Tag: hydroacoustics

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Johanna Mendillo: Hello pollock…. can you hear me now? August 7, 2012

NOAA Teacher at Sea
Johanna Mendillo
Aboard NOAA ship Oscar Dyson
 July 23 – August 10

Mission: Pollock research cruise
Geographical area of the cruise: Bering Sea
Date: Tuesday, August 7, 2012

Location Data from the Bridge:
Latitude: 59○ 52 ’ N
Longitude: 177○ 17’ W
Ship speed:   8.0 knots ( 9.2 mph)

Weather Data from the Bridge:
Air temperature: 7.3○C (45.1ºF)
Surface water temperature: 8.4○C (47.1ºF)
Wind speed:  4 knots ( 4.6 mph)
Wind direction: 75○T
Barometric pressure:  1018 millibar (1 atm)

Science and Technology Log:

We are wrapping up our final few sampling transects.  Now that you are practically fisheries biologists yourselves from reading this blog, students, we must return to the fundamental question— how do we FIND the pollock out here in the vast Bering Sea?  The answer, in one word, is through ACOUSTICS!

Look at all of these birds off the stern! Why do you think they are following us? Are we about to haul up a catch, perhaps?
Look at all of these birds off the stern! Why do you think they are following us? Are we about to haul up a catch, perhaps?

Hydroacoustics is the study of and application of sound in water.  Scientists on the Oscar Dyson use hydroacoustics to detect, assess, and monitor pollock populations in the Bering Sea.

Now, you may have heard of SONAR before and wonder how it connects to the field of hydroacoustics.  Well, SONAR (SOund Navigation and Ranging) is an acoustic technique in which scientists send out sound waves and measure the “echo characteristics” of targets in the water when the sound waves bounce back— in this case, the targets are, of course, the pollock!  It was originally developed in WWI to help locate enemy submarines!  It has been used for scientific research for over 60 years.

(PLEASE NOTE: The words sonar, fishfinders, and echosounders can all be used interchangeably.)

The transducer sends out a signal and waits for the return echo...
The transducer sends out a signal and waits for the return echo once it bounces off the fish’s swim bladder… (Source: http://www.dosits.org)

On the Dyson, there is, not one, but a collection of five transducers on our echosounder, and they are set at five different frequencies.  It is lowered beneath the ship’s hull on a retractable centerboard.  The transducers are the actual part of the echosounder that act like antennae, both transmitting and receiving return signals.

The transducers transmit (send out) a “pulse” down through the water, at five different speeds ranging from 18-200kHz, which equals 18,000-200,000 sound waves a second!

When the pulse strikes the swim bladders inside the pollock, it gets reflected (bounced back) to the transducer and translated into an image.

First of all, what is a swim bladder?  It is simply an organ in fish that helps them stay buoyant, and, in some cases, is important for their hearing.

Swim Bladder (Source: www.education.com)
Swim Bladder (Source: http://www.education.com)

Now, why do the pulses bounce off the swim bladders, you ask?  Well, they are filled mostly with air and thus act as a great medium for the sound waves to register and bounce back.

Think of it this way: water and air are two very different types of materials, and they have very different densities.  The speed of sound always depends on the material through which the sound waves are traveling through.  Because water and air have very different densities, there is a significant difference in the speed of sound through each material, and that difference in speed is what is easy for the sonar to pick up as a signal!

It is the same idea when sound waves are used to hit the bottom of the ocean to measure its depth- it is easy to read that signal because the change in material, from water to solid ground, produces a large change in the speed of the sound waves!

Here is a sonar system measuring the depth of the ocean...
Here is a sonar system measuring the depth of the ocean… (Source: http://www.dosits.org)

Interestingly, different types of fish have different shaped and sized swim bladders, and scientists have learned that they give off different return echos from sonar signals!  These show up as slightly different shapes on the computer screen, and are called a fish’s “echo signature”.  We know, however, that we will not encounter many fish other than pollock in this area of the Bering Sea, so we do not spend significant time studying the echo signatures on this cruise.

