acoustics – Page 16 – NOAA Teacher at Sea Blog

June 8, 2009April 5, 2021

Susan Smith, June 8, 2009

NOAA Teacher at Sea
Susan Smith
Onboard NOAA Ship Rainier
June 1-12, 2009

Mission: Hydrographic survey
Geographical area of cruise: Trocadero Bay, Alaska; 55°20.990’ N, 33°00.677’ W
Date: June 8, 2009

Weather Data from the Bridge
Temperature: Dry Bulb: 13.9°C (57°F); Wet Bulb: 12.2C (54°F)
Cloudcover: Overcast 8/8
Wave Height: 0-1
Visibility: 10 nautical miles
Wind: 325, 4 kts.
Sea Wave Height: 0-1
Sea water temperature: 12.2°C (54°F)

Science and Technology Log

Before I explain the science we did today, I will answer the question posed on log number 3: What is a patch test and why is it run? A patch test is used to find offsets in sonar setup (continuous errors) and timing errors. It is done whenever physical alterations occur with the sonar. Such problems can occur when it is mounted skewed, or not in perfect line with the ship.

The Patch Test checks pitch, roll, and yaw. The ship is run out from the shore and back into shore, along the same line. The computer has all offsets set to zero. A swath is sliced at the edge so the computer is looking at the outer beams from the side. With a roll offset it must be changed from an X pattern to a single, flat line. With a pitch offset, a nadir view is taken, the angle is adjusted until the two lines (one out from shore, one into shore) form a single straight line. Yaw also has two lines offset so they must be combined to one line configured identical to the two lines. The Patch Test takes approximately one to two hours to complete.

Today I was involved in obtaining data relevant to tides. We used a tide gauge, levels, GPS, and a staff placed in the water, with a nitrogen being pumped under it. The tide gauge measures the unit of pressure it takes for a nitrogen bubble to be squeezed out. The greater the amount of water covering it the greater pressure is required to release a bubble. To get water depth, someone reads the staff water level and continually records this information for three hours. This will enable us to know the difference in the pressure gauge readings and the staff water level. A Global Positioning System (GPS) is used to determine where the staff is by getting a good constellation (satellites in orbit) reading.

It was my job to hold a level rod on the primary benchmark location while someone else recorded measurements using the surveyor’s level (The level rod is measured in centimeters). The surveyor’s level has three lines, or stadia, inside the level. These lines are read as upper, middle, and lower. I placed a smaller bubble level against the rod to make sure it was straight up and down. Once my location was recorded a second person, also holding a level rod, placed hers on a staff (a triangular wood structure) set in the water. The surveyor’s level was disturbed, then a second reading was taken at the staff, and a second reading was taken at my benchmark. If the numbers did not match within a certain range, or historical data, the measurements had to be repeated.

We went through this process for five benchmarks. These benchmarks were placed in specific locations based on elevation and stability of the ground above high tide level. This procedure is completed to ensure the benchmarks and the staff have not been moved, by either human disturbance or a natural occurrence, such as an earthquake. As a side note, in some locations these benchmark rods have had to be drilled down 125 feet. In the Arctic they may be drilled 25 feet into the permafrost. When drilling the holes for the benchmarks care must be given to ensure the surface is smooth, not skewed, or at an unusual angle.

Sometimes a temporary benchmark, called a turtle, must be used. This is a small, heavy, circular piece of equipment, which can be placed anywhere solid. The person holding the staff can turn all the way around it to allow for different measurements. All data collected in this activity are sent to NOAA’s tides office.

Personal Log

After viewing the ship’s photography server I have become interested in what actually goes on in the dry dock. The dry dock is in Seattle where the ship goes for repairs, restoration, and refitting. After the launches and other things are removed from the ship it goes to the dry dock. Gates close off the ends. On the floor of the dock are blocks for the ships hull to sit on, placed exactly in line for this particular ship. Divers go down to check for precise placement before the water is drained. The ship is tied to the dock to stabilize it (prevent it from tilting or falling off the blocks) and if you are not off the ship before it goes into dry dock you are not getting off anytime soon! On the hull are numbers used to identify the ship’s sections. When it is being retrofitted the workers must know where each section came from so the ship can be put back together correctly.

