Basic study on estimation of water content using brightness changes in soil sample images caused by food coloring

Abstract

In this study, as a simple method for estimating the water content of soil samples, we calculated the rate of change in the brightness histogram due to coloring from images taken before and after coloring with food coloring and analyzed the correlation with water content. In order to evaluate the effect of ambient light at the time of shooting, we compared images taken with and without light shielding and found that the rate of change was highly dependent on ambient light. In addition, a clear negative correlation was obtained in experiments with a constant dry density between the rate of change and the water content. On the other hand, in experiments without adjusting the dry density, a minimum value appeared in the change rate as the water content increased, which may reflect relationships with water retention or permeability. These results suggest that the change rate due to coloring is closely related to the soil's dry density and permeability coefficient. This method is expected to be practical for field applications as a labor-saving and rapid method for evaluating water content.