Emix MT Magnetotelluric
Sounding Processing Software
General
The EMIX MT package is offered to
interpret MT, AMT and CSAMT data. EMIX MT performs
forward and inverse modeling of layered earth models.
Solutions are in terms of either apparent resistivity or
apparent resistivity and impedance phase data.
EMIX MT uses the input impedance
concept of J.R. Wait (Theory of Magnetotelluric Fields,
National Bureau of Standards, 1962) for forward modeling
of the impedance at the surface of the earth or on the
bottom of a lake or sea. Sounding curves are then
converted into apparent resistivity and phase of the
impedance in degrees. EMIX MT uses the Inmanstyle ridge
regression approach of nonlinear least squares curve
fitting for inversion calculations.
EMIX MT is an interactive,
graphically oriented, forward and inverse modeling
program for interpreting Magnetotelluric (MT), audio
Magnetotelluric (AMT), and controlled source audio
Magnetotelluric (CSAMT) sounding data in terms of a
layered earth (1D) model. Sounding curves can be
entered as a function of period or frequency, and
apparent resistivity amplitude data can be interpreted
with or without impedance phase data.
Data can be shifted (scaled by a
constant) either by using mathematical operation in the
Magnetotelluric Data and Error Bars spreadsheet, or by
using the Shift curve option while in interactive
graphics mode of the INTERPRET command.
Inverse modeling enables you to
obtain a model that best fits the data in a least
squares sense. This is done using ridge regression
(Inman, 1997) to interactively adjust the parameters of
a starting model supplied by the user. Starting models
for inversion can have up to 8 layers. You can
constrain some of the starting model parameters so the
inversion will not adjust them. Constants can be applied
by fixing (or freezing) a parameter, or by imposing
limits on a parameter. Parameters can be resistivity +
thickness of layers, or resistivity + depth to bottom
of layers. If phase data are present, each layer has an
additional parameter.
Smooth modeling enable you to
automatically interpret MT amplitude and impedance phase
sounding data in terms of a smooth model with up to 19
layers. The model depths are logarithmically spaced and
are generated from a minimum and maximum depth. The
minimum and maximum depth can be userspecified or can
be automatically generated. Model resistivity are
normally initialized to the best fit homogeneous
halfspace resistivity. Inversion can be carried out in
either interactive or batch mode, using ridge regression
or William of Occan's smooth model concept.
Equivalence analysis enables you to
generate a set of equivalent layered models, which are
alternative models that fit the data nearly as well as
the bestfit model, but differ from it. Equivalence
analysis also indicates the allowable range of each of
the model parameters.
New Emix MT allows for the
specification of a profile distance, landbased or
lake/sea bottom and TE, TM or No specified mode. For
lake bottom data, magnetic sensor position is specified
in addition to profile distance. This allows Emix MT2D
to access the Emix MT database and assign a TE and a TM
mode sounding to a station at the specified location
along the profile.
Emix MT can also handle controlled
source data taken with a grounded wire. The grounded
wire is assumed to be a dipole and the receiver is
assumed to be oriented so that the electric field
receiver is parallel to the source wire.
Standard Components
Emix MT v2 software and manual.
