基于地表温度-植被指数特征空间的土壤干旱监测

以张掖市甘州区绿洲为研究区,采用5期遥感影像(2011~2015年),运用ENVI 5.2提取归一化植被指数(NDVI)、改进型土壤调节植被指数(MSAVI)和地表温度(Ts),构建Ts-NDVI和Ts-MSAVI特征空间,对比分析两种特征空间。结果表明,Ts-MSAVI特征空间的干边和湿边斜率均小于0,这与前人的研究干边斜率是负值,湿边斜率是正值的结论有所不同。Ts-NDVI和Ts-MSAVI这两种特征空间具有相同的趋势,其中2012、2013、2014年这3年两种特征空间系数r~2较高,其余2年系数r~2较低。整体而言,TsNDVI特征空间的干湿边系数相比Ts-MSAVI特征空间的干湿边系数要高,稳定性好。从TVDI旱情等级分布图上可以得出2012年的受旱面积最大,干旱和重旱面积占总面积的70.39%,2013年干旱情况最严重,重干旱面积为1 611.972 km~2,重旱面积占到总面积的43.5%,2014年干旱程度开始缓解,轻旱、干旱和重旱面积开始降低,湿润和正常面积开始增加,2015年干旱程度得到全面缓解,湿润和正常面积占到总面积的21.9%,但是干旱和重旱面积比重依然很大,说明张掖市甘州区绿洲旱情依然很严峻。

Soil Drought Monitoring Based on Land Surface Temperature-Vegetation Index Characteristic Space

Selecting oasis of Ganzhou district as the study area in Zhangye city,using ENVI 5.2 software to extact normalized difference vegetation(NDVI),modified soil adjusted vegetation index(MSAVI)and temperature of surface(Ts),Ts-NDVI feature space and Ts-MSAVI feature space were built. The two feature spaces were compared and analyzed. The results showed that the slope of dry-edge and wet-edge of Ts-MSAVI feature space was less than 0,which was not consistent with the previous research. The previous research thinked the dry-edge slope was negative and the wet edge slope was positive. The feature space of Ts-NDVI and Ts-MSAVI had the same trend. The r2 coefficient of two feature spaces was higher in the three years of 2012,2013 and 2013,and the r2 coefficient of the other two years was lower. On the whole,the wet-edge coefficient of the Ts-NDVI feature space was higher than that of the Ts-MSAVI feature space,and the stability was good. From the TV DI drought severity map,it could be concluded that the drought area was the largest in 2012,the drought and heavy drought area accounted for 70.39% of the total area. In 2013,the drought was the most serious,the area of heavy drought was 1611.972 km2,the area of heavy drought occupied 43.5% of the total area and the degree of drought in 2014 was lightened. And heavy drought area began to decrease,wet and normal area began to increase. In 2015,the degree of drought had been fully relieved, wet and normal area accounted for 21.9% of the total area. But the proportion of drought and heavy drought area was still great, indicating that the drought of Ganzhou district oasis in Zhangye city was still very serious.