Sidescan is an signal of acoustic backscatter strength from the water. The signals can be collected in digital form and they can be produced digital images of the seafloor. It is equivalent to a satellite image from remote sening. There are many advanced sidescan sonar systems, e.g. GLORIA, SeaMARC I and II capeable of producing high-resolution digital seafloor images.

The following picture illustrates how the sidescan data were collected by towing the sidescan instructment (towfish) to scan the seafloor.

This picture is (modified) reprinted with permission by the author J. G. Blackinton.

Depended on which sidescan system was used, the cover swath width for each scan line can be ranged from 0.5 km to 10 km. For most of the systems, each scan line will contain 2048 1-byts pixels of the sidescan data.

Two programs were written to generate the navigated sidescan images. The first is the mapping program. It reads the specified range of sidescan data and maps the data onto a grid file where its boundaries are defined by user. The second program is the plotting part. It reads a grid file created by the mapping program and products a graphic file for the VERSATEC electrostatic plotter which can produce plots as big as 40"x(>40").

The 2 programs were written in FORTRAN and run under the VAX/VMS environment. The mapping program has been rewritten in C and run in a HP UNIX workstation.

This has been a very successful project. The NOAA/OERD office is the first research agency or at least among one of the very earlest research group to develop the programs above, and produre a digital mosaic of sidescan data. OERD had processed sidescan data every years between 1986 and 1988. OERD also helped the Scripps Institution of Oceanography (SIO) process their sidescan data in 1993. Many other agencies such as U.S. Naval Oceangraphic Office, University of Hawaii, SIO, have requested the source codes of the sidescan mapping and plotting programs. Since then there are many good software for processing and visualizing sidescan data have been developed by other research agencies and companies.

A paper was written by me and my supervisor Dr. Chris Fox that shows detail about the NOAA/OERD sidescan data mapping process using both flat and non-flat seafloor bottom assumption by incorporating Sea Beam bathy.

The title of the paper is " A Technique for Combing SeaMARC I Sidescan Sonar and Gridded Bathymetric Data to Display Undistorted Seafloor Imagesi. It is published at the Oceans '91 Conference, Proceedings Volume 2, page 1140 to 1145, October 2, 1991.

Another related paper " Constrainted Iterative Deconvolution Applies to SeaMARC I Sidescan Sonar Imagery" contains how the raw sidescan data were processed. Reprints are available upon on request.