The Comparison and Application of the Methods for Monitoring Farmland Drought based on NIR-Red Spectral Space

In this paper, we develop a new method called distance drought index (DDI) to monitor land surface dryness condition, which is based on an extensive analysis of spatial distribution features of soil moisture in NIR-Red spectral space. The DDI can be considered as an improvement of the model perpendicular drought index (PDI). To validate the drought indices proposed in this paper, MODIS images are used to calculate the DDI and PDI over ground measuring points in NingXia of China. The DDI and PDI are then compared to an in-situ drought index obtained from field measurements made synchronously with the satellite overpass. Results show that DDI and PDI have significant correlation with 0-20 cm averaged soil moisture. The highest correlation of R²=0.59 for the DDI and R²=0.57 for the PDI is obtained when compared with average soil moisture from 0 to 20 cm soil depth. It is evident from the results showing that the DDI has better performance than the PDI and the potential to provide a simple and real-time drought monitoring method in the remote estimation of drought phenomena.