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Methodology for estimating surface soil temperature from high-frequency microwave observations

A methodology for deriving spatially averaged emitting layer temperature from high frequency microwave observations is presented. Microwave brightness temperature is a function of the emissivity and the physical temperature of the emitting soil layer, thereby possessing a strong physical basis for estimating soil temperature. Field observations have shown that maximum and minimum daily air temperatures are strongly related to midday and midnight surface soil temperature. Field measurements of surface temperature are also compared to METEOSAT thermal observations. Long term daily maximum and minimum air temperatures are used to derive data sets of daytime and nighttime surface temperatures. Results indicate that 37 GHz vertical polarization brightness temperature provides a reasonable estimate of the emitting layer soil temperature. This technique is especially useful for normalizing microwave brightness temperatures at longer wavelengths for soil moisture retrieval algorithms. It could provide a useful tool for climate modelling, land surface processes investigations, and other energy balance applications by providing consistent and independent long term estimates of daily global surface temperature.