Assessment of NDVI and NDWI spectral indices using MODIS time series analysis and development of a new spectral index based on MODIS shortwave infrared bands

We put forward a new spectral index, Shortwave Angle Normalized Index (SANI), based on the NIR and SWIR MODIS bands. The new index parameterizes the general shape of this part of the spectrum by measuring the angle at SWIR1 and the normalized index between NIR and SWIR2. Preliminary results show that it performs well in tracking moisture and discriminating between soil, vegetation and dry vegetation. We use Time Series Analysis to explore the temporal evolution of NDVI, NDWI and SANI and climatic data for the years 2000 to 2005. Our analyses show that SANI is synchronized with precipitation in grasslands but not in irrigated cropland where irrigation is a major source of moisture. NDVI does not follow precipitation closely in either of the two regions. SANI also shows an overall negative trend, which corresponds to the overall positive trend in precipitation levels from 2000 to 2005. Thus, this index seems to be a powerful tool for uncovering subtle sources of variability, interannual trends in environmental variables and dynamic relationships between soil and plant variables.

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