Project Title:

Investigator(s):

08/1991 - Present

Type 1

National Science Foundation, DEB-9632854 (Text Version) and DEB-0218001 (Text Version) to Coweeta LTER.

See Project Summary Sheet 1048 and Terrestrial Gradient Sites: Characteristics (photographs) for detailed information about plot locations and physical descriptions, respectively.

X and Y tape-measurement coordinates submitted by Paige Carithers on 14 May 2001.

Current QAQC procedures are conducted monthly using SAS software to plot data and examine the ranges of soil and air temperature and soil water content. Data determined to be inaccurate are deleted.

Water Content:
Volumetric water content at the Top 0-30 cm and 30-60 cm and Bottom 0-30 cm and 30-60 cm commenced March 1999. These measurements are collected with the CS615 Water Content Reflectometer from Campbell Scientific, Inc. The sensors are installed at two locations (at the top of the original 20 by 40 m plot and at the bottom of the original 20 by 40 m plot) at two depths (0 to 30 cm and 30 to 60 cm). See attached table and maps for grid locations. On October 4, 2006 all CS615 sensors were upgraded to CS616 sensors for sites 118, 218, and 318. And on October 5, 2006 sensors were upgraded at sites 427 and 527. Prior to these automated readings, soil moisture was measured with a Tektronix 1502B Time Domain Reflectomer (TDR). For 23 months beginning 21 April 1997, a CS615 reflectometer was installed horizontally near the TDR rods at site 427 with probes at depths of 5 and 20 cm. Readings were taken to compare the CS615 with the Tektronix.

Please see Metadata #1023 for onsite comparison of TDR readings to CR10 readings (using the Campbell Scientific Model CS615 Water Content Reflectometer) for gradient site 427 from April 1997 through March 1998.

Please also reference Metadata #1023 for a laboratory comparison of TDR vs. reflectometer readings.

See attached table and maps for grid locations.

Comments:
On 27 August 1996 at 118 and on 18 September 1996 at all other sites, model 10TCRT Thermocouple Reference junction sensors were installed on CR10 dataloggers. Before that date, daily means of thermocouple observations are judged to be valid but the daily range of hourly values was exaggerated because the logger internal temperature was used for the reference junction value. The hourly departures of the thermistor observations from the daily mean were used to generate the hourly thermocouple values around its daily mean for the period up to the switch-over to the terminal board reference temperature.

On 11 February 1998, relative humidity and vapor pressure observations were terminated rather than investing in new sensors.

Data Accuracy:
Sensor and datalogger manufacturer states that both air and soil temperature measurements with thermistors have overall accuracy typically better than +/- 0.2 C and relative humidity observation accuracy is better than +/- 5 percent. Campbell states that the sum of various cumulative errors of thermocouple measurements can be between +/- 0.5 to 1.0 C. The variability due to sensor placement and exposure is greater than these errors of measurement. Degradation of the relative humidity and thermistor soil temperature sensor is the greatest source of error.

None.