A Study On Microwave Drought Indices Using AMSR-E Data And Aplication In Hebei Province

Based on the AMSR-E data, this study attempts to find the simplest and best drought index for identifying drought areas.In the first part of this article it represents drought monitoring remote sensing methods using thermal infrared,visible-near infrared and microwave data at home and broad. As the microwave is sensitive to moisture, the drought monitoring method of microwave remote sensing has a better future.First using anomaly vegetation index and vegetation condition index to monitoring summer drought condition in Hebei province in 1997, the error of drought area in 1997 between remote sensing method and statistics from agriculture department is 11.3%. Drought monitoring methods using NDVI needs a long series of data cumulation, and they are liable to be affected by weather condition and cannot be used where is bare while the microwave method can overcome these disadvantages.Due to the shape of the Earth, AMSR-E records active scene measurements at equal intervals of 10 km (5 km for the 89 GHz channels) along the scan. Based on the brightness temperature observations of AMSR-E in 2005 and 2006, composite successive three days observations for a full coverage map and the simplest way is to compute the three day average if there are more than one observation for the specific pixel. Totally 43 candidate drought indices were calculated from the AMSR-E brightness temperature data using 10 wave band. Assuming that the NASA AMSR-E soil moisture data obtained from complicated retrieval algorithms are the best currently available soil drought indicator, the computed index with the best correlation with the SM data should the best drought index and we find 8 drought indices is available. As the microwave is affected by the land surface types, the drought indices would be affected also. We analyze the 8 available drought indices with the digital map of land surface types and find that drought indices 27 (TBv06.9/TBv36.5) and 29 (TBv10.7/TBv36.5) is available under most land surface types. For each of the selected three stations in Hebei province, the temporal correlations between the two drought indices and the their corresponding precipitation anomalies were computed for the two years, and then find they have a similar change in temporal variations. The spatial variations of these two drought indices and the precipitation anomaly were also compared with each other for Hebei province in March 2006 and also find that they have a similar change in spatial variations. Based on these comparisons, the selected drought indices 27 and 29 were found to be available for monitoring drought in Hebei province. These microwave drought indices are established in specific time and area, much more work needs to do to find out the drought indices' feasibility in other areas and the spatial resolution needs to be raised.