Please note: You are viewing the unstyled version of this website. Either your browser does not support CSS (cascading style sheets) or it has been disabled. Skip navigation.

Dispatch 20: Finding Your Way in Ice

   Print  PDF  Change text to small (default) Change text to medium Change text to large

Related Multimedia

October 10 Photos
» View Slideshow

Joey Wenig

October 10, 2014


As I mentioned in a recent dispatch, during this latter portion of the cruise we have been traveling through consistently thick, multi-year ice—conditions the Louis was built to handle. But just because she was built for it doesn’t mean she likes doing it. Crunching through heavy ice is tedious and requires a lot of power, and can occasionally be fruitless. It’s faster and more fuel-efficient to follow leads in the ice. And even if there’s no open water to be found, there are usually weak spots or cracks to be exploited. At the very least, whoever’s navigating the ship will do their best to avoid the meters-thick ridges created by floes rafting together.

The winds have been blowing out of the north recently. (Apparently there’s just enough ‘north’ for the winds to blow out of. And that begs the question—if you were at the North Pole, what direction would you say the winds were coming from?) Since there is open water south of us, the northerly winds loosen the ice pack and create open channels among floes. As far as navigation is concerned, the result is like if the urban planning of a downtown core was left up to amoebas: chaotic. Getting from one station to the next as quickly as possible (an important consideration when cruise time is incredibly expensive) means finding the shortest route through a maze of leads. There’s an extra twist, though, because, if necessary, it’s possible to barge straight across an ice floe. The result is a tricky problem in minimization. Imagine if you were trying to get from one end of Manhattan to the other by car, except instead of a grid, the streets were oriented randomly. Not only that, but you also have the option of slowing down to drive directly across, for example, Central Park.

Even if you don’t have a notoriously poor sense of direction like I do, you still need maps for this. But how can you map an icepack that’s constantly in motion, pushed hither and yon by fickle winds and swirling currents? Fifty years ago, the best guide available would have been drawn in the clouds—the ‘water sky’ that I described earlier. Luckily we’re better off nowadays with two key sources of ice maps: satellites and onboard radar.

The satellite images we have on the ship come from RADARSAT-2, a Canadian Synthetic Aperture Radar (SAR) satellite. Fact: RADARSAT-2 orbits the earth 14.29 times per day. It takes lots of radio-wave pictures of earth’s surface from different angles as it passes over and then combines them to create a higher resolution image. That image, downloaded to ship’s computers once daily, is a definite improvement on water sky but still less than perfect because the icepack will shift about after having its picture taken—buoys frozen in floes have recorded displacements of 50 nautical miles in a day. The navigator has to account for this inter-image pack movement, and that’s where the second source of ice map, available in real time from onboard radar, comes in handy. Radar provides a view of the ice surrounding the ship in a three-mile radius. Comparing this image to the one from RADARSAT-2 to figure out how the icepack has moved since the satellite flew over is the Navigation Officer’s job.

The Louis, unlike most coast guard ships, has both Chief and First Officers (or Mates) as well as Second and Third Officers. Starting with Chief, they are Rod Strowbridge, Neil Casey, Sydney Swaine, and Telissa Leblanc-Rioux. The latter three rotate through watches on the bridge as Navigation Officer. They decide on a course for the ship based on the cruise plan, factoring in weather conditions and information from the satellite and radar images. With them at all times on the bridge is a Quartermaster, one of the deckhands or seamen, who actually steers the ship according the Navigation Officer’s instructions.

A further complication in Arctic navigation comes from proximity to the magnetic north pole. Traditional compasses don’t point in the direction of true north, they point towards the magnetic version. At most latitudes, the approximation is good enough, but up here it isn’t. In days past, ships used gyrocompasses to point them towards true north. (I recommend Googling gyrocompasses if you have a spare five minutes). Now, however, we have a device called a Fiber Optic Gyroscope (FOG, ironically) onboard that uses lasers to point us towards the celestial pole. If you have a spare half-hour, then please, by all means, Google this one as well. And if you don’t mind, you can explain to me how it works when you’re done.

Last updated: September 18, 2017
 


whoi logo

Copyright ©2007 Woods Hole Oceanographic Institution, All Rights Reserved, Privacy Policy.
Problems or questions about the site, please contact webdev@whoi.edu
Contact | Site Map | Arctic Group