Gravity anomalies from airborne measurements — experiments using a low cost IMU device

Abstract

The gravity field may be determined using different techniques, but airborne gravity surveying is becoming a powerful tool mainly due to its potential in remote areas.

In the scope of the AGMASCO (Airborne Geoid MApping System for Coastal Oceanography) project a navigation system has been developed in support of airborne measurements acquired during a gravimetric and altimetric campaign that took place in the Azores region, Portugal, in October 1997. This system was originally developed with the purpose of determining the navigational parameters (attitude, velocity and position) of an aircraft. However, it is also capable of producing estimates of the vertical gravity anomaly. Since this anomaly is an important perturbation to the performance of the navigation system, it had to be estimated together with the inertial sensor biases, in order to improve the final solutions. As a result, one decided to test the ability of a low cost Inertial Measurement Unit (IMU) to work as a gravity measuring device.

This paper describes the methodology followed to obtain estimates of the local gravity anomaly by integrating GPS and inertial measurements.

The results show that the gravity anomaly measured by the differential GPS/IMU integrated system matches quite well the results obtained with the Lacoste & Romberg (L&R) sea and air gravimeters. The ability of this kind of inertial system to recover gravity anomalies, focused on medium wavelengths perturbation signals, was evaluated. The lack of long term stability of the IMU sensors renders long wavelength gravity anomaly determination impracticable for precise.

The DGPS/IMU integrated system can be seen as a complement to a gravimeter, which exhibits long term stability.