‘They call ‘im Crowie’: An investigation of the Aboriginal significance attributed to a wrecked River Murray barge in South Australia

The Indigenous intangible heritage related to wrecked vessels has been poorly studied and documented. This article provides a counter to dominant maritime archaeology discourses via the investigation of the Aboriginal significance attributed to a wrecked and submerged River Murray barge (Crowie) in South Australia. There are numerous layers of Aboriginal significance that may be attributed to Crowie including the relationship of the community with their ‘underwater country’, Indigenous contributions to the riverboat industry, and the use of Aboriginal terms in vessel-naming practices. Geophysical data from multibeam and sidescan sonar surveys allowed for confirmation of the proposed location of the wreck and through comparison with historical descriptions and photographs provided evidence to substantiate the assignation of the wreck as the Crowie barge.

Spatial distribution and thickness of fine-grained sediment along the United States portion of the upper Niagara River, New York

Over 220 linear miles of geophysical data, including sidescan sonar and chirp sub-bottom profiles, were collected in 2016 and 2017 by the US Army Corps of Engineers and the US Fish and Wildlife Service in the upper Niagara River. In addition, 36 sediment grab samples were collected to groundtruth the geophysical data. These data were used to map the spatial distribution of fine-grained sediment, including volume data in certain locations, along the shallow shorelines of the upper Niagara River. Overall, the most extensive deposits were spatially associated with either small tributaries or with man-made structures that modified the natural flow of the system. Extensive beds of submerged aquatic vegetation (SAV) were also mapped. Although always associated with a fine-grained matrix, the SAV beds were patchy in distribution, which might reflect subtle differences in the grain size of the sediment matrix or could simply be a function of variations in species or growth. The maps generated from this effort can be used to guide sampling plans for future studies of contamination in fine-grained sediment regions.

Submarine geomorphology

Submarine geomorphology underwent significant development in the second half of the 20th century, largely thanks to advances in technology by the military, navigation and hydrocarbon industry, which were later transferred to the academic and commercial sectors. In this chapter we summarise the development of the key methods used in submarine geomorphology between 1950 and 2000, which include sidescan sonar, multibeam echosounder, reflection seismology, seafloor sampling and marine robotic systems. We then highlight the progress in our understanding of seafloor processes and landforms made using these methods, focusing on continental shelf landforms, slope instability, submarine canyons, submarine fans and channels, and current-controlled landforms.

Mapping shallow water bubbling reefs – a method comparison between topobathymetric lidar and multibeam echosounder

<p>Bubbling reefs are submarine structures formed by aggregating carbonate resulting from leaking gases. The reef formations can form pillars rising several meters above the sea floor. They support a high diversity of benthic communities, and in the EU Habitat Directive they are specifically mentioned as a natural habitat type that require conservation.</p><p>Knowledge about the presence, locations and shape of bubbling reefs are usually obtained by geophysical surveying using multibeam echosounder (MBES), sidescan sonar and/or seismic acquisition systems, combined with ground truth verification. However, this traditional survey method is time consuming, especially for full coverage surveys in shallow water. Full coverage surveys are a requirement to capture the bubbling reefs due to their relatively small spatial extent. Besides, traditional geophysical vessel borne surveys have their limitations in shallow water due to low spatial coverage and vessel draft.</p><p>In recent years, airborne topobathymetric (green wavelength) lidar has emerged as a new possible surveying method in shallow water (e.g. Andersen et al., 2017). Compared to vessel borne MBES, full coverage lidar surveys can be conducted within hours instead of days/weeks, while also including full coverage in the shallow water and a seamless transition between land and water. Thus, topobathymetric lidar may be a good choice for carrying out full coverage surveys in large shallow water areas. However, the accuracy and the resolution of the collected dataset are important in these surveys, not least when mapping small scale features such as bubbling reefs.</p><p>In this study, we investigated the potential of mapping bubbling reefs in shallow water (<10 m) using topobathymetric lidar. The main objective was to assess the performance of airborne topobathymetric lidar to detect and resolve small scale objects, i.e. bubbling reefs, by comparison to MBES data. Both MBES and lidar data were acquired in spring 2019 in a designated Natura 2000 area close to Hirsholmene in the northern Kattegat region in Denmark. The comparison of the two datasets included a quantification of the accuracy, and an assessment of the performance for mapping bubbling reefs.</p><p> </p><p>Reference:</p><p>Andersen M.S., Gergely A., Al-Hamdani Z., Steinbacher F., Larsen L.R., Ernstsen V.B. (2017). Processing and performance of topobathymetric lidar data for geomorphometric and morphological classification in a high-energy tidal environment. Hydrology and Earth System Sciences, 21: 43-63, DOI: 10.5194/hess-21-43-2017.</p>

Generating Synthetic Sidescan Sonar Snippets Using Transfer-Learning in Generative Adversarial Networks

The training of a deep learning model requires a large amount of data. In case of sidescan sonar images, the number of snippets from objects of interest is limited. Generative adversarial networks (GAN) have shown to be able to generate photo-realistic images. Hence, we use a GAN to augment a baseline sidescan image dataset with synthetic snippets. Although the training of a GAN with few data samples is likely to cause mode collapse, a combination of pre-training using simple simulated images and fine-tuning with real data reduces this problem. However, for sonar data, we show that this approach of transfer-learning a GAN is sensitive to the pre-training step, meaning that the vanishing of the gradients of the GAN’s discriminator becomes a critical problem. Here, we demonstrate how to overcome this problem, and thus how to apply transfer-learning to GANs for generating synthetic sidescan snippets in a more robust way. Additionally, in order to further investigate the GAN’s ability to augment a sidescan image dataset, the generated images are analyzed in the image and the frequency domain. The work helps other researchers in the field of sonar image processing to augment their dataset with additional synthetic samples.

Operation of a multi-frequency parametric sidescan sonar in an ice waveguide

Hydroacoustic systems for mineral exploration, solving engineering problems and monitoring the ecological state of the world’s oceans are currently being intensively developed. However, the practical use of hydroacoustic systems for solving the problems under consideration, operating in the traditional mode, has some significant limitations. These restrictions are largely related to the state of the marine areas in which such work is carried out. Especially little is known about the patterns of propagation and interaction of acoustic waves in marine basins with ice cover. These areas are rich in minerals and intensive shipping is developing in them. Therefore, an important place in acoustic research is occupied by the study of the acoustic properties of the ice cover of the polar regions of the Earth. This is determined by the fact that the ice sheet is a unique constantly collapsing and renewable natural system. In this regard, the conditions for the propagation of acoustic waves are changing. More than 70% of the Arctic basin is covered with ice, the lower boundary of which has significant irregularities with a standard deviation of up to 3 m, so the scattering of acoustic waves at such a boundary is significant and different at different frequencies. The formation of the acoustic field of the hydroacoustic systems used in these conditions is quite complex. Therefore, the task of assessing changes in the characteristics of the field and the use of appropriate hydroacoustic systems for their effective use is urgent.