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  • 1
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    Assessment of VAS soundings in the analysis of a preconvective environment (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The ability of geosynchronous satellite soundings to analyze a preconvective environment is studied. VAS data of temperature, dewpoint, equivalent potential temperature, precipitation, and lifted index from the central U.S. on July 13, 1981 are derived with 30 km resolution at three hour intervals. It is observed that the VAS retrievals identify mesoscale regions with convective instability, and significant spatial gradients and temporal changes in the thermal and moisture fields are detected. The presence of small clouds degrades the VAS data; however, the study reveals that VAS soundings produce high-resolution spatial and temporal measurements of potential thunderstorm regions.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 114; 62-87
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Delineating mid- and low-level water vapor patterns in pre-convective environments using VAS moisture channels (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Infrared and visible imagery from VAS are used to delineate mid- and lower-tropospheric moisture fields for a variety of severe storm cases in the southern and central United States. The ability of sequences of images to isolate areas of large negative vertical moisture gradients and apparent convective instability prior to the onset of convective storms is assessed. A variety of image combination procedures are used to deduce the stability fields which are then compared with the available radiosonde data. The results for several severe storm cases indicate that VAS can detect mid- and low-level mesoscale water vapor fields as distinct radiometric signals. The VAS imagery shows a strong tendency for thunderstorms to develop along the edges of bands of midlevel dryness as they overtake either preexisting or developing low-level moisture maxima. Image sequences depict the speed with which deep moist and dry layers can develop and move.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 112; 2178-219
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Use of the VAS for analysis of a prethunderstorm environment (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The information content of the VAS radiances can be converted to meteorological parameters useful for analyzing a severe weather environment. The method by which the VAS variances are converted to vertical profiles of temperature, dewpoints, and equivalent potential temperature involves a basic regression technique using the most local radiosonde data available for establishing a correlation matrix. The results indicate that mesoscale features apparent within images of the radiances can be converted to usable temperature and moisture fields using regression when surface temperature and dewpoint observations are included within the total data base. In addition, results indicate that surface data are very important for better defining lower tropospheric structure that the VAS radiances alone cannot properly resolve. Analyses of these retrievals distinctly show mesoscale structure in the temperature and moisture fields derived with VAS radiances collected every 3 hours, and 0000 GMT. The retrievals capture the moisture structure. More important, convective instability is clearly detected immediately before the onset of convection. The results indicate that the VAS is capable of providing valuable mesoscale information suitable for analyzing a preconvective environment that is generally clear.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: VISSR Atmospheric Sounder (VAS) Res. Rev.; p 9
    Format: text
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  • 4
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    Diagnosing convective instability using VAS data (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The utility of combining visible and various infrared images from the VAS to produce a forecasting tool, that can be available on a near real time basis, to predict severe weather development is shown. Areas where dry air in the midtroposphere overlays substantial moisture at low levels are used to diagnose mesoscale regions that have the potential for being convectively unstable before the onset of severe convection. Specifically, 6.7 micron water vapor imagery, used for isolating regions of substantial midlevel dryness, are combined with images of low level clouds or with split-window low level moisture images to delineate regions that have the potential for convective instability. In areas where scattered low level clouds are present, computer generated, color image combinations are used to isolate those warm, low level clouds that are in potential convectively unstable environments from clouds that exist under a deeply moist atmosphere. In clear regions, the split window technique is used for delineating areas of substantial boundary layer moisture. These images are again computer overlayed by the midlevel dryness to produce a color coded image of potential convective instability.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: VISSR Atmospheric Sounder (VAS) Res. Rev.; p 7
    Format: text
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  • 5
