Layer: Backscatter 5m (ID: 7)

Name: Backscatter 5m

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Description: This Backscatter map shows how hard or soft the seabed is in Irish waters. The seabed in Ireland’s inshore area is between 0 and 200 metres deep. The data was collected from 2007 to 2008. Bathymetry is the measurement of how deep is the sea. Bathymetry is the study of the shape and features of the seabed. The name comes from Greek words meaning "deep" and “measure". Backscatter is the measurement of how hard is the seabed is. Bathymetry and backscatter data are collected on board boats working at sea. The boats use special equipment called a multibeam echosounder. A multibeam echosounder is a type of sonar that is used to map the seabed. Sound waves are emitted in a fan shape beneath the boat. The amount of time it takes for the sound waves to bounce off the bottom of the sea and return to a receiver is used to determine water depth. The strength of the sound wave is used to determine how hard the bottom of the sea is. A strong sound wave indicates a hard surface (rocks, gravel), and a weak signal indicates a soft surface (silt, mud). The word backscatter comes from the fact that different bottom types “scatter” sound waves differently. The data are collected as points in XYZ format. X and Y coordinates, Z (depth) and backscatter value. The boat travels up and down the water in a series of lines (trackline). An XYZ file is created for each line and contains thousands of points. The line files are merged together and converted into gridded data to create a Digital Terrain Model of the seabed. This is a raster dataset. Raster data stores information in a cell-based manner and consists of a matrix of cells (or pixels) organised into rows and columns. The format of the raster is an image (GeoTIFF). The image cell size is 5m by 5m. This means that each cell (pixel) represents an area on the seabed of 5 metres squared. The map is coloured using grey shades. The darker shading represents a hard seabed (e.g. rock) and lighter shading represents a soft seabed (e.g. sand, silt or mud). The dataset was mapped as part of the Joint Irish Bathymetric Survey Project (JIBS). The Maritime and Coastguard Agency was the Project leader, approved under the INTERREG IIIA Programme, with the Marine Institute of Ireland as project partner. The objective of the JIBS Project was to promote joint action to survey the seabed in such a way as to satisfy the needs of many organisations. The JIBS project commenced on 10 April 2007 and was completed in June 2008.

Service Item Id: fb8b178661ea4acea8fcdfa3f520d94f

Copyright Text: Joint Irish Bathymetric Survey Project (JIBS)

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