Correlation between sediment properties and seafloor characterization maps based on multibeam backscatter data from three regions off the coast of Norway

Multibeam echo sounder data from Kongsberg EM 1002 and EM 710 (70– 100 kHz) acquired between 2003 and 2014 were processed using QPS Fledermaus Geocoder Toolbox (FMGT) to produce backscatter mosaics and maps of estimated grain size. The regions surveyed (the Oslo fiord, the North Sea and off the coast of Mid-Norway) measured 36 000 km2 , with depths up to 600 m. Ground truth data acquired in 2004–2015 consisted of 64 gravity cores and 151 Van Veen grab samples. Particle size analysis was conducted on 125 sediment samples. Correlations between backscatter, estimated grain size and seabed sediment properties are examined in the paper. The Pearson’s correlation coefficient squared was 0.46 between estimated and measured median sediment grain size in a subset of the data; the estimated grain size was in general coarser than measured. The 2 mm limit of the estimated grain size in the Angular Range Analysis of FMGT was reached in areas of coarsegrained sediments. The correlation between backscatter and the geoacoustic parameters (sound speed, density) averaged over the upper 20 cm of the cores varied significantly with region, from absent to strong. The correlation coefficient squared was 0.70 between estimated grain size and core density off the coast of Mid-Norway. To conclude, estimating the grain size using FMGT worked well as a method to characterize the seafloor of the surveyed regions.