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Data Processing and Interpretation

Multibeam Processing

INFOMAR multibeam surveys are designed to meet internationally recognised standards for data quality. This means that acoustic soundings taken from multibeam systems must be processed by a Hydrographer before these standards can be met. During acquisition, multibeam data quality can be affected by several variables; the type of vessel, its survey speed, weather conditions, composition of the water column are just some of the factors which produce “noise” artefacts in multibeam datasets. The noise which usually appears as depth-spikes in the data must be cleaned and rejected from the final data-set.

The Hydrographer or Data Processor uses a program called CARIS HIPS & SIPS to apply filters, tidal and refraction corrections and to manually clean and quality-check the survey data after it comes on-board. Tidal adjustments are especially important as the final depth values must be accurate to within a few centimetres, so knowing and compensating for the height of the tide at a given point in time is crucial to ensuring an accurate end product. In order to know tide heights a series of tide gauges are deployed both offshore and onshore. Onshore tide gauges allow the end chart depths to be related to known heights on land.

Once the processing of a dataset is complete, the depths are leveled to their shallowest possible occurrence which happens at “lowest astronomical tide”, and these depth values are then used to update nautical charts and to produce a range of INFOMAR chart deliverables, including shaded relief charts, backscatter charts and contoured bathymetry charts

Image showing multibeam echosounder (MBES) data being processed using Caris HIPS (top) and an example of a MBES dataset showing the moraine feature on the seabed discovered by INFOMAR off the Kerry coast.

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Seabed Classification using Multibeam Backscatter

A key deliverable of the INFOMAR seabed mapping programme is the production of seabed classification charts derived from multibeam data. Seabed classification is an advanced process in which a backscatter image is interrogated using special software in order to divide it into areas which have similar characteristics. The software initially divides the image up into manageable rectangular areas of a few metres. Once these rectangles have been placed over the image the acoustic data is examined in several ways taking into account factors such as texture, morphology, hardness and other statistical variables.

Areas which have a similar nature are grouped together and divided into separate classes. These classes are colour coded and developed into seabed classification charts. Finally, the classes on the chart are then physically sampled in order to ground truth the classification. This allows INFOMAR to match different sediment types with their corresponding colour class thereby producing classified geological maps of the seafloor.

For details about the progress of INFOMAR surveys in the 26 priority bays and 3 priority areas, navigate to the 'Surveying' section of the website.

 

 

Images of multibeam backscatter data being analysed using QTC Multiview software where divisions are made in the datasets based on their attributes in 'Q-space' (top) and the finished product showing a classification of the seabed from the surveyed area of the East Coast Priority Area (bottom).

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Shallow Seismic Data

Shallow seismic data is recorded to data tapes and hardcopy offshore. Traditionally, this product has been supplied to the end user on a case by case basis due to the specific nature of the dataset. These have taken the form of profile images generated in .jpeg format for visual assessment of the subseafloor sediments and/or the actual shallow seismic data in .segy format which allows interested users to interpret and process their own data to their required end use.

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Ground Truthing/Seabed Samples

Analysis of ground truthing samples is dependant on the nature of the sample. All sediment samples undergo particle size analysis (PSA) to determine the size range of sediment contained in the sample which can often reveal an insight about the processes operating in the depositional environment. These samples are also critical for the testing or 'supervision' of seabed classifications based on acoustic properties of the multibeam data. Vibrocores are scanned, logged and stored.

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3D Virtual Scenes and Fly Through Movies

Using the 3D visualisation programme Fledermaus, INFOMAR datasets are used to build up a virtual environment which allows users to navigate through the datasets to gain an impressive perspective and useful overview of the surveyed bays.

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