In this article, a new index, the visible and shortwave infrared drought index (VSDI), is proposed for monitoring both soil and vegetation moisture using optical spectral bands. VSDI is defined as , where ρ represents the reflectance of shortwave infrared (SWIR) red and blue channels, respectively. VSDI is theoretically based on the difference between moisture-sensitive bands (SWIR and red) and moisture reference
band (blue), and is expected to be efficient for agricultural drought monitoring over different land-cover types during the plant-growing season. The fractional water index (FWI) derived from 49 Mesonet stations over nine climate divisions (CDs) across Oklahoma are used as ground truth data
and VSDI is compared with three other drought indices. The results show that VSDI generally presents the highest correlation with FWI among the four indices, either for whole sites or for individual CDs. The NDVI threshold method is applied to demonstrate the satisfactory performance of VSDI
over different land-cover types. A time-lag analysis is also conducted and suggests that VSDI can be used as a real-time drought indicator with a time lag of less than 8 days. The VSDI drought maps are produced and compared with the US Drought Monitor (USDM) maps. A good agreement has been
observed between the two products, and finer spatial information is also found in VSDI. In conclusion, VSDI appears to be a real-time drought indicator that is applicable over different land-cover types and is suitable for drought monitoring through the plant-growing season.
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Document Type: Research Article
Affiliations:1: Institute of Remote Sensing and GIS, Peking University, Beijing, 100871, PR China 2: School of Civil Engineering and Environmental Sciences, The University of Oklahoma, Norman, OK, 73072, USA