Software Advances in Forward-Looking Sonar

By: 

Cheryl M. Zimmerman • Matthew J. Zimmerman • Paul Elgar

Author E-mail: 

Situational awareness is key for safe navigation. As more and more vessels operate in challenging environments, the risk of allusions with uncharted or wrongly placed obstacles and collisions with transient obstacles (such as ice and submerged shipping containers) increases significantly. Groundings on large underwater structures such as rocks, reefs, sandbanks and shoals are unfortunately significant risks for the mariner.

Requirements in an FLS

There are several important metrics to consider when designing a forward-looking sonar (FLS) system. The first is 3D capability. The sonar should be capable of generating a 3D image and determining range, bearing and depth with a single ping.

The next metric to consider is coverage zone. To be an effective navigation tool, an FLS system must have a wide field of view, be capable of detecting obstacles at navigationally significant ranges and also provide depth information.

Next, in order to make quick decisions, the sonar must have a fast update rate. This means the entire coverage zone should be updated with a single ping. Mechanically scanned sonars, which build an image from multiple pings, take too long to be useful as a real-time navigation solution.

Last, and most important, the image the sonar displays should be easy to understand. In order to be an easy-to-understand and effective tool, particularly in real-time applications, the FarSounder (Warwick, RI) team focuses on three mantras when making design choices: simple controls, easy visualization and good situational awareness. 

FarSounder’s State of the Art

FarSounder’s latest generation sonar processing is no exception to this design process. As far as focusing on simple controls, this latest processing includes an auto-squelch for in-water targets, as well as in-water stabilization for both in-water targets and the sea-floor. The auto-squelch may be overridden by the operator, if desired.

The SonaSoft 3.0 software is easy to visualize, with each generation building upon the last. A 3D display is one of the standard views for operators. There is also the option to display a 2D slice at any bearing to be viewed at the bottom of the display, in a manner similar to an echosounder. However, instead of showing a historical view, this shows the depth in front of the vessel, before one approaches the area.

Another visualization technique that is employed is for the sea floor, which may be set for either color mapped to depth or color mapped to signal strength, depending on need. 

In regards to increasing the situational awareness, FarSounder has incorporated a chart overlay. Early on, the company incorporated raster charts, then vector charts, followed by vestor with IWT (in-water target) overlay, and now includes a full overlay, with both IWT and the sea floor below ahead of the vessel out to eight water depths.

Jeppesen C-MAP Professional+ Database

The charts used in FarSounder’s platform come from the Jeppesen (Denver, Colorado) Professional+ database. Jeppesen Professional+ is a global vector chart database that seafarers have benefited from for years in ECDIS and ECS systems. The chart sources are based on official charts (both paper and digital). This ensures high chart quality, while also making sure the appearance of the viewed chart is similar to the ECDIS onboard. This increases both safety and simplicity for the mariner. It also ensures that the data facilitate the full functionality of an ECDIS, and is an excellent training choice for navigators before switching from paper to ENC.

Though many users are running a full ECDIS side by side with the FarSounder sonar, having basic chart plotting capabilities built into the FarSounder software adds a lot to the user experience. By seeing the sonar image as an overlay on top of a chart, the user can quickly confirm whether the sonar is detecting a known target or an unknown, uncharted obstacle. In some locations, the chart may only have general indication of what is outside the channel. With the forward-looking overlay, a captain can see exactly where the reef lies, for example. Having charting capabilities built into the sonar’s display also allows the user to set the ECDIS for a very long-range scale while maintaining the FarSounder display at a scale more suitable for forward-looking sonar.

To support safe navigation, Professional+ also contains additional information that can be updated daily through Jeppesen’s online updating service. For example, compatible ECDIS/ECS can display worldwide temporary and preliminary notices – valid temporary & preliminary updates (T&P NtMs) published by Hydrographic Offices.

Chart Overlay With Third-Party ECDIS Systems

For users that demand a complete ECDIS solution rather than the FarSounder-supplied ECS option, yet still want to have sonar data shown as an overlay on top of the charts, FarSounder has an SDK that allows third-party developers to access the data for use inside their own software systems. The sonars are networkcentric and the processed sonar data used to generate the 3D Sonar and chart displays can be accessed via an Ethernet connection. Therefore, an ECDIS developer could have a single unified chart display with radar, AIS, and FarSounder sonar all displayed as separate overlays.

New FarSounder Approach to Color Mapping

SonaSoft 3.0 brings along with it a paradigm shift in the way the sonar data are displayed. Previously, the software always used a colormap based on jet (a.k.a “rainbow”) for both depth and signal-level color mapping. Not only did this prevent displaying depth and signal-level information in a single display, the colormap itself was not optimal. The software now uses two separate colormaps for depth and signal level. A multicolor, uniform luminance gradient colormap is used to indicate depth, while an orange-copper colormap is used to indicate signal level.

The new colormap has fewer colors and a linear luminance gradient. This makes it much easier to see areas of interest without creating false features. Again, this improves situational awareness, an important goal that FarSounder designers always keep in mind.

The color mapping enhancements could have stopped with switching from the rainbow colormap to a new single-uniform luminance gradient colormap for both depth and signal level. However, the design team goal was to also make the signal-level display more intuitive. 

