The IEEE Seventh Working Conference on Current Measurement Technology

Current and Wave Monitoring and Emerging Technologies

March 13-15 | Bahia Hotel | San Diego, CA, USA

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A comparison of simultaneous measurements from shipboard narrowband and phased array acoustic Doppler current profilers.

N P Holliday

Southampton Oceanography Centre, Southampton, UK

R T Pollard and G Griffiths
Southampton Oceanography Centre
Empress Dock, Southampton SO14 3ZH, UK.
Tel: +44 (0) 2380596004
Fax: +44 (0) 2380596149
email: gxg@soc.soton.ac.uk

The RDI VM-150 narrowband ADCP has been installed on RRS Discovery since 1986 and has given excellent service. The performance of the instrument has been documented in several papers. The adoption of new vessel mounted profiler technology seems slow. This may signify a lack of confidence. RRS Discovery, fitted with two transducer spaces, has served as a platform for previous intercomparisons of the VM-150 with an experimental correlation profiler and in 2001 a 75 kHz Ocean Surveyor phased array ADCP was installed for evaluation as a future replacement for the aging VM-150.

In this paper we report on the intercomparison of 150 kHz narrowband and 75 kHz phased array instruments undertaken during two recent North Atlantic cruises. Both instruments were calibrated against GPS and gyrocompass heading corrections were applied using carrier-phase GPS. Particular attention was paid to time synchronisation and time stamping.
On-station mean current profiles over 60-380 m differed by less than 0.2 cm s-1 in u and v with standard deviation from 0.6 to 2 cms-1. Differences will be described in detail. Range performance of the instruments will be discussed. Under ideal conditions the 75 kHz phased array returned profiles to 700-750 m, while the maximum range of the VM-150 was 350-400 m. However, as the weather deteriorated the achievable range from the 75 kHz instrument decreased faster than the VM-150. Reasons for this rapid fall-off in performance will be explored.

Submitted on January 15, 2003

Sponsored by the Current Measurement Technology Committee (CMTC) of the IEEE Oceanic Engineering Society.

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