A high-precision digital astrogeodetic traverse in an area of steep geoid gradients close to the coast of Perth, Western Australia

Abstract

We present results from a new vertical deflection (VD) traverse observed in Perth, Western Australia, which is the first of its kind in the Southern Hemisphere. A digital astrogeodetic QDaedalus instrument was deployed to measure VDs with $${\sim }$$ 0.2 $$''$$ precision at 39 benchmarks with a $${{\sim }}1~\hbox {km}$$ spacing. For the conversion of VDs to quasigeoid height differences, the method of astronomical–topographical levelling was applied, based on topographical information from the Shuttle Radar Topography Mission. The astronomical quasigeoid heights are in 20–30 mm (RMS) agreement with three independent gravimetric quasigeoid models, and the astrogeodetic VDs agree to 0.2–0.3 $$''$$ (north–south) and 0.6–0.9 $$''$$ (east–west) RMS. Tilt-like biases of $${\sim }1\,\,\hbox {mm}$$ over $${\sim }1\,\,\hbox {km}$$ are present for all quasigeoid models within $${\sim }20\,\,\hbox {km}$$ of the coastline, suggesting inconsistencies in the coastal zone gravity data. The VD campaign in Perth was designed as a low-cost effort, possibly allowing replication in other Southern Hemisphere countries (e.g., Asia, Africa, South America and Antarctica), where VD data are particularly scarce.