Frank Hubacz: ADCP Deployment, May 2, 2013

NOAA Teacher at Sea
Frank Hubacz
Aboard NOAA ship Oscar Dyson
April 29 – May 10, 2013

 

Mission: Pacific Marine Environmental Laboratory Mooring Deployment and Recovery
Geographical Area of Cruise: Gulf of Alaska and the Bering Sea
Date: May 2, 2013

Weather Data from the Bridge:

Partly sunny, WindsN 5-10 knots
Air Temperature 1.3C

Relative Humidity 60%

Barometer 1008.2 mb

Surface Water Temperature 2.8C

Surface Water Salinity 31.37 PSU

Science and Technology Log

As I described previously, one of the instruments being deployed on this cruise is an Acoustic Doppler Current Profiler (ADCP), which measures speed and direction of ocean currents across an entire water column using the principle of Doppler shift (effect).  The Doppler Effect is best illustrated when you stop and listen to the whistle of an oncoming train.  When the train is traveling towards you, the whistle’s pitch is higher. When it is moving away from you, the pitch is lower. The change in pitch is proportional to the speed of the train.  The diagrams below illustrates the effect.

Doppler Effect

Another view of the Doppler Effect

The ADCP exploits the Doppler Effect by emitting a sequence of high frequency pulses of sound (“pings”) that scatter off of moving particles in the water. Depending on whether the particles are moving toward or away from the sound source, the frequency of the return signal bounced back to the ADCP is either higher or lower. Since the particles move at the same speed as the water that carries them, the frequency shift is proportional to the speed of the water, or current.

The ADCP has 4 acoustic transducers that emit and receive acoustical pulses from 4 different directions. Current direction is computed by using trigonometric relations to convert the return signal from the 4 transducers to ‘earth’ coordinates (north-south, east-west and up-down. (http://oceanexplorer.noaa.gov/technology/tools/acoust_doppler/acoust_doppler.html).  The most common frequencies used on these units are 600 KHz, 300 KHz, and 75 KHz.  The lower the frequency the greater the distance that the wave can propagate through the ocean waters.

Determining current flow helps scientist to understand how nutrients and other chemical species are transported throughout the ocean.

Typical 4 beam ADCP sensor head. The red circles denote the 4 transducer faces.

Prior to sailing, ADCP mooring locations are selected by various research scientists from within NOAA.  Next, engineers develop a construction plan to secure the unit onto the ocean floor.  Once designed, the hardware needed to construct the mooring is sent to the ship that will be sailing in the selected mooring locations.  Prior to arriving at the designated location it is the responsibility of the science team to construct the mooring setup following the engineering diagram shipped with each ADCP unit. ADCP moorings can be constructed to hold a wide variety of measuring instruments depending upon the ocean parameters under study by the research scientist.

ADCP Construction Diagram

The moorings are built on the ship’s deck starting with an anchor.  The anchor weight is determined based upon known current strength in the area where the mooring will be located.  Anchors are simply scrap iron railroad train car wheels which bury themselves into the sediment and eventually rust away after use.  The first mooring unit that we assembled had an anchor composed of two train wheels with a total weight of 1,600lbs.  Although this mooring was built from the anchor up this is not always the case.  When setting very deep moorings the build is in the reverse order.

Selecting the anchor

Anchor on the back deck below the gantry

Next, an acoustic release mechanism is attached to the anchor by way of heavy chains.  This mechanism allows for recovery of the ADCP unit as well as the release mechanism itself when it is time to recover the ADCP.  The units that we are deploying will remain submerged and collect data for approximately 6 months.

Acoustic Release Mechanism

Bill attaching the acoustic release mechanism

Finally, an orange closed-cell foam and stainless steel frame containing the actual instrumentation is connected to the assembly and then craned over the back deck.  The stainless steel frame has a block of zinc attached to it which acts as a sacrificial anode.  Sacrificial anodes are highly active metals (such as zinc) that are used to prevent a less active metal surface from rusting or corroding away.  In fact, our ship has many such anodes located on its hull. Once the entire unit is in position, a pin connected to a long chord is pulled from a release mechanism and the unit is dropped to the ocean floor.  Date, time, and location for each unit are then recorded. 

Hoisting ADCP

ADCP unit assembly

Assembling mooring unit

Ready for launch

To recover the unit, an acoustic signal (9-12 Khz) is sent to the ship from the sunken mooring unit to aid in its location.  Once located, a signal is used to activate a remote sensor which powers the release mechanism to open.  The float unit then rises to the surface bringing all of its attached instruments along with it.  The stored data within the units are then secured and eventually sent along to the research scientist requesting that specific mooring location for ocean current analysis.

Recovering a mooring with a rope lasso

Personal Log

On my first day of “work” I was able to watch the science teams deploy three different ADCP moorings as well as conduct several CTD runs.  I will discuss CTD’s in more detail in future blogs.  I was impressed by the camaraderie among all of the science team members regardless of the institution that they represented as well as with members of the deck crew.  They all work as a very cohesive and efficient group and certainly understand the importance of teamwork!

