TVDI用于干旱区农业旱情监测的适宜性

Suitability of TVDI Used to Monitor Agricultural Drought in Arid Area

基于地表温度/植被指数(Ts/VI)特征空间建立的温度植被干旱指数(TVDI)受诸多因素的影响,其中一个重要的影响因素是植被指数,该指数在高、低植被覆盖时的敏感性不同,从而导致TVDI对旱情监测的准确度不同。针对这一问题,以新疆塔里木盆地北缘渭干河-库车河三角洲绿洲为研究区,选择2011年4月、8月两景TM影像,利用归一化植被指数(NDVI)和比值植被指数(RVI)分别建立Ts/VI特征空间,线性拟合特征空间的上、下边界,计算得到两种温度植被干旱指数(TVDI-NDVI、TVDI-RVI)。用TVDI与同期野外实测的土壤含水量数据进行回归分析。结果表明:(1)植被指数、地表温度、土壤水分之间有显著互动关系,以不同植被指数计算得到的两种TVDI与表层土壤水分相关性较好,均能够反映区域土壤干旱状况;(2)由于植被指数对植被探测的敏感性,在4月低植被覆盖时,TVDI-NDVI与表层土壤水分的相关性较高,为0.4299,8月高植被覆盖时,TVDI-RVI与表层土壤水分的相关性较高,达到0.5791;(3)在低植被覆盖区域,NDVI较RVI敏感,而在高植被覆盖区域,RVI敏感性较高。RVI适用于高植被覆盖时反演土壤湿度,NDVI则更适用于中、低植被覆盖时。

Vegetation index has different vegetation detection capability which could result in the different sensitivity on temperature vegetation dryness index.Therefore,two sets of image in April and August of 2011 were chosen to construct the Surface Temperature(Ts)/Vegetation Index(VI)feature space which used Normalized Difference Vegetation Index(NDVI),Ratio Vegetation Index(RVI)and LSTin the Delta Oasis of the Weigan and Kuqa Rivers in Xinjiang.In the establishment of the Ts/VI space,linear regression functions were used to approximately fit the lower and upper boundaries of the Ts/VI space so that the dry and wet edges of the space could be determined.Two Ts/VI spaces were established based on the Ts/NDVI and Ts/RVI and the difference between the two spaces were investigated.Temperature Vegetation Dryness Index(TVDI)was calculated from the Ts/NDVI and the Ts/RVI spaces.Make use of TVDI and contemporaneous field measured soil gravimetric water moistures data carrying through regress analysis and establish experienced models of TVDI to assess soil moisture.The main results were as follows:(1)It was significantly associated among VI,Tsand soil moisture.TVDI-NDVI and TVDI-RVI could be used to predict the near surface soil water moisture.(2)TVDI-NDVI had a higher correlation(0.4299)with the soil surface moisture in April(low vegetation coverage month)but TVDI-RVI had a higher correlation(0.5791)with the soil surface moisture in August(high vegetation coverage month).(3)Analyzing and comparing NDVI and RVI,it was showed that NDVI was sensitive in the low vegetation coverage and RVI was sensitive in the high vegetation coverage.The conclusion was the Ts/RVI feature space was more suitable for inversing soil moisture in high vegetation coverage and the Ts/NDVI feature space was more suitable for inversing soil moisture in low vegetation coverage.