GPS (GLOBAL POSITIONING SYSTEM)
The Global Positioning System (GPS) is a space-based navigation system which provides information on location and time under all weather conditions, anywhere on or near the earth where there is an unobstructed line of sight to four or more GPS satellites. The system provides critical capabilities to military, civil, and commercial users around the world. The United States government created the system, maintains it, and makes it freely accessible to anyone with a GPS receiver. The US Department of Defense (DoD) developed the system, which originally used 24 satellites. It became fully operational in 1995. Bradford Parkinson, Roger L. Easton, and Ivan A. Getting are credited with inventing it. GPS technology was
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GPS has become a widely deployed and useful tool for commerce, scientific uses, tracking, and surveillance. GPS's accurate time facilitates everyday activities such as banking, mobile phone operations, and even the control of power grids by allowing well synchronized hand-off switching.Many civilian applications use one or more of GPS's three basic components: absolute location, relative movement, and time transfer. The wide variety of fields of application of GPS for civilian use includes Astronomy, Cartography, Cellular telephony, Clock synchronization, Disaster relief/emergency services, Radio, aircraft tracking, Navigation, Tours, Mining, Surveying, Tectonics, etc.
The military applications of GPS include Navigation, Target tracking, Missile and projectile guidance, Search and rescue, Reconnaissance, attaching guidance kit to dumb bombs, etc.
Demodulation and decoding
Since, all of the satellite signals are modulated onto the same carrier frequency, the signals must be separated after demodulation. This is done by assigning each satellite a unique binary sequence known as a Gold code. The signals are decoded after demodulation using addition of the Gold codes corresponding to the satellites monitored by the receiver.
Data transfer and storage mechanism Data
Often times its hard to imagine how the world survived without cell phones. Its an automatic response, when you see a car accident you take out your cell phone and dial for help, or when a child is waiting for a ride they will call their parents to see how far away they are. It is a great convenience for society to be able to do such things. Imagine if you didn't even have to call somebody to find out where they were. It may seem like a futuristic idea, humanity being capable of such mind reading; however, the advancement of GPS, global positioning systems, those ideas are coming to life in the present. GPS is a way to track one's position at anytime. This is done through the use of satellites monitored by stations on the ground. There are signals transmitted from a given satellite to the receiver on Earth. It is this information that gives precise location to one's whereabouts.
The space-based global navigation satellite system that provides reliable location and time information in all weather and at all times and anywhere on or near the Earth with sub-meter accuracy is called Global Positioning System (GPS) [1]. It consists of a constellation of 28 satellites in six different orbits which give the information of the position of the user with sub meter accuracy [3]. If there are four or more GPS satellites in unobstructed line of sight with the receiver, accurate spatial co-ordinates can be obtained [2]. The datum obtained from the satellites, contain the information about the position and timing by calculating the the Keplerian orbit elements. The location information from GPS is based on the choice of coordinate system and datum [3]. The coordinate systems that are mostly used in GPS are Wor...
The question you might ask next is; well, how does this global positioning technology work today? There are three main key words which are essential in the understanding of how GPS technologies work in our world today. These are Trilateration, Synchronization, and Time Travel…yes time travel.
The use of Global Positioning System navigation technology was established in the early 1970’s, long before the idea of a GPS “safely bubble” existed. Up to this time the required satellite technology to support global positioning systems had not been developed. In 1978 the first GPS satellite was launched (Rand McNally). It took nearly fifteen years to perfect GPS for public use, but since this has happened, land navigation has been revolutionized. GPS was initially developed by the Department of Defense for primarily military uses, but has since been made available to the general public. In 1996 the National Security Council published the following goals for the GPS system:
The basic concept behind understanding GPS is a technique called “triangulating.” By using this technique, we can pinpoint any place on Earth by using only three different satellites. More specifically, we would want to use our distance from these three satellites. Hypothetically speaking, say we measured our distance from one satellite to be 10,000 miles. Our position would be narrowed down to a point on the surface of a sphere, centered on the satellite, with a radius of 10,000 miles. Now, say that the next measurement is 11,000 miles from another satellite and we imagine a similar sphere....
