I presume that is homogeneous-halfspace apparent resistivity. As long as they
didn't heavily filter it (and it is likely they did) then you can forward model
the apparent resistivity and height to get in-phase and quadrature, subtract
the host I and Q (assuming it is significant) and then invert anomalies for a
plate model. Rough, but better than nothing.
Is there an apparent depth channel? That would indicate a pseudo-layer (i.e.
phase-amplitude) resistivity model, which would be better than an
amplitude-altitude model. If there is an apparent depth, add it to the
measured altitude when you forward model the apparent resistivity to I and Q
and it will do a better job of accommodating surface layers and/or altitude
error.
I'd be interested to know if EMIT includes apparent resistivity forward
modeling in frequency domain. (Don't tell them I said this, but them
Australians don't do FDEM very well! )
Greg Hodges
On Saturday, November 21, 2020, 03:08:00 p.m. EST, S E Geoscience and
Exploration <[email protected]> wrote:
Thank you, Greg.
I should have asked that question in more simple words: I am working with a
dataset (5 frequency Hummingbird system) which contains only the calculated
apparent resistivity. Measured amplitudes (In-Phase and Quadrature) are
missing. Would that be enough to do plate (forward) modeling? I guess it is.
Perhaps it is best to contact EMIT to get an evaluation license.
Regards
On Sat, Nov 21, 2020 at 2:08 PM Greg Hodges <[email protected]> wrote:
Hi, Sergio.I'm not sure I understand the question - or the problem - so maybe
others don't either.
If you're inverting (FDEM), the input is in-phase and quadrature (normally) and
apparent conductance (conductivity-thickness product, or CTP) is a product
along with the other plate parameters.
If you're forward modeling, the conductivity is an input as part of the CTP,
and the EM response is the product, or output. From that EM we can estimate a
CTP (and then assign a thickness to get conductivity), but that derived CTP
depends on the plate model used. Changes in the size of the plate
(particularly the minimum dimension) change the phase angle (or decay constant
in TDEM) and therefore the estimated apparent CTP and conductivity.
Of course, when forward modeling you can use the size of the model plate in
your calculation of apparent conductance, but then you should get back the
initial model conductance (in the absence of other interfering factors, like
host response).
So, what kind of model are you running, and what are you trying to get out of
it?
Greg Hodges
On Friday, November 20, 2020, 05:17:12 p.m. EST, S E Geoscience and
Exploration via SEGMIN <[email protected]> wrote:
Re: Question about plate modeling with Maxwell
Dear all,
It has been a while since I worked last with Maxwell.
Do you know whether we can model plates with just the calculated apparent
conductivity and without the in-phase and quadrature amplitudes?
Regards
--
Sergio Espinosa, Ph.D., P.GeoDirector, GeophysicsS E Geoscience &
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