| Global Positioning System: A satellite based | | | | amazing. Accuracy varies based on various |
| navigation system providing accuracy usable for | | | | factors, but it can be as good as a few meters! |
| side scan sonar surveys on a worldwide basis. | | | | Land-based supplemental devices can be used to |
| GPS has become a universal, reliable positioning | | | | improve accuracy if higher precision is |
| system. Inherent errors in GPS (implemented by | | | | required.The application of the GPS is very broad, |
| the Department of Defense) create inaccuracies | | | | and as the prices come down the number of |
| of more than 100 meters. Differential base | | | | uses is increasing. Portable GPS devices are used |
| stations can reduce these errors to less than two | | | | by fisherman and hikers to help them navigate in |
| meters but are time consuming to survey-in and | | | | the wild. Many new cars are being equipped with |
| have limited range.GPS stands for the Global | | | | GPS systems to help drivers with navigation. The |
| Positioning System. It refers to a system of | | | | military uses GPS to guide cruise missiles to |
| satellites and receivers that allow people and | | | | pre-specified targets. For a new activity inspired |
| devices to pinpoint their precise location on the | | | | by GPS, you can read out our answer to: What is |
| earth. The heart of the system relies on 24 | | | | geocaching?On 2 May 2000, the Department of |
| satellites that orbit the earth twice per day. | | | | Defense switched off selective availability (SA) |
| Devices that are equipped with GPS equipment | | | | which made GPS readings less accurate. They |
| receive transmissions from at least a few of the | | | | reserve the right to turn it back on during national |
| satellites and are able to discern very precise | | | | crises and the like, but for the most part GPS |
| positioning data.The first GPS satellite was | | | | devices are now about 10 times more accurate |
| launched in 1974 and the 24th was launched in | | | | than they were when selective availability was |
| 1994. The system is operated by the United | | | | turned on!(Global Positioning System), a worldwide |
| States Department of Defense and use of the | | | | MEO (medium or middle, earth orbit) satellite |
| system is free for anyone. New satellites are | | | | navigational system formed by 24 satellites |
| periodically launched to replace aging ones. As the | | | | orbiting the earth and their corresponding |
| technology has improved, the cost of GPS | | | | receivers on the earth. The satellites orbit the |
| devices has plummeted while the accuracy has | | | | earth at approximately 12,000 miles above the |
| increased. Small portable GPS receivers have | | | | surface and make two complete orbits every 24 |
| become very affordable, and the accuracy is | | | | hours. |