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  • Other Sources  (45)
  • METEOROLOGY AND CLIMATOLOGY  (18)
  • Spacecraft Design, Testing and Performance  (14)
  • SPACE RADIATION  (13)
  • 1
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    Comparison of monthly rain rates derived from GPI and SSM/I using probability distribution functions (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Three years of monthly rain rates over 5 deg x 5 deg latitude-longitude boxes have been calculated for oceanic regions 50 deg N-50 deg S from measurements taken by the Special Sensor Microwave/Imager on board the Defense Meteorological Satellite Program satellites using the technique developed by Wilheit et al. (1987, 1991). The annual and seasonal zonal-mean rain rates are larger than Jaeger's (1983) climatological estimates but are smaller than those estimated from the GOES precipitation index (GPI) for the same period. Regional comparison with the GPI showed that these rain rates are smaller in the north Indian Ocean and in the southern extratropics where the GPI is known to overestimate. The differences are also dominated by a jump at 170 deg W in the GPI rain rates across the mid-Pacific Ocean. This jump is attributed to the fusion of different satellite measurements in producing the GPI.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Applied Meteorology (ISSN 0894-8763); 32; 2; p. 323-334.
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  • 2
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    Wind field model-based estimation of Seasat scatterometer winds (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A model-based approach to estimating near-surface wind fields over the ocean from Seasat scatterometer (SASS) measurements is presented. The approach is a direct assimilation technique in which wind field model parameters are estimated directly from the scatterometer measurements of the radar backscatter of the ocean's surface using maximum likelihood principles. The wind field estimate is then computed from the estimated model parameters. The wind field model used in this approach is based on geostrophic approximation and on simplistic assumptions about the wind field vorticity and divergence but includes ageostrophic winds. Nine days of SASS data were processed to obtain unique wind estimates. Comparisons in performance to the traditional two-step (point-wise wind retrieval followed by ambiguity removal) wind estimate method and the model-based method are provided using both simulated radar backscatter measurements and actual SASS measurements. In the latter case the results are compared to wind fields determined using subjective ambiguity removal. While the traditional approach results in missing measurements and reduced effective swath width due to fore/aft beam cell coregistration problems, the model-based approach uses all available measurements to increase the effective swath width and to reduce data gaps. The results reveal that the model-based wind estimates have accuracy comparable to traditionally estimated winds with less 'noise' in the directional estimates, particularly at low wind speeds.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; C8; p. 14,651-14,668.
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  • 3
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    Retrieval of monthly rainfall indices from microwave radiometric measurements using probability distribution functions (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An algorithm for the estimation of monthly rain totals for 5 deg cells over the ocean from histograms of SSM/I brightness temperatures has been developed. There are three novel features to this algorithm. First, it uses knowledge of the form of the rainfall intensity probability density function to augment the measurements. Second, a linear combination of the 19.35 and 22.235 GHz channels has been employed to reduce the impact of variability of water vapor. Third, an objective technique has been developed to estimate the rain layer thickness from the 19.35- and 22.235-GHz brightness temperature histograms. Comparison with climatologies and the GATE radar observations suggest that the estimates are reasonable in spite of not having a beam-filling correction. By-products of the retrievals indicate that the SSM/I instrument noise level and calibration stability are quite good.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Atmospheric and Oceanic Technology (ISSN 0739-0572); 8; 118-136
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  • 4
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    Probability distribution of wind retrieval error for the NASA scatterometer (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The NASA scatterometer (NSCAT) is a spaceborne scatterometer scheduled to be deployed in the mid-1990s. An analysis of the wind retrieval error distribution for wind estimates based on backscatter measurements made by the NSCAT instrument is presented. The results are based on an end-to-end simulation of the scatterometer instrument and data processing. In general, the distribution of the wind speed error, when normalized, is independent of the true wind speed and direction. The wind speed error can be characterized by a normal distribution. The wind direction error is independent of the true wind speed, but depends on the true wind direction. Details for wind vectors with true wind speeds from 3 m/s to 33 m/s and true wind directions from 0 to 360 deg are presented.
