Tuesday, May 18, 2010

Mission Accomplished!

After 3 weeks at sea and 7 (successful!) mooring deployments, we are now safely back in San Diego. Even the dock rock (when you close your eyes and still feel the motion of the ocean) and jet lag are in the past. Now comes the hard part: sitting back and waiting for a whole year until we can go back and collect our data!

A lot of people ask if it is hard to be on a ship for such a long time, but it's really not as intolerable as you might think. Since the ship is only about 300 feet long, we just had to climb up or down a ladder to get pretty much everything we needed, whether it was a snack, a nice cozy bunk, or a place to do laundry.

Although the Revelle can accommodate up to 37 scientists, we only had 12 people in our science party so we each got our own stateroom. The staterooms each have two bunks, dresser drawers, a desk, and a sink. There is a bathroom, or "head" as we call it at sea, shared between two staterooms.

We had three meals prepared for us every day in the galley, which is what we call the kitchen on the ship, and there was ice cream and other treats available at all hours. To counter all the intake of food, there is an exercise room with a stationary bicycle, rowing machine, treadmill (jogging in place on a moving ship can be quite an adventure!), and a stair-stepper. The ship also has public computers with internet connectivity, a library full of books, a lounge with a TV and hundreds of DVDs, and even a Wii!

That said, it is nice to be back on solid ground where we don't have to worry about the seas knocking us over in the shower or sliding our lunch off the table if we aren't paying attention!

We would like to thank to the Office of Naval Research for funding the experiment and Dr. Peter Worcester, the chief scientist, for leading it. We couldn't have done it without Captain Desjardens and the crew of the R/V Roger Revelle, especially the resident and computer techs Josh, Brent, and John. We would also like to acknowledge the hard work of the rest of the science crew:

Rex Andrew (University of Washington)
Scott Carey (Scripps Institution of Oceanography)
Jim Dunn (Woods Hole Oceanographic Institution)
Matt Dzieciuch (Scripps Institution of Oceanography)
Lloyd Green (Scripps Institution of Oceanography)
David Horwitt (Scripps Institution of Oceanography)
John Kemp (Woods Hole Oceanographic Institution)
Matt Norenberg (Scripps Institution of Oceanography)
Marla Stone (Naval Postgraduate School)

We also thank you for following along with us in the Philippine Sea! We hope that you have learned a little bit about acoustical oceanography and that you have enjoyed the adventure! If this blog sparked your interest in studying ocean science, and acoustics in particular, we encourage you to learn more about it. The Discovery of Sound in the Sea website has some great resources, as does the Scripps Institution of Oceanography website. Your local aquarium probably has great exhibits, too. Whatever you do, we encourage you to keep learning about the ocean!

Tuesday, April 27, 2010

Able Sea Chick (and Girl Scout!) Marla Stone

Marla Stone, another member of the science party here on the R/V Revelle, is even abler a sea chick than we are! She has practically lived her life on the ocean, captaining fishing boats and scuba diving boats and even working for the state as a scuba diver doing inspections. Marla now goes to sea in the name of science and has been doing oceanography cruises while working for the Naval Postgraduate School (NPS) in Monterey, California for the past 21 years.

Growing up in the 1960s in Claremont, California, Marla was a girl scout from the time she was in 3rd grade through the time she reached seniors in the 9th grade. She has some wonderful memories from her girl scout days and told us about a time her troop chartered a sailboat, the Swift of Ipswich, and sailed it from Santa Barbara out to the Channel Islands. She said they felt like they were pirates, paddling around in rowboats, singing pirate songs, swimming, and sleeping in hammocks. She also remembers being impressed by the marine life they saw, like a basking shark and a pod of dolphins.

One meets a lot of interesting people at sea, and living on a ship with Marla for the past few weeks gave us a great opportunity to get to know her better and hear some of her sea stories. We also had a couple questions for her about what her job is like and how she ended up doing the work that she does.



US: How did you get interested in marine science?
MARLA: I grew up in the mountains, but always loved reading books about the ocean and stories about sailing. I was particularly influenced by the book The Silent World, by Jacques Cousteau. I was 13 years old when I read that book and decided then and there that I wanted to spend my life learning about the ocean. I took lots of math and science classes when I was in high school and had my heart set on studying oceanography.

