Vol.:(0123456789) Surveys in Geophysics https://doi.org/10.1007/s10712-020-09596-3 1 3 The Use of Gravity Reductions in the Indirect Strapdown Airborne Gravimetry Processing Mehmet Simav 1 Received: 18 March 2020 / Accepted: 14 May 2020 © Springer Nature B.V. 2020 Abstract Strapdown airborne gravimetry (SAG) is one of the most efcient techniques used in geod- esy and geophysics for acquiring gravity data on relatively large regions in a faster and cost-efective way or to fll in the gravity data gaps on areas where it is neither practical nor possible to make terrestrial measurements. Recent studies have shown that accuracies of 1 mGal and precision of sub-mGal levels are possible with the strapdown inertial systems modifed for gravimetry (e.g., temperature stabilization). Besides the advancements in the instrumentation, data processing and integration algorithms are evolving consistently. This study investigates the contribution of long- and short-wavelength gravity reductions fol- lowing the remove–restore procedure in the indirect SAG processing, where the gravity disturbance at fight altitude is modeled stochastically as an additional system state in the Kalman flter sense. The proposed method is implemented to the airborne data collected in central Turkey in 2018 with a thermally stabilized strapdown inertial measurement unit of navigation-grade type. The inclusion of the long- and short-wavelength gravity reductions in the SAG processing limits the in-run bias variations of the Z-accelerometer and changes the parameters of the third-order Gauss–Markov gravity state model signifcantly. Utiliza- tion of the reduced gravity disturbance in the processing provides better long-wavelength stability in the solution by reducing the mean bias of about 2.60 to 0.65 mGal between the airborne gravity estimates and a high-resolution global gravity model. Moreover, a remark- able improvement in the internal precision is achieved when the gravity reductions are introduced into the SAG solution. Comparisons at the crossover points demonstrate that the application of gravity reductions yields considerably lower crossover residuals than the standard solution without reductions. The non-adjusted crossover diferences of the long- and short-wavelength removed and restored SAG solution result in an RMSE value of 0.79 mGal, that is, 40% better precision than the standard solution. Keywords Strapdown airborne gravimetry · Indirect approach · Gravity reductions · Global geopotential model · Residual terrain modeling · Remove–restore * Mehmet Simav mehmet.simav@harita.gov.tr 1 Geodesy Department, General Directorate of Mapping, Tıp Fakültesi Caddesi, Cebeci, 06590 Ankara, Turkey