Geodesy: It’s about time
Prof. Geoff Blewitt
Department of Physics
University of Nevada, Reno
It has been said, “Geodesy is the oldest science.” Over 2000 years ago, ancient Greece concluded that the Earth is spherical. Moreover, Sun’s shadows were used to determine Earth’s circumference to within 2%. So, what is meant by “Geodesy: it’s about time”? (1) In a societal sense, “it’s about time” that geodesy is now solving society’s problems, from positioning our devices, to “saving the Earth.” (2) Scientifically, the accurate determination of slow time variations of Earth’s shape, gravity field, and rotation requires an accessible reference frame that is stable in time. Now 60 years into the space age, geodesy uses VLBI, SLR, and GPS to realize a stable reference frame which, together with geodetic satellite missions, can accurately track signals associated with tectonics, interior processes, volcanism, sea level, cryosphere, hydrology, atmospheric loading, water vapor, and climate change. (3) Instrumentally, geodetic observations depend inextricably on the stability of timing, importantly, in the context of general relativity. Continued exponential improvement in clocks (e.g., nuclear transitions) guarantees geodesy will continue to advance. Relativistic geodesy will enable direct sensing of gravitational potential and velocity, hence physical height and orbit parameters. Also, improved clocks could lead to fundamental discoveries. For example, dark matter constitutes 85% of all matter in the universe, yet direct detection remains elusive. Experiments are now using GPS atomic clock data to search for dark matter sweeping through the Earth system. GPS clocks are also being used to search for exotic low-mass quantum fields (ELFs) associated with black hole mergers. Improved timing, reference frame, and novel techniques together hold the key to geodesy’s future advances for science and society. Geodesy: It’s about time!