School of Forest Resources and Conservation		UF / IFAS
	GEOMATICS AREAS OF STUDY
Areas of Study Geomatics Faculty Research Undergraduate Courses Graduate Courses Facilities	GLOBAL POSITIONING SYSTEM is a world-wide satellite-based radio navigation system developed and operated by the US Department of Defense (DOD) NAVSTAR (NAVigation System with Timing And Ranging) program; GPS first satellite launch was in 1978 but the system became fully operational in 1994. GPS was originally conceived as a military system to provide its ground, sea, and air users with all-weather all-time navigation and positioning capabilities. Today, civilian users surpassed military users in numbers and applications to the point that GPS is now an inevitable tool for them. Surveying, mapping, and navigation professionals rely on GPS to provide basic positioning information with the ease of pressing a button. Positioning with GPS is accomplished through trilateration by measuring at least four ranges between the satellites and the receiver on the surface of the Earth. Applications of GPS are enormous including surveying and mapping. One can use GPS in any project requiring positioning, timing, and navigation. Cars, boats, airplanes, tractors, … etc are currently equipped with GPS receiving and processing units. The GPS system itself consists of three main segments, space, control, and user segments. The space segment consists of a constellation of at least 24 satellites orbiting the Earth’s in nearly circular orbital plane at an approximate altitude of about 22,000 km above the Earth’s surface. Each satellite orbits the Earth twice every day. The expected life span for modern satellites is around 10 years after which the satellite has to be replaced. Each satellite is equipped with a precise atomic clock accurate to one billionth of a second. The satellites transmit radio signals which when received on the Earth’s surface by a GPS receiver enables the observer to locate itself with respect to an Earth-Fixed-Earth-Centered Coordinate system with high accuracy. The user segment is in effect the receiver and the antenna used to receive and decode the satellite signal. The control segment consists of five ground monitoring stations in Hawaii, Ascension Island, Diego Garcia, Kwajalein, and Colorado Springs. The station in Colorado Springs also serves as a master station that transmits corrections to the satellites for satellite ephemeris parameters and clock coefficients.
	Last updated: 2/22/08 - Comments and suggestions welcome - webmaster