Quality Control for USDA NRCS SM–ST Network Soil Temperatures: A Method and a Dataset*

In 1991, the U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) established its Soil Moisture–Soil Temperature (SM–ST) Pilot Network consisting of 21 stations in 19 states in the contiguous United States. At each station, soil temperatures were measured at up to six different depths from 5.08 to 203.20 cm (or 2–80 in.) below the surface. Before 1997, the observations were made every 6 h, and they increased to hourly beginning in 1997. The goal of this network is to provide near–real time soil temperature and soil moisture observations in different regions across the United States for agricultural and water use management as well as for climate research. To improve the usefulness and increase the value of both the data and this network, a quality-control method for the soil temperature data was developed. The method used a soil heat diffusion model and its solution at individual sites to screen and distinguish erroneous soil temperature data and to provide their estimates. Evaluation of the quality-control method showed its accuracy and reliability, particularly when it was applied to hourly data. Application of this method to the data has yielded a high-quality, high-resolution soil temperature database from 1994 to 1999 for the network, which is accessible at the USDA National Water and Climate Center’s Web site.