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  • 1
    Publication Date: 2011-08-24
    Description: A technique is presented to steer the antenna beam to the zero-Doppler line for a spacecraft platform which operates in a non-zero roll attitude. The purposes of employing this attitude steering technique are reduction of the Doppler centroid error caused by the variation in target elevation; reduction of the Doppler centroid bound; and reduction of the Doppler drift. It is shown that a fixed attitude sequence can be easily accommodated in the radar command sequence to achieve nearly zero-Doppler steering. Implementation of this technique improves the image quality as well as simplifies the processor design.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 297-301.
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  • 2
    Publication Date: 2011-08-24
    Description: The inversion of snow parameters from passive microwave remote sensing measurements is performed with a neural network trained with a dense media multiple scattering model. A constrained iterative inversion scheme is used. Inversion of four parameters is performed from five brightness temperatures. The four parameters are: mean grain size of ice particles in snow, snow density, snow temperature, and snow depth. The five brightness temperatures are that of 19-GHz vertical polarization, 19-GHz horizontal polarization, 22-GHz vertical polarization, 37-GHz vertical polarization, and 37-GHz horizontal polarization. Based on the neural network constrained iterative inversion algorithm, synthetic mapping of the terrain is performed. The retrieval of synthetic mapping has been achieved. The incorporation of ground truth information is considered.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 2 (A93-47551 20-43); p. 1061-1063.
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  • 3
    Publication Date: 2011-08-24
    Description: The two-dimensional transfer functions of several synthetic aperture radar (SAR) focusing algorithms are derived considering the spaceborne SAR environments. The formulation includes the factors of the earth rotation and the antenna squint angles. The resultant transfer functions are explicitly expressed in terms of Doppler centroid frequency and Doppler frequency rate, which can be accurately estimated from the SAR data. Point target simulation results show that the algorithm based on the two-dimensional Fourier transformation outperforms the one-dimensional one for processing data acquired from high squint angles. The two-dimensional Fourier transformation approach appears to be a viable and simple solution for the processor design of future spaceborne SAR systems.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 355-359.
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  • 4
    Publication Date: 2011-08-24
    Description: The photographic and videographic documentation of the Earth during STS-46 mission has enhanced the Space Shuttle Earth Observations Project (SSEOP) database. Increasing numbers of scientists are using this database; many are downloading the imagery from our electronic database for specific scientific analyses. We believe the scientific returns of the Earth Observations photography from this mission will add to the global change databases and will contribute to the better understanding of our home planet. The use of manned space flights in understanding the global process first hand is a vital component in NASA's Mission to Planet Earth. The following are discussed along with photographs from the mission: landforms and geologic observation; environmental observations; meteorological/atmospheric observation; and oceanographic observations.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Geocarto (ISSN 1010-6049); 8; 3; p. 67-80
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  • 5
    Publication Date: 2011-08-24
    Description: An effort is made to measure snow reflectance under different snow and surface conditions, as well as to improve current capabilities for measuring snow reflectance over large regions of space, on the basis of visible and near-IR measurements of clean and dirty snow near Yellowknife, Canada, using both a portable spectrometer and the Landsat TM. Similar measurements were acquired over snow-covered glaciers in Alaska. Visible reflectance of the dirty snow was 30 percent lower than for cleaner snow; the shapes of the reflectance curves were also flatter for the dirty snow. The shape of the reflectance curves and the anisotropic reflectance properties are more useful in differentiating snow type and moisture type than actual reflectances.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 30; 3, Ma
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  • 6
    Publication Date: 2011-08-24
    Description: Simultaneous inversion of the three parameters was performed which included mean-grain size of ice particles in snow, snow density, and snow temperatures from five brightness temperatures. Good results for the inversion of parameters were obtained using the neural network based on the simulated data computed from the dense media radiative transfer equation that takes into account the effects of multiple scattering.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 30; 5; p. 1015-1024.
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  • 7
    Publication Date: 2011-08-24
    Description: Airborne and satellite passive microwave measurements acquired simultaneously with ground measurements of depth, density, and stratigraphy of the snow in central and northern Alaska between March 11 and 19, 1988, are reported. A good correspondence in brightness temperature (TB) trends between the aircraft and satellite data was found. An expected inverse correlation between depth hoar thickness and TB was not found to be strong. A persistent TB minimum in both the aircraft and the satellite data was detected along the northern foothills of the Brooks Range. In an area located at about 68 deg 60 min N, 149 deg 20 min W, the TB as recorded from the aircraft microwave sensor dropped by 55 K. Satellite microwave measurements showed a TB decrease of up to 45 K at approximately the same location. An examination of microwave satellite data from 1978 to 1987 revealed that similar low late-winter values were found in approximately the same locations as those observed in March 1988.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Remote Sensing of Environment (ISSN 0034-4257); 38; 161-172
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  • 8
    Publication Date: 2011-08-24
    Description: Multiple-channel microwave radiometric measurements made over Alaska at aircraft (near 90 and 183 GHz) and satellite (at 37 and 85 GHz) altitudes are used to study the effect of atmospheric absorption on the estimation of snow depth. The estimation is based on the radiative transfer calculations using an early theoretical model of Mie scattering of single-size particles. It is shown that the radiometric correction for the effect of atmospheric absorption is important even at 37 GHz for a reliable estimation of snow depth. Under a dry atmosphere and based on single-frequency radiometric measurements, the underestimation of snow depth could amount to 50 percent at 85 GHz and 20-30 percent at 37 GHz if the effect of atmospheric absorption is not taken into account. The snow depths estimated from the 90-GHz aircraft and 85-GHz satellite measurements are found to be in reasonable agreement. However, there is a discrepancy in the snow depths estimated from the 37-GHz (at both vertical and horizontal polarizations) and 85-GHz satellite measurements.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 30; 4; p. 785-792.
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  • 9
    Publication Date: 2011-08-19
    Description: The reflectance of snow-covered surfaces in Minnesota is analyzed using Landsat-5 Thematic Mapper satellite data. Calculations are performed for satellite-derived reflectances integrated over the spectral region (0.45-0.9 micron). Corrections are applied for atmospheric effects and integrated reflectances (R1) are compared over agricultural and forested areas and over a lake using TM scenes acquired in November 1984 and January 1985. Integrated reflectances are then mapped and inter- and intra-scene comparisons of surface reflectance are compared. Temporal analysis of reflectance changes can then be performed rapidly and efficiently using color-coded images. It is noted that the average R1 within the November 1984 subscene was 0.429 + or - 0.176, whereas R1 within the January 1985 subscene was 0.669 + or - 0.236.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Remote Sensing of Environment (ISSN 0034-4257); 33; 87-96
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  • 10
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    In:  Other Sources
    Publication Date: 2011-08-19
    Description: The snow parameters affecting sensor responses at different wavelengths are discussed. The effects of snow depth and background radiation on gamma ray sensors and of crystal size, contaminants, snow depth, liquid water, and surface roughness on visible and near-infrared sensors are considered. The influence of temperature, crystal size, and liquid water on thermal infrared sensors and of liquid water, crystal size, water equivalent depth, stratification, snow surface roughness, density, temperature, and soil condition on microwave sensors are addressed.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: EOS (ISSN 0096-3941); 68; 682-684
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