With it you can quickly determine your present position by plotting the course and speed from a previously known position.
There are many agencies that have the ability to perform Signals Intelligence, electronic reconnaissance and most of all signals intelligence from all available sources inducive to the environment. The United States Army uses the Joint Surveillance Target Attack Radar System (Joint STARS) as its main entity for signals collection. The Joint STARS platform was designed to provide a highly effective, real-time, collection tool to the ground task force commanders during battlefield engagements, but for the past ten years, the sensor has been used for peacekeeping missions. Army analysts can predict the enemy’s behavior by identifying choke points, potential avenues of approach and operating patterns such as supply routes and logistical points. The analysis gives the ground commander a more complete view of the enemy’s weaknesses. The United States Air Force employs the Joint STARS in a different mission than the Army. The Air Force uses Joint STARS as a battlefield management tool versus a collection tool as used for by the Army. The Air Force uses the platform to provide immediate and direct support to the Air Component Commander and continue to observe the enemy’s movement from a far distance in the sky. Providing essential data to commanders such as size, direction, and speed of the adversaries, with minimum casualties while under battlefield conditions, makes the Joint STARS an extremely effective tool. The Air Force also employs the Predator vehicles, which are unmanned aerial vehicles that are used for reconnaissance.
The following is a brief illustration of the principles of GPS. For more information see previous chapter. The Global positioning System (GPS) is a satellite-base navigation system that provides a user with proper equipment access to positioning information. The most commonly used approaches for GPS positioning are the Iterative Least Square (ILS) and the Kalman Filter (EKF) methods. Both of them are based on psuedorange equation:
There was a time a person would use a roadmap to get from one location to another. Some also would stop and ask for directions. Today, you seldom see paper maps and people stopping at a local gas station for directions. Many vehicles come with a navigation system that provides a real-time map of the vehicle’s current location as well as systematic directions to requested destination.
GPS is a system of satellites radio-transmitters that orbit the planet in great numbers; their purpose is to be able to pinpoint the exact location of an individual or any type of vessel that is equipped with a receiver transmitter within a very small radius. GPS navigation has had a great impact upon society in general as well and its commercial and military applications. Global Positioning is made available at no cost to anyone who has a GPS receiver unit anywhere on the planet. A GPS unit is able to give the user longitude/latitude information as well as, altitude, traveling speed, distance traveled, distance remaining and time in any type of weather conditions imaginable.
Geographers plan new communities, decide where new highways should be placed, and establish evacuation plans. Computerized mapping and data analysis is known as Geographic Information Systems (GIS), a new frontier in geography. Spatial data is gathered on a variety of subjects and input onto a computer. GIS users can create an infinite number of maps by requesting portions of the data to plot.
The top two panels of Fig. 2 show the day to day variation of GPS-TEC for the month of April 2013 as observed at Agra station. Here, the vertical-TEC is shown by dotted line and the corresponding sum (m + σ) and difference (m – σ) are shown solid and dashed lines respectively. The days of occur...
...regarded GPS – an indispensable part of GIS. Discussions on cartographic principles, commercial GIS software programs, satellite images, aerial photos, and geodatabases are some of the other conspicuous omissions in this book. There is an inconsistency in the depth of topics explored; for example map projections are explored in great depth, while vector topology is merely glossed over. These omissions and inconsistencies would in my opinion make this book marginally less beneficial to all the three audiences together. However, there is something for all them; structure for engineers, equations for engineers and students, and GIS concepts for students, engineers and users. This book will therefore be undeniably valuable if used to complement the material in some of the other fundamental GIS books in the discipline. It has merits, but there is room for improvement.
In most of the cases, navigation system is used to detect the position of an object. The general motion of a land vehicle is typically calculated by the values that are given by accelerometer and gyroscope.
The data from the satellite based navigation systems can also be used for trains, buses and other locomotives. Further the navigation data are also important for military in warfare and in battlefield. Thus the high speed and precise satellite based navigation systems are becoming a necessity of the future. However there are many challenges to overcome to make fast and accur...