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A Pathway to Multithreat Assessment Through Integrated Multibeam Sonar

By Chris Malzone • Danny Wake • Jeff Bartkowski

Data showing an object identified as a 25-centimeter zinc ventilation pipe laying on the seafloor in 10 meters of water.
The use of multibeam echosounders for hydrographic applications is well-documented and has been widely accepted for decades. Improvements in resolution, accuracy, sampling rates, signal processing and software enhancements have further expanded the number of requirements that these sensors can address.

For instance, for Q-route applications, which ensure that navigable routes to and from ports are clear of dangers and obstructions, surveyors are now able to simultaneously collect the full water column information along with the bathymetry and seafloor imagery data (e.g., backscatter, snippets, side scan) to identify dangers on and above the seafloor. In ports and harbors, a single sonar can produce 512 soundings per transmission up to 50 times per second while also electronically steering the entire swath within 5 degrees of horizontal without having to physically remount the head.

Improvements in software have paved the road for vessel-mounted lidar systems to interface with multibeam systems and provide real-time 3D imagery above and beneath the water surface. Such innovations are providing valuable decision-making data for ports and harbors to better assess conditions within their infrastructure to enhance threat prevention and promote safety.

Applications and Solutions
The first commercial multibeam echosounder put into service provided 60 soundings per ping over a swath that was twice the water depth. These systems have evolved to provide more than 500 soundings per ping, with a swath more than 6.5 times the water depth, can acquire the qualitative backscatter data (seafloor and water column) and have doubled in resolution. To address the needs within a port or harbor infrastructure, multibeam technology needed to evolve beyond simply providing the geomorphology but to allow users to identify discrete targets both on and above the seafloor.

Since 2010, RESON (Slangerup, Denmark) has worked with local survey companies and port authorities to demonstrate how surveyors can collect full data-rate water column backscatter data while also obtaining the bathymetric and seafloor backscatter information with the 7000 series of its SeaBat multibeam echosounders. This feature was achieved through improvements to the sonar's electronic architecture, which combined the sonar-processing electronics with computing electronics. This increased the sonar's signal-processing capability to take advantage of standard personal computer components, such as central processing units, video-card graphics processing units and RAM.

To address route survey requirements, including those for Q-route surveys, RESON introduced a programmable beamformer in 2010 that utilizes equiangular (EA) and equidistant (ED) bottom detection modes, separately or combined.

The use of EA and ED has been well-documented in literature, however, combining the two detection methods into a single swath is just now being implemented. A programmable beamformer allows the user to define the density of three sectors within the swath: two low-density ED and one high-density EA.

The density of each sector is user-defined and allows the operator to focus on obtaining the highest resolution over the primary route while also obtaining information in the secondary outer section of the corridor. This feature is called Flex Mode.

In a demonstration near the Port of Oslo in Norway in 2011, the operator detected 25-centimeter-diameter circular debris on the seafloor and, utilizing Flex Mode, obtained 155 soundings per ping within a 25-centimeter diameter while maintaining a 140-degree swath. Further, the operator can also implement beam steering of the entire sector, the high density sector or both to ensure the region of interest is always properly resolved.

At the Port of Savannah, Georgia, in January 2013, RESON implemented automation routines to further improve the efficacy of Q-route surveys. At the core of RESON's sonar automation is Tracker, which allows the surveyor to get high-quality data, regardless of seafloor substrate, without the need of constant supervision. It dynamically adapts sonar settings to the environment, ensuring the system is not oversaturated and bottom detection is optimized. To continue this article please click here.

Chris Malzone is the vice president of sales for RESON Inc. His prior positions at RESON include field engineer, test and verification engineer, and scientific and autonomous applications manager. Malzone holds a master's in oceanography and geology and has more than 20 years of experience in the academic and private sectors.

Danny Wake is a senior product manager at RESON Inc. After graduating from the University of Glasgow with a degree in geomatics, he worked in the offshore survey industry prior to joining RESON in 2005, where he commissioned fully integrated multibeam hydrographic solutions. He lectures in hydrographic surveying at the University of Glasgow.

Jeff Bartkowski is the RESON Inc. sales manager responsible for the defense, homeland security and autonomous vehicle market sectors. After graduating with a master's in biology from Rensselaer Polytechnic Institute in 2005, he began his career in the marine technology industry focusing on the navigation and acoustic positioning of subsea vehicles.

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