seafloor mapping – Page 13 – NOAA Teacher at Sea Blog

July 25, 2007April 1, 2021

Ginger Redlinger, July 23–25, 2007

NOAA Teacher at Sea
Ginger Redlinger
Onboard NOAA Ship Rainier
July 15 – August 1, 2007

Mission: Hydrographic Survey
Geographical Area: Baranof Island, Alaska
Date: July 23–25, 2007

Weather Data from the Bridge
Visibility: 10 Nautical Miles
Wind directions: 150°
Wind Speed: 10 Knots
Sea Wave Height: none
Seawater Temperature: 14.4° C
Sea level Pressure: 1015.9 millibars (mb)
Temperature: 15.5° C

Mariner Word of the Day: Geodesy

Geodesy is the science of measuring and monitoring the size and shape of the Earth and the location of points on its surface.

Survey Tech Boles holds a Navigational Chart developed by NOAA that also includes Hydrographic survey data

Science and Technology Log: Charts vs. Maps

The RAINIER returned to the Gulf of Esquibel to gather a few more swaths of data to complete their survey of this area. The ship is anchored in Steamboat Bay and several boats are out gathering data around the shoals in the area to identify navigational hazards. Tomorrow I will be on one of those boats – I can’t wait!

Since I am on the ship today, I can tackle a bigger question in my journal entry. This question popped into my head (it didn’t hurt : ) when I was talking with the data processing crew. I want to know what the difference is between charts and maps? Based on the attention to detail that the RAINIER pays to the collection and quality of data to put into their charts I knew it had to be very different from maps! I am figuring there is a clear distinction that is important for everyone to know since we all use maps at some point for driving, cycling, hiking, or boating. I will begin to tackle this question now, but a fuller, more rigorous explanation will evolve as I develop lessons to support this TAS assignment! Let’s start with some basic information:

What is the difference between a chart and a map?

Charts

Has special unique characteristics including a very detailed and accurate representation of the coastline, which takes into account varying tidal levels and water forms, critical to a navigator.
is a working document used to plot courses for navigators to follow in order to transit a certain area It takes into account special conditions required for one’s vessel, such as draft, bottom clearance, wrecks and obstructions which can be hazardous. Way points are identified to indicate relative position and points at which specific maneuver such as changing courses, must be performed.
provide detailed information on the area beneath the water surface, normally not visible to the naked eye, which can and is very critical for the safe and efficient navigation.

Maps

emphasize landforms, including the representation of relief, with shoreline represented as an approximate delineation usually at mean sea level.
is a static document, which serves as a reference guide. A map is not, and cannot be used to plot a course. Rather it provides a predetermined course, usually a road, path, etc., to be followed. Special consideration for the type of vehicle is rarely a consideration. Further, maps provide predetermined points-road intersections-to allow one a choice to change to another predetermined direction.
merely indicate a surface path providing no information of the condition of the road. For instance a map will not provide information on whether the road is under repair (except when it is a new road) or how many potholes or other obstructions it may contain. However the driver is able to make a visual assessment of such conditions.

Source of the above information? You guessed it – NOAA! Here is the website.

An example of one type of chart made from Hydrographic survey data

Charts and maps are clearly different. Now lets look at the science behind creating charts. The science is called Hydrography. (I found the next set of information on this site) Hydrography is “the science which deals with the measurement and description of the physical features of bodies of water and their land areas.” (CDR Gerd Glang – Chief, Hydrographic Surveys Division) To paraphrase: Special emphasis is placed on elements that affect safe navigation. Side scan sonars are often deployed to detect submerged dangers to navigation. Hydrographic data are collected and processed with specialized computer systems that store data in digital form and generate graphic displays. Charts must include enough hydrographic detail in order to adequately depict the bottom topography and portray the least (lowest) depths over critical features. (Like rocks that your boat will hit if you don’t know they are there!) This paragraph describes exactly what we are doing here in Alaska!

