Long-term seafloor tidal gravity and pressure observations in the North Sea: Testing and validation of a theoretical tidal model

Citation:
Sasagawa, G, Zumberge M, Eiken O.  2008.  Long-term seafloor tidal gravity and pressure observations in the North Sea: Testing and validation of a theoretical tidal model. Geophysics. 73:WA143-WA148.

Date Published:

Nov-Dec

Keywords:

gravimeters, gravity, oceanographic regions, tides

Abstract:

Seafloor gravity and pressure measurements for 4D reservoir monitoring require precise models of the time-varying tidal signals. Current seafloor instrumentation can resolve 0.003 mGal in time-lapse gravity differences and 0.05 kPa (5 mm) in pressure. To verify model accuracy, a seafloor gravimeter and pressure gauge were operated continuously for 446 days next to the Troll A gas platform in the North Sea (60.64227 degrees north, 3.72417 degrees east) at a depth of 303 m. The seafloor gravity and pressure time series were filtered and corrected with estimates from the tidal model, which predicts the solid earth tide, ocean loading, and direct gravitational attraction of the varying water level. The rms difference between the observed tidal gravity signal and the prediction is about 0.0013 mGal during periods when there are no surface storms. A slight difference is observed for the direct attraction of the water overhead as computed from the tidal prediction versus that computed from direct seafloor pressure measurements when the entire 446-day record is analyzed; it shows an rms difference of 0.708 kPa, equivalent to 7 cm of water-height variation, yielding a gravity effect of 0.003 mGal. We conclude that existing theoretical tide models in combination with in situ pressure records are sufficiently precise for correcting time-lapse gravity observations.

Notes:

n/a

Website

DOI:

10.1190/1.2976778