Drop-In Integration: How LAUV Became Subnero Ready

Snapping shrimp blanket the warm, shallow soundscape with intense impulsive clicks, at source levels above 190 dB re 1 µPa at 1 m, producing heavy-tailed, non-Gaussian noise that degrades receivers designed around the usual Gaussian assumptions [1]. The shipping lanes add a second layer. Breaking waves and passing ships inject bubbles into the water column, and while the dense clouds clear within minutes, long-lived microbubbles of around 100 µm and smaller persist for hours and drift with the currents far beyond the lanes. With a ship passing every few minutes, their presence is effectively constant [2].

Subnero modems were built in exactly these waters, designed around the true noise statistics rather than the Gaussian ideal, and they bring advanced networking features well suited to AUV operations. The LAUV, however, runs on the Dune software ecosystem, and no integration between the two existed. The open questions were how hard it would be, at what level the work would sit, mechanical, electrical, or software, and who would have to carry it.

The software bridge between UnetStack, the network stack that runs on every Subnero modem, and Dune was built entirely by ARL and is now open source at github.com/org-arl/unet-dune. No source code was modified on either side. Dune was not patched and UnetStack was not touched. The bridge is a pair of small UnetStack agents, LAUVModem on the vehicle modem and MantaModem on the topside modem, written in Groovy and running on the modems themselves, so no companion computer or extra hardware went into the vehicle.

What made it simple is that Dune already defines a generic abstraction for an underwater acoustic modem, and the bridge implements it. Each agent speaks IMC, Dune's native message protocol, over TCP to its co-located Dune, and forwards traffic acoustically to the peer modem. To Dune, the acoustic link looks like an ordinary TCP transport.

[Transports.TCP.Client]
Enabled          = Always
Entity Label     = Acoustic Modem
Server - Address = <IP of the co-located Subnero modem>
Server - Port    = 9999
Transports       = UamTxFrame,
                   UamTxRange,
                   VehicleMedium

A matching block on the topside points at the modem in the MANTA gateway on port 9998. Those few lines are the entire Dune side of the integration. As a bonus, the same link carries acoustic ranging alongside communication, so range to the vehicle comes free with the comms. Deploying the bridge is simple: the compiled agents are uploaded to the two modems, the modems are rebooted, and the bridge is running.

Subnero shipped the modems to OceanScan MST along with GA drawings and electrical interface details, one modem for the vehicle and one for the topside MANTA gateway. OceanScan MST fitted them, handled the mechanical and electrical integration, and wrote no software at all.

Once the fit was done, they placed the software libraries provided by ARL in the appropriate locations, powered the modems on, and the acoustic link was instantly available in the console on both the vehicle and the gateway.

Since the integration, ARL has been operating the vehicle and its acoustic link for more than a year, in precisely the conditions the lab set out to work in: shallow tropical waters, strong currents, and busy shipping channels. Across that time the link has delivered strong performance and reliable communication in the field.

For the projects the LAUV serves, that reliability is the whole point. Knowing what the vehicle is doing at all times, rather than launching it and holding your breath until it resurfaces, is what makes the difference.

The Subnero modem is available as a drop-in, and the LAUV team at OceanScan MST can now support Subnero modem integration requests for any customer. Work with Subnero or OceanScan MST to get your vehicle fitted.

The larger point is openness. ARL did this integration as a third party, on their own terms, with their own tools, without depending on Subnero to support any step, and the code is open source for anyone to build on.

Subnero smart modems are now natively supported in the OceanScan MST's LAUV. The integration code developed by ARL is open source at github.com/org-arl/unet-dune and includes a two-node simulator and a self-test that verifies the bridge round trips in both directions, so the whole thing can be tried on a laptop without any hardware.

The integration gets even easier going forward. Subnero's latest Gen4X modems come in a smaller form factor than the previous generation used in ARL's vehicle, so a new fit takes up even less space inside the LAUV.