The common approach to analysing data collected with multibeam and
sidescan sonars is to visually interpret charts of contoured bathymetry and
mosaics of seabed images. However, some of the information content is
lost by processing the data into charts because this involves some
averaging; the analysis might uncover more information if done on the data
at an earlier stage in the processing. Motivated by this potential, I have
created a software system which can be used to analyse data collected with
Simrad EM1000 (shallow water) and EM12 (deep water) multibeam sonars,
as well as to generate bathymetry contour charts and backscatter mosaics.
The system includes data preprocessing, such as navigation filtering, depth
filtering (removal of outlying values), and amplitude mapping using the
multibeam bathymetry to correctly position image pixels across the swath.
The data attributes that can be analysed include the orientation and slope of
the seafloor, and the mean signal strength for each sounding. To determine
bathymetry attributes such as slope, the soundings across a number of
beams and across a series of pings are grouped and a least-squares plane
fitted to them. Bathymetric curvature is obtained by detrending the grouped
data using the least-squares plane and fitting a paraboloid to the residuals.
The magnitudes and signs of the paraboloid's coefficients reveal depressions
and hills and their orientations. Furthermore, the seafloor geology can be
classified using a simple combination of these attributes. For example, flat-
lying sediments can be classified where the backscatter, slope and curvature
fall below specified values.
Mitchell, N. C., "Processing and analysis of Simrad multibeam sonar data", Marine
Geophysical Researches, 18, 729-739, 1996.