Error analysis of airborne gamma radiation soil moisture measurements

Abstract The National Weather Service (NWS) maintains an operational airborne gamma radiation snow survey program in North Dakota, South Dakota, Minnesota, and portions of Saskatchewan to provide airborne snow water equivalent and soil moisture data to the NWS offices in the region. Measurements of the natural terrestrial gamma radiation flux near the soil surface are used to infer mean areal soil moisture. Airborne gamma radiation data are collected over a network of 300 flight lines (each approximately 6km2) in the upper Midwest and used to calculate real-time, areal soil moisture values. Ground-based soil moisture data collected along 155 calibration flight lines indicate that airborne soil moisture values can be calculated with a root mean square (RMS) error of 3.9% soil moisture. Approximately 80% of the error is due to airborne instrumentation sensitivity, while only 20% results from the flight line calibration using ground-based soil moisture data.