Tape where the symbol and number were painted

Underside of ship on the blocks; the black hole is on for anchor storage

Dry dock operations can take from two months to over a year, depending on the work needing to be done. Crew stays on board as long as possible. When berths are being refurbished they stay in local hotels. Other personnel either work on other NOAA ships or go to other project sites. (All dry dock photographs courtesy of Rainier picture server)

For more information visit these sites:

http://www.osha.gov/SLTC/shipbuildingrepair/drydocking.html http://en.wikipedia.org/wiki/Dry_dock (has history of ancient dry docks)

June 7, 2009April 5, 2021

Susan Smith, June 7, 2009

NOAA Teacher at Sea
Susan Smith
Onboard NOAA Ship Rainier
June 1-12, 2009

Mission: Hydrographic survey
Geographical area of cruise: Trocadero Bay, Alaska; 55°20.990’ N, 33°00.677’ W
Date: June 7, 2009

Weather Data from the Bridge
Temperature: Dry Bulb 12.8° C (55°F)
Wet Bulb 11.7°C (53°F)
Cloudcover: Overcast 8/8
Visibility: 4 nautical miles
Wind: VRB, light speed
Sea Wave Height: 0-1
Sea water temperature: 9.4°C (49°F)

Science and Technology Log

Today we left Craig to finish our grids in Trocadero Bay, Alaska. It was a time to clean up or capture data from isolated locations which had either been missed or not completely surveyed. For the first few hours we spent our time surveying areas very close to the shoreline and areas very difficult in which to maneuver.

We did our first cast with the CTD (Conductivity, Temperature, Depth) equipment and I finally asked if I could run it. Ian, the survey technician, happily obliged. The CTD calculates speed of sound through water. I have finally gotten the gist of sonar settings. The following information will help you understand why it is all necessary for getting accurate data to the surveyor and coxswain.

Range- How long it takes for the sonar beam to go to the bottom and return, or in layman’s terms, tells the sonar when to ping and listen.

Pulse length– Pulse length sets how long the sonar transmits, thus allowing more power to be put out bythe sonar, but it results in decreased resolution. The longer the length of the pulse the lower the resolution, so shorter is optimal. For instance, when going through kelp it should be set at low so the kelp isn’t all being picked up by the sonar beam.

I really enjoyed driving the launch today.

Sonar Beams- There are 512 beams at high frequency (400khz). Low frequency (200 khz) equals 256 beams. There are two yellow gates on the screen which surveyors utilize. One is positioned above the shallow water, one is positioned beneath the deepest water measurement. When in shallow water most surveyors disable them. When in deep water, if the top gate is positioned too low, you lose valuable data on the outer limits. If the lower gate is positioned too low it records too much noise. However, if it is set too high the outer beams are missing and no data is recorded. Surveyors must constantly watch this screen when these gates are active to ensure all data they want is being captured.

The airplane indicates the launch position and the color is the area which has been logged.

The surveyor must ensure the data is placed in appropriate folders, enter data in spreadsheets, and basically keep things running smoothly for the entire time data is being logged. So, in essence the surveyor must watch the sonar screen, set the polygons on the screen for him/herself and the coxswain, continually check the settings, remember to log on for data retrieval and log off when the swath is completed, set the CTD for casts every four hours, and monitor as many as ten folders at one time.

The rule of safety: Never shall safety for life or property be compromised for data acquisition.

The coxswain’s job is to drive the launch into areas to be charted, based on the POD, the Plan of the Day, grids. When data is being recorded he/she drives approximately four to eight knots, depending on the wave action. High swells require slower forward progress. The coxswain has two computer screens-one showing the grid being logged or charted, and another displays depth of water in feet, meters, and fathoms and several other pertinent pieces of data. He or she is ultimately responsible for making decisions about when to enter dicey locations and determining when to stay out of a risky situation.

When traveling in either extremely shallow water or water full of kelp and known rocky locations, a bow watch will stand on the bow and give visuals for the coxswain to avoid. Obviously, this person must wear a safety jacket and hold a rope around an arm or wrist, due to the precarious position he or she is in. High swells could cause serious accidents in a second.

Did you know when backing up a launch, sonar cannot penetrate the bubbles formed when the water is getting stirred? The readings inside the launch show the color red, or dangerous zones, because the sonar thinks the boat is at the bottom. As the surveyors and coxswains say, “No worries! We know where we are.”

Question of the day: What is a patch test and why is it run?

Humpback whale photo courtesy of Ian Colvert

Personal Log

Now that I felt much more comfortable with understanding the sonar I was able to relax more on the launch today. Perfect timing, as this was such a great day for biological observations. Five different humpback whales were sighted in the bay with us; in one location two were in position as forward observers on either side of our launch. The last whale we spotted surfaced fairly close to our launch so we had to stop, mainly because the regulations state you must stay 100 yards from humpback whales. This whale went under the launch and surfaced about 50 meters from us. Off and on during the day they would surface in the areas we were surveying so we had to just wait until they moved along.