US: What exactly is your job?
MARLA: My official title at NPS is Staff Oceanographer. I design moorings and then go out and deploy them in the ocean. People tell me where they want to make measurements and I design a mooring based on what the currents are like at their chosen site, how deep the water is, and what kind of instruments they want on the mooring. I do a lot of work with instrumentation and data collection, but I don't do much data analysis. I enjoy the independence of my job and the fact that I don't have to sit in front of a computer all day.

US: What education did you need for your job?
MARLA: I went to Humboldt State University in Northern California and got a bachelor's degree in oceanography, just like I always wanted. Oceanography is not a common college major, and in the 1970s they didn't know what to do with an oceanography degree so they required another one. I then earned a separate degree in biology. After that, I went to Moss Landing Marine Labs to get a master's degree. I got a lot of field experience while working on the degree, but left to work as a ship's captain. When I started at NPS, I finished my master's degree in physical oceanography.

US: What lead you to your current position?
MARLA: I randomly walked into NPS one day, figuring that if it was run by the Navy it had to have something to do with oceanography, and asked if they were hiring. They told me they needed somebody to do mooring work, and when they heard about the experience I had from college and at Moss Landing, they took me directly to chairman of department and told me I could start work the next day. I've been there keeping the mooring program alive and well ever since.

US: How often do you go to sea?
MARLA: It varies from year to year depending on what is going on. Generally I go on about 8-10 sea trips per year. Some of them last several weeks, like this one, and some are just a couple of days.

When Marla started working in oceanography, it was not as common to see women on a research vessel. In fact, on one research cruise, they had Marla stay in the sick bay because she was the only woman aboard and there was not a room for her! This didn't bother Marla, though. She said she was always the first girl they every hired for every job she had growing up, including fixing cars, working at a hydroelectric power plant, working at a boat shop, and captaining a dive boat. When she was captain of the dive boat, she was actually the only female captain on the west coast at the time! Marla's story is an inspiring one about following a dream and not letting anything stop her. We can attribute much of the opportunity we have today to pioneers (and ABLE SEA CHICKS!) like Marla.

Monday, April 26, 2010

Hydrophones galore!

A couple days ago we deployed the final mooring of this cruise: a large receiving array located inside the pentagon of our set of source moorings. This array contained 150 hydrophone modules that are set up to listen to the sources.

The picture below shows what a hydrophone module looks like when it is opened up:

The silver colored case on the left is the pressure case. It is what keeps the electronics (the parts on the right) from being crushed when the module is deployed deep in the ocean. On the right side, you can see the lithium battery that powers the module during the year it sits in the ocean. The part labeled "inductive modem enables communication between the module and a control unit located above it on the array. The control unit tells the module when it should turn on and listen to the sources. Of course the module has to have someplace to record the sounds it hears from the sources. An SD card (like the one you probably have in your digital camera) is used to store the recordings. The hydrophone (the underwater microphone) is inside the blue tube at the bottom of the module.

Before we could deploy all these modules, we had to run a series of tests on them to make sure they worked properly. The following video clip shows how we tested that the hydrophone was working before we sealed everything up.

video

Thursday, April 22, 2010

Where in the world is the mooring?

When we deploy an acoustic mooring, we start with the buoy (the big yellow top float) first. Then we attach more wire and instruments as the ship slowly moves forward. By the time we're ready to attach the anchor, we have about 3.5 miles of wire strung out behind the ship. The last step in the deployment is to dump the anchor and let it sink to the bottom. The anchor pulls the rest of the mooring underwater.

video

We let go of the anchor at our chosen site, but the anchor doesn't fall straight to the bottom because it's being dragged back by the buoy and other equipment on the 3.5 mile wire. After the anchor has reached the bottom (it takes about 50 minutes), we have to do a survey to figure out exactly where it landed.

Naturally, we use acoustics to do the survey. Similar to how we measured the bottom depth, we send a short "ping" from the ship to the anchor. The acoustic release (a piece of equipment attached the anchor) replies with another ping. By measuring the time it takes for this signal to travel to the bottom and back, we can figure out how far away the anchor is from the ship. The picture below shows what we might learn from making one distance measurement:


A single distance measurement tells us that the anchor could lie anywhere on that blue circle. (The distance from the ship to any point on the circle is the same.) Since we need to know the exact anchor position, we obviously have to make some more measurements. So we move the ship and make a second measurement of the travel time (thus the distance) to the anchor. The picture below shows us what that second measurement tells us:



Now we know that the anchor has to lie on both the blue and the red circles. That means that the anchor could be at one of two places (indicated by the stars on the plot). Taking a second measurement obviously narrowed down the list of possible locations for the anchor. Let's see what happens when we take a third measurement:



Now the anchor has to lie on all three circles, so we know it must be located at the intersection point (marked with a triangle). Hooray! We've found our anchor!

