Flare imaging with multibeam systems: Data processing for bubble detection at seeps

Multibeam sonar surveys have been conducted since their invention in the 1970s; however, mainly
reflections from the seafloor were considered so far. More recently, water column imaging with multibeam
is becoming of increasing interest for fisheries, buoy, mooring, or gas detection in the water column. Using
ELAC SEABEAM 1000 data, we propose a technique to detect gas bubbles (flares) although this system is
originally not designed to record water column data. The described data processing represents a case study
and can be easily adapted to other multibeam systems. Multibeam data sets from the Black Sea and the
North Sea show reflections of gas bubbles that form flares in the water column. At least for reasonably
intense gas escape the detection of bubbles is feasible. The multibeam technique yields exact determination
of the source position and information about the dimension of the gas cloud in the water. Compared to
conventional flare imaging by single-beam echo sounders, the wide swath angle of multibeam systems
allows the mapping of large areas in much shorter time.