Superconducting quantum interference device (SQUID) can be used to
detect the signal of transient electromagnetic method (TEM) due to its
superiority of high sensitivity in the low frequency range. However, the
measuring direction of SQUID is hardly consistent with the normal direction
of the transmitting coil of a TEM system because of the undulating
topography in the field. In this case, the central magnetic field measured
by SQUID is only a component of the theoretical central magnetic field.
There will be larger errors if we directly use the measured central magnetic
field for geological interpretation. To solve this problem, we propose a
topographic correction method for the data of SQUID-based TEM using ground
loop. The theoretical central magnetic field of the ground loop is
calculated after the trapezoidal transmitting current wave is turned off.
Then, we use the theoretical central magnetic field of the ground loop as
the reference to correct the measured central magnetic field of SQUID-based
on the trigonometric function relation between the measuring direction of
SQUID and the topographic inclination. The experiment of SQUID-based TEM
using a ground loop was carried out in the field. The result shows that at
the measurement point with larger topographic inclination, the average
absolute error of the measured central magnetic field reduces significantly
with the proposed correction method. This method can also be applied to the
correction of complex topographic effects when using SQUID to measure three
components of magnetic field.