CTDs vs XBTs

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XBTs are deployed from the back corner of the ship
while underway.

A sound velocity profile is helpful for calibrating instruments that rely on a ping sent from a source that reflects back to that source’s location. In some cases, it’s enough to assume sound travels through seawater at 1500 meters per second. However, there are many exceptions and an accurate profile of the water column can shift data points from other instruments significantly. Pressure, temperature, and salinity are all factors that change how quickly sound travels through water.

As you may recall, on the trip from San Francisco to San Diego, the computer tech aboard R/V Sally Ride used an instrument called an XBT (eXpendable BathyThermograph) which measures temperature to determine a sound speed profile of the water column. This was used to calibrate the data gathered by the multibeam echosounders, which reflect sound off the seafloor in order to map it. An accepted standard profile of pressure and salinity are used for these calculations, as temperature is the variable that affects the calculation the most. XBTs are deployed while the ship is underway (preferably moving at a speed of 10+ knots), and take only as much time as the weight does to drop through the water column. An XBT profile was recorded about once per day, and done at specific locations strategically chosen to represent data that could be used for an average sound speed. In cases where there are multiple variables that could affect sound speed, such as mixing of fresh and salt water near river outlets, XBTs are deployed far more often, if not almost continuously. Click here for much more about the history of XBTs at Scripps Institution of Oceanography.

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CTDs are deployed off the starboard side with the ship stopped
on station.

During SVC1, with Dr. Bill Hodgkiss’ acoustic arrays and thermistor strings, the scientists used a CTD (Conductivity, Temperature, and Depth sensor) to determine the profile and calibrate the ship multibeam system and for comparison with the thermistor string measurements. The main difference is that it factors salinity (determined through the conductivity measurement) into the equation for sound speed, which makes for a more accurate profile. But it also requires stopping the ship and deploying the instrument, which takes a minimum of 30 minutes start to finish, and can take much longer if the water is deep. As previously mentioned, temperature is the biggest factor, so many XBT and CTD profiles look similar to each other, and may make minimal adjustments to the data when used to calibrate instrumentation.

On hydrographic cruises, which are focused mainly on properties of the seawater itself, a CTD rosette also includes niskin bottles mounted around the frame containing the sensors, which capture samples at different depths throughout the water column. The seawater is then analyzed onboard and used to calibrate the various CTD sensors.

Whether or not seawater samples are analyzed depends on how exact of a measurement each group needs. On long-term repeat cruises like the GO-SHIP decadal surveys and CalCOFI seasonal expeditions, seawater analysis onboard of 20-36 depths (called bottle checks) are a necessary step to ensure the sensors that measure the complete profile (which logs data 24 times per second) are calibrated properly. The adjusted sound speed profile is then passed on to the acoustic group onboard to calibrate their instruments and can be used for the multibeam data as well.


WIRED tour and unanswered questions

Scripps Ships Operations director Bruce Appelgate gave WIRED magazine a tour of the R/V Sally Ride while it was docked in San Francisco.  It was done via Facebook Live, so there were a lot of questions asked in the comments. The videos below cover many of them, and more have been covered already in other blog posts, but I’m going to get to some of the others below.

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Click to watch the Facebook Live video tour of the ship.

 

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Click to watch the video from WIRED posted a week later.

Question from Justin Moss: Top speed?

Answer: 12.8 knots. For sustained speed, 11.5 knots.

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Monitors in the lab show real-time data from
the echosounders.

Q from Robert Focht: Can it explore to the bottom of the Mariana’s Trench ?

A: A few other questions were asked about the Mariana Trench in particular, which is the deepest part of the ocean at nearly 11,000 meters. The ship itself has to stay on the surface of course, but is capable of carrying instruments to be deployed to the seafloor. Most of the instruments usually used max out at 6,000m so specially designed equipment would be necessary. The multibeam echosounder aboard could be used to map the seafloor even at this depth.

Q from Dion Og: What sort of bottom scanning sonar/em sensors does the ship use?

