This dataset represents the network-adjusted results of relative- and absolute-gravity surveys. Relative-gravity surveys were carried out using a Zero Length Spring, Inc. relative-gravity meter. The effect of solid Earth tides and ocean loading were removed from the data. Instrument drift was removed by evaluating gravity change during repeated measurements at one or more base stations. Absolute-gravity surveys were carried out using a Micro-g LaCoste, Inc. A-10 absolute-gravity meter. Vertical gradients between the different measuring heights of the absolute- and relative-gravity meters were measured using a relative-gravity meter and tripod, and used to correlate the measurements between the two instruments. Relative-gravity differences and absolute-gravity data were combined using least-squares network adjustment. Additional information about the network adjustment is provided under Data Quality. Data processing was carried out using GSadjust (https://code.usgs.gov/sgp/gsadjust).
First posted - May 23, 2017
Revision posted - March 16, 2021
Changes in version 2.0
This dataset includes additional data from 3 microgravity surveys carried out in 2017-2018. Data from the initial data release, which included 4 surveys from 2016-2017, are also included in this data release. Slight differences in gravity values and standard deviation may exist between this and the original data release. In all such cases, this version's values should replace those in the original.
Station names are updated in this version to reflect the names used for collocated monitoring wells and in accompanying publications. Changes include capitalization, punctuation, and replacing "usbr" with "MES" at certain stations.
The original data release included gravity-change values converted to meters of water. For clarity, these are ommitted in this version. Storage change in meters of water can be calculated from gravity change using the Bouguer infinite slab approximation, whereby [change in gravity, in microGal]/41.9 = meters of water.