Navigational charts contain accurate and reliable information about features that assist ships in their travel. It can take up to two years to create a navigational chart! There are multiple sets of data that are used to ensure the charts are accurate. Just think about the data I have discussed so far. There are ELAC sonar readings of the deep water. The RAINIER takes ELAC readings in the deeper waters off the coastline, and the smaller boats take ELAC readings of the deeper waters closer to shore where navigational hazards to the RAINIER are present. This is also data the smaller boats using RESON sonar readings of shallower waters, the gathering of tide gauge readings, and the measurement of GPS benchmark levels.

While it is unusual for both the RAINIER and the smaller boats to be surveying at the same time, it helped complete this project in good time. Usually, the six smaller research boats complete the survey work while the RAINIER serves as a command, logistics, and data processing center. Layers upon layers of data from all the boats and ship go into making charts. Like I said before, it can take up to two years to complete a chart with all the new survey information. While charts are being developed, sometimes new information becomes available that is critical to navigators, like a new hazard. This information is communicated immediately and notices are sent out monthly so mariners can update their charts. NOAA has set a goal to move from survey to chart in 90 days – based on the amount of time it takes to gather data safely, this will be challenging! But if newer technologies can provider quicker turn around time it will speed up the process.

I watched the careful and deliberate review of data gathered by multibeam sonar, and as with any technology, there are limitations. Human oversight, review, and careful analysis of the data are important links between the gathering and use of the survey.

A note of interest pertaining to navigational charts

Did you know that Thomas Jefferson created the US Coast Guard & Geodetic Survey Office in 1807? (1807 – 2007… NOAA is celebrating its 200^th anniversary!). The US Coast Guard & Survey Office was the first scientific agency of the United States government. The Coast Survey Office and the USGS benchmarked, mapped, and charted the United States as it grew, and now there are multiple agencies providing data that describe a global model. This mathematical model is called Geodesy (Pronounced Ge-oh–des- see.) It has helped us understand the actual shape of the earth – it is not a perfectly round sphere, it is an oblate spheroid squashed down at the poles and bulging a bit at the equator! The Geodesy group is developing and refining a mathematical model that starts from the center of the earth and works its way out in to solar system. It takes into account the movement of the earth around the sun, and the sun within the spiral of the galaxy. As the entire unit of our solar system moves, subtle changes to the tides occur. It seems that this occurs on a nineteen-year cycle. Being able to track data over time at different locations – satellites, sonar readings, survey readings, etc. help us understand changes from the earth’s core, to the surface (tectonic plates, sea floor and land formations), and the oceans tides. It is quite amazing to think that a mathematical model can take all of that into account. Learn more here.

Think about how important it was to back in Thomas Jefferson’s day to understand navigation to and from the United States. For example, how to travel in order to trade and discover where to develop ports, and where not to! Think now about how important it is to understand how changes in earth impact human activity – trade, recreation, where to build homes away from storm zones, flooding, etc. What are safe numbers of fish to harvest so they can replenish? With the melting of the polar caps, imagine how important knowing how the mean high and low tides will change. The Tide Gauge survey that we completed in Dorothy Cove was last done in 1924! The work of NOAA, its’ agencies and that of the RAINIER are very important.

In the week since I have boarded this ship, the RAINIER and it’s crew have surveyed 462 Nautical miles, checked tide gauge data, reviewed data from the surveys to ensure their quality, and planned the next stage of their journey. In 2006, 1,464 Square Nautical Miles (SNM) were surveyed. There are 21,660 SNM that are considered critically important and have yet to be surveyed. See the 2007 Hydrographic Survey Priorities Report for more information.

