Leica Geosystems GPS Basics - Manual (Page 23)

23
GPS Basics -1.0.0en How GPS works
4
5
6
3.3.2 Why use Carrier Phase?
The carrier phase is used because it
can provide a much more accurate
measurement to the satellite than using
the P-code or the C/A code. The L1
carrier wave has a wavelength of 19.4
cm. If you could measure the number of
wavelengths (whole and fractional parts)
there are between the satellite and
receiver, you have a very accurate range
to the satellite.
3.3.3 Double Differencing
The majority of the error incurred when
making an autonomous position comes
from imperfections in the receiver and
satellite clocks. One way of bypassing
this error is to use a technique known as
Double Differencing.
If two GPS receivers make a measure-
ment to two different satellites, the clock
offsets in the receivers and satellites
cancel, removing any source of error that
they may contribute to the equation.
Double Differencing