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Hydraprobe calibration O. Merlin, J. Walker, R. Panciera, H. Meade, D. Biasioni, R. Young, L. Siriwardena, A. Western 3 rd 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 ( ε r -> SM) and imaginary ( ε i -> 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 εrεr SM HP response

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Temperature effect Effect of a 15°C increase on the measured DC εrεr εiεi Correction proposed

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Application to Y2 Temperature correction Uncorrected DCT-corrected DC

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Loss-corrected equation Seyfried et al., 2005 Function of loss tangent 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’05 Saturation

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Intrinsic limitation Moisture content (% v/v) Voltages (% v/v)

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Assumptions tan δ ~ tan δ sat T HP ~ T 0-5cm 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

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