Multibeam backscatter data processing and map production

Processing of backscatter data is done by the Geological Survey of Norway using specialist software designed for multibeam data.

The available software has evolved considerably since MAREANO started in 2005 and the MAREANO backscatter data archive includes backscatter data processed with several different software as well as different generations of the same software.  In interpreting backscatter data it is important to remember that the resulting mosaic quality and values are influenced by processing software as well as the source data.

In order to produce a more harmonised version of the data for web-display the backscatter values currently presented on mareano.no have been levelled relative to reference surveys. Whilst this gives a general overview of the relative backscatter intensity across a wider area it can also obscure important differences in the backscatter values due to system and operational reasons, which may render data over larger areas, misleading.

For example, the backscatter intensity returned by lower frequency (deep water) echosounders will capture the acoustic response of a deeper layer of sediment, over a wider area (i.e. potentially more mixed) to that detected by a high frequency (shallow water) system which more precisely captures the response of the sediments in the upper few centimetres of the seabed over a limited area. Further, the recorded acoustic backscatter value depends on operational issues and will typically vary with acquisition settings, and from boat to boat.

MAREANO makes a dedicated effort to uphold standards in any new backscatter data acquisition, with a section in the technical specification for bathymetric mapping in MAREANO specifically addressing backscatter data. It is also worth noting that, in contrast to bathymetric mapping, standards for backscatter mapping are not yet well defined in the scientific and data acquisition community. A recent document from the GeoHab backscatter working group, which MAREANO has contributed to, has made a welcome first step in addressing this issue ‘Backscatter measurements by seafloor‐mapping sonars Guidelines and Recommendations’.

Contact

Margaret Dolan
Tlf. 73 90 42 67