Case Studies

AutoCAD used to map Irish seabed

Until now, Ireland's seabed area has been a largely unmapped and untapped resource. However, a multi-million euro project to provide baseline maps of the country's offshore territory is set to change all of that. The Irish National Seabed Survey (INSS), which covers an area of around ten times the size of Ireland's overall land area, is one of the world's largest seabed mapping programmes and is being carried out by the Geological Survey of Ireland (GSI) in partnership with the Marine Institute.

The results, which are being partly generated using AutoCAD, will provide vital information that will assist in developing policy for and managing Ireland's marine resources. A wide range of other parties involved in offshore activity will also benefit from the findings of the survey. For example, the maps will be useful for indicating the likely location, distribution and extent of mineral deposits in Irish waters. They are also expected to provide valuable information for those involved in the fisheries industry, offshore navigation, aquaculture, heritage, renewable energy development and waste management.

The Marine Institute and GSI are currently working on the continental shelf area of the INSS, which extends coastward from the 200 meter depth contour. For five months of each year, during the summer season, one or other of the Marine Institute vessels - the Celtic Explorer and the Celtic Voyager - is dedicated to collecting and processing relevant data. To meet the requirements of the survey as efficiently as possible, all data processing is carried out on board the vessels by teams of experienced offshore hydrographic surveyors, underwater engineers, multibeam data processors, marine geologists, and CAD/GIS operators.

Both ships have full processing and chart creation facilities on board, where final digital and paper deliverable products can be developed and produced. The vessels travel in parallel lines to gather the sea floor information using state-of-the-art hydrographic and geophysical equipment. Located on the underside of each ship are multi-beam echo sounder transducers, which emit fans of acoustic signals at angles of up to 75º, ensuring 100% coverage of the seabed. As the signals hit off the seabed or other hard surfaces, pulses are bounced back to the transducers. The travel times of the signals are then analysed to determine the depth of the seabed, as well as its reflectivity, which can indicate its composition.

After the information is collected, it is fed into multi-beam processing software - Caris Hips and Sips - to create a mosaic of survey lines into a single image. "From here we export geotif images into AutoCAD in order to generate aerial or spatial maps," explains Tommy Furey, geophysical team leader on the project.

Autodesk Land Desktop and AutoChart are used for generating the map grids for multiple chart creation during batch processing. The team has a pre-defined chart boundary layout which allows it to automatically generate maps of any chart scale. Following selection of chart limits and legend, and insertion of latitude and longitude graticules, a georeferenced mosaic image of each data type is inserted for completion of each north up chart. The results include a range of charts such as colour-coded contoured bathymetry and shaded relief, greyscale backscatter and side-scan sonar, vessel track and seabed classification maps. The team also produces vertical profile charts of the upper 40 to 50m of sediment below the seabed.

At the time of choosing AutoCAD for this project, the Marine Institute was under pressure to find a solution that would produce high quality georeferenced charts as quickly as possible. "Off-the-shelf solutions are few and far between and AutoCAD happened to have a very easy solution that would add on to the separate AutoChart package. The two together provide specific capabilities for doing batch processing of charts," says Tommy Furey. "We needed to find a solution for generating the sub-bottom profiles, which is quite a tedious process. It would have required us to do a lot of in-house programming and potentially spend several months trying to deal with that, which would have left us with a backlog of data to process. This was a straight off-the-shelf option that we knew worked, and worked very well."