The joke among geocachers is that our hobby uses multi-million dollar satellites to find tupperware in the woods. And it’s true! Launching a single satellite into space can cost anywhere between ten to four hundred million US Dollars. It’s common knowledge that we have access to this technology thanks to US President Bill Clinton, who famously “flipped the switch” on selective availability.
Twenty years later, most of us take GPS in our phones, our cars, or our computers for granted. So how do satellites, the cornerstone of our favorite game, actually work to help us find those tupperware?
Let’s find out!
A system of over 30 GPS (short for Global Positioning Satellites) are whizzing around in orbit right now. Each has its own specific trajectory, so that we know precisely where each one is at any given time. They are constantly sending out signals, both to ground stations that make sure the satellites maintain their intended trajectory, and to receivers like the ones in your phone or GPS unit.
When they receive these signals, your phone or GPS then uses a process called trilateration to calculate its exact location in relation to each satellite. But what is trilateration? Simply put, it is the process of determining a location by measuring distance using circles.
Each satellite sends out a signal in all directions, and if your GPS receives a signal from a satellite, it knows where you are in relation to that one satellite. So you could be in multiple locations around the outside of a sphere.
It takes three different satellites to trilaterate a specific location in two dimensions, and four different satellites in three dimensions.
So for example, if you’re on a flat plain, you may only need three satellites for an accurate location, whereas if you’re hiking in the mountains you may need four. In reality, your GPS is receiving signals from many satellites constantly, and using all of them to get an accurate fix on your location.
The GPS now knows where you are (and more importantly, where the geocache is!), but how does it communicate that with you?
The geographic coordinate system uses latitude and longitude to label and locate every single place on Earth using a specific set of letters, numbers, and signals. The original geographic coordinate system dates all the way back to the 3rd century BCE!
Latitude measures points on the Earth’s surface on parallels, or lines drawn parallel to the equator. Longitude measures points on the Earth’s surface in meridians, or lines drawn perpendicular to the equator.
Much like with trilateration, if you know just latitude or just longitude, you could be in any place on a long line around the Earth.
But when you combine latitude and longitude, you can specify your exact location at any point on Earth!
Now, the next time you go out geocaching, you can think about all the science and technology behind your smiley! Have fun!