On 1/23/17 4:28 AM, Steve Maki wrote:
On 1/22/2017 22:25 PM, Jim Brown wrote:
For GPS to determine azimuth the observer must be moving. That works
fine in a vehicle, but not when you're walking. Ask me how I know. :)
Or you must have two GPS antennas in one unit, separated by some
distance, usually 18" or more. We use such units to align cell antennas.
They are supposedly accurate to one degree or better.
I can't imagine how a stationary single antenna GPS can measure azimuth.
I'm not aware of any commercial systems that do this, but it is possible
by designing the antenna to have a deliberately non uniform phase
behavior as the spacecraft moves. That puts a "pseudo doppler" on top of
the true doppler. If you've got a position fix already, and you have
the current ephemeris, you know what the doppler should be and where the
spacecraft is in the sky. By comparing the phase/doppler you measure
with the phase/doppler expected, you can figure out the orientation of
the antenna.
Much easier to just have 2 or 3 antennas separated by a couple of feet.
That makes it easy to do attitude determination. It was done quite a
few years ago (more than 10-15) for determining artillery position and
orientation and for input to aircraft autopilots for landing assistance.
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