Tag: bathymetry

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Denise Harrington: The Best Day Ever, April 30, 2014

NOAA Teacher at Sea
Denise Harrington
Aboard NOAA Ship Rainier
April 20 – May 3, 2014

Mission: Hydrographic Survey

Geographical Area of Cruise: North Coast Kodiak Island

Date:  April 30, 2014, 11:44 a.m.

Location: 58o  03.175’ N  127o 153.27.44’ W

Weather from the Bridge: 6.3o C (dry bulb), Wind 5 knots @ 250o, clear, 1-2′ swell.

Our current location and weather can also be seen at NOAA Shiptracker: http://shiptracker.noaa.gov/Home/Map

Science and Technology Log

The last couple of days have been the best ever: beautiful weather, hard work, deep science. We acquired data along the continental shelf and found a cool sea floor canyon and then set benchmarks and tidal gauges.

In hydrography, we gather data in seven steps, by determining: our position on Earth, depth of water, sound speed, tides, attitude (what the boat is doing), imagery and features.  Step 1 is to determine where we are.

In this picture you can see a GOES satellite antenna and a GPS antenna that helps us determine our precise location.
In this picture you can see a GOES satellite antenna (square white one) that is used to transmit tide data ashore and a GPS antenna (the small white eggs shaped one) that provides the tide gauge with both position and UTC time. Photo by Barry Jackson
In this picture Brandy Geiger, Senior Survey Technician, uses the GOES from various locations to determine the exact location of the tide gauge.
In this picture Brandy Geiger, Senior Survey Technician, uses GPS to record the positions of the benchmarks we have just set for the tide gauge. Photo by Barry Jackson
tide gauge install 023
Where we are happens to be the most beautiful place on earth. Photo by Barry Jackson

 

In Step 2, we determine the depth of the water below us.

Bathymetry is a cool word that means the study of how deep the water is.  Think “bath” water and metry “measure.”  When your mom tells you to get out of the tub, tell her to wait because you’re doing bathymetry.

As I explained in my first blog, we measure depth by sending out a swath of sound, or “pings,” and count how long it takes for the pings to return to the sonar, which sits beneath the ship or smaller boat.

Yesterday we used the multi-beam sonar to scan the sea floor.  Here is a screen shot of the data we collected.  It looks like a deep canyon, because it is!

Here is the image of the trench Starla Robinson, a Senior Survey Technician, and I discovered. We decided it should be named Denla Canyon, after us.
Here is the image of the sea floor canyon Starla Robinson, a Senior Survey Technician, and I discovered. We decided it should be named Denla Canyon, after the two scientists who discovered it.

Here I am, gathering pings.

Here I am talking with "the bridge," the team responsible for navigating the ship while surveyors collect data.
While collecting data, I kept in contact with “the bridge,” the team responsible for navigating the ship, by radio to ensure the ship’s safety and maximum, quality data acquisition.     Photo by Starla Robinson

 

Step 3, we take into consideration the tide’s effect on the depth of the water.  Tides are one predictable influence on water depth. There are over 38 factors or “constituents” that influence the tides.  The gravitational pull of the sun and the moon at various times of the day, the tilt of the earth, the topography, and many other factors cause water to predictably bulge in different places on earth at different times. The Rainier crew works 24 hours a day and 7 days a week, so they must find a way to measure depth throughout the days and month, by taking into account the tide. Arthur Doodson, who was profoundly deaf, invented the Doodson Numbers a system taking into account the factors influencing tide in 1921. Flash forward to the 21st century, our Commanding Officer, Commander Rick Brennan worked with a team of NOAA scientists to develop a software program called TCARI, as an alternate method to do tide adjustments, taking into account 38 factors, even the moon’s wobble. Inventions abound at NOAA.

The Rainier crew worked for 14 hours today to set up a tide gauge station, an in depth study of how the tide affects our survey area.  On this map, there is a Red X for each tide gauge we will install.  This process only happens at the beginning of the season, and I feel fortunate to have been here–the work we did was….amazing.

 

Each Red X is approximately where a tide gauge will be installed. The one we installed today in Diver's Bay is in the north west corner of the sheet map.
Each Red X is approximately where a tide gauge will be installed. The one we installed today in Driver Bay is in the north west corner of the sheet map.

You can see an animation here that shows the combined effect of two sine waves that produce a signal like our tide data.  Just imagine what it looks like when you factor in 38 different variables.

The earth goes around the sun in 24 hours and moon goes around the earth in a little more than 12 hours, much like these two gray sine waves. Interestingly, when you add two different waves, you get the wonky blue sine wave, with ups and downs. This combined effect of the sun and the moon (two dots) causes the ups and downs of the tide (blue wave). Graph taken from Russell, D. Acoustics and Vibration Animation, PSU, http://www.acs.psu.edu/drussell/demos/superposition/superposition.html.

