AIDJEX Bulletin #40 - Polar Science Center - University of Washington

eceivers, we were able to have two receivers at each camp and thus gained
reliability through redundancy. As a result, out of a total of 1400 operating
days, equipment problems prevented collecting any data on only 7 days
at one camp.
With two antennas at each camp separated by about 100 m, a comparison
of fixes taken with each antenna permitted continuous monitoring of system
accuracy and floe rotation. Accuracy in measuring distance was enhanced
by adding a local clock to the receivers to remove timing errors and by
selecting and acquiring passes under computer control.
TRANSLOCATION
For a stationary or slowly moving receiver, the largest error sources
for single-channel positioning are uncorrected refraction and imperfect predic-
tion of the satellite orbit.
These errors are correlated between receivers
tracking the same satellite for the same time interval.
Therefore, the
difference in position errors between the two receivers is much smaller than
the errors in the position of each.
h important condition is that the time intervals over which Doppler
measurements are made at each station must be identical.
we attempted to enforce this condition in real time.
To avoid recomputing,
interval for each pass to begin on the third even-minute mark before closest
approach and to end on the third even-minute mark after closest approach,
ieee9 10 minutes of data around the time of closest approach. When the times
of closest approach for the two receivers fell in the same 2-minute interval,
the critical intervals for the receivers were identical.
Real-time
We defined the cktieaZ
translocation fixes were computed by using all data within the
critical interval and eliminating all data outside it. Data collected during
the IO-minute critical interval (20 Doppler counts, integrated for 30 seconds
each) contain the essential features of the Doppler curve, so that discarding
data from the beginning and end of the pass does little to degrade fix
accuracy.
(The critical interval concept was also used in the receiver con-
trol algorithm; see the next section.)
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