As you can see from this post, acoustic surveys require knowing a bit of geometry (to find the intersection points of these circles). It's a practical application of the mathematics you have learned (or will learn) in school.

Last Source Mooring Deployment!

We have now deployed all six of our source moorings and confirmed that they are all working. Whew! Tomorrow we deploy our last mooring with all the hydrophones that will listen to these sources.

It doesn't take a scientist to figure out what would happen if we started with the anchor...it would sink right away! We start with the buoy because it floats. The ship then moves into the wind at a speed of about 1 knot (which is about 1 mile/hour) so the wire doesn't all pile up in one spot and get tangled. We keep feeding the wire out using a winch until we have the entire 3-1/2 miles of mooring floating on the surface behind the ship. When we reach the end we can't even see the buoy anymore! We then drop the anchor, and it pulls everything else down with it.

The wire comes in sections, usually 500 meters long, so we have to keep adding to the mooring as we go along. These shots of wire are on reels which are spun around by a winch to pay the wire out. The most important thing is to never let it go when we are adding another piece of the mooring! Sometimes we can hook onto a chain to hang onto the mooring, but if we are just adding another piece of wire there isn't anything to hook onto so we use a Yale grip, or Chinese fingers. This is a loop with 4 ropes attached that are wrapped around the wire very tightly so it looks like a braid (you can see it in the video). It holds onto the wire so tight that we can just hook onto the loop and that will hold the whole mooring.

The entire deployment takes about 10 hours, but the following video condenses it to just over a minute. Don't blink!

video

Saturday, April 17, 2010

Sounding Out the Ocean's Depths

We saw from the last post on CTDs that the ocean in the area where we are working is about 3-1/2 miles deep. The ocean is not necessarily flat at that depth, but it can have hills and even mountains, called seamounts, and deep trenches. When we deploy an acoustic mooring we don't want the anchor to land on the side of a seamount and go sliding down, so before we do a mooring deployment we always take a bathymetric survey to get a map of what the bottom of the ocean looks like. We then pick out a nice flat spot to put in the mooring.

We take bathymetry (bottom depth) measurements using the ship's multibeam sonar. It sends out high frequency signals (called "pings") from transducers at the bottom of the ship. When the pings hit the bottom of the ocean, they bounce back to the ship. If we measure the time it takes for the sound to travel to the bottom of the ocean and back again and we know the sound speed of the water from the CTD, we can figure out how far away the bottom is. The multibeam sonar keeps pinging as it moves, so we put together the results from thousands of pings to get a picture of the bottom like the one below. Here, blue is deep and red is more shallow. You can see there is a seamount with a red peak next to the valley where we put the mooring (indicated by the red arrow).


As you can imagine, if we drop an anchor from a ship to the ocean floor 3-1/2 miles below, it does not always land directly below the point where we dropped it. In our next post we'll describe how we find out exactly where the anchor landed. Here's a hint: acoustics again!

Thursday, April 15, 2010

Good morning CTD!

The Chicks are a bit bleary-eyed this morning after getting up at 4:30 AM to make a measurement of the sound speed at the location of the acoustic mooring we put in yesterday. We need to know the sound speed in order to figure out exactly where the anchor of the mooring landed. (More on that in a future post.)

Sound speed depends on the temperature and salinity (saltiness) of the water, as well as on depth. To compute the sound speed, we first measure the salinity and temperature using an instrument called a CTD, which stands for Conductivity-Temperature-Depth. The CTD has a thermometer to measure temperature, a pressure sensor to measure depth, and a conductivity sensor to measure how well the sea water can carry an electrical current. Saltier water carries more current, so by measuring conductivity we can determine the salinity of the water.