 

Low tide is the best time to see sea stars, mussels and barnacles, but it is also a more hazardous time in the tidal cycle for mariners to travel. Therefore, navigational charts use the mean lower low water level, low tide, for the soundings, or depth measurements on a chart.  The black numbers seen on a nautical chart, or soundings, represent depth measurements relative to mean lower low tide. Driver Bay, the area on the chart where we installed the tide gauge today, is the crescent shaped bay at the northwest end of Raspberry Island.

This is a nautical chart used to help mariners navigate safely.
This is a nautical chart used to help mariners navigate safely.

Installing Tide Gauge Stations

Before gathering sonar data, ground and boat crews install a tide gauge to measure changes in water level and to determine the mean lower low water level datum. A tide gauge is a neat device that has air pumped into it, and uses air pressure, to determine how deep the water is.   The tide gauge uses a formula of (density of sea water)(gravity)(height) = pressure.  The gauge measures pressure, and we apply factors for gravity and sea water.  The only missing factor is height, which is what we learn as the gauge collects data.  This formula and nuances for particular locations is a fascinating topic for a blog or master’s thesis.  Scientists are looking for tidal fluctuations and other location specific variances. Then, by computer they determine the mean lower low tide depth, factoring in the tidal fluctuations.

There are permanent tide gauge stations all over the world.  The nearest permanent tide gauge station to our study area is in Kodiak and Seldovia.  These permanent gauges take into account many factors that affect tides over a 19 year period of time, not just the gravitational pull of the moon.

The tide gauge stays in place for at least 28 days (one full tidal cycle).  During the month, data of the tides is collected and can be compared to the other tide gauges we install.

Installing the Tide Gauges and Benchmarks

Excitement built as the crew prepared for the “Tide Party,” packing suitcases full of gear and readying the launches.  Installing Tide Gauges signals the beginning of the season and is one of the few times crew gets paid to go on shore.

 

Why Bench Mark?

There are three reasons I have figured out after many discussions with patient NOAA crew as to why we put in bench marks.

 

I installed this benchmark by having a hole drilled in bedrock and affixing the benchmark with concrete if anyone ever returns and needs to know their exact location.
I installed this benchmark in Driver Cove by having a hole drilled in bedrock and affixing the benchmark with concrete if anyone ever returns and needs to know their exact location. Photo by Barry Jackson

The first reason we install benchmarks is to provide a reference framework to ensure both our tide staff and the tide gauge orifice are stable and not moving relative to land.  The second reason is if we ever come back here again to gather or compare data to previous years, we will know the elevation of the tidal datum at this location relative to these benchmarks and can easily install a new tide gauge.  The third reason is that the earth and ocean floor changes constantly.  As scientists, we need to make sure the survey area is “geologically stable.”  We acquire several hours of GPS measurements on the primary benchmark to measure both its horizontal and vertical position relative to the earth’s  reference frame.  Should there ever be an earthquake here, we can come back afterwards and measure that benchmark again and see how much the position of the Earth’s crust has changed.  After the last big earthquake in Alaska, benchmarks were found to move in excess of a meter in some locations!

Teacher on Land Polishing Her Benchmark Photo by Brandy Geiger
Teacher on Land
Polishing Her Benchmark
Photo by Brandy Geiger

Installing the Benchmark

Today, our beach party broke into two groups.  We located stable places, at about 200 foot intervals along the coastline.  We drilled 5 holes on land and filled them with concrete.  A benchmark is a permanent marker you may have seen at landmarks such as a mountain peak or jetty that will remain in place for 100 years or more.  We stamped the benchmark by hand with a hammer and letter stamps with our station identification.   If we chose a good stable spot, the benchmark should remain in the same location as it is now.

Tide Gauge

As one group sets up benchmarks, another group installed the tide gauge.

 

Here, Chief Jim Jacobson, Lead Survey Technician, sets up a staff, or meter stick, I used to measure the change in water depth and others used for leveling.
Here, Chief Jim Jacobson, Lead Survey Technician, sets up a staff, or meter stick, I used to measure the change in water depth and others used for leveling.  Photo by Barry Jackson

To install the tide gauge, you must have at least three approved divers who install the sensor in deep water so that it is always covered by water.  Because there were only two crew on board trained to dive, Lieutenant Bart Buesseler, who is a dive master, was called in to assist the team.   The dive team secured a sensor below the water.  The sensor measures the water depth with an air pressure valve for at least 28 days.  During this time there is a pump on shore that keeps the tube to the orifice pressurized and a pressure sensor in the gauge that records the pressure. The pressure is equal to the number of feet of sea water vertically above the gauge’s orifice. An on-board data logger records this data and will transmit the data to shore through a satellite antenna.