So, what happens when these signals return to the Dyson?  They are then processed and transmitted onto the computer screens in the hydroacoutsics lab on board.  This place is affectionately known as “the cave” because it has no windows, and it is, in fact, the place where I spend the majority of my time when I am not processing fish!  Here it is:

Here is Anatoli observing potential fish for us to go catch!
Here is Anatoli observing potential fish for us to go catch!

We spend a lot of time monitoring those computer screens, and when we see lots of “specks” on the screen, we know we have encountered large numbers of pollock!

Here we are approaching a LARGE group of pollock!
Here we are approaching a LARGE group of pollock!

When the scientists have discussed and confirmed the presence of pollock, they then call up to the Bridge and announce we are “ready to go fishing” at a certain location and a certain depth range!  Then, the scientists will head upstairs to the Bridge to work with the officers and deck crew to supervise the release, trawling, and retrieval of the net.

Now, in addition to the SONAR under the ship, there are sensors attached to the top of the net itself, transmitting back data.  All of the return echos get transmitted to different screens on the bridge, so not only can you watch the fish in the water before they are caught, you can also “see” them on a different screen when they are in the net!  As I told you in the last post, we will trawl for anywhere from 5-60 minutes, depending on how many fish are in the area!

Left: Echosounder at work/ Right: The "return signature" is visible on the computer!
Left: Echosounder at work/ Right: The “return signature” is visible on the computer!  (Source: http://www.dosits.org)
A full catch- success! Without acoustics, it would be much harder for NOAA to monitor and study fish populations.
A full catch- success! Without acoustics, it would be much harder for NOAA to monitor and study fish populations.

Personal Log:

In these last few days, we have crossed back and forth from the Russian Exclusive Economic Zone (EEZ) and the U.S. several times.  There were some nice views of Eastern Russia before the clouds and fog rolled in!

I can see Russia from my ship!
I can see Russia from my ship! (Photo Credit: Allan Phipps)

In addition, we crossed over the International Date Line!  It turns out that everyone on board gets a special certificate called the “Domain of the Golden Dragon” to mark this event.  This is just one of a set of unofficial certificates that began with the U.S. Navy!  If you spend enough time at sea, you can amass quite a collection- there are also certificates for crossing the Equator, Antarctic Circle, Arctic Circle, transiting the Panama Canal, going around the world, and more…

I will award a prize to the first person who writes back to tell me what does it mean when one goes from a “pollywog” to a “shellback”, in Navy-speak!

Here is a picture of me with the largest pollock I have seen so far- 70cm!

If I am 5' 4", how many 70cm pollock would it take to equal my height?
If I am 5′ 4″, how many 70cm pollock would it take to equal my height?

Lastly, on to some, perhaps, cuter and more cuddly creatures than pollock- pets!  Here in the hydroacoustics lab, there is a wall dedicated to pictures of pets owned by the officers, crew, and scientists:

Those are some pretty cute pets left ashore...
Those are some pretty cute pets left ashore…

Clearly, this is a dog crowd!   I did learn, however, that our Chief Scientist, Taina, has her cat (Luna) up there!  Students, do you remember the name of my cat and, what do you think, should I leave a picture of her up here at sea?

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Allan Phipps: Re-verify Our Range to Target… One Ping Only, August 6, 2012

NOAA Teacher at Sea
Allan Phipps
Aboard NOAA Ship Oscar Dyson
July 23 – August 11, 2012

Still enjoying fishing! Here I’m holding an arrowtooth flounder.
Mission: Alaskan Pollock Mid-water Acoustic Survey
Geographical Area: Bering Sea
Date: August 6, 2012

..

Location Data
Latitude: 60°55’68” N
Longitude: 179°34’49” E
Ship speed: 11 knots (12.7 mph)

Weather Data from the Bridge
Wind Speed: 10 knots (11.5 mph)
Wind Direction: 300°
Wave Height:  2-4 ft with a 4-6 ft swell
Surface Water Temperature: 8.7°C (47.6°F)
Air Temperature: 8°C (46.4°F)
Barometric Pressure:  1013 millibars (1 atm)

Science and Technology Log

Previously, we learned how the biological trawl data onboard the NOAA Research Vessel Oscar Dyson are collected and analyzed to help calculate biomass of the entire Bering Sea Walleye pollock population.  Last blog, I mentioned that the scientific method for estimating the total pollock biomass is not complete without acoustics data, more specifically hydroacoustics!  In fact, hydroacoustic data are the real key to estimating how many pollock are in the Bering Sea!  That is why our mission is called the Alaskan Pollock Midwater ACOUSTIC-trawl Survey.

