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Notes from the Field

Seaglider #189 Away!

September 14th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

We just launched the first of our autonomous vehicles – a pink Seaglider with the sexy name of #189.

The story of Seaglider 189 begins.

Underwater gliders are the longest-range autonomous undersea vehicles in the oceans by virtue of their very simple propulsion mechanism: the translation of a vertical force into an horizontal one through use of wings. Gliders adjust their buoyancy by alternately inflating and deflating a small swim bladder appended to the vehicle’s body, a mostly rigid pressure hull. A volume variation of only a couple of thousandths of the overall vehicle’s volume is enough to provide an upward or downward buoyancy force that balances a combination of lift and drag forces, resulting in forward and vertical motion, the essence of gliding. Gliders, in effect, use wings as their propellers.

About an hour away from deployment.

Once made heavy, Seagliders sink to a prescribed depth where an electric motor drives a pump to change the vehicle’s density from heavier to lighter than the surroundings, causing them to ascend. They slice through the ocean along sawtooth paths.

The fixed supply of electrical energy aboard the glider in the batteries is used for propulsion and instrument operation. At SPURS we are using gliders in somewhat opposite extremes: some of them (the Slocum gliders — more about them later) are packed with power-needy instruments that limit their mission length to a couple of weeks, while others (Seagliders) direct a greater portion of energy to propulsion and operate a less hungry suite of sensors to achieve the 7-month mission duration required by the SPURS ship schedule.

Gliders were developed to probe the oceans independently of ships. Persistence is their virtue. The Seagliders launched from R/V Knorr are meant to repeatedly survey a limited region of the ocean, every fortnight repeating a 150-nautical mile (480-kilometer) circuit to provide a four-dimensional description of the upper ocean across wide area of ocean centered on the SPURS moored array. Profiles of temperature, salinity, oxygen, chlorophyll fluorescence, and optical backscatter will be transmitted ashore at the end of dive cycles to 0.6 miles (1 km) depth, repeated about thrice daily.

A close-up of Seglider 189’s sensors.

These gliders are completely autonomous once submerged, until they make a call over the Iridium satellite network to report data collected and accept new instructions from ashore controllers that manage everything, from flight to sampling strategy. They steer toward instructed target positions by moving the battery pack to one side or the other, inducing a vehicle roll that results in a turn. They follow a calculated compass heading to approach each target and, once there, dive toward the next. Seagliders even predict the effects of currents on their progress to choose an efficient heading with which to approach the next target. Vehicle pitch is similarly controlled during flight and the nose is depressed at the sea surface to raise the trailing antenna above the waves to gather position information and communicate.

In addition to the standard suite of measurements, the SPURS Seagliders are carrying brand new temperature microstructure probes. These are intended to measure turbulence in the upper ocean over nearly 2000 km (more than 1000 nautical miles) of track through the ocean by each vehicle on each mission. The hope is that upper ocean turbulence, long exclusively measured by ship surveys, will in SPURS be extended over the course of a year in autonomous surveys. The salinity and temperature profiles collected by more conventional aboard instrumentation, together with turbulence profiles, will reveal where the ocean mixes with respect to the myriad fronts and eddies to be encountered in the SPURS region.

Members of the SPURS team, ready to deploy the Seaglider.

Getting lowered…

Free at last!

Finally, to answer the inevitable question: to what does Seaglider #189 owe its garish color? The original project engineer in Seaglider development, Jim Osse, had some paint left over from a human powered submarine contest his University of Washington team entered in Florida. He chose the hue selected by the customer ahead of him at the counter of a Seattle auto parts store, destined for a 1942 Ford Coupe (and, it turns out, a bevy of Seagliders, too): Hot Rod Pink. We are hoping that #189 stays in the pink and safely hot rods around the ocean until recovered next March!

Bring SPURS and Aquarius Into the Classroom!

September 13th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

“Why do sharks swim in saltwater? Because pepper water makes them sneeze!”

Jokes aside, why is saltwater so important? Find out using our educational resources about ocean salinity.

Along with our expedition, there are many web resources for educators wishing to incorporate oceanography and salinity into their curricula. This post highlights some of the resources and points of contact for Aquarius and SPURS expedition.

First, the Aquarius mission teamed up with Annette DeCharon and the Centers for Ocean Science Education Excellence-Ocean Systems (COSEE-OS) over the past several years to create educational materials on the Aquarius mission website. Created throughout the life of the Aquarius mission, these materials include classroom activities and data-driven tools that allow non-scientists to see the implications of ocean change on the environment. Here you will also find standards-oriented lessons, such as “Salinity Patterns & the Water Cycle,” which are organized according to grade-level and highlight the role of salinity in Earth and Ocean processes.

