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The Oklahoma Mesonet’s Soil Temperature and Soil Moisture Networks Chris Fiebrich Manager, OK Mesonet.

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Presentation on theme: "The Oklahoma Mesonet’s Soil Temperature and Soil Moisture Networks Chris Fiebrich Manager, OK Mesonet."— Presentation transcript:

1 The Oklahoma Mesonet’s Soil Temperature and Soil Moisture Networks Chris Fiebrich Manager, OK Mesonet

2 Soil Temperature Observations  Mesonet Sites:  120 sites with 10-cm soil temperatures under bare and sod  116 sites with 5-cm soil temperatures under bare soil  113 sites with 5-cm soil temperatures under sod  112 sites with 30-cm soil temperatures under sod  Micronet Sites:  35 sites with 5, 10, 15, and 30-cm soil temperatures under sod (pre-2009); at 5, 25, and 45 cm ( since 2009).

3 Soil Temperature Sensors  Mesonet Sites  BetaTHERM sensor that uses a chip thermistor, housed in a sealed stainless steel tube filled with electronics potting material.  Calibrated using a bath of 50% water and 50% antifreeze, compared with NIST- certified Hart Scientific reference thermometer between -25 and 60°C. Every sensor must meet ±0.5°C accuracy over entire range.  Micronet Sites  Pre 2009, used same BetaTHERM sensor as Mesonet, now uses Stevens Hydra Probe.  Calibration process is evolving. For now, only verify that sensor in deionized water produces real dielectric constant around 80 and imaginary dielectric constant less than 5.

4 Soil Temperature Calibrations

5 Soil Temperature Data  Sampled every 30 seconds, averaged every 15 minutes

6 Soil Temperature Data  Good agreement between the Hydra Probe soil temperatures and the BetaTHERM thermistor measurements

7 Soil Temperature Considerations  Soil Temperature gradients can be substantial in the top ~10 cm of soil. Field technicians monitor depth using PVC guide. I personally have lower confidence in 5-cm temperatures.  Heaving occasionally occurs in winter.

8 Soil Temperature Considerations  On rare occasions, solar panel casts afternoon shadow on soil temperature plot for up to 30 minutes. In extreme instances, this shading results in an artificial, 1-2°C decrease in 5-cm soil temperature.

9 Soil Temperature QA  Soil Temperature Data  Automated tests include range, step, persistence, spatial, like-instrument, heat transfer, climate, and various adjustment tests  Manual analysis includes looking at plots of average values and cumulative differences between sensors at different depths.

10 Soil Temperatures Can Be Quite Heterogeneous  Monthly Average Soil Temperature at 5 cm, September 2008 (~5 km spacing)  Monthly Average Soil Temperature at 5 cm, September 2008 (~30 km spacing)

11 Moving on to Soil Moisture…

12 Soil Moisture Observations  Mesonet Sites:  108 sites with 5-cm soil moisture  106 sites with 25-cm soil moisture  80 sites with 60-cm soil moisture  33 sites with 75-cm soil moisture (this depth is being decommissioned as sensors fail)  Micronet Sites:  35 sites with 5, 25, 45-cm soil moisture

13 Soil Moisture Sensors  Mesonet Sites  Campbell Scientific 229-L Water Matric Potential Sensor: heat dissipation sensor that utilizes a thermocouple as a temperature sensor and a resistor as a heating element, both housed within a hypodermic needle embedded within a porous ceramic matrix.  Calibrated by immersing in distilled water for 5 days to achieve wet point and then sealing in desiccant for 5 days to achieve dry point. After the sensors are deployed in the field, individual coefficients are updated if the soil creates drier or wetter situations than observed in the lab.  Micronet Sites  Stevens Hydra Probe  Tested by placing in deionized water and ensuring that real dielectric constant is ~80 and imaginary dielectric constant is less than 5.

14 229-L Mesonet Calibration Certificate

15 Soil Moisture Data: August 2008  Top plot: Fractional Water Index as measured by 229-L at Mesonet Site Apache, OK. “Saturates”  Bottom plot: Volumetric Water as measured by Hydra Probe at ARS Site A152 (approximately 7 km away). “Pulsates” Red: 5 cm depth Green: 25 cm depth Black: 45/60 cm depth Blue: Rainfall (in)

16 Soil Moisture Quality Assurance  Soil Moisture Data  After installation, all data is manually flagged for 21 days to allow the soil to heal (sometimes longer during extended drought periods)  Range tests, calibration tests, step tests, frozen soil tests, preferential flow tests  Manual inspection and monthly analysis (max and min for each depth), time series analysis

17 Oklahoma Mesonet Soil Moisture Data, Monthly Analysis  Monthly Total Rainfall (mm), December 2008  Maximum Fractional Water Index at 5 cm, December 2008

18 ARS Soil Moisture Data, Monthly Analysis  Monthly Total Rainfall (mm), September 2008  Maximum Volumetric Water at 5 cm, September 2008

19 Hydra Probe Sensitivity to Soil Classification

20 Maintenance Metrics 229-LHydra Probe # of Sensors Used # of Failures301 (13 years of use)38 (3 years of use) Common ProblemsMice, gophers, deer, and other cable damage; lightning, ceramic hardening Cable damage, lightning

21 Common Symptoms of Failed Hydra Probes  Sensor voltages report out of range: either zero or -9.23*10 18  Derived volumetric water values have large oscillations within range, but are not associated with rain or other phenomena

22 Hydra Probe Wiring Problems/Errors  Mistakes in wiring can cause depths to be “crossed”  Wiring errors can cause soil moisture to decrease during rain events and increase during dry-down periods  A good verification of the wiring is to plot the derived soil temperatures from the sensor

23 229-L Considerations  Need valid thermocouple reference junction temperature (noise in reference temperature can cause noise in the 229-L measurement) because we use separate multiplexer  Resistive heater can fail or the device supplying power to the resistive heater can fail

24 Measurement Representativeness  Soil Temperatures:  Vegetation differences can cause soil temperatures to vary > 15°C between neighboring stations  Some soil types are more likely to have erosion problems, cracking, and heaving  Soil Moisture  Vegetation differences, slope, and soil type can make the difference between a dry and a moist soil  If you thought rainfall was heterogeneous between neighboring stations, wait until you look at soil moisture data!

25  Samples collected from 12 locations within 20 m of the site

26 Journal of Oceanic and Atmospheric Technology 2008


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