Impact of Rapidly Growing Vegetation On COSMOS Measurements.

Soil moisture affects the amount and variability of precipitation and determines the occurrence of flooding through its control on the amount of rainwater that infiltrates into the soil. A new remote sensing satellite is now producing global maps of soil moisture at the 40 km scale to complement scattered point measurements and improve our knowledge of the current soil moisture state. However, a gap still exists in soil moisture information at the 1 km or field scale, the scale at which agricultural management occurs. In this presentation we will investigate the use of new cosmic-ray soil moisture sensors to produce the critical 1 km scale soil moisture measurements needed for this long-term vision. Our central hypothesis is that water contained within the tissue of vegetation will affect the measurements of this new soil moisture sensor. Our rationale for this project is that the effect of the water content of the vegetation canopy on the soil moisture measurement must be taken into account before accurate measurements of soil moisture can be obtained. One of the first of these cosmic-ray sensors has been installed through the COSMOS project at a heavily-instrumented outdoor laboratory managed by our research group. The sensor was surrounded by a growing crop of maize during the summer of 2011. We made regular measurements of soil moisture and vegetation water content. We will present how the relationship between the sensor output and soil moisture changed as the growing season progressed. Once the effect of vegetation canopy water on cosmic-ray soil moisture measurements has been determined, a planned 500-sensor network of these sensors may be able to provide critical soil moisture information across the United States and aid in the validation of satellite measurements.