A: The ship has two Kongsberg multibeam systems, an EM122 deep water system best suited for 1000 meters or more, and the EM712 for shallower water. There are also two Knudsen systems, a single-beam echosounder that operates at 12kHz and a sub-bottom profiler that operates at 3.5kHz.

Q from Myles Blackwood: What type of fuel does that ship use?

A: There are four 12-cylinder diesel engines aboard the Sally Ride. Each one is 1400 brake horsepower and generates 1000kW of power, which is converted to electricity that is used to power the ship’s propulsion, as well as everything else electronic on the ship. Take a 360 degree tour of the engine room here.

Q from Robert Kidwell: Why’s it named after Sally Ride?

A: I think astronauts and oceanographers have a lot in common – both groups of scientists are true explorers, studying the vast unknown in order to better understand how Earth is unique. Dr. Sally Ride was a professor at UC San Diego after retiring from NASA. Once the class of vessel and its sister ship were named after an astronaut, Neil Armstrong, it seemed like the perfect choice. More about the decision and christening of the ship here. 

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The ship’s name plate.

Q from Joaquin Molina: Is this military or a civilian ship?

A: R/V Sally Ride is owned by the U.S. Navy’s Office of Naval Research and operated by Scripps Institution of Oceanography. The crew is made up of civilians, though many of them are veterans of the armed forces. The scientists are also civilians, though may have funding from military projects along with other sources. More about this dynamic here. 

Q from Donald Brian Mix: Where was this ship built?

A: Dakota Creek Industries in Anacortes, Washington built both the Sally Ride and her sister ship, the Neil Armstrong. Construction began in 2012, with both ships being christened in 2014 and arriving at their home institutions for the first time in 2016. The ships were built to the same specifications, though now that they’re in the hands of SIO and WHOI, small differences are likely to pop up in terms of instrumentation and equipment onboard.

Q from Judy Cash Lee: What is your next mission?

A: The first official science cruise is coming up in November. It will be the fall CalCOFI cruise, which is made up of scientists from SIO and NOAA. More about their test cruise here. Follow the blog for photos and posts from the upcoming cruise!

Q from Birch Hansen: What is the crew complement of the Sally Ride?

A: The ship has 20 crew members, you can check out more about the current group here. As mentioned in the video, Scripps does strive for a mix of male and female crew members. There aren’t currently any women assigned to the Sally Ride, but there are female crew members on other ships in the SIO fleet.

Q from Jason Vincent: How long can you stay out to sea at one time?

A: The ship can carry 140,000 gallons of fuel, enough for 10,545 nautical miles at 12 knots. The storerooms can hold 40 days of food assuming a full complement of 20 crew and 24 scientists.

And perhaps the most important question, from Oscar Torres Vazquez: Have you eaten tacos on the ship?

A. Yes, I have. Mexican food is an important part of the rotation on the Sally Ride. Being that her home port is San Diego, California, the cooks have access to excellent ingredients. Tacos, burritos, enchiladas, and huevos rancheros are all served aboard the ship on a regular basis.

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Carnitas lunch aboard R/V Sally Ride

There are some more questions I will get to next week, so check back!


SVC2 - testing the ship

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The usual CalCOFI grid of 75 stations.

The second science verification cruise took place on R/V Sally Ride last week. CalCOFI (California Cooperative Oceanic and Fisheries Investigations) is a collection of scientists from SIO and the National Oceanic and Atmospheric Administration (NOAA), that run transects off the coast of California once per season. Thus there are four research cruises a year, occupying the same stations, and sampling the same parameters. What began in 1949 as a study into California’s collapsing sardine fishery has become an important record of oceanic changes. The autumn trip will be the first official science cruise on the Sally Ride, taking place over 16 days in November. Coming aboard for a few days in advance of that trip to test out how everything will get deployed, recovered, and sampled makes sense for the scientists, and for the ship and her crew.

