Field evaluation of four state-of-the-art astrogeodetic systems along the Mississippi River: CODIAC, VESTA, QDaedalus and TSACS

• Deflections of the vertical characterize the precise direction of local gravity and the slope of the geoid. They are an increasingly valuable tool to ensure accurate modeling of heights for applications related to water and natural hazards. • The deflection of the vertical can be measured astronomically by comparing directions to stars observed with a telescope and camera with the direction of gravity established by sensitive inclinometers in the instrument body. Modern systems can achieve accuracies of ∼ 0.1 arcseconds with less than an hour of observing. • Four different operational measurement systems—CODIAC, QDaedalus, TSACS, and VESTA—were gathered to perform colocated observations along a stretch of the Mississippi River between Baton Rouge and New Orleans to compare their performance and assess gaps in the gravity field. • The study reveals both quantitative performance characteristics and practical operational tradeoffs of each of the participating instruments under typical field conditions, providing insights into future survey design. Deflections of the vertical, which quantify the direction of gravity near the Earth’s surface, are conventionally observed using astrogeodetic instruments. Our research compared four astrogeodetic systems together for the first time at similar observing sites: the zenith cameras COmpact DIgital Astrometric Camera (CODIAC) and VErtical by STArs (VESTA), and the robotic total station-based astrogeodetic systems QDaedalus and Total Station Astrogeodetic Control System (TSACS). We deployed the four systems at 32 sites along a 190 km profile Mississippi River between Baton Rouge and New Orleans, using 14 primary sites for direct comparison and evaluating performance with analysis of variance (ANOVA) and least-squares bias analysis. This analysis finds that CODIAC was able to have an internal consistency better than ± 0.05 arcseconds for its 20-minute observations. Relative to CODIAC, the results suggest that, for 45-minute occupations in a typical astrogeodetic campaign, the VESTA, QDaedalus, and TSACS are capable of 0.15–0.20 arcsecond accuracy. One of the main goals of the survey was to fill gaps in geoid validation data in this region; these results will be used to test the National Geodetic Survey’s new GEOID2022 model and design future field campaigns. This survey also highlights the challenges of designing an astrogeodetic profile in a busy commercial corridor and serves as an instructive experience in 21st century operational geodetic astronomy.