Abstract
This paper reports a methodology to estimate soil moisture of non-inundated paddy fields on conditions that the field data synchronously measured is not available. Two L-band synthetic aperture radar (SAR) sensor data, i.e. Japanese Earth Resources Satellite-1 (JERS-1) /SAR, and Advanced Land Observing Satellite (ALOS) /Phased Array type L-band Synthetic Aperture Radar (PALSAR), were used. First, parameters of a model used for the soil moisture estimation were calibrated. Integral Equation Method (IEM) model, theoretical model to represent surface scattering in the microwave region, has several parameters. Among those parameters, two parameters, standard deviation of surface height, and autocorrelation length, were calibrated with actual volumetric soil moisture measured in 2007, and PALSAR backscatter coefficients. Then, the calibrated IEM model was applied to estimate volumetric soil moisture in 1990s using JERS-1/SAR. Finally, the volumetric soil moisture distribution maps in different years of 1990s were produced. While it is impossible to validate the estimated volumetric soil moisture because of the absence of field measurement data, it was found that the trend of the estimated volumetric soil moisture is similar to the trend of the actual volumetric soil moisture. It is concluded that the proposed methodology is quite effective to estimate soil moisture of non-inundated paddy fields on conditions that the field data synchronously measured is not available.
