Attribute_Label: grid cell
An equivalent source method based on long-wavelength
characterization using satellite data was
used to correct for long-wavelength shifts.
We produced an aeromagnetic grid in which the wavelengths
longer than 500 km have been replaced by downward-continued
CHAMP satellite data. Steps 0 and 6 were performed by
Bob Kucks. Steps 1-4 were performed by Tiku Ravat.
Step 5 was performed by Jeff Phillips.
0. The North American 1 km merged grid was decimated to 5 km.
1. This 5 km grid was converted to a 0.05 degree grid. This
grid was low-pass filtered using a Gaussian filter with a 500 km
cutoff, then decimated to 1 degree.
2. A joint inversion of this 1 degree low-pass aeromagnetic grid
and CHAMP satellite data, with the aeromagnetic data weighted
very low, produced a stabilized downward continuation of the
3. The inverted data were interpolated to 0.05 degree and again
low-pass filtered using the same Gaussian 500 km filter to remove
4. The low-pass grid from step 1 was subtracted from the original
0.05 degree aeromagnetic grid to create a 500 km high-pass aeromagnetic
grid. This grid was added to the low-pass inverted grid from step 3
to get a corrected 0.05 degree aeromagnetic grid.
5. The corrected 0.05 aeromagnetic degree grid was projected to the
DNAG projection and regridded to 5 km. This was subtracted from the
decimated 5 km aeromagnetic grid to generate a 5 km correction grid.
A matched filter was used to remove short-wavelength artifacts
resulting from the projection and regridding process.
6. The resulting 5 km correction grid was regridded to the original
1 km grid and subtracted from the original 1 km aeromagnetic grid
to generate the final 1 km corrected aeromagnetic grid.
Ravat, D., Whaler, K.A., Pilkington, M., Sabaka, T., and
Purucker, M., 2002, Compatibility of high-altitude aeromagnetic
and satellite-altitude magnetic anomalies over Canada:
Geophysics, v. 67, p. 546-554.
Enumerated_Domain_Value_Definition: missing data