2021 EM 304 Sea Acceptance Testing and Mapping Shakedown

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5. Paving the Way with a Wider Swath

Have you upgraded your smartphone lately? Some people upgrade every time a new model comes out—but many of us wait until our current phone is broken or failing before deciding to pull the increasingly expensive trigger of technology refresh. The downside to technology is that if you wait too long to upgrade, you risk losing support—in parts or service. If you encounter a problem, it may not get solved, and then your hand is forced to make the call on a newer model whether or not your wallet is ready.

NOAA Ship Okeanos Explorer has so many different technologies onboard that the NOAA crew and staff responsible for operating the ship’s suite of scientific equipment continuously consider when is the most appropriate time to upgrade each particular system. Recently the EM302 deepwater multibeam, which has been operated nearly every day the ship has been offshore since her original commissioning in 2008 as the very first of this model in the world, was reaching the end of its life cycle when NOAA decided to move forward with an upgrade to the new model EM304 MkII rather than wait until there was an issue. As the only federal program dedicated to exploring the ocean, it is imperative for NOAA Ocean Exploration to stay at the forefront of technology, continuously paving the swath for others to follow.

Instead of swapping the multibeam system all at once, a phased replacement was planned, which was completed this past winter. The receive array was replaced in 2018. The topside transceiver unit was replaced during the winter 2019/2020 alongside repair period, and the transmit array was replaced during the winter drydock of 2020/2021.

Kongsberg Maritime designed the EM304 Mk II Deepwater multibeam  to have a variety of features that are anticipated to enhance mapping efficiency as well as data quality:

• The electronic boards in the topside unit were redesigned to produce lower internal self-noise, leading to more favorable Signal to Noise Ratio  (SNR), which can result in cleaner, more accurate data.
• The frequency range used by the system was increased from 26 to 32 kilohertz to 20 to 32 kilohertz. Lower frequencies can travel larger ranges under water and thus result in larger areas mapped by enabling the outer beams of each swath to travel farther and maintain a signal strong enough to be received back by the receive array.
• The new frequency range is also predicted to allow for efficient mapping in even deeper water than before, now 11,000 meters (6.8 miles) versus the 6,000-meter (3.7-mile) depth limit of the ship’s previous multibeam system.
• Each “ping” now will contain up to 800 individual beams versus the previous 432 beams, which results in higher data resolution across wider swaths.
• SIS5, the new version of the multibeam data acquisition software, comes with a remote control option, which connects a shoreside computer to the onboard acquisition computer to enable remote watchstanding by experts onshore. NOAA Ocean Exploration is actively pursuing integrating this capability into operations.

Now comes the fun part—making sure it all works. Every installation engineer or technician works to ensure that a new system works as expected, but there are often quirks with these kinds of systems—unique to each vessel—that need to be understood by the NOAA Ocean Exploration team in order to deliver the highest quality data.

Over the years, the team has recognized that it is far more efficient to conduct thorough testing (particularly after a major upgrade) via a “shakedown” expedition like this one, prior to the start of the rest of the field season than trying to intermittently assess the performance of the system. This enables the team to efficiently plan and execute surveys, ensuring the best use of the vessel’s time, predicting accurate coverage for a given survey area, and ensuring the highest quality of data collected and shared with the community.

As this is one of the first complete EM 304 systems in operation worldwide, the testing performed during this expedition will be invaluable not only to NOAA Ocean Exploration, but also to the broader ocean mapping community.

At the time of writing this feature, the onboard team had officially accepted the new system, through successfully performing the Sea Acceptance Trials defined by Kongsberg and additional testing routines defined by the Multibeam Advisory Committee . System performance will continue to be evaluated against the manufacturer’s expectations based on system design and theory. System performance typically varies with environmental and oceanographic conditions such as sea state, seawater temperature and salinity variability, and seabed reflectivity.