[chbot] Interesting radio tech: GPS Radio Occultation

[Charles Manning]

Hello Everyone

One of my customers in USA designs and runs GPS radio occultation
satellites and I thought I'd tell you a bit about this fascinating tech.

Basically, Radio Occultation is a way of doing a bunch of maths with radio
signals to be able to "see" detail of the things between the radio
transmitter and the observer.

GPS RO does the same thing  but using GPS satellites as the radio source.
Since GPS satellites are moving, this gives a "slice" of information about
the atmosphere that the radio signal is travelling through as the satellite
disappears over the horizon. Each of these "slices" is called a sounding.

So how can you make this even more cool? Make the observer a satellite too!
Now each sounding can be measured in a minute or two rather than taking
many hours. Each satellite can observe many GPS or similar satellites and
get many soundings - up to 2500 soundings a day. With 20 satellites, they
get 50,000 soundings a day.

Mathematically this is very similar to CT scans etc. used to image inside
the human body - just here they are basically doing a CT scan of the whole
atmosphere. Neat eh?

This allows continuous realtime weather updates anywhere in the world:
extremely valuable to all sorts of people. For example it allows extremely
precise measurement and tracking of hurricanes without putting people at
risk. Of course the military love this stuff too :-).

For those that want to read/watch a bit further:
http://planetiq.com/gps-ro-101/
https://www.youtube.com/watch?v=V4lPNrDm9Kw

For the curious, the satellite contents is really not much more than an
FPGA-based Software Defined Radio + a data link + a lot of cool software.

Regards

Charles
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