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  • Other Sources  (33)
  • EARTH RESOURCES AND REMOTE SENSING  (21)
  • SPACECRAFT INSTRUMENTATION  (12)
  • 2005-2009
  • 1990-1994  (33)
  • 1955-1959
  • 1
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    GPS tracking of TOPEX/POSEIDON: Results and implications (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A reduced dynamic filtering strategy that exploits the unique geometric strength of the Global Positioning System (GPS) to minimize the effects of force model errors has yielded orbit solutions for TOPEX/POSEIDON which appear accurate to better than 3 cm (1 sigma) in the radial component. Reduction of model error also reduces the geographic correlation of the orbit error. With a traditional dynamic approach, GPS yields radial orbit accuracies of 4-5 cm, comparable to the accuracy delivered by satellite laser ranging and the Doppler orbitography and radio positioning integrated by satellite (DORIS) tracking system. A portion of the dynamic orbit error is in the Joint Gravity Model-2 (JGM-2); GPS data from TOPEX/POSEIDON can readily reveal that error and have been used to improve the gravity model.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; C12; p. 24,449-24,464
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  • 2
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    Precision orbit determination for TOPEX/POSEIDON (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The TOPEX/POSEIDON mission objective requires that the radial position of the spacecraft be determined with an accuracy better than 13 cm RMS (root mean square). This stringent requirement is an order of magnitude below the accuracy achieved for any altimeter mission prior to the definition of the TOPEX/POSEIDON mission. To satislfy this objective, the TOPEX Precision Orbit determination (POD) Team was established as a joint effort between the NASA Goddard Space Flight Center and the University of Texas at Austin, with collaboration from the University of Colorado and the Jet Propulsion Laboratory. During the prelaunch development and the post launch verification phases, the POD team improved, calibrated, and validated the precision orbit determination computer software systems. The accomplishments include (1) increased accuracy of the gravity and surface force models and (2) improved peformance of both laser ranging and Doppler tracking systems. The result of these efforts led to orbit accuracies for TOPEX/POSEIDON which are significantly better than the original mission requirement. Tests based on data fits, covariance analysis, and orbit comparisons indicate that the radial component of the TOPEX/POSEIDON spacecraft is determined, relative to the Earth's mass center, with an root mean square (RMS) error in the range of 3 to 4 cm RMS. This orbit accuracy, together with the near continuous dual-frequency altimetry from this mission, provides the means to determine the ocean's dynamic topography with an unprecedented accuracy.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; C12; p. 24,383-24,404
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  • 3
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    Covariance of biophysical data with digital topograpic and land use maps over the FIFE site (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This paper discusses the biophysical stratification of the FIFE site, implementation of the stratification utilizing geographic information system methods, and validation of the stratification with respect to field measurements of biomass, Bowen ratio, soil moisture, and the greenness vegetation index (GVI) derived from TM satellite data. Maps of burning and topographic position were significantly associated with variation in GVI, biomass, and Bowen ratio. The stratified design did not significantly alter the estimated site-wide means for surface climate parameters but accounted for between 25 and 45 percent of the sample variance depending on the variable.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; D17; p. 19,009-19,021.
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  • 4
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    Polarimetric and multifrequency SAR signatures of wet snow (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: C-, L-, and P-band polarimetric signatures of wet snow surfaces have been analyzed, based on airborne synthetic aperture radar (AIRSAR) surveys of an Alpine test site. The importance of surface roughness is evident in the C- and L-band signatures, whereas the diffuse scattering contribution by internal inhomogeneities in the snowpack increases from the C- to the P-band at incidence angles below 50 deg due to increasing penetration.
    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. 1658-1660.
