Downscaling advanced microwave scanning radiometer 2 surface soil moisture using normalized multi-band drought index and leaf area index

Soil moisture is one of the most significant variables for various applications in meteorology, climatology, hydrology, and ecology. To monitor surface soil moisture (SSM) for large scale, Advanced Microwave Scanning Radiometer 2 (AMSR2) provides SSM data with a spatial resolution of 10 km and 25 km. Experiments from previous studies have revealed that SSM can be possibly functionalized by normalized multi-band drought index (NMDI) and leaf area index (LAI). Since NMDI and LAI are both acquired from the Moderate Resolution Imaging Spectroradiometer (MODIS) data, with resolutions of 0.5 km and 1 km respectively, a downscaling method by incorporating AMSR2 and MODIS data is therefore expected to generate SSM data with a finer resolution of 1 km. The main objective of this study is to formulate relationships between AMSR2 SSM and MODIS-derived NMDI and LAI. The study area is located in Central America, and we mainly focus on the dry season, which extends from January to April. The period of acquisition for image data of AMSR2 and MODIS is from January to February, 2014. The study was conducted by first generating a transformation function based on the observations each day, and the results confirmed the validity of the method for AMSR2 SSM downscaling. Furthermore, the method is expected to develop the analysis for the rainy season in order to finalize the method, and is also expected to be transferable to other regions to obtain the SSM data in finer scale.