the navigation systems

Navigation Networks

Navigation networks have existed since the dawn of sailing, with information passing on from generation to generation. Traveling around the world without landmarks is impractical without these systems. Over time, navigation systems have evolved into a complex set of sensors and algorithms that work together to provide capabilities such as providing graphical maps with geographic data, suggesting better routes while providing estimated time to arrival if a certain route was used, locating obstacles or convenience areas in the route being used, and providing traffic information, amongst other things. This paper covers some of the most efficient navigation systems ever developed and their uses during the time they were used.

Global Navigation Satellite System (GNSS)

The GNSS is a satellite system describing a collection of satellites which provide signals from space and transmit the data to GNSS receivers on ground stations. The satellite system pinpoints any geographic location of a user's receiver located anywhere in the world using this data. Some examples of GNSS are the United States Global Positioning System (GPS), Europe's Galileo, China's BeiDou Navigation Satellite System and the Russian Federation's Global Orbiting Navigation Satellite System(GLONASS) (What is GNSS?, 2019).

Performance of the GNSS

- Integrity: This refers to the capacity of the system to provide precise and accurate data and in the occurrence of inconsistency; an alarm.
- Accuracy: This is the variation between the measured position of the receiver and the actual position. It also applies to both time and speed.
- Continuity: Describes the ability of a system to function with limited or no interruption.
- Availability: Refers to the time in the percentage that a signal fulfills the criteria named above, integrity, continuity, and accuracy.

Each of the satellites conveys coded signals at specific intermissions. A receiving gadget transforms the signal information to estimates of velocity, time and position. By use of this information, a receiver near or on the surface of the earth can compute the precise distance between the transmitting satellite and the receiver. One can also determine the position of the transmitting satellite. GNSS uses calculations that involve information from different satellites to locate the user in a process known as triangulation (Posted, 2011).

However, the accuracy of GNSS varies depending on the type of technology used. The Galileo navigation system has an accuracy of one meter while the United States GPS has a potential accuracy within fifteen meters.

Inertial Navigation System (INS)

The INS is a navigation aid which consists of three essentials devices; a computer, accelerometers (motion sensors) and gyroscopes (rotation sensors) or other devices that can sense motion through dead- reckoning (License, n.d.). These devices calculate the velocity (speed and direction), position and orientation of a moving object. Dead- Reckoning is a navigation method, which enables the user to trace their location by determining which direction they flew, the flying speed, for how long they were flying and where they started flying.

Gyroscopes are rotation sensors which calculate the angular velocity while accelerometers calculate the linear acceleration of a moving object. The computer compiles the time and the provided initial position to determine the current position of an object. The INS require no external references in determining the velocity, position, and orientation of an object. This means that they can be used anywhere despite the presence of a GPS or other navigation aids and are self- contained in the aircraft.

Several names are used to describe the INS. Some of these are Inertial Navigation Unit (INU), Inertial

Reference

System (IRS) and Inertial Reference Unit (IRU). There are two types of Inertial Navigation Systems, strap down and gimballed (License, n.d.). Gimballed systems are mounted in gimbals on a platform level. It has two gyroscopes and 3 accelerometers in each direction, east/west, north/south and up/down. An advantage of the gimballed is that they the platform level is maintained by mechanical gyroscopes. Also, due to the fact that the accelerometers are already oriented of each of the directions, the calculation of position and velocity can be determined by simpler electronics.

On the other hand, strap down systems have three acceleration sensors and three other precise gyroscopes that determine the orientation of the system. These three gyroscopes sense the rate of pitch, yaw, and roll and then integrates them to determine the orientation which is then used to calculate the acceleration in all the three directions as the gimballed system. Strap down systems are simpler and more reliable to use but require more accurate gyroscopes and more efficient computers.

Celestial Navigation

Celestial navigation is a science that allows a navigator to move into space without relying on calculations estimates to know their position. It is known as position fixing. This navigation system uses angular dimensions measured between a celestial body and the visible horizon to find one’s position on land, sea or anywhere else on the globe. A celestial body can be the moon, the sun, a star or a planet.

At any time, a celestial body is positioned directly over a point on the surface of the earth. The longitude and latitude of this point are referred to as the celestial body’s geographic position (GP). The angle measured between the visible horizon and any celestial body is associated with the distance between the position of the viewer and the geographic location of the celestial body. A line of position (LOP) is plotted on a navigational chart with the position of the observer is on that line.

The position of a celestial body is described by horizontal coordinates. The observer is located in a fictional sphere, celestial sphere divided into two parts by the plane of the celestial horizon. When the body is invisible, the vertical angle between the visible (horizontal) line is measured from 0 degrees to -90 degrees and is known as the altitude denoted by H. The corresponding angular distance between the body and an imaginary point directly above is known as the zenith distance denoted by z. This distance is measured from 0 degrees to 180 degrees. The celestial horizon, sensible horizon, and geoidal horizon are parallel to each other. Celestial horizon denotes the horizontal plane through the center of the earth, the sensible horizon is the horizontal plane passing through the eye of the observer, and the geoidal horizon is the horizontal plane tangent to the earth at the position of the observer (Umland, 2010).

In summary, the calculations in celestial navigation for finding one’s position includes the zenith distances or altitudes of the chosen celestial body, the geographic position of each of the celestial body at the time it was observed and finally deriving one’s position from the given

Conclusion

Apart from the navigation systems discussed above, many more have been developed due to technological advancement. Most modern navigation systems involve little or no calculations and a higher accuracy, an example is the Galileo navigation system which has an accuracy of one meter. From this article, it is clear that GNSS is so far, the best and the latest navigation system that humankind has developed. Celestial navigation suited the early societies more, and is only learnt today as a foundation of navigation to be used when the situation demands it.

References

License, T. (n.d.). Inertial navigation systems- FlightGear. Retrieved March 10, 2017, from http://www.flightgear.org/inertia_navigation_systems

Posted, &. R. (2011, September). What is GNSS?(global navigation satellite system)? definition. Retrieved 09 2017, March, from TechTarget: http://searchnetworking.techtarget.com/definition/GNSS

Umland, H. (2010, April 10). A Short Guide to Celestial Navigation. Retrieved March 10, 2017

What is GNSS? (2019, November 25). Retrieved March 9, 2017, from http://www.gsa.europa.eu/european-gnss/what-gnss