Soil moisture content estimation using active infrared thermography technique: An exploratory laboratory study

Abstract

Small scale laboratory testing was conducted to estimate the moisture content of sandy soils using a non-destructive and non-contact infrared thermography (IRT) technique. Tests were carried out by applying an external halogen lamp light (400 ​W). In this study, the aim was to explore the feasibility of using IRT to assess the moisture content of sandy soil. The laboratory tests conducted included evaluating soil physical characteristics such as grain size distribution. Soil samples were prepared with five different moisture content percentages. The soil moisture content was then evaluated using two different techniques. The first is the gravimetric oven dry method as per (ASTM D2216, 2019). The second is the IRT Technique. During the second procedure the samples were photographed with an ICI IR-Pad 640 ​P Series camera, which had an image resolution of 640 ​× ​480 pixels and a capture rate of 6 frames/minute. The emissivity correction used was 0.98. The soil surface temperature was captured in both the heating and the cooling phase, with the temperature taken from a specific thermal image area called the region of interest (ROI). Moisture content measurements were taken for each sample using the oven-drying method at the initial stage, and at the end of the heating and cooling phases. The procedure produced a good correlation between moisture content and surface temperature in the heating phase. The soil moisture content and surface temperatures were inversely related and formed a linear line with a high degree of accuracy (r2 ​= ​0.9138). A validation check is done at the end for a sample with random moisture content using the IRT technique where the moisture content was found to be 6.81%, this value was confirmed with the oven dry procedure. It was found that IRT successfully estimated soil moisture content.