Adjusting to my new work schedule is a bit of a challenge. After my work day ended today at 1200 hours, I fell asleep around 1500 hours for about 4 hours.  After trying to fall back asleep again, but to no avail, I decided to have a “midnight” snack at 2000 hours (8pm).  I finally fell asleep for about 2 more hours before showering for my next shift.  I think I now have more empathy for students who come to my 8am chemistry class and occasionally “nap”!

A wide selection of food is always available in the ship’s galley. I have discovered that I am not the only one taking advantage of this “benefit”!  I will definitely need to reestablish an exercise routine when I return home.  We are currently heading for Unimak Pass which is a wide strait between the Bering Sea and the North Pacific Ocean southwest of Unimak Island in the Aleutian Islands of Alaska.

Did you know that since the island chain crosses longitude 180°, the Aleutian Islands contain both the westernmost and easternmost points in the United States. (172° E and 163° W)!

180 longitude

Stephen Bunker: Current Drifter, 24 October 2011

NOAA Teacher at Sea
Stephen Bunker
Aboard R/V Walton Smith
October 20 — 24, 2011

Mission: South Florida Bimonthly Regional Survey
Geographical Area: South Florida Coast and Gulf of Mexico
Date: 24 October 2011

Science and Technology Log

A current drifter we lowered off the RV Walton Smith.

At a couple of stops on the cruise we dropped some current drifters overboard. These current drifters will float at the surface of the water and travel with the gulf current. On top of the drifter there is a transmitter that will send a signal to a satellite. The scientists can then track movement of these drifters and map the ocean currents.

This drifter, I learned, was simply made. The materials, except for the GPS transmitter, can be found at a local hardware store and tackle shop.

Personal Log

(from left to right) Brian, Maria, Nelson & Kuan at work on the RV Walton Smith.

My cruise with the R/V Walton Smith has been exciting. It has been great to learn how science — in particular oceanography — is done. Scientists are dedicated, focused people. I can tell they love what they do.

The crew of the R/V Walton Smith are incredible. I have a lot of respect for anyone that can parallel park something the size of a house. Talk about teamwork!

To finish off, here are some sunset photos taken on the voyage.

Caitlin Thompson: Zooplankton, Ocean Currents, and Wave Gliders, August 7, 2011

NOAA Teacher at Sea
Caitlin Thompson
Aboard NOAA Ship Bell M. Shimada
August 1 — 14, 2011

Mission: Pacific Hake Survey
Geographical Area: Pacific Ocean off the Oregon and Washington Coasts
Date: August 7, 2011

Weather Data from the Bridge
Lat. 47 degrees, 00.8N
Long. 124 degrees, 29.8W
Present weather: Cldy 8/8
Visibility: 10 n.m.
Wind direction: 323
Wind speed: 08 kts
Sea wave height: 1 feet
Swell waves – direction: –
Swell waves – height: –
Sea water temperature: 13.7 degrees C
Sea level pressure: 1018.8 mb
Temperature – dry bulb: 15.8 degrees C
Temperature – wet bulb:  14.7 degrees C

Science and Technology Log

On the fish deck in my work clothes

The Shimada conducts research around the clock, with crew members working twelve-hour shifts. So far, I have worked with the acoustics team studying hake during the day, when the hake school together and are easy to fish. Last night I branched out, staying up with Steve Pierce, the oceanographer studying ocean currents, Jennifer Fisher, a faculty assistant at Oregon State University (OSU) who is studying zooplankton, and her intern, Angie Johnson, a graduate student at OSU. All the different research on this trip complements each other, and I learned more about the acoustic team’s work from the night people.

Gray's Harbor Transects

The map at right shows the transects we follow and the stations that the night team takes samples, which Steve chooses. Just like the acoustics team, he only chooses sites on the east-west transects. The night team usually works one transect ahead of the day team, and must have the ship back where they started by sun-up. Steve is mapping small currents because, he says, surprisingly little is known about ocean currents, even though they have a tremendous impact on ocean life.

He is especially interested in the polar undercurrent that brings nutrient-rich water from the south up along the west coast. A small current, it is nonetheless important because of the nutrients it carries, which come to the surface through upwelling. He uses an acoustic device, the Acoustic Doppler Current Profile (ADCP), to find the velocity of the water at various depths. The data from the ADCP is skewed by many factors, especially the velocity of the ship. Later, Steve will use trigonometry to calculate the true velocity. He also uses the Conductivity, Temperature, Depth (CTD) meter, lowered into the water at every station during the night. The CTD gives much more information than its name would suggest, including salinity, density, and oxygen. It is deployed with a high-speed camera and holds bottles to capture water samples. I was impressed by the amount of work – and math! – that Steve does in between cruises. When he has down time on this cruise, he told me, he is calculating work from two years ago.

