The Comparison of FY-3A/VIRR and TERRA/MODIS Data for Drought Monitoring
2017, 32 (7):
Drought is the key factor to restrict the development of agriculture and animal husbandry in northern Tibet. Temperature Vegetation Drought Index (TVDI) is one of the commonly used remote sensing methods for monitoring drought, which couples surface temperature (Ts) and vegetation index (VI ). The TERRA/MODIS L1B, MODIS-LST, FY/VIRR L1B and FY/VIRR-LST, at 1 km spatial resolution, are used for the monitoring and analysis. The monitoring period is from 25 July to 4 August 2015. The space of VI-Ts for the whole study area is typically triangular, from which a linear regression analysis is conducted to get the equations of the dry and wet line. TVDI for northern Tibet is extracted. Then, the measured soil moisture data and cumulative total precipitation data in the same period are used to verify the accuracy of TVDI to monitor drought by comparing TVDIE (E represents EVI) and TVDIN (N represents NDVI). The result shows that noise and number of pixels effect monitoring precision, and the precision is better after removing the noise. Small number of fitting pixels will lower their correlation with the equations of the dry and wet line, which affect the accuracy of drought monitoring. There is a significant linear correlation between TVDI and measured soil moisture (P < 0.05), and the coefficients between MODIS-TVDIE, MODIS-TVDIN, FY/VIRR-TVDIE, FY/VIRR-TVDIN and measured soil moisture were 0.611, 0.581, 0.420 and 0.386 respectively. Correlation between MODIS-TVDI and measured soil moisture is higher than that between FY/VIRR-TVDI and measured soil moisture. The correlation between TVDIE and measured soil moisture is also higher than that of TVDIN and measured soil moisture. The coefficients between MODIS-TVDIE, MODIS-TVDIN, FY/VIRR-TVDIE, FY/VIRR-TVDIN and cumulative total precipitation were 0.370, 0.336, 0.275 and 0.171 respectively (P < 0.05). The correlations are consistent with the correlations between TVDI and measured soil moisture. The result suggests that the TVDI based on MODIS and FY/VIRR data are both feasible for drought monitoring in the study area, and TVDIE is better than TVDIN to monitor drought. The monitoring precision of MODIS-TVDI is higher than that of FY/VIRR-TVDI, but FY/VIRR data is also a reliable product for monitoring drought.
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