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

One part in lo5 of the nominal RAMS transmission interval of 60 seconds
is 0.6 msec, which is the order of accuracy needed to determine the transmission
interval. so that the clock can be corrected to 0.1 mb equivalent error.
The 0.1 second resolution in measuring time in the RAMS flown on Nimbus
requires that 10,000 seconds elapse between observations used in the solution
for transmission interval to meet the accuracy goal of 0.1 mb. The interval
between sequential satellite passes is about 6,600 seconds; this is sufficient
to obtain! an accuracy of 1.5 parts in lo5, or about 1 msec uncertainty
in the transmission interval.
This is the accuracy obtained in the clock correction used in this
study. The shortcoming introduced a 0.15 mb random error Pn the barometric
pressure measurements. Clock correction based on measurements separated by
two orbital periods would have been more appropriate to the test.
The temperature dependence of the clocks in the field, when compared
with the spacecraft clock, is seen to be of the same sign as the laboratory
calibrations,'but about half the magnitude (Fig. 12). This difference in
magnitude is probably due to temperature differences between the clock
circuits and the internal temperature sensor located at the barometer. The
results could also have been affected by clock aging, which would be indistinguishable
from seasonally varying temperature effects. Direct measurement
of (and correction for) clock behavior makes the distinction unimportant.
APPENDIX B
The following design criteria are stated with respect to pressure
accuracy.
If 1 mb errors are acceptable in pressure measurement,
0 No temperature compensation need be used for barometers with coefficients
less than about 0.04 mb per degree Celsius.
0 An opaque but uninsulated buoy hull may be used.
0 Only initial and long-term corrections for clock variations are necessary.
If 0.3 mb accuracy is nscessaq,
0 Barometers with coefficients greater than 0.01 mb/OC must be temperature
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