NOAA Teacher at Sea
Bill Lindquist
Aboard NOAA Ship Rainier
May 6-16, 2013
Mission: Hydrographic surveys between Ketchikan and Petersburg, Alaska
Date: May 13, 2013
Weather on board. Taken at 1600 (4:00 in the afternoon)
Latitude: 56° 02.49 N
Longitude: 131° 6.93 W
Overcast skies with a visibility of 5 nautical miles
Wind variable at 1 knot
Air temperature 9.9° C
Sea temperature 7.2° C
Science and Technology Log: Evening Data Processing
I continue to be struck by the vast amounts of data and processing a hydrographic survey crew takes on as they go about their work. I have sat in the ship’s Plotting Lab as we controlled the multibeam sonar equipment, plotted lines for the bridge to follow, and cast out the MVP “fish” to gather sound velocity data of the water column in the immediate survey area – all while corrections for tidal, GPS and the ship’s heave, pitch, and roll data are being made. I spent a day in a launch as we navigated waters too shallow for the ship activating the launch’s data collection system as it traversed back and forth in its prescribed areas.
Last night, I had the opportunity to “help” with the evening processing of data as the launches return to the ship. “Help” is a loose term – my ignorance of the required technical skills situated me at best an observer. My “partners” (people really doing the work) were gracious enough to let me look over their shoulder as they patiently explained the processes they were following. They allowed me to take control of the computer for a bit to have a hand in the cleaning of data. All this despite confounding computer glitches that seemed to bog down the process. As the work that typically would close out well before 10:00 drew on, I excused myself and allowed the technicians to work unimpeded by a guest looking over their shoulder. Attention to that work continued on into the early hours of the morning.
The data is brought from launch to Plotting Lab on an external hard drive. It is transferred to the central computer housing all the raw data. From there, sound velocity data is brought in allowing algorithms in the software to make appropriate adjustments. Accurate GPS, heave, pitch, and roll data adjustments are made. Tide levels as defined by the tidal gauges installed earlier are accounted and corrected for.
After those data are crunched, a map of the surveyed area is brought up. A small rectangle of data approximately 50 meters by 50 meters is selected and viewed in cross-section. From this vantage point each point measurement is visible as if you were standing on the seafloor. Erroneous acoustic returns that are not part of the seafloor are quickly identified and can be flagged so they will not contribute to the final measurements. Once this small section of the seafloor has been examined, another box immediately adjacent to the first one is opened until the entire survey has been examined. Each data set has a defined level of allowance for uncertainties, eg. at a depth of 300 fathoms 25 cm isn’t significant. Using these allowances, the computer will run a Total Propagated Uncertainties (TPU) analysis report to determine if the data falls within acceptable levels. If so, the data can move forward. These data help create a plan for targets to survey the next day.
This is only the beginning of the data processing to collate and clean major inaccuracies. From there it becomes the responsibility of the sheet (prescribed survey area) manager to further clean and analyze all the data within the sheet. Any areas that contain gaps or inconsistencies are examined to see if they can be resolved within prescribed allowances. Those that remain in question are described in the DR (Descriptive Report), reviewed by the Field Operations Office and Commanding Officer/Chief Scientist on board the ship, and finally submitted to the Pacific Hydrographic Branch. In turn, they review all data and reports, make any changes deemed necessary and send it off to update nautical charts.
As this process can take some time, there are procedures in place in the event a DTON (Danger to Navigation) is found. On this survey we identified a rock projection that projected much higher than the current charts – to that extent that had the Rainier went over it would have hit. DTONs are immediately submitted and updates are sent out that all ships navigating these waters would be alert to it.
By the time the Rainier completes the 2013 field season, it will have acquired massive amounts of data that will go on to assure safe navigation of our ocean waters.
Personal Log
We took a slight detour yesterday into Walker Cove to witness the grandeur of its majestic fjords. Cliffs climbed straight out of the sea on their way to the sky. Waterfalls cascaded back down its side. I took picture after picture – never quite capturing the experience of seeing it first hand. All members of the crew no matter how much time they have spent in these waters came up to gaze at these sights. There are some things on this earth that carry such beauty no matter how many times you have seen them maintain the power to hold your rapt attention. This was one of those sights.
A favorite place to write this blog is in the ship’s galley. In doing so, I have been gifted by a number of people who have stopped, sat down, and talked about their experiences on board a ship at sea. As much as any official orientations could provide, these conversations continue to present me a great way to help capture an understanding of this life at sea. A ship’s galley seems to be the soul of the ship. It is where people gather – to eat, to take a break, to tell stories, to enjoy each other’s presence.