Geophysical Survey Design can be defined as the plan (structure) of a geophysical survey. It describes what the survey will contain and how it will be done. It can be regarded as one of the key decisions to decide whether to conduct or terminate the geophysical survey. It gives the direction of where the geophysical survey would be running. Here down I have written an idea on how it should be done.by explaining the factors to be considered.
Target identification
Here you consider what you are looking for? Such a contrast that can be detected remotely because it gives rise to a geophysical anomaly.
Geophysical Anomaly can be defined as variations in physical properties relative to some background value.
Geophysical targets can be considered as the physical source of any anomaly. Some examples of targets are trap structures for oil and gas, pipelines, ore lodes, cavities, groundwater, just to mention a few.
So we have to know the target in order to be familiarized with which method to apply so as to produce the best results. Since geophysical methods are very sensitive to physical properties of the given geophysical target.
For Example if your geophysical target has high conductivity (low resistivity) such as saline water intruded in freshwater, it is best to apply electrical resistivity or electromagnetic conductivity methods, in order to detect such a target successfully. Other techniques such as gravity methods would be inappropriate in such cases because there would be virtually no density contrast between the saline and freshwater.
Also if the target is a buried metal sphere here you apply a gravity method it would produce the best results since there would be a density contrast between such a sphere and the soil.
Optimum Line Configuration
Here what you should consider is how to collect the data in order to define a geophysical anomaly.
Two important techniques applied in data collection are Profiling and Mapping.
Profiling can be defined as measuring a variation of physical parameters in two (2) dimensions (2D) laterally along a given profile.
Golden Rule: The orientation of the profile should be at right angle (90°) to the strike of a given target. Also the length of the profile should be greater than the width of the suspected target in order to define the true amplitude.
Selection of the station interval
Station: It is a specific point where geophysical measurement is done.
Station Interval: Is the distance between two successful stations.
The selection of station Interval is a vital part of geophysical survey, because if not planned well it would affect data acquisition and even data quality in some ways. For Example if you use too small an interval it would add more time to end the survey and increase significant survey cost. In other ways if you use a wide interval you may end up with data that would not represent the reality.
The great rule to use is to select the station interval by considering the size of the causative body. Because the expected anomaly is always greater than the size of that body. Such as if the causative body is 2m then it would be a great idea to use intervals greater than size such as twice.
Data Analysis
After having collected data successfully, you have to think on how to process the data into meaningful results.
Here is to ask yourself which technique will produce the best results: manual or computer Automatic. There are standard methods for several geophysical data processing. Even softwares such as Golden Software (Surfer) or Geosoft can aid the process.
Geophysical survey design is very important to lead a successful geophysical survey, so plan it with care to avoid additional wastes of time, survey costs, and unsuccessful geophysical projects.
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