Tag: doppler velocity log

NOAA Teacher at Sea
Nichia Huxtable
Aboard NOAA Ship Bell M. Shimada
April 28-May 9

Mission: CINMS Mapping
Geographical area of cruise: Channel Islands, California
Date: May 2, 2016

Weather Data from the Bridge: 17-20kt winds; clear skies; 0-1ft swells

Science and Technology Log:

There is a lot of amazing equipment on board Shimada, but my favorite, by far, is the REMUS 600 AUV. Really, it should be everyone’s favorite. What other piece of equipment can you release in the middle of the ocean, have it swim around for a few hours collecting data, then have it ready and waiting for you in the morning? I’m pretty sure my laptop wouldn’t be able to do that if I threw it overboard (although, on a few occasions, I’ve been tempted to try).

On Shimada’s mission, the AUV is used when scientists need detailed, high-resolution imaging of deep water areas or areas of special interest. The ship’s ME70 multibeam sonar can map the seafloor up to 350m deep, whereas the AUV can map as far down as 400m. Now remember, this is an AUTONOMOUS Underwater Vehicle; this means that you are literally dropping it off the side of the boat, leaving it to propel itself along a pre-programmed route, then, hours later, returning to a set location with the hope of seeing your million-dollar robot pop back up to the surface to be retrieved.

 

There is a lot that needs to go right in order for this to happen. In the REMUS 600, there are three separate systems that must all function correctly in order to successfully complete its mission. The navigational system includes an Inertial Measurement Unit (IMU) for pitch, roll, and heading compensation, a Doppler Velocity Log (DVL) for speed over land measurements, GPS for location, and processing software. The communication system includes a micromodem to receive status messages while AUV is up to 1500m away, an Iridium satellite communications system, and, of course, Wi-Fi. The sensors include multibeam sonar, obstacle avoidance sonar, a depth sensor, and a CT (conductivity, temperature) sensor to analyze sound speed for beam formation.

 

If these systems aren’t working correctly, there’s a good chance you’ll never see this AUV again (which would make a lot of people very unhappy). Basically, all these systems ensure that the AUV stays at a specific height above the seafloor (around 75m), runs a specific course that you programmed, and collects data for you to analyze when it returns. Every hour or so while it’s running its course, the AUV rises to the surface, makes a satellite phone call to check in with Shimada, then goes back down to continue its data collection. When it’s done with its course, it runs in circles (think underwater donuts) until the ship returns and the scientists call it back up to the surface where it can be retrieved.

 

Remember how I said that all the systems must be working correctly in order for the AUV to successfully complete its mission? Well, this first launch and retrieval went off without a hitch, but it turns out something went wrong with the data collection (as in, there were no data collected after the first 45 minutes). The scientists are once again on the phone with customer support to try to figure out what went wrong.

 

On the bright side, there are far worse things that could have gone wrong: the AUV successfully ran its course, checked in with the ship, and came up to the surface at the time and place it was supposed to. That doesn’t always happen, which is why the AUV has an “If found, please call this number” sticker right on top of it. Just like what’s written on your retainer case…except your retainer didn’t cost one million dollars.

Personal Log:

Even though it seems like the hours are filled with troubleshooting and problem solving, there are still many things going our way. The ME70 and EK60 have been successfully running all day, the weather is fully cooperating with calm seas and beautiful skies, and, last but not least, dolphins decided to play right next to the ship. Bring on tomorrow!

Words of the Day: AUVs and ROVs. Autonomous Underwater Vehicles are pre-programmed and complete their mission without supervision. Remotely Operated Vehicles are connected to the ship by a cable and are directly controlled by a human operator.