The CTD is attached to a round frame that is lowered over the side of the ship. Since we're in very deep water (about 5600 meters or 3.5 miles!) it takes about three and a half hours for the CTD to make the trip to the bottom and back. Just to be safe, we stay about 100 meters off the bottom so that we don't risk crashing into the sea floor by mistake!


Once it's back onboard we have all the data we need to compute the sound speed. The plot below shows the measurements we made this morning (temperature, salinity, and sound speed). Note that the temperature is nice at the surface, and gets very cold down deep. The sound speed increases towards the surface due to higher temperature and increases towards the bottom due to higher pressure.



CTD's don't always have to be done so early in the morning, but we needed to get this one out of the way to leave time for some other work today. While it was painful to hear the alarm go off at 4:30 AM, we did get to see a great sunrise!

Wednesday, April 14, 2010

Safety First!

Safety is very important when we are out here in the ocean because we are over a day's steam from dry land and help! We can't just dial 9-1-1 if there is a problem, so everybody on the ship has to work together in an emergency situation. We do regular training drills on the ship so we know what to do if there is a fire or if we have to abandon ship or if somebody falls overboard. The ship's crew also instructed us how to launch the lifeboats in case of an emergency. When we hear the ship's whistle for the abandon ship drill, we all have to meet, or muster, to get a head count and make sure to bring our life vests, long pants, a long sleeve shirt, and a hat for sun protection to prepare for a situation in which we would be left bobbing around in the water for a while. The ship also provides immersion suits, or "Gumby suits," which are not the easiest things to put on (check out our video!), but they would keep us warm and floaty if we had to jump ship.
video


When we are working on deck deploying a mooring, we have to be very safety conscious as well. We wear steel-toed boots because there is a lot of heavy equipment out on deck that could fall on our feet. We also wear work vests, which are not quite as bulky as life vests, but would still provide flotation in case we were to fall overboard while working on deck. The ship has 2 cranes aboard to help us move around our big, heavy equipment. Whenever we are moving things around we have to make sure to hold the equipment using tag lines (check out the photo) so it doesn't swing out of control when the ship moves with the waves. And of course, we always wear our (PINK!) hardhats.

Sunday, April 11, 2010

Anatomy of an Acoustics Mooring


Taking measurements in the ocean is a lot different than taking measurements on land. If you want to take a temperature measurement on land, you don't have to worry about your sensor floating away! Oceanographic moorings anchor instruments to the bottom so they can stay in the same place for long periods of time. We want to make acoustic measurements for a year, and we need our sound sources and receivers to stay put, so we install, or deploy, acoustic moorings.

An acoustic source mooring, like the one shown on the left, consists of an anchor at the bottom and a buoy at the top with the source suspended in between. It is all connected by shackles and chains, and, most of all, jacketed wire rope. You can think of wire rope as the skeleton of the mooring. Everything between the anchor and the buoy is attached to it.

The buoy at the top is a subsurface buoy, meaning that it does not bob around in the waves at the surface, but it sits about 180 meters below the ocean surface so that passing ships will not hit it. The buoy provides flotation so that the wire will be pulled tight and the mooring will stand up straight.

Because the mooring is over 5 km long, we need some additional buoyancy to help the buoy keep the mooring as straight as possible. For this we use glass spheres that are filled with air so they float. These glass spheres are encased in hard yellow plastic shells so there is a way to attach them to the rest of the mooring and to protect them so they don't crack.

In the mooring drawing we show here, the sound source is located 1050 meters below the surface. Above the source is an array of four hydrophones. These four hydrophones will listen to the other sources that we deploy and the other source moorings will listen to this source. We also have an ADCP (Acoustic Doppler Current Profiler) on this mooring, which sends out much higher frequency sound in the upward direction, which will be used to measure the strength and direction of the currents passing over it. A picture of the ADCP and some of the other mooring elements is shown on the right. Pictures of the glass balls and anchors can be seen in our earlier post describing the loading of the ship.

These moorings will stay in the water for a whole year collecting data, but what happens when that year is over and we want to get our hands on the data? We have to go back to the mooring location and pop up the mooring and bring it back onto the ship. It would be pretty difficult to bring a 2-ton anchor back on board so, well, we don't. Just above the anchor we have 2 acoustic releases. These instruments have a hook (where the red arrows are pointing in the picture on right) that stays locked on a chain that is attached to the anchor. When we go back to pick up the moorings, we send out a special coded acoustic signal from the ship, and when the acoustic release "hears" it, it unhooks the chain to the anchor and floats up to the surface with the rest of the mooring, leaving the anchor on the bottom.

