NOAA Teacher at Sea
Onboard NOAA Ship Fairweather
June 15 – July 1, 2009
Mission: Hydrographic Survey
Geographical area of cruise: Shumagin Islands, Alaska
Date: June 18-20, 2009
Weather Data from the Bridge
Position: Koniuji Strait
Visibility: less than 0.5 mile
Wind: 11 knots
Waves: 2 feet
Temperature: 8.6 dry bulb
Temperature: 8.0 wet bulb
Science and Technology Log
Launches are used to acquire data in areas where it doesn’t make sense for larger ships to go. They are more maneuverable and their hulls don’t extend as far into the ocean. Small crews can travel in the launches and work together to cover specific areas, commonly called polygons. This week, we are using the launches to survey the ocean floor in the Koniuji Strait area. Getting ready for the launch requires some preparation. Dressing for the weather is a must; so layers and layers of clothing are necessary, especially on foggy, chilly days. Additionally, a float coat or life jacket vest and a hard hat are necessary for safety reasons. There are a lot of lines and cables moving around when a launch is being deployed and the safety equipment helps protect everyone involved.
Launches use a device called the Multibeam Echo Sounder (MBES, or commonly called the multibeam) to collect data about the ocean floor. The mulitbeam is a device that sends out sound waves. The sound waves bounce off the ocean floor and then back to the launch. The sound waves are commonly called “pings.” It is necessary to watch a computer screen to ensure that the pings are being collected to the fullest capacity. Sometimes adjustments must be made because pings are being lost or there is too much interference, or noise, in the data acquired. Another computer screen that must be watched shows the depth of the ocean floor being surveyed. Depths are color coded throughout the spectrum with reds being shallow and violets being deep. Watching the depth coloration helps to predict when ocean floor features may be changing from deep to shallow and vice versa. It is also possible to infer where ocean floor features like hills and valleys may be located.
Other computer screens show different views and aspects of the data being collected from the multibeam. These screens help to troubleshoot problem areas and make decisions about data being gathered. In fact, there are four computer screens to watch while using the multibeam! Multitasking is a necessity when you are the person in charge of the computer screens. Multibeams collect data from the ocean floor in wide sweeps so that no area is missed or skipped over. Overlaps are also built in to help prevent missed areas. Sometimes an area is missed; these areas are called “holidays.” It is sometimes necessary to resweep an area to fill in these holidays. The driver of the boat helps to keep the boat on the line being swept. Additionally, the driver helps to keep the boat traveling at approximately 6 knots so that data can be collected at the appropriate speed. This job is more difficult than it looks especially in a thick fog.
The use of the CTD device is necessary when collecting data from the launches. CTD stands for conductivity, temperature, and density. Since ocean water can vary in all of these depending on location, the CTD helps collect this information. The information is then uploaded into the computer system on board the launch. The sound velocity is determined using a formula containing these readings. Then, the computer helps to correct for differences in the ocean water when using the multibeam. A cast on the CTD is usually done every few hours.
Launches are great for acquiring data, but they require the assistance of many people to be used effectively. Plans must be made to create polygons to survey. People must use the radio to retain communications with the bridge of the main ship. Different people are responsible for working the lines, or ropes, that attach the launch to the ship. People must be able to use the multibeam computer software and information for the CTD appropriately so that significant data is collected. Someone must drive the launch so that it follows the lines for the sweeps. People from the engineering crew must maintenance the launches so that the engines work properly.
Each of these jobs requires certain training and experience to be completed in an effective way. I attempted to work the line to attach the launch back to the ship. It was difficult to keep the line untangled and throw it to the receiver in the correct location. I also attempted to steer the launch along the line for a sweep, but found myself overcorrecting and going in circles much of the time. It amazes me how the launches involve such a wide variety of skills and knowledge. With each task being accomplished, there are different problems that present themselves. Knowing how to deal with those problems involves a certain kind of personality. Being flexible, knowledgeable, and able to think on your feet while still remaining calm seem to be very important skills when working at sea!
Create Your Own NOAA Experiment at Home
You can simulate the way that the NOAA multibeam devices acquire data to help you get a better picture of how this complicated system works. Using a paint roller, some paint, and a piece of cardboard, you can better envision the sweeps of the multibeam system. First, draw a sketch of your cardboard on a piece of paper. You can even add islands and land features to the cardboard to make it more complex. Determine shapes of polygons that you will be sweeping; squares and rectangles work well in large spaces, but you may need to create some different shapes around your islands and land masses. Lay out the cardboard on a flat surface. Then, use the paint and roller to make wide sweeps on the cardboard. You can even use different colors of paint for each line you sweep to keep your information more organized. Since the paint and roller are simulating the path of the launch, try to keep your paint and roller going at the same speed (remember in a launch this would be around 6 knots). Try not to create any holidays during your sweeps because you will need to go over those again. The picture below may also help you to visualize how multibeam works.