Divers install the tide gauge, and spent most of the day in the cold Alaska waters. Good thing they were wearing dive suits! Photo by Barry Jackson
Divers install the tide gauge, and spent most of the day in the cold Alaska waters. Good thing they were wearing dive suits! Photo by Barry Jackson

Leveling Run

After the gauge and benchmarks are in place, a group does a leveling run to measure the benchmark’s height relative to the staff or meter stick.  One person reads the height difference between 5 different benchmarks and the gauge. Then they go back and measure the height difference a second time to “close” the deal.  They will do the same measurements again at the end of the survey in the fall to make sure the survey area has not changed geographically more than ½ a millimeter in height!  Putting the bubble in the middle of the circle and holding it steady, leveling, was a highlight of my day.

Observation

Finally, a person–me– watches the staff (big meter stick above the sensor) and takes measurements of the water level with their eyes every six minutes for three hours.  Meanwhile, the sensor, secured at the orifice to the ocean floor by divers, is also measuring the water level by pressure. The difference between these two numbers is used to determine how far below the water’s surface the orifice has been installed and to relate that distance to the benchmarks we have just leveled to.  If the numbers are consistent, then we know we have reliable measurements.  I won’t find out if they match until tomorrow, but hope they do.  If they don’t match, I’ll have to go back to Driver Bay and try again.

As we finished up the observations, we had a very exciting sunset exit from Raspberry Island.  I was sad to leave such a beautiful place, but glad to have the memories.

Last minute update: word just came back from my supervisor, Ensign J.C. Clark, that my tidal data matches the gauge’s tidal data, which he says is “proof of my awesomeness.” Anyone who can swim with a car battery in tow is pretty awesome in my book too.

The data Starla Robinson and I collected is represented by the red line and the data the gauge collected is represented by the blue line. The exact measurements we collected are on the table.
The data Starla Robinson and I collected is represented by the red line and the data the gauge collected is represented by the blue line. The exact measurements we collected are on the table.

Spotlight on a Scientist

Lieutenant Bart Buesseler came to us straight from his family home in the Netherlands, and before that from his research vessel, Bay Hydro II.  The main reason our CO asked him to leave his crew in Chesapeake Bay, Maryland, and join us on the Rainier is because he is a dive master, capable of installing our sensors under water, and gifted at training junior officers.

 

Lieutenant Beusseler knows he needs to be particularly nice to Floyd Pounds, an amazing cook from the south who cooks food from every corner of our ocean planet.
Lieutenant Beusseler knows he needs to be particularly nice to the amazing chefs aboard Rainier, including Floyd Pounds, who cooks food from every corner of our ocean planet with a hint of a southern accent.

During his few years of service, LTJG Buesseler adventured through the Panama Canal, along both coasts of North America, and has done everything from repairing gear to navigating the largest and smallest of NOAA vessels through very narrow straits.  He loves the variety: “if I get tired of one task, I rotate on to another to keep engaged and keep my mind sharp.”  He explains that on a ship, each person is trained to do most tasks.  For example, he says, “during our fast rescue boat training today, Cal led several rotations. But what if he is gone? Everyone needs to be ready to help in a rescue.”  Bart says at NOAA people educate each other, regardless of their assignments, “cultivating information” among themselves. Everyone is skilled at everything aboard Rainier.
In the end, he says that all the things the crew does are with an end goal of making a chart.   His motto? Do what you love to do and that is what he’s doing.

Personal Log

Today was a special day for me for many reasons.  It is majestic here: the stark Alaskan peninsula white against the changing color of the sky, Raspberry Island with its brown, golden, crimson and forest green vegetation, waterfalls and rocky outcroppings.  I’m seeing whales, Puffins, Harlequin Ducks and got up close with the biggest red fox ever.  Most importantly, I felt useful and simultaneously centered myself by doing tide observations, leveling and hiking.  I almost dove through the surf to make it “home” to the ship just in time for a hot shower. Lieutenant Buesseler’s reference to “cultivating information” rings very true to me.  In writing these blogs, there is virtually nothing I came up with independently.  All that I have written is a product of the patient instruction of Rainier crew, especially Commander Brennan. Each day I feel more like I am a member of the NOAA crew here in Alaska.

 

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Marla Crouch: Gumbi Marla and Setting Course, June 18, 2013

NOAA Teacher at Sea
Marla Crouch
Aboard NOAA Ship Oscar Dyson
June 8-26, 2013  

Mission: Pollock Survey
Geographical area of cruise: Gulf of Alaska
Date: June 18, 2013

Weather Data from the Bridge: as of 1900
Wind Speed 13.48 kts
Air Temperature 7.0°C
Relative Humidity 99.00%
Barometric Pressure 1,010.00.5 mb

Latitude:  54.31N   Longitude: 159.80W

Science and Technology Log

Another fashion statement – Gumbi Marla

Here I am, all zipped up in my immersion suit.
Here I am, all zipped up in my immersion suit.

