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Leica GRX1230 GPS While a multi-frequency GPS delivers centimeter and can deliver millimeter accuracy, we aren't using it to measure the movement of the house (I shared in this confusion; one of my first thoughts was "Where are you expecting it to go? - and when?"). Multi-frequency GPS are used so cancel out time differences in arriving signals, these time differences are almost entirely due to ionospheric noise (moisture and oxygen in the troposphere have a lesser effect). This is how they achieve that crazy precision. Flip this correction methodology upside down and use it at a fixed position (providing the house does not move). These techniques can now be used to derive the total electron content (TEC) between one of the satellites and the house. TEC is a count of the the number of electrons in a 1-meter cube of ionized plasma (extreme UV and cosmic radiation in the upper atmosphere photo ionizes the gas molecules at altitudes between 50-1000 km). Since there can be up to 12 satellites visible at a time scattered from horizon to horizon, the TEC can be calculated along as many as 12 rays through the atmosphere nearly simultaneously (within a second) giving one the ability to produce a 2-dimensional map over time. So . . . the GPS can be used to detect changes in the plasma density changes due to the time of day, season, atmospheric water vapor, and solar activity (especially during solar geomagnetic storms): it can be used to monitor the intrinsic ionosphere variability in near real-time. I know you won't be happy without at least one equation, so here's a simple one (you'd probably appreciate the ones about general relativity speeding up time in the satellite's weaker gravitational field and special relativity slowing it due to the satellite's high velocity all knotted up with an earth-centered, non-rotating frame of reference - but I'm not going there right now): TEC = (Delay * c * f^2) / 40.3
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