CalCOFI trips involve pretty much every science system and deployment apparatus onboard, and that’s saying something! A CTD is deployed on every station, being sent to a depth of 500 meters to collect samples throughout the water column. Sensor data, as well as analysis of the collected seawater, provides salinity, dissolved oxygen, nutrients, and chlorophyll concentrations. Various nets are also deployed along the starboard side of the ship, collecting plankton, krill, small fish, and other animals along the way. An acoustic array is launched from the A-frame on the back deck and towed as the ship travels between stations. Researchers record and study the data in order to understand marine mammal populations and behaviors. Observers are also located out on deck during daylight hours, recording all the birds and marine mammals seen from the ship.

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Chief Scientist Jim Wilkinson rinses the bongo nets after recovery.
This moves the captured material into a container called a cod-end.
Picture by Debbie Nail Meyer.
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Everything in the net is then transferred to collection jars,
where it is catalogued and used to make inferences about
oceanic populations. Picture of technician Taylor Wirth,
krill, and a tuna crab by Debbie Nail Meyer.

 

 

 

 

 

 

 

 

Stay tuned for more pictures and posts from onboard R/V Sally Ride during the cruise in November, where I’ll be documenting the cooperative effort it takes to successfully run 24-hour science operations at sea for the first time on a new ship.


Deploy, Recover, Repair, Repeat

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Restech Matt Durham prepares to deploy an acoustic array from the fantail of R/V Sally Ride.

The first science verification cruise (SVC) took place on R/V Sally Ride earlier this month. If you’ve read the earlier posts, about the project goals and loading of the ship, you know that the objective of the chief scientist, Dr. Bill Hodgkiss of UCSD, was to record acoustic signatures from ships in the Santa Barbara Channel. We departed SIO’s marine facility in Point Loma on a busy morning in San Diego Bay. Another of SIO’s research vessels, the R/V Robert Gordon Sproul, also departed that morning, and there was a lot of other traffic – from sailboats to Navy destroyers. It took us about 20 hours to get up to our target area, where we would spend the next 12 days in a roughly 60 square mile box.

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Schematic of the thermistor arrays.

The thermistor strings were the first to be deployed. They run from the bottom of the ocean (500-580 meters in this area) to about 20 meters below the surface (to leave plenty of room between it and the bottom of any passing ships). There are 46 temperature sensors along that length, along with floats to keep the string as straight up and down in the water column as possible. It’s anchored by an old train wheel and just above that is a transponder-controlled release mechanism so that, at the right time, a signal sent from a transducer lowered over the side of the ship activates that release and the whole array pops up to the surface. The train wheel remains on the seafloor. Which is why the group brought plenty of spares, a total of 12 for the 6 arrays. If any part of the array malfunctions, it can be released, brought back on board, repaired or replaced, and then sunk again with a new anchor. Indeed, we came back to San Diego with only 4 train wheels, as two of the acoustic arrays had to be recovered, repaired, and re-deployed over the course of the cruise.

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Train wheels waiting to be craned aboard.

Both thermistor arrays were deployed without incident, taking 2-3 hours each to unspool the cable and attach all the temperature-recording devices (using clips, zip ties, and electrical tape). The arrays are deployed top to bottom, so that the last piece to be connected is the train wheel anchor. The ship is steadily moving during the entire deployment, in order to keep anything from getting tangled. This means that the top of the array is trailing ~500 meters behind the ship by the time the anchor is ready to be released. The captain or mate on the bridge radios down to the restech running operations on the back deck to notify them when the ship is passing over the spot where the scientists want the array to come to rest. A line is pulled, releasing the anchor, which drops to the ocean floor and pulls the other elements of the array into formation above it.

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The top of the array is deployed first, including the huge torpedo-shaped buoy.

It’s at this moment that the giant torpedo-shaped buoy near the top of the array starts moving slowly but steadily towards the ship. Which, even knowing that it’s just a float and not enemy fire, is a bit ominous. If everything has been calculated correctly, the last of the equipment should sink below the surface well before reaching the ship. Dr. Hodgkiss deployed both thermistor strings right along the shipping lane, one north (outbound from Long Beach) and the other south (inbound) of the separation zone, which is the equivalent of a highway median. Next up to be deployed was four acoustic arrays, set up right in the middle of the separation zone, and each 1km apart from each other.