I’ve donned an immersion suit, also known as a survival suit.  One of the first things I did when I came aboard was to locate this suit and my life vest, two pieces of equipment that save lives.  In the event we had to abandon ship, the survival suit would keep me both warm and afloat until rescue.  During our evacuation drill we needed to unpack and get into the suit, and be completely zipped up in 60 seconds or less.  Getting into the suit was much easier after I took my shoes off, as the soles caught on the fabric of the suit.  The suit is made of neoprene, which was invented in 1930.  SCUBA wetsuits are also made of neoprene, and even some laptop and tablet cases.

In an earlier blog I talked about the CTD being used to calibrate the sonar aboard the Oscar Dyson, but not all technologies on the Dyson are as high tech as the CTD and sonar equipment.  In fact you can build a weather station at home that is similar to some of the equipment used by the Dyson’s crew.  Below is a picture of a hygrometer.  There are actually two hygrometers aboard, one is located on each side of the bridge.  Hygrometers are used to measure relative humidity (how much moisture is in the air).   Also pictured is the wind bird which shows the direction the wind is moving.  The propeller was actually turning rapidly when the picture was taken.  The camera was able to “stop” the action.  The wind bird is mounted atop the jack staff, high above the bow.

Hygrometers are weather instruments used to measure relative humidity.
Hygrometers are weather instruments used to measure relative humidity.

Wind bird

The following link shows you how to build six instruments for monitoring the weather.

http://oceanservice.noaa.gov/education/for_fun/BuildyourownWeatherStation.pdf

If you checked out the above link, how many snow days to you think the kids in North Dakota had?

Did you check out ship tracker?  If you did, the screen shot below will look familiar.  The blue lines in the water display the Dyson’s course.  Each segment of the course is called a transect.  Transects are numbered, enabling scientists to easily reference a location.

Oscar Dyson's course as of 6 18 13
Oscar Dyson‘s course as of 6 18 13

Are you wondering why we have traveled in rectangular patterns?  The scientists establish this course for a several reasons:

  1. Transects run perpendicular to the coast line, covering a wide range of bathymetry over the shortest distance.
  2. Regularly spaced transects (as opposed to randomly spaced or scattered) are correlated with historical data, and are the best way to describe the distribution of pollock.
  3. The combination of transects collects sufficient data to allow scientists to estimate the overall size of the pollock population with a high degree of certainty.

Does anyone have an idea about the meaning of “bathymetry” and a “leg”?  No, in this case a leg is not something you stand on.  Bathymetry is the shape and depth of the ocean floor, and a bathymetry contour line on a chart connects points of equal depth (like a topographic map).  A leg, in this context, is a segment of the overall distance covered in the survey.

The information collected during this year’s survey helps determine the number of pollock that can be caught in next year’s fishing season.

Here is the ship tracker link, you can check out the Dyson’s course and other NOAA ships as well.

http://shiptracker.noaa.gov/shiptracker.html

Personal Log 

I want to revisit the sonar of Mystery Mix One.  In my last blog I talked about what was happening near the surface of the ocean.  This time I want to focus beneath the sea floor.

Graphic provided by NOAA
Graphic provided by NOAA

Look beneath the red, yellow, and green bands, depicting the sea floor, at the blue color, notice how the density of color changes over time.  The density of the color tells scientists about the composition of the sea bed.  The denser the color, the denser or harder the seafloor is likely to be; probably, the places with the dark, dense color are rocky areas, which attract the fish schools seen in the water above.

Looking at this graph reminds me of an experiment that my husband worked on, when he worked for Charles Stark Draper Labs, in Boston, MA.  He worked on a Gravity Gradiometer that was sent to the moon on Apollo 17.  The gradiometer measured the changes in gravity.  The changes in gravitational strength give scientists information about what lays beneath the moon surface, like the sonar provides information about the sea bed.  The Gravity Gradiometer was a very specialized version of equipment that is commonly used in prospecting for oil on Earth.  I am sharing this story because, in class, one of our foci is to take what we know and apply the knowledge to a new scenario.  Next question:  Where will what we know now, take us in the future?

Did You Know?

Some fish can see color.

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Kaitlin Baird: The Importance of Sound, September 16, 2012

NOAA Teacher at Sea
Kaitlin Baird
Aboard NOAA Ship Henry B. Bigelow
September 4 – 20, 2012

Mission: Autumn Bottom Trawl Survey with NOAA’s Northeast Fisheries  Science Center
Geographical Area: Off the Coast of Maryland
Date: September 16th
.

