Geodetic Astronomy with an Imaging Robotic Total Station

Abstract:

Astronomical measurements of the deflection of the vertical offer unambiguous, robust indications of the shape of the geoid. Compared with popular methods of geoid measurement, such as GNSS/leveling and gravimetry, astrogeodetic data can also be gathered rapidly and cost-effectively. Astrogeodetic methods are therefore a desirable complement to these techniques. NOAA's National Geodetic Survey has developed an astrogeodetic measurement system for the Leica TS60 imaging robotic total station. This total station is distinguished by its built-in image sensor, which eliminates the need for an external image sensor and modifications to the total station's optics. The total station's observation sequence is coordinated with inexpensive peripheral hardware. During an observation session, a microcontroller communicates with the total station and controls its movements, directing it to capture video of selected stars with GPS-referenced timing. The video, total station orientation, and timing data captured by the system are later analyzed to measure the elevation angles of the target stars and estimate astronomic latitude and longitude. Initial results suggest an accuracy better than ±0.2 arcseconds, which is sufficient for geoid validation and datum orientation. In this work, we characterize the suitability of the Leica TS60 for astrogeodetic observations; describe the hardware and software that coordinate data collection and analysis; and characterize the performance of the instrument using comparisons to historical measurements. The accuracy achieved with low-cost control hardware and rapid data collection distinguishes this project from other astrogeodetic systems.