Humans have looked to the skies to find their way since ancient times. Ancient sailors used the constellations in the night sky to figure out where they were and where they were going. Today, all we need is a simple hand-held GPS short for Global Positioning System receiver to figure out exactly where we are anywhere in the world.
But we still need objects high in the sky to figure out where we are and how we get to other places. Instead of stars, we use satellites. Over 30 navigation satellites are zipping around high above Earth. These satellites can tell us exactly where we are. Satellites act like the stars in constellations—we know where they are supposed to be at any given time.
A receiver, like you might find in your phone or in your parents car, is constantly listening for a signal from these satellites. The receiver figures out how far away they are from some of them.
The receiver multiplies this time by the speed of light to determine how far the signal traveled. Assuming the signal traveled in a straight line, this is the distance from receiver to satellite. In order to make this measurement, the receiver and satellite both need clocks that can be synchronized down to the nanosecond.
To make a satellite positioning system using only synchronized clocks, you would need to have atomic clocks not only on all the satellites, but also in the receiver itself. The Global Positioning System has a clever, effective solution to this problem. Every satellite contains an expensive atomic clock, but the receiver itself uses an ordinary quartz clock , which it constantly resets. In a nutshell, the receiver looks at incoming signals from four or more satellites and gauges its own inaccuracy.
In other words, there is only one value for the "current time" that the receiver can use. The correct time value will cause all of the signals that the receiver is receiving to align at a single point in space.
That time value is the time value held by the atomic clocks in all of the satellites. So the receiver sets its clock to that time value, and it then has the same time value that all the atomic clocks in all of the satellites have.
The GPS receiver gets atomic clock accuracy "for free. When you measure the distance to four located satellites, you can draw four spheres that all intersect at one point. Three spheres will intersect even if your numbers are way off, but four spheres will not intersect at one point if you've measured incorrectly.
Since the receiver makes all its distance measurements using its own built-in clock, the distances will all be proportionally incorrect. The receiver can easily calculate the necessary adjustment that will cause the four spheres to intersect at one point. Based on this, it resets its clock to be in sync with the satellite's atomic clock. The receiver does this constantly whenever it's on, which means it is nearly as accurate as the expensive atomic clocks in the satellites.
In order for the distance information to be of any use, the receiver also has to know where the satellites actually are. This isn't particularly difficult because the satellites travel in very high and predictable orbits. The GPS receiver simply stores an almanac that tells it where every satellite should be at any given time. Things like the pull of the moon and the sun do change the satellites' orbits very slightly, but the Department of Defense constantly monitors their exact positions and transmits any adjustments to all GPS receivers as part of the satellites' signals.
In the next section, we'll look at errors that may occur and see how the GPS receiver corrects them. So far, we've learned how a GPS receiver calculates its position on earth based on the information it receives from four located satellites.
This system works pretty well, but inaccuracies do pop up. For one thing, this method assumes the radio signals will make their way through the atmosphere at a consistent speed the speed of light. In fact, the Earth's atmosphere slows the electromagnetic energy down somewhat, particularly as it goes through the ionosphere and troposphere. The delay varies depending on where you are on Earth, which means it's difficult to accurately factor this into the distance calculations.
Problems can also occur when radio signals bounce off large objects, such as skyscrapers , giving a receiver the impression that a satellite is farther away than it actually is. On top of all that, satellites sometimes just send out bad almanac data, misreporting their own position. The basic idea is to gauge GPS inaccuracy at a stationary receiver station with a known location. Since the DGPS hardware at the station already knows its own position, it can easily calculate its receiver's inaccuracy.
The station then broadcasts a radio signal to all DGPS-equipped receivers in the area, providing signal correction information for that area. Sign up for monthly news and tips from our award-winning fleet management blog. You can unsubscribe at any time. What will drive new innovation in an enterprise via the fleet? Find out everything you need to know about unplugged devices with insights from the Geotab Community and Blog. Read about the past, present, and future of the Geotab GO device.
Learn all about the Geotab Drive app for Hours of Service, electronic logging and vehicle inspection. Skip to main content. What are the three elements of GPS? The three segments of GPS are: Space Satellites — The satellites circling the Earth, transmitting signals to users on geographical position and time of day. Ground control — The Control Segment is made up of Earth-based monitor stations, master control stations and ground antenna.
Control activities include tracking and operating the satellites in space and monitoring transmissions. There are monitoring stations on almost every continent in the world, including North and South America, Africa, Europe, Asia and Australia.
User equipment — GPS receivers and transmitters including items like watches, smartphones and telematic devices. How does GPS technology work? Here is an illustration of satellite ranging: As a device moves, the radius distance to the satellite changes. What are the uses of GPS? Navigation — Getting from one location to another.
Tracking — Monitoring object or personal movement. Mapping — Creating maps of the world. Timing — Making it possible to take precise time measurements. Some specific examples of GPS use cases include: Emergency Response: During an emergency or natural disaster , first responders use GPS for mapping, following and predicting weather, and keeping track of emergency personnel. Read more about GPS tracking for first responders. Health and fitness: Smartwatches and wearable technology can track fitness activity such as running distance and benchmark it against a similar demographic.
Construction, mining and off-road trucking: From locating equipment, to measuring and improving asset allocation, GPS enables companies to increase return on their assets. Check out our posts on construction vehicle tracking and off-road equipment tracking. Transportation: Logistics companies implement telematics systems to improve driver productivity and safety. A truck tracker can be used to support route optimization, fuel efficiency, driver safety and compliance.
How accurate is GPS? Some factors that can hinder GPS accuracy include: Physical obstructions: Arrival time measurements can be skewed by large masses like mountains, buildings, trees and more. Atmospheric effects: Ionospheric delays, heavy storm cover and solar storms can all affect GPS devices. Ephemeris: The orbital model within a satellite could be incorrect or out-of-date, although this is becoming increasingly rare.
Numerical miscalculations: This might be a factor when the device hardware is not designed to specifications. Artificial interference: These include GPS jamming devices or spoofs. A brief history of GPS Humans have been practicing navigation for thousands of years using the sun, moon, stars, and later, the sextant.
This means standard GPS radio frequency components, such as antennas, filters and amplifiers, cannot be used for GNSS receivers, resulting in a greater cost impact. Power consumption would be slightly higher than with GPS receivers as it connects to more satellites and runs the calculations to determine location. Scientists and rescue workers are finding new ways to use GPS technology in natural disaster prevention and analysis in the event of an earthquake, volcanic eruption, sinkhole or avalanche.
For the COVID pandemic, researchers are looking at using cellphone location data to assist with contact tracing in order to slow down the spread of the virus. By broadcasting on the L1C civilian signal for interoperability with other satellite systems.
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