Browsing by Subject "Meteorological satellites"
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Item A study of clouds using satellite radiance data in comparison with raingage network and radar observations(Texas Tech University, 1980-06) Chao, Shih-ChengThe objective of this study was to use Geostationary Operational Environmental Satellite (GOES) visible and infrared radiance data to determine cloud characteristics, including cloud population, albedo, cloud top temperature and height, as well as the changes of cloud parameters with time. Verification of the satellite-derived results was achieved by comparison with the corresponding raingage network measurements and observations by radar. Four cases, 22, 24 and 27 June and 8 July 1977, have been chosen for this study. All four occurred during the operational period of the 1977 Texas HIPLEX (High Plains Cooperative Program) field season when visible and infrared images and digital radiance data, surface and rawinsonde data, precipitation analyses from the raingage network as well as PPI and RHI radar displays were available. In the first portion of this study, visible radiance data were used to determine cloud populations, percent cloud cover and cloud albedos, while cloud top temperatures were computed from the infrared data. Cloud top heights have been determined by using the cloud top temperature and comparing with rawinsonde data obtained from the nearest station. The second portion of the study compared the results derived from satellite data with raingage network measurements and radar observations in the Texas HIPLEX area. The analysis indicated that the information derived from satellite, radar and raingage data correlated closely on the four case study days. The precipitation analyses indicated that two of the four case study days had heavy rain but the others had little or none. Synoptic, subsynoptic, and small-scale features were investigated to determine the mechanisms of precipitation. PPI radar displays from a WSR-57 radar at Midland and both digital PPI and RHI data from a M-33 radar at Snyder were used in this investigation. On 22 June a squall line, a subsynoptic feature, and on 8 July a cold front, a synoptic feature, triggered the development of a line of convective clouds which produced the observed precipitation.Item A study of the radiative and satellite-observed properties of the dew point front(Texas Tech University, 1984-08) Mickelson, Mark AlanThe dryline is a narrow zone or discontinuity across which a sharp moisture gradient exists. The nighttime progression of this discontinuity is called the dew point front, and appears to reveal itself on satellite infrared photographs as a distinct boundary. The purpose of this study is to establish that the satellite-observed feature is indeed the dew point front. Two methods have been used in proving this assumption. The first was to utilize meteorological surface network data to analyze parameters which frequently indicate the presence of the dew point front. In this study, fields of temperature, dew point temperature, mixing ratio, adiabatic equivalent potential temperature, and streamlines were chosen. The position of the dew point front from each of these analyses was then compared to the satellite-inferred position of the dew point front. These comparisons showed that fields of mixing ratio, dew point temperature, and adiabatic equivalent potential temperature align to within 40-50 km of the satellite-inferred boundary, allowing a large measure of confidence to be placed in using the satellite photograph to interpret the position of the dew point front. The second method consisted of adapting a radiative model, based on standard assumptions and theories of radiative transfer, utilizing atmospheric sounding data to calculate the longwave radiative flux leaving the top of the atmosphere on either side of the boundary. If the difference in calculated fluxes across this boundary were to match the satellite-observed differences in fluxes, there would be no doubt that the satellite boundary was indeed the dew point front. Due to the simplicity of the model and its inability to treat cloud layers, the flux differences did not match. However, statistical analysis showed that the satellite imagery enhanced the ground temperature differences across the dew point front, amplifying the boundary on the infrared photographs. Thus, a second factor exists to confirm the fact that the visual satellite boundary is indeed the dew point front.Item Determination of cloud properties from bispectral satellite measurements(Texas Tech University, 1978-08) Chi, Shwe-YiAn analysis technique is presented in this paper to determine cloud parameters from geostationary satellite data. The principal data source is visible and infrared radiance measurements from the Geostationary Operational Environmental Satellite (GOES). A brightness critical value to distinguish clouds from underlying non-cloud surfaces is determined as a primary factor to identify the cloud measurement spot. Percentage of cloud cover and number of clouds are analyzed and compared with results derived from photographic images. Through a cloud summary computer program, cloud size, maximum brightness, as well as mean and standard deviation of brightness value for every individual cloud are found, categorized, and compared in time series. Infrared radiance data are used to deteinnine the cloud top temperature, allowing cloud height to be obtained from corresponding rawinsonde data. Cloud movement is estimated by a subjective method based upon computer-generated plots of the satellite data. Comparing simultaneous visible and infrared data sets, cirrus clouds are detected as regions with high infrared radiance value and low visible radiance value. The analysis is done with all of these data sources to study the properties and patterns of clouds for a case study on 22 June 1976 in the Texas High Plains area.