hydraprobe calibration o. merlin, j. walker, r. panciera, h. meade, d. biasioni, r. young, l....
TRANSCRIPT
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Hydraprobe calibration
O. Merlin, J. Walker, R. Panciera, H. Meade, D. Biasioni, R. Young,
L. Siriwardena, A. Western
3rd NAFE Workshop 17-18 Sept. 2007
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Objective
Derive/validate a calibration equation for:
• Roving HP measurements (HDAS)
• Continuous HP measurements (stations)
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Hydraprobe (HP)
Dielectric sensor at 50MHz of 0-5cm soil
Measure real (εr -> SM) and
imaginary (εi -> SAL) dielectric constant (DC) + Temperature
Output is 4 voltages:
V1, V2, V3 (DC) and V4 (temperature)
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Calibration data sets
NAFE’06 field measurements:
1 volumetric sample at 5 points in each of the 6 farms, every sampling day + 1 (or more) HP measurement
Complementary laboratory experiments– Goulburn soils (Lab’05, Daniele Biasioni)– Yanco soils (Lab’06, Hanna Meade)– Goulburn soils (Temp’06, Rocco Panciera)
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Calibration approaches
Comparison HP / Grav measurements
Two different approaches:– Polynomial interpolation– General (multi-data) equations
Account for a range of:– Moisture conditions (linearity)– Soil types (from sand to clay)– Other parameters (temperature, ?)
HP
Grav
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Calibration
1. Direct comparison between HP response (silt) and grav measurements
2. Estimate temperature effect on DC measurements
3. Test different calibration approaches:• Polynomial fit• Multi-data equations (from measured DC)
4. Apply calibration equations to • Roving measurements• Station-based HP data
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Manufacturer-supplied algo versus grav measurements
Saturation of the predicted SM + soil-dependent
Linear behaviour of the real DC
εr
SM
HP response
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Temperature effect
Effect of a 15°C increase on the measured DC
εrεi
Correction proposed
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Application to Y2
Temperature correction
Uncorrected DC T-corrected DC
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Loss-corrected equation
Seyfried et al., 2005
Function of loss tangent r
i
tan
Real DC
Grav
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Comparison of calibration approaches
General equation (Seyfried et al., 2005)
Loss-corrected equation(Seyfried et al., 2005)
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Polynomial fit
NAFE’05Saturation
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Intrinsic limitation
Moisture content (% v/v)
Vol
tage
s (%
v/v
)
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Assumptions
tan δ ~ tan δsat THP ~ T0-5cm
Applicability of the loss-corrected equation and temperature correction to roving measurements
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Illustration
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Conclusions
Seyfrield et al.’s equation validated with NAFE’06 data set
Developed a temperature correction for the measured real DC from lab data
Calibration applied to the NAFE data sets (about 17000 measurements for NAFE’06)
The application of this calib to all the new sites (20) in the Murrumbidgee is underway