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