Personal Log: Food equals Happiness

I have yet to talk about the food, and since my students love to eat I have to let them know how well fed I am on this ship! Imagine keeping sixty people of various taste-preferences happy. This is job of the cooks and stewards in charge of feeding and providing stores to the crew. I have never had such a variety of food before! There are always two or three choices or combinations of foods for every meal in hopes of making everyone happy. Fresh soups every night! There are fresh vegetables cooked just right – never over cooked! The salad bar and the ice cream freezer are always available (and a banana sundae with two or more ice cream types, chocolate sauce and chopped nuts is a great dessert. My favorite end of the day treat is “Foye Hot Coco” – a recipe he shared with me. If you meet him, be sure to ask him to teach you how to make it!) Over the week I have had the choice of barbeque ribs, prime rib, beef tips, roast veal, chicken, different varieties of rice, different styles of potatoes, and a host of tasty vegetarian dishes (yams masala, gado gado, pesto wraps). (Did I mention the gravies – they are delicious!) There are six different types of hot sauce and a host of condiments! Fresh fruit is always available (pineapple, mango, melons, grapes, cherries, you name it!) There are fresh made desserts every night and fresh-baked cookies during break times. All the water, coffee, juices, Nesquick, hot coco, tea, etc. that you could want.) I haven’t even started to talk about breakfast and lunch –there are treats galore- at least six kinds of cereal- and I will be lucky to leave this ship at the same weight as when I climbed aboard. There are even special occasions – like when Raul caught a 50-pound halibut the other day and donated it to our dinner one night. He made his own homemade batter and deep-fried pieces of halibut so we could have fish tacos! They were awesome! (Guacamole and mango salsa on top!) Floyd, Sergio, and Raul know how to keep us happy, healthy, and keep our bellies full!

The other really cool thing I have learned about here is satellite radio! I have got to get it installed in my boat, camper, truck, heck even the lawn tractor! The sound quality and choice of programming (without commercials) is incredible! Speaking of music, there are two really cool bands I have learned about on this trip – Great Big Sea, and Flogging Molly (which my students who love My Chemical Romance will really enjoy!)

Question of the Day

Topic 1: Are there internship opportunities for students who are interested in exploring careers in navigation, charting, mapping, computer sciences, Officer Corp, etc? How many NOAA agencies are there?

Topic 2: What geometric theorem can you use to determine the length of an unknown side? Hint: Hypotenuse.

Topic 3: What other expeditions and scientific endeavors did Thomas Jefferson initiate?

July 22, 2007April 1, 2021

Ginger Redlinger, July 22, 2007

NOAA Teacher at Sea
Ginger Redlinger
Onboard NOAA Ship Rainier
July 15 – August 1, 2007

Mission: Hydrographic Survey
Geographical Area: Baranof Island, Alaska
Date: July 22, 2007

One of five Geodetic Survey Benchmarks at Dorothy Cove

Weather Data from the Bridge
Visibility: 4 Nautical Miles
Wind directions: 190°
Wind Speed: 6 Knots
Sea Wave Height: 0 – 1
Seawater Temperature: 12.8° C
Sea-level Pressure: 1010.0 millibars (mb)
Cloud cover: Cloudy &
Rain Temperature: 13.9° C

Mariner Words of the Day: Port & Starboard

Port and starboard are directional words indicating the sides of the ship. As you are facing the bow (front) of the ship, port is on the left side, and starboard on the right side. How to remember? Port and left both have four letters.

Science and Technology Log

Today was the day that we wrapped things up in this area by re-surveying a few sections to improve the quality of the initial set of readings, took horizontal measurements of the water-level (by hand) in order to improve the accuracy of area mean tide (high and low) data, and prepared the ship to move south. I have written earlier about the attention to detail, safety, and teamwork in the day-to-day operations, the gathering and processing of data, and daily production of results. Today I am adding the noticeable value of the work done by NOAA vessels as noted by a gentleman and his family who came to watch our tide gauge survey crew work this morning. He said, “You people with NOAA do a great job, and the folks in Sitka use your information all the time. We are thankful that you have provided us with the information we need so we can enjoy navigating the waters around here.” That was a good way to start the day. I highly recommend that you read TAS Beth Carter’s description of mechanics and tools involved in Tide Gauge Surveys.

