Microwave sensors on Skylab collected data as part of the Earth Resources Experiment Package (EREP). An investigation was designed to obtain field observations of soil moisture content for comparison with data from Skylab. The 21‐cm radiometer has been shown to be highly responsive to the moisture content of the upper 2.5‐cm layer of soil. A composite relationship between the radiometric temperature and soil moisture content has been determined from five data sets obtained over Kansas and Texas. This relationship, having a correlation index of −0.96, has been used as a basis for calculating the soil moisture content of large areas across the United States.
A formula for estimating the evapotranspiration rate from temperature and relative humidity data is given. Results of some tests of the accuracy of the equation indicate that it is better than other equations based on a similar number of variables. The accuracy was not as good as equations requiring more variables for their utilization, however. It was found from an investigation of the amount of water required for crop production that average yields of corn, soybeans and wheat were obtained when the total precipitation during the growing season averaged 72% of the maximum evapotranspiration. This average actual evapotranspiration rate may be more appropriate than potential evapotranspiration for some general purposes such as assessing the water resources of undeveloped countries, or determining the aridity indices in climatic studies.
In preparing for future L-band passive microwave soil moisture satellite missions, investigators have employed ground, aircraft and satellite sensors. Of the satellite sensors, there has been only one instrument that provides any heritage at L-band: the Skylab S-194 instrument that operated in the 1970s. Here a dataset from the S-194 was located and recovered. Data from these Skylab missions have been analysed and reported in a few applications, however, these studies utilized limited validation and exploited only a portion of the data collected. In this investigation we explored the use of products from climate model reanalysis projects as ancillary or alternative validation data. Analyses showed that the reanalysis outputs were not accurate and would be of limited value. Tests using a radiative transfer based soil moisture retrieval algorithm matched the observations available for validation. These results support the use of this approach as a tool in understanding a wider range of vegetation condition effects on soil moisture retrieval.
Dual-Doppler radar data were analyzed for three different times during the life cycle of a severe thunderstorm. The thunderstorm developed a double vortex inside as a tornado was generated beneath the cloud.The organized kinematic and precipitation internal structure of the thunderstorm support a theoreticaldouble-vortex thunderstorm model that was developed earlier. The horizontal perturbation and relativewinds, vertical winds, horizontal divergence and vorticity are compared for the three different times ofmeasurement. The measurements and theoretical model provide new explanations of the severe thunderstorm and the relationship of associated tornadoes.
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