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The land surface microwave emissivity at 10 GHz over Australia is estimated using brightness temperature measurements from the Tropical Rainfall Measuring Mission Microwave Imager. The emissivity characteristics of dominant surface classes and its seasonality are analysed and reported, which is a vital information to study soil moisture and effect of precipitation. However, the deeper penetration of microwaves into dry soil media leads to the departure of effective radiating temperature from the skin (surface) temperature due to diurnal heating of the dry arid surfaces. The emissivity retrieved from satellite observations thus exhibits diurnal variability associated with the disparity between effective radiating temperature and skin temperature. The manuscript projects the utility of this diurnal variability to understand the thermo-physical properties of the subsurface.