NOAA Teacher at Sea
Rosalind Echols
Aboard NOAA Ship Rainier (NOAA Ship Tracker)
July 8 — 25, 2013
Mission: Hydrographic Survey
Geographical Area of Cruise: Shumagin Islands, Alaska
Date: July 16, 2013
Current Location: 54° 55.8’ N, 160° 09.5’ W
Weather on board: Overcast skies with a visibility of .5 nautical miles, South wind at 18 knots, Air temperature: 10°C, Sea temperature: 7.2°C, 1-2 foot swell
Science and Technology log: Shoreline Verification
When you think of a shoreline, you might think of a straight or curved “edge” made of sandy beaches that gradually retreat into deeper and deeper water. In the Shumagin Islands, a sandy cove is a rare occurrence and a place for a beach party! Towering, jagged cliffs patched with Artic moss and blanketed by a creeping fog are the typical “edges” here. Below the cliffs, in the water, lie sporadic toothed rocks and beds of dense rooted bull kelp, swaying with the current. As I sit on the edge of the skiff (small dinghy-like boat), which gently trudges along the outside of the protruding rocks, I think to myself how this place evokes an ethereal mood and you really feel like you are in one of the most remote places in the world.
Remote it is and that is why we are here. These are, for the most part, uncharted or poorly documented waters and shorelines and in this post, I am going to talk about the shoreline aspect. Besides taking bathymetric data (depth data), hydrographic ships like the Rainier must also verify that the shorelines of various land-masses are portrayed accurately and that all necessary “features” are documented correctly on nautical charts. Features include anything that might be a navigational hazard such as rocks, shoals, ledges, shipwrecks, islets (small islands) and kelp beds. For shoreline verification, a 19 foot skiff is used for maneuverability and shallow water access. This boat will go out during the “shoreline window”, when the tide is the lowest, with the hopes that if there is a dangerous feature present, it will be visible above the water. In the best case scenario, we can investigate the shoreline fully with the skiff before sending in the bigger launches to survey the area with the sonar, so that we know they won’t hit anything.
The main goal of the scientists aboard the skiff is to establish a “navigational area limit line” (NALL). This is a boundary line delineating how far off shore the launch boats should remain when they are surveying. This boundary line is obtained in one of three ways:
1) presence of a navigational hazard such as a dense kelp bed or several protruding rocks
2) a depth of 4 meters
3) distance of 64 meters to shore
Whichever of these is reached first by the skiff will be the navigational area limit line for the launches. Here in the Shumagins, kelp beds and rocks have been the boundary line determinant and often these hazards are in water that is deeper than 4 meters because we have been encountering these before we get within 64 meters of the shoreline.
While scientists are determining the NALL, they are also verifying if certain features portrayed on older charts are in fact present and in the correct location. Using navigational software on a waterproof Panasonic Toughbook, they bring up a digitized version of the old chart of a specific survey area. This chart depicts features using various symbols (asterisk=rock above water, small circle=islet). This software also overlays the boat’s movement on top of the old chart, allowing the boat to navigate directly to or above the feature in question.
If the feature is not visually seen by the human eye or the single beam sonar on the skiff, it will be “disproved” and a picture and depth measurement will be taken of the “blank” location. If the feature IS seen, more data will be recorded (height of feature above the water, time of day observed, picture) to document its existence. This same verification procedure is used for newfound features that are not present on the old charts. All of this data is written on a paper copy of the chart and then back in the “dry lab”(computer lab), these hand-written notes are transferred to a digital copy of the chart.
Note: Kelp buffers are the large shaded red areas and the smaller red circle is the actual position of the islet. The three southernmost rocks (marked by red asterisks) inside the black box were disproved.
On the two shoreline verification adventures I went on, many rocks and islets were disproved and several new features were found. Most of the new features were rocks, islets or large kelp beds. It is important to note that if scientists find a new feature which is a serious present navigational hazard (ex. Shipwreck, huge jutting rock or shoal far offshore) it will be marked a DTON (Danger to Navigation) and communicated to mariners within a short time frame. Other less significant features take 1-2 years to appear on updated nautical charts.
