Navigation and Seamanship

6.4.1. Global Positioning System (GPS)

Navigation is the act of fixing the position and determining the course of movement of a vessels. Since prehistoric times, the sailors have been using various traditional techniques to fix their position at sea. Moreover, the ancient mariners followed the near coast navigation. When navigators first sailed into the open ocean, they discovered they could chart their course by following the stars. In the early 20th century several radio wave -based navigation systems and equipments were developed, which were used in the World War II. The problem with the radio wave based navigation systems was that they were restricted to use only in certain parts of the world. High-frequency radio waves can provide accurate position location but can only be picked up in a small, localized area. Lower frequency radio waves can cover a larger area, but cannot provide accurate position location.

Then it was decided to have one method to provide coverage for the entire world. A transmitter high above the Earth sending a high-frequency radio wave can cover a large area. This is one of the main principles behind the GPS system. The first GPS satellite was launched in 1978. The first 10 satellites were developmental satellites, called Block I. From 1989 to 1993, 23 production satellites, called Block II, were launched. The launch of the 24th satellite in 1994 completed the system. Initially, they were defense devices developed by the US government. It was then opened up for civilian use since 1993. GPS, the Global Positioning System, is the only system today able to show you your exact position on Earth at any time, any where, and in any weather. In the late twentieth century, the global positioning system (GPS) largely replaced the Loran. GPS uses the same principle of time difference from separate signals as Loran, but the signals come from satellites. GPS is an acronym stands for Global positioning system. These satellites are maintained and operated by U.S. Dept of Defense. Although originally conceived for military needs, GPS has a broad array of civilian applications including surveying vehicle tracking, land, aviation and marine navigation.