An two-dimensional spectral space based model for Drought monitoring and its re-examination

Drought indices based on spectral space have a great potential in remote sensing drought monitoring. With the discussion of two-dimensional spectral space, we introduce a model named Distance Drought Index (DDI) as an improvement of the well recognized method Perpendicular Drought Index (PDI) for drought monitoring. By constructing the NIR-Red spectral space, we found that the scatter diagram characterized with a triangle shape in the two-dimensional space. The point distribution in the scatter diagram varies with its moisture content and vegetation conditions. The higher moisture the target possesses, the nearer it is located to the coordinate origin. Thereby, the distance between the random point and the origin point can be used as a drought monitoring indicator, where DDI is developed. Larger DDI value indicates a more severe drought condition. 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 Hui Autonomous Region of China in March, April, June and August, 2008. Finally, we come to the conclusion that DDI is an effective drought monitoring index and achieves better result than PDI.