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  • 5
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    Estimating chlorophyll content and bathymetry of Lake Tahoe using AVIRIS data (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Data on chlorophyll content and bathymetry of Lake Tahoe obtained on August 9, 1990 by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) are compared to concurrent in situ surface and in-water measurements. Measured parameters included profiles of percent transmission of monochromatic light, stimulated chlorophyll fluorescence, photosynthetically available radiation, spectral upwelling and downwelling irradiance, and upwelling radiance. Several analyses were performed illustrating the utility of the AVIRIS over a dark water scene. Image-derived chlorophyll concentration compared extremely well with that measured with bottle samples. A bathymetry map of the shallow parts of the lake was constructed which compares favorably with published lake soundings.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Remote Sensing of Environment (ISSN 0034-4257); 44; 2-3; p. 217-230.
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  • 6
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    Opportunities in the commercial uses of remote sensing and GIS technologies - An overview of NASA's Visiting Investigator Program at Stennis Space Center (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Visiting Investigator Program (VIP) developed at NASA-Stennis' Science and Technology Laboratory (STL) allows U.S. industry to use the specialized resources of STL in the fields of remote sensing and GIS, with a view to the development of new commercial processes and improved services. Attention is given to the novel agreement mechanisms developed by NASA to implement VIP. These agreements encompass a memorandum of understanding, a technical exchange agreement, a sponsored-transfer agreement, a proprietary work agreement, and a joint endeavor agreement.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: PE&RS - Photogrammetric Engineering and Remote Sensing (ISSN 0099-1112); 59; 6; p. 935-939.
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  • 7
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    Inversion of snow parameters by neural network with iterative inversion (1992)
    In:  Other Sources
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    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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  • 8
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    Inversion of parameters for semiarid regions by a neural network (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Microwave brightness temperatures obtained from a passive radiative transfer model are inverted through use of a neural network. The model is applicable to semiarid regions and produces dual-polarized brightness temperatures for 6.6-, 10.7-, and 37-GHz frequencies. A range of temperatures is generated by varying three geophysical parameters over acceptable ranges: soil moisture, vegetation moisture, and soil temperature. A multilayered perceptron (MLP) neural network is trained with a subset of the generated temperatures, and the remaining temperatures are inverted using a backpropagation method. Several synthetic terrains are devised and inverted by the network under local constraints. All the inversions show good agreement with the original geophysical parameters, falling within 5 percent of the actual value of the parameter range.
    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. 1075-1077.
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  • 9
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    Imaging solar flares in hard X-rays using Fourier telescopes (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The sun emits hard X-rays (above 10 keV) during solar flares. Imaging hard X-ray sources on the sun with spatial resolutions on the order of 1-5 arcsec and integration times of 1 sec will provide greater insight into the energy release processes during a solar flare. In these events, tremendous amounts of energy stored in the solar magnetic field are rapidly released leading to emission across the electromagnetic spectrum. Two Fourier telescope designs, a spatial modulation collimator and a rotating modulation collimator, were developed to image the full sun in hard X-rays (10-100 keV) in an end-to-end simulation. Emission profiles were derived for two hard X-ray solar flare models taken from the current solar theoretical literature and used as brightness distributions for the telescope simulations. Both our telescope models, tailored to image solar sources, were found to perform equally well, thus offering the designer significant flexibility in developing systems for space-based platforms. Given sufficient sensitive areas, Fourier telescopes are promising concepts for imaging solar hard X-rays.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: In: EUV, X-ray, and gamma-ray instrumentation for astronomy III; Proceedings of the Meeting, San Diego, CA, July 22-24, 1992 (A93-29476 10-35); p. 433-449.
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  • 10
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    The GPS flight experiment on TOPEX/POSEIDEN (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The precision orbit determination (POD) experiment on TOPEX/POSEIDON using the Global Positioning System (GPS) is yielding concrete results. Orbit consistency and accuracy tests indicate that GPS is routinely providing satellite altitude with an accuracy of better than 3 cm. Here we review the GPS experiment, its basic concepts, POD techniques and key results, and discuss the possible cost and performance benefits that may flow to future missions.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 19; p. 2171-2174
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