Saturday, April 10, 2010

How signal processors earn their paychecks

As we noted earlier, acoustic tomography relies on accurate measurements of the time it takes for a signal to travel between a source and a receiver. The speed of sound depends on the water temperature. Since sound travels faster in warmer water, we would expect the travel time between two points to get shorter as the water warms up.

Yesterday we showed you what the source signal looks and sounds like. That recording was made during one of source tests conducted a couple days ago. During these tests the source was lowered on a wire from the ship to a depth of about 1 kilometer. The receiver was located on the same wire, about 500 meters above the source. Since the receiver was so close to the source, it was quite easy to hear it.

In a typical acoustic tomography experiment the source and receiver are much further apart. In the experiment we are setting up right now, the shortest range between source and receiver is about 125 kilometers, and the longest range is about 640 kilometers! Since sound signals lose energy as they travel, hearing them at these long distances is difficult. The picture below shows the signal received from one of these sources at a range of 500 kilometers:



Can you tell where the signal starts and ends? Probably not from this picture! In order to see when the signal arrives, we have to use tools developed by signal processors. Applying these tools to the signal above, we get the following picture:



This picture is a lot easier to read since it contains only two big spikes. These spikes correspond to the arrival times of two signals.

Signal processors earn their paychecks by designing signals (like the one we're using) and processing tools to make those signals easier to detect at long distances. In addition to oceanographic applications, signal processing is also used in cellular phones, digital tv's, MP3 players, and lots of other electronic devices. Most signal processors are trained as electrical engineers (like Kathleen). If you're interested in learning more about signal processing, feel free to email Kathleen. You can find her email address on her website.

Friday, April 9, 2010

What do our source and a trombone have in common?




The picture below shows one of our acoustic sources being moved into the warehouse in Kaohsiung. This type of source is similar to a trombone. To change the pitch on the trombone, the trombonist moves the slide in or out, which changes the length of the instrument and alters the pitch (frequency). To change the pitch our source is playing, we adjust its length by moving part of the black tube.



Our source produces sound in the band of frequencies between 225 and 325 Hz. For reference, 261 Hz is the C below middle C on the Western musical scale. A baritone singer could easily sing our source signal (though we haven't found any singers eager to be lowered to a depth of 1000 meters in the ocean just to sing for a year!).

Our source plays a very simple type of "music". The figure below shows a picture of the signal we recorded during one of our source tests this week. If you click on the picture, you'll hear what the source sounds like.

video

The source signal is the humming sound that increases in pitch over time. The picture below (called a spectrogram) shows how the frequency of the source signal changes with time. The source signal corresponds to the dark red line. From this picture you can see that the source starts at a frequency of 225 Hz and slowly increases to 325 Hz over a period of 135 seconds.



While this signal may not make any of the Top 40 music charts, it is very useful to acoustic tomographers. We'll show you more about this in a later post when we discuss how signal processors (like Kathleen) earn their paychecks!

Wednesday, April 7, 2010

Loading the ship



There's a joke among the people in our lab that we don't know how to travel light. All in all we shipped about 180,000 pounds of equipment to Kaohsiung, Taiwan for this cruise. After the equipment passed through Taiwanese customs, it was brought to the dock in shipping containers and had to be fork-lifted out onto the dock before being loaded onto our ship, the R/V (Research Vessel) Roger Revelle using a crane.

video

It took about 3 days to get everything set up and ready to go. This may seem like a long time, but we set up a portable electronics lab inside the ship and all the computers and other support equipment as well as all the gear that is loaded onto the the ship's deck have to be securely tied down so they don't go flying when the ship takes a roll!

The last frame of the movie shows the back deck of the ship. Some of the things you see on the deck are buoys (the big yellow spheres and disk-shaped things) and acoustic sources (the long tube-shaped things - we'll talk more about these in the next post). We also brought along a whole container full of glass balls encased in yellow plastic to serve as flotation for the moorings (left), enough wire rope to run the length of a marathon, and ten 2-ton anchors for the moorings (right), all chained down so they won't budge until the time comes to release them overboard.

