BATHYMETRIC SURVEYS IN SUPER-SHALLOW WATER: CASE STUDY OF THE LAGOON OF VENICE, ITALY Fantina Madricardo a , Federica Foglini b , Renato Tonielli c a Istituto di Scienze Marine-Consiglio Nazionale delle Ricerche, Venice, Italy b Istituto di Scienze Marine-Consiglio Nazionale delle Ricerche, Bologna, Italy c Istituto per l'Ambiente Marino Costiero-Consiglio Nazionale delle Ricerche, Neaples, Italy Contact author: Fantina Madricardo, ISMAR-CNR, Arsenale - Tesa 104, Castello 2737/F 30122 Venezia, Italy, Fax (+39) 041 2407940, e-mail:fantina.madricardo@ismar.cnr.it Abstract Transitional environments like lagoons and estuaries have generally a complex morphology characterized by the presence of channels, salt marshes and tidal flats. These environments are often very anthropised areas where a constant bathymetric monitoring is needed. At the same time, being often super-shallow (with average depth of the order of 1 m), lagoons and estuaries represent a challenge for acoustic bathymetric surveys since the water shallowness requires an high measurement accuracy. Moreover, high reverberation and multiple reflections can substantially distort the acoustic signals, increasing the error range of the bathymetric instruments. Within this context, a series of experiments are currently ongoing in the Lagoon of Venice with the newest bathymetric instruments designed for very shallow water surveys in order to test their functioning in different conditions: in correspondence of navigation channels, natural channels or creeks, tidal flats and close to salt marshes. The aim of these trials is to assess and compare the operational capability of the instruments considered and, more generally, to find the best instrumental setup for super-shallow water conditions in terms of minimal relative error on the bathymetric data and of minimal survey costs. Keywords: Bathymetric survey; super-shallow water, interferometric and beam forming systems, Venice Lagoon 1. INTRODUCTION The management of very anthropised coastal areas often requires high resolution bathymetries. Bathymetric data are commonly used for the monitoring of navigation canals and as a starting point for any coastal engineering intervention. Bathymetric data are employed for geomorphological studies and modelling of the evolution trends of the highly dynamical coastal areas. Moreover bathymetric and backscatter data can provide information for seafloor sediment characterization and habitat mapping (for recent applications see [1] and reference therein). Among the coastal systems, transitional environments, like lagoons and estuaries, are often super-shallow (of the order of 1m deep or less) and morphologically complex. This kind of environment represents a challenge for acoustic bathymetric surveys since the water shallowness requires an high measurement accuracy. At the same time, high reverberation and multiple reflections can substantially distort the acoustic signals, increasing the error range. To assess the possibilities and the limits of acoustic surveys in super-shallow environments, we carried out three surveys in the Lagoon of Venice with two interferometric sonars (IS) and a multibeam echosounder (MBES). These field tests were carried out to directly compare the data acquired with 4th International Conference and Exhibition on "Underwater Acoustic Measurements: Technologies & Results" - 1283 -