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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

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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

wgamcollins@earthlink.net

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.



Mean: Depth:

T1: 16.27

T2: 16.35

T3: 16.42


Mean: Std Dev: Depth:

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: Depth:

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: Depth:

M1: 0.143

M2: 0.155

M3: 0.125


Mean: Std Dev: Depth:

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: Depth:

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 Depth:

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 Depth:

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 Depth:

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 Depth:

Dry and Wet Periods

For the Same Sensor


Best response would be Depth:alone 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 Depth:

Between Pairs of Sensors at Hole 1

Full Time Record

Possible use in quality control…


Line is not linear fit; has 1:1 slope. Depth:Ideal fit would be along this line.




Since the inter-sensor standard deviation for 1-hour change Depth: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 indicates Depth:even greater value of 1-hour change for qualitycontrol than for dry period.


  • Summary Depth:

  • 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?


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