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Evaluation of the OhmMapper Instrument for Soil Moisture Measurement

^a Hydrological Sciences Branch, Lab. for Hydrospheric Processes, NASA's Goddard Space Flight Center, Greenbelt, MD 20771
^b Dep. of Civil and Environmental Engineering, Univ. of Melbourne, Parkville, Victoria 3010, Australia

View larger version (13K): [in a new window]   Fig. 1. Calibration of (a) 6-cm Theta Probe and (b) 15-cm TDR against thermogravimetric soil moisture measurements as compared to 1:1 line.

View larger version (24K): [in a new window]   Fig. 2. Schematic of the OhmMapper instrument.

View larger version (25K): [in a new window]   Fig. 3. Scatter plots of apparent resistivity and soil moisture measurements with fitted relationship, for the moisture measurement depth yielding the greatest coefficient of determination for the given OhmMapper configuration of dipole cable and tow-link lengths. Nominal 1-m dipole cable length with (a) nominal 0.25-m tow-link length against 15-cm point measurements; (b) nominal 0.5-m tow-link length against 30-cm point measurements; (c) nominal 1-m tow-link length against 60-cm point measurements; and (d) nominal 2-m tow-link length against 70-cm point measurements.

View larger version (25K): [in a new window]   Fig. 4. As for Fig. 3 but nominal 2.5-m dipole cable length with (a) nominal 0.25-m tow-link length against 15-cm point measurements; (b) nominal 0.5-m tow-link length against 60-cm point measurements; (c) nominal 1-m tow-link length against 60-cm point measurements; and (d) nominal 2-m tow-link length against 45-cm point measurements.

View larger version (23K): [in a new window]   Fig. 5. As for Fig. 3 but nominal 5-m dipole cable length with (a) nominal 0.5-m tow-link length against 30-cm point measurements; (b) nominal 1-m tow-link length against 70-cm point measurements; (c) nominal 2-m tow-link length against 70-cm point measurements; and (d) nominal 4-m tow-link length against 70-cm point measurements.

View larger version (19K): [in a new window]   Fig. 6. Comparison of 60-cm point soil moisture measurements (symbols) with the inferred OhmMapper soil moisture (continuous line and symbol) from the 2.5-m dipole cable length and 1-m tow-link length configuration; the different symbols correspond to the different dates for which measurements were made.