The effect of soil moisture upon soil albedo

The relation between albedo and water potential was determined for three soils and compared to the corresponding relation between albedo and water content. Homogeneous disks of soil were equilibrated at different water potentials, and their albedo measured outdoors, using a pyranometer with a 28° view angle. The albedo varied with water potential over a small range, different for each soil, but apparently related to texture. Outside that range, the albedo was essentially constant. This abrupt change in albedo with water potential does not accord with the mechanism proposed by Dolgov and Vinogradova (1973), which explains that the change in albedo results from the change in conformation of the soil water body, as the amount of water in the soil varies. However, it does support the mechanism of total internal reflectance proposed by Ångstrom (1925). Our findings suggest that the relation between albedo and water potential can be established with fewer measurements than the relation between albedo and water content.