Screenshot showing our transects on leg 3 of the pollock midwater acoustic survey. Fish icons indicate where we validated acoustic data with biological sampling.  Hydroacoustic data were collected continuously along north/south transects.

The Oscar Dyson is using hydroacoustics to collect data on the schools of fish in the water below us, but we do not know the composition of those schools.  Hydroacoustics give us a proxy for the quantity of fish, but we need a closer look.  The trawl data provide a sample from each aggregation of schools and allow the NOAA scientists that closer look.  The trawl data explain the composition of each school by age, gender and species distribution.  Basically, the trawl data verifies and validates the hydroacoustic data.  The hydroacoustics data collected over the entire Bering Sea in systematic transects combined with the validating biological data from the numerous individual trawls give scientists a very good estimate for the entire Walleye pollock population in the Bering Sea.

So what is hydroacoustics and how does it work???

Hydroacoustics (“hydro” = water, “acoustics” = sound) is the field of study that deals with underwater sound.  Remember, sound is a form of energy that travels in pressure waves.  Sound travels roughly 4.3 times faster in water than in air (depending on temperature and salinity of the water).  Here is a link with an interactive animation comparing the speed of sound in water, air, and steel!  This change in speed will become very important later… keep reading!

Lower sound frequencies travel farther.  This is how humpback whales can communicate over great distances with their whale songs!  Click on whale songs to hear one!

Whales are not the only aquatic organisms to use sound!  Much like dolphins use sound to echo-locate, people use technology to “see” under water using sound energy.  We call this technology SONAR (Sound Navigation And Ranging).

An animation of dolphin echo-location (courtesy of Discovery of Sound in the Sea).

On a typical recreational watercraft, this technology can be found in the form of a “fish-finder.”

Recreational “fish-finders” can be found on many personal watercraft (courtesy of Discovery of Sound in the Sea).

In commercial fishing, this technology is used in much the same way, just on a larger scale.  Here is an animation showing a commercial trawler using SONAR to locate fish.

Commercial fishing boat using hydroacoustics to locate fish. This animation illustrates how a fish shows up as an arch on the onboard display (courtesy of Discovery of Sound in the Sea).

The Oscar Dyson has a much more powerful, extremely sensitive, carefully calibrated, scientific version of what many people have on their bass boats.  These are mounted on the pod, which is on the bottom of the centerboard, the lowest part of the ship.  The Oscar Dyson has an entire suite of SONAR instrumentation including the five SIMRAD EK60 transducers located on the bottom of the centerboard that operate at different Khertz, the SIMRAD ME70 multibeam transducer located on the hull, and a pair of SIMRAD ITI transducers on the trailing edge of the centerboard (one pointed toward the starboard side, the other toward port).

Illustration of the Oscar Dyson showing the hydroacoustic transducers located on the centerboard and the hull of the ship.

This “fish-finder” technology works by emitting a sound wave at a particular frequency and waiting for the sound wave to bounce back (the echo) at the same frequency.  The time between sending and receiving the sound wave determines how far away an object is, whether it be the bottom or fish.  When the sound waves return from a school of fish, the strength of the returning echo helps determine the fish density (how many fish are there).

An echogram taken from the Oscar Dyson. Shades of yellow and red show extremely large, dense schools of fish. The solid red at the bottom of the picture is the bottom of the sea which is at 94.12 meters at this location.

Another piece of the puzzle… how reflective an individual fish is to sound waves.  This is called target strength.  Each fish reflects sound energy sent from the transducers, but why?  For fish, we rely on the swim bladder, the organ that fish use to stay buoyant in the water column.  Since it is filled with air, it reflects sound very well.   When the sound energy goes from one medium to another, there is a stronger reflection of that sound energy.  The bigger the fish, the bigger the swim bladder; the bigger the swim bladder, the more sound is reflected and received by the transducer.  We call this backscatter, or target strength, and use it to estimate the size of the fish we are detecting.  This is why fish that have air-filled swim bladders show up nicely on hydroacoustic data while fish that lack swim bladders (like sharks), or that have oil or wax filled swim bladders (like Orange Roughy) have weak signals.

