Space Based Real-Time Kinematic GPS for National Geodetic Survey Texas Height Modernization

Global Positioning System (GPS) are utilized to obtain a person location on the Earth.  GPS provides users of their location in Latitude, Longitude and Ellipsoid Height.  The Ellipsoid Height is how far away a person is from the spherical shape or globe shape that represents the Earths surface.  The perfect sphere does not coincide with the Earth surface in all locations. The sphere or a spheroid (the mathematical latitude and longitude lines on the surface) is actually a little flatter on the top and bottom.  This is to mean that the Earth is “squashed” down making an elliptical shape or Ellipsoid.

Most people want an elevation from Mean Sea Level (MSL).  In order to obtain this value surveyors and engineers will utilize Differential GPS, where one GPS unit is placed on a known MSL elevation (Base Station) and another on the point (Rover Station) in which you wish to determine a new elevation. Currently all the information from the Base Station is sent to the Rover Station via cellular phone internet connections.  This system is called Real-time Kinmatic GPS (RTS-GPS).  Cellular internet connection are not conducive to remote or rural areas of Texas.

It is proposed that a space based (SB) RTK-GPS should be used to provide corrections in areas where no other corrections can be obtained without additional terrestrial infrastructure development. A solution was developed that connects to the internet using Hughes Network System’s Directway broadband satellite between the Base Station and Rover Station. Data would be received at a mobile vehicle and then locally broadcast to a Rover Station.

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