ABSTRACT:

Monitoring methane emissions from the seafloor is a task of widely recognized and increasing importance, demanded in several applications like geo-hazards and global change studies as well as oil & gas industry activities. Original solutions for multi-parametric surveying and monitoring methane occurrence in seawater have been recently developed and qualified in the framework of major international projects. These solutions are based on an integration of gas sensors with traditional oceanographic sensors and tools, all with a unique time-reference and control by a specific data acquisition system. For fast aeral characterization and execution of explorative surveys including casts and towing close to the seabed, a module, named GAS-SCIPACK, was developed. In a first explorative mission performed in 2004 within submarine mud volcanoes offshore Sicily, the module was equipped with 2 solid-state methane sensors, CTD and transmissometer, Niskin bottles, echo sounder, color camera, light, attitude sensors (heading, pitch, roll) and internal status sensors (internal T, voltage, current, water detector). For long-term gas monitoring at the seafloor, a small observatory (GMM - Gas Monitoring Module) has been developed in the framework of the European Commission ASSEM project (Array of Sensors for long term SEabed Monitoring of geohazards). The module is designed to host a series of sensors controlled and managed by a data acquisition and control system capable of performing first-level data quality checks. The prototype includes three semi-conductor methane sensors, a H2S electrode, a CTD for temperature, salinity, pressure recording, as well as interfaces available for further sensors. The multiparametric surveying or monitoring has been specifically effective in assessing causal-effect links in gas leakage phenomena

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