Gravity measurements in an airplane using state‐of‐the‐art navigation and altimetry

Abstract

In 1976 the U. S. Naval Oceanographic Office made experimental gravity measurements over the Atlantic in an airplane using a LaCoste and Romberg shipboard gravity meter, a Honeywell electrostatic gyro inertial system, a Rosemont pressure port altimeter, a Honeywell radar altimeter, Loran C and other electronic navigational aids. Preliminary results were reported at the 47th Annual International SEG Meeting in Calgary, Canada, in 1977. These preliminary results were compared with sea gravity data furnished by the Naval Oceanographic Office and were found to be in general agreement. However, there were some unexplained systematic errors of about 15 mgal and the airplane gravity profiles were considerably more noisy than helicopter gravity profiles reported by William Gumert (1977, personal communication). After the paper was given, we found that corrections for Schuler oscillations in the inertial system significantly reduced the systematic errors. We also found that by making full use of a half‐second sampling rate of the radar altimeter, we could make meaningful vertical acceleration corrections relative to sea level as well as relative to an atmospheric pressure surface. A comparison of the two corrections showed that variations in the isobaric surfaces were the main cause of the noise in the airplane gravity profiles. It also became apparent that the noise could be reduced by flying slower or making successive flights at different speeds.