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    The impact of conventional surface data upon VAS regression retrievals in the lower troposphere (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Surface temperature and dewpoint reports are added to the infrared radiances from the VISSR Atmospheric Sounder (VAS) in order to improve the retrieval of temperature and moisture profiles in the lower troposphere. The conventional (airways) surface data are combined with the twelve VAS channels as additional predictors in a ridge regression retrieval scheme, with the aim of using all available data to make high resolution space-time interpolations of the radiosonde network. For one day of VAS observations, retrievals using only VAS radiances are compared with retrievals using VAS radiances plus surface data. Temperature retrieval accuracy evaluated at coincident radiosonde sites shows a significant impact within the boundary layer. Dewpoint retrieval accuracy shows a broader improvement within the lowest tropospheric layers. The most dramatic impact of surface data is observed in the improved relative spatial and temporal continuity of low-level fields retrieved over the Midwestern United States. Previously announced in STAR as N83-27522
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate and Applied Meteorology (ISSN 0733-3021); 22; 1853-187
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    VISSR atmospheric sounder /VAS/ simulation experiment for a severe storm environment (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: (Previously announced in STAR as N82-19774)
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: Monthly Weather Review; 110; Mar. 198
    Format: text
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  • 7
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    Assessment of VAS soundings in the analysis of a preconvective environment (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Retrievals from the VISSR Atmospheric Sounder (VAS) are combined with conventional data to assess the impact of geosynchronous satellite soundings upon the analysis of a preconvective environment. VAS retrievals of temperature, dewpoint, equivalent potential temperature, precipitable water, and lifted index are derived with 60 km resolution at 3 hour intervals. When VAS fields are combined with analyses from conventional data sources, mesoscale regions with convective instability are more clearly delineated prior to the rapid development of the thunderstorms. The retrievals differentiate isolated areas in which air extends throughout the lower troposphere from those regions where moisture is confined to a thin layer near the Earth's surface. The analyses of the VAS retrievals identify significant spatial gradients and temporal changes in the thermal and moisture fields, especially in the regions between radiosonde observations.
    Keywords: GEOPHYSICS
    Type: NASA-TM-86205 , NAS 1.15:86205 , REPT-85B0292
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    A description of the NSSL cases used for a simulated VAS retrieval study (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A documentation of eight National Severe Storm Laboratory severe storm cases, which serve as a basis for a simulated VISSR Atmospheric Sounder retrieval study, is presented in this paper. Six of the selected cases provide a control data set to complete the statistical information needed for retrieval techniques based upon the use of regression matrices. The other two cases are to be used in the actual retrieval experiments. The selection was based upon the presence of moisture gradients in the analysis region, the availability of satellite images at the selected time periods, and the extent of cloud cover within the observing network.
    Keywords: GEOPHYSICS
    Type: NASA-TM-82023
    Format: application/pdf
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  • 9
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    VISSR Atmospheric Sounder (VAS) simulation experiment for a severe storm environment (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Radiance fields were simulated for prethunderstorm environments in Oklahoma to demonstrate three points: (1) significant moisture gradients can be seen directly in images of the VISSIR Atmospheric Sounder (VAS) channels; (2) temperature and moisture profiles can be retrieved from VAS radiances with sufficient accuracy to be useful for mesoscale analysis of a severe storm environment; and (3) the quality of VAS mesoscale soundings improves with conditioning by local weather statistics. The results represent the optimum retrievability of mesoscale information from VAS radiance without the use of ancillary data. The simulations suggest that VAS data will yield the best soundings when a human being classifies the scene, picks relatively clear areas for retrieval, and applies a "local" statistical data base to resolve the ambiguities of satellite observations in favor of the most probable atmospheric structure.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: NASA-TM-83822
    Format: application/pdf
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  • 10
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    Assessment of the first radiances received from the VSSR Atmospheric Sounder (VAS) instrument (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The first orderly, calibrated radiances from the VAS-D instrument on the GOES-4 satellite are examined for: image quality, radiometric precision, radiation transfer verification at clear air radiosonde sites, regression retrieval accuracy, and mesoscale analysis features. Postlaunch problems involving calibration and data processing irregularities of scientific or operational significance are included. The radiances provide good visual and relative radiometric data for empirically conditioned retrievals of mesoscale temperature and moisture fields in clear air.
    Keywords: GEOPHYSICS
    Type: NASA-TM-83827
    Format: application/pdf
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