Friday, April 13, 2007

GPS logging in the air?

I flew to Las Vegas this morning, and I, er, accidentally forgot to turn off my Sony GPS-CS1. And I sorta accidentally left it on the windowsill of the plane. So I sorta got some data of the trip.

OK now can someone please tell me why you're supposed to turn GPS off in flight? It's not a transmitter, it's a receiver, right? Is it *pulling* data from the satellites, or is it just picking up data in the air, like FM radio? The pilots use GPS. Why on earth would GPS not be permitted to be used in flight?
So since I now, er, had the data, I figured I'd, you know, have a look at it. And here's the curious thing. I have some really cool data on the runway, take-off, and a few points after take-off, but then nada for most of the flight. I got one point somewhere about half-way, (bizarrely enough over a populated area) then once we got close to Vegas, it kicked back into gear again.

What gives? Am I completely missing something about how GPS works at high altitudes, in airplanes, at high speeds, or ??

You can download the KMZ file for Google Earth here.


Bob davis said...


Cool. Take some amazing images. I look forward to following along on your adventure.

Keep on keepin' on

Bobby D.

Klaus Busse said...

Hi Joseph,

Your normal travel GPS is simply not designed to work at air speed. Many GPSs fail at around 200 km/h, as can be tested in the right car on the Autobahn.

All the best in Kenya


dad L said...

Don't be too hard on the Sony. Since it only queries for satellite lock every 15 seconds, at 500mph you will have moved over 2 miles between queries. Cool device though.

jparris said...

There another possible explanation. I'm a Mech and Aero Eng student. And on of the project I've worked on is lauching weather ballon with payload satellites. One of the payloads is typicaly a gps unit. After the first launch I worked on we looked at the data and it just went exploded after 100k ft (if I remember correctly) just random noise completely useless. We contacted the manufacture (garmin) and were informed that there were altitude and velocity caps (caused by how often it quered the satilites) and these were set by the government. Presumably for matters of defense aka you can't use it for a rocket or something.

Joseph said...

ahh, speed and possibly altitude. Makes perfect sense. I couldn't get my Garmin to pick up the sat's from the plane either.