C IL | So the radio waves coming from the GPS satellites travel through the ionosphere, which basically means the path is warped through a magnetic field, very slightly changing the distance/path the radio wave travels. Recall the speed of light is constant in a vacuum and atmospheric density, heat shimmer, ionosphere all cause slight but detectable/measurable changes.
A single base station corrects that deflection at a single point and broadcasts it, so if your rover is fairly close, you assume the satellites hitting your rover and passing through the same ‘slice’ of atmosphere/ionosphere and you are getting a fairly accurate correction.
For super high precision earthwork, there are systems to set up multiple base stations around the area of interest, say a square mile, and connect them to more accurately model these slight shifts in that area of interest because at some scale, that ‘slice’ of atmosphere is not homogeneous and the differences can be measured.
So if you have enough base stations, you can model the atmospheric disturbances and create a ‘virtual’ base station based on interpolating between the known measurements. So it is like the super high precision multiple base station example, just at a lower resolution of measurement because your base stations may be 50 miles apart but you can model/guess the correction factors for a virtual base station point that could only be a couple miles away drop your rover.
Remember that the geometry of the satellites means that you get much better horizontal accuracy than vertical accuracy, so you can get away with a lot less precise measurement for steering than for elevation. |