Location Data:
Latitude: 37’72.10
Longitude: 75′ 17.02

Weather Data:
Air Temperature: 21.0 (approx.70°F)
Wind Speed: 8.71 kts
Wind Direction:  West
Surface Water Temperature: 22.99 °C (approx. 73°F)
Weather conditions: overcast

Science and Technology Log:

It’s day 13 aboard the Henry B. Bigelow and we have made the turn at our southern stations off the coast of North Carolina and are working our way back to port at some of our inshore stations off the coast of Maryland. You may wonder how each of the stations we sample at sea are chosen? The large area of Cape May to Cape Hatteras are broken into geographic zones that the computer will assign a set amount of stations to, marking them with geographic coordinates. The computer picks a set number of stations within each designated area so all the stations don’t end up all being within a mile of each other. Allowing the computer system to pick the points removes human bias and truly keeps the sampling random. The vessel enters the geographic coordinates of the stations into a chartplotting program in the computer, and uses GPS, the Global Positioning System to navigate to them.  The GPS points are also logged on a nautical chart by the Captain and mate so that they have a paper as well as an electronic copy of everywhere the ship has been.

You may wonder, how does the captain and fishermen know what the bottom looks like when they get to a new point? How do they know its OK to deploy the net? Great question. The Henry B. Bigelow is outfitted with a multibeam sonar system that maps the ocean floor.  Some of you reading this blog might remember talking about bathymetry this summer. This is exactly what the Bigelow is doing, looking at the ocean floor bathymetry. By sending out multiple pings the ship can accurately map an area 2.5-3 times as large as its depth. So if the ship is in 20 meters of water it can make an accurate map of a 60 meter swath beneath the boats track. The sonar works by knowing the speed of sound in water and the angle and time that the beam is received back to the pinger . There are a number of things that have to be corrected for as the boat is always in motion. As the ship moves through the water however, you can see the projection of the bathymetry on their screen below up in the wheelhouse. These images help the captain and the fisherman avoid any hazards that would cause the net or the ship any harm.  A good comparison to the boats multibeam sonar, is a dolphins ability to use echolocation. Dolphins send their own “pings” or in this case “echos” and can tell the location and the size of the prey based on the angle and time delay of receiving them back. One of the main differences in this case is a dolphin has two ears that will receive and the boat just has one “receiver”. Instead of finding prey and sizing them like dolphins, the ship is using a similar strategy to survey what the bottom of the sea floor looks like!

bathymetric data being collected by multibeam sonar technology on the Bigelow
Bathymetric data being collected by multibeam sonar technology on the Bigelow
Bigelow multibeam sonar (NOAA)
echolocation schematic courtesy of the Smithsonian Institute
Echolocation schematic courtesy of the Smithsonian Institute

Personal Log:

The last few days I have been trying my hand at removing otoliths from different species of fish. The otoliths are the ear bones of the fish. Just like the corals we have been studying in Bermuda, they are made up of calcium carbonate crystals. They are located in the head of the bony fish that we are analyzing on the cruise. A fish uses these otoliths for their balance, detection of sound and their ability to orient in the water column.

If you remember, at BIOS, we talk a lot about the precipitation of calcium carbonate in corals and how this animal deposits bands of skeleton as they grow. This is similar in bony fish ear bones, as they grow, they lay down crystalized layers of calcium carbonate. Fisheries biologist use these patterns on the otolith to tell them about the age of the fish. This is similar to the way coral biologists age corals.

I have been lucky enough to meet and learn from scientists who work specifically with age and growth at the Northeast Fisheries Science Center Fishery Biology Program. They have been teaching about aging fish by their ear bones. These scientist use a microscope with reflected light to determine the age of the fish by looking at the whole bone or making slices of parts of the bone depending on what species it is. This data, along with lengths we have been recording, contribute to an age-length key. The key allows biologists to track year classes of the different species within a specific population of fish. These guys process over 90,000 otoliths a year! whew!

The information collected by this program is an important part of the equation because by knowing the year class biologists can understand the structure of the population for the stock assessment.  The Fishery Biology program is able to send their aging and length data over to the Population Dynamics Branch where the data are used in modeling. The models, fed by the data from the otoliths and length data,  help managers forecast what fisheries stocks will do. It is a manager’s job to the take these predictions and try to balance healthy fish stocks and the demands of both commercial and recreational fishing. These are predictive models, as no model can foresee some of the things that any given fish population might face any given year (ie food scarcity, disease etc.), but they are an effective tool in using the science to help aid managers in making informed decision on the status of different fish stocks. To learn more about aging fish please visit here.

otoliths (fish ear bones) that i removed from a Butterfish
Otoliths (fish ear bones) that I removed from a Butterfish
You can see here is an otolith that is 1+ years old. It was caught in September and that big 1st band is its Year 0. You can see that the black dot demarks the fish turning 1. You can then see the Summer growth but not yet the winter growth. This fish has not yet turned 2, but it will Jan 1st of the next year.
You can see here an otolith that is 1+ years old. It was caught in September and that big 1st band is its Year 0. You can see that the black dot demarks the fish turning 1. You can then see the Summer growth but not yet the winter growth. This fish has not yet turned 2, but it will be Jan 1st of the next year.

