NOAA Teahcer at Sea
Onboard the NOAA Ship Fairweather
May 29 – June 17, 2016
Mission: Hydrographic Survey
Geographical Area of the Cruise: along the coast of Alaska
Date: June 10, 2016
Weather Data from the Bridge:
Latitude: 55˚ 10.643′ N
Longitude: 132˚ 54.305′ W
Air Temp: 19˚C (66˚F)
Water Temp: 12˚C (54˚F)
Ocean Depth: 33 m (109 ft.)
Relative Humidity: 60%
Wind Speed: 4 kts (5 mph)
Barometer: 1,014 hPa (1,014 mbar)
Science and Technology Log:
On Sunday with everyone who needed to be here for the next leg of the hydrographic survey onboard, we set off for the survey site. Transiting through Alaskan fjords and associated mountains is a real treat to say the least. The abundance of wildlife and picturesque views of glaciers, mountains, and forests lend one easily susceptible to camera fatigue. Every vista resembles a painting or photograph of significance. The views are stunning and the wildlife breathtaking. After a day’s worth of transiting, we arrived in our survey area just west of Prince of Wales Island on the southern tip of Southeast Alaska and its Alexander Archipelago. The chain of islands that makes up the Alexander Archipelago represent the upper reaches of the submerged coastal range of mountains along the Pacific. A mere 20,000 years ago, the sea level was roughly 120 meters (400 ft.) lower than what it is today as our planet was in the grips of the last major ice age. To put that into perspective, the Fairweather is currently anchored in a calm bay with about 30 meters (100 ft.) of water. During the recent ice age, this entire ship would be beached hanging precariously next to ledges dropping 100 meters (300 ft.) to the ocean below. The mountains and steep island banks continue down to the sea floor providing for wildly changing topography below sea level. This type of environment is perfectly geared toward Fairweather’s capabilities.
While mapping survey areas that include shallow near-shore water, the Fairweather anchors in a calm bay maximizing ideal conditions for launching and retrieving boats whenever possible. Survey launches are dispatched out to their assigned polygons with the survey area while a skiff boat carries out near-shore marking of rocks and obstructions. Each of the four survey launches have a RESON 7125sv multibeam echosounder to collect data for mapping. Survey launches are sent out for much of the day and return with hydrographic data concerning their assigned area. All of the data is compiled into one file after extensive processing and quality control.
Dear Mr. Cody,
We arrived in Sitka, Alaska, with bald eagles flying overhead. The islands with the tall mountains are amazing. Some even have snow on them still. They have a lot of trees and wildlife. The mountains are all over the island and come right down to the ocean with a very tall dormant volcano across the sound from Sitka. (Dillion is one of my science students who went on an Alaska cruise with his family in May and will be corresponding with me about his experiences as I blog about my experiences on the Fairweather.)
We are not that far to the southeast of you in our survey area. That is part of the challenge of mapping this area and ensuring that nautical maps are accurate and up to date. Those tall mountains that you see so close to your ship really do continue down into the ocean in many places. I was able to go out on one of our survey launches to see how hydrographic data is collected using the Fairweather’s fleet of survey launch boats. It started with a mission and safety briefing before the launches were turned loose. Our operations officer went over the assigned polygon mapping areas with us. We were then reminded of some of the hazards that a small boat needs to be cognizant of such as the log debris in the water and the potential of grounding a boat on rocks. Both our commanding officer and executive officer repeatedly stressed to us the importance of being careful and alert and always defaulting to safety versus more data collection. Once the briefing was over, our boats were launched one at a time to our assigned survey polygons. We were to map the area just north of the McFarland Islands. Parts of the this area had known hazards hidden just below sea level. Complicating matters was the fact that many of these hazards marked on existing maps were instances in which someone hit a rock but did not know the exact location or a rock was potentially spotted at low tide. It was our job to carefully map the area without damaging the boat or putting any of the passengers in harm’s way.
Mapping an assigned area can be anywhere between the two extremes of incredibly uneventful to nimbly avoiding obstacles while filling in the map. Since the multibeam echosounder requires sound waves to travel farther through a deeper column of water, the swath covered by the beam is wider and takes longer to collect. In such stretches of water, the boat is crawling forward to get the desired amount of pings from the bottom needed to produce quality hydrographic data. When the boat is in shallow water, the reverse is true. The beam is very narrow, and the boat is able to move at a relatively fast pace. This makes mapping shallow regions challenging. The person navigating the boat must work with a narrower beam at faster speeds while avoiding the very hazards we were sent to map. Additionally, in this area kelp forests are very common. The long brown algae forms a tangled mass that can easily bind up a boat propeller. Add massive floating logs from all the timber on these islands, and now you have a situation in which a trained driver needs to have all their wits about them.
While the person navigating the boat tries to orderly fill in the polygon with a swath of hydrographic data, a person must be stationed at a work station inside the cabin modifying the data stream from the beam to help keep out noise from the data making the survey data as clean as possible. Sloppy data can result in more time in cleanup during the night processing of data once the boats return to the Fairweather. In addition, to control what is recorded, the station also determines when the multibeam echosounder is on or off. It takes some practice to try to keep multiple tasks on multiple screens functioning within an acceptable range. The topography in the map area also adds to the challenge since drop offs are commonplace. There were many times were the difference from one end of the beam to the other end was 100 meters or more (300 feet or more). It was like trying to survey the cliff and bottom of the canyon including the wall of the canyon in one swipe. Sometimes the ridges are so steep underwater that shadows are produced in the data were the sound waves were blocked by the ridge and our relative angle to it preventing a complete swath. This requires us to move over the ridge on the other side to map the gap.
There is something inherently exciting about being the first to see topography in such detail. Much of this area was last surveyed by lead line and other less advanced means of surveying than our current capabilities. In many respects they were accurate, but as we filled in our data over the existing maps, one could not help but to feel like an explorer or as much as one can feel like an explorer in this modern age. We were witnessing in our little assigned piece of the ocean something never seen before: land beneath the water in striking detail. The rocks and navigational hazards no longer resembled mysteriously vague asterisks on a navigation map to be simply avoided. We were replacing the fear of the unknown with the known by using science to peer into those asterisks on the map and paint them in a vivid array of well-defined contours later to be refined and made ready for the rest of the world to utilize and appreciate through upgraded navigation charts. Once our assigned polygon was filled to the best of our abilities, we moved on to the next and so on until it was time to head back to the Fairweather completing another successful day of data collection.
Did You Know?
Kelp is a long brown algae that forms underwater forests that serve as an important habitat for many marine organisms. Kelp is one of the fastest growing organisms on the planet. Some species can grow a half a meter (1.5 ft.) per day reaching lengths of 80 m (260 ft.) long.
Can You Guess What This Is?
A. search and rescue transponder B. an emergency flashlight C. a marker buoy D. a flare gun
The answer will be provided in the next post!
(The answer to the question in the last post was B. an oil filter. Getting an oil filter change for the Fairweather is a little different than for your car though the premise is similar. The four long filters used for each of the two diesel engines onboard are many times larger to accommodate the oil volume and are more durable to handle circulating oil 24 hours a day.)