Intro to GNSS On-Demand Webinars
How do you measure a position through GPS satellites? What happens to a satellite’s signal as it travels toward the Earth? Which calculations or technologies do we use to generate the most accurate positioning possible?
As a leader in positioning and autonomy, Hexagon | NovAtel® wrote the book on GNSS. Now, we’re making that knowledge shareable far and wide in our webinar series.
Through the series, we follow a satellite’s signal through space, reception by antennas, computations by receivers, and applications across user equipment. We’ll explain how satellite infrastructure and atmospheric effects can contribute to positioning errors, and how technologies compensate for and resolve them.
We hope this series sparks your imagination! When you’re ready to learn more about GNSS technologies and its applications across industries, download our Introduction to GNSS book here.
Our on-demand webinar series begins with James Chan, North America team lead and core customer support at Hexagon's Autonomy & Positioning division, explaining the underlying calculations GNSS technologies use to determine positioning. We include a transcript below.
Hello, and welcome to episode one of the Hexagon | NovAtel® webinar series An Introduction to GNSS. My name is James Chan, I’m the North America team lead and core customer support at Hexagon’s Autonomy and Positioning division. Thanks for joining me!
This presentation is the first of seven designed to introduce you to GNSS basics. This presentation will explain the underlying math that happens when using satellites to determine your position in the world. The webinar series will explore what happens to the signal as it leaves the satellite, through the atmosphere to user equipment and across industries. This series builds off our existing expertise in the industry as literally writing the book on GNSS. If you’re ready to dig deeper into these concepts, then check out our book, An Introduction to GNSS.
To determine your location, this is the basic equation you need: Speed equals distance divided by time. When using this formula, we’re solving for distance. This equation is a very simplified version of the calculations; we go into more detail in episode three of our series.
Here’s what we need to know about the formula: Speed is always going to be the speed of light; that’s how quickly a signal travels through space. The time is how long it took for the signal to reach the receiver. We calculate this based on the receiver’s timestamp when it receives the signal, minus the satellite’s broadcast time stamp. Once we have these pieces, we can solve for our distance from the satellite.
The calculation assumes the speed of light, but once signals reach our atmosphere, that speed isn’t completely accurate. So, we call the calculated distance a “pseudorange” -- it’s our estimated range, and we have other calculations to increase the equation’s accuracy.
Let’s visualize this in space. First, we have a satellite in space. They share their position in orbit and the time of broadcast. All satellites have a certain range they can reach. Within that range, we calculate for distance. With that information, we know we are somewhere within the satellite’s range. To narrow down our possible location, we consider other satellite locations. And now, we know we are at the point where all three spheres intersect on Earth. This process is how we apply the equation to determine our pseudorange to satellites, and find our position. But let’s dig deeper and look at the infrastructure that the satellite signal goes through.
At its basics, a satellite broadcasts a signal to a control segment with a ground-based network of master control stations, data uploading stations, and monitor stations. The control segment helps maintain the accuracy of a satellite’s position and timing, and provides an element of quality control to the signal. The satellite signal also travels to the user segment. This segment includes equipment that processes the received signals and calculates your position. Thes