Notes from the Field

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!

Of ship meals and science

September 10th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

Saturday’s lunch menu at Chez Knorr.

Saturday, 8 September 2012 — Given the talk around the Knorr’s dinner table, you would have to say that oceanographic expeditions run on their stomachs. Key to surviving weeks away from home and family is good food and good moods. The food on the Knorr is excellent, so we are likely to have happier people and better results. Most people will come back a few pounds heavier. There is a gym on the ship but it can be dangerous to be on a treadmill or lifting weights in rolling seas…so, more than likely most will lose the weight battle to the dining experience!

Bobby, preparing for lunch.

Everyone has a mug.

Today was the day we passed in front of the predicted track of Hurricane Leslie. We felt a bit of the swell coming from the storm, but otherwise we had fine conditions. In the early afternoon, we slowed for a few minutes to deploy the first Argo float of the voyage. Deploying the floats is pretty easy since they have all been powered up and are ready to go right out of the box. We just have to slow the ship and lower the instrument over the stern and gently into the water.

We plan to deploy two Argo floats in front of the predicted hurricane track. They will measure temperature and salinity profiles before, during, and after storm passage. In addition the profiling instruments “listen” to ocean acoustics and can make an estimate of wind speed and rain rate based on the noise of those actions on the sea surface (pretty cool!) So, we especially wanted to see how the acoustic sensors deal with a big signal like a hurricane. Steve Riser at University of Washington is the Principal Investigator for the Argo floats in SPURS.

First Argo float deployment.

The float disappears over the stern.

I also received my first official science training of the voyage. We have a small device called an underway CTD  for measuring a profile of conductivity, temperature, and depth of seawater. Two people will work together to deploy and recover this instrument on an hourly basis throughout most of the experiment. The device is tethered to a small winch and boom (like a fishing rod and reel) at the stern of the vessel and dropped in the water to make measurements from the surface to 400 meters (about 1312 feet) depth while the ship is steaming at 10 knots. It finishes a profile in 100 seconds and is then reeled back aboard. It is kind of like hauling in a fish with an electrically-powered rod and reel. It takes 20 minutes to haul in the beast and then another few minutes to download the data from its internal memory to a laptop computer. We plan to deploy this instrument every hour once we begin normal operations in the SPURS region next Friday.

The latest wind and wave information from Hurricanes Leslie and Michael suggest that our path to the SPURS site is just about perfect for seeing the minimum impact from the storms. The seas are still lumpy, but Knorr looks to be slipping through the gap between the storms. Fingers crossed!

Hurricanes, make way for Knorr!

September 7th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

Cloudy skies over the Atlantic, with Hurricane Leslie in the distance.

We knew when we left Woods Hole yesterday that we had two hurricanes (Leslie and Michael) standing between us and our study site, far southeast of Woods Hole in the mid-Atlantic. How Captain Adam of the Knorr chooses to deal with this over the next days is a study in weather and ocean forecasting – and calculated risks. We considered at least three options: delay departure until the coast is clear, make a significant departure to the cruise track (sail far south, then east), or leave on time but travel quickly to the east and then south to miss the worst of the hurricane weather.

The last option is what we are doing. We abandoned plans to do test stations and do science training for a few days so we can make hast to the east, to the east side of Leslie’s track. Then we can make our way south and around Michael. Tom Farrar and Fred Bingham of the SPURS science team have provided the bridge with Gulf Stream analyses that we hope will help us take best advantage of ocean currents in our race eastward. We could easily have found ourselves in an eddy that would hinder our progress, and no one wants that with bad weather coming toward us! It was a fabulous start to the voyage to have the crew of the Knorr and the SPURS team working so closely on the strategy to both keep us safe and on schedule.

The Knorr's new track to avoid Hurricane Leslie.

It’s worth mentioning too that satellite data and the shore-based team play a crucial role in our cruise planning. Zhinjin Li and Michelle Gierach at the NASA Jet Propulsion Lab have been feeding us the latest satellite images from the Atlantic so we can better understand the wind, waves, and currents in our path. We rely on these contributions because it is difficult to surf the web from sea – we have Internet access, but it can be quite slow.

Today we feel the enormous forces of the tropical storms on the western Atlantic. There is a good swell running – speaking clearly of some strong wind at a distance. Some aboard are feeling seasick, but the mess is still full of hearty eaters and smiling faces!

SPURS scientist Fred Bingham goes through safety training.

One of the things you notice in these conditions are all the items that can shake, rattle, squeak, groan, or otherwise move and make noise. I have been up and down in my cabin a number of times during the night to silence rattling cupboard doors, toppling books, sliding glasses – it’s almost an endless battle. At sea you don’t just put something down – you secure something, wedge something, pad something, or it becomes something broken, lost, dangerous or just plain noisy! Sometimes one even has to wedge oneself in a place and just stop moving around! All of us have greater appreciation than most for the stability of land and the silence that stability brings. When things are shipshape, all is secure and in its place. We are living shipshape today.

Off to sea!

September 7th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

Loading a SPURS Mooring on the R/V Knorr.

We had a whirlwind of preparations after the Labor Day Weekend.  All the gear was loaded on the ship and lashed down. The scientific party (22 people) arrived and set up in various spaces around the ship.  Bill Ingalls, a NASA Headquarters photographer, captured many great shots of the Knorr and the equipment. His photos are online at NASA Headquarter’s Flickr account.

Bill Ingalls, NASA photographer.

SPURS researchers held a press conference the day before departing. From left to right: Eric Lindstrom, Dave Fratantoni and Ray Schmitt,

I also had the pleasure of meeting Naomi Harper, a teacher from Will Rodgers Middle School in Fair Oaks, CA. She was visiting Woods Hole and stopped by the ship. I am looking forward to interacting with her students via this blog during the voyage.

We cast off and set sail at 8:30 a.m., on Thursday, Sept. 6. While it’s a very beautiful calm day, we know that we have storms in the Atlantic between us and our destination (Hurricanes Leslie and Michael). The cruise plan is being adjusted a little so we spend the first few days focused on “outrunning” the storms. We can do out test stations and other such preparations after we have reached calmer waters west of the hurricanes. So, we are expecting rough seas at some points during the next few days and the first order of business as we set sail is to get all our gear secure on deck and in our cabins. Everything that can move needs to be secured before we face the storm waves.

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There was a nice gathering of friends and family at the wharf to see us off on our voyage. We are lucky to have such a beautiful sunny morning and calm winds for the send-off.

Family and friends of the SPURS researchers gather at the Woods Hole dock to see the cruise off.

Thirty minutes after setting off from Woods Hole, we have our first meeting of the entire scientific party. There are people from several institutions and we all need to put names to faces. There are also scheduled safety meetings and boat drills during our first day and before we leave the calm waters of Massachusetts behind.

The first SPURS science meeting aboard the R/V Knorr.

The only scientific work planned for the first few days, as we race past the storms, is regular sampling of surface waters to calibrate the ship’s thermosalinograph. This instrument monitors ocean temperature and salinity continuously from water coming in through a port in the ship’s hull. It will operate continuously during the voyage, but we need to collect calibration samples every 4 hours for precision salinity determination.

We are all learning about the rhythms of shipboard life. We will have people on many different watch schedules. The watches will operate on local time. That shifts as we move east across time zones. As your blogger on the SPURS cruise, I plan to float across different groups and schedules as the expedition progresses to give you multiple perspectives. On the ship, meal times are very important. We will have breakfast every day from 7:30 to 8:15 a.m., lunch from 11:30 a.m. to 12:15 p.m., and dinner from 5:00 to 5:45 p.m. I’ll let you know more about the delicacies we eat at sea!