DEVELOPMENT AND APPLICATION OF AN OPEN APPROACH TO ACOUSTICAL MARINE BENTHIC HABITAT CLASSIFICATION AND MAPPING PACS: 43.30.Zk Noela Sánchez a , Cristina Bernárdez b , Enrique Godínez-Domínguez b & Juan Freire a a Grupo de Recursos Marinos y Pesquerías Universidad de A Coruña Campus da Zapateira s/n E-15071 A Coruña, Spain b Departamento de estudios para el desarrollo sustentable de zonas costeras Universidad de Guadalajara Gómez Farias 82 48490 Melaque, Jalisco, México . 1. Aim Knowledge of benthic habitats plays a key role in the establishment of strategies for sustainable exploitation of marine resources (Botsford et al. 1997, Vallega 1999). Acoustic surveys have been widely used in seabed classification studies (Brown et al. 2002, Caddell 1998, Greenstreet et al. 1997, Legendre et al. 2002; Tuck et al. 1998), but a unified and standadized methodology has not been developed. Our aim is to develop an open protocol, using a combination of acoustic tools, statistical data analysis and groundtruthing for the identification, description and classification of marine benthic habitats. The output from this procedure will be used as input in a GIS, aiming for an efficient use in marine resource management.Acoustic waves produced by transducers travel through the water column producing a backscatter every time they reach a transition between two different acoustic impedance materials. These backscatter waves give us information on the water column. The impinging wave and the element or medium that produced the wave, characterize the backscatter. Two different frequency impinging waves will result in different backscatters, giving different information on various characteristics of the target. Due to the strength loss and transformation on the impinging wave once it has backscattered first on the bottom and then on the sea surface, the energy values from the bottom reflection will contain information on every element of the floor, while those from the surface reflection will consist just on information on the highest acoustic impedance elements of the bottom. Based on this rationale, a methodology for benthic habitat classification using a comparative analysis of the first echoes of two different frequencies, 38 kHz and 200 kHz, and the second and third echo at 38 kHz is being designed and applied to different field datasets. Field work was designed to be carried out with a minimum of infrastructure and logistics. 2. Field work Three acoustic surveys were done using an EA400P echo-sounder (Simrad, Norway). This is an hydrographic echo-sounder working simultaneously at 38 and 200 kHz. During the surveys, parameters were adjusted to enhance performance for future data analyses. Maximum ping rate and a pulse length of 1,024 milliseconds were set. The speed of the boat was 4 to 6 knots. Small fishing boats (7 to 10 meter long) were used. The transducer was mounted on the side using a portable device, at a depth of approximately 1 m. The surveys consisted of a series of transect grids, mostly perpendicular to the coastline, from depths of 15 to 150 m. Distance