Inversion of soil moisture content based on UAV thermal infrared image
XU Honggang, CHEN Zhen, CHENG Qian, LI Peng, FAN Yongshen*
Farmland Irrigation Research Institute of Chinese Academy of Agricultural Sciences, Henan Key Laboratory of Water-saving Agriculture, Xinxiang, Henan 453000, China
Abstract：This study takes summer maize in different growth periods as the research object. The accuracy and inversion methods of the UAV thermal infrared inversion of soil moisture content in summer maize fields were discussed. The visible light and thermal infrared images of the test area were acquired by UAV. The canopy mask was extracted from the visible light image and superimposed on the thermal infrared image to extract the corn canopy temperature. The change trend of the canopy temperature and its correlation with the leaf area index(LAI)were analyzed. Finally, a new index(DTL)was constructed by using the inverse number of atmospheric temperature difference and leaf area index, and the accuracy of retrieving soil water content by canopy atmospheric temperature difference or the DTL index was discussed. The experimental results showed that using visible light image to obtain the canopy mask and superposed with thermal infrared image to extract the maize canopy thermal infrared could effectively improve the accuracy of canopy temperature extraction. In the same period, canopy temperature decreases with the increase of soil moisture content(regardless of marginal effect). Summer maize LAI can represent canopy temperature to a certain extent. Comparing the data of the four periods, it is found that the inversion effect of canopy air temperature difference is better after irrigation(for example, R2 was 0.614 6 and 0.463 7). Compared with canopy air temperature difference, the DTL index inversion can improve the accuracy of soil moisture retrieval. For example, R2 was improved from 0.614 6 and 0.463 7 to 0.661 6 and 0.485 0 at depth of 0-20 cm. This study is a new attempt to retrieve the soil moisture content of summer maize field by thermal infrared.
