Abstract
Traditionally the horizontal orientation in a ship (heading) has been obtained from a gyrocompass. This instrument is still used on research vessels but has an estimated error of about 2-3 degrees, inducing a systematic error in the cross-track velocity measured by an Acoustic Doppler Current Profiler (ADCP). The three-dimensional positioning system (GPS 3DF) provides an independent heading measurement with accuracy better than 0.1 degree. The Spanish research vessel BIO Hesperides has been operating with this new system since 1996. For the first time on this vessel, the data from this new instrument are used to estimate gyrocompass error. The methodology we use follows the scheme developed by Griffiths (1994), which compares data from the gyrocompass and the GPS system in order to obtain an interpolated error function. In the present work we apply this methodology on mesoscale surveys performed during the observational phase of the OMEGA project, in the Alboran Sea. The heading-dependent gyrocompass error dominated. Errors in gyrocompass heading of 1.4-3.4 degrees have been found, which give a maximum error in measured cross-track ADCP velocity of 24 cm s-1.
Highlights
In the last 20 years the use of the Vessel Mounted Acoustic Doppler Current Profiler (VM-ADCP)has been continuously increasing within the oceanographers community
In this paper we focus on the first issue, in order to evaluate and correct the ADCP velocity error induced by inaccuracy of gyrocompass heading measurements
The method is based on the estimation of the gyrocompass error by fitting a function to a representative heading error series obtained during the cruise
Summary
In the last 20 years the use of the Vessel Mounted Acoustic Doppler Current Profiler (VM-ADCP)has been continuously increasing within the oceanographers community. The scientific importance and the quantitative use of the ADCP data can be found in many recent works: Chereskin and Trunnell (1996) combined ADCP records with hydrographic data to obtain absolute geostrophic velocities. Pollard and Regier (1992) and Allen and Smeed (1996) used ADCP to compute the stream function that they use as a reference level for dynamic height derived from CTD data. Gomis et al (2001) performed a multivariate analysis of hydrographic and velocity data to obtain the optimal estimation of both (dynamic height and current) fields through their mutual influence. From a general point of view the quantitative use of ADCP data is strongly conditioned by two main aspects: i) the accuracy of the ship’s attitude measurements (mainly positioning and heading) and ii) the post-acquisition data analysis (e.g. tidal filter, spatial objective analysis). In this paper we focus on the first issue, in order to evaluate and correct the ADCP velocity error induced by inaccuracy of gyrocompass heading measurements
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
