Technical Description - Software



Bathyswath acquires, processes and displays data whilst a survey is underway, using a program called “Swath”. This also allows for control and set-up of the system, and gives error diagnostic information. The software stores data in two forms: ‘raw’ and ‘processed’. The raw data is exactly as it was acquired by the system, unfiltered and unprocessed. The processed data is filtered, and then written out in a file format that suits the post processing system being used.

Post processing software converts the data acquired in real-time into Digital Depth Models. These depth models are used to produce displays and plots of the surveyed area. Users may use Bathyswath post processing software, or a third-party program, to suit their application.

The Swath program is used to provide the first pass of post-processing when using the Bathyswath software. It reads its own raw data files, and produces processed data files. The second pass of the post-processing converts the processed swath data files into Digital Terrain Models. This program is called “Grid”. Grid also allows 3D visualization, filtering, data correction and calibration functions.


Swath runs on a PC computer, and performs all the real-time functions. These include:

  • Controlling the sonar electronics system.
  • Acquiring data from the sonar electronics system.
  • Acquiring data from the auxiliary systems, through the PC's serial ports.
  • Storing all the raw data.
  • Converting the raw data to depth, position and amplitude [xyza], combining auxiliary data, such as motion, position, heading, tide and speed of sound.
  • Filtering the data to remove noise and unwanted targets.
  • Displaying the data.
  • Storing processed [xyza] data in a range of formats.

All of these functions are controlled by the operator using parameters that are stored in a "session file". This allows the operator to store the parameters used on a particular project. In addition, the configuration parameters used to generate a particular processed data set are automatically stored in the processed data file. This feature is only available in the Bathyswath processed data file format.

There is an extensive context-sensitive software help system to assist the user with all aspects of using the Bathyswath.


The Grid program runs off-line, either after the survey on the survey PC, or on a separate PC. It performs the following functions:

  • Placing all the processed data (depth and amplitude) into a gridded digital terrain model (DTM).
  • Displaying depth and amplitude for each node of the grid.
  • Displaying statistical information about the depths in each node of the grid, including mean, standard deviation, range and data count.
  • The data for each ping and line of the survey are stored separately in the grid, allowing simple comparison of overlapping data sets.
  • The data from overlapping survey lines is compared to provide automatic post processing calibration.
  • This includes derivation of the roll offset between transducers. This calibration information is stored in the session file for subsequent re-processing of the raw data with the swath program.
  • Filtering and moving the data in the grid, to enable the operator to quickly and easily clean and correct the processed data.
  • 3D views of the data in the grid, allowing the operator to see the seabed in three dimensions and to “fly” across the seabed using the mouse or in pre-defined routes. The grid can be edited in the 3D mode, using the mouse to “lasso” points and groups of points that are not required, for example mid-water targets.

Grid data can be stored in “point cloud” format. In this mode, every data point from the Swath program is retained in the grid. Although memory-intensive, this allows for high-resolution views. In this mode, the views are not restricted to a single surface, and so complex objects and mid-water targets can be imaged.


Given an experienced operator and available secondary data, the processing time requirement for Bathyswath does not exceed 100% of acquisition time for a normal survey. At no stage in data manipulation is the raw data file modified. An audit file is available to quickly indicate which processing and calibration parameters have been applied in order to create the processed file.


Bathyswath provides facilities to calculate instrumental and positioning offsets and alignments. Such calibrations use surveyed data, and provide accuracy of calibration to allow the survey system to meet the overall accuracy requirements. All calibration parameters are available for changing and can be reapplied at the processing stage. The changing of calibration parameters does not change the raw stored data file.


The Bathyswath data file format description is open and described in the Bathyswath File Formats document. In addition, source code fragments, example programs and technical advice are provided to developers and users who wish to exploit the Bathyswath data in their own software tools.


Sidescan sonar data is stored in the Bathyswath raw data before any normalization or time-varying gain (TVG) is applied. The sonar raw data includes the full time series of amplitudes and phases from each ping at a user selectable sample rate. All the data is recorded for each shot (i.e. everything from the trigger to the end of the swath) to allow for full reprocessing of the data. The system applies software normalization (TVG) to the data and displays the results (as well as recording the raw data) in real-time, and the sidescan can be replayed and reprocessed during post processing.

This feature, together with the angular measurements and auxiliary sensor data, allows the full sonar equation to be solved, thus permitting the acoustic properties of the seabed to be analysed for research and mapping purposes.


The community of Bathyswath sonar users encompasses a very wide range of operational requirements. Although the Bathyswath software provides a comprehensive set of functions, it naturally cannot exactly match the needs of every one of these users. Therefore, Bathyswath has provided links to many of the industry-standard software packages available today. The following list gives some of the systems that have been used with Bathyswath sonars. The list of systems that are supported is growing. Many systems not on this list will also read in one or more of the standard file formats that the software provides.



Bathyswath can be used with “fully-functioned” third-party sonar processing and control systems, allowing the user to perform all data acquisition and processing functions in the third-party system. In this mode, the Bathyswath Swath processor application acts as the interface to the Bathyswath hardware, and performs some initial processing and filtering before sending the data to the third-party process. The data that results from this process is as raw as possible whilst maintaining a consistent range-and-angle data format.

This format is known as the “Parsed Data” format. The user can elect to use the Swath processor with minimal processing and displays, just passing the Parsed data to the third-party system or alongside the third-party system, with all displays enabled. Swath and third-party application can be run on the same computer, or on different computers, connected by Ethernet.


Bathyswath software provides a coverage chart, showing which areas have been covered in the survey. Tasks such as planning the survey route and giving the helmsman a display to steer from are provided by third-party software, integrated with the Bathyswath system.


The standard Bathyswath software, that is, Swath and Grid, are supplied with unlimited licenses to run on the real-time computer used for surveying, and also on a single office-based PC, for post-processing. Licenses for third-party software can be obtained either direct from the suppliers of such software or via Bathyswath team and agents.