I also observed at least eight bald eagles either sitting in trees, flying over the water, or harassing the whales. One eagle flew down close to the water and looked as though it was taunting the whale! Then it quickly flew back up to a tree top and perched on a branch. Several eagles would fly off together, separate, then come back together before landing on a tree. Early in the morning we ran into a group of seals swimming around in kelp. They poked their heads out and just stared at us as we drove by. Luckily we saw them in time to slow down, so as to not disturb them anymore than necessary.

June 4, 2009April 5, 2021

Susan Smith, June 4, 2009

NOAA Teacher at Sea
Susan Smith
Onboard NOAA Ship Rainier
June 1-12, 2009

Mission: Hydrographic survey
Geographical area of cruise: Trocadero Bay, Alaska; 55°20.990’ N, 33°00.677’ W
Date: June 4, 2009

Weather Data from the Bridge
Visibility: 10 nautical miles
Wind: light
Temperature 11.1 C (52 F)
Cloud Cover: FEW 1/8-2/8

A nautical chart indicating underwater cables

Science and Technology Log: Bottom Sampling

This morning I spent time in the Plot Room, and on the Fantail, involved in bottom sampling. The Plot Room has nine work stations with at least two screens per technician. The airplane symbol is the location of the Rainier and the colored dots show locations of bottom sampling areas. One purpose bottom sampling serves is to determine areas suitable for anchoring.

The chart to the right shows there is an underwater cable area (pink dotted lines) from which we cannot take samples, because it could accidently get damaged, thus rendering residents without power. The numbers shown on these When the ship takes bottom samples, from the Fantail, it uses a spring loaded clamp shell device. It is attached to an A frame and uses a winch to lower it into the sea by cable. The operator calls out the depth, using a cable counter, as it is lowered into the water and when it raised. This enables the plot room to know when a sample is coming and it verifies the information received remains accurate. The numbers on these charts indicate water depth in fathoms (1 fathom=6 ft.). As you can see there are drastic dropoffs in some locations.

Identifying the samples: small coarse pebbles

If the cable is not straight down, the ship must move around it, avoiding the screws (propellers) at all costs. When the clamp hits bottom it scoops up the debris under it immediately and is brought back to the surface. When the sample arrives at the top it is shaken to release a majority of the water. Then it must be dismantled to see the solid matter inside. This is a two person job, as it is heavy and impossible to control for just one person. One holds the spring loaded clamp shell, the other takes off the sample section by pulling on either side of the device.

Because safety is always an issue the clamp must be kept from swinging once the collection unit is removed. The items found in the sampler are placed on the chart (shown to the right) to make sure identification is accurate. The chart is divided into sand, gravel, and pebbles. Each type of rock found is divided further into fine, medium, and coarse. This information is relayed to the plot room where someone labels the survey chart in the appropriate location. In the first four samples green, sticky mud was identified near the coastline of Ladrones Island, Madre de Dios Island, and on the southwestern arm of the Prince of Wales Island. These were deep areas where people are not likely to anchor their boats. In the sixth sample we were in fairly shallow water and sampled gritty sand and small pebbles.

This sample was full of sand and some pebbles.

Sometimes the water arrives only with living things in the sampler. Samples eight through ten provided us with living things. Shells with little creatures inside were found in one sampling, and in another the only item was a black sea star. Finally after three such samples in the same location we moved on to the next location. This is a somewhat tedious process when the samples do not provide a great deal of useful data. However, that in itself gives sufficient information as to what is NOT in a location. Now imagine being charged with this assignment is an area where surveys have either never been done, or it has been decades since the previous survey. Remarkably the survey charts are fairly accurate, even from when lead weights and ropes were used to survey. NOAA certainly has a daunting task when it comes to surveying Alaska.

Personal Log

This sample had only a little black sea star!

Yesterday, and today, allowed me the opportunity to see the technical aspects of the Rainier’s mission. Small sections of the oceans and bays are meticulously mapped and charted for use by recreational boaters, the fishing industry, large shipping companies, and the military. Without the information gleaned by the people and ships of the NOAA Corps our waters would continue to go uncharted, perhaps unused, and remain hazardous to all. I am amazed at the patience needed for this work, but it is well worth their efforts to provide the necessary tools to keep our waterways safe for everyone.

I was discussing interesting things I noticed on the Rainier with several of the officers. Did you know there are two flags we fly on the NOAA ships? There is the Jack, a flag with the 50 stars and blue field, and the Stars and Stripes, our nation’s flag. When it is flown on a ship it is called an Ensign. The Jack is flown on the Jackstaff (origin 1865-1895) located on the ship’s bow. The Ensign is flown on the fantail while in port or anchored at sea. I suppose I have now become a student of vexillology, the scholarly study of flags.

