Geoid heights in Costa Rica, Case of Study: Baseline Along the Central Pacific Zone

Abstract

A precise orthometric height (H) and orthometric height difference (ΔH) determination is required in many fields like construction, geodesy and geophysics. H is often obtained from an ellipsoidal height (h) and geoid height (N) of a geoid model (GM) because this computation does not have the spirit leveling restrictions on long distances. However, the H accuracy depends on the GM local area adaptation, and current global geoid models (GGMs) have not been yet evaluated for Costa Rica. Therefore, this paper aims to determine which GGM maintains a better fit with a GPS/levelling baseline that contains the gravity full spectrum. A 74 km baseline was measured using GPS, spirit leveling and gravity measurements to validate the N computed from EGM2008, EIGEN-6C4, GECO, EGM96, GGM05C and GOCO05C. First, an absolute N assessment was made, where geoid height from the GGMs (N^GGM) were directly compared to the geometric geoid heights (N^geo) obtained from GPS and spirit levelling. A bias fit (N_bias) of about 2 m was computed from this comparison for most GGMs with respect to the local vertical reference surface (W₀). By subtracting the N_bias, a relative geoid height (ΔN) assessment was designed to compare the differences between GGM relative geoid height (ΔN^GGM) and geometric relative geoid height (ΔN^geo) on segments along the baseline. The ΔN comparison shows that EGM2008, EIGEN-6C4 and GECO better represent the Costa Rican Central Pacific Coastal Zone and over long distances, ΔH can be computed with a decimeter to centimeter precision.