AN EVALUATION OF THE GRAVITY CONTROL NETWORK IN NORTH AMERICA

Abstract

Observations with a LaCoste and Romberg geodetic gravimeter having a very low nearly linear drift rate, a high reading precision, and a world wide range were made at approximately three hundred sites in order to check and extend the gravity control network in North America. The sites occupied were mostly at former gravimeter bases located at airports, harbors, universities, and pendulum stations. The instrument was calibrated against the North American standardization range of pendulum measurements from Paso de Cortes, Mexico, to Fairbanks, Alaska, using the weighted mean values of the observations established with the U. S. Coast and Geodetic Survey, Cambridge University (England), and Gulf‐University of Wisconsin pendulum equipment. A statistical evaluation of the precision of the network based on the reoccupations at 40 major control stations gives an estimated standard deviation of 0.08 mgal. The airport network of bases previously reported by Woollard (1958) that was established with high range Worden gravity meters was found to require a systematic correction of 0.3 mgal per 1,000 mgal change because of the difference in calibration standard used. The adjusted values for the forty airport stations reoccupied agree on the average to 0.2 mgal with the results of this study. The reoccupations of the old pendulum observation sites of the U. S. Coast and Goedetic Survey suggest that much of this network is in error by over 3 mgals. Descriptions of sites occupied and the principal facts for position, elevation, observed gravity, and free‐air and Bouguer anomalies are presented.