Welcome to AGT’s documentation!

Introduction

This plugin is a toolbox for processing electrical resistivity (Geoscan Research RM15/RM85), magnetic (Sensys MXPDA / Bartington Grad601) and electromagnetic induction (Geonics EM31) data with shapefiles creation.

Electrical data processing module (Geoscan Research RM15/RM85) - grid survey

This module enables basic processing of resistivity data collected with a regular grid. For the moment, only the Pole-Pole configuration is available.

Input file

The input file is an ascii file (.dat) that contains the data and header that gives all the information concerning the configuration of the resistance meter and the survey mode:

Column file containing the data

  • RM85  Name of the resistance meter
  • 2  Number of grids
  • 30  Grid length (m)
  • 30  Grid width (m)
  • 0.5  Probe spacing (m)
  • 3  Number of channels
  • 4  Number of probes
  • 1  Line step (m)
  • Pole-Pole  Probe configuration
  • 10  Current intensity
  • 1  Number of the first grid
  • 0  Coordinates of grid’s first point (bottom-left point)
  • 0
  • 2  Number of the second grid
  • 0  coordinates of grid’s first point (bottom-left point)
  • 30
  • 20.95  Resistivity measurement
  • 25
  • 20.5
  • 8.55
  • 8.9
  • 5.26
  • .
  • .
  • .

The value of dummy log is 999.

Header has two different roles, so must be accurately completed because it is used:

  1. for data processing (automatically read by the software)
  2. for storing metadata of the survey

Processing

The basic processing consists of reorganizing the raw data in order to separate each channel and assign the right X,Y position of each measurement.. The measured resistance values are transformed into apparent resistivity, depending on the chosen probe configuration (for the moment only the pole-pole configuration is available). Data can be exported in shapefiles (.shp) or ascii files (.dat). Two sub-modules are subsequently proposed:

Median filtering

This function allows noise removal using a median filter algorithm. The user has to define the kernel size and the threshold defined as a percentage tolerance with the median value.

Georeferencing

This function allows grid georeferencing using geometric translations and rotations. The method uses two control points provided by the user.

Magnetic data processing module (Sensys MXPDA / Bartington Grad601) - grid survey

This module allows basic processing of magnetic survey data, collected with a Sensys MXPDA or Bartington Grad601 magnetometer.

Input file

The input file is an .dat file, generated by Sensys Magneto-Arch software or a .dat file generated by Bartington software. File configurations are as follows:

Sensys MXPDA

  • X Y Value
  • 0 0 2.8
  • 0 0.1 2.87
  • 0 0.2 3.08
  • 0 0.3 2.59
  • 0 0.4 1.89
  • .
  • .
  • .

Bartington Grad601

  • Time = 09:16:55
  • Date = 06/10/2017
  • Grid Number = 1
  • Number of Sensors = 2
  • Grid Size = 40 x 40
  • Method of collection = ZigZag
  • Starting Direction = West
  • Data Range = 100 nT
  • Line Spacing = 1.00 m
  • Sampling = 4 samples / m
  • Sensor Spacing = 1.0 m
  • Mean = 0.50
  • Max = 21.40
  • Min = -4.01
  • 0.125 0.5 0.87  Y, X, value
  • 0.375 0.5 0.86
  • 0.625 0.5 1.21
  • 0.875 0.5 1.78
  • 2.875 0.5 1.16
  • .
  • .
  • .

Processing

The basic processing consists of reorganizing the data in order to separate each profile (a profile is defined with a fixed X coordinate). Data can be exported in shapefiles (.shp) and ascii files (.dat).

Three processing modules are proposed:

Median removal

This function removes the median value of each profile, in order to eliminate the shift due to electronic components of the sensors and constant magnetic disturbances. It is possible to limit the number of points used to determine the median value by using a percentile. Using a percentile threshold excludes strong magnetic anomalies from the median value computing.

Trend removal

This function allows a first-, second- or third-order polynomial removal on each profile.

Georeferencing

This function allows grid georeferencing using geometric translations and rotations. The method uses two control points provided by the user.