X-ray of fish showing the presence of a swim bladder (courtesy of DeAnza College).

Target strength is how we determine how dense the fish are in a particular school.  Scientists take the backscatter that we measure from the transducers and divide that by the target strength for an individual and that gives you the number of individuals that must be there to produce that amount of backscatter.  100 fish produce 100x more echo than a single fish.  We extrapolate this information to all the area of the Bering Sea to estimate the pollock population.

A close look at part of Transect 27. In this echogram, the area backscatter numerical values are included. At the top of the water column, you can see what are probably jellyfish which have little backscatter since they have no swim bladders. Along the bottom are groundfish. In the center of the water column are several large schools of Walleye pollock with strong backscatter. The square that has a value of 2403.54 shows several large schools!

So the goal is to measure the hydroacoustic density along each transect and extrapolate that data to represent the entire survey area between transects (the area not sampled because the Oscar Dyson can’t cover every square meter of the Bering Sea).  When you combine the hydroacoustic data for all of the 30 transects (a total of ~5,000 nautical miles in an area of 100,000 square nautical miles) and the lengths collected in the biological trawl data, you can convert the length data into target strength data to create a distribution of target strengths and find the average target strength for the population.  In doing so, you get a complete picture of the Walleye pollock population in the Bering Sea.

The BIG picture. This is the combination of hydroacoustic data and biological trawl data analyzed to show what the entire walleye pollock population looked like for 2009 (courtesy of the Alaska Fisheries Science Center www.afsc.noaa.gov/Publications/ProcRpt/PR2010-03.pdf). Analysis is still being done on the current survey. This year’s results will be out in a report this fall.  Expect some changes!

But there’s more!!!  Scientists ALSO use hydroacoustic data when trawling to determine if they have caught a large enough sample size to collect fish length data to validate their target strength data.  If you recall reading my first blog from sea that taught about the parts of the net, I wrote about and had a drawing of the “kite” on which the “turtle” was attached.  The “turtle” is a SIMRAD FS70 trawl SONAR.  It has a downward facing transponder that shows a digital “picture” of the size of the net opening.  You can also see individual fish and/or schools of fish enter the net by watching this display.  Since the scientists only need about 300 fish for a statistically significant sample, they watch this screen carefully so that they do not take more fish than they need.  When the lead scientist thinks there are enough fish in the net, she gives the request to the Officer on Deck to “haul back.” Unlike commercial trawlers, a typical trawl on the Oscar Dyson only lasts 25 minutes.  Sometimes, we are only officially fishing for 5 minutes if we pull through a large school.

What are the data telling us?

The Walleye pollock data suggest that the population is currently stable; however, there is some evidence of pollock in waters that have traditionally been north of their uppermost documented population range.  Are warmer waters due to climate change to blame for this possible shift?  Here is an interesting article that addresses this issue and raises several other trends regarding pollock population response to changes in food source and predation due to climate change.  Click on the picture to open the article!

How might climate change affect fish sticks? Click on the picture to read more!

The economic and ecological implications of a shifting pollock population range are a bit unsettling.  Fish do not know political boundaries.  As the pollock population range possibly shifts north, more of that range will lie within Russian waters than in previous years.  This may hurt the U.S. commercial fishing industry as they settle for less of a resource that was once abundant.  Since quotas are set based on last year’s numbers, there is a time lag which may result in overfishing in U.S. waters that might lead to a collapse in the Alaskan Walleye pollock fishing industry.  The U.S. has invested a tremendous amount of research into maintaining a sustainable pollock fishery.  Other countries may be responding to a variety of factors in which sustainability is just one when they are managing pollock stocks and setting catch quotas. Since pollock is a trans-boundary stock, this could lead to greater uncertainty in management of the entire population if pollock increasingly colonize  more northern Bering Sea waters as influenced by climate change.

