Gravity Change from 2014 to 2015, Sierra Vista Subwatershed, Upper San Pedro Basin, Arizona

Relative-gravity data were collected at 58 stations over ten days between May 27, 2015 and June 25, 2015 using a Zero Length Spring, Inc. Burris relative gravity meter (mention of a particular trade name does not imply endorsement by the U.S. Governement). In total, 179 relative-gravity differences were observed. Relative-gravity-meter drift was removed from the observations by modeling drift as a continuous function of time (Kennedy, 2015; Kennedy and Ferré, 2015). Absolute-gravity data were collected at 14 stations during the week of May 18–22, 2015 using a Micro-g Lacoste, Inc. A-10 absolute gravity meter. Network adjustment was performed using Gravnet software (Hwang, 2002) to provide representative station values as of June 1, 2015. During the adjustment, an iterative procedure was used to identify bad relative-gravity observations as those with high residuals (the difference between the observed value and the network-adjustment-predicted values). The a priori standard deviation of the gravity differences was estimated by summing in quadrature the standard deviation from several samples collected during each occupation; this estimate was revised upward by a factor of 3 based on the a posteriori variance of unit weight and Chi-square test statistic. In total, 16 out of 179 observations were excluded from the adjustment. The residuals are approximately normally distributed with standard deviation of 4.1 µGal. Also included are 2014 values from Kennedy (2015), and the change in gravity from 2014 to 2015 is calculated.

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  "fn": "Jeffrey R Kennedy",
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                                            [
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  "Sierra Vista, AZ",
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