利用改进温度植被干旱指数反演农田表层土壤水分的研究

Surface Soil Moisture Retrieval in Crop Fields Using Improved Temperature Vegetation Dryness Index

土壤水分作为土壤的重要组成部分,是气候、农业和生态系统的关键组成要素。快速、大面积和实时地监测土壤含水量,对旱情预报、农田灌溉和作物估产有着十分重要的作用。本文主要结合Landsat 8光学影像数据对地表土壤含水量进行反演,在温度植被干旱指数(TVDI)的地表温度-植被指数特征空间基础上引入分形覆盖度,构建地表温度-分形覆盖度特征空间,从而计算得到改进温度植被干旱指数(ITVDI),采用研究区实测土壤含水量数据对计算的结果进行对比分析。为了分析TVDI和ITVDI与土壤体积含水量的关系,分别制作TVDI、ITVDI与土壤体积含水量的散点图并分析相关性。研究结果表明:在小麦拔节期内,研究区域大部分地区处于干旱状态,轻旱地区主要分布在研究区西部、北部以及中部的高植被覆盖地区;重旱地区主要分布在城市中心及部分裸露地面和小麦种植地区。TVDI和ITVDI与地表土壤含水量线性相关显著,两者均可表征研究区干旱的实际情况。但ITVDI引入分形植被覆盖度参数,在一定程度上避免干旱指数受到地表覆盖类型的限制,使得ITVDI与实测土壤含水量的相关性和反演精度都高于TVDI。因此,ITVDI能够更好地反映研究区域土壤含水量的状况,更适合高植被覆盖度地区土壤含水量反演。

Soil moisture,as an important component of soil,is a key parameter of climate,agriculture and ecosystems.The rapid,large-scale and real-time monitoring of soil moisture plays an important role in drought forecasting,farmland irrigation and crop estimation.In this study,Landsat 8 data was utilized to improve the accuracy of surface soil moisture retrieval.The feature spaces of surface temperature and vegetation index could be formed to calculate the temperature vegetation drought index(TVDI)and the improved temperature vegetation drought index(ITVDI).The measured soil moisture data obtained from the fields were used to compare the estimated soil moisture calculated from TVDI and ITVDI.The results showed that the most of study area were in drought state during the jointing stage of wheat.The light drought regions of the study area were mainly distributed in the high vegetation-covered regions of western,north and central.The heavy drought regions were mainly located in the cities,bare soils and wheat-planted regions.In order to analyze the relationship between TVDI/ITVDI and soil moisture content,the least squares method was used to produce the scatterplots of TVDI/ITVDI and soil moisture content,respectively.The TVDI and ITVDI had a significant linear relationship with surface soil moisture,respectively,presenting an actual situation of drought in the study area.In addition,the ITVDI was introduced into the fractional vegetation cover to avoid the drought index that was limited by the type of land cover.For ITVDI,the correlation coefficient and the accuracy of estimated soil moisture were slightly higher than that of TVDI.Therefore,the ITVDI could effectively reflect the soil moisture status in the study area and will be more conducive to soil moisture retrieval in the high vegetation-covered areas.