June 1, 2009April 5, 2021

Susan Smith, June 1, 2009

NOAA Teacher at Sea
Susan Smith
Onboard NOAA Ship Rainier
June 1-12, 2009

Mission: Hydrographic survey
Geographical area of cruise: Trocadero Bay, Alaska; 55°20.990’ N, 33°00.677’ W
Date: June 1, 2009

Weather Data from the Bridge
Sea Temperature: 10.0 C (50 F)
Visibility: Clear, 10+ nautical miles

Science and Technology Log

What a way to start the day- learning how to deploy launches and all that goes into that process. Each new person onboard the ship who was going to be taking a launch, or responsible for their deployment, was required to attend this training meeting. Safety is of utmost importance on the NOAA ships and the smallest things when not done properly can result in disaster.

I learned a great deal of new vocabulary this morning, mostly pertaining to launch equipment, rope terms, and parts of the launch. It was stressed that in order for us all to have a positive experience we had to learn these terms and their procedures as quickly as possible.

Vocabulary: davit, lizard line, frapping line, bitter end, bite of line.

Three launches were deployed this afternoon to various areas around the Trocadero Bay. Using a Conductivity, Temperature and Depth(CTD) cast three times, we were able to determine salinity, depth of water, and temperature, all measurements used to calculate speed of sound. We set off to finish collecting data from areas missed, called “getting the holiday”. These are generally very small white areas on the screen which need to be surveyed. The wide pink line on the screen to the right indicates the section being surveyed. The pink section is actually made of many tiny lines as the sonar pings back to the launch.

Beautiful screen showing sonar return, most likely a rocky bottom. There are no breaks in the line, or acoustic shadows. The surveyors and techs really like this display of information.

This display is not so beautiful. The bottom was most likely mud or other soft bottom type, preventing a strong sonar return. The line with orange and yellow dots under the bright green line is very weak and blurry. There are blank sections called acoustic shadows, or locations the sonar does not reach.

Animals Sighted: Red jellyfish, blue jellyfish, deer on the coastline

Personal Log

Brown Kelp often deceives the sonar as it may appear as rocks.

What a grand time to be on a NOAA ship in Alaska! The weather has been fantastic, the scenery quite beautiful, and wonderful people who enjoy their jobs. Upon my arrival I was assigned “The PIT”, A C desk sleeping berth areas. It is below the laundry room, but very dark and surprisingly quiet considering its proximity to other mechanical areas of the ship. The suggested ear plugs were certainly a welcome item in the event I just couldn’t get to sleep.

Once I got my bearings, most of the areas I had to be in were easy to find. I was a little apprehensive that the onboard drills would be stressful, especially if I happened to be on the bridge or in the plot room. Going down three sets of steps, getting my survival suit, climbing back up one set of steps, and making it to my muster station as quickly as possible was not my idea of fun. However it was not as I imagined, as there were plenty of other new people who had to maneuver themselves around as well. Plus, we did not have to don the suits…this time!

Here I am working the sonar on a launch. Computer screens showing a vast array of data being collected and the charts used to record the data.

As for the food…it is wonderful, as our cooks know what really drives the ship—a hunger-satisfied crew. And we get service with a smile, something not found in most public restaurants in this day and time. After my dinner Tuesday night I was able to go kayaking in the Trocadero Bay, located inside the Tongass National Forest. Never having done this activity before, I was quite excited to get going. Four of us took to the water for about two hours, kayaking around a large island. While sitting as still as the current would allow I was able to see quite a few seals pop their heads up, look around, then dive under again. Maybe we were infringing upon their recreation area!

The view was spectacular, the water was calm, and I finally got to view a few eagles close enough to actually see the white feathers on their necks. Bird calls were also abundant. Such a nice way to end the day at sea.

July 23, 2007April 1, 2021

Roy Arezzo, July 23, 2007

NOAA Teacher at Sea
Roy Arezzo
Onboard NOAA Ship Oscar Dyson
July 11 – 29, 2007

Mission: Summer Pollock Survey
Geographical Area: North Pacific, Alaska
Date: July 23, 2007

Weather Data from Bridge
Visibility: <1 nm (nautical miles)
Wind direction: 220° (SW)
Wind speed: 8 knots
Sea wave height: <1 foot
Swell wave height: 0 feet
Seawater temperature: 9.8 °C
Sea level pressure: 1006.7 mb (millibars)
Air Temperature: 10°C
Cloud cover: 8/8, fog

