Measuring Soil Moisture in Skeletal Soils Using a Cosmos Rover.

The presence of coarse fragments directly influences the volumetric water content of the soil. Despite this influence, current surface soil moisture sensors often do not account for the presence of coarse fragments, and little research has been done to calibrate these sensors under these conditions. This lack of coarse fragment inclusion can lead to over or underestimations of surface roughness for remote sensing validations, as well as improper land management. The cosmic-ray soil moisture observation system (COSMOS) rover is a passive, non-invasive surface soil moisture sensor with a footprint greater than 100 m giving it the potential to accurately estimate surface soil moisture in skeletal (rocky) soils. However, the COSMOS rover has yet to be validated in these soils. The goal of this study was to quantify the impact of coarse fragments on surface soil moisture measurements taken on a skeletal soil. Several COSMOS rover surveys to measure volumetric water content were taken, as well as electrical conductivity surveys to estimate the spatial distribution of coarse fragments in the soil. The COSMOS estimates were then compared to ground truth water content measurements. As expected, there was a decrease in water content as the percent volume of coarse fragment increased. COSMOS measurements responded to both changes in coarse fragment volume and the ground-truth volumetric water content. We were able to accurately measure the volumetric water content of a skeletal soil without an additional correction factor.