INFOMAR Seabed Survey Acoustic Backscatter (seafloor hardness)

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 2001 to 2022. The seabed in Ireland’s offshore area is between 200 and 5000 metres deep. The data was collected from 1996 to 2002.

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 for inshore is 10m by 10m and offshore is 40m by 40m. This means that each cell (pixel) represents an area on the seabed of 10 metres squared or 40 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).

This data shows areas that have been surveyed. There are plans to fill in the missing areas between 2020 and 2026. The deeper offshore waters were mapped as part of the Irish National Seabed Survey (INSS) between 1999 and 2005. INtegrated Mapping FOr the Sustainable Development of Ireland's MArine Resource (INFOMAR) is mapping the inshore areas. (2006 - 2026).