Roy and Tamara get excited about birding on the bridge of the OSCAR DYSON

Science and Technology Log

Consumers became very aware of the issue of by-catch when the media reported the canned-tuna industry was killing dolphins in their nets nearly a decade ago. The industry responded by changing some of their fishing methods and marketing “dolphin-safe tuna”. NOAA monitors and sets catch limits for commercial fishing, regulating by-catch, among other things. The Coast Guard assists by also enforcing these fishing regulations. Some of the scientists working here on the pollock survey have worked as fishery observers on commercial vessels, monitoring by-catch in the Alaska fleets. The by-catch regulations vary based on the region, species and season. For example, on the Bering Sea none of the finfish outfits are allowed to keep any crab, they need a special permit to keep halibut and they need to keep cod if they are fishing for pollock. Commercial trawling for pollock results in typically low by-catch. Some environmental groups have listed pollock as a sustainable fish food compared to other seafood in that the harvest does not seem to significantly harm the environment or severely deplete fish stocks. The Marine Stewardship Council, an independent global nonprofit organization, has certified Alaskan pollock as a sustainable fishery.

NOAA Scientist Abby separates out Chrysaora melanaster, common name Lions Mane. — NOAA Scientist Abby separates out a Chrysaora melanaster jellyfish.

Although we are not dealing with by-catch directly, I find the connection between by-catch, sustainability and fish stocks very interesting. The Echo Integration Trawl Survey uses acoustic data to estimate pollock populations. When we put out our nets we do so to obtain a sample of fish, detected by our acoustic instruments. Since we are conducting mid-water trawls we bring up mostly pollock. The non-pollock species that occasionally get caught in the net are important in verifying the acoustic data and to know what is in the water column with the target species. As a science teacher, the diversity makes for interesting fishing and I have been able to observe a few organisms that spend most of their time in deep water. I have shared some of my images of the unusual species below, all of which I had never seen before this trip. Many of the organisms we bring up go back into the water after we record the data but some of our catch makes it to the galley to be served up for meals.

More Invertebrates

Flathead Sole (Hippoglossoides elassodon). Flatfish tend to swim higher in the water column in the evening following the plankton

Greenland Turbot (aka Greenland Halibut)

Great Sculpin (Myoxocephalus polyacanthocephalus)

Smooth lumpsucker (Aptocyclus ventricosus)

Kier, Chef and Assistant to the Chief Steward, makes a serious shrimp bisque.

Catch of the day: Chief Steward Rick cooks up Pollock Fish and Chips

Bird of the Day: Turns out, there is no such thing as a seagull. This was passionately explained to me by birder who will remain nameless. You ask, why no seagulls? Simply the term is not used in the scientific community. There are seabirds and of this general group there are well over 100 species of gulls. Some gulls are found well inland. Some species of land-based gulls have become popularized due to their opportunistic feeding around humans. Many of the pelagic gulls I have seen this trip are not as well trained as the ones in NYC and stick to wild foods, not even accepting the occasional fish scraps I have tempted them with off the back deck. I had reported in a previous log seeing Kittiwake’s and some immature Herring Gulls. Today we saw a Slaty-back Gull. It is a handsome gull with striking contrasts of black, dark grey and white. They seem to turn up more each time we reach the northern end of a transect line (above 60° latitude). I also learned that the red spot on the beak is a sign of maturity in many adult gulls. I have a renewed appreciation for gulls and look forward to identifying the species back home.

Bottom trawls, conducted on the previous leg of this study, tend to have more diversity in the sample

Personal Log

We are approaching the northwestern edge of our transect field and the water is deeper and colder and we are finding less fish. I am lucky to find more time to spend on the bridge and witness the communication with Russian fishing vessels, jumping salmon and occasional marine mammal sightings. I have a little camera envy. Some of the folks aboard have the right lens and the right camera to catch the action out at sea. My little 4X zoom digital is looking mighty bleak on the deck and thus I need to rely on the serious photographers for images of some of these exciting finds; their generosity in sharing their images is most appreciated.

Question of the Day

Today’s question: How does one become a Golden Dragon?

Previous Question: Why do pollock rise in the water column at night?

Much of the food eaten by pollock fluctuates in their vertical migration depending on light penetration. During the daylight hours many of the euphausiids (krill) can be found lower in the water column. It seems that by staying lower in the darker portions of the water column during the day, zooplankton may be more protected from their major predators. Near the surface, the phytoplankton (algae) uses the sun’s energy to produce food all day. As the light fades the zooplankton rise, feeding on algae, and the pollock follow their food source.

Krill from one of our nighttime raids with the Methot Trawl

Krill (pollock food): Partially digested from inside the stomach of a pollock

Pollock gill rakers screen food from leaving the oral cavity as the water passes out of the gill slits, oxygenating the gills