Kathyrn Johnston – the tides are nearly perfectly vector Newtonian at earth based gravimeter stations

Cool Worlds Podcast: #5 Kathryn Johnston – The Milky Way, Dark Matter vs MOND, Gaia at https://www.youtube.com/watch?v=UHNYvK4-MJY

Kathyrn Johnston, The vector tidal signal at a superconducting gravimeter or more modern gravimeter detector shows a nearly pure Newtonian signal. You can get the JPL time series of precise positions for the sun moon earth every second, use a WGS84 ellipsoid and station position, International Earth Rotation Service rotation rate and calculate GM/R^2 for the sun at the station minus the sun at the center of the earth, add the moon at the station minus the moon at the center of the earth, add the centrifugal acceleration from earth rotation and put that into station North East Vertical. It is nearly perfect fit with a linear regression. Two numbers for each axis will lock the station data to a global standard reference model. The broadband seismometers are just barely able to detect the “sun moon vector tidal signal” but all three time series for the three axes each only require a linear regression. So 6 numbers. The MEMS gravimeters and others like atom interferometer gravimeters will drift. But since you only need to solve for 6 parameters you can calibrate the otherwise drifting baseline to the model every hour or every day. The residual after you remove the calibrated signal is all “earth local” and mainly atmosphere, ocean surf, cars trucks and such. The raw data is archived to update models over time. It is a convenient way to set global reference gravity for low cost local gravity efforts. There are a LOT of local gravity measurement and mapping efforts. About 20 kinds of sensors. Richard Collins, The Internet Foundation