Abstract: In recent years,Temperature Vegetation Drought Index (TVDI) has been widely applied in monitoring drought with remote sensing. However,the influence of topographical factors on the index accuracy is not considered in the traditional TVDI. In this paper,a case study on the TVDI modification in Shaanxi Province was carried out so as to reduce the influence of topographical factors on the monitoring accuracy of TVDI,the DEM data were used to make an elevation correction of surface temperature,the NDVI was replaced by the Normalized Difference Mountain Vegetation Index (NDMVI) so as to reduce the influence of topographical fluctuation on vegetation index,and the new TVDI indexes were constructed. Four kinds of TVDI indices were constructed by using the surface temperature and NDMVI and NDVI before and after correction,and the relationships among the 4 indexes and soil moisture and precipitation were analyzed so as to compare the accuracy of monitoring agriculture drought. The results showed that the elevation and terrain fluctuation affected significantly the TVDI precision in monitoring drought,and the TVDI after the correction of surface temperature and vegetation was better for monitoring drought compared with the traditional TVDI,its correlation coefficient with relative soil humidity was increased from 0.342 to 0.711,and it could be used to accurately reflect the change of precipitation. The results revealed that the modified TVDI could be used to effectively reflect the soil water conditions,and could also be used to accurately monitor agricultural drought.

Key words: drought monitoring, topographic correction, TVDI, NDMVI, modification, Shaanxi