The CORIM System is a continuous profiling resistivity system withr eal time display of apparent resistivity. The system has an investigation depth of about 3 meters. It has been designed to be pulled by a car at a few km/hour. The system can be broken up into two parts:
Set of Carpets
Each of the carpets consists of two copper capacitive electrodes spaced 1.5m apart, located on the underside of the carpets. Since the electrodes are dragged across the surface, rather than sunk into the ground, it is necessary that the electrodes have good contact with the ground for optimum data resolution. One carpet is designated as the transmitter dipole, and up to six other carpets are used as receiver dipoles. The spacing between two consecutive dipoles is 1 meter.
The transmitter electronic unit is powered by a sealed 12V lead acid rechargeable battery and sends an alternating 2mA current to the receiver dipoles. Both the Tx electronic unit and its battery are placed on top of the Tx carpet.
The measurement is performed in a differential mode. For this reason a differential receiver must be placed on each receiver carpet and connected to the copper electrode plates. An A/D converter , 7V rechargeable battery and an amplifier, are housed in each receiver unit.
The transmitter dipole must be placed at the end of the system in order to avoid parasitic noise for the receivers. All carpets are screwed to each other using a metallic link that serves as a reference electrode for the differential measurement of each dipole receiver. One cable originating from the controller multiplexer in the trolley, connects to each receiver unit and runs the length of up to 6 consecutively placed receiver carpets.
All receiver units, a distance encoder and a portable PC are connected to a controller multiplexer located inside the trolley. This controller is powered by a 12V battery. The trolley has been designed to carry the main battery and a spare transmitter battery which is conveniently kept charged by the main 12V battery (pictured right). All the carpets are linked together and joined to the trolley. A hitch allows the trolley and carpets to be pulled by a car at a few km/hour.
The CORIM System is run in conjunction with a software program called EXPLORER. This software allows the operator to check battery voltages of the receiver units, calibrate the distance encoder, set measurement configuration and display parameters, as well as display and store acquired data. Offset values can be automatically computed and stored at the beginning of each profile. These offset values are computed with the transmitter off, allowing the receivers to measure a signal corresponding to natural noise, depending on the kind of ground and on the contact resistance. Data will later be automatically corrected by these offset values .
Explorer Software "Master" Window
|Once the system begins to move, measurements stream in real time
into the "Master" display window. The speed at which the system is moving is
displayed in km/hour in the right bottom part of this window. Results can be visualized in
three different display modes; list of measurements, line profile of each channel, or as
an image with up to 6 color stripes. The measurements that are displayed are the apparent
resistivity values for each receiver channel.
The resistivity values are computed according to the standard DC resistivity formula:
K is the geometrical factor defined according to the following formula:
K(m)=2p/(1/AM - 1/AN - 1/BM + 1/BN)
|This geometrical factor K only depends on the geometry of the
configuration and values for the supplied carpets are listed in the instruction manual.
During acquisition the operator has the possibility to change the parameters of the display and to place reference markers in the data record. There are four different markers available, each distinguished by a different color. These markers will be displayed in the line profile display mode by vertical lines with the corresponding color. They will also be stored in the data files.
Measurements are stored in a binary file and can be converted into an ASCII file with the .txt extension. This .txt file is compatible with data sheet (such as Notepad...) or spread sheet (such as Excel...) software. To the right is a .txt converted file with corrected data calculated for two sets of compensation measurements (offset values), the first at the beginning of the profile and the second one at a change of soil type. Data conversion can be made with or without measurement compensation.
Corim View Software
Further data viewing and processing is accomplished with the CORIM VIEW software also supplied with the system. CORIM VIEW will display the results of the data files according to line profile or pseudo-section representations. The operator also has the possibility to filter data and print the results.
Real Time Line Profile Post-Processed Pseudo-Section