TESTS OF AN AIRBORNE GRAVITY METER

Abstract

Gravity measurements have been made in an airplane and a contour map using 20 mg interval constructed for 12,000 ft elevation. The LaCoste and Romberg instrument used is similar to that recently tested on a surface ship. The meter was installed in a B-17 aircraft equipped with APR (precision radar altimeter) and aerial mapping cameras for the accurate navigation needed for determination of the centrifugal (Eötvös) and elevation corrections. A series of nine lines over the Imperial Valley gave results believed to be accurate to about 10 mg or better as indicated by (1) the general consistency of the contour map and its similarity to a free air gravity map drawn from ground data, (2) repeat observations over almost the same courses, (3) agreement of independent values at line crossings (with Eötvös correction differences of as much as 2,000 mg), and (4) agreement with values calculated from ground gravity stations. Short period disturbances due to accelerations of the airplane are averaged over a certain time interval. This results in an “uncertainty principle,” in that the accuracy of observation increases as this time interval is lengthened, but details of the gravity variation are lost due to the increased distance traveled during each measurement. The values reported are for an averaging time of approximately three minutes corresponding to a travel distance of about ten miles. The quality of the results is adequate for geodetic purposes and possibly for certain regional geophysical problems.