I have to end with a critter photo! This is a Cobia (Rachycentron canadum).

Me and a Cobia caught off the coast of Maryland
Cobia caught off the coast of Maryland

Thanks for reading!

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Marsha Skoczek: Plotting Our Course, July 15, 2012

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.

Planned acoustic survey lines

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.

Echogram of ridge

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.

Completed multibeam image

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

This is the engine monitoring station.

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.

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.  

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Staci DeSchryver: A Front Row Seat to the Bottom of the Ocean, August 12, 2011

NOAA Teacher at Sea
Staci DeSchryver
Onboard NOAA Ship Oscar Dyson
July 26 – August 12, 2011 

Mission: Pollock Survey
Geographical Area:  Gulf of Alaska

Location:  Kodiak, AK
Heading: back to the docks
Date: August 12, 2011

Weather Data From the Bridge: N/A

Science and Technology Log

My last night on the Oscar Dyson was a busy one!  Because our trip was cut so short, we had to “break protocol” so to speak.  Typically, nighttime operations consist of seafloor mapping (which I will get to in a minute), and do not consist of trawling for Pollock.  For science students, you probably have a good idea why – running operations only in the daytime means that the experiment is controlled.  Since Pollock behave differently in the night-time, it is important to only run operations when their behavior is consistent.  However, because we were so short on time, we had to make a “run” for the shelf break that got us to the area well after dark.  So we got to do one more trawl!  This one was the best kind, in my humble opinion.  We completed a bottom trawl, which means that the net went almost down to the bottom of the ocean – within a couple of meters.  The reason why bottom trawls are so neat is because there are plenty of ocean critters down there that the average Joe doesn’t get to see on a daily basis.  Of course, the scientists do their absolute best to catch only Pollock to minimize bycatch, but one or two fish of different species are difficult to avoid.  On this trawl, we had a few jellies, two Pacific Ocean Perch, and a Herring.  We finished late – right around one in the morning.  At that time, we began our night-time operations.

Night time operations are run by Dr. Jodi Pirtle.   Dr. Pirtle is a Post-Doctoral Research Associate at the University of New Hampshire  Center for Coastal and Ocean Mapping.  Her research is a collaborative effort between the UNH CCOM and the NOAA Alaska Fisheries Science Center.   Even though Jodi is traveling all the way from New Hampshire,  she is actually very close to home right now.  She is quite connected to the Alaska fisheries – she grew up in Alaska, and has both family and friends who are involved in the commercial fishing industry.  The fisheries hold a place very close to her heart, and her passion for her current line of work is well evident.

So, why, then, does Dr. Pirtle work in the cover of night?

acoustics lab
Here, the scientists are working in the acoustics lab on daytime operations. As you can see, most of the electronic equipment is used during the day. At night, Dr. Pirtle gets the opportunity to chart her own path and select an area to map without interfering with the ship's primary operations.

At first I suspected it was some sort of secret service operation, but the reality is much more strange and explainable.  Her line of work is a side project on the Oscar Dyson, which means that she can work when the ship is not working for its primary purposes.  Hence, she works from 6pm until 6am.   One focus of her research is to identify whether or not certain areas of the Gulf of Alaska are trawlable or untrawlable by the Alaska Fisheries Science Center bottom-trawl survey for groundfish.   How is an area determined to be untrawlable?  Let’s say, for example, there is a commercial fishing ship somewhere in the Gulf of Alaska.  This ship decides to do a similar trawl as the one that I did earlier this evening, but they use a net that makes contact with the seafloor because they are fishing for groundfish species – say, Rockfish, for example.  But, something happens.  When the net comes up, it is all torn up – as though it got caught on a series of rocks or ledges.  In order to warn other ships of the dangers of losing a very expensive net, the fisherman deems the area “untrawlable.”  It’s kind of like putting caution tape around the area.

Untrawlable areas are problematic for scientists because every area deemed untrawlable is an area where they can’t sample with the bottom-trawl gear.  For example, a large component of the groundfish fishery are several species of rockfish (Sebastes spp.) that associate with a rocky habitat.  Rockfish are delicious with garlic and butter, but they are sneaky little guys because they like hanging out around rocks (who knew?).  Many rockfish could be in areas that are untrawlable, but scientists would never know because it is inadvisable to tow a bottom-trawl net in the area to find out.  In a sense, untrawlable areas are a source of error, or uncertainty in the population estimate for species of groundfish in those areas.  This is where Dr. Pirtle’s research starts.