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Map showing deployment locations: triangles are acoustic arrays, asterisks are thermistor strings.
Green lines mark the outbound shipping lane, red lines mark the inbound lane.
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The entire array is laid out in order across the ship’s fantail before
deployment. The acoustic array’s cable fairing and instrumentation
has to be kept from getting kinked.

The acoustic arrays are only 110 meters long, so were quicker to deploy, taking under an hour each. They have the same train wheel anchor, but the buoy requirements and locations are shifted due to the different equipment connected to the cable. Even the cable is different – it has fairing along it, which is a sort of fringe that keeps the cable from vibrating at a resonance that will disrupt the instrumentation. The whole point of this array is to listen, so it shouldn’t make any noise of its own. Check out the video below that was shared as a tweet during the cruise. It shows cable without fairing during deployment, and the vibration is obvious.

After each deployment, communication with the array is attempted. A transducer is lowered over the side of the ship, a code is entered into a deck box that then sends out a ping, which should be received by the acoustic release just above the anchor weight. It pings back and the deck box determines the distance the sound traveled, and that tells the scientists if everything was deployed correctly. The range should be close to that the total depth of the ocean floor, as the acoustic release is near the bottom of the array.

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Dr. Hodgkiss watches as the ship prepares to recover an acoustic array.

All of the instruments were left for multiple days, gathering data the whole time, and only recovered if necessary for replacement or repairs, or when it was time to collect the gear and head back to port. One foggy morning, with visibility less than 300 feet throughout the day, we began the final recoveries. It definitely wasn’t ideal conditions. Even knowing roughly when and where the equipment should surface doesn’t guarantee that you’ll spot it. Thankfully, operations went smoothly and the gear was all safely recovered.

To release, the transducer is again lowered into the ocean, and this time a different code is entered into the deck box that causes a switch to disengage the array from the anchor. In about 5 minutes, the gear should be at the surface. All science hands were on the forward decks to help locate the equipment. A member of the crew who assists with bridge watch was the official spotter and radioed up to the bridge as soon as a visual was confirmed. The ship then maneuvered so that the gear would come along its starboard side, creeping towards it at 0.5 knots.

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Everyone has a job during the recovery operations.

A grappling hook was thrown to snag the line and guide the array to the back of the ship so that it could be brought onboard using the A-frame. This again required all hands in the science party. Once every piece was back onboard, it had to be rinsed and secured. Even in calm seas, everything has to be lashed down.

The deployment and recovery of arrays such as these takes tremendous planning, coordination, and communication between the scientists and ship’s crew. Part of this science verification cruise was to confirm that R/V Sally Ride is capable of such work. And she passed with flying colors!


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Photo taken by Erik Jepsen, UC San Diego publications, as he rode in a small boat around R/V Sally Ride off the SIO pier.
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At least a hundred people came out to welcome the ship to La Jolla.
Photo by Erik Jepsen, UC San Diego.

R/V Sally Ride’s homecoming on August 26, 2016 was a big event. The ship’s home port is in Point Loma, about 20 miles south of La Jolla, where Scripps Institution of Oceanography is located. There is a pier at SIO, but it’s for launching small boats, instrumentation, and scuba divers – not ships like those in the Scripps fleet. So on our way south, the ship stopped by La Jolla to salute our home institution. The pier was opened for the SIO community (it’s usually closed off to anything but scientific purposes), and faculty, grad students, staff, and more came out to get a closer look at the ship. The captain brought the Sally Ride in as close as was prudent, performed a few pirouettes, and blew the ship’s whistle. I hope the people on shore appreciated that, it was SO loud from the forward decks of the ship. The captain would send out a quick warning over the radio, which a few crew members had on them, and we would all rush to cover our ears. It always seemed to happen just as I had lined up and focused my camera and therefore didn’t want to sacrifice the shot. At some point, the bridge decided to blast out S.I.O. in Morse code. I wondered how many people got it, but realized that many people know S.O.S. (3 short, 3 long, 3 short), which has two of the same letters.

