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Transient
Electromagnetic
Methods
TEMIX and TEMIX XL interpret
electro-magnetic sounding data taken with the transient electromagnetic (TEM)
method. These software packages allow for the forward and inverse modeling of
TEM data acquired in terms of 1-D sounding curves. TEMIX & TEMIX XL run in
protected mode on 386, 486 and Pentium based machines with standard math
coprocessor.
Both packages in the TEMIX family
produce forward and inverse results using layered earth models for transient EM
data collected with a variety of commonly available field instruments. The base
version, TEMIX, has the same interpretational capabilities as TEMIX XL, but does
not have the interactive mapping and profiling capability. The new consolidated
TEMIX replaces the previous series of five TEMIX v3 packages, with additional
enhancements. The features of TEMIX Plus have been incorporated in the mapping
and profiling features of TEMIX XL.
TEMIX computes the forward model using
an Anderson style digital filtering technique to carry out the Hankel and
Fourier transforms. Fitterman-Anderson style integrations account for the ramp
time. Rather than removing effects from the observed data, TEMIX takes the
calculated curves and applies corrections for previous pulse (also known as
run-on) and ramp turn-off time.
The inversion process uses the Inman
style ridge regression approach of nonlinear least squares curve fitting. Prior
to inversion, you may constrain parameters of the starting model so that they
will not be adjusted by the inversion algorithm, or so that their adjustment is
limited.
TEMIX Family Features
The TEMIX family is a pair of
interactive, graphically oriented, forward and inverse modeling programs for
interpreting transient electromagnetic (TEM) data in terms of a layered earth
(1-D) model.
 The following
instruments are accommodated in both versions, with mixed instrument types
allowed in a single database:
-
Bison TDEM 2000 System
-
Crone Pulse EM
-
Geonics EM-37, 47, 57, Protem and
Protem D
-
Phoenix Geophysics V-5 System
-
SIROTEM Mark 2 and Mark 3
instruments
-
LOTEM generic system
-
Zonge Engineering GDP 12, 16 and 32
Systems
Processsing screen from TEMIX showing
interactive model construction.
Geometries
available are
Central Loop, Coincident Loop, Fixed Loop and Grounded Wire. Different
geometries and instruments can be mixed together in a single database.
Sounding curves
are entered as
a function of time. Where applicable to the selected instrument, interactive
work sheets are provided for reducing the measurements taken directly from the
respective instruments. The out-put, in terms of normalized received voltage
versus time, interfaces directly with the rest of the program, and is
transparent to the user.
Forward modeling
allows the
user to calculate a synthetic electromagnetic sounding curve for a model with up
to ten plane layers. Electromagnetic sounding curves are calculated using
filters designed by Anderson, 1979 (USGS Open File Report 79-590). The forward
modeling routines have been optimized to provide great computational speed and
increased accuracy. Forward modeling calculations use an equivalent dipole
approximation after Stoyer, 1990. (Geophysical Prospecting, 38, 87-99)
Model parameters (resistivities
and depths or ) can be entered numerically or graphically. With graphical entry,
TEMIX automatically performs conversions between time and depth using the
average conductivity of the model and the diffusion depth formula.
Ramp times
are accounted for by
convolving the turn-off ramp with the synthetic curve for the specific layered
model as described by Fitter man and Anderson (1987).
Run-on, the influence of previous
turn-on and turn-off cycles in the transmitter wave train, is accounted for by
summing the transient voltage from delayed pulses, according to the user’s
specification.
Inverse modeling
allows you to
obtain a model that best fits the data in a least squares sense. This is done
using ridge regression (Inman, 1975, Geophysics, 40, pp 798-817) to iteratively
adjust the parameters of a starting model supplied by the user. You can
constrain some of the starting model parameters so the inversion will not adjust
them. Starting models for inversion can have up to 8 layers. Forward models can
have as many as 10 layers. Constraints can be applied by fixing (or freezing) a
parameter, or by imposing limits on a parameter.
Masking
enables the user to
keep "bad" or unwanted data points as part of the data set, while excluding them
from Forward (percent error) and Inverse calculations.
