Title: Sea-gravimeter trials on the Halifax test range aboard CSS BAFFIN
Abstract:Two precisely located and calibrated lines on the Halifax Sea Gravimeter Testing Range were traversed back and forth for a total of 100 times while gravity measurements were made with both the LaCoste...Two precisely located and calibrated lines on the Halifax Sea Gravimeter Testing Range were traversed back and forth for a total of 100 times while gravity measurements were made with both the LaCoste and Romberg and the Askania-Graf sea-surface gravimeters. During the three-week test, which was concluded in October 1963, the rms heave accelcrations experienced varied from 2 to 78 gals with a median value of 13 gals. Useful gravity readings were obtained with t he LaCoste gravimeter up to heave accelerations of about 30 gals and up to at least 50 gals for the Askania. (Cross coupling determinations were not possible at greater accelerations.) The LaCoste gravimeter occasionally hit its stops at accelerations greater than 35 gals, and the results in general were 'noisier' than those for the heavier-damped A kania gravimeter. Gravimeter errors were determined by subtracting observed values, corrected for Eotvos effect, from reference values determined previously from ocean-bottom measurements. The mean LaCoste gravimeter error observed during a traverse varied from run to run to form a near normal distribution with mean +0.6 mgal and tandard deviation 3.9 mgal. Corresponding figures for the Askania were: mean -0.4 mgal and standard deviation 2.7 mgal. The distribution, however, was markedly skewed toward negative values. Long-period accelerations recorded by the horizontal accelerometers used with the LaCoste gravimeter frequently proved to be fictitious and the computed Browne corrections accordingly to be too large. Corrections for cross-coupling effect were determined after the test by using magnetic-tape records of heave and surge acceleration. Thesc determinations generally agreed closely with the observed Askania errors except in very rough scas and when course-keeping was poor. Instrument drift, determined by periodic dockside mcasurements, was negligible for the LaCoste gravimeter and somewhat irregular over a 7.0-mgal range for the Askania.Read More