Recently, the rapid development of the seabed mapping industry has allowed researchers to collect hydroacoustic data in shallow, nearshore environments. Progress in marine habitat mapping has also helped to distinguish the seafloor areas of varied acoustic properties. As a result of these new developments, we have collected a multi-frequency, multibeam echosounder dataset from the valuable nearshore environment of the southern Baltic Sea using two frequencies: 150 kHz and 400 kHz. Despite its small size, the Rowy area is characterized by diverse habitat conditions and the presence of red algae, unique on the Polish coast of the Baltic Sea. This study focused on the utilization of multibeam bathymetry and multi-frequency backscatter data to create reliable maps of the seafloor. Our approach consisted of the extraction of 70 secondary features of bathymetric and backscatter data, including statistic and textural attributes of different scales. Based on ground-truth samples, we have identified six habitat classes and selected the most relevant features of the bathymetric and backscatter data. Additionally, five types of image processing pixel-based and object-based classifiers were tested. We also evaluated the performance of algorithms using an accuracy assessment based on the validation subset of the ground-truth samples. Our best results reached 93% overall accuracy and a kappa coefficient of 0.90, confirming that nearshore seabed habitats can be accurately distinguished based on multi-frequency, multibeam echosounder measurements. Our predictive habitat mapping of shallow euphotic zones creates a new scientific perspective and provides relevant data for the management of natural resources. Object-based approaches previously used in various environments and areas suggest that methodology presented in this study may be scalable.

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part ment of Geo mor phol ogy and Qua ter nary Ge ol ogy, Baayńskiego 4, 80-952 Gdańsk, Po land Rudowski, S., Rucińska-Zjadacz, M., Wróblewski, R., Sitkiewicz, P., 2016. Sub ma rine land slides on the slope of a sandy bar rier: a case study of the tip of the Hel Pen in sula in the South ern Bal tic. Geo log i cal Quar terly, 60 (2): 407-416, doi: 10.7306/gq.1291 The aim of the study is to pres ent the oc cur rence of land slides on the sub ma rine slope of a sandy bar rier. The scale and sig-nif i cance of this phe nom e non is dis cussed. The study area is the Hel Pen in sula. It is a 35 km long young sandy spit. The landform is prograding into the deep part of Gdańsk Bay, and the un der wa ter ex ten sion of its tip is a steep sandy slope. The tip is still poorly in ves ti gated, as it was a mil i tary area closed to re search ers un til 2003. The first de tailed sur vey of the tip on the sea bed was con ducted aboard the re search ves sel "IMOR". A multibeam echosounder, a sub-bot tom profiler and a side-scan so nar were used, while grab and core sam ples of sed i ment were ob tained. Many forms, com monly cre ated as the re sult of un der wa ter mass move ment, were rec og nized and de ter mined (main scarps, main bod ies, land slide steps, landslide foots, se ries of small slides, "sheet" slides and struc tural slides). On the one hand, the land slide pro cesses that oc cur in the tip of the Hel Pen in sula are re lated to the nat u ral de vel op ment of sandy spits. On the other hand, they threaten the shore's sta bil ity. The gen e sis of the land slides is still not known. Key words: un der wa ter mass move ments, sandspit, dig i tal ter rain model, side-scan so nar, sub-bot tom pro fil ing.

The Hel Peninsula is a 35 km long spit that extends into water depths of almost 60 m. Unlike most sandy barriers, the distal end of the Hel Peninsula is prograding into the deep water. This affects unique conditions for the evolution of this section of the Peninsula. The aim of this study is to determine the morpholithodynamic changes on the tip of the Hel Peninsula. Shore studies were performed in 2006-2008 and 2012. Measurements included: beach profiling, determination of shoreline and dune base line positions, and collection of sediment samples. The different nature of the eastern, central and western part of the Hel tip is evident. The eastern part is accumulative, the central part is variable with the general nature of strong and differently directed redeposition and accumulative periods, while the western part is highly erosive.

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