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January 2011 Issue

Symbiosis: Why Your AUV Needs an ROV (and Vice Versa)
By Sean Newsome
Unmanned underwater vehicle manufacturers are often asked why they continue to market tethered technology—remotely operated vehicles (ROVs)—when autonomous underwater vehicles (AUVs) are able to operate without a tether, a source of drag and entanglement. This seems like a reasonable question.

But an ROV's greatest weakness (the tether) is also its greatest strength. Similarly, an AUV's greatest strength (the lack of tether) is also its greatest weakness. Together, they complement each other, compensating for what the other lacks. Understanding why having both an AUV and an ROV in the mission toolkit is an advantage requires understanding the fundamental difference between ROVs and AUVs.

Simply put, AUVs provide vast amounts of data from the past, while ROVs provide data from the present. This means that AUV data only becomes available once it has surfaced and either sent its data wirelessly or been retrieved. Do not confuse this statement to mean AUVs are not practical; they are extremely useful devices that require very little human intervention to do their job. They can work for hours, days, even months at a time gathering massive amounts of quality data.

Then there are ROVs, which provide smaller amounts of data, but from the present. ROVs use human intelligence: There is a brain (sometimes several brains) attached via the tether and enhanced by the sensor suite. Because of this human link, the ROV "knows" that it might be worth taking a break from the current mission to investigate the shiny objects in its peripheral vision. ROV operators can make decisions, switch to a more relevant mission on-the-fly, tune and adjust sensor outputs to optimize incoming data, and focus on unexpected details (e.g., we didn't find the victim, but we found the gun). ROVs have this advantage over AUVs because they have a conduit—the tether—to transmit relevant bandwidth great distances through water.

Transmitting large amounts of bandwidth a meaningful distance directly through water is physically impossible with today's technology. To illustrate this, let's define a critical mission with a relatively short distance between the operators and the objects of interest. Say an explosive ordnance disposal team must maintain a 50-meter standoff while verifying that a ship hull is 100 percent free of improvised explosive devices (IEDs) using a robotic platform. Imaging sonar, used frequently to identify objects in poor visibility, requires at least 10 megabits per second of bandwidth, while standard-definition video requires at least twice as much.

If the setup is to avoid using a tether, the choices are limited to acoustic transmission, radio frequency (RF) and free-space optics (FSO). Neither acoustic nor RF is anywhere near capable of approaching 10 megabits per second over 50 meters (or even five meters). An expert with FSO told me they might get 10-megabits-per-second data rates at 75 meters, provided there is both a direct line of sight and essentially pure water. In the real world of underwater operations—where you need to fly in turbid waters, in and around pier pilings, moorings and running gear, and to the other side of the ship—these prerequisites for tether-free transmission are not practical. That leaves us with copper wire or a fiber-optic line, which means a physical tether is required. So a tethered ROV is the only platform at this time that, using a human brain, can ensure 100 percent coverage of the hull.

Let's try the same mission with an AUV. Remember, our goal is 100 percent assurance that there are no IEDs. Here is the problem: Machine intelligence is not advanced enough for humans to trust a fully autonomous robot to confirm 100 percent of a ship hull clear of IEDs. Finding four out of five IEDs would not qualify as a successful mission.

The clearest way to emphasize this point comes from Barbara Fletcher, a project manager at the U.S. Navy's Space and Naval Warfare Systems Command and a member of the team that deployed the hybrid ROV Nereus to the bottom of the Mariana Trench. Fletcher said this two years ago: "When I started in 1982, full autonomy for underwater vehicles was '10 years away.' I would not be so bold as to state today that full autonomy is 10 years away, but great progress has been made."

Or, to put it more simply, "In the future, everything will work." Until then, we need to rely on tethered platforms for many of these critical missions.

Rather than try to compare ROVs and AUVs, we are better off combining them into one toolkit for the ultimate observation package. They are both excellent platforms for their given applications, and they complement each other in many ways.

When we combine the two platforms into one kit, each fills the capability gap of the other; a cooperative relationship. For example, what if the mission is to clear all suspicious objects in a harbor The AUV will generate a large amount of useful data that analysts can then use to determine the most likely targets to investigate. AUVs simply aren't smart enough to discriminate between an empty truck tire and a truck tire packed with explosives. It will not be until you get a "visual" by a human that you can confirm or exclude many of these targets. Conversely, trying to perform a complete bottom mapping of a large harbor with an ROV would not only take weeks or months to accomplish; it would be impossibly fatiguing to the operators.

If anything, the next time your AUV is stuck 100 meters under ice or 130 meters deep under a ledge, you may really appreciate having an ROV with a tether.

Sean Newsome is the global sales manager for SeaBotix Inc., a San Diego-based manufacturer of remotely operated vehicles. A former nuclear reactor operator for Trident-class submarines, he has more than 16 years of experience in underwater manned and unmanned vehicles and technologies, as well as six years of experience in manufacturing automation.


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