Rapid environmental assessment of marine coastal areas for naval operations using sequential space filling designs

A thorough understanding of environmental variability greatly increases the likelihood of naval mission success. Present-day naval operations are increasingly focused on coastal-littoral waters rather than the open ocean. Historical data records may be sparse or inexistent in these areas. Survey methodologies to rapidly collect data in unknown, dangerous and contested shallow territorial seas are required.This work applies space filling designs to build sampling strategies that can provide accurate estimations of oceanographic fields with a modest navigation time. The design results from sequentially optimizing a cost metrics that combines the benefit of a potential sample location in filling up the holes in space and the cost of visiting that point and collecting a measurement. Optimization is done using a Simulated Annealing approach. The space filling approach has been employed to carry out a rapid environmental assessment of the Bay of Palma de Mallorca, Balearic Islands (Spain). The considered region occupies an extension of 65.18 Km2, being the longest and widest measures 12.4 and 4 km, respectively. The design parameters were a survey time limited to 5 h, a navigation speed of 15 knots and a measuring time of 300 s. The designed survey was physically performed in 4 h and 25 min using the R/V IMEDEA1 equipped with two thermosalinometers at 2 m deep. The environmental characterization shows the existence of a westward temperature gradient with a thin filament of warm waters intruding the centre area of the bay. Results indicate that space filling designs seem adequate to rapidly characterize the environment of a marine region where no prior oceanographic knowledge is available. However, it has been found that this approach is sub-optimal and suffers from the existence of multiple local minima that difficult the optimization process to build the design.