A net under pressure

Working and sleeping underwater for nine days created a different sense of what’s important for scientist Kristen Davis.

Like noticing the lobster that crossed part of the Florida reef every morning with the regularity of a commuter going to work.

Like watching thunderstorms at night through a porthole 60 feet below the surface, the lightning flashes illuminating the tops of the fish outside.

Like coping with the persistent “two-beer buzz” that’s the result of elevated levels of nitrogen in the air.

And like relying on the broadband wireless link that to Davis and her fellow scientists was almost as important as the umbilical cord carrying power and air to the underwater pressure chamber called Aquarius.

The wireless Ethernet bridge is one part of a unique network for computerizing underwater research, and for protecting the scientist-divers who are doing it.

Aquarius is an underwater ocean laboratory in the Florida Keys National Marine Sanctuary, about 10 miles from Key Largo. Its cigar-shaped pressure chamber, like a stationary submarine, is mounted on four legs attached to the sea floor. (See the Aquarius Web cam.)

The lab owner is the National Oceanic and Atmospheric Administration (NOAA). It’s operated by the NOAA Undersea Research Center at the University of North Carolina at Wilmington. Aquarius is the only such lab in the world, where scientists, Navy divers and NASA astronauts live underwater for as long as 18 days, but usually for 10. Because they remain in a constant high-pressure environment, without having to decompress and return to the surface, they can dive for seven to nine hours daily instead of two.

The man in charge of Aquarius’ network and computers is Dominic Landucci, who has introduced over the past several years a series of innovations that gives researchers in Aquarius broadband access to onshore servers, VoIP telephony, telemetry data from instruments on the reef and streaming video.

There are three parts to the Aquarius network: the underwater chamber, the surface weather buoy and the onshore LAN at Key Largo (see a network diagram).

In the habitat, a rack holds a Cisco 2950 24-port switch. Plugged into it are a Linksys wireless LAN (WLAN) access point, telemetry servers, video servers and IP cameras, and a VoIP Session Initiation Protocol (SIP) phone from Polycom. The WLAN lets users with wireless laptops work and surf the Internet from their bunks, as “desk” space is a premium.

Landucci created a voice system, dubbed “hoot & hollar,” between the habitat and the onshore Watch Desk, which monitors safety instruments and is manned around the clock during a mission. Hoot & hollar is separate from the IP PBX: pick up the phone at either end, and it directly dials the corresponding phone at the other.

Client laptops have been the toughest problem because they’re not tough enough to withstand the atmospheric pressures in the habitat. In some cases, PC boards will shatter under pressure. More commonly, the fine tolerances of today’s computer hard drives mean that the arm reading the disk is pressed or even crushed onto the disk itself.

Ruggedized computers didn’t help. These are usually sealed devices, trapping small amounts of air inside. The difference between inside and outside pressures caused them to malfunction or even break. And their hard drives also were not designed to work under pressure.

The solution had been to use older laptops, with hard drives that have more give. But Landucci changed this by introducing at the end of 2005 the habitat’s first thin client, a Ntavo NTA 6010B. Via Microsoft Remote Desktop Protocol, the thin client connects to Microsoft Terminal Services on an onshore Microsoft Windows 2003 Server.

As part of the change, Landucci upgraded this server to a box with two 3.4GHz Xeon processors, with 4GB of RAM, and a RAID 5 storage array. “It’s like having it right in the habitat,” he says. A user can then access a wide range of onshore server-based applications and data.

He plans to add a second thin client in time for the next NASA underwater mission next month. “They’ll be able to do a remote desktop session from the habitat to their own mission control at Johnson Space Center,” Landucci says. “It’s like you’re sitting right there [at JSC].”

The onshore network also includes the open source Asterisk IP PBX, which supports more than a dozen Polycom SIP phones, file servers, databases and video servers.

Floating lifelines

The two sites are linked through a big NOAA weather buoy, basically a raft about 30 feet across, with a mast the same distance high, positioned over the habitat. The buoy carries the antennas, twin power generators and air compressors, network gear and other equipment. A 160-foot-long cord links the buoy with the habitat, carrying power and air and a 100Mbps Ethernet cable to the scientists below.

A wireless Ethernet bridge from Orthogon Systems links shore and buoy. Until recently, the link was based on Orthogon’s OS-Gemini radio, which the vendor rates at delivering up to 43Mbps in the unlicensed 5.8GHz band. Landucci says he was typically getting about 30Mbps.In late 2005, he replaced that bridge with Orthogon’s Spectra radio, which boosts throughput in the 5.8GHz band. “We get up to 100 megs, depending on the sea state,” Landucci says.

Aquarius posed special challenges, says Bob Shaw, senior systems and sales engineer for Orthogon.

One was the constant 3-D motion of the buoy, making it difficult to keep the two ends in sync. Second, radio waves reflect off the water and cancel each other out.

Spectra’s architecture solves a lot of this, Shaw says, by using multiple transmitters and receivers at both ends of the link, a technique known as multiple input multiple output. The radio is able to use the multipath effect to essentially combine all these signals to maximize throughput. For Aquarius, Orthogon combined a vertical and a horizontal sectorized antenna: the combination always keeps at least part of the antenna focused onshore.

Davis was onboard Aquarius before the Spectra radio was deployed. But even with the older 30Mbps connection, broadband had huge practical benefits for her research. She’s with the Environmental Fluid Mechanics Laboratory at Stanford University in California, and her underwater mission was studying the effect of a special kind of underwater wave that breaks on the Continental Shelf and carries rich nutrients from lower colder regions to the coral reefs.

Her team placed sensors on the reef, cabled back to the habitat. But the older laptops onboard couldn’t process the stream of telemetry data or monitor the data quality. The data was passed via the wireless bridge back to a laptop at the onshore site for collection and processing. Then, the researchers were able to do a remote connection to the onshore laptop to view the data.

An engineer with a Florida company called PrimeTest, which makes the Labview application used to monitor oxygen and carbon dioxide levels in the habitat, donated time to modify the software so Davis could track the quality of the sensor data, and if necessary adjust the sensors.

The wireless connection was almost like working in her Stanford lab. “We could control the data collection, stop it, back it up, and keep an eye on the data as it was streaming,” she says.