Test your knowledge of salinity on the Aquarius web page.

In addition, the COSEE-OS website has a variety of resources related to the Aquarius mission and ocean salinity. These include the COSEE-Ocean Systems/UMaine publication “Teaching Physical Concepts in Oceanography: An Inquiry-Based Approach,” and content-driven webinars and interactive concept maps created by NASA Aquarius scientists. These webinars focus on the technology and scientific process involved in measuring ocean salinity from space, emphasizing the role of salinity in regulating ocean circulation and Earth’s climate and weather.

View of the concept map created by Aquarius Principal Investigator, Gary Lagerloef, explaining the science goals and broader implications of studying sea surface salinity.

Example of one of the many freely-available assets from interactive concept maps and searchable on the COSEE-OS website.

Second, Phoebe Jekielek, also from COSEE-OS, joined us in Woods Hole for the pre-expedition media event. She certainly got up to speed on SPURS if you have questions! Currently available resources on the SPURS website include a Sampling Strategy Challenge, using the JPL Trajectory Tracking Tool, designed for in-class use to introduce teachers and students to one of the modeling tools SPURS scientists use to plan their cruise. Check back for more materials, pictures and interviews highlighting the scientists, technology and instrumentation of the cruise and the importance of understanding ocean salinity. Phoebe collected much of that information last week.

Example of the viewing window in the JPL Trajectory Tracking Tool showing “balloons” representing deployed drifters, long/lat coordinates and the “drifter track”output after running the simulation.

Dr. Andrey Shcherbina aboard the R/V Knorr with seagliders being deployed during the SPURS cruise.

Other, more general, resources include the NASA Physical Oceanography Program production on ocean motion dedicated to providing materials about ocean surface currents using figures, movies and links to other resources. Additionally, this site provides useful data visualization tools for use by teachers and students.

The BRIDGE also provides a wide selection of teacher-approved marine-related resources.

But the biggest resource for the next month is the team at sea on Knorr working on SPURS. I would welcome feedback and questions from students and teachers on my postings. Your questions might stimulate fresh directions on the postings and there is interest from those aboard ship in helping to answer your questions. Hope to hear from you soon!

Profiling Salinity from the Ship

September 13th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

A workhorse of our voyage is the two primary means of measuring salinity from the ship. We use two different Conductivity, Temperature, and Depth (CTD) instruments. One is used on station, when the ship is stationary and the other is used while we are underway (smartly dubbed the underway CTD). Remember that salinity is directly related to conductivity, so each of these instruments provides salinity profiles. On station, the CTD package can be lowered (via winch) all the way to the ocean bottom and is capable of also collecting water samples at 23 different levels. The underway CTD is a small, self-contained unit that makes measurements to only 1300 feet (400 meters) depth and it’s deployed on the end of a string and recovered using a small electric reel.

First CTD cast away.

I say these are our workhorses because we will use these instruments 24/7 for weeks on end. We plan stations 4-6 times a day with CTD casts to 3280 ft (1000 m) and an additional deployment per day to 6561 ft (2000 m). While en route, we plan to drop the underway CTD every hour.

Jeff, holding the underway CTD unit prior to deployment.

Gradually, over the course of many days, we will be able to map the upper ocean salinity and temperature fields from the individual profiles.

When we are out on deck deploying these instruments during the day, it is always remarkable how the color of the ocean and sky change from hour to hour. I think everyone marvels at the deep blue of the Sargasso Sea and the contrasting blues of the ocean and sky. The hues change as the sun angle changes during the day or clouds intervene. The cloud shadows on the water give the blues of the ocean a varying texture.

Shades of blue.

We love the color of the Sargasso Sea.

Everyday in the Sargasso Sea we see flying fish. They are best seen leaping from the bow wave of the Knorr and flying hundreds of feet to escape the ship. They are adapted to escape predators with their speedy swimming and wing-like fins that allow them to stay airborne when they leap out of the water. It’s a show that is always available while we are underway. We just go to the bow and watch for a few minutes. I have not yet heard reports of whales or large fish observations. I did see one small school of smaller fish go by quickly while underway. It’s always fun to take a few minutes to just watch the ocean. There are plenty of things to see, if only you are prepared to observe them!

When we start 24/7 operations later in the week we will have deck lights on at night and that provides another observing opportunity. The lights may attract fish and squid to our locale. More on that next week!

Are We There Yet?

September 12th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

If you all are waiting to see some action at sea, I am sorry it is taking a bit to unfold. It takes about a week from Woods Hole to reach our study site at 25N, 38W. It’s good for us to have the time to check and re-check the instruments, get people trained in various procedures and ready to stand watch for 24/7 operations, and get to know our work mates. However, everyone that has prepared for more than a year for the expedition finds this week a long one. We want to be getting gear in the water and a flood of data passing through our computers. We want to be up all night, busy with deployments, water sampling, and scientific analysis. Everyday on the research site will be brimming with new data and constant planning for the next event.