While it sounds easy, it is actually very challenging to collect accurate measurements to the specifications required for this work, which are to the millimeter. Everything has to be level and measured at precise locations using benchmark geodetic locaters installed. Using the same locations (the geodetic benchmarks) each time you take measurements ensures consistent use and interpretation of horizontal measurements. The horizontal measurements between the benchmarks tell us whether or not the land height has changed. This is important information to give context to any changes the tide gauge measures. If the mean tide level has changed, you need to know if the land level has changed too! Much of the data we gathered today is also connected to the GPS (Global Positioning System.) I have an old farmhouse and level is not a word I can use to describe most of it. Making a precise measure by establishing a level place on a slippery, rocky beach makes taking measurements in my house seem like a piece of cake! The survey scopes at the benchmarks are looking across about 50 feet of water to their left at the picture on the left (below) – which is the rod at another benchmark. The next picture is the rod at the third position, which would be on the beach about 90 degrees, and 50 feet to the left of the survey scope (and the same, but the right, of the rod on the other side. When the lines connect, we have a triangle!

If you would like to see how challenging this can be, here is a simulation that reverses the location of the surveying scope eyepiece (with the crosshairs) and the rod (with the height indicators), but it will definitely give you an appreciation for the challenge of accurate measurement over distance: Imagine yourself with a standard size metric ruler and a piece of paper with a crosshair pen line about 10 cm long each direction. About one centimeter from the top and the bottom of the vertical line draw another crossing horizontal line 2 cm long, about 1cm on each side. Tape the paper to the wall across the room and walk to the other side facing the paper you just taped to the wall. Now hold up your ruler an arm’s length away, vertically, with the 0 on the bottom so you are reading the measure up from the bottom of the lines. Close one eye. Try to identify exactly the millimeter at each horizontal line, for each of the horizontal lines. Could you line it up exactly? Was your ruler and paper both “level” so you could? Hard to see? Hard to measure? Now you see how challenging this can be! Imagine making an accurate measurement over a distance of 50 to 75 feet! It is also important to note that multiple measures must be taken that have to agree on the same result, with allowance for a tiny margin of error (again, a two millimeter margin of error is allowed – that is one millimeter error for the upper half of the cross hair and one for the lower half).

Here is another view of the survey scope lining up with the rod. If you look at the bottom of the rod you can see Geodetic Benchmark.

In the case of Dorothy Harbor, there are five Geodetic benchmark markers. When the line of sight is either obstructed, or too great to make an accurate reading, then a “turn point” is established. The turn point is set on a turtle (not a real turtle) which is a heavy disk that serves as set location upon which to balance the rod so measurements can be taken. Measurements must be taken from, and at, each location that needs the turn point to ensure that the data is correct. Since this data is used to ensure the accuracy of tidal data in this area, and to supply information to the GPS – it must be done correctly. In the natural environment, this is quite challenging. The measurements are recorded on a PDA and returned to the ship for processing. Right triangle geometry, simple algebra, or trigonometry can be used to determine the accuracy of the measurements at each point. If you have the markers at two line-of-site points (say to your right and your left) and are measuring the distance from where you are to each of the two points, you can figure out from your findings what the distance is between the two line-of-site points. By moving the rods to each of the five markers, you can verify that the measurements made from each location are accurate. Taking and using multiple measures is common sense to those who do it all the time like the NOAA crew. For many people, learning why is important. Some people learn it through building things — like the common sense rule to measure more than once before you decide to cut lumber, or to measure from two directions before you square a corner – you have to be sure you are right before you move to the next step!

