Measurement of water content at bare soil surface with infrared thermal imaging technology

In this study, infrared thermal imaging technology is adopted to measure water content at soil surface by cali-brating the linear relationship between water content at soil surface and interfacial temperature difference of a given soil type. The method is suitable for the soil surface which is unsaturated. First of all, the theoretical considerations of the new method are introduced. Infrared thermal imaging technology can directly measure soil surface temperature and the difference between the soil surface temperature and the ambient temperature is named as the interfacial temperature difference. For over-saturated soils, at a certain environmental condition, the interfacial temperature difference of a given soil type is a constant value. For unsaturated soils, there is a linear relationship between water content at soil surface and interfacial temperature difference. For the tested four types of soils with different textures, all the values of R2 for the linear fitting are greater than 0.9. Then, the water content at soil surface can be calculated based on the surface temperature measured by the infrared camera. Moreover, in this study, a cracked soil sample with an uneven surface water content field is tested for validating the feasibility of the proposed method. There is a good match between the data measured by the proposed method and traditional oven drying. It indicates that the proposed method can be used to obtain the distribution of water content on the soil surface and may provide a new idea for the future research on the spatio-temporal evolution characteristics of in-situ soil under climate change and provide a new choice for leakage detection of structures like dams, tunnels, etc.