In campaign-style surveys, 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. The pressure differences, corrected for gauge drift, reveal the relative heights of the benchmarks. The process is similar to relative gravity measurements. 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.
An important consideration is the tides.
The ocean tides are fairly predictable, however the pressure gauges have such high sensitivity (mm in equivalent height), that predicted tides are not adequate. A much better tidal correction can be made using observed tides. Consequently better results are obtained when an array of recording pressure gauges is deployed in the area being surveyed.
Data from the tide gauges are then used to build a local tidal model that allows detailed corrections for tidal effects on the gauges being carried in the survey.
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Nooner, S. L., and W. W. Chadwick Jr. (2009), Volcanic inflation measured in the caldera of Axial Seamount: Implications for magma supply and future eruptions, Geochem. Geophys. Geosyst., 10, 14 pp, doi:10.1029/2008GC002315.
Stenvold, T., O. Eiken, M. A. Zumberge, G. S. Sasagawa, and S. L. Nooner (2006), High-precision relative depth and subsidence mapping from seafloor water-pressure measurements, SPE J., 11, 380–389, doi:10.2118/97752-PA.