Preliminary Results from ATDD’s Soil Moisture/Temperature Testbed Soil Moisture and Soil Temperature Observations and Applications: A Joint U.S. Climate Reference Network (USCRN) – National Integrated Drought Information System (NIDIS) Workshop, Oak Ridge, TN, March 3-5, 2009 William Collins firstname.lastname@example.org USCRN
Characteristics of Oak Ridge Data From 2000 day 172 of 2007 through 0900 day 100 of 2008 Instrument Deployment— 4 holes with temperature and moisture sensors: 3 at 5 cm depth 3 at 10 cm depth 2 at 20 cm depth 1 at 50 cm depth 1 at 100 cm depth The moisture sensors are Vitel moisture instruments,measuring the dielectric constant to get water content.The water content is given in m3 water/m3.
Study Objective This study will exclusively examine the characteristics of the soil moisture and temperature data at 5 and 10 cm since only those 2 depths have 3 sensors. The use of 3 sensors at the same location has proven invaluable in the quality control of temperature and precipitation (from the 3-wire Geonor gauges) for the U. S. Climate Reference Network. This study will take a first look at that utility here.
Statistics for Full Time Period by Individual Hole and Depth: • Mean Temperature by Sensor • Inter-sensor Temperature Differences • Distributions (0.2 C bins) • Means • Standard Deviations • (Only a few typical examples are shown.)
Mean: T1: 16.27 T2: 16.35 T3: 16.42
Mean: Std Dev: T2-T1: -0.083 T2-T1: 0.212 T3-T1: -0.260 T3-T1: 1.038 T3-T2: -0.177 T3-T2: 0.875 Mean: T1: 16.51 T2: 16.42 T3: 16.25
Mean: Std Dev: T2-T1: -0.216 T2-T1: 0.671 T3-T1: -0.296 T3-T1: 0.840 T3-T2: -0.079 T3-T2: 0.648 Mean: T1: 16.67 T2: 16.46 T3: 16.38
Mean: M1: 0.143 M2: 0.155 M3: 0.125
Mean: Std Dev: M2-M1: 0.046 M2-M1: 0.012 M3-M1: -0.001 M3-M1: 0.020 M3-M2: -0.047 M3-M2: 0.012 Mean: M1: 0.088 M2: 0.134 M3: 0.087
Mean: Std Dev: M2-M1: -0.032 M2-M1: 0.041 M3-M1: -0.062 M3-M1: 0.049 M3-M2: -0.029 M3-M2: 0.046 Mean: M1: 0.187 M2: 0.155 M3: 0.126
Comparison of Moisture for 3 Co-located Sensors The moisture during the period of record begins dryand ends wet. The data were divided as follows: Dry period: 2000 day 172 2007 to 2400 day 295 2007 Wet period: 0100 day 329 2007 to 0900 day 100 2008 Transition period: data in between The following plots show a comparison of the moisture at 5 and 10 cm depth, individually for each sensor and hole for a selected time period spanning dry to wet.
Comparison of Average Moisture At 4 Holes Individually at 5 and 10 cm Depth Selected Time Period (Dry to Wet) Note! Without quality control, the best estimate of the moisture should be the average of the 3 sensor values. The following plots have the 3 sensor values averaged, and in addition, they are smoothed in time with values (0.25, 0.50, 0.25).
Examples of Large Inter-Sensor Differences Lower Limits for Example Choices (8 s): Moisture (m3water/m3soil): 5 cm – 0.192 10 cm – 0.184 Temperature (C): 5 cm – 6.10 10 cm – 5.44
Comparison of Mean Moisture for Dry and Wet Periods For the Same Sensor
Best response would bealone line of slope 1:1, with vertical displacementand sensors from samehole grouped together. Line has slope 1:1
Comparison of 1-Hour Changes in Moisture Between Pairs of Sensors at Hole 1 Full Time Record Possible use in quality control…
Line is not linear fit; has 1:1 slope.Ideal fit would be along this line.
Comparison of Moisture Standard Deviations— • Inter-sensor differences versus Inter-sensor 1-hour change differences • Individually for Dry and Wet Periods • Implications for Quality Control
Since the inter-sensor standard deviation for 1-hour change becomes smaller as the inter-sensor standard deviation becomessmaller, the inter-sensor 1-hour change provides independentinformation for the quality control of soil moisture.
Steeper slope of line for wet period indicateseven greater value of 1-hour change for qualitycontrol than for dry period.
Summary • Preliminary comparison was made between the 3 co-located soil temperature and moisture sensors from nearly 300 days of data fromfour holes at Oak Ridge, TN. • The inter-sensor differences show wide differences in the performanceof individual sensors. Also, there are significant differences betweenthe mean values of moisture at the 4 holes at 5 and 10 cm depths. • The results have implications for quality control for both temperatureand moisture— • The use of 3 sensors is invaluable for error and value determination. • Sensor value and change in time are both useful for qc. • Individual sensor characteristics, if developed, might be valuable. • Question for research: Can differences in individual sensor characteristics be linked to calibration, installation, or other factors?