Publicación online disponible en: http://www.icm.csic.es/scimar/index.php[EN] 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 Hespérides 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.[ES] Tradicionalmente, la orientación horizontal (heading) de los barcos se ha obtenido a partir de una giroscópica. Este instrumento todavía es utilizado en los barcos de investigación, pero tiene un error asociado de entre 2 y 3 grados, provocando un error sistemático en la velocidad medida por el perfilador de corriente por efecto Doppler (ADCP) perpendicular a la trayectoria del barco. El sistema de posicionamiento tridimensional GPS 3DF permite obtener medidas independientes del heading con una precisión mayor de 0.1 grados. El BIO Hespérides dispone de este nuevo sistema desde 1996. Por primera vez en este barco, los datos de este nuevo instrumento se han utilizado para estimar el error de la giroscópica. La metodología usada está basada en el método de Griffiths (1994), el cuál compara datos del sistema GPS y de la giroscópica a fin de obtener una función representativa del error. En este trabajo aplicamos dicha metodología a una campaña realizada en el mar de Alborán, durante la fase observacional del proyecto OMEGA. El error de la giroscópica dependiente del rumbo dominó. Se detectaron errores comprendidos entre 1.4 y 3.4 grados, que producen un error máximo de 24 cm s -1, en la componente de la velocidad medida por el ADCP perpendicular a la trayectoria del barco.We wish to express our gratitude to all scientists and technical staff who participated in the OMEGA- 1 cruise in the Western Alboran sea, as well as to the BIO Hespérides crew. OMEGA was a project of the Marine Science and Technology (MAST) Programme of the European Commission funded under contract MAS3-CT95-0001. OMEGA-1 was partially funded by the Spanish R+D National Plan (grant AMB95-0901). Special thanks to Pablo Rodríguez for the technical information about the GPS 3DF system.Peer reviewed