Airborne gravimetry

BGR helicopter at the airport (Banda Aceh) Source: BGR

Measuring aircraft Cessna 402 Source: Hansa Luftbild

Method:

Knowledge about gravity allows geoscientists to create models on density distribution in the underground and thus on the build-up of the earth’s crust. In former decades, measurements of gravitational variations were carried out selectively on land and continually along profiles at sea. In order to carry out these measurements also from the air by helicopter or airplane, BGR modifies the marine gravitymeter KSS31M, so that it can also be used as a part of an airborne gravimetric measuring system. Modifications mainly affect technical details of gravity data acquisition and other parameters, but also weight reduction of the system. Furthermore, also commercial systems are used by BGR.

The KSS31M system with GPS receivers Source: BGR

Measuring technique:

A gravity sensor installed on a moving platform measures the sum of gravity and inertial acceleration of the system in the aircraft. Interferences caused by inertial acceleration on a normal survey flight can show 100 – 1000 times the amplitude of the wanted signal of a measured, geologically caused gravity variation, depending on the filtering of the data. The inertial acceleration, however, can be deduced from the movement of the aircraft. The flight path has to be determined by a non-inertial system, like satellite-supported GPS. Thus, the reduction of the vertical acceleration and the influence of the horizontal accelerations are important components of data processing. BGR’s scientists use ultra-modern GPS receivers and kinematic DGPS post processing software.

The KSS31M consists of two main components: a gyro-stabilized platform with the gravity sensor and the rack with control electronics and power supply. Furthermore, the rack contains an industrial PC for control and data recording, a computer-controlled precision multimeter and the GPS receivers.

After vehicle-borne experiments on the ground, test flight were carried out in 2003 and 2005 with the system in an airplane of the type Cessna 402.

Principle sketch of the helicopter gravimetry Source: BGR

Besides, a gravity measurement project from the helicopter will be realized. Here, a commercial system shall be used for a survey of the Dead Sea Rift System.

Applications:

• exploration of deposits
  
• geologic–tectonic mapping
  
• geodetic surveys (regional geoid)
  
• large scale engineering-geological surveys

Projects:

• GEO-DESIRE
• Entwicklung eines aerogravimetrischen Messystems auf Basis des KSS31 Gravimeters
• An airborne gravity survey south of the Prince Charles Mountains, East Antarctica