Recent Development in IR Sensor Technology for Monitoring Subsea Methane Discharge

Abstract

Recently developed methane sensors, based on infrared (IR) absorption technology, were successfully utilized for subsea methane release measurements. Long-term investigation of methane emissions (fluid flux determination) from natural methane seeps in the Hikurangi Margin offshore New Zealand were performed by using seafloor lander technology. Small centimeter-sized seep areas could be sampled at the seafloor by video-guided lander deployment. In situ sensor measurements of dissolved methane in seawater could be correlated with methane concentrations measured in discrete water samples after lander recovery. High backscatter flares determined by lander-based Acoustic Doppler Current Profiler (ADCP) measurement indicate bubble release from the seafloor. Highest methane concentrations determined by the IR sensor coincided with periods of high ADCP backscatter signals. The high fluid release cannot be correlated with tidal changes only. However, this correlation is possible with variability in spatial bubble release, sudden outbursts, and tidal changes in more quiescent seepage phases.A recently developed IR sensor (2,000 m depth-rated) with a detection limit for methane of about 1 ppm showed good linearity in the tested concentration range and an acceptable equilibration time of 10 min. The sensor was successfully operated offshore Santa Barbara by a small work-class ROV at a natural methane seep (Farrar Seep). High background methane concentration of 50 nmol L−1 was observed in the coastal water, which increases up to 560 nmol L−1 in dissolved methane plumes south of the seepage area. ROV- and lander-based sensor deployments have proven the applicability of IR sensor technology for the determination of subsea methane release rates and plume distribution. The wide concentration range, low detection limit, and its robust detection unit enable this technology for both subsea leak detection and oceanographic trace gas investigations.

Greenland melt drives continuous export of methane from the ice-sheet bed

“…An underwater pump (SBE 5T, Sea-Bird Scientific) mounted to the sensor continuously feeds water to the membrane equilibrator. Dissolved gases diffuse through a composite membrane into the internal gas circuit where partial-pressure is measured via tunable diode laser absorption technology 14 . The CONTROS HydroC ® sensor was deployed completely submerged within a solid metallic cage moored by cables attached to boulders on the river bank, with the sensor head facing the river current (Extended Data Fig.…”

“…We focused on a 600 km 2 catchment of the GrIS which has been extensively studied over the last decade, both in terms of ice dynamics and subglacial geochemistry (Supplementary Information 1a). Between 19 May and 13 July 2015, we deployed a CONTROS HydroC ® CH4 sensor 14 (Kongsberg Maritime Contros, Germany) < 2 km of the ice margin in the proglacial river of the Leverett Glacier (LG) (Supplementary Information 1.a; Extended Data Fig. 1) 15,16 .…”

Autonomous Optofluidic Chemical Analyzers for Marine Applications: Insights from the Submersible Autonomous Moored Instruments (SAMI) for pH and pCO2

“…There are few chemical sensors that satisfy the accuracy and precision requirements that have also been successfully commercialized. These include fluorescent lifetime dissolved O 2 sensors (Tengberg et al, 2006), UV nitrate analyzers (Johnson and Coletti, 2002), ISFET pH sensors (Martz et al, 2010), infrared pCO 2 and CH 4 sensors (Schmidt et al, 2013;Sutton et al, 2014), and the SAMI indicator-based technology for pCO 2 and pH (DeGrandpre et al, 1995(DeGrandpre et al, , 2000Seidel et al, 2008). Of this list, the SAMI technology is the only one that uses a pumped "renewable" reagent.…”

Novel Online Digital Video and High-Speed Data Broadcasting via Standard Coaxial Cable Onboard Marine Operating Vessels

“…These CH 4 measurements conducted with the CONTROS HydroC ™ CH 4 depict the same pattern as measured with the inline MIMS system (Sommer et al, submitted). The combination of the online video CTD with MIMS, the CONTROS pCO 2 (Fietzek et al, 2013), and CH 4 sensors (Schmidt, Linke & Esser, 2013) has been used now during several cruises to abandoned wells in the North Sea (Linke, 2012; and natural CO 2 gas release sites in the Mediterranean Sea (Schmidt, Linke et al, 2015). The combination allows for intercomparison and intercalibration, and several gas plumes emitted from abandoned wells and natural gas release sites could be nicely mapped despite strong currents and tidal changes.…”