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

l+b 1 ,t 2+b 2
The right-hand side can be rewritten as
-
where b = (bl + b2)/2 is the average delay.
difference between the measured and the desired interval.
The desired
interval length can be estimated using the fundamental Doppler navigation
equation:
A
D = (Po - F s ) ~
change in slant range
+ Fo
speed of light ’
The quantity (bl - b2) is the
where Fs and F, are the frequencies of the satellite and receiver oscilla-
tors (roughly 400 MHz), and T is 120x1526/6103 seconds for the first three
counting intervals in each 2-minute period and 120x1525/6103 seconds for
the fourth.
The duration of the measured interval was determined by counting
the cycles of the receiver clock during the interval between the first
DOPP
whe r
t2+b,.
er zero crossing of successive counting intervals:
N
measured interval length = -
Fo
N is the number of cycles at the navigator frequen c F, from t,+b, to
The equation for the corrected Doppler count is
where the 5 term corrects for average delay and the last term corrects for
jitter. In this expression fi is the Doppler frequency at ti estimated by
counting Doppler cycles di during the first 20 msec after t;+bi:
fi = di/2Q msec.
The typical magnitudes of the corrections are 0.3-1.8 counts for delay
and about 1.5 counts for length. This correction reduces the error in the
corrected Doppler counts to less than 0.1 count.
100