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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

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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.


  • 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.


Note! Same vertical scale used for all these plots.


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


Large Temperature Difference (Dry)


Large Temperature Difference (Transition)


Large Temperature Difference (Wet)


Large Moisture Difference (Dry)


Large Moisture Difference (Transition)


Large Moisture Difference (Wet)


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.


Line is not linear fit; has 1:1 slope.


  • 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?


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