Suites of forward models, for
which field recording or model parameters are varied, enable you to clearly see
the effect of such variations on the sounding curve.
Equivalence analysis
enables
you to generate a set of equivalent models, that is, alternative models that fit
the data nearly as well as the best-fit model, but differ from this model.
Equivalence analysis is done by using the parameter resolution matrix to show
the linear combinations of model parameters that are unknown. Also, the forward
calculations for each model are used; these are selected to determine the extent
to which modifications to the model can be made according to these guidelines
without exceeding a user-specified error. Equivalence analysis also indicates
the allowable range of each of the model parameters.
Advanced
batch processing allows the user to set flags for forward, inverse, smooth
and equivalent models. Batch execution then uses these flags to determine which
soundings to include in the batch process. Flags are set in a spreadsheet like
editor. Batch processing also features a batch fix and substitute command to fix
inversion parameters for groups of models. This also allows for setting of a
starting model for a whole group of soundings.
Batch
Plotting of all soundings in the database allows you to produce plots for a
complete survey, using user defined parameters for both plot components and
number of soundings per page. A newly introduced GROUP ID is can also be used to
group soundings for plotting.
Screen from TEMIX showing smooth model
and data.
TEMIX also features the smooth
model inversion which utilizes constant thickness layers to approximate a
quasi-continuous model; only the resistivities are used as parameters in the
inversion.
The binary data base format enables up
to 200 soundings to be stored in a single, variable-size data base file. You can
view and plot the survey field geometry.
Interactive model input via the
mouse allows the user to see changes in the calculated curve as he enters or
changes the model (times are automatically converted to depths).
TEMIX XL contains all the features
of TEMIX but with additional facilities for creating maps and profiles from the
data.
MAP FUNCTIONS A newly introduced MAP category allows the user to display the location map of
the survey with icons representing the soundings as well as a data window and a
model window.
Individual soundings can be selected
for interpretation from the displayed map using the mouse or cursor keys. Model
copy and paste commands allows for fast and easy starting model generation.
The map can be contoured with the
apparent resistivity at any time, the resistivity at any depth or elevation or
of any layer. Thickness, elevation or depth of any layer can also be contoured.
Conductivity can be substituted for resistivity in every case.
Map based interactive interpretation
screen from TEMIX showing map with contours, smooth and layered models, data and
synthetic curves.
PROFILE
FUNCTIONS
Profiles can be selected from the map
display by drawing a polygon around the desired points with a mouse. A best-fit
profile line is generated and the soundings are projected onto the profile line.
A second new interactive display shows the selected profile, selected (from
profile) sounding curve, synthetic data, smooth and layered model. The profile
display can be selected from a wide variety of data and interpreted model
parameters, from layered cross-sections to profile plots to contoured
pseu-dosections.
Profile plots can be in contoured
section or pseudosection form. Vertical axis can be elevation or depth for
sections. Model cross section is also available. Resistivity, conductivity or
voltage can be displayed.
Both contour map data values and
profile section and pseudo-section values can be exported in Geosoft XYZ format
for import into more sophisticated contouring or 3-D display software.
DISPLAY
OPTIONS
Final results for multiple sounding
interpretations can be presented in "PLATE" style format. These can include the
map (with profiles and contours), along with data and model displays for the
selected profile. There are many options available for the model section and
data displays.
Vertical axes for data and model can
be linear or loga-rithmic. Data can be presented as profiles, as a
pseu-dosection or as a sequence of laterally displaced sounding curves ("Zaborovsky"
plot).
Models can be presented as layered
model sections or contoured sections of layered or smooth models, with ei-ther
depth or elevation as the vertical axis. Smooth and/or layered models can be
drawn beneath each station in "well log" form.
Interactive processing screen from
TEMIX XL showing map with profile, Zaborovsky plots and contoured model section
with smooth and layered model overlays.
In addition to the above, location
maps can be produced with user definable "icon" plots of the sounding data and
models at the correct location on the plan view. Tools are provided to move "icons"
of plots to new locations if they overlap.
Interactive processing screen from
TEMIX XL showing smooth model contoured section on top as well as the sounding
curve and smooth and layered model being edited.
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