ORCID Profile
0000-0001-9301-0803
Current Organisations
The Geological Survey of Norway (NGU)
,
NIWA - The National Institute of Water and Atmospheric Research Ltd.
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Publisher: Springer Science and Business Media LLC
Date: 28-05-2016
Publisher: Schweizerbart
Date: 08-2016
Publisher: Wiley
Date: 09-07-2014
DOI: 10.1002/ESP.3615
Publisher: MDPI AG
Date: 26-04-2020
DOI: 10.3390/RS12091371
Abstract: Modern multibeam echosounders can record backscatter data returned from the water above the seafloor. These water-column data can potentially be used to detect and map aquatic vegetation such as kelp, and thus contribute to improving marine habitat mapping. However, the strong sidelobe interference noise that typically contaminates water-column data is a major obstacle to the detection of targets lying close to the seabed, such as aquatic vegetation. This article presents an algorithm to filter the noise and artefacts due to interference from the sidelobes of the receive array by normalizing the slant-range signal in each ping. To evaluate the potential of the filtered data for the detection of aquatic vegetation, we acquired a comprehensive water-column dataset over a controlled experimental site. The experimental site was a transplanted patch of giant kelp (Macrocystis pyrifera) forest of known biomass and spatial configuration, obtained by harvesting several in iduals from a nearby forest, measuring and weighing them, and arranging them manually on an area of seafloor previously bare. The water-column dataset was acquired with a Kongsberg EM 2040 C multibeam echosounder at several frequencies (200, 300, and 400 kHz) and pulse lengths (25, 50, and 100 μs). The data acquisition process was repeated after removing half of the plants, to simulate a thinner forest. The giant kelp plants produced evident echoes in the water-column data at all settings. The slant-range signal normalization filter greatly improved the visual quality of the data, but the filtered data may under-represent the true amount of acoustic energy in the water column. Nonetheless, the overall acoustic backscatter measured after filtering was significantly lower, by 2 to 4 dB on average, for data acquired over the thinned forest compared to the original experiment. We discuss the implications of these results for the potential use of multibeam echosounder water-column data in marine habitat mapping.
Publisher: MDPI AG
Date: 16-12-2019
DOI: 10.3390/GEOSCIENCES9120516
Abstract: Seafloor backscatter mosaics are now routinely produced from multibeam echosounder data and used in a wide range of marine applications. However, large differences ( dB) can often be observed between the mosaics produced by different software packages processing the same dataset. Without transparency of the processing pipeline and the lack of consistency between software packages raises concerns about the validity of the final results. To recognize the source(s) of inconsistency between software, it is necessary to understand at which stage(s) of the data processing chain the differences become substantial. To this end, willing commercial and academic software developers were invited to generate intermediate processed backscatter results from a common dataset, for cross-comparison. The first phase of the study requested intermediate processed results consisting of two stages of the processing sequence: the one-value-per-beam level obtained after reading the raw data and the level obtained after radiometric corrections but before compensation of the angular dependence. Both of these intermediate results showed large differences between software solutions. This study explores the possible reasons for these differences and highlights the need for collaborative efforts between software developers and their users to improve the consistency and transparency of the backscatter data processing sequence.
Publisher: Public Library of Science (PLoS)
Date: 13-05-2014
Publisher: Springer Science and Business Media LLC
Date: 03-01-2018
Publisher: Elsevier BV
Date: 12-2015
Publisher: Springer Science and Business Media LLC
Date: 31-01-2018
Publisher: American Association for the Advancement of Science (AAAS)
Date: 02-03-2018
Abstract: Coseismic canyon flushing reveals how earthquakes drive canyon development and deep-sea sediment dispersal on active margins.
Location: New Zealand
No related grants have been discovered for Alexandre Schimel.