Once we were done with our measurements we ate lunch, then began to disassemble the Tide Gauge measurement assembly. The divers came in later to remove the equipment anchored underwater, and everyone returned to the ship to prepare for the evening’s departure. The crew was exhausted as we had to climb, wade, carry, move, hold, disassemble, dive, and concentrate intently on our tasks. Tonight we head south at 2100 towards Ketchikan and begin surveying a different area tomorrow.

After helping the crew complete today’s work, I realized how difficult it is to gather precise measures by hand in dynamic, ever-changing conditions. (The wind picking up in the middle of a read — moving the 15’ high rods just enough to throw off the desired accuracy – so you have to start all over, the trees interfering with the line-of-site between the benchmarks and rods – people pushing back tree branches, trying to triangulate points on an unstable rocky beach, you get the idea…) Despite all these challenges, the crew gets the job done. This is what the navigating public (and commercial navigators), appreciate about NOAA’s work. As I heard, straight from the pilot and family of the Sitka-based pleasure craft anchored in Toy Harbor.

I also appreciated the seafloor mapping tools provided by the technology on the ship. What if we had to take seafloor readings by hand! (And hope that we had found all the submerged rocks!) I think technology for surveying has made mapping the seafloor easier, at least at the measurement stage : )

Question of the Day

Topic 1: How are navigational charts, topographical maps, and road maps alike? How are they different? (The answer to this question will be explored in the next journal).

Topic 2: Where can you find a geodetic benchmarks in your area? Outside of your area: What is special about the markers that are used in Disneyland (not created by the USGS)?

Topic 3: What are the tools and techniques of surveying?

July 18, 2007April 1, 2021

Ginger Redlinger, July 18, 2007

NOAA Teacher at Sea
Ginger Redlinger
Onboard NOAA Ship Rainier
July 15 – August 1, 2007

Mission: Hydrographic Survey
Geographical Area: Baranof Island, Alaska
Date: July 18, 2007

Weather Data from the Bridge

Visibility: 10 Nautical Miles
Wind directions: 325°
Wind Speed: 10 Knots
Sea Wave Height: 1 – 2 feet
Seawater Temperature: 13.9° C
Sea level Pressure: 1009.2 millibars (mb)
Cloud cover: Partly Cloudy

Science and Technology Log

Today’s Mariner word: Fiddly (Pronounced Fid-lee) the fiddly is the room above the engine compartment.

Survey Techs Hertzog & Boles prepare to measure sound velocity with CTD.

Wow – what a day. At 0800 hours we were briefed on our day’s work plan. I was joining an experienced pilot (Coxswain) and two survey technicians on a research boat to take sound velocity readings in an area off the coast of Baranof Island. First, we had the launch the boats from the ship. The experience boat crew and I watched as the ship’s deck hands lowered the boats from their racks by crane to the side of the ship at a level that allowed us to climb aboard. (A few feet above water level). The deck hands held the boat in position from above by crane, and on the sides to keep it from rocking back and forth and bouncing against the ship. Additional hands held ropes attached to the hooks and cables that we were going to release fore and aft hooks once the boat was in the water. Of course, the boat pilot needed to get the engine running right when the boat hit the water to keep it in the correct position against the side of the ship. Launching while underway is challenging, and must be done correctly in order to ensure everyone’s safety. The boat’s personnel released the hooks and the deck personnel winched the hooks back to the starting positions. Deck hands on ship held the boat in position with ropes fore and aft. Once everything on the boat was checked and running the aft line was called in, then the bowline, and we were underway. This was another example of the amazing teamwork I have witnessed everyday on this ship.

When we arrived at our survey area the technicians used a CTD to take an initial reading of the speed of sound at the surface of the water, then lowered it again to take the same reading at a much lower depth. (If you remember the last journal entry, this is the same process used to correct for the speed on sound on the RAINIER.) The readings are entered into the boat’s computer prior to taking any readings. While we took readings along our survey lines I asked the survey crew a question, “what about large mammals, won’t they interfere with the sonar readings? The answer was “yes, if a whale is below us it would appear as a shadow on the computer screen. Algal blooms and kelp beds can also affect the quality of the readings.”

