On the accuracy of marine gravity measurements

We have assessed the accuracy of Lamont-Doherty Geological Observatory's global marine gravity data bank by examining the crossover errors (COEs) at intersecting ship tracks. More than 63,000 COEs were found, having a standard deviation of 22.43 mGal (mGal = 10−5 m s−2). We use the COEs to find and remove linear drifts and DC shifts present in the data set. This adjustment reduces the standard deviation to 13.96 mGal. COEs generally decrease with latitude, which we attribute to uncertainties in the Eotvos correction. High COEs occur in areas of high gravity gradients. These two features point to poor navigation as the principal source of error in marine gravity surveys. COEs have generally been decreasing during the last two decades, reflecting improvements in instrumentation and quality of navigation. A comparison of the shipboard gravity data to Seasat derived gravity revealed a 9-mGal bias in the terrestrial data, which probably reflects uncertainties in choice of reference field. The adjusted data set was used to generate a gravimetric geoid for the NW Atlantic Ocean. By removing this geoid from the Seasat sea surface heights, a residual “geoid” was obtained. A special feature of this map is an elongate ENE trend that appears to correlate with the edge of the Gulf Stream.

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