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Gravity Survey

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

Definition And Purpose

Gravity is a resultant force due to the universal gravitation of the earth and the centrifugal force generated by the rotation of the earth. The strength and direction of gravity varies according to position and time. Gravity, in other words, is a physical index that contains much information about the earth. By measuring the distribution of gravity and its change with time it is possible to know the shape and size of the earth, to estimate underground construction, to study the seismic and volcanic activities and to investigate the viscosity and elasticity of the earth.

Gravity field is required for the following:-

  1. To determine the local geiod enabling the reduction of geodetic measurements from the surface of the earth to the reference ellipsoid.
  2. To determine the orthometric correction to be applied to precise levelling measurements enabling orthometric heights to be computed.
  3. Other uses include prospecting for oil and other minerals, prediction of artificial satellite orbits, measurement of earth tides and other crustal movements and to detect possible changes in the gravitational constant.

 

      

 

 

Eligibility Criteria

To ensure accountability and professionalism in the conduct of Gravity Survey it is a must that quality, regulatory and disciplinary control be imposed on firms involved in this filed. The proprietor or partners of these firms must therefore be professionally qualified as well as registered with the Land Surveyors Board

To be eligible to carry out this specialized survey, a firm must be equipped with at least a portable gravimeter.

Methodology and Instrumentation

Gravity observations are either absolute or relative. In absolute measurement it is necessary to measure the actual gravity that exists at the observation point. In relative observation it is necessary to measure only the difference or ratio between the gravity at the base station and the gravity at the field stations. However, we are concerned here with only the relative measurements. For all gravity measurements, all observation points need to be coordinated by appropriate survey techniques.

Instruments used for relative gravity observations are portable gravimeters. These instruments are deployed for first and lower orders gravity surveys for the purpose of determining relative gravity values.