Magnetic data processing module (Sensys MXPDA) - GNSS survey

This module allows basic processing of magnetic survey data, collected with a Sensys MXPDA magnetometer coupled with a GNSS.

Input file

The input file is an .asc file, generated by Sensys Magneto-Arch software. Its configuration is as follows:

X, Y, difference of the vertical component of the magnetic field, profile name, the number of the probe.

  • 30694328.591 5432511.556 5.5 “20161010-110332_GZP.prm” 1
  • 30694328.717 5432511.772 31.2 “20161010-110332_GZP.prm” 2
  • 30694328.844 5432511.987 -21.6 “20161010-110332_GZP.prm” 3
  • 30694328.971 5432512.203 -8.3 “20161010-110332_GZP.prm” 4
  • 30694329.098 5432512.418 -12.3 “20161010-110332_GZP.prm” 5

Collected data are georeferenced in UTM coordinates. The two first digits of the X coordinate correspond to the UTM zone (UTM-30 in this example).

Processing

he basic processing consists of reorganizing the data in order to separate each profile (a profile is defined as a set of data collected with one probe along one line). Points are then georeferenced in the chosen mapping system. Data can be exported in shapefiles (.shp) and ascii files (.dat).

Four processing modules are proposed:

Decimation

This function reduces the number of collected points by keeping a fraction of them (1 / n, n is chosen by the user). The user can use raw data or median filtered data (computed with a n data point moving median).

Median removal

This function removes the median value of each profile, in order to eliminate the shift due to electronic components of the sensors and constant magnetic disturbances. It is possible to limit the number of points used to determine the median value by using a percentile. Using a percentile threshold excludes strong magnetic anomalies from the median value computing.

Trend removal

This function allows a first-, second- or third-order polynomial removal on each profile.

Stationary point removal

This function eliminates stationary data points collected while the magnetometer is immobile.

EMI data processing module (EM31 from Geonics)

The module transforms the electrical conductivity values provided by the EM31 (based on McNeil, 1980). This processing overpasses the boundaries of the linear approximation which is only valid in first approximation for an instrument held on the ground (Z=0) and respecting the low induction number condition (i.e. low electrical conductivity). Data is transformed into a .shp file and can be uploaded into GIS.

Input file

Input file is an ascii file format (.dat) as delivered by DAT31W (Geoncis software). It contains the X, and Y position of each measurement, as well as the quadrature (QV1 in mS / m), in-phase part of the electromagnetic signal (IV1 in ppt) and a time stamp:

  • / EAST, NORTH, QV1, IV1, TIME /
  • 642039.43420000 7097622.22880000 30.10 1.03 15: 32: 39.555
  • 642039.43560000 7097622.22740000 30.25 1.03 15: 32: 39.904
  • 642039.43548000 7097622.22934000 30.18 1.03 15: 32: 40.262
  • 642039.43478000 7097622.23249000 30.13 1.01 15: 32: 40.614
  • 642039.43402000 7097622.23591000 30.02 1.00 15: 32: 40.991
  • 642039.50925000 7097622.14500000 29.95 1.00 15: 32: 41.353
  • 642039.58235000 7097622.05660000 29.98 1.00 15: 32: 41.699
  • 642039.67784000 7097621.93750000 30.18 1.02 15: 32: 42.071

The user has to specify the coordinate system used during the survey.

Processing

The processing module estimates the apparent electrical conductivity values based on the solution of the integrals and the Hankel transform (Thiesson et al., 2014). This solution takes into account the height of the device and the coils configuration. It can therefore be applied regardless of the type of soil studied even valid in salty soil contexts.

McNeill J.D., 1980 - Electromagnetic terrain conductivity measurement at low induction number, technical note TN6, Geonics Ltd, Toronto, 15p.

Thiesson J., Kessouri P., Schamper C., Tabbagh A., 2014 - Calibration of frequency-domain electromagnetic devices used in near-surface surveying. Near Surface Geophysics, 12, 481-491.

Code source

The source code is available at:

https://github.com/narimanInrap/AGT.git

Future developments

  • Electromagnetic processing module (GeoPhex gem-2, dualEM)
  • RM15/RM85 Download module
  • Advanced processing module

Indices and tables