Campbell Scientific TDR100 Time Domain Reflectometry Systems - Manual (Page 36)

TDR100
water content = 18%
water content = 37%
FIGURE 8-3. Waveforms collected in a sandy loam using CS610 probe
with RG8 connecting cable. Volumetric water content values are 10,
18, 26, 30 and 37%. Solution electrical conductivity is 10.2 dS m
-1
.
The combined effect of long cable runs and high soil electrical conductivity
must be considered when TDR measurements are taken.
9. Algorithm Description and Parameter Adjustment
9.1 Introduction
This section presents a general description of the algorithms in the TDR100 for
electrical conductivity and water content measurement.
9.2 Algorithm for Calculation of TDR Probe Rod Apparent
Length
9.2.1 Algorithm Description
Equation [2] of Section 7 shows the relationship between apparent dielectric
constant,
K
a , and apparent TDR probe rod length, L
a . The equation is
repeated here for convenience. L is the actual rod length.
K
L
L a
a =
[2]
K
a is calculated using equation [2] then converted to volumetric water content
using empirical equations such as equations [3] and [4] of Section 7.
30