by Ensign Hadley Owen, NOAA, Junior Officer, NOAA Ship Fairweather (S-220)
1200 hours, August 17, 2012: 70°13.7’N 144°49.6’W, approximately 250 nautical miles along the coast SSE of Barrow, AK
The water turned a silty gray-green early afternoon yesterday, Thursday, August 16. The Fairweather was transiting through areas with depths under our keel of between 8 and 20 meters – a somewhat caution-inducing sight for a vessel of our size. But the ice has opened up and we have made it east of Barrow. We are currently the furthest east along the North Slope of any NOAA or U.S. Coast and Geodetic Survey hydrographic ship, as previous surveys were last conducted by field parties with much smaller boats, in the 1950s and 1960s. As the crow flies, we are currently 90 miles or so west of the Canadian border and our turn-around point. However, we are of course not transiting in a straight line but in the zigzag/argyle pattern, so have a bit more sea floor to cover.
For a normal hydrographic survey, we use the Fairweather and her launches to drive over an area slowly and methodically with set parallel line spacing. With the multibeam echo-sounders, we are able to record data for a swath of between five and seven times the depth in which we are surveying. The survey lines are spaced to have a minimum of 25% overlap and thus comprehensive coverage of an area as well as moderate redundancy to ensure accuracy of the data collected.
As this Arctic trip is a “reconnaissance” survey, we are using the argyle pattern to cover as much area as possible while still ensuring quality of data via some overlap of tracklines. The image below provides a good visual. This pattern allows us to evaluate the data on the charts though varying depths. The blue lines represent one year (out and back) and the red the next year (out and back again). By crossing over previously surveyed lines – both within one season’s trip to the border and back, and potentially from one year to the next – we can both verify the data from the prior acquisition and help determine where there might be relatively rapid changes in the bottom characteristics (due to strong currents and a soft bottom, for instance).
Our current trackline has been modified yet again. Due to the ice, instead of surveying an area between 5 nautical miles (nm) and 60 nm out from shore, we have compressed our accordion to range between 1.5 nm and 30 nm out. From our observations, looking at aerial images of the sea ice, and listening in on radio traffic between the limited vessels transiting the area, it is looking promising that we will make it to Demarkation Point, on the Canadian border.
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We weren’t feeling so optimistic a week ago.
A combination of heavy fog and ice fields unexpectedly far south made data acquisition – bottom samples and CTD casts (measuring conductivity, temperature, and depth) – impossible at our scientists’ scheduled sample sites, and required deviation from the intended survey route. However, our plans on the Fairweather continued to adapt to the developing conditions, and not only were we able to satisfy our scientists research needs, but we also were able to experience some pretty cool Arctic phenomena. Oh, and squeeze in a little extra surveying just outside of the town of Barrow – in order to provide “ground truth” data to support a study on the feasibility of satellite-derived bathymetry to update nautical charts.
This past week, however, is best told in pictures taken this Arctic trip by NOAA Ship Fairweather crewmembers.