A few years ago, a group did research in an area called Snakehead Bank – a location previously deemed to be untrawlable.  They wanted to tighten the definition of “untrawlable.”  For example, there is a possibility that an untrawlable area is covered with steep cliffs, many sharp, large rocks, and impossibly tough relief.  However, there is also the possiblity that the area is relatively flat and trawlable, but the fisherman was just unlucky enough to drag his or her net over a rogue boulder that found its way onto the vast, flat, continental shelf.  So, the scientists decided to see what kind of “untrawlable” this particular area was.   The group took the time to make a bathymetric profile of the area and couple that research with camera drops – video cameras that would make the trek to the bottom of the ocean and provide a second set of data for scientists to confirm what the bathymetric profile showed them.  From the camera drops and the bathymetry, the scientists determined that Snakehead bank was not completely untrawlable – in fact, most areas could support trawl nets without the risk of tearing the nets.  Dr. Pirtle is continuing with this important work.

One focus of the research is determining seafloor trawlability in the Gulf of Alaska using the same acoustic transducers that we use to catch fish in our daytime operations.  The fishery that the  survey is concerned about  is groundfish –   a general term that encompasses many species such as flatfish, cod, and rockfish.  These sneaky guys enjoy habitats that are associated with rocky areas, so we are not getting the best estimate of populations in those areas.  Dr. Pirtle is looking in to alternative methods to determine whether an areas of the seafloor is untrawlable or trawlable using the mulibeam sonar.  Not only is she looking for areas that can now be considered trawlable, she’s also using the data she collects to determine certain seafloor characteristics.  Hardness, roughness, and grain size are all data that can be collected using the acoustic transducers.  This information will help her to determine the relative trawlability of an area, as well.  Therefore, the groundfish survey benefits because she is either finding areas to be trawlable (thus, they can now sample there) or somewhat trawlable, which can tell them ahead of time that alternative sampling methods might be needed in a particular area.

Her research is also concerned with developing alternative sampling methods for untrawlable locations.  These methods could involve a combination of acoustic seafloor mapping to characterize seafloor habitats for groundfish, acoustic midwater data (to observe the fish that like to hang out on tall pinnacles and rocky banks) and, the most fun method – dropping a camera to the ground to identify species and biomass assessment (which is a fancy term for seeing how many fish are in a particular area).  Improved understanding of groundfish habitats can lead to better management models, and the work Dr. Pirtle is doing can also contribute to conservation of areas that are sensitive to fishing gear that touches the seafloor.

The area that Dr. Pirtle decided to survey this evening was an area that was deemed to be untrawlable surrounded by many trawlable areas.  These areas are often good candidates for mapping and camera surveys because both untrawlable and trawlable seafloor types are likely to be encountered, so the area can more easily be compared against existing data.  We began our transects – driving transects with the ship over the area while sending sound waves to the bottom of the ocean to figure out differing ocean depths and seafloor type.  Transect lines are close together and driven in a pattern similar to mowing a lawn, which gives Dr. Pirtle 100% coverage of her targeted area.  Dr. Pirtle selects a location to drop a CTD – Conductivity, Temperature, and Depth meter – usually in the middle of the mapped area.  The CTD is used to estimate sound speed in the location she is mapping.  This is important because ocean depth is measured by the amount of time it takes for a sound wave to leave the ship, bounce off the ocean floor, and return back to the ship.

This is a photograph of a halibut on the uncharted pinnacle discovered by Dr. Pirtle, similar to what I saw real-time on the camera late at night.

She then selects three to five areas to conduct camera drops.  The camera travels to the bottom of the ocean where she can see if the area is untrawlable or trawlable based on what the camera shows her.  I, on the other hand, get to see deep ocean critters in their habitats, which is also very cool.   There are two types of camera drops – ones that record the information and then get played back later, and real-time camera drops where we can literally watch the camera make the trek to the bottom of the ocean in real-time.  Dr. Pirtle uses the camera data to “groundtruth” or check the seafloor type against her acoustic map, to identify fish and other animals in the area, and to observe how species use the seafloor habitat.

As my shift was coming to a close, I could barely keep my eyes open, but I didn’t want to miss this.  Tonight, we dropped the live camera into the depths.  I stayed awake for the first drop so I could see what these operations looked like.  Dr. Pirtle expertly maneuvered the camera into the deep using something that looked much like an old-school Atari controller.

slide o' fun
This photograph shows Dr. Pirtle's work in combination - the area she surveyed is in the bottom right corner. The other three photos are snapshots of the surveyed area.

As the camera dropped, we saw a few pollock and some other unidentified neritic creatures, but the real fun started when we got to the bottom.  It was intense as Dr. Pirtle relayed information back to the bridge about the direction in which to travel, holding the ship still in the waves and currents when she wanted to examine an area more closely, and communicate with the technicians on the hero deck to relay the height that she wanted the camera held at.  We saw all sorts of interesting creatures on the ocean floor – some arrowtooth flounder, a halibut, and Pacific Ocean Perch.  We also observed beautiful cold-water corals and sponges that form a living component of seafloor habitat for many marine animals, including our target – rockfish.   We even saw a shark!  It was completely worth getting to bed a little bit later to see this incredible work in real-time.

unmapped pinnacle
This is the unmapped pinnacle discovered by Dr. Pirtle and her colleague! Now, seafloor maps have been updated to include this potentially dangerous sea hazard.

