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