COSMOS: An In Situ Soil Moisture Observational Network At Intermediate Spatial Scales.

The recently developed cosmic-ray method for measuring soil moisture over a horizontal footprint of hectometers and the depth of decimeters is currently being implemented in the COsmic-ray Soil Moisture Observing System (COSMOS). Currently 50 probes are operational around the continental US and Hawaii, with future expansion consisting of a network with 500 probes. The probe measures cosmic-ray fast neutrons that are generated within air and soil and are moderated mainly by hydrogen atoms in soil water, and emitted to the atmosphere where they form a well-mixed reservoir of neutrons whose density is inversely correlated with soil moisture. The novel soil moisture datasets at this intermediate scale are useful for calibrating and validating existing climate and hydrological models as well as soil moisture data retrieved from satellite remote sensing. Here we present a general update on the project status, current data available to the scientific community, and future project directions. In addition, we will present some numerical modeling results from the neutron transport code MCNPx. Specifically, we will address the effects of varying soil moisture and soil chemistry on average neutron counts with the objective of defining a set of calibration functions.