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GPS APPLICATIONS AND REQUIREMENTS 32 Findings The implementation of the FAA's WAAS should enable all navigation requirements through Category I precision approach to be met with wide-area DGPS. Category II/III approaches and landings will still require local DGPS augmentations. The presence of SA and A-S increases the cost and complexity of WAAS and limits the effectiveness of RAIM. The full navigation and surveillance capabilities of GPS will not be realized until air traffic management procedures and related technical systems are revised and modernized. In addition, GPS requirements based on the simultaneous use of the system for both navigation and surveillance must be established. Radio frequency interference with GPS signals could prove to be a significant problem for aviation applications. Techniques to mitigate its effects, such as the use of a second GPS frequency, must be explored. MARITIME USE OF GPS In general, mariners use GPS for either navigation or positioning, although GPS has recently been applied to surveillance applications as well. It is important to define these broad categories of use before discussing more specific marine GPS applications and their requirements. Marine navigation can be defined as the process of planning, recording, and controlling the movement of a craft or vessel from one place to another. During this process, there are generally concerns regarding commerce, expediency in transport, human safety, and environmental protection. When a vessel is navigating, it is often in situations where it is committed to a course of action based on these concerns. This has led to specific requirements for accuracy, integrity, availability, and area of coverage. Marine positioning usually refers to activities such as hydrographic surveying, locating underwater objects, or other activities on the water where a vessel is not traversing a path to a destination. As with marine navigation, marine positioning generally has well-defined accuracy requirements, but because of the amount of time on station, integrity requirements can often be relaxed. Because of the cost of the resources used in conducting some positioning operations, however, lack of availability can have a severe economic impact. In an effort to avoid the economic and environmental costs of vessel collisions and groundings, many of the nations ports and harbors are being equipped with surveillance systems known as vessel traffic services (VTS), which monitor the course and speed of ships, just as the air traffic control system tracks the flight paths of aircraft. Some of these systems operate with personnel similar to air traffic controllers who monitor and advise ships and