Overview

We were eager to start recovering our moorings, but the sea is pretty choppy today, so we are going to wait until tomorrow. While we’re waiting, we thought we’d give you a little refresher as to what we are doing out here so that you know what to expect in the coming weeks.

As you may recall, last year we deployed six acoustic sources and a Distributed Vertical Line Array (DVLA) in the Philippine Sea. The map shows the locations of the 6 sources and the DVLA. Right now we are at he location of Source 5. The DVLA consists of approximately 5km of wire with 150 hydrophones (underwater microphones) attached to it. Each of the six source moorings also has a smaller array with four hydrophones on it. All of the moorings are anchored to the bottom and held vertical by a subsurface buoy. The basic idea is to transmit sound back and forth between the different sources to map out the temperature and currents of the ocean in between the moorings. Check out our earlier post “An ocean acoustic tomography experiment” for more info.

The sources have been out here transmitting and collecting data for almost a year now, so we are going to go pick up the moorings one by one and start downloading the data. We are also going to be making some of the same types of measurements we made during our last cruise. For example, we plan to make more maps of the ocean floor between our moorings (see our post Sounding Out the Ocean’s Depths) and we will be doing some more CTDs (see our post Good Morning CTD). In addition we have a couple other exciting side projects that are going on during this cruise as well. We will be recovering a couple acoustic seagliders, which are underwater robots that have been listening to the sources and measuring temperature and salinity in the upper ocean. We'll also be sampling some mud from the bottom of the ocean!

Back, by popular demand

The able sea chicks are back! Remember all those moorings we deployed last year? Well, the time has come for us to head back out into the Philippine Sea to recover them and download all the data that has been collected over the past year.

We are experiencing a little deja vu as we sail out of the harbor in Kaohsiung, Taiwan on the R/V Roger Revelle, but a lot has happened since we set out on our deployment cruise a year ago.

Able Sea Chick Kathleen finished up her sabbatical at the Scripps Institution of Oceanography in San Diego and is back teaching at George Mason University. Lucky for us, she could take a few weeks off and join us for another oceanographic expedition.

Able Sea Chick Lora finished up her postdoc at Scripps, and has started a research position at the University of Hawaii (Aloha!). She was out on the Revelle here in the Philippine Sea last November to deploy acoustic Seagliders, which have been swimming around the moorings making measurements since that time. We will be recovering two of these gliders during this cruise and will tell you all about them in later posts.

Welcome aboard for another cruise, and feel free to spy on us on the ship's webcam.

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!

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.

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.

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.



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!