André, M., van der Schaar, M., Zaugg, S., Houégnigan, L., Mas, A., Morell, M., Solé, M., Castell, J.V. Listening to the deep Proceedings of the 24th Conference of the European Cetacean Society, Stralsund, Germany, 22nd to 24th of March 2010, p.120, Mar 2010 Abstract: The development and broad use of Passive Acoustic Monitoring techniques have the potential to help assessing the large-scale influence of artificial noise on marine organisms and ecosystems. Deep-sea observatories are meant to play a key role in understanding these recent acoustic changes. LIDO (Listening to the Deep Ocean environment, ESONET, European Network of Excellence) has become a research concept that is allowing the real-time long-term monitoring of marine ambient noise, as well as marine mammal sounds in European and international waters at cabled and standalone observatories. Here, we present the overall development of the project and the use of Passive Acoustic Monitoring techniques to provide the scientific community with real-time data at large spatial and temporal scales. A series of detectors covering different frequency bandwidths allows the detection of broad classes of events. For the classification and feature extraction of the sources a more complex approach is adopted. Short pieces of audio (21ms) centred on the detected event are extracted and enter a feed forward neural network that gives as output the estimated probability of positively classifying the detected source. False positive detection rates range from 3 to 6% depending on the sources. Special attention is given to the extraction and identification of high frequency cetacean echolocation signals. This is done considering the relevance of immediately detecting target species, like beaked whales, in mitigation processes, e.g. during military exercises or pile driving operations. The online connection to the Flash client currently allows to follow the real-time analysis (detection, classification and tracking) of the acoustic events, especially marine mammals, at three European locations: the West-Mediterranean coast (OBSEA), the Ligurian Sea (ANTARES) and the East-Sicily coast (NEMO). Project: LIDO, Listening to the Deep-Ocean Environment Project: ESONET, Network of Excellence