Laboratory Measurements of Drift Rates in Pressure Gauges Proposed for Seafloor Geodesy

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Pressure gauges installed on the seafloor are key instruments for monitoring tides, offshore earthquakes and tsunamis, seafloor volcanoes, and offshore oil and gas fields. While valuable, the instruments slowly drift, which make long-term measurements more difficult or even impossible to use. This research will simulate seafloor pressure and temperature conditions in the laboratory, and periodically re-calibrate the instruments to determine the drift behavior. New sensors and methods to correct the drift in place will also be tested. The results will improve the characterization and application of pressure measurements for such important problems.Pressure observations for seafloor geodesy provide important data on many seafloor deformation processes, including volcanism and tectonic deformation. Pressure observations are also relevant to rates of sea level rise and other oceanographic signals. Existing pressure sensors all drift in
time (dominated by linear and exponentially decaying functions of time), which limits their use in the aforementioned applications to relatively short period signals (days to months). Methods such as seafloor pressure campaign surveys and in-situ
calibration can effectively remove the drift, but these methods are costly and thus limited
in usage. The manufacturers of pressure gauges have proposed new sensors and methods to address the drift issue, which are significantly simpler and would be much less costly to implement. One approach uses a secondary sensor to measure only sensor drift due to residual water vapor contamination (hypothesized to be a dominant term), independent of the applied pressure.
 Another method hypothesizes that the drift rate can be measured by comparison to a one-atmosphere low drift sensor. This research will subject an array of existing and new sensors to simulated seafloor pressures and temperatures over extended periods of time (4-6 months at a minimum). The sensors will be periodically calibrated with a primary, drift free metrological standard known as a deadweight tester. Drift determinations with the new sensors and methods will be made, and compared to the estimates determined by primary standard. This experiment will determine the efficacy and uncertainties of these new methods. If these new approaches are validated, this will enable the development of new seafloor instruments, and the ocean sciences will have access to new methods that will benefit observations of important phenomena. In turn, better understanding of seafloor tectonics and volcanism will improve the assessment and response to potential geological hazards.