
TEM Smoothmodel Inversion

Onedimensional Inloop TEM Inversion

Onedimensional Inloop TEM Forward Modelling

Twodimensional Smoothmodel CSAMT Inversion

Smoothmodel CSAMT Inversion

Onedimensional CSAMT Inversion

Resistivity and IP SmoothModel Inversion

Twodimensional Electromagnetic Modelling

Smoothmodel twodimensional IP/Resistivity Inversion with Topography
TEM Smoothmodel Inversion
Smoothmodel inversion is a robust method for transforming movinginloop TEM soundings to profiles of resistivity versus depth. Observed transient data for each sounding are used to determine the parameters of a layeredearth model. Layer thicknesses are fixed and set to sum to the soundings's maximum depth of investigation. Layer resistivities are then adjusted iteratively until model TEM responses are as close as possible to observed data. Smoothness constraints limit model resistivity variation from layer to layer.
STEMINV's algorithm for calculating the TEM response of a layered model includes the effects of rectangular transmitter loops and finite transmitter turnofframp times. Accurate transient voltages are calculated for all window times.
The result of smoothmodel inversion is a set of estimated resistivities which vary smoothly with depth. Lateral variation is determined by inverting successive soundings along a survey line. Results for a complete line can be presented in pseudosection form by contouring model resistivities. For contouring, model resistivity values are placed at the midpoint of each layer, forming a column below every station. The columns form an array representing a crosssection of model resistivity.
Inverting apparent resistivity and phase to smoothly varying model resistivities is an effective way to display the information inherent in TEM soundings. Smoothmodel inversion does not require any a priori estimates of model parameters. The observed data are automatically transformed to resistivity as a function of depth. Models with smoothness constraints are complementary to more detailed models incorporating a priori geologic constraints.
Onedimensional Inloop TEM Inversion
TCINV inverts the transient response of an inloop TEM system to a layered earth model. TCINV uses an iterative inversion algorithm which constrains changes to layered model parameters while minimizing the difference between observed and calculated data. The forward modelling routine calculates the transient fields excited by a ramped current step in a large, circular transmitter loop. The inloop transient response is measured as voltage in a small loop antenna placed at the center of the transmitter loop. TCINV supersedes NLSTCI with a more efficient inversion algorithm, compensation for finite transmitter turnoff time, and a simpler user interface.
Onedimensional Inloop TEM Forward Modelling
TEM1D calculates the transient response of an induction loop system on the surface of a layered earth. Source fields are excited by a ramped current step in a large, rectangular transmitter loop antenna. The transient responses are calculated as voltages in receiver coil antennas placed at arbitrary locations on the earth's surface. TEM1D supersedes the program TCI. It allows rectangular loops, a finite transmitter turnoff time, and arbitrary placement of the receiver coil.
Twodimensional Smoothmodel CSAMT Inversion
Smoothmodel inversion is a robust method for converting farfield CSAMT or naturalsource AMT data to resistivity model crosssections. SCS2D inverts observed apparent resistivity and impedance phase data from a line of soundings to determine resistivities in a model crosssection. Either TMmode data, TEmode or both may be inverted. To start the inversion, the model crosssection is usually given a background resistivity generated from a moving average of apparent resistivity data or a 1d smoothmodel inversion section. Specific geologic structure may be added to the background model if there is drilllog or geologicmapping information available. During the inversion, modelsectionpixel resistivities are adjusted iteratively until calculated apparent resistivity and impedance phases are as close as possible to observed data, consistent with model constraints. Model constraints include backgroundmodel constraints, which restrict the difference between the inversion model and a background model section, which represents known geology, and smoothness constraints, which limit resistivity variation from pixel to pixel.
To calculate apparent resistivity and impedance phase for a given model section, SCS2D uses a twodimensional, finiteelement algorithm to calculate farfield CSAMT or naturalsource MT data. To model areas with rough terrain, the finiteelement mesh is draped over an alongline topographic profile. Either TM or TEmode data can be calculated for scalar, vector or tensor survey configurations for frequencies ranging from less than 0.01 Hz to 10 kHz.
Inverting apparent resistivity and impedance phase to smoothly varying model sections is an effective way to display the information inherent in CSAMT and AMT measurements. As smoothmodel inversion does not require any preliminary information about geologic structure, observed data are automatically transformed to a resistivity model crosssection providing an image of the subsurface. Model sections generated with smoothness constraints are complementary to more specialized inversions incorporating specific geologic models.
Smoothmodel CSAMT Inversion
Smoothmodel inversion is a robust method for transforming CSAMT soundings to profiles of resistivity versus depth. Observed apparent resistivity and phase data for each station are used to determine the parameters of a layeredearth model. Layer thicknesses are fixed by calculating sourcefield penetration depths for each frequency. Layer resistivities are then adjusted iteratively until model CSAMT responses are as close as possible to observed data. Smoothness constraints limit model resistivity variation from layer to layer.
The algorithm for calculating the CSAMT response of a layered model includes the effects of finite transmitterreceiver separation and a three dimensional source field. Accurate impedance magnitude and phase values are calculated for all frequencies and transmitterreceiver separations.