All eyes in CTD operations.

The chief scientist has his hands full keeping the entire show operating smoothly. We have mooring, Argo float, and drifter deployments, glider operation, underway profiling, station profiling, autonomous profilers, and more meteorological sensors than can be easily counted. Everything needs to be working, providing good data, calibrated, checked and re-checked, and while many things can happen simultaneously, nothing should interfere with anything else.

Meteorological tower on the bow of the R/V Knorr.

Preparing a slocum glider.

The order of business is, very roughly, to get the sensors we want in the water (to supplement what the research vessel can do), off the ship and doing their job. The moorings and Argo floats take a lot of space and only serve us when deployed, so we will spend much of the first days on site getting these in the water. While we move from one site to another deploying equipment, we will also be mapping the ocean with instruments we lower from the ship on station or tow behind the boat while underway. During just about every moment, we try to gather data from the upper 1300 feet (400 meters), to characterize the salinity field and ocean circulation.

Once we have all our assets in the water, we can focus on using them in conjunction with the ship to characterize the ocean environment on time scales from minutes to weeks and from inches to a hundred miles. Over about three weeks we will do our best to map and understand how salinity varies at this spot in the ocean and why it does what it does. When the ship leaves, we leave many of these instruments in the water, to continue our work for the next 12 months. Expeditions in six months and 12 months from now will maintain and eventually recover many of the instruments we deploy in the coming week.  We think of it as deploying a sensor web in the ocean.

This kind of intense study is the basic work that helps us understand and interpret the weekly global maps of salinity we get from Aquarius. There are more esoteric and nerdy scientific questions that get answered along the way (making it very satisfying to all the scientists involved), but everyone is highly motivated by the opportunity Aquarius offers to study the global salinity field. SPURS is realizing that opportunity.

Measuring Salinity from Space

September 11th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

Recent years have seen significant developments in satellites for oceanographers. The European Space Agency launched the Soil Moisture and Ocean Salinity (SMOS) mission and NASA launched the Aquarius instrument on the Argentine SAC-D mission.

Artist’s concept of the Aquarius/SAC-D spacecraft. (Credit: NASA)

Salinity has always been a challenging but critically important measurement for oceanographers. The small changes in salinity that we sea in the ocean are important in determining the density of seawater and density differences are partly responsible for ocean circulation (direct forcing by the wind being another big factor). It’s a challenging measurement because we estimate salinity by simultaneously measuring the temperature and conductivity of seawater and using a well-established formula to calculate salt concentration. The salinity of the open ocean ranges from about 33 to 38 parts per thousand and the target accuracy of satellites is to measure differences of 0.2 parts per thousand. That is like measuring the change in salinity from adding a pinch of salt to a gallon of waters. I challenge you to taste the difference!

It’s the relationship between conductivity and salinity that allows for its remote sensing of salinity from space. As the conductivity of ocean surface waters change (with salinity) there are minute detectable changes in the “brightness” of the surface in microwave emissions. So, in theory, if we have a sensitive enough microwave radiometer we should be able to detect these variations from low earth orbit and translate them into salinity. In fact, the scientific and technical complexity of this task is enormous (and luckily space agencies feast on such challenges!)

SMOS and Aquarius are two very different solutions to the technical problem of measuring a small microwave signal from Earth orbit. But they both face the daunting task of making adjustments for the sea surface temperature and roughness, the intervening atmosphere and ionosphere, and galactic signals reflected off the sea surface (there are strong sources for the microwaves that astronomers have mapped for decades: in fact we measure salinity at a frequency band 1.4 Ghz that is “protected” for astronomical research.)

Well, you can surf the web sites if you want to go into all the details… but let’s get back to the ocean, since I am out here! The advent of SMOS and Aquarius has renewed interest in the details of surface salinity properties of the ocean. Never before had oceanographers had weekly maps of the global salinity field. We have been looking at temperature maps for decades, but salinity is new. It’s worth a whole posting on what it means to know both the temperature and salinity maps of the surface of the ocean year-round, and I’ll do that another day.

Aquarius’s first map of global ocean surface salinity, released in September 2011. (Credit: NASA)

SMOS and Aquarius drive scientists to wonder exactly how the variations of salinity seen from space come to be the way they are. That’s where detailed study of a few key ocean sites is so important.

Meanwhile, we are continuing to enjoy beautiful weather despite the hurricanes out and about in the Atlantic. The blue waters of the Sargasso Sea are delightful!