GPS (Global Positioning System)

GPS, which is the world’s most accurate method of navigation, was conceived to enhance navigation accuracy for U.S. military forces during the early 1970s. Since 1984, the GPS has found application in a myriad of systems–from automotive monitors advising drivers of the locations of hotels and restaurants to guidance systems which allow bombs and missiles to make direct hits on targets. Of the two global satellite navigation systems currently operating, the GPS has gained preference in most international markets. GPS receivers take information transmitted from the satellites and uses triangulation to calculate a user’s exact location. GPS is used on incidents in a variety of ways, such as:

To determine position locations; for example, you need to radio a helicopter pilot the coordinates of your position location so the pilot can pick you up.
To navigate from one location to another; for example, you need to travel from a lookout to the fire perimeter.
To create digitized maps; for example, you are assigned to plot the fire perimeter and hot spots.
To determine distance between two points or how far you are from another location.

GPS is primarily a navigation system for real-time positioning. However, with the transformation from the ground-to-ground survey measurements to ground-to-space measurements made possibly by GPS, this technique overcomes the numerous limitations of
terrestrial surveying methods, like the requirement of intervisibility of survey stations, dependability on weather, difficulties in night observations, etc.. These advantages over the conventional techniques, and the economy of operations make GPS the most promising
surveying technique of the future. With the well-established high accuracy achievable with GPS in positioning of points separated by few hundreds of meters to hundreds of km, this unique surveying technique has found important applications in diverse fields.

The three segments of GPS are the space, control, and user:

Space Segment — Satellites orbiting the earth
The space segment consists of 29 satellites circling the earth every 12 hours at 12,000 miles in altitude. This high altitude allows the signals to cover a greater area. The satellites are arranged in their orbits so a GPS receiver on earth can receive a signal from at least four satellites at any given time. Each satellite contains several atomic clocks. The satellites transmit low radio signals with a unique code on different frequencies, allowing the GPS receiver to identify the signals. The main purpose of these coded signals is to allow the GPS receiver to calculate travel time of the radio signal from the satellite to the receiver. The travel time multiplied by the speed of light equals the distance from the satellite to the GPS receiver.

Control Segment — The control and monitoring stations. The control segment tracks the satellites and then provides them with corrected orbital and time information. The control segment consists of five unmanned monitor stations and one MasterControl Station. The five unmanned stations monitor GPS satellite signals and then send that information to the Master Control Station where anomalies are corrected and sent back to the GPS satellites through ground antennas.

User Segment — The GPS receivers owned by civilians and military
The User Segment consists of the receivers and the agencies or individuals that deploy them. Originally conceived of as a military system, the User Segment now contains many thousands of commercial and recreational civilian users as well as military users around the world.

GPS has benefited fromservice policies consistently set forth and applied that enabled its flourishing worldwide exploitation. With such a stable policy foundation in place, including assured continuity of separate military and civil signal resources available free of direct user fees, several key objectives for GPS services suggest themselves. Working to satisfy these objectives will promote continued growth in satel- lite-based Pt services, while expanding the myriad uses and international economic benefits derived from application of those services.

Justifying use of and preserving adequate frequency spectrum for GPS, its augmentations, and complementary space-based services, so they may operate free of unintentional disruption and interference on a global basis.

Continuing to improve the effectiveness and robustness of civil GPS as a commodity service operated for the public good.

Capitalizing on the technology investment by continuing to evolve national security, economic, and scientific applications of the technology for the benefit of U.S. and global infrastructures.

Consistently applying a customer-oriented service philosophy along with a policy of open signal availability to encourage international acceptance of civil GPS and its augmentations as international standards, while promoting open-market competition in GPS equipment and applications.