Development of angle indexes for soil moisture estimation, dry matter detection and land-cover discrimination

A new index was proposed to estimate soil and vegetation moisture based on NIR (858 nm) and SWIR (1240 and 1640 nm) MODIS bands. The Shortwave Angle Slope Index (SASI) parameterizes the general shape of the NIR–SWIR part of the spectrum. We expand on the novel approach used to develop SASI by proposing another index, the Angle at NIR (ANIR). We use laboratory and simulation datasets to validate the ability of SASI to estimate soil and vegetation moisture, and evaluate the advantage for using both SASI and ANIR as land-cover discrimination tools. Our results demonstrate that SASI is a good indicator of soil and vegetation moisture. ANIR shows promise in discriminating dry plant matter from soil and quantifying the amount of dry matter irrespective of changes in soil moisture or green vegetation. When SASI is combined with ANIR, discrimination between soil, dry plant matter, and low to high amounts of green vegetation is significantly improved. Angle indexes are an exciting new way to engineer indexes that contain valuable environmental information not accessible from other indexes.