Report from the new technology testing cruise in Sognefjorden in February 2024

Abstract

During a five days survey with G.O. Sars in February 2024, we simultaneously collected data with marine robotics and standard sampling. The main goals of the test survey were to 1) assess data types and quality of data when sampling with robotics and evaluate what we gain/loose when using autonomous sampling as compared to standard sampling from a vessel, and 2) evaluate the suitability of autonomous sampling. During the survey we ran three gliders from two manufacturers and with diverging sensors. In addition, we deployed and recovered a vertically profiling CTD-drone. We also collected in situ data with CTD, nets and Multinet. The results show that gliders indeed are promising, but there are challenges associated with a rapid implementation of gliders in the monitoring program with the aim of reducing the ordinary surveys with research vessels. These challenges include build-up of institutional competence on the new technology, but also the functionality/ease of use of the gliders. Glider leakages are a concern. Different glider types work better for different applications. The small simple Hefring Oceanscout dealt a lot better with the strong currents in the fjord, but its small size also prevents integration of larger sensors. These can be integrated in the larger Slocum glider, but they affect the efficiency of the glider behaviour and robustness. Further work includes testing mobility offshore and developing routines for deployment/recovery of gliders using smaller boats close to the coast, as this would prevent use of research vessels for glider activity. Further work also includes building more experience with using gliders during longer missions. The short data sets from the fjord deployments also highlight the need to develop data processing routines and tools, largely based on existing correction and processing protocols.