NOAA Teacher at Sea
Marsha Skoczek
Aboard NOAA Ship Pisces
July 6-19, 2012
Mission: Marine Protected Areas Survey
Geographic area of cruise: Subtropical North Atlantic, off the east coast of Georgia.
Date: July 15, 2012
Location:
Latitude: 32.47618N
Longitude: 78.19054 W
Weather Data from the Bridge
Air Temperature: 27.6C (81.7 F)
Wind Speed: 6 knots (6.9 mph)
Wind Direction: From the SE
Relative Humidity: 75 %
Barometric Pressure: 1018.3
Surface Water Temperature: 28.4C (83.12 F)
Science and Technology Log
In order for the scientists to find the fish they are studying on this cruise, they need to know where the areas of favorable habitat are located. Old nautical charts are not one hundred percent accurate–sometimes they can be hundreds of kilometers off. Early ocean floor mapping used long lines with a lead weight which was hung off the side of the ship. As the ship moved forward through the water, the long lines would get behind the ship making it very difficult to get an exact reading. It wasn’t until sonar came into general use during World War II, that it was discovered to be useful for bathymetric mapping.
Sonar works by sending a single sound wave to the ocean floor. As it reflects back toward the ship, a hydrophone listens for the return sound. The length of time it takes for that sound wave to return to the ship can be used to calculate the depth of the ocean in that location. The speed of sound in water travels at approximately 1,500 meters per sec (m/s) which is about five times faster than sound travels in air. The problem with single beam sonar is that the data only plots the one single line beneath the ship. It does not give the complete picture and gaps in data were often filled in using the readings taken around the area as an estimate.
So how is multibeam sonar different from single beam sonar? With multibeam sonar, it is just as the name implies–multiple sound beams are sent toward the ocean bottom. For the depths we are working on, the multibeam sonar on the Pisces sends out 70 beams of sound every .67 seconds. Within a fraction of a second, these “pings” are reflected off of the ocean bottom and back to the transducer. The time it takes for all 70 of those pings to return to the transducer determines the depth at each point. The echogram screen illustrates the bottom features in real time and will even pick up large schools of fish in the water column. As the ship continues to move up and down the survey lines, the raw data is collected. The distance between the survey lines is determined by the depth of the area to be mapped. To set the survey lines, we are using 1.5 times depth so, if the water depth averages 100 meters at the mapping location, the survey lines are set at 150 meters, (.08 nautical miles) apart. Tonight, the ocean depth at our mapping location is about 60 m so the survey lines are set at 90 meters (.05 nm) apart. The goal when laying out the survey lines is to overlap the previous lines by about 25%. This will insure a more complete picture.
It is not simple enough to just take the raw data from the return pings. The temperature, salinity and depth of the ocean in the mapping area can create slight variations in the return speed. Temperature, salinity and depth can influence the speed of the return signal, so we use the CTD to gather readings each morning as they are wrapping up the mapping for the night. This information along with the information on the ship’s roll, pitch, and yawl from the Position and Orientation System for Marine Vessels (POSMV) are plugged into software that helps process and clean up the data. From there, the data is converted into a “geo tif” file where it can be plugged into GIS mapping . The final product is a full color 3-dimensional image of the mapping area.
Ideally the scientists would have multibeam information for each of the sites they want to study that day. To make this happen, the night before the ROV dive the ship will make its way to the next day’s study area so the geographers can map all night. The survey lines are selected using bathymetry maps as well as looking at the existing multibeam maps of the area to see if there are any gaps that need to be filled in. The idea is to give the scientists as much information as possible so they can make informed decisions about where to study. Time on the ship is extremely expensive and they want to make sure they take full advantage of that time by finding the best habitats to study. Without the multibeam images, the scientists have to make a best guess as to where to map using old and possibly out of date information.
Personal Log
Today I took a tour of the Pisces’ engine room. Engineer Steven Clement was nice enough to show me around and explain everything for me. It is amazing to me how this ship is like its own little city. The ship creates its own electricity using diesel-powered generators. It takes four generators to power the ship at full speed which is about 15 knots. The engines are so loud that I had on double ear protection and it was still extremely loud to walk past them. Using all four engines all day would burn up 3,000 gallons of diesel fuel. The Pisces is capable of holding 100,000 gallons of fuel which should last the ship several months at sea. The electricity that is left over from powering the engines is used as the power supply for all of the electronics on board.
