Geology Reference
In-Depth Information
True resistivity
Ω
m
100
1
10
1000
EM 31 induction number = 0.5
100
EM 34 induction number = 0.5
EM 31
induction number = 0.1
10
EM 34
induction number = 0.1
1
10
100
1000
True conductivity mS m
-1
Figure 8.10
Plots of indicated against true ground conductivity for the
EM34-3 (all separations, dashed curves) and the 'long' EM31 (dotted
curves), based on Geonics Technical Notes 6 and 8. For both instruments,
the deviation from true conductivity is smaller when they are used with the
dipoles horizontal (H-curves, i.e. loops vertical) than when they are vertical
(V-curves, i.e. loops horizontal). The vertical dipole curve for the EM31
and horizontal dipole curve for the EM34-3 almost coincide. The EM31-SH
curve is not shown but deviates least, since it operates, under all conditions,
at little more than half the induction number of the EM31. The logarithmic
scales tend to disguise the magnitudes of the deviations.
