The forecast: partially cloudy with a chance of... satellites
Gotta love science... In an effort to be completely meticulous about every possible source of systematic error that might creep into our positioning system, we have incorporated tropospheric corrections into our GPS satellite signal interpretation code.
What's the troposphere? Well, the big bubble of gas and crap floating around the Earth (held there by its gravity, by the way) can be divided up into a couple of different layers. The troposphere is the lowest of these layers, and it's made up mostly of air and a little water. Next comes the stratosphere, and finally the ionosphere, stuffed full of weird plasma and other charged things. A GPS signal originating from a satellite and going on its merry way toward our receiver needs to pass through all three of these atmospheric layers, and of course, it would be far too easy for this signal just to pass right through unaffected. No, instead it's curved and bent up in a very sensibly-nonsensical way, and if you don't account for that, then your computed position will be wrong. So what do we do?
We turn our position estimator into a weather station, that's what we do. Yes that's right, our position now depends on barometric surface pressure, ambient temperature, and relative humidity. If it rains, we want to know about it.
Sheesh, I feel like a weatherman. I swear at some point I was actually a Mechanical Engineer, honest!
What's the troposphere? Well, the big bubble of gas and crap floating around the Earth (held there by its gravity, by the way) can be divided up into a couple of different layers. The troposphere is the lowest of these layers, and it's made up mostly of air and a little water. Next comes the stratosphere, and finally the ionosphere, stuffed full of weird plasma and other charged things. A GPS signal originating from a satellite and going on its merry way toward our receiver needs to pass through all three of these atmospheric layers, and of course, it would be far too easy for this signal just to pass right through unaffected. No, instead it's curved and bent up in a very sensibly-nonsensical way, and if you don't account for that, then your computed position will be wrong. So what do we do?
We turn our position estimator into a weather station, that's what we do. Yes that's right, our position now depends on barometric surface pressure, ambient temperature, and relative humidity. If it rains, we want to know about it.
Sheesh, I feel like a weatherman. I swear at some point I was actually a Mechanical Engineer, honest!
posted by iceman at 10:12 AM
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