Survey Tech Boles monitoring the data recorded by the ELAC transducer

We tracked back and forth across our survey area. The direction and length of each survey line was determined the day before, and provide to the boat’s survey technicians. No whales, algal blooms, or kelp beds today. Part of NOAA’s mission is to provide useful information to commercial navigators, and that includes fishermen. We were very careful to adjust our movement across survey lines to avoid interfering with the fishing vessels. During our time on the boat I asked the crew questions about their background, the Coxswain (person who pilots the boat and ensures our safety) has been at sea for over 30 years. He is amazing. He taught me how to pilot the board correctly. My first try was not very successful. The second time I was much better. I guess you could say that he is a good teacher, and a good seaman.

The two survey technicians on board track and record data. They have different backgrounds, but bring important skills to the task of gathering and reading data. The first, a young woman, has a degree in geology and works as a cartographer for the United States Geologic Service. She is working on this boat this summer. The other is a young man from Tennessee who received his certificate in Geographic Information Systems. I have to admit, without the man who piloted the boat and kept it on a narrow track of water fighting swells, currents, and avoiding fishing boats – the rest of us wouldn’t have been able to take readings. Everyone has something critically important to do.

Coxswain Foye keeping the boat on the correct lines to record data. — Coxswain Foye keeping the boat on the correct lines to
record data.

How did we get the data from the boat to the on-ship computers? The data is cabled in from the boat to the plotting room where all the cartography hardware and software is located. (One way is to plug in a cable and download!) The database contains recent and historical charts made of waters that NOAA surveys. The FOO (remember, Field Operations Officer) showed me a chart created in 1924 of the same area. The technology used back then was lead lines and sextants. They would start by moving to a location, and then drop a lead line until it hit the bottom, counting the fathoms from surface to seafloor. After recording it, they pulled up the lead line, and then traveled along as straight a path as possible, recorded latitude and longitude, and took another reading. I didn’t count all the readings taken in this fashion on the old map, but there were well over one hundred readings in the small section we were surveying, and the old map covered a region much greater – the entire coastline and out to sea in the area we are working. The FOO then did an amazing thing by overlaying the new map readings over the old map – it was amazing how accurate the old map still is!

You can find out more about early navigation and see maps made a long time ago here.

Coast & Geodetic Survey

Soundings (depth readings)

For information about prior work done in this area visit the NOAA photo library.

The need for accurate navigation information is as important now as it was back then. Personal and commercial craft need to know where it is safe and where it is dangerous. The FOO and I talked about how nice it would be someday to have a holographic representation of an area you are navigating (whether it is sea, lake, or river) that would allow you to see the bottom of the sea, the coastline, and the cloud layers. Maybe future mariners, oceanographers, and technicians can make that available for everyone.

Questions of the Day

Topic 1: There are additional corrections that the survey team includes in the analysis of the tracking data. Besides velocity of sound readings, what other data about the water in an area would be important to take into account? Hint: The moon has something to do with it.

Topic 2: Where can you earn a certificate in Geographic Information Systems (GIS), or a degree is Geology or Oceanography in the Northwest? Where else can you learn about GIS? Where can you learn the skills you need to work with the engineering crew, deck crew, or the Officer Corp in NOAA?

Topic 3: Can you name the earliest cartographer of this area, and when he did his work? Who else has surveyed this area?

