APLIS POSTCARD #9
20 March 2007
Position:
73-10N/145-50W
Temperature: -12ºF
Greetings from APLIS, adrift in the Arctic Ocean.
Our movement to the northwest has stopped and we’ve actually
started moving slowly back to the southeast.
Never predictable. Our floe has
also rotated about 5 degrees clockwise.
Today’s big event is another surfacing for ALEXANDRIA. We’ve found a new “Marvin Gardens” (our
third) for ALEX to surface in - a couple miles further away but better
ice. The site we had been using was
ok. But the 18 inches of ice tended to
break free from the boat once the boat completed its surfacing. Ordinarily, this would be just fine. But, since the main reason we’ve been
surfacing ALEX is to get people on and off, keeping the ice intact is an
important consideration. So we’re going
with thicker ice.
ALEXANDRIA on the Surface
Whoops. Randy just
called from Marvin Gardens 3 to say that the thin ice there collapsed overnight
- that’s why we check first thing in the morning. He and the submarine are headed over to Marvin Gardens 2. Best laid plans and all that.
There are a couple things we can do to designate where we
want the submarine to surface and help them get to that location. But to explain those, let me first explain
how a submarine normally surfaces through the ice.
US submarines have four sensors that assist them throughout
the surfacing process.
- A sidescan sonar that provides an image of
the underside of the ice in a swath about 600 yards either side of the
submarine. Arctic Submarine Laboratory
(ASL) installs these temporarily on all submarines traveling to the
Arctic. A similar sonar is permanently
installed on Royal Navy submarines as part of the Sonar 2077.
- A low-light underwater camera that looks
straight up at the bottom side of the ice.
ASL also temporarily installs these - called Submarine Remote Video
System (or SRVS) - on US submarines.
These cameras can discern small imperfections in the ice and
irregularities in the snow cover, giving the submarine reference points for
determining its movement relative to the ice.
Similar cameras - called FINTEL - are installed on RN submarines.
- An upward-looking sonar (topsounder) -
permanently installed on submarines of both navies - that measures the draft of
the ice above the submarine.
- An ahead-looking sonar, normally used to
avoid ice keels, but which can be used to map the area of ice in front of the
submarine. The two navies have
different sonars but they serve the same functions.
To begin the surfacing process, a submarine normally uses
its sidescan sonar to search an area for large, thin-ice features. Maneuvering to drive underneath the
features, the submarine uses the topsounder and the underwater camera to
evaluate the thickness and uniformity of the feature. Once the submarine has decided to surface, it uses its
ahead-looking sonar to help steer into the feature. All of the sensors are then used to monitor the submarine’s
position relative to the ice while the submarine stops and hovers beneath the
feature. When everything is ready, the
submarine slowly ascends until it impacts the ice. If the ice is thin, it will normally break right through. For thicker ice, the submarine needs to blow
air from its ballast tanks, creating a buoyant force on the ice and causing it
to give way.
We can help this process along by taking care of the first
two steps for the submarine. Our field
team can use our helicopter to find a good, large feature and hand-auger a hole
through the ice to verify its thickness.
Then, from the camp, we can pass the position of this feature on our
tracking range and vector the submarine directly to it. Our field team also uses a shovel to scrape
an X in the snow. This serves to
designate exactly where we want the submarine to surface and to give the
cameras a good reference for judging the submarine’s movement relative to the
ice floe.
Royal Navy Petty Officer Darren
Davies shovels an X in the Snow
That’s what we did with ALEX this afternoon. Accompanied by reporters from the Los
Angeles Times and Alaska Public Radio, our away team marked a new location at
Marvin Gardens 2. Using the X placed in
the snow, ALEX got lined up and broke through inside the X.
At our last ice camp in 2003, we had a polar bear visit the
USS CONNECTICUT and investigate its rudder.
Photos of this made it onto the internet and were seen worldwide within
days. Not to be outdone, Bruno (who
watched today’s surfacing) asked to get his photo taken with ALEXANDRIA’s
rudder. Here’s Bruno’s rudder picture.
Jeff Gossett
Arctic Submarine Laboratory