Display & Analysis
EM
Flow 3.3 offers display, analysis and interpretation of single or multi
component airborne time and frequency EM data. The software is designed
to operate on largeEM datasets and provide
conductivity depth
sections plus anomaly identification and analysis tools. The program
operation is usually tailored by processing one or two lines and then
applying the parameters to the remainder of the survey or specified
lines.
Fast Airborne Data Processing
EM
Flow provides accurate and fast processing of EM data. Highly optimised
routines developed by CRC-AMET researchers have revolutionised the
speed at which airborne EM data can be processed to produce a
conductivity image of the subsurface.
Integrate with Profile Analyst
Use
Encom Profi le Analyst to integrate EM Flow results with other data
such as magnetic, terrain, spectrometer, remote sensing and drillholes
in 1D, 2D and 3D views.
Airborne
EM
In
recent years the exploration industry has witnessed an unprecedented
increase in the application of both time and frequency domain EM
techniques for geological mapping, orebody search, salinity and
environmental applications. A typical EM survey will produce 500 line
kilometres per day averaging 400,000 transient records usually sampled
in 20
to
256 channels. Some 50 million data values can be acquired per day.
Manual
interpretation
of this data volume is slow and previous quantitative inversion
techniques using conventional layered earth approximations could take
many multiples of the flying time
to
be processed.
In
contrast, EM Flow can process and produce interpretation products from
a day’s survey data in a fraction of the survey time.
Rapid
Depth Sections
EM
Flow uses newly developed EM theory and sophisticated mathematics
developed by CRC-AMET. Theoretically defi ned EM system waveforms or
measured waveforms are used to deconvolve the EM multi-component,
multi-channel line data. You have full control over the processing and
production of conductivity depth images (CDI).
EM
System Definition
An
interactive editor is provided to allow the EM system, its geometry and
the input data to be specifi ed. The initial processing phase of EM
Flow requires specifi cation of the EM system geometry, transmitted
waveform and data format with different measurement
units
being allowed. An interactive formatter simplifi es input fi le
definition so that waveform specifi cations from external programs,
such as Microsoft Excel, can be easily imported.
EM
System Specification
Once
the EM system transmitter waveform and recording channels are
specified, the waveform is transformed through a
complex
matrix inversion to a series of basis functions which equate to time
constant (Tau domain) equivalents. The waveform is converted into a set
of basis functions that can be tuned by the user. This allows for the
use of many different waveforms containing different spectral
characteristics. An advantage of this approach is that either time or
frequency domain EM data can be processed since either type of
transmitted signal can be expressed in the Tau domain. The Tau domain
data enables rapid inversion and modelling to be undertaken.
Deconvolution
Conversion
of observed EM data to the time constant (Tau) domain is achieved by
deconvolving the line data with the pre-computed basis functions. The
deconvolution is represented graphically so real-time monitoring of the
process can be displayed. Available choices include fitting algorithms,
error tolerances, weighting, normalisation and primary field data
inclusion. Noise estimates, multiple components and system specifi
cations
are
presented for all processed data. Individual record analysis can be
undertaken if desired. Display controls can be manipulated to optimise
the estimation of noise levels and so provide checks of processing
quality.
Data
Import
An
interactive import utility provides a generic interface for most EM
multi-column ASCII file types, including Geosoft. Additional utilities
to define the EM system waveform, recorded
time
windows and transmitter-receiver geometry are also included.
Conductivity-Depth
Sections
CDI
section processing can be customised using component weighting,
selected taus, selected depth ranges and resolutions and by use of
discrete conductivities. The result of the CDI processing can be
displayed in EM Flow or output to external ASCII files suitable for
display in software packages such as Geosoft Oasis montajTM or ER
Mapper. Conductivity depth sections can be presented in coloured log or
linear formats. Topography can be taken into account for depth
solutions and will form the upper surface of the displays if specified.
Interpretation Facilities
Individual
anomalies based on specific EM response criteria can be identified by
an automated Anomaly Picker. Anomaly shape criteria such as peaks,
troughs and gradients are used for the anomaly selection and these are
indicated by various symbols in conjunction with their location and EM
response. Decays for individual anomalies can be displayed to assist in
determining conductor characteristics. Anomaly statistics and output to
ASCII fi les detailing the location and nature of the anomalies is
available.
Individual
anomalies can also be selected and passed with their associated EM data
to
an interactive modelling tool. A variety of model types is available
for analysis using both
forward or inverse modelling.
Body
types available include plate, prism and
fi lament style conductors. Multiple
bodies with full EM coupling are
accommodated since modelling is
undertaken in the Tau domain.
Constraints
can be applied during inversion
to limit the variability of models.
|
