Dear All
Airborne magnetic survey practice is in the midst of a revolution.
People are
collecting gradient data by running magnetic sensors on both wingtips
and
possibly also two tail stingers with vertical separation. In fact a 1.7
million km survey in Saudi Arabia is about to be let for triaxial
magnetic
gradient surveying. Compensating the effects of the aircraft on the
gradients
is a challenge, but is largely solved.
The problem is, what do we do with the data?
Solutions so far have been:
1. Use the vertical measured gradient because (for part of the spectrum)
it's
less noisy than a calculated measured gradien (GSC).
2. Use the measured cross-line gradient to constrain the gridding of the
total field (Fugro Aurborne Surveys and Kevron).
3. Use the measured cross-line and along-line gradients (after gridding)
to
generate a diurnal-free total field grid estimate using Fourier filters
(Geometrics and Intrepid).
4. Use the measured along-line gradient (after integration) to estimate
the
shorter wavelengths of the total field, even in the presence of
micropulsation or mild magnetic storm activity (Fugro).
5. Use all three measured gradients as inputs to something like Euler
Deconvolution which requires gradients anyway (they're normally
calculated).
- (yours truly).
6. Use the measured gradients to constrain modelling. No-one in
commercial
practice to my knowledge - yet.
The measured gradients contain new information in some parts of the
spectrum,
because the calculation of gradients (by Fourier methods) includes
noise,
aliasing problems and the standard ills of the Fast Fourier Transform.
So the challenge is this: Develop a better way to use all three measured
gradients. Any ideas? I'm interested in entering into joint research
with
other parties on the topic. Might make a good NERC funding application
topic.
Any interest?
--
Alan B Reid PhD
Reid Geophysics
49 Carr Bridge Drive
Leeds LS16 7LB
UK
Phone: +(44)-113-261-0252
Fax: +(44)-113-293-0062
e-mail: mailto:[log in to unmask]
website: http://www.reid-geophys.co.uk
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