For some survey areas, the Rainier uses aircraft-acquired LiDAR (Light Detection And Ranging) to get an initial idea of various features and water depths of a shoreline area. (This is a service that is contracted out by NOAA.) LiDAR data is obtained by a plane flying over an area at 120 mph, emitting laser beams to the water below. Like SONAR, LiDAR measures the time it takes for the laser beam to return to its starting point. Using this measured time and the speed of light, the distance the light traveled can be obtained, using the equation distance = speed*time, accounting for the fact that it travels through air and then water. Because light travels much faster than sound, the plane can travel significantly faster than a boat and a large area can be surveyed faster. Unfortunately LiDAR can only be used in clear, calm water because light is easily reflected by various solids (silt in the water, floating wood), specific color wavelengths (ex. White foam on ocean surface) and absorbed by biological specimens for photosynthesis (ex. Surface bull kelp). LiDAR surveys do reduce the time hydrographers spend at a shoreline site thus increasing the safety and efficiency of an operation. As with any data acquisition method, it must be cross-checked by another method and in this case because of the obvious downsides, it is used as a guide to shoreline verification.
After spending several days “disproving” a lot of rocks and islets that were clearly not present in their identified location, we started to wonder why someone would have thought there was a specific feature there. One possibility is that it was just an ink blot on the original chart, made by accident (from a fountain pen), and then interpreted as a rock or islet in the process of digitizing the chart. It’s better to be safe than shipwrecked! Another possibility is that these features were “eyeballed” in their documented location, and thus were present but just in the wrong spot. Lastly because of limitations previously mentioned, LiDAR occasionally mis-reports features that are not present. Fortunately, our current survey methods use sophisticated navigational technology and several cross-checks to minimize data errors.
After shoreline verification has been completed, launches can survey the ocean floor (using SONAR) outside the boundary (NALL) that was established by the skiff. Each launch will be in charge of surveying specific polygons (labeled by letters and names). The picture above shows the polygon areas which are outlined in light orange (most are rectangles). I will talk more about SONAR and surveying on the launch in my next post. 🙂
Personal log:
During a rare break from the hustle and bustle of work and ship life, I joined several other people on an expedition to the beach to do some exploring and beach-combing on Bird Island. We initially tried to hike up and over one of the saddles on the island to reach a beach on the other side that was more exposed and thus might have had more items washed up, but after 30 minutes of hiking, we had only just reached the top of the saddle, which included a lake with a noisy flock of white birds on it, mostly hidden in the fog. Although it was a bit disappointing not to reach the other side, hiking on the tundra was a fascinating experience. Aside from the mist-shroud, which has been with us for the past few days, walking on the tundra itself was unlike anything else I have experienced. The spring bed of mosses, shrubs, and small flowers make every step feel like two, but should you chance to fall down, it is an incredibly comfortable landing. An ideal place for a nap, as long as it is not wet. Overall, between my less-than-graceful shoreline-to-skiff entrance, scrambling uphill through waste-high damp grass, exploring the coastline, which really looked more like a sea urchin graveyard, and getting to know some of my fellow shipmates better, it was a truly delightful outing.
Aside from occasional excursions like this, we are generally on the ship or a launch 24 hours a day, which means that crew members have to be creative about getting exercise. Underneath the “fantail” (the outside deck at the stern of the ship), there is a small space that has been converted into a workout room, complete with treadmill, elliptical, exercise bike, and a sizable collection of weights. There is a group of crew members who have a sort of weight-lifting club, under the guidance of the third mate; one crew member likes to jump rope on the fantail so she has a good view for her exercise, and a number of people are intrepid enough to use the treadmill. I have now experimented with running a few times, and can only say that running on a treadmill on a rocking ship, even an ever-so-gently-rocking one, adds a new and exciting element to the treadmill that is sadly lacking in your typical gym.
Did you know?
The ship can rock in two different directions with the seas. When it is rocking forward and backward, it’s called pitch. When it’s rocking side-to-side, it’s called roll. The whole treadmill experience is quite different depending on whether the ship is pitching or rolling, but I always keep one hand on the bar for extra stability.
