Seafloor Segmentation Based on Bathymetric Measurements from Multibeam Echosounders Data

Bathymetric data depicts the geomorphology of the seabottom and allows characterization of spatial distributions of apparent benthic habitats. The variability of seafloor topography can be defined as a texture. This prompts for the application of well developed image processing techniques for automatic delineation of regions with clucially different physiographic characteristics. In the present paper histograms of biologically motivated invariant image attributes are used for characterization of local geomorphological feahires. This technique can be naturally applied in a range of spatial scales. Local feature vectors are then submitted to a procedure which divides the set into a number of clusters each representing a distinct type of the seafloor. Prior knowledge about benthic habitat locations allows the use of supervised classification, by training a Suppolt Vector Machine on a chosen data set, and then applying the developed model to a full set. The classification method is shown to perform well on the multibeam echosounder (MBES) data from Piscataqua River, New Hampshire, USA

Seismic Stratigraphy of the Eastern Equatorial Pacific Ocean: Paleoceanographic Implications

The collection of Leg 138 well-log and shipboard physical-property data, in conjunction with high-resolution seismic profiles, provides an opportunity to understand the paleoceanographic significance of seismic reflectors and to gain insight into the paleoceanographic evolution of the eastern equatorial Pacific Ocean. A series of eight reflectors or reflector packages were traced between two transects connecting five Leg 138 sites. By generating synthetic seismograms at each of these sites and comparing these to the field records, the origin of these seismic reflectors was determined in terms of physical-property variations and other core measurements. In particular, these reflectors were usually associated with sharp variations in density, which in turn, are related to variations in carbonate content. Intervals with moderate or poor nannofossil preservation indices were generally restricted to intervals below the reflectors traced in this study, suggesting that dissolution played little role in producing these reflectors. However, intervals with T. longissima mats were associated with many of the reflectors (R3-b, R4, R5-t, R5-b, R6) at the three sites (847, 849, and 850) where this diatom was encountered. This suggests that the reflectors found in this study are related to productivity events, although these events manifested themselves in a different way at the sites in which T. longissima mats were not observed. Interpreted seismic stratigraphic sections were compiled from the reflector horizon data for the two transects. Along the western transect, the section between reflectors R3 and R8 thins abruptly north of l°40\u27 to l°50\u27N, suggesting that this marks the northern limit of high equatorial productivity at that time (3.9-9.5 Ma), because the seafloor is reasonably constant in depth along this transect. Unfortunately, statements about sharp productivity gradients cannot be made for the eastern transect where sediment thinning corresponds to a deepening of the seafloor and thus may be related to variations in dissolution. Finally, six reflectors were found to be associated with major paleoceanographic events; three of these reflectors correspond to those found by Mayer et al. (1985,1986) in the central equatorial Pacific Ocean, suggesting that these correspond to Pacific-wide Oceanographic events. One of these reflectors (R8-b) is caused by a pervasive dissolution event as is its central equatorial counterpart. The others (R3-b and R5-t), however, appear to be the result of productivity events in the eastern equatorial Pacific that are synchronous with dissolution events in the central equatorial Pacific. We suggest that while localized high productivity creates low carbonate intervals (and thus reflectors) in the eastern equatorial Pacific, steep gradients in the CCD result in enhanced dissolution and low carbonate intervals (and thus reflectors) in the deeper central equatorial Pacifi

Sensor-assisted Video Mapping of the Seafloor

In recent years video surveys have become an increasingly important ground-truthing of acousticseafloor characterization and benthic habitat mapping studies. However, the ground-truthing and detailed characterization provided by video are still typically done using sparse sample imagery supplemented by physical samples. Combining single video frames in a seamless mosaic can provide a tool by which imagery has significant areal coverage, while at the same time showing small fauna and biological features at mm resolution. The generation of such a mosaic is a challenging task due to height variations of the imaged terrain and decimeter scale knowledge of camera position. This paper discusses the current role of underwater video survey, and the potential for generating consistent, quantitative image maps using video data, accompanied by data that can be measured by auxiliary sensors with sufficient accuracy, such as camera tilt and heading, and their use in automated mosaicking techniques. The camera attitude data also provide the necessary information to support the development of a video collage. The collage provides a quick look at the large spatial scale features in a scene and can be used to pinpoint regions that are likely to yield useful information when rendered into high-resolution mosaics. It is proposed that high quality mosaics can be produced using consumer-grade cameras and low-cost sensors, thereby allowing for the economical scientific video surveys. A case study is presented with the results from benthic habitat mapping and the ground-truthing ofseafloor acoustic data using both real underwater imagery and simulations. A computer modeling of the process of video data acquisition (in particular on a non-flat terrain) allows for a better understanding of the main sources of error in mosaic generation and for the choice of near-optimal processing strategies. Various spatial patterns of video survey coverage are compared and it is shown that some patterns have certain advantages in the sense of accumulated error and overall mosaic accuracy