Food for thought…

Next blog, we will learn about cutting edge technology that may eventually make hauling back fish and collecting biological fish data on board the acoustic survey missions obsolete.

Personal Log

It’s tomorrow, TODAY!  This morning at 6am Alaska Time, we crossed the International Date Line (IDL).  The IDL is at 180° longitude.  General Vessel Assistant Brian Kibler and I went out to the bow of the ship so we would be the first onboard to cross the line!

Map of the Bering Sea showing both the International Date Line and the 180th longitude. Our closest point to Russia was 12 nautical miles from Cape Navarin which is very close to 180 longitude.

Over the next two days, our transects take us back and forth over the IDL 3 more times.  Fortunately, onboard our Oscar Dyson time warp machine we simply observe the Alaska Time Zone (the time zone from our port of call).  With everyone onboard operating different shifts, and with 24/7 operations, it would be quite confusing if we kept changing our clocks to observe the local time zone.

The Order of the Golden Dragon!

Mariners who cross the IDL when at sea are inducted into the “Order of the Golden Dragon” and receive a certificate with the details of this momentous crossing.  There are several other notorious crossing that receive special recognition.  They are:

▪     The Order of the Blue Nose for sailors who have crossed the Arctic Circle.
▪     The Order of the Red Nose for sailors who have crossed the Antarctic Circle.
▪     The Order of the Ditch for sailors who have passed through the Panama Canal.
▪     The Order of the Rock for sailors who have transited the Strait of Gibraltar.
▪     The Safari to Suez for sailors who have passed through the Suez Canal.
▪     The Order of the Shellback for sailors who have crossed the Equator.
▪     The Golden Shellback for sailors who have crossed the point where the Equator crosses the International Date Line.
▪     The Emerald Shellback or Royal Diamond Shellback for sailors who cross at 0 degrees off the coast of West Africa (where the Equator crosses the Prime Meridian)
▪     The Realm of the Czars for sailors who crossed into the Black Sea.
▪     The Order of Magellan for sailors who circumnavigated the earth.
▪     The Order of the Lakes for sailors who have sailed on all five Great Lakes.

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Amanda Peretich: Awesome Acoustics, July 13, 2012

NOAA Teacher at Sea
Amanda Peretich
Aboard Oscar Dyson
June 30, 2012 – July 18 2012

Mission: Pollock Survey
Geographical area of cruise: Bering Sea
Date: July 13, 2012

Location Data
Latitude: 59ºN
Longitude: 174ºW
Ship speed: 11.7 knots (13.5 mph)

Weather Data from the Bridge
Air temperature: 7.3ºC (45.1ºF)
Surface water temperature: 7.6ºC (45.7ºF)
Wind speed: 4.3 knots (4.9 mph)
Wind direction: 12ºT
Barometric pressure: 1010 millibar (1.0 atm, 757.5 mmHg)

Science and Technology Log

How sonar works: energy (sound) waves are pulsed through the water. When it strikes an object, it bounces back to the receiver. (from http://www.dosits.org/)
How sonar works: energy (sound) waves are pulsed through the water. When it strikes an object, it bounces back to the receiver. (from http://www.dosits.org/)

Before stepping onto the Oscar Dyson, I wasn’t quite sure about much of the science going on. Did they just put the nets in the water every so often and hope to catch some fish? Carefully lean over the side of the ship saying “here fishy fishy” with the hope that the pollock would find their way into the net? Neither of these scenarios is correct (good thing I’m not actually a fisherman!). So today’s lesson is going to be all about what the chief scientist actually uses to find fish: hydroacoustics (hydro meaning water and acoustics meaning sound). This also involves SONAR, which is short for SOund Navigation And Ranging.

Fishfinding Basics
Fishfinding basics.

If you’ve ever been on a smaller boat, yacht, fishing vessel, or the like, you may have seen something called a fishfinder. The basic concepts are the same as what is happening on the Oscar Dyson. An echosounder sends a pulse of energy waves (sound) through the water. When the pulse strikes an object (such as the swim bladder in fish), it is reflected (bounced) back to the transducer. This signal is then processed and sent to some sort of visual display.

