Measurement Techniques

Quad Geometrics offers two solutions to combat the problem of pressure gauge drift.

The first approach involves performing campaign-style surveys, as is done with relative gravity measurements.  In these, a pressure gauge is carried from benchmark to benchmark with a Remotely Operated Vehicle (ROV) and the gauge’s drift rate is determined by repeatedly occupying one or more reference benchmarks.  In this way the relative heights of the benchmarks can be inferred with high precision (e.g., to within a few mm).  If one or more stations are sited away from the region of expected deformation, such campaigns can reveal year-to-year uplift of, for example, a subsea volcano, or the subsidence over a producing natural gas reservoir. Read more about this technique.

For applications requiring continuous monitoring of multiple seafloor sites Quad manufactures a novel sensor called the Self Calibrating Pressure Recorder (SCPR), in which two redundant quartz pressure gauges are periodically switched using motor-driven valves from the ocean pressure signal to a stable and reproducible reference pressure generated by a piston gauge on board the instrument.  From these calibration signals, which can be programmed to occur every few weeks, it is a simple matter to estimate the pressure gauge drift function and remove it from the pressure time series.  The corrected pressure record then yields the long period deformation signals.

See the time series below as an in-field example of an SCPR collecting pressure data and calibrating periodically or read further details about this product.

Time series of an SCPR on the seafloor. Note the regular tidal changes and the larger spikes. In the magnified portion of the plot in the center, one can clearly see the spikes as regular 20 minute calibrations of the sensor, occurring every 10 days.

 

 

 

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