Carrying out Electrical resistivity data collection is the one step among others that you should pass through when conducting your resistivity project. The process is procedural and systematic, involving field set up of resistivity equipment such as resistivity meters. And the best and unique fact of resistivity surveying is that metal electrodes should be directly plugged into the ground. As the basic rule of thumb is that if you want to win your geophysical project your data should be quality collected and checked. Also the same rule applies in resistivity surveying that we should qualify that rule so as to increase our chances to win the project. However one among the challenges for poor quality resistivity data you may be faced are contributed by sensitivity of resistivity instruments and tools themselves utilized during resistivity data acquisition. This is why I have presented to you through this post these equipment that are at least the basics for any resistivity data acquisition. Then at the end of this article I hope the simple statement like which instruments are used in electrical resistivity survey will be cleared.
Let's move together till the end of this article, and I hope this will add a great value to your ongoing resistivity acquisition project in one way or another.
The following are the basic equipment and tools required in most electrical resistivity data acquisition, so you should consider when planning your resistivity survey.
Resistivity meter
What is a Resistivity meter? Resistivity meters consist of Voltmeter and Ammeter housed in one equipment. This means the measured potential difference (P.d) at potential electrodes should be recorded by voltmeter while the electric current injected in ground is recorded by the Ammeter. So that the division of measured voltage to current will give us the resistance (R). Depending on electrode design when this resistance is multiplied by a geometric factor the apparent resistivity is obtained. It is simple like that! This gives us the idea that a resistivity meter is the most important instrument that determines the quality of data collected.
There are many types of resistivity meters you can purchase however to get it right can be seen as a bit of a challenge. This resistivity meter is among the best resistivity meter you can use it for general DC resistivity survey because it is engineered to suit many applications (multi-function) such as you can use it to conduct Induced Polarization (IP) survey as this will reduce your cost of purchasing other equipment for such purpose, in simple we can say it is two in one. Also you can operate it in eight (8) types of electrodes configurations of resistivity imaging. And the best of this equipment is that its low cost with high efficiency and suitable to solve many geologic problems related electrical resistivity, so you can have it, in your geophysical store so that you can check list it when you prepared for your next survey. Lastly its accuracy is high so we expect high precision to the expected resistance value.
Handheld gps receivers.
gps stands for Global Positioning System. As the term suggests, GPS receivers receive ranging signals from several satellites of known position. Handheld GPS receiver is used to track (locate) the geographic position such as x, y, z at which (x,y) coordinates may represent Latitude and Longitude respectively while z may be used to represent the elevation. Knowing the exact position of a place will simplify the Mapping task.
The best Handheld GPS receiver should show route, having fast operating speed for signal exchange, high accuracy (95% Confidence level) to about 15m of horizontal distance. Also you have to make sure it should run in two most commonly used units, Latitude & Longitude units and metric grid coordinates units such as Universal Transverse Mercator (UTM). For Example this handheld GPS receiver is suitable to be used and gives the best results as it satisfies these criteria. While its batteries are available in a wide range even at your local shops. This makes it easy to have the spare parts of this handheld receiver. You can see various best GPS receivers
You have to be aware that Most GPS receivers require line of sight to the satellites, meaning that you should operate these devices in an open and clear sky. And avoiding highly forested areas or at the base of the tall buildings because these structures may interfere with line of sight make it difficult to take accurate positions.
Measuring tape
Since metal electrodes must be plugged directly into the ground at some fixed points. It is important to measure horizontal distance to ensure correct positioning of current and potential electrodes. Measuring tape plays this role in the field because it is easy to use, However glass-Fiber tape is adequate since it is durable and has a waterproof cover with P.V.C Also the material made with can be easily stretched when a certain tension is applied. This is highly recommended, remember that it is better to have the measuring tape with maximum length so as you can avoid unnecessary ranging out in your field surveying.
If you are a geologist there is no need for such measuring tape, just use a simple cloth tape with 30 m length is suitable in most of your geological task.
Other equipments and tools
As described above those three (3) equipment are most important, However these down are necessary ,But if you purchase the full set of Resistivity meters from a geophysical manufacturer or supplier may compose all these except for the hammer. I have tried to explain them briefly. If you want to buy them as individuals you can consider some of these descriptions.
Metal electrodes
These are metals used to inject current into the ground, Also they receive Potential difference results due to sent current in subsurface. The best Metal electrode should be a good conductor for easy passing of electric currents. Your metal electrodes should be narrow and chopped at one end to make it easy for them to penetrate into the ground. Also they should be galvanized so that to prevent unnecessary rust that may interfere with current conduction.
Electrical cables
Cables simply means connecting wires. There are two (2) types of cables mostly utilized in resistivity surveys. Current cables for passing electric currents from the source (battery) to the current electrodes through metal Clamp while Potential cables are connected to Potential electrodes. Your cables should be Long enough to allow easy spreading along a survey line. If necessary cables should have a Roller to ensure they are easy spreading and collected at the end of resistivity survey. And the fact that some cables have colored blue and red to make it easy to connect to respective terminals without any confusion.
Geological hammer
This tool is used to be considered as the friend of geologists, it is used to inject (plugs) metal electrodes into the ground. Your hammer's head should be made from hard and tough metal so that it fits various plugging tasks. For Example steel shafted Prospecting pick is mostly preferred hammer by field geologists, however when it comes to electrode plugging it is the best strategy to use this hammer as its head side is flat enough to suit plugging tasks. Make sure your operator does this hammering task properly and follow Health and Safety rules. You can see the simple figure below for more insight about these tools. You can see various best geological hammer which you should have in your frog leather held (pocket) when visiting field.
Figure: Simple representation of geological hammer (a) Bricklayer's club - hammer (b) Steel shafted prospecting pick - hammer
All in all these equipment and tools form the basis for most electrical resistivity field data acquisition surveys. Although there is rapid advancement of technology these will still play a key part to ensure your survey is complete and successful.
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