Vertical gravity gradient modeling and its influence on gravity datum transfer

In the past, the free-air gradient −308.6 × 10⁻⁸ s⁻² was used as the vertical gravity gradient of the measuring point in gravity data processing, which resulted in inaccurate instrument height corrections. To investigate the influence of using the vertical gravity gradient, theoretical gradients of the Jinzhai baseline field in the Dabie Mountains were calculated using DEM data and WGM2012 gravity anomaly data. Adjustment results were compared with those using the free-air gradient. Using the theoretically calculated vertical gravity gradient correction improved the scale factor calibration precision by an average of 0.00007. The average precision of gravity adjustment results under different datum controls increased from 2.23 × 10⁻⁸ m/s² to 1.45 × 10⁻⁸ m/s². In a single-datum control adjustment, the maximum effect of the actual vertical gravity gradient on datum transfer is 8.7 × 10⁻⁸ m/s², while the effect without it is as low as 9.0 × 10⁻⁸ m/s² and as high as 27.5 × 10⁻⁸ m/s². In a multi-datum system, using the actual vertical gravity gradient yields the best results. Even with the three-datum control adjustment, the average effect of the free-air gradient correction on the results reaches 3.9 × 10⁻⁸ m/s². Therefore, incorporating measured or theoretically calculated vertical gravity gradients into gravity data processing is essential for significantly enhancing its accuracy and precision.