Smoothmodel inversion produces a set of estimated resistivities which vary smoothly with depth. Lateral variation is determined by inverting successive stations along a survey line. Results for a complete line can be presented in pseudosection form by contouring model resistivities. For contouring, model resistivity values are placed at the midpoint of each layer, forming a column below every station. The columns form an array representing a crosssection of model resistivity.
Inverting apparent resistivity and phase to smoothly varying model resistivities is an effective way to display the information inherent in CSAMT measurements. Smoothmodel inversion does not require any a priori estimates of model parameters. The observed data are automatically transformed to resistivity as a function of depth. Models with smoothness constraints are complementary to more detailed models incorporating a priori geologic constraints.
Onedimensional CSAMT Inversion
CSINV inverts CSAMT frequencysounding data into a layeredearth model. The forwardmodelling routines in CSINV include the effects of finite transmitterreceiver separation and a threedimensional source. CSINV computes accurate impedances for nearfield, transition, and farfield data. CSINV uses an iterative inversion algorithm which constrains changes to layeredmodel parameters while minimizing the difference between observed and calculated data.
CSINV can be used either as a standalone program or as one module in a group of programs designed for interactive interpretation. Supplemental programs distributed with CSINV provide utilities for data entry, editing, and display. The utilities include a program for direct inversion of far field data. Also included are reformatting programs to convert data from or to specialized file formats. Screen and printer plotting capabilities allow quick review of modelling results.
Resistivity and IP SmoothModel Inversion
2DIP is a finite element program which computes the lowfrequency electrical response of twodimensional models. Models may include both subsurface structure and surface topography. Voltage responses for arbitrary electrode configurations may be calculated. Configurations may use up to ten transmitter electrodes and twenty receiver electrodes. The default survey configuration is dipoledipole, with the model response calculated as apparent resistivity and phase. Up to nine resistivities may be specified. Voltages are calculated for all combinations of transmitter and receiver electrode locations. For the default dipoledipole configuration, the model response is presented as pseudosections of apparent resistivity and phase.
Twodimensional Electromagnetic Modelling
EM2D calculates the electromagnetic fields excited by a planewave source over 2D resistivity and topographic structures. The electricfield component of the source can be oriented at any angle relative to strike. EM2D calculates both transverse magnetic and transverse electric modes.
EM2D can evaluate models with arbitrary twodimensional resistivity variations. An analytical solution is used to obtain exact values for electromagnetic field components over a layered earth. The effects of further twodimensional variation relative to a layeredearth are approximated by a finitedifference algorithm. Fields over or within arbitrarily complex, twodimensional models can be computed. The results are particularly accurate for models which are close to a layered earth.
Smoothmodel twodimensional IP/Resistivity Inversion with Topography
Twodimensional, smoothmodel inversion of resistivity and induced polarization data produces imagelike, electrical property sections which improve the data's interpretability.
Recent software improvements enable routine smoothmodel inversion of resistivity and induced polarization (IP) data. Nearly uniform starting models are generated by running broad moving average filters over lines of dipoledipole or poledipole data. Model resistivity and IP properties are then adjusted iteratively until calculated data values match ovserved values as closely as possible, given constraints which keep the model section smooth.
Calculated values are generated with a finite element algorithm which can be adapted for accurate twodimensional modelling of data collected in routh terrain. Smoothmodel inversion of sample data show the method's utility as an interpretation aid and the importance of modelling topography in areas with significant relief.
Twodimensional Smoothmodel CSAMT Inversion
Smoothmodel inversion is a robust method for converting farfield CSAMT or naturalsource AMT data to resistivity model crosssections. SCS2D inverts observed apparent resistivity and impedance phase data from a line of soundings to determine resistivities in a model crosssection. Either TMmode data, TEmode or both may be inverted. To start the inversion, the model crosssection is usually given a background resistivity generated from a moving average of apparent resistivity data or a 1d smoothmodel inversion section. Specific geologic structure may be added to the background model if there is drilllog or geologicmapping information available. During the inversion, modelsectionpixel resistivities are adjusted iteratively until calculated apparent resistivity and impedance phases are as close as possible to observed data, consistent with model constraints. Model constraints include backgroundmodel constraints, which restrict the difference between the inversion model and a background model section, which represents known geology, and smoothness constraints, which limit resistivity variation from pixel to pixel.
To calculate apparent resistivity and impedance phase for a given model section, SCS2D uses a twodimensional, finiteelement algorithm to calculate farfield CSAMT or naturalsource MT data. To model areas with rough terrain, the finiteelement mesh is draped over an alongline topographic profile. Either TM or TEmode data can be calculated for scalar, vector or tensor survey configurations for frequencies ranging from less than 0.01 Hz to 10 kHz.
Inverting apparent resistivity and impedance phase to smoothly varying model sections is an effective way to display the information inherent in CSAMT and AMT measurements. As smoothmodel inversion does not require any preliminary information about geologic structure, observed data are automatically transformed to a resistivity model crosssection providing an image of the subsurface. Model sections generated with smoothness constraints are complementary to more specialized inversions incorporating specific geologic models.