    Keywords: METEOROLOGY AND CLIMATOLOGY
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  • 5
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    Validation of Nimbus-7 cloud and SMMR data (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The relationship between cloud amount, water content (WC), and liquid water content (LWC) is studied. Nimbus-7 cloud data and LWC and WC data derived from the SMMR for July 1979 are analyzed and compared. The SMMR sea surface temperature (SST) data are also compared to Air Force SST data. The comparisons reveal that Nimbus-7 cloud data and the SMMR WC and LWC data correlate well, and there is also good agreement between the SMMR SST and the Air Force data. The data demonstrate that there is a relation between the WC, LWC, and cloud amount data.
    Keywords: METEOROLOGY AND CLIMATOLOGY
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  • 6
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    An analysis of the threshold method for measuring area-average rainfall (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Experimental evidence shows that the area-average rain rate and the fractional area covered by rain rate exceeding a fixed threshold are highly correlated; that is, are highly linearly related. A precise theoretical explanation of this fact is given. The explanation is based on the observation that rain rate has a mixed distribution, one that is a mixture of a discrete distribution and a continuous distribution. Under a homogeneity assumption, the slope of the linear relationship depends only on the continuous part of the distribution and as such is found to be markedly immune to parameter changes. This is illustrated by certain slope surfaces obtained from three specific distributions. The threshold level can be chosen in an optimal way by minimizing a certain distance function defined over the threshold range. In general, the threshold level should be not too far from the mean rain rate conditional on rain. The so-called threshold method advocates measuring rainfall from fractional area exploiting the observed linear relationship of the later with the area average rain rate. The method is potentially useful for the estimation of rainfall from space via satellites.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Applied Meteorology (ISSN 0894-8763); 29; 3-20
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  • 7
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    Estimation of mean rain rate - Application to satellite observations (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A method for the estimation of the mean area average rain rate from dependent data is developed and applied to the GARP Atlantic Tropical Experiment data. The method consists of fitting a mixed distribution, containing an atom at zero, by minimum chi-square in combination with certain time-space sampling designs. In modeling the continuous component of the mixed distribution, it is shown that the lognormal distribution provides a very close fit for the nonzero area average rainrates. A comparison with the gamma distribution shows that the lognormal distribution is a better choice as expressed by the minimum chi-square criterion. Some of the time-space sampling designs correspond to satellite sampling. The results indicate that a satellite visiting an area of about 350 x 350 sq km in the tropics approximately every 10 hours over a period can provide a rather close estimate for the mean area average rain rate.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 1965-197
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  • 8
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    Preliminary evaluation of the FGGE special effort for data enhancement (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Man-computer Interactive Data Access System (McIDAS) terminals were utilized for data evaluation, quality assessment, and satellite data enhancement.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Modeling and Simulation Facility: Res. Rev., 1980 - 1981; p 52-60
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  • 9
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    Interactive processing of SEASAT scatterometer data (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The Man-computer Interactive Data Access System (McIDAS), adapted for the interactive processing of satellite-derived temperature soundings and cloud-track winds for the FGGE Special Effort, was adapted for the processing and evaluation of SEASAT data. The implementation of the McIDAS SEASAT processing system required (1) extensive modifications to the data base structure to store and display SASS winds, as well as corroborative level II data, model first guess fields and level III analyses, and (2) the development of software to dealias and analyze SASS wind vectors interactively.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Modeling and Simulation Facility: Res. Rev., 1980 - 1981; p 49-51
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  • 10
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    Mars Reconnaissance Orbiter Interplanetary Cruise Navigation (2007)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Carrying six science instruments and three engineering payloads, the Mars Reconnaissance Orbiter (MRO) is the first mission in a low Mars orbit to characterize the surface, subsurface, and atmospheric properties with unprecedented detail. After a seven-month interplanetary cruise, MRO arrived at Mars executing a 1.0 km/s Mars Orbit Insertion (MOI) maneuver. MRO achieved a 430 km periapsis altitude with the final orbit solution indicating that only 10 km was attributable to navigation prediction error. With the last interplanetary maneuver performed four months before MOI, this was a significant accomplishment. This paper describes the navigation analyses and results during the 210-day interplanetary cruise. As of August 2007 MRO has returned more than 18 Terabits of scientific data in support of the objectives set by the Mars Exploration Program (MEP). The robust and exceptional interplanetary navigation performance paved the way for a successful MRO mission.
    Keywords: Spacecraft Design, Testing and Performance
    Type: Proceedings of the 20th International Symposium on Space Flight Dynamics; NASA/CP-2007-214158
    Format: application/pdf
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