Sensing through the Fog
March 26, 2009
As we travel across the Weddell Sea toward iceberg TK-231, the bridge is
monitoring the surrounding area for other, smaller icebergs we may pass
by. The day was foggy and snowy, making a visual search difficult.
Radar increased the bridge’s ability to search and to make the transit
The ship's radar system shows an image of an iceberg. Photo by Rob Sherlock
Radar allows the bridge to detect small icebergs in the water; however,
radar also shows choppy waves and more intense regions of snowfall.
Choppy water hides small pieces of ice floating near the ship, requiring
visual lookouts in addition to the radar. The ship’s able-bodied
seamen—Sam Villanueva, Lauro Garde, Fernando Naraga, and Louie
Andrada—rotated shifts so that someone was constantly watching for
growlers, small icebergs that can be up to ten meters long but drift
less than one meter above the water line. Growlers weigh up to 120
tonnes and can cause hull damage if the ship hits them too fast, so the
ship posts lookouts and reduces its speed in low-visibility weather. In
clear weather, lookouts on the bridge can see about 14.5 kilometers to
the horizon, but that range was reduced to about half a kilometer today
because of snowfall. Radar is the only long-distance sight the bridge
has in low-visibility weather, and it doubles the bridge’s ability to
see ice in clear weather (to about 32 kilometers).
As an interesting side note, radar cannot follow the curvature of the
Earth. It only detects objects that are a straight line away, meaning
flat objects are visible only as far as the horizon. But mountains rise
above the horizon and can be seen from far away. Mountain peaks and the
coastline over 150 kilometers away have been visible on radar.
— Amanda Kahn