Arzu Soycan, Yalcin Yilmaz

Evaluation and Regional Adjustment of the Ultra-High-Resolution GGMplus Geoid Model: A Case Study in Türkiye

Abstract The Global Gravity Model plus (GGMplus) ultra-high-resolution geoid model and its regionally adjusted version, ADJ_GGMplus, are evaluated over Türkiye by comparing them with national geoid models (TG-03 and TG-20) and GNSS/levelling observations. The GGMplus model, with a spatial resolution of approximately 200 meters, offers a significant potential for regional geoid modelling, particularly in topographically and geologically complex areas. However, systematic biases – especially in regions with steep gravity gradients – necessitate regional calibration. In this context, the primary objective of this research is to derive and evaluate the ADJ_GGMplus model by incorporating 187 GNSS/levelling control points to improve local geoid accuracy. National-scale comparisons and local-scale analyses across 17 regions with varying geographical characteristics were conducted to quantify model performance. The results indicate that unadjusted GGMplus tends to underestimate geoid heights, with deviations reaching several decimetres in rugged terrain, whereas ADJ_GGMplus significantly improves model performance by reducing absolute mean errors from over 0.9 m to 0.19–0.35 m in critical regions and substantially mitigating systematic biases across the study areas.. Statistical metrics such as RMS, skewness, kurtosis, and Kolmogorov-Smirnov test results support these findings. Overall, the adjusted model demonstrates enhanced reliability and suitability for geodetic, engineering, and sea-level-related applications in Türkiye.

Doi https://doi.org/10.5200/baltica.2026.2.4

Keywords GGMplus; TG-03 geoid model; TG-20 geoid model; Geoid modelling

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