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

temperature effects in the primary operating temperature range (Fig. 6).
single temperature correction curve taken at the standard pressure will thus
have pressure-dependent errors of less than 0.1 mb throughout the temperature
and pressure ranges of interest.
There were no significant temperature-related errors when buoy pressures
were corrected according to the laboratory calibrations and compared with NWS
pressures over the test period (Fig. 7). This suggests not only that the
laboratory calibrations were appropriate to the field application, but also
that the temperature sensitivity of the pressure sensors was stable with time
The latter point has been verified by repeating laboratory calibrations after
field use.
An important part of compensation for temperature effects is the accuracy
and stability of the internal temperature sensors. Field checks of laboratory
calibrations of the thermistors have agreed within l0C, which is sufficient.
The lack of temperature-related errors throughout the test period further
suggests that the temperature sensors are stable with time.
Since temperature dependence is a function of full-scale sensor range,
it is possible to reduce temperature sensitivity per unit pressure at the
expense of decreased pressure accuracy by selecting a sensor with increased
full-scale range. For example, a sensor with two bars full-scale rating would
be expected to have half the temperature sensitivity per n%ZZibar of a one-bar
sensor, but twice the aging and sensitivity to clock errors.
1
A
C1 ock Correction
To measure barometric pressure using a sensor with a frequency output
requires an accurate time base from which to reference the counting of sensor
output. Time base errors of one part in lo5 contribute 0.1 mb pressure errors
for the sensors used here. Nonstandard initial values, long-term aging, and
seasonal and diurnal temperature effects can easily combine to produce clockrelated
pressure errors of the order of 1 mb. It is possible to observe the
behavior of the clock through the transmissions to the satellite and correct
the pressure measurements accordingly (see Appendix A).
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