Since bottom-mapping range is limited by water depth, and the depth of targets beyond that range cannot be accurately determined, coloring targets beyond the sonar’s water depth limit with the same color scale, or assuming all these targets are shallow, could be confusing. Displaying signal level, however, can offer a clearer picture of what is known. By switching to a separate colormap, we can indicate depth (where possible to determine) and signal level (for all other targets) on the same display.

Many side scan sonar displays use a colormap similar to afmhot. This is due to sidescan sonars only displaying signal level, as they cannot display depth.

Challenges of Testing

Proper testing requires opportunities in many environments, with different bathymetry, varying sound speed profiles, different currents and sea states, as well as different bottom compositions and different vessel speeds. FarSounder is in the fortunate position of being located close to Narragansett Bay in Rhode Island. Narragansett Bay has a great deal of diversity within a small geographic location and large changes in propagation conditions throughout the year.

FarSounder field engineers record raw hydrophone data of every ping along with ship’s NMEA and metadata per sea trial, whether local or otherwise. Data collection trips also include CTD measurements and above-water camera shots whenever possible.

Temporary installations have been used to gather data around the world. Examples of varying locales have included the Gulf of Mexico; Port Canaveral, Florida; Vancouver, Canada; Atchafalaya River; Rotterdam, The Netherlands; and Buzzards Bay. Data have also often been recorded during visits to customers with permanent installations, including locales in the Caribbean; the Mediterranean; the North Sea; off Japan; Hong Kong, China; the Middle East; Seattle, Washington; and Alaska. Customers also send back data from their locations, such as Antarctica, Greenland and South America.

Diver Detection Using 3D FLS

Another configuration of FarSounder’s navigation software is integration into the company's diver detection system. The ship protection system (SPS) offers a fixed installation, with minimal internal and external form factor and with all solid state sensors embedded in the hull. This eliminates the need to deploy sensors via a cable, hydraulic hoist, crane, or other moving and mechanical methods. No time is wasted on deployment or retrieval once the vessel is underway.

FarSounder's SPS software couples robust automatic processing with advanced tools for easy-to-use human verification. When an automatic alarm is triggered by the SPS software, the operator can quickly verify if the target triggering the alarm is likely a true threat. Waterfall views of all tracks are available for a detailed look.

FarSounder’s SPS can operate as a stand-alone system with its own user interface display, or the information can be exported over a network connection, enabling a third-party command and control system to integrate the FarSounder SPS information.

Future of FLS

Real-time Chart Generation and Survey Applications. One area that FarSounder's design team is quite excited about, is real-time chart generation and survey applications. There are already crowd sourced bathymetry efforts being worked on, typically with echosounders. This approach is limited in that there is only the collection of an average depth for a large bin size. Also, neither coverage for in-water targets nor any large-swath coverage is available.

Using FarSounder’s 3D FLS systems, with existing commercial and other vessels, future communication technology will enable data that can easily be collected and shared. The systems cover a large area with a single ping, have good statistics for small reflectors, and offer wide swaths with just a single vessel passage. Mapping of underwater real-time features will improve situational awareness and increase safety for mariners. As bandwidth increases, we see great opportunities for the sharing of real-time data within a fleet, or user base.

Fisheries Sustainability Using 3D FLS. Over the past five plus years FarSounder has worked with The Netherlands Organization for Applied Scientific Research (TNO), as well as with the Dutch fishing company Jaczon B.V. (The Hague) on advanced fisheries by-catch reduction applications. 

Using the FarSounder 3D FLS sonars, and applying fisheries classification algorithms, enables a more sophisticated processing than traditionally available classification tools. Utilizing FarSounder's advanced wideband 3D sonar systems, coupled with different classification algorithms, can advance the state of the art in fisheries by-catch technology and offer companies, such as Jaczon, a new tool for sustainable fishing.

Conclusion

These are just two future areas of interest that the FarSounder team is excited about. The future will bring more and more opportunities for forward-looking sonar.

Cheryl M. Zimmerman is CEO of FarSounder, a marine electronics company which develops and manufactures advanced 3D sonars for navigation, security and fisheries applications. Zimmerman is responsible for leading the team to commercialize technology and market the product line globally. She has experience as a successful entrepreneur, having started and grown several technical and commercial businesses. Zimmerman received her bachelor’s in engineering science from the University of Hartford, magna cum laude, and holds a master’s
degree in mechanical engineering from Tufts University.

Matthew J. Zimmerman, as a founder, director and vice president of engineering, has been responsible for the technical development and vision of FarSounder since its inception 14 years ago. Zimmerman focuses on building and grooming a unique team capable of translating customer needs into best-in-class commercial products. He graduated magna cum laude from the University of Rhode Island’s international engineering program and is fluent in French and German. Zimmerman holds four patents in sonar technology.

Paul Elgar has been employed at Jeppesen since 1996 and has worked exclusively in the marine business from the Norway office. Elgar is responsible for managing the Jeppesen OEM partners that develop systems that utilize Far-
Sounder products. This involves extensive travel to meet, inform and assist these partners with their planning and development of navigation systems for the commercial marine market. Elgar was educated in the United Kingdom and moved to Norway in 1983.