Tag: multibeam echo sounder

NOAA Teacher at Sea
Kristin Joivell
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
Clouds: foggy
Visibility:  less than 0.5 mile
Wind: 11 knots
Waves: 2 feet
Temperature: 8.6 dry bulb
Temperature: 8.0 wet bulb
Barometer: 1005.9

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.

Personal Log 

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.

 

NOAA Teacher at Sea
Kristin Joivell
Onboard NOAA Ship Fairweather
June 15 – July 1, 2009 

Mission: Hydrographic Survey
Geographical area of cruise: Shumagin Islands, Alaska
Date: June 17, 2009

Weather Data from the Bridge  
Position: Big Koniuji Island
Clouds: Light Drizzle
Visibility: 5 miles
Wind: 17 knots
Waves: 2 to 3 feet
Temperature: 8.0 dry bulb
Temperature: 7.1 wet bulb
Barometer: 993.4

Science and Technology Log 

Today I had the opportunity to travel to Herendeen Island in one of the launches.  The two main tasks that I worked on were placing a new benchmark and taking measurements from a tidal gauge.  Benchmarks and tidal gauges are used to help the surveying team vertically reference their survey data to the tidal datum.

The first task to accomplish after landing on the island was placing the new benchmark.  Benchmarks can be found in many places.  You might even walk near a benchmark everyday and not even be aware of it! The national geocaching website describes a benchmark as “a point whose position is known to a high degree of accuracy and is normally marked in some way.” On this website, you can also search for benchmarks in an area by typing in the zip code where you would like to search. I’ve seen benchmarks in my travels hiking and biking; one was even near an old fire tower.  Benchmarks can be very old, but today I helped to place one that was brand new! I think the most exciting part about placing the benchmark was the knowledge that it is a permanent fixture.  Years from now, I will be gone, but the benchmark I helped place on Herendeen Island will still be there!

The second task that I worked on today involved some very basic process skills of science:  observing, recording, and calculating data.  My task was to record the level of the ocean’s water using a tide staff. I watched the water for one minute over six minute intervals for three hours.  During that one minute, I recorded the high and low water levels displayed on the tide staff. Then, I calculated the average of those water levels to be used by the surveying team.  This important information helps the surveying team reference the measurements from the automatic tide gauge to the benchmarks we installed.

I reached an understanding of the importance of this type of data collection by thinking about a ship traveling through the ocean during high tide and then during low tide. The ship traveling at high tide might read 30 feet deep on their depth gauge, but the same ship traveling at low tide might read 20 feet deep on their depth gauge. If the ship’s hull is close to those depths, it may be in danger of scraping the bottom. Knowing the depth of the water at the lowest of the low tides is important for the safety of the ship traveling through the water.

Even though the tide staff had been placed some time ago, it was still embedded firmly in the rock.  However, the seaweed growing on the rocks near the base of the tide staff seemed to be getting in the way of the observations initially.  This required some cutting and trimming of the material to improve data accuracy.  I think this is a good real world example of reducing the number of variables in an experiment that can’t be overlooked.

Personal Log 

Yesterday, I was part of a shore party in the small port town of Sand Point.  The ship needed to stop there for a personnel change and to pick up some mail from the post office. In my past travels, I saw some small fishing villages in Costa Rica, Venezuela, and Mexico, but here is a town in the United States whose existence revolves around fishing. The docks seemed to take up much of the area of the town. There were many boats docked there and the majority of which were fishing boats. I even got to see some boats coming back from the day’s fishing trip and begin to unload their catches. There were also people working on boats, nets, and general items associated with the fishing trade. Some boats looked like they were abandoned, but most looked as if they were used daily.  Living and working near the ocean must be an interesting life, especially in such an isolated place as Sand Point, Alaska.

Create Your Own NOAA Experiment at Home 
You can collect and record data using the same technique that NOAA scientists use for their tide staff data experiment.  Select an area in your backyard on which to make observations.  Perhaps a simple selection such as the growth rate of the grass would be appropriate for your first attempt at this experiment.  Next, decide on your observation times.  It’s a good idea to make your observations at the same time each day so that you can compare results and reduce variables.  Finally, you’ll need something to record your data, usually a pen and paper, but you could also take a photograph for data collection.  Record your data and try to make inferences and draw conclusions based on the data collected in your experiment.