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Signal Amplitude Uncertainty of a Digiquartz Pressure Transducer Due to Static Calibration Error

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  • 1 Joint Institute for the Study of Atmosphere and Ocean, University of Washington, Seattle, Washington
  • | 2 NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington
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Abstract

Standard calibrations of Digiquartz pressure transducers are performed over a very wide range of pressure and temperature, typically 14–10 000 psia and 1°–125°C. Compared to this large calibration domain, deep ocean bottom pressure recorders encounter relatively small changes of pressure and temperature during a typical deployment, that is, changes of only a few pounds per square inch and a few tenths of a degree Celsius. In principle, more detailed calibrations in the expected operating range of each instrument could improve accuracy. In practice, recalibration can be expensive and time consuming and, depending on the temporal stability of the calibration constants, may not be necessary if the accuracy of the original standard calibration is sufficient. The accuracy of the original calibration as it applies to ocean bottom pressure changes induced by tides, tsunamis, and other geophysical processes is examined. For typical ambient conditions of 0°C and depth 4000 m, absolute uncertainty has been computed to be approximately 40 cm. The uncertainty in a signal varying about a mean deployment pressure (amplitude uncertainty) is 0.02% of the signal amplitude. Though the absolute uncertainty is large in relation to geophysical signals of interest, the amplitude uncertainty, which is the figure of merit for tidal and tsunami observations, is small compared to these signals and compared to the inherent resolution of the pressure measurement system.

Abstract

Standard calibrations of Digiquartz pressure transducers are performed over a very wide range of pressure and temperature, typically 14–10 000 psia and 1°–125°C. Compared to this large calibration domain, deep ocean bottom pressure recorders encounter relatively small changes of pressure and temperature during a typical deployment, that is, changes of only a few pounds per square inch and a few tenths of a degree Celsius. In principle, more detailed calibrations in the expected operating range of each instrument could improve accuracy. In practice, recalibration can be expensive and time consuming and, depending on the temporal stability of the calibration constants, may not be necessary if the accuracy of the original standard calibration is sufficient. The accuracy of the original calibration as it applies to ocean bottom pressure changes induced by tides, tsunamis, and other geophysical processes is examined. For typical ambient conditions of 0°C and depth 4000 m, absolute uncertainty has been computed to be approximately 40 cm. The uncertainty in a signal varying about a mean deployment pressure (amplitude uncertainty) is 0.02% of the signal amplitude. Though the absolute uncertainty is large in relation to geophysical signals of interest, the amplitude uncertainty, which is the figure of merit for tidal and tsunami observations, is small compared to these signals and compared to the inherent resolution of the pressure measurement system.

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