Deep Sea Tide Gauge with Optical Readout of Bourdon Tube Rotations

Abstract

THE traditional method of measuring the tide by referring sea-level elevations to a stationary structure cannot be applied to the open ocean. Tidal pressure fluctuations on the sea floor, however, are a good indication of the mass variations of the water column. In order to detect changes of water head of 0.5 cm in 5 km depth an instrumental stability and resolution of 10⁻⁶ is required. Records obtained with vibrating wire transducers, corrected for temperature effects, indicate that this is possible^1–4. The association of an adequately heat treated Ni Span C Bourdon tube with a sensitive optical detector⁵ permits deep-sea tide gauges of great simplicity to be made, with ample resolution, negligible temperature dependency and predictable creep characteristics.