Depth-averaged instantaneous currents in a tidally dominated shelf sea from glider observations
Ocean gliders have become ubiquitous observation platforms in the ocean in recent years. They are also increasingly used in coastal environments. The coastal observatory system COSYNA has pioneered the use of gliders in the North Sea, a shallow tidally energetic shelf sea. <br><br> For o...
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-12-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/6637/2016/bg-13-6637-2016.pdf |
| Summary: | Ocean gliders have become ubiquitous observation platforms in the ocean in
recent years. They are also increasingly used in coastal environments. The
coastal observatory system COSYNA has pioneered the use of gliders in the
North Sea, a shallow tidally energetic shelf sea.
<br><br>
For operational reasons, the gliders operated in the North Sea are programmed
to resurface every 3–5 h. The glider's dead-reckoning algorithm yields depth-averaged currents, averaged in time over each subsurface interval. Under
operational conditions these averaged currents are a poor approximation of
the instantaneous tidal current.
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In this work an algorithm is developed that estimates the instantaneous
current (tidal and residual) from glider observations only. The algorithm
uses a first-order Butterworth low pass filter to estimate the residual
current component, and a Kalman filter based on the linear shallow water
equations for the tidal component. A comparison of data from a glider
experiment with current data from an acoustic
Doppler current profilers deployed nearby shows that the
standard deviations for the east and north current components are better than
7 cm s<sup>−1</sup> in near-real-time mode and improve to better than
6 cm s<sup>−1</sup> in delayed mode, where the filters can be run forward and
backward.
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In the near-real-time mode the algorithm provides estimates of the
currents that the glider is expected to encounter during its next few
dives. Combined with a behavioural and dynamic model of the glider,
this yields predicted trajectories, the information of which is
incorporated in warning messages issued to ships by the (German)
authorities. In delayed mode the algorithm produces useful estimates
of the depth-averaged currents, which can be used in (process-based)
analyses in case no other source of measured current information is
available. |
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| ISSN: | 1726-4170 1726-4189 |