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The Global Positioning System consists of three separate parts. The first section includes twenty-four satellites that are traveling 20,000 km around the Earth in twelve-hour circular orbits. So basically, every satellite takes 12 hours to finish a full cycle or lap around the Earth. The satellites are separated into 6 groups of 4 to ensure that they could be detected from any position on the surface of the Earth. This means that there are 6 orbital planes that surround the Earth completely. The satellites send out radio signals to the Earth, these signals consist of information found by the satellite. With the use of GPS unit ground-based receivers, these signals are identified and utilized to figure out the location of the receivers. These radio signals are transmitted at 2 different types of L-band frequencies. An L-band is a variety of frequency ranging from 390 to 1550 MHz. Within every signal, a sequence that is coded is transmitted. Making comparisons with the sequence received and the original sequence gives scientists a chance to figure out the length of time for the signal to get to the Earth coming from the satellite. When learning about the Troposphere and the Ionosphere, the 2 atmospheric layers that are around the surface of the Earth, the signal delay is helpful. There is a 3rd signal coming from the satellite, which is transmitted to the hand held GPS receivers. What this signal consists of is data regarding the health and location of the satellite. The ground station is the second section of the GPS unit, which includes an antenna, a receiver, and tools for communication that will send out information to the data center. At every site there is an omni-directional antenna that acts similar to a radio antenna in a car. This detects the satellite signals and sends them as electric currents to the site receiver. It is the job of the receiver to divide the signals into various channels chosen for a specific satellite and frequency at a specific time. As soon as the signals are isolated, the receiver can decipher them and segregate them into separate frequencies. Using this data, the receiver creates a general location (height, longitude, and latitude) for the antenna. Later on, the data obtained by the receiver could be processed once more by scientists to figure out various things like a different set of location coordinates for the antenna but this time around using millimeter accuracy. The data center is the third section of a GPS unit. The data center has two roles. It is used to control and monitor the global hand held GPS stations, and also to obtain and analyze information from the receivers in those GPS stations with the use of automated computer systems. When processed, the information, together with the initial raw data can be accessed by scientists worldwide for use in different applications. Seeing as hand held GPS sites are built and monitored by various institutions in the globe, there are a lot of data center locations. Mike Moore is published on more than 300 websites. He writes recreational and commercial transport topics that cover topics from Fleet management and Commercial Trucking Equipment to Travel and Personal GPS Systems. He is published on various website including http://www.drivengps.com
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