July 18, 2007April 1, 2021

Richard Coburn, July 18, 2007

NOAA Teacher at Sea
Richard Coburn
Onboard NOAA Ship Rainier
July 17 – August 1, 2007

Mission: Hydrographic Survey
Geographic Region: Alaska
Date: July 18, 2007

Weather Data from the bridge

Visibility: 10 Nautical Miles
Wind directions: 325 degrees
Wind Speed: 10 Knots
Sea Wave Height: 1-2 feet
Seawater Temperature 13.9 degrees Celsius
Sea level Pressure: 10009.2 millibars
Cloud cover: Partly Cloudy

Science and Technology log

Most days start at 6:30 am with breakfast served promptly at 7:00. We then get our protective gear on for our days work on the smaller boats. The gear consist of what is called a “float coat” which is basically a brightly orange colored jacket designed to keep the wearer afloat and warm in the water should they accidentally fall in. We also wear hard hats and when hoisting the launch, a life jacket, and ear protection (the diesel engines are very loud when underway). The boats are located on top of the ship and they are lowered into the water using a series of hoists or cranes depending on the boat and where they are located.

At 8:00 am there is a morning meeting on the fantail of the ship (this is a large area on the back of the vessel). The meeting involves most of the senior officers as well as the crew that will be directly involved in the day’s operation. The commanding officer speaks first, he will give everyone data regarding the weather and his best guess as what to expect out on the water he then turns the meeting over to another officer who will detail the plans that he has worked on more fully with the rest of the crew. Lastly the chief engineer will recount the basics of what boat will launch first and reiterate the constant vigilance regarding safety.

I feel very comfortable on the water and extremely safe with this crew. This is likely because of the constant checking and rechecking of systems and personnel that continually occurs. The entire crew is mindful that the safety of one depends upon the persistent and sometimes annoyingly extreme attention to detail. Accidents most often happen when people get too lax or over confident, are tired or in a rush. Accidents even happen when none of the situations are present which is why the constant mindfulness is so important.

This is a truly collaborative effort. If one person in the lineup fails to do their job the mission risks failure: someone else has to step in and do the job of the person missing as well as their own. Deck hands ensure that the boat is fueled and has the necessary equipment on board and is in working order. Engineers check the engines and the electrical equipment and the kitchen staff prepare the lunches and snacks to take on board. When the launches are out they are usually deployed for the whole day. Everything must be ready in the launch for the entire day otherwise the mission risks failure.

Andy (an intern from Penn State) monitors the computer screens to ensure that the data collected is valid and usable. This picture is from the interior of the launch.

Our job on most days is to get on the launch and survey the area that the larger ship could not safely operate in. The larger ship the RAINIER takes up far too much draft (the water the hull displaces when the boat is underway). This does not mean that the RAINIER is simply sitting idly by while the launches do the work. The ship also runs back and forth patterns in the area and it too collects data. The larger and smaller launches are always on the lookout for any hazards to navigation, other boats or any marine life-like a whale and make sure that collisions do not occur.

TAS Redlinger underway for the morning survey

Once we arrive at the survey area we need to prepare the CTD cast. CTD is a device that measures the conductivity, temperature, depth, and salinity of the water about to be surveyed. This establishes a baseline for the work in the area. If a survey is going longer than four hours a new baseline must be established. This test establishes a sound profile that shows exactly how the fast the sonar beams travel in the water under the specific conditions at the time. This information is critical to maintain accurate and credible data. The procedure is simple, first, the CTD is attached to a rope turned on and warmed up, next the device is lowered in the water and data is collected. It is then lowered to the bottom of the sea and more data is collected. Once the CTD is brought back from the ocean, the information is then uploaded to a computer on board and a new baseline is established. This information is then embedded into the sonar data collected for the day’s survey. All information collected is held against this baseline to ensure the delivery of clean, accurate information for the new charts.

Tide marker on the left of boat, me facing coxswain and biologist. We stopped to check out the tide monitoring equipment today.

The best part of this trip is that I traveled with another teacher who teaches Science in Oregon. TAS Redlinger is a wonderful lady who shared with me all of the photos she took while she was out too. Often we would spend time sharing what we had done the during the day and what was in store the following day.

