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Seafloor classification using the RoxAnn ground-discrimination system and a new tool for visualization and classification

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Citation:
Hass, H. C. (2012): Seafloor classification using the RoxAnn ground-discrimination system and a new tool for visualization and classification , GV Sediment Meeting, 23 September 2012 - 28 September 2012 .
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Abstract:

Acoustic investigation of the seafloor is a widespread tool to understand the sedimentary processes that move sediments and that lead to the formation of distinct bedforms and habitats. While sidescan-sonar and swath-bathymetry systems are able to measure transect lines of distinct width, they usually lack the ability to classify the seafloor other than according to depth and reflectivity. Seafloor-classification systems aim at classifying the seafloor according to its acoustic properties using parameters such as the strength and the waveform of the echoes, respectively. However, they use to be single-beam systems that require data interpolation in order to produce area-wide maps. RoxAnn systems detect and interpret two echo returns per measurement: the first (E1) is represented by the energy that forms the last third of the first echo return (to avoid adverse effects of echoes between the ship's hull, the sea surface and the transducer). The second parameter (E2) is derived from the energy that forms the second return. E1 is a measure for the roughness; E2 is a measure for the hardness of the seafloor. To visualize the data the software tool RoxProc was developed. It is composed of a filter module that basically checks whether the recorded data are plausible, a module that calculates statistics such as frequency distributions of the measured parameters, a module that performs gridding at variable scales and a module that produces digital terrain models (DTM) and maps of the parameters water depth, roughness and hardness including options to drape any parameter onto any DTM. A further module assigns RGB values to each data point according to E1 and E2 values. Hence each data point is equipped with 8 values (latitude, longitude, water depth, E1, E2, R, G, B). The module allows to plot the transect lines in a map with line colors according to the RGB values of the measured data points. In a further step the colors can be interpolated to produce an area-wide map. Both types of RoxAnn maps must be equipped with 2D legends. The final RoxProc module allows to combine the RoxProc plots with DTMs, sidescan-sonar images, and groundtruth data for seabed classification. Examples show how a properly interpolated and gridded visualization of RoxAnn data supports the classification process. It becomes also obvious that groundtruthing is mandatory and that supporting data of sidescan sonar and/or multibeam systems are most helpful to achieve a reliable seafloor classification.

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