Knowing About Some Methods Being Done In The Ground Magnetic Surveys

الأربعاء، 7 ديسمبر 2016

By Frank Fox


A magnetic survey is a type of method which is being used for archeological geophysics. The survey is going to record the spatial variation of magnetic field of the Earth. In the field of archeology, the survey will be utilized for detecting and mapping the archeological features and artifacts. This is also being used for both the marine and terrestrial archeology.

A magnetometer is one main instrument being utilized for conducting this survey. This contains two different types, one having one sensor and another one having two sensors. The type with only one sensor gets the measurement of total strength in an Earth field. And the other type having two sensors gets the measurement for a fields gradient and these sensors are spatially separated. The aim of these ground magnetic surveys is to conduct an investigation of subsurface geology basing on the magnetic fields anomalies.

These anomalies are the results of magnetic properties from underlying rocks. Generally, the rocks magnetic contents are extremely variable but these are dependent upon the rock type and as well as the environment. The three most common causes of these anomalies are the faults, lava flows, and dykes. In geothermal environments, the susceptibility will decrease because of high temperatures.

The survey method would also involve the measurement of the intensity and also for the vertical, horizontal, and total components and gradients. A magnetism is considered to have the same features as gravity and one is potential field. Usually, the anomalies can be caused by some residues of a magnetism which is induced. The anomaly that is induced will be the result of the secondary magnetization that is induced in a ferrous body.

The induction of these anomalies result to having dimensions, shape, and amplitude and these three will then be considered as functions in orientation, geometry, susceptibility, depth, and size. These three will also become functions in the intensity and the inclination of a field when surveys are done in a certain area. There are 4 important purposes of the method and these are stated below.

First, locating the buried tanks, metallic debris, abandoned casings of steel well, and pipes. Second, mapping the landfill boundaries and sites of old waste. Third, mapping the basic igneous intrusives and basement faults. And lastly, investigating the archeological sites.

To be able to explore the geothermal energy, both the data for aero magnets and grounds is being used for the investigation of geothermal resource presence with the combination of gravity. Usually in the data of aero magnets, anomalies are often in correlation with the surfaces of volcanism expressions. These would include cones or domes, plugs or localized basaltic lavas, and craters.

Portable instruments are being used for a ground magnetism to be measured. These instruments contain regular intervals together with some straight and also parallel lines, covering the survey area. These intervals are often placed between locations. The intervals are lesser compared to the spaces between lines. Electromagnetic sources have intense fields are these are very common problems of most surveys.

To maintain the accuracy of mapping the anomalies, during the survey period, temporal changes must be considered. The normal changes are often called as diurnal drift. The corrections of diurnal drift are made through the repetition of instruments of the base station having frequent intervals. These measurements of stations are then made with correction for the temporal variations. Another thing is to avoid on conducting these surveys during severe storm that may occur infrequently.




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