Each of the observation sites measures soil temperatures at up to 8 different depths from surface to 80 inches below the surface. Before 1995, observations at each site were made in every 6 hours. The measurement frequency increased to hourly since 1995. Soil temperature data were transmitted using meteor communication technology to the central data control at the USDA National Water and Climate Center, where they were made available on the Internet.
To improve the value of the data and the network, a quality control procedure on the observation data is required. This procedure will examine the data and filter random errors. It will improve the quality and thus, applicability of the data of this unique soil temperature observation network.
In this presentation, we will describe a soil temperature quality control (QC) method developed for the SM/ST Network. This method applied heat transfer and energy balance principles. It calculated a set of theoretical reference soil temperatures at given time and depth for locations at each of the sites. This set of temperatures includes the average, maximum, and minimum temperatures. In this calculation, soil thermal properties at individual sites derived from observed site-specific soil profiles were used.
These reference temperatures were applied in conjunction with the surface air temperature observation to examine observed soil temperatures and temperature variation range at various depths. A flag system was developed to separate potentially erroneous soil temperature data and indicate the nature of potential errors. A set of calculation methods was developed to estimate soil temperatures and replace the flagged data that were confirmed to be erroneous. Both the flag system and the estimation methods will be discussed in the presentation.
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