Other ways that the Pisces reminds me of a small city is the water. The ship creates its own drinking water with a reverse osmosis system complete with UV filter and is capable of producing 2.8 gallons per minute. It also has two hot water heaters attached to a compressor to keep the hot water pumped up into the pipes of the ship. I do have to say that the hot water on this ship is extremely hot!! There is no need to wait for hot water, it comes out instantly when I turn on the faucet. When I shower, I have the cold on full blast and just a smidge of hot water to get a normal temperature shower. Even our waste water is cleaned up in the Pisces’ own waste water treatment facility which uses microbes to break down the waste products before it is released back out to sea.
Other than pulling into port occasionally for fuel and supplies, the Pisces is really a self-contained vessel capable of cruising at sea for long periods of time.
Ocean Careers Interview
In this section, I will be interviewing scientists and crew members to give my students ideas for careers they may find interesting and might want to pursue someday. Today I interviewed Dr. Laura Kracker.
What is your job title? I am a Geographer with NOAA National Ocean Service in Charleston, South Carolina.
What type of responsibilities do you have with this job? Usually I work on projects using acoustics to map fish in the water column. Using fisheries acoustics, we can map the distribution of fish in an area and detect large schools as well. On this mission, I am using multibeam to map seafloor habitats.
What type of education did you need to get this job? I earned my Associate’s Degree in agriculture from Alfred College in New York. When my children were little, I stayed home with them. While I was home with them I earned my Bachelors in Painting. Then I went to work in a fisheries office for a couple of years before deciding to go back to college to get my Master’s Degree in Interdisciplinary Science from the University of Buffalo. I then continued on to my PhD in Geography and GIS, also from the University of Buffalo. My dissertation was on Using GIS to Apply Landscape Ecology to Fish Habitats. So I have combined all of my experiences to get me to where I am today.
What are some of your best experiences have you had with this job? I love being on a ship. I spend as many as 55 days a year on ships, often at the request of other scientists that need help with multibeam sonar. I love geography, it gives us a framework to put everything together, you can layer more and more information onto a map to find a complete picture.
What advice do you have for students wanting a career in marine biology? Get a broad foundation before you specialize. You don’t have to take a direct route to where you want to go.
what does GIS stand for?
GIS stands for Geographic Information Systems. It is a mapping software that allows you to import data as layers of information in order to build a more complete picture of what you need to analyze. For example on our cruise, the scientists would start with a map of the ocean floor topography at our study site. They would then add in layers of the multibeam sonar and the ROV dive sites to give a complete picture to the ROV crew of where we were going to dive for that day. To take that even further, now that we have returned from our trip, the scientists will analyze the data they collected and add yet another layer to that GIS map of the habitat we saw in each location along with the types and number of each species that was living there. They can then use this completed picture to compare what was found inside the MPAs with what we found outside the MPAs.
For more information on GIS, check out: http://www.esri.com/what-is-gis/overview.html#overview_panel
You keep mentioning “real time” what is this exactly?
The return information from the multibeam is nearly instantaneous, so we can see the features and schools of fish almost as we are passing over them.
what is the back up plan for engine failure?
Since there are four engines aboard the Pisces, if one of the engines fails, the other three engines will be able to get the ship back to port. That actually happened to us while we were out on our research cruise and we had to finish the expedition with only three of the engines. The ship’s engineers are able to repair just about anything that goes wrong, but sometimes new parts are needed. So at the end of our trip the Pisces had to remain at the Mayport Naval Station over the weekend for the repairs to be made before the crew could head out to their next assignment in Beaufort, NC.
How does temperature, salinity, and depth influence the accuracy and return speed of the data?
Water density is impacted by temperature and salinity. This change in density causes the sonar waves to bend ever so slightly as it passes through the different density layers. To make corrections for this change in sound speed, a CTD is cast to record the temperature and salinity at each mapping location. This information is then used to correct any error that might have occurred during mapping in order to create the most accurate map possible.