Total field magnetic intensity, contour interval is 10 nanotesla. Tightly packed near circular contours illustrate effect of debris on or near the ground surface. The prominent north-south corrugation is in the direction of acquisition with a Cesium

1
Total field magnetic intensity, contour interval
is 10 nanotesla. Tightly packed near circular
contours illustrate effect of debris on or near
the ground surface. The prominent north-south
corrugation is in the direction of acquisition
with a Cesium vapor magnetometer. The tall axis
trends 130o east of north.
2
Decorrugated total field intensity with regional
field of about 54,000 nT removed

• Decorrugation steps Urquhart (1988)
• Apply a low pass filter to separate the grid of
  data into its short and long wavelength
  components in the acquisition direction.
• the resulting long wavelength component of the
  grid is long-wavelength filtered (low pass) in
  the direction perpendicular to the acquisition
  direction. This removes short wavelength
  components, perpendicular to acquisition, that
  result from varying heights of the sensor.
• Add the smoothed results from step two to the
  short wavelength components isolated in step one.

Urquhart, T., 1988. Decorrugation of enhanced
magnetic field maps. 58th Annual International
Meeting, SEG, Expanded Abstracts, 371372
3
Original TMI on left, decorrugated TMI on right.
Contour interval 5 nanotesla.
4
Decorrugated TMI on left, that part of the
observed field removed on right.
5
Enhanced signals from causative sources on or
near the surface. Left analytic signal of the
total magnetic intensity. Right synthetic
vertical gradient calculated by differencing the
total field intensity with an upward continuation
of 0.2 meters the zero contour is suppressed
for clarity.
6
Radially averaged power spectrum of the total
field magnetic intensity. Lines fit to symbols
indicate separation of two equivalent layers as
basis for matched bandpass filters
Decorrugated TMI.
7
Radially averaged power spectrum of the total
field magnetic intensity. Lines fit to symbols
indicate separation of two equivalent layers as
basis for matched bandpass filters.
Matched bandpass filters in the spatial
frequency domain. Triangles show bandpass for
long wavelength signal, diamonds indicate
bandpass for short wavelength signals.
8
Total field magnetic intensity separated into two
equivalent layers. Left deeper layer resulting
from applying the long wavelength bandpass filter
to total field intensity contours are 2 nT to
illustrate separation of signals from shallow
dipolar sources. Right anomalies from on or near
surface sources the zero contour is removed for
clarity. The sum of these two maps equals the
original decorrugated data.
9
Original (unfiltered) TMI Decorrugated lower
equivalent layer