Swim Bladder
Swim bladder in a fish.
(from https://www.meted.ucar.edu/)

The Oscar Dyson uses acoustic quieting technology where the scientists can monitor fish populations without altering their behavior. The Scientific Sonar System and various oceanographic hydrophones (underwater microphones) are raised and lowered through the water column beneath the ship on a retractable centerboard. This is important so that the transducers can be lowered away from the flow noise generated by the hull, which in turn will improve the quality of data collected. In addition, there is a multibeam sonar system located on the forward hull. Ultimately the hydroacoustic data is all used as one piece to the puzzle of measuring the biomass of fish in the survey area.

OD acoustics
The different sonar signal transmitter/receivers (transducers) used on this leg of the pollock survey and their location on the ship.
Neal at work
Chief scientist Neal working away in the Acoustics lab. The second screen from the left on the upper row is showing the information from the ME70 multibeam.

So how does this all work when we are looking for fish? The chief scientist (Neal on the 0400-1600 watch) or another scientist (Denise on the 1600-0400 watch) will spend a lot of time analyzing the various computer screens in the acoustics lab, which has been affectionately termed the “cave” (no windows). They are looking at the information being relayed from both the multibeam and the EK60.

What is a multibeam? The Oscar Dyson has the Simrad ME70 scientific multibeam echosounder. It is located on the hull (underside) of the ship on the front half and sends 31 sonar beams per second down to the bottom of the sea floor.

Multibeam
Multibeam echosounder.
(from http://www.simrad.com/)

Aft of the multibeam (on the centerboard) are the five Simrad transducers. It may seem confusing, but hopefully I can walk you through a teensy little bit of how it works when we are looking to trawl for fish.

EK60 Transducer
Information from the EK60 transducer at 18kHz (top) and 38kHz (bottom).

Information from the EK60 echosounder is displayed on the far left screen in the acoustics lab while information for the ME70 multibeam is displayed on the next screen. The darker patches are showing that there are fish in that area. When the scientist first starts to see a good amount of fish, they will “mark” it and keep watching. If the screen fills up with fish (as in the EK60 image), the scientist will call upstairs to the bridge and tell them where to head back to on the transect line to start trawling. Depending on the location of the fish in the water column, it may be a bottom trawl (83-112 net), a midwater trawl (AWT net), or a methot trawl. Side note: the 83-112 midwater comparison trawl that I’ve mentioned before is done almost immediately after an AWT midwater trawl to compare the fish caught in a common area.

ME70 Multibeam
Information from the ME70 multibeam. You can determine the sea floor depth and there are five narrow beam slices from the mid-section of the multibeam (of the 31 different beams that span 120 degrees) displayed on screen.
Neal on bridge
Chief scientist Neal up on the bridge.

Then the scientist will head upstairs as the deck crew is preparing the net. One of the many sensors attached to the net is called the FS70 fishsounder or “the turtle”, and it is only used during trawls (because it is attached to the headrope). The scientist can “watch” the fish swimming under the ship using the EK60 information combined with the information from the fishsounder. The yellow “turtle” on the right in the image shows how the FS70 is flying in the water. You want minimal pitch and roll and for the front of it to be facing the back of the ship. This way, we can “see” the fish as they are going through the net. The officer of the deck and lead fisherman or head boatswain can adjust various things to keep the turtle in the right orientation. The middle image below is constantly changing on the screen in the bridge as the sonar is sweeping back and forth, so you can almost watch the individual fish enter the net. It was interesting to watch the delay between when you would see the fish from the EK60 (on the left) and when you saw them with the FS70 (middle).

Trawl Fishsounder
Display screens on the bridge used during a trawl.

Once the scientist is satisfied that enough fish have been caught for a sufficient sample size, the net will be hauled back and the acoustics work is done for just a little bit (giving Neal some time to grab some well-deserved coffee and the rest of us time to get our rain gear on to process the fish).

So some of the questions I had asked (that don’t really fit nicely in the information above):

Why do we use different frequencies in the acoustic studies?

Frequency Wavelength
Relationship between frequency and wavelength. (from http://emap-int.com)

This ties right back in to chemistry (and other sciences) with an equation and the relationship between frequency and wavelength (yay!). Basically there is an inverse relationship which means that at a high frequency there is a smaller or shorter wavelength (wavelength is the distance for peak to peak of a wave). At a low frequency, there is a higher or longer wavelength.

