Airborne Gravity Surveying Explained

gravity survey

Gravity surveying is the process of measuring the local gravitational field of the Earth. Airborne gravity surveying revolves around the process of measuring and mapping changes in the gravity field with an airborne gravimeter on a helicopter or an aircraft. This ultra-sensitive equipment reveals information about the subsurface density of rock within the Earth. The idea is based on a "Causative Body”, which produces a gravity anomaly. These anomalies are analyzed by geophysicists who can assess the depth, size, and shapes of the subsurface anomalies.


Gravity surveying is based on the theory of Newton's Law of Gravitation, which says that "the force of attraction between two bodies of known mass is directly proportional to the product of the two masses and inversely proportional to the square of the distance between them”. Essentially, denser formations in the subsurface have a slightly higher gravitational pull than normal formations.


The measurement of these anomalies is done with a gravimeter. A traditional gravimeter works with an ultra-sensitive spring and mass system. These instruments have a weight attached to a beam and also to a spring. As gravity increases, the weight is pulled downward and also pulls on the spring. As gravity normalizes once past the increased gravitational force, the weight and spring return to their original locations. Now, newer systems are attempting to use lasers to achieve even more accurate results.


Once these measurements have been taken, corrections need to be made on the gravity survey results to reduce sources of noise. Airborne gravity surveys have four factors to correct for;

  1. Drift; A minor correction for stretching in the spring throughout the survey.
  2. Coriolis; A correction for the Coriolis Effect due to the rotation of the earth.
  3. Elevation; Correction for being above sea level.
  4. Latitude; Correction for the location on Earth, due to its shape.

The past decade has seen the constant development of new and improved gravimeters from a number of different manufacturers measuring an extremely high degree of accuracy. Accuracy is determined by analyzing the differenced at cross-over points from the survey data. The resolution of the gravity data along line in a function of the speed of the vehicle/vessel and the filter length applied to the data, typically from 3.5 to 5 km of resolution. (Source; CMG)


New generation gravimeters remove the movement of the aircraft from the data, providing a more accurate measurement. Once corrections are made to the data, critical data information can be derived for mapping purposes.


By examining the variations in local or regional gravity, one can interpret the different densities beneath the surface. Parameters of interest include the size, shape, and depth of the formation. The most common applications for airborne gravity surveying are exploration for petroleum and natural gas, and minerals, including lead, zinc, copper, gold, uranium, and iron.


 Airborne Gravity Survey Specifications


Although results vary from system to system, superior gravity data is generally acquired at night when survey aircraft can fly in less turbulent conditions. Gravity systems cannot operate will in conditions above 15 knot, or on more than a 20 degree bank of the aircraft. Therefore, Terraquest specifically selects aircraft that can provide the most stable flight path possible at a relatively slow rate of speed, typically 200-240 km/h and stay airborne for as long as possible.


Gravity surveys are typically flown at ~1,000 ft elevation and with traverse lines of not less than 250 m line spacing.


Gravity surveys can be flown with in combination with magnetics and radiometrics instruments to increase the survey benefits. Airborne gravity surveys provide an economical alternative to ground and gravity technology and are therefore an excellent starting point for an exploration program.


Specialists in Airborne Gravity Surveys


Terraquest was established in 1984 and since then, our dedicated team has flown over 1,500 airborne geophysical surveys using both fixed wing and helicopter platforms.  Our professional crews provide significant experience having carried out airborne magnetic surveys, airborne gravity surveys, airborne radiometric surveys, and airborne electromagnetic surveys on five continents. 


Our quality data sets have been utilized in the exploration for base and precious metals, kimberlite, hydrocarbons, uranium, rare earth minerals and water.  The company has performed exemplary surveys for both small and large exploration groups as well as many government agencies, including the USGS. References can be provided upon request. Visit

Powered by RWARDZ