Designing an improved soil moisture index in the near-infrared and shortwave plane

Drought index plays an important role in the assessment of drought severity as one sensitive indicator of land drought status. A simple and accurate method of expressing ground drought from remote sensing data is in urgent. Firstly, a brand-new frame has been developed by coordinate system transformation, with (x´, y´) expressing (soil water content, vegetation coverage), which made the meaning more clearly. Secondly, a new drought index - the modified Shortwave Infrared Perpendicular Water Stress Index (MSPSI) has been proposed, with additive of vegetation fraction f, (expressed as a distance from LAI contour to soil baseline) as a vegetation coverage adjusting factor, which makes ground drought status with vegetation coverage variance be considered as belonging to the new coordinate system. To evaluate the new index, the correlation analysis between the in-situ observation data from the meteorological sites and simulated values from MOD09A1 has been performed on a regional scale. We found them to be in good agreement. To further confirm that the drought index is feasible with higher precision than original drought indices (DIs), comparison experiment has been done.