Optimizing Observation Networks Combining Ships of Opportunity, Gliders, Moored Buoys and FerryBox in the Bay of Biscay and English Channel

Designing optimal observation networks in coastal oceans remains one of the major challenges towards the implementation of future Integrated Ocean Observing Systems to monitor the coastal environment. In the Bay of Biscay and the English Channel, the diversity of involved processes requires to adapt observing systems to the specific targeted environments. Also important is the requirement for those systems to sustain coastal applications. An efficient way to measure the hydrological content of the water column over the continental shelf is to consider ships of opportunity. In the French observation strategy, the RECOPESCA program, as a component of the High frequency Observation network for the environment in coastal SEAs (HOSEA), aims to collect environmental observations from sensors attached to fishing nets. In the present study, we assess that network performances using the ArM method (Le Hénaff et al., 2009). A reference network, based on fishing vessels observations in 2008, is assessed using that method. Moreover, three scenarios, based on the reference network, a denser network in 2010 and a fictive network aggregated from a pluri-annual collection of profiles, are also analyzed. Two other observational network design experiments have been implemented for the spring season in two regions: 1) the Loire River plume (northern part of the Bay of Biscay) to explore different possible glider endurance lines combined with a fixed mooring to monitor temperature and salinity and 2) the Western English Channel using a glider below FerryBox measurements. These experiments combining existing and future observing systems, as well as numerical ensemble simulations, highlight the key issue of monitoring the whole water column in and close to river plumes (e.g. using gliders), the efficiency of the surface high frequency sampling from FerryBoxes in macrotidal regions and the importance of sampling key regions instead of increasing the number of Voluntary Observing Ships.