© JEHC, Ocean Mapping Group, Univ. New Brunswick

SwathEd
A deranged software toolkit developed by :
John Hughes Clarke
Ocean Mapping Group, UNB


Overview

SwathEd is a collection of software that runs on generic UNIX/C/X platforms. It main aim is to support research and development within the Ocean Mapping Group at the University of New Brunswick . It is designed to take manufacturer-specific data telegrams from a variety of swath sonar systems. The tools allow the user to investigate the quality and information content of both the bathymetric data and the backscatter data.

As part of this investigation, standard by-products include map-like outputs such as Digital Elevation Models (DEM's) and Sidescan Mosaics. Thus, although not specifically designed as such it can act as a standard swath sonar processing package.

The software is made available as binaries (for SGI, SUN, DEC and LINUX ) and source code to sponsors of the Chair in Ocean Mapping. A reasonably complete set of documentation is maintained as a series of web pages (note that these pages are password protected for sponsor access only). It should be noted that the software is provided on an as-is basis, with no guarantee of reliability or support. The fact that the software is currently being used for mapping purposes by a number of our sponsors should not be taken as an indication of robustness. In practise, the user should be reasonably cogniscent of basic UNIX command line, scripting and editing methods.

The following description represents just a brief overview of the system capabilities. Refer to the online documentation for fuller details.


Input Formats

SwathEd handles a wide variety of input sonar formats. It should, however, be recognised that, as the majority of our sponsors (CHS, NavO, NRL, C&C, USGS, NJW, MBARI, SUNY) utilise the code for handling Simrad products, the tools are most robust and proven for those sonars. This should not however, be taken as an endorsement of those particular products by us.

Supported formats include:


Real Time Tools

The RT tool is a real-time display module that allows one to monitor the acquisition of Simrad/ELAC or RESON format data. It does this by establishing a pointer into the file in which the sonar data telegrams are arriving. As the file grows, the data is reformatted and mapped to a variety of graphical displays including:

The user can select a survey line to run using mouse clicks and a helmsman display is then available for left/right of line indication. The line may be nudged to left or right (remaining parallel) and inverted for offset inverse lines. Geocoordinates can be extracted by mouse interrogation.

The main aim of the tool is to assure data quality in the field including specifically:

In addition the tool has been used for bottom sampling campaigns in which bottom camera and samplers (gravity cores and grabs) are positioned with respect to recently acquired multibeam imagery.

RT is also used in the background as a data converter to take the manufacturer specific data telegrams and reformat into the OMG specific data processing format.

 


Navigation Tools

To aid in the manipulation of navigation data, jview, the graphical viewing tool allows interactive viewing, interrogation and flagging of asynchronously provided navigation information.

This navigation information can then be merged onto the bathymetric solutions, knowing the relative position and orientation of the transducer with respect to the navigated point.



Swath Sounding Manipulation Tools

"swathed" is the core swath bathymetric editing tool for all the sounding data. It can be used in two main modes:

Various utilities for converting tidal records into compatible formats are available. Up to two tidal records can be used simultaneously using a distance based interpolation scheme.

Once the data has been cleaned and tidally reduced it can be gridded to generate digital elevation models (DEM's) at various scales, projections and rotations. Our gridding software (weigh_grid) uses non standard surface creation techniques that weight individual beams according to their acoustic footprints, and relative quality. In this way we aim to retain the full resolution content of the sonar.

Note that the swathed tool works using the derived gridded/mosaiced products so that the final mapsheets may be investigated while allowing the user to go back to the original source data from which the DEM/mosaic was derived. As so many of the artifacts generated by imperfect integration of sonar systems are very subtle, this is an important feature so that mis-interpretation of the final data does not occur. If residual artifacts are noted, the final DEM/mosaic can be recreated after subsequent data adjustment.



Sidescan Manipulation Tools

Most swath sonar systems provide an estimate of the seabed backscattered intensity. Increasingly, this estimate is reduced for variables such as source power, receiver gains, beam patterns, ensonified areas and seafloor slope. SwathEd provides a series of tools for manipulating the backscatter time series provided by various sonars.

The Simrad family of sonars are the ones that are most standardly handled, requiring that the time series for each beam be intertwined to form the equivalent of slant-range corrected sidescan trace. As part of this process, corrections may be applied for the following:

Once this has been performed, one has the equivalent of a conventional sidescan output (except that the slant range correction accounts fully for orientation, offtrack topography and refraction). This strip format can now be mosaiced (geographically registered) within a mapsheet whose pixel size, projection, and bounds are predefined. Note that in general this map sheet will correspond exactly to that of the DEM so that the two data sets may be viewed, exactly coregistered (using jview).

An important point to note, is that the processing of multibeam sidescan requires that the bathymetry be already processed (navigated and cleaned). For conventional sidescans, a separate pre-processing sequence exists to take time-series data (GLORIA/Klein/Simrad/Edgetech). On request filters can be easily written to convert most simple time-series data formats.

For those sonars that provide a reasonably calibrated estimate of the seabed backscatter strength (e.g.: the Simrad ones) a series of research tools exist that allow one to extract the seabed angular response and attempt seafloor classification (see related references) based on various attributes of this inherent property. Note that these tools are strongly research driven and not in the least bit robust.



Data Analysis Tools

jview: is the core image visualisation tool allowing you to look at both floating point and 8bit raster image data. Allows you to zoom and pan within the image, dynamically adjusting the colormap.

If the image data is geographically registered, all points can be interrogated for position and attribute (depth or BS).

DelayEditor: this is an analysis tool that views all swath data together with the output of all peripheral sensors in a time framework. This is for the purpose of investigating a variety of problems including:

Most recently, with the new Simrad formats (EM300/3000) it can retrieve the full 100Hz orientation data logged asynchronously to assess motion sensor output problems.

swathed:within swathed there are a series of additional subwindows that investigate a variety of things:



Output Formats

The swath oriented data and the raster based derivatives are all stored in a variety of OMG specific data formats. These data can be exported to other simple formats (ASCII listings, gif/tif's with projection attributes listed).


Last modified May, 1998, by John E. Hughes Clarke (jhc@omg.unb.ca)