On a side note, in a previous leg of the survey, Dr. Pirtle and her colleague from UNH CCOM, Glen Rice,  found an underwater pinnacle that was later determined to be a navigational hazard!  This pinnacle came so close to the surface of the water that in a “perfect storm” of low tide and a large enough ship with a deep enough hull, it could have unknowingly collided with this unmapped pinnacle – which could have potentially been disastrous.  Glen, a NOAA hydrographer, was able to update the navigational charts in the area, alerting ships to the pinnacle’s presence.  It just further supports the idea that the our oceans are so vastly unexplored – there is so much we don’t know about the feature that takes up the biggest portion of our Earth!   I asked her if she named it because she discovered it – I quickly learned that just because you find something in the Ocean, it doesn’t mean you get to keep it.  Apparently, you can’t name it, either.  But I still called it Pirtle’s Pinnacle.  I think it has a nice ring.

Personal Log

It was a sad day today watching the scientists pack up and box and tag the lab equipment and computers.  As everyone bustled about, I spent some time hanging out for the last time on the bridge, in the galley, and in the fish lab thinking about my journey coming to its close.  Although we spent the majority of it tied to the dock, I am so grateful for the opportunities we experienced that we otherwise would not have – it was a blessing in disguise, because we really got to experience all of Kodiak, and much of the bays and inlets around the island from the ship.  The pictures will bring no justice to the beauty I’ve experienced in the last three weeks, whether it was walking along a beach with wild horses or staring in all directions to find nothing but water for as far as the eye could see.  I spent an hour one night on the bridge watching the Leonids streak across the sky – a front row and first class seat, in my opinion.  I never though that dodging whales would be an area of concern in my small life until we sailed through pods of them every day.  If you would have told me three years ago I’d be petting an octopus three weeks ago, I would have called you a fool.  If you would have told me three hours ago that this experience would be coming to a close three minutes from now, I would believe you even less.  In the last three weeks, I have never laughed harder, worked more eagerly, or learned more with and from these incredible individuals who call this ship Home.  As I quietly stood on the bridge watching the fast rescue boat dart off to the docks, I remembered the last time it was in the water watching carefully over us as we swam around the ship in our gumby suits.  As we drove silently through the still waters to the city docks, we bade farewell to the animals that accompanied us on our trips – otters, eagles, puffins, and even sea lions gathered around to see us off to our homes and families.  Or, they just so happened to be there looking for food and doing other instinctual things, but I do really think I saw an otter wave me goodbye.

whale!
Here is a whale "waving goodbye" with his fluke in the Gulf of Alaska - I will never forget the journey I had here!

Thank you so much to the crew and scientists of the Oscar Dyson – you fed my soul this summer and rejuvenated me in a way I never could have imagined.  I am more revived today than I was on the first day of my second year of teaching (because, let’s face it, the first day of your first year you spend most of your time trying not to vomit) and I owe it completely to the Teacher at Sea Program and to all of the fine people I got to work with.  To my partner in crime, Cat Fox – I’ll see you when we’re landlocked again!  It was a total blast working with you.  Thanks for always being there for a good laugh and for finding me so many salmon berries!  If you are wondering whether or not you should apply for this program in the 2012 season – this is the advice I will give to you:  JUST APPLY!  It will change your life – promise.

Until our next adventure,

Staci DeSchryver

Did you know…

While I was working my night shift, I got the opportunity to help Dr. Pirtle “log the turns” of the ship as it was “mowing the lawn” in the zigzag pattern.  This meant that I got to communicate with the bridge via radio every time they ended a transect and began turning in the opposite direction.  I’m sure you may have predicted that this was most certainly a highlight of my work.  It took great restraint on my part to behave myself with the radio, as everyone knows that radios can be a lot of fun.  I did, however, let a few nautical words fly on the airwaves up to the bridge, one of them being “Roger, Willco.”

I had no clue where the origin of the word “Roger” came from.  But now I do…

Roger, which starts with the letter R, means “Received”, which means, “I received your last transmission.”  A long time ago, the radio alphabet (you know, Alpha, Bravo, Charlie, Foxtrot, Whiskey, etc.) used Roger to represent the letter R.  It has since been changed to “Romeo.”  Adding Willco to the end, means “I received your transmission, and I WILL COmply.”   So saying that I received a message from the bridge and I was going to comply with it really made me look like a navigational moron – because they weren’t asking me to comply with anything.  But I still had fun.