Detection and Visualisation of Oceanic Fronts from Satellite Data, with Applications for Fisheries, Marine Megafauna and Marine Protected Areas

The polar-orbiting AVHRR and Aqua-MODIS infrared sensors provide frequent views of a wide range of physical processes occurring at the sea surface, including: fronts, mesoscale eddies, currents and upwelling. Remote sensing of the marine environment is an established field, exploiting satellite data to study the development and distribution of oceanic processes (e.g. Haynes et al., 1993; Peckinpaugh and Holyer, 1994), and their effect on fisheries, sea mammals, ocean margin exchange and global warming (e.g. Podesta et al., 1993; Huthnance, 1995; Bost et al., 2009). Oceanic fronts are formed at the boundary between water masses of different temperature or density, and are often associated with mixing and enhanced biological production. Fronts that extend to the sea surface may be observed by satellite if the water masses differ in temperature or colour. Identifying fronts in satellite images manually is a tedious and subjective task, so several researchers have proposed image processing algorithms to do this semi-automatically (e.g. Bardey et al., 1999; Simpson, 1990), or entirely automatically (Cayula and Cornillon, 1992). Tracking thermal features through a time-sequence of images allows sea-surface currents to be estimated (Breaker et al., 1994). Relationships have been established between fronts and fish abundance, for instance swordfish (Podesta et al., 1993), tuna and billfish (Worm et al., 2005). In addition, Worm et al. (2005) determined a global correlation of predator diversity with fronts. Priede and Miller (2009) applied front detection techniques to reveal a strong relationship between the track of a tagged basking shark and a thermal front. The shark followed the N-S front for a whole day, keeping just to the warmer side. A 10-year time-series (30,000 satellite images) was processed and aggregated