Navigation has many changes over the past century with the introduction of aviation. The first forms of navigating relied on knowledge of the area and being able to recognise landmarks and features of the ground.
When travelling by the sea, this was not very useful and ships would use the stars and sun and time to find their way via large areas of water. The celestial navigation (the term used for navigating using the stars) had its limitations too, the biggest of course being the weather.
Both of these navigation methods relied on dead reckoning by calculating a rough estimate of distance travel and direction. This gave the navigators a place to start when confirming their location.
The process of dead reckoning was improved with the use of accelerometers acting in 3 orthogonal directions to calculate distance travelled and direction. This still how was subject to many limitations. This was known as Inertial Navigation Systems (INS)
The next big step came with the discovery of Radio waves. This discovery lead to the ability to reference the subject’s location to a stationary unit. The early units used a number of principles of radio waves to transit their location. (Or information that could be used to determine the subjects location). LORAN, OMEGA, NDB, VOR are some of the examples of ground bases radio navigation systems.
Next came the ability to enter space. With the knowledge of radio waves quite extensive and technology allowing object to operate in space, in the late 1950’s a system called Transit was developed, sponsored by the Navy, to provide fixes and resets for INS.
Improvements to this system lead to the most commonly known GNSS system NavStar GPS (known as GPS). In 1973/74 the system met all needs1.
The GNSS stands for Global Navigation Satellite System. It refers to the whole system that includes infrastructure, users, management and applications that use one of the systems. There are several different GNSS which are at different stages. Each tab will explain the different GNSSs that are available2.
The GNSS systems operate by using a network of satellites that cover an area to give position information. Each satellite knows its own position and time in relation to earth. The unit then sends a signal to multiple satellites interrogating it receiving both the satellite position and information to calculate the distance from it. Once the unit has at least 3 satellites it can work out its position. In order to get actually height above the ground, the unit requires at least 4 satellites. The more satellites the unit is in contact with the more accurate the position. With more than 5 satellite, the some devices have the function to determine the accuracy of the satellite and know if any are not functioning (this however, does have limitation because it works on the theory majority rules).
Once the unit has their position it can be used in multiple ways.
One point to note is that the devices are always giving past information. It takes time to calculate and display the information. The position will be different depending on the speed of the device. The accuracy can decrease with an increase in speed. To overcome this problem the unit will need to know the time in which the signals were sent.
The position information can also come from ‘ground satellites’, which are unit on the ground that act as a satellite, which helps reduce error time or in other words not enough satellites. These ground satellite are used in aviation to help increase reliability of the service in order for aircraft to use them for landing in very low visibility conditions.
There are many different systems that use the GNSS to help people or organisations with their day to day lives. The most commonly known is navigation. With the ability determine location it is possible to use that information against maps to work out were you are. These devices can be found in aircraft, boats and ships, equipment, personal use and even spacecraft. There are also devices for the visually impaired.
The devices though are used for other scenarios than navigation. For example this information is useful for search and rescue to located people. It can be used for surveying. Anytime that position information is useful the GNSS can more often than not offer the solution.
Here is a list of other Global Navigation Satellite Systems also in development
This is U.S.'s answer of a GNSS system. Click here
Information about Europe's upcoming system. Click here
China attempt to rival the current GPS system. With 5 satellites already in place with more planned. There were talks of China combing their system will Galileo, however, these have fallen through due to political reason (Levin D., Mar 2009). Click here for more info (Wiki)
Russia’s GNSS was fully operational in 1995 under the Soviet Union. However, after their collapse the system was left to rot. Recently though the system was restored. Now in October 2011 the system is now fully functional and global. Click here for more info
This is india attempt to join the number of systems floating in space. As of April 2010 the system is in development. Click here for more info
This is a network of ground basic antennas with the purpose of augmenting the current GNSS. These stations act as satellite providing very accurate data to aircraft in order to combat the Selective Availability which presents a problem for precise navigation needed in some commercial industries such as aviation. With the use of these networks the accuracy can be pinpointed to within cm. This makes the GNSS systems useful for bad weather conditions because it provides the aircraft with the much needed accuracy to land in very low visibility. Click here for more info (Wiki)
Want to know more?
- GNSS in Aviation
- http://en.wikipedia.org/wiki/Global_Positioning_System or http://en.wikipedia.org/wiki/GNSS_applications
- Brief History
- Sat Nav
- GNSS Accuracy
- Inside GNSS