Once everything was loaded and tied down, we waved goodbye to Kaohsiung as we were escorted out of the harbor by a pilot boat and into the open ocean.

Monday, April 5, 2010

Our starting point: Kaohsiung, Taiwan

Our deployment cruise is leaving from Kaohsiung, Taiwan. Taiwan is a large island located to the east of China. Japan is to the north and the Philippines are to the south. Kaohsiung, the second largest city in Taiwan, is located on the southwestern coast of the island (see map to the right). Kaohsiung is a major shipping port in Asia. In 2004 it was ranked the 6th largest container shipping port in the world!
Our group has been in Taiwan for a little over two weeks preparing the equipment for the cruise. We've been pretty busy with work, but have had a little time to see a bit of the city. We visited the Jade market the first weekend we were here. This market is best known for the jade jewelry sold there (in addition to paintings, antiques, and other interesting items).

The video and pictures show a bit of the local scenery. The video shows a short clip of an area near our hotel. The pictures show an opera that we saw being performed as a part of a local festival, one of the many statues decorating the bike path near the warehouse where we've been working, a golden Buddha statue, and Lora riding a scooter!



video










Our ship is docked in Kaohsiung and is currently being loaded with all our equipment. In the next post we'll tell you more about the ship, and show you some pictures of the loading process!

Sunday, April 4, 2010

An ocean acoustic tomography experiment

Have you ever seen an unborn baby on an ultrasound? To get that picture, a transducer placed on the mother’s belly sends out sound waves that bounce off the baby, producing an acoustic image of the baby inside. Acoustics can also be used in the ocean to get an image of things we cannot see with our eyes. Fish finders send out sound from a boat into the water, looking for the sound to bounce back from fish below. Whales and dolphins also use echolocation to find their way underwater by making sounds in the water and listening for it to bounce back to them. During our experiment, we will use sound in much the same way to get an image of the sea floor.

Acoustics is a great tool for looking for things in the ocean, whether that be the ocean bottom itself or things swimming around in the water, but it can also be used to look at the water itself. The speed that sound travels in the ocean depends on a number of things like the temperature of the water, the salinity of the water, and how fast and in what direction the water is moving. By taking extremely precise measurements (on the order of micro-seconds!) of the time it takes for the sound to travel from a sound source to a listening receiver, we can learn a lot about the ocean that the sound has traveled through. Some things in particular that we can look at are the temperature of the water and the speed and direction of ocean currents. This is called ocean acoustic tomography. To learn more about how sound is used underwater, check out the Discovery of Sound in the Sea website.

In this experiment, funded by the Office of Naval Research (ONR) and led by Dr. Peter Worcester, we will put out six acoustic sources, arranged a few hundred km apart in a pentagon shape, that will all transmit to a vertical line array (VLA) receiver which will have 150 hydrophones, or underwater microphones, that will be listening to the sources. Because the sources are positioned around the array, the sound transmitted from each source will travel through a different part of the ocean to reach the receiving array, giving us measurements of six different paths or “slices” of the ocean. The sources and receivers will stay in position for 1 year and we will go and pick them up and collect our data. The sources transmit for about 2 minutes at a time a few times a day every few days, allowing us to see how the ocean is changing throughout the year.

Saturday, April 3, 2010

Welcome to our blog!

What does the word “acoustics” mean to you? Some things that may come to mind are acoustic guitars or the acoustics of a room. Acoustics is the branch of physics that deals with the properties of sound, whether it is in a room, in a guitar, for medical use in the body, or in the ocean.

The Acoustical Society of America is planning a special session on April 21, 2010 during it’s meeting in Baltimore, MD, entitled “Listen up and get involved,” which will introduce the science and applications of acoustics to local Girl Scouts by highlighting the work of female scientists in various branches of acoustics.

We are two female scientists who are interested in how sound travels in the deep ocean and how we can use acoustics to study the ocean (check out our bio pages!). Collecting deep-water acoustic data for our research is no small task. Just getting the instruments positioned to take data can take weeks of work at sea! In fact, we will be on a ship in the Philippine Sea doing just that at the time of the Baltimore meeting. We obviously won’t be able to attend the special session in person, but we thought that keeping a blog of our day-to-day experiences at sea would be a great way to introduce the Girl Scouts (and anybody else who is interested!) to what is involved in an ocean acoustics experiment.