A downscaling approach of phase transition water content using AMSR2 and MODIS products

A useful indicator to evaluate the soil freeze-thaw intensity is the amount of phase transition water content (PTWC) in soil pores. In this research, a power function relation between soil phase transition water content (PTWC) and the variation rate of land surface temperature (V_TS) was found by analyzing of ground measured soil moisture and temperature data obtained in the Tibet plateau during the winter of 2012. Then a downscaling approach combining MODIS V_Ts and AMSR2 products was employed to retrieve high resolution PTWC. The downscaled result was tested using in situ observations from the CTP-SMTMN network and found that it quite followed the trend of ground data with a RMSE of 0.0034 (m³/m³) and MAE of 0.0025 (m³/m³). The comparisons indicate that PTWC-V_TS model has combined the advantage of microwave remote sensing and optical remote sensing; it has a high precision and can generate PTWC in small scale.