At a low frequency, you will see only see things that are larger, like pollock, whereas you will see very small things like krill and zooplankton at higher frequencies. Having information from both types of frequencies is necessary to complete the scientific research on the Oscar Dyson.

Single Fish
Traveling at 1 knot, showing single fish from EK60 sonar.

Is it possible to see a single fish?
Yes! From sunset to sunrise, the Oscar Dyson doesn’t actually travel the transect lines. This is because the pollock behave differently during darkness than during the day. So instead of traveling between 11 and 12 knots (which is what happens between trawls), it’s almost like the boat is just sitting around for a couple of hours. But during this time, since the boat isn’t moving along quickly, it’s possibly to see individual fish on the sonar as shown in the image.

Hydroacoustics
Hydroacoustic surveys can involve any number of different types and locations of the transducers. (from http://btechgurus.blogspot.com/2012/06/sonar.html)

Personal Log
Today is Friday the 13th but it was far from unlucky – I finally saw something out in the water other than fog: a boat! Again, all good sightings seem to come from up on the bridge, so I’m thankful for Lieutenant Matt for allowing me to ask a billion questions while I’m up there and teaching me more than I ever thought my brain could hold. He has all of the qualities of a great teacher, which is nice to see.

Ship
The ship we saw up on the bridge this morning from about 5 nautical miles away (left), on the sonar (middle), and through the binoculars (right).
Dancing in the fish lab on the Oscar Dyson
Neal and I dancing while waiting for the fish!

Highlight from the other day? Chief scientist Neal finally dressed out in his Grundens (rain gear) and came to help process a catch in the fish lab! While waiting, he even took a quick second to dance in the doorway (we were “Dougie”-ing) to my music that was playing over the speaker system.

References
NOAA Oscar Dyson flier
NOAA Oscar Dyson Ship Electronics Suite
HTI Sonar
Wikipedia: Sonar
Simrad

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Marilyn Frydrych, September 25, 2008

NOAA Teacher at Sea
Marilyn Frydrych
Onboard NOAA Ship Delaware II
September 15-25, 2008

Mission: Atlantic Herring Hydroacoustic Survey
Geographical area of cruise: New England Coastal Waters
Date: September 25, 2008

Weather Data from the Bridge 
41.27 degrees N, 70.19 degrees W
Partly Cloudy with wind out of the W at 19 knots
Dry Bulb Temperature: 26.0 degrees Celsius
Wet Bulb Temperature:  20.9 degrees Celsius
Waves: 2 feet Visibility:  10 miles
Sea Surface Temperature:  21.6 degrees Celsius

Science and Technology Log 

We received a call from the Coast Guard yesterday telling us to seek shelter because of the impending interaction of Hurricane Kyle with a strong cold front approaching us. We cut our cruise a day short and headed for Woods Hole. As we headed back in I had time to reflect on my experiences over the last couple weeks. I particularly appreciated all the positive energy of the scientific crew. They were always very helpful and thoughtful as well as efficient. I learned a lot from them.  Each morning I found myself looking forward to what might unfold as we worked together.  I totally enjoyed my four or five hours of free time each day. Often I would spend this time on the bow or the fantail taking in the rhythm of the sea.  It was a very soothing experience much like watching a camp fire. The sunsets, too, brought a sense of awe and peace.

Each of the crew was a master of multiple tasks.  Jon Rockwell was not only an expert cook, but a medic as were three others aboard.  As part of their initial training with the NOAA Corps the four officers had entered a room fully in flames and totally filled with smoke.  If they had to, they could navigate by the stars. Two of the officers were NOAA trained SCUBA divers.  The engineers could fix anything whether it had to do with distilling water, leaking hydraulic pipes, stuck drawers, broken toilets, cracked welds, or the various diesel engines.  They were experts in the “green” rules governing disposal of waste.  The ET specialist could fix both hardware and software.  The scientists knew their software programs backwards and forwards.  All very impressive.

Each day brought a new, wondrous sunset.
Each day brought a new, wondrous sunset.