GMM - A GAS MONITORING MODULE FOR SEABED METHANE LEAKAGE

Methane monitoring in marine environments is an urgent task demanded by the scientific community in the framework of geohazard, biological and global change studies. In this respect a new seafloor lander module (GMM - Gas Monitoring Module) has been developed by the European Commission ASSEM project (Array of Sensors for long term SEabed Monitoring of geohazards) for continuous and long-term measurements of methane concentration in seawater at the benthic boundary layer. 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 semi-conductor methane sensors and a CTD for temperature, salinity, pressure recording, as well as interfaces available for further sensors. The electronics can perform a series of tasks including: data acquisition from all scientific packages and status sensors, preparation and continuous update of a periodic (e.g. hourly) data message, ready to be transmitted via serial link on request, management of the sensors (switch on/off of individual sensors according to command from operator; event detection), reception and management of commands from external units (data request, system reconfiguration, restart, etc.), monitor internal status parameters and external power supply, back-up of data in internal memory. The methane sensor (METS by Capsum) is an improved version of a commercial product used for short-term deployment such as profiling. It uses a semi-conductor as sensing element, integrated in a small gas volume in the sensor-head. Protection against the outside water and pressure is given by a special membrane. The improved version for GMM addresses long-term operativity, increased operation depth and increased sensitivity. A series of tests showed the improved METS performance. GMM can be linked to submarine cables for real-time data transmission to onshore operators. The system is suitable to monitor, for long periods, natural gas emission from seafloor or leakages from pipelines and boreholes.