A comparison of stable platform and strapdown airborne gravity

Abstract

To date, operational airborne gravity results have been obtained using either a damped two-axes stable platform gravimeter system such as the LaCoste and Romberg (LCR) S-model marine gravimeter or a strapdown inertial navigation system (SINS), both with comparable accuracies. In June of 1998 three flight tests were undertaken which tested a LCR gravimeter and the Honeywell Laseref III (LRF III) strapdown INS gravity system side-byside in the same airplane. To our knowledge this was the first time such a comparison flight was undertaken. The flights occurred in Disko Bay, off the west coast of Greenland. Several of the flight lines were partly flown along existing shipborne gravity profiles to allow for an independent comparison of the results. The flight height was 300 m and the average flying speed was 70 m/s.

The results of the flight tests show that the gravity estimates from the two systems agree at the 2–3 meal level, after the removal of a linear bias. This is shown in Figure 1. This small discrepancy is near the combined noise levels of the two systems. Also evident in Figure 1 is the fact that the estimates provided by both systems agree very well with the shipborne data that was available directly below the flight line. Tables 1 and 2 summarize the statistics for flight lines where both systems operated free of the power supply and hardware problems that affected both systems on some flight lines.

It appears that a combination of both systems would provide an airborne gravity survey system that would combine the excellent bias stability of the LCR gravimeter with the higher dynamic range and increased spatial resolution of the strapdown INS.