Hemisphere GPS

Website Links

Description

GPS is based on a constellation of 24 U.S. government-owned satellites (plus several working back-ups) that circle 22,000 kilometres above the Earth twice a day in precise orbits. The satellites constantly transmit coded information in ultra-high or UHF frequencies (1.575 GHz) back to GPS receivers on the ground. There are two GPS services: the Precise Positioning Service (PPS) that the U.S. Department of Defense reserves for itself and authorized partners for security reasons, and the Standard Positioning Service (SPS) available free for all worldwide civilian users. The Department of Defense, to maintain a strategic advantage, used to intentionally degrade the accuracies of the SPS or civilian GPS system. But it stopped doing so in 2000 to encourage more development of GPS technology and of related economic and social benefits. A ground-level GPS receiver, using pre-programmed data, knows where each satellite is in its orbit. The receiver takes this information and compares it with the time required to receive each satellite's signals at ground level, to calculate a specific geographic position on Earth. A GPS receiver can "observe" only those satellites orbiting above the horizon, which normally totals from four to 12. The receiver selects the satellites offering the best "view" to do its calculations. If some satellites become blocked or "shaded" by tall buildings or other major obstacles, the receiver automatically uses alternate satellites to maintain the position fix. ...

Products & services

Similar companies nearby