[0:00]Hello, and welcome to JXJ Aviation. In this video, we will be looking at what is Global Navigation Satellite System or GNSS, and how it is used in an aircraft.
[0:16]Modern aircraft use satellite navigation to fly from origin to destination. Conventional navigation uses ground-based navigation aids. However, with the help of satellites, way points can be created, and an aircraft's position can also be accurately computed. This type of navigation provides a more direct routing, which means less time and less fuel consumption. Satellite navigation makes use of Global Positioning System or GPS and augmentation systems. They are together called as Global Navigation Satellite System or GNSS. Let's look at this in more detail.
[1:03]First, let's understand what is GPS. GPS or Global Positioning System is a space-based radio navigation system. This consists of a constellation of satellites and a network of ground stations for monitoring and controlling the satellites. Currently there are 31 satellites. GPS is operated and maintained by the Department of Defense. GPS was initially known as NAVSTAR Global Positioning System. There are other satellite constellations such as GLONASS from Russia, Galileo from European Union, Beidou from China. Now, let's understand how GPS is used for position computation.
[1:55]Position computation using GPS. Each of the GPS satellites emit signals which are captured by the receivers. The receivers may be on ground or on an aircraft. The receiver should receive information from at least four satellites for determining the location and time. The GPS satellites have an atomic clock which provide accurate time information. The signal sent by the satellites contain time and location information of the individual satellites. Using the distance information from three satellites, the aircraft is able to compute its latitude, longitude, altitude, which is the current position of the aircraft. The fourth satellite provides the time information to the receiver. So with the help of four satellites, an aircraft can compute its position and time.
[2:52]Now let's look at the GPS Augmentation System. An augmentation system is a system which aids GPS by providing accuracy, integrity, availability, and any other improvements for position computation and navigation. There are different types of augmentation systems that can be classified as aircraft-based, ground-based and satellite-based. Let's look at aircraft-based augmentation system in more detail.
[3:28]Aircraft-based augmentation system. This equipment is available on board the aircraft to enhance the GPS information. There are two techniques which are used. One technique is aircraft autonomous integrity monitoring. In this technique, on-board navigation sensors such as the inertial navigation system are used for checking the data integrity. The position computed by the on-board navigation system is combined with the position information computed from the GPS satellites for checking the integrity.
[4:06]The second technique is RAIM or Receiver Autonomous Integrity Monitoring. In this technique, position information is collected from an extra satellite in addition to the four satellites used for position and time. The additional satellite information is used to monitor the data integrity and accuracy of the other satellite signals. This technique keeps an additional satellite as backup. This backup satellite will replace any satellite which is faulty or sending incorrect data. This is called as Fault Detection and Exclusion or FDE.
[4:47]In addition to the aircraft-based augmentation system, there are ground-based and space-based augmentation systems that enhance the accuracy of the GPS signals and are transmitted to the aircraft from ground stations or through satellites. A combination of GPS and augmentation system is called as the Global Navigation Satellite System. That's all from my video on the GNSS. Thank you for watching. If you like the video, please share and subscribe. And you can continue
