Campbell Scientific CS616 and CS625 Water Content Reflectometers - Manual (Page 37)

CS616 and CS625 Water Content Reflectometers
if there are free ions in soil solution, polar solid constituents such as organic
matter or some clay, or conductive mineral constituents.
The general calibration equation for the CS616/CS625 will provide good
results with attenuation equivalent to about 0.5 dS m -1 bulk electrical
conductivity. Between 0.5 dS m -1 and 5 dS m -1 , the CS616/CS625 will
continue to give a well-behaved response to changes in water content but a soil
specific calibration is required. See Section 8, Water Content Reflectomer
User-Calibration, for calibration information.
7.6 Temperature Dependence and Correction
The error in measured volumetric water content caused by the temperature
dependence of the CS616/CS625 is shown in FIGURE 7-4. The magnitude of
the temperature sensitivity changes with water content. Laboratory
measurements were performed at various water contents and over the
temperature range from 10°C to 40°C to derive a temperature correction for
probe output period. The following equation can be used to correct the
CS616/CS625 output period, τ
uncorrected
, to 20°C knowing the soil temperature,
T
soil
. See sample datalogger programs. The temperature correction assumes
that both the water content and temperature do not vary over the length of the
probes rods.
( ) ( )
( )
τ τ τ τ
corrected soil uncorrected soil uncorrected uncorrected
T T = + − − + 20 0526 0 052 0 00136 2 * . . * . *
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