July 17, 2007April 1, 2021

Ginger Redlinger, July 17, 2007

NOAA Teacher at Sea
Ginger Redlinger
Onboard NOAA Ship Rainier
July 15 – August 1, 2007

Mission: Hydrographic Survey
Geographical Area: Baranof Island, Alaska
Date: July 17, 2007

Weather Data from the Bridge
Temp: 56 degrees
Wave height: Negligible
Cloud: Cloudy and Fog
Visibility: ••• mile or less

Mariner word of the day: Strait A strait is a body of water – straight straits are straight bodies of water, but there are no wiggly straits. (Commanding Officer Noll provided today’s definition.)

Science and Technology Log

I got up early (0600 hours) to be sure to watch the crew navigate the ship from Peril Strait through Neva Strait, and then Olga Strait. Can you imagine navigating a 231 foot ship though a channel that is a slightly wider than the ship and its wake, with only 14 feet of water below the keel? Did you see the visibility distance in the conditions report? Imagine how difficult it would be to see another ship approaching! Well, these people are professionals. The deck hands steered the ship and watched from the decks with binoculars to catch any movement or objects on the surface of the water. The officers monitored two radar screens and checked the bearings constantly as they approached navigation markers. They checked their route on the gyroscope compass to be sure they were not drifting. They constantly communicated with each other in their own terminology so everyone knew exactly who was doing what and where the ship was at all times. Needless to say, the margin of error for passing through VERY narrow straits is small. The crew made a difficult navigation task looks easy. This crew, deck hands, engineering, electronics, stewards, survey crew, and officers are exemplary. I wish I could describe how well they work as a team – and I will try to help my students understand how important it is to work as a team –everyone has an important job to do.

The massive ship being loaded with supplies

When the fog cleared a bit I was able to see a variety of jellyfish in the water off the side of the ship. A junior officer told me that when we drop anchor I will see more jelly fish than I can imagine. I just hope my supply of camera batteries holds out! We will be entering deeper water in a few hours were I will be able to test my sea legs. (Which means that I will find out whether or not I will be seasick, or if will I be ok.) When we enter the sea beyond the bays, harbors, and straits that are protected from the seas constant motion, the boat will begin to move up and down and side to side with the waves and swells. After reading about the experiences of other Teachers at Sea, I decided to go the safe route and begin taking seasickness medicine ahead of time. Does that make me Pollo Del Mar? (Chicken of the Sea – just a little chiste (joke) there!)

If you want to follow our journey on a map start at Juneau, go south to Gastineau Channel then head through Stephen’s Passage, north to Peril Strait, then west through Neva and Olga Strait. Pass Stika then head towards Biorka Island. From this area we will head to our hydrography starting location and work as we travel.

A multibeam sonar transducer is installed on the bottom of the hull that will send signals to the ocean bottom and receives the data when it bounces back. How does it work? Commanding Officer Noll describes it best, “The multibeam sonar precisely measures the time and angle of transmission/reception of the sound signal. The ConductivityTemperature-Depth (CTD) casts help us determine the speed of sound, which more or less allows us to apply Snell’s Law layer-based corrections to the ray-tracing of the sound vector that results. The data is converted to a picture of the bottom of the ocean.” Here is a picture of the transducer on the hull of the ship. It is on the bottom of the ship’s hull, between the two posts that are holding the ship off the ground.

You may be asking, “why take speed of sound readings in the water before you survey?” Well, the speed of sound changes with the depth of the water so readings that pass through different layers have different velocities. Accounting for those changes by correcting the data creates more accurate charts and maps. For more information about Snell’s Law and the refraction of sound waves, visit here. The ship runs a 24-hour hydrography work schedule. The boat and crew will continue to collect and process data all day and night. This means that everyone will be working hard the entire time. If you would like to see a short animation clip of this work – click on this link.

Questions of the Day

How much faster does sound travel in the water than in the air? Why is the velocity of sound faster in deeper waters than at the surface? When you are mapping a deep part of the ocean, what impact would the changing velocity of sound have on the time it takes to travel from the transducer to the bottom, and back to the top again?