Jennifer divides a sample in the Folsom plankton splitter

Jennifer and Angie are studying plankton, the organisms at the very bottom of the food web. Immediately, I recognized euphausiids, or krill, from the contents of hake stomachs. Actually I recognized their small black eyes, which always reminded me of poppy seeds when I saw them in hake stomachs. Jennifer is conducting this work through her group Northwest Fisheries Science Center, which, as she describes it, gives her a wonderful freedom to research different projects related to ocean conditions, especially salmon returns. In this project, they measuring phytoplankton, tiny, photosynthetic organisms, by measuring chlorophyll and nutrients. They are also looking at zooplankton, like euphausiids, salps, and crab larvae, which we examined other the microscope. To help the acoustics team refine their ability to use sonar to identify zooplankton, Jennifer and Angie record certain species. The acoustics team will match up the acoustics data that is continuously generated on this ship with the samples.

Angie takes water samples from the CTD.

Today, the second catch of the day was aborted because of whales too close to the ship. However, the NOAA’s Pacific Marine Environmental Laboratory (PMEL), had asked the Shimada to investigate its waveglider. A waveglider is type of robot called an autonomous underwater vehicle (AUV). Programmed to travel and record data, it does not need an operator. The PMEL folks were concerned, however, that its AUV might have a problem.The bridge set the course for the AUV, described as a yellow surfboard, and I headed up to the flying deck, the highest deck and an ideal spot for observation, to watch for it. Immediately we saw a humpback whale, just starboard of the ship, spout and roll through the water, its tail raised in the air. Soon the AUV appeared. We saw nothing wrong with it but communicated our observations, photographs, and video tape of it to PMEL. The PMEL’s system of wavegliders monitor carbon dioxide levels and use the kinetic energy of ocean waves to recharge the batteries. The acoustics team hopes to get their own waveglider next year to collect acoustic data in between transects. As I was peering  over the edge of the boat, examining the surfboard-like robot below, I heard a loud splash. A bout ten  Dall’s porpoises were playing around the bow of our boat, rippling in and out of the water. Dall’s porpoises are tremendously playful creatures, and will often play around ships. But our ship was barely moving, and the porpoises soon lost interest and swam away.

Wave Glider, seen from above

Personal Log

I’m getting a little of everything on this cruise. I would have stayed up two nights ago for the deploymentof the CTD and zooplankton samples, but the propeller developed a loud enough whamming sound to suspend all operations indefinitely. I woke up at 4:00 AM yesterday because the boat was swaying back and forth violently. (Violently by my standards, that is; more experienced mariners insist the swell is nothing.) Since our bunks go port to starboard, I could feel my weight sliding from hip to head to hip to head as I was rocked back and forth in bed. Meanwhile a discarded lightbulb in a metal shelf was rolling back and forth steadily – rattle-rattle-WACK! rattle-rattle-WACK! – until Shelby Herber, a student at Western University and my roommate, got up, found the culprit, and wrapped it in a shirt. When I woke again, it was eleven hours after the discovery of the problem with the prop and well past breakfast, and I started to get up until Shelby told me we were off transect, headed to shore because of the propeller.

Wave Glider from beneath the water, taken from PMEL's website

So we took our time getting up. But when I finally arrived in the acoustics lab, Rebecca was running up the hall, saying, “Caitlin, I was looking for you! There’s a great big shark outside, and we’re pulling up the ROV!” The ROV is the remotely controlled vehicle, a robot like the AUV, but one that requires an operator to make it move. Unfortunately, out on the fish deck, the ROV was being put away and the shark gone off on his fishy business. To console me, John had the videotaped footage from the ROV and the dorsal fin of the shark, and showed me both. The ROV revealed no damage and I was invited down to the winch room, where the bang-bang-bang coming from the propeller was unnerving.

Puzzled birds approach the ROV

Everyone was in an uproar trying to decide what to do, an uproar made all the more dramatic by the steady lurching and swaying of the ship, which throughout the day has sent most of the scientists to their room for at least a few hours and most of the deck hands to tell stories of unhappy tourists who couldn’t find their sea legs. Finally, the engine guys decided the warped propeller would not prevent us from getting to Port Angeles, and Rebecca decided it would not interfere with the acoustics, and we got back on transect.

ROV

I’m getting a little bit of everything on this cruise. I’ve seen sharks and marines mammals, calm seas and rockier seas, an impressively well-functioning ship and a number of technological problems. I’ve interviewed scientists, NOAA Corps officers who command the ship, and crew members who recount endless adventures at sea. I’m even signed up for the cribbage tournament, which I’m not entirely thrilled about since I don’t know how to play bridge. I’ve been impressed by how much time and information everyone seems to have for me. I am constantly thinking how I can bring this experience back to my students. Some ideas are to have a science and math career day, collect weather data like the data the bridge collects, dissect hake, and examine zooplankton under a microscope. Various people on board have volunteered to help with all my ideas.