ARM/GCIP NESOB-96 USDA-ARS Grazinglands Research Laboratory Soil Moisture Dataset 1.0 General Description The United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Grazinglands Research Laboratory Soil Moisture Dataset is one of several sub-surface datasets provided for the GEWEX Continental-Scale International Project (GCIP) Near Surface Observation Data Set (NESOB) 1996 project. This dataset contains data from one station (station 151) within the NESOB 1996 domain (100.5W to 94.5W longitude and 34N to 39N latitude) and time period (01 April 1996 through 30 September 1996). 2.0 Detailed Data Description The soil moisture data sets provided by the United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Grazinglands Research Laboratory are experimental data sets collected for specific research objectives and are not subject to and/ or may not conform to published ARS standards. These ARS data sets are accepted and used by the recipient upon the express understanding that ARS and it's employees make no warranties, expressed or implied, concerning the accuracy, completeness, reliability or suitability for any given purpose, and that ARS and it's employees shall be under no liability to any person by reason of any use made thereof. The ARS requests that the recipient of these soil moisture data sets does not distribute, publish or disseminate the data under the recipients name without full and up-front acknowledgement of ARS as the source of the data, and that the recipient acknowledges the support and role of ARS in publications that use these data. The data are from a site located on the Little Washita River watershed, which is located in southwestern Oklahoma. For more information explore the Grazinglands Research Laboratory home page at http://grl.ars.usda.gov. Soil moisture data Soil moisture measurements are made via a Campbell Scientific soil heat dissipation sensor (Model 229-L). This device is a matric potential sensor. The sensor consists of a hyperdermic needle buried within a ceramic "wick". The needle contains a heater and thermocouple. The wick is placed in the soil, and after some time has passed, the water potential of the sensor comes into equilibrium with that of the soil. An initial soil temperature is obtained with the sensor, then the sensor is subjected to a 21 s heating cycle. A delta T is then calculated from the ending and beginning temperatures. Calibration relates delta T to matric potential. Conversion of matric potential to volumetric water content is performed by relating matric potential to volumetric water content via a soil water release curve. Soil moisture is measured hourly, and is an instantaneous value. Soil moisture is measured at 5 cm, 10 cm, 15 cm, 20 cm, 25 cm, and 60 cm depths. There are three measurements taken at 5 centimeters, labelled by ARS as 5a, 5b, and 5c. These 3 sensors are located 10 cm apart in order to measure spatial variability. Station 151 is located in sandy soil. Performance of these sensors is being evaluated at present. Error bounds are not available for either the matric potential values or estimates of water content. However, it is believed that the matric potentials provided by the sensor are relatively good. Less confidence is placed in the volumetric estimates at this time, although initial results are encouraging. For more information please contact Dr. Patrick Starks, USDA-ARS, Grazinglands Research Laboratory, 7207 W. Cheyenne St., El Reno, Oklahoma, (405)-262-4316. 2.1 Detailed Format Description The USDA-ARS Soil Moisture Dataset contains eight metadata parameters and thirty-two data parameters and flags. The metadata parameters describe the date, time, network, station and location at which the data were collected. Data values are valid for the 30 minutes preceeding the time of observation. All times are UTC. The data parameters consist of quartets for each depth. Soil moisture is measured at 5 cm, 10 cm, 15 cm, 20 cm, 25 cm, and 60 cm depths. There are three measurements taken at 5 centimeters, labelled by ARS as 5a, 5b, and 5c. The measurements for 5a are in the first 5 centimeter quartet, those for 5b are in the second 5 cm quartet, and those for 5c are in the third 5 cm quartet. Table 1 below details the data parameters. The data parameters have an associated Quality Control (QC) flag. A description of the possible QC flag values is listed in Table 2. Table 1 ------- Parameters Units ---------- ----- Date of Observation UTC Time of Observation UTC Network Identifier Abbreviation of platform name Station Identifier Network Dependent Latitude Decimal degrees, South is negative Longitude Decimal degrees, West is negative Station Occurrence Unitless Station Elevation Meters Soil Volumetric Water Content Cubic meters per cubic meter Soil Matric Potential kilopascals Soil Depth centimeters (5cm, 5cm, 5cm, 10cm, 15cm, 20cm, 25cm, or 60cm) QC flag (See Table 2) Table 2 ------- QC Code Description ------- ----------- U Unchecked G Good M Normally recorded but missing D Questionable B Unlikely N Not available or Not observed. X Glitch E Estimated C Reported precipitation value exceeds 9999.99 millimeters or was negative. T Trace precipitation amount recorded. I Derived parameter can not be computed due to insufficient data. 2.2 Data Remarks None. 3.0 Quality Control Processing No QC was performed on this dataset by the University Corporation for Atmospheric Research/Joint Office for Science Support (UCAR/JOSS). 4.0 References USDA-ARS, cited 1999: Grazinglands Research Laboratory Home Page [Available online from http://grl.ars.usda.gov.]