Four boats of photographers, including one with a drone, circled around the ship taking beautiful shots of the historic homecoming. Then the Sally Ride took one last turn and headed out of La Jolla and down the coast to San Diego’s “big bay.” The boat with the drone followed us the whole way, getting some nifty footage. There was also a small plane nearby that got some great shots. Check those out here. 

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Happy hour at SIO. Picture by Megan Roadman.

At Scripps, the party continued with a happy hour event that included cookies with a picture of the ship on them. Those of us onboard had a few more hours to go. Rounding Point Loma and heading into my favorite port, which I’ve done many times, felt different on this occasion. It was special, knowing it was the ship’s first trip and that, as the sun was setting behind the peninsula, coworkers would be waiting on the dock to see her come home. After tying up and lowering the gangway, I took a few last pictures and headed home. As on any first night back in San Diego, whether I’ve been gone for two months or just a few days, I picked up carne asada fries from my local taco shop, sat down on my couch, and toasted to another safe journey home.

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Data technician Courtney Schatzman and Research Oceanographer
Dr. Jim Swift pour beer in celebration of R/V Sally Ride’s
homecoming. Picture by Megan Roadman.

Loading the ship for science!

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Crew members remove cleats from the back deck
in preparation for bringing science gear aboard.

The R/V Sally Ride leaves tomorrow morning for its first science verification cruise (SVC)! Click here for the previous blog post with more information about the project. Today was spent loading all the science equipment onboard, and securing it. First, the setup on the fantail had to be changed to accommodate the science plan. Cleats and other items that were stored on the back deck had to be removed in order to fit all the science gear and the plan to deploy it over the next two weeks.

Click here for the 360 degree view of the setup. 

The Hodgkiss laboratory is located at the Marine Physical Lab in Point Loma, so all their gear just had to be transported down to the wharf via forklift. It took more than 40 trips to get everything alongside the ship. Then it was lifted with the ship’s crane, and brought over onto the back deck of the ship.

Everything will have to be secured, either on deck or in the lab, before we leave tomorrow morning.

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Scientist Gabriela Chavez uses a forklift
to move buoys down to the wharf.
These provide 500lbs of buoyancy to keep the
instruments straight in the water column.

 


(Seafloor) Mapping the Way Home

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Map showing where my oceanography career has taken me.
Winkel tripel projection of course.

I love maps. When my family drove across the country when I was a kid, I was the navigator, tracking how many miles until the next junction, or Dairy Queen. When my dad asked me what I wanted for my 25th birthday I told him a globe, the kind with sea monsters on it! I love that it’s easy to find Tahiti on pretty much any map – the legend is usually near French Polynesia because that’s the only spot on Earth you can put it without covering anything up. If you’ve read the “About the Author” section, you know that I have always wanted to be an explorer. The 29% of Earth that is land is already mapped, and the ocean floor has been mapped as well, but not in nearly as much detail. We have the technology now, and it feels like modern day exploration.

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US Geological Survey infographic showing the various
instruments that can be used to map the seafloor.

I was excited to hear that during R/V Sally Ride’s transit home to San Diego for the first time, the ship would be testing out its state of the art seafloor mapping equipment. Dr. Eli Silver and his graduate student Joel Edwards, from UC Santa Cruz, were on board. They used multibeam echo sounders that are mounted to the bottom of the ship. These instruments send out sound pulses and measure the angle and elapsed time when the signal bounces back to gather data about the seafloor. We mapped along the Santa Lucia Bank, Hosgri, and Catalina-San Clemente faults systems off the coast of Central and Southern California. In the 1970’s, Dr. Silver did seismic mapping of this area, which generates basic bathymetry (underwater topography) maps, but no one had been back since specifically to map the fault systems in better detail. Echo sounders have the ability to generate more detailed profiles. The Sally Ride has two multibeam systems (the swath bathymetry shown above) that are capable of a variety of frequencies, some better for shallow waters while others are capable of detailed measurements to the depth of the Mariana Trench at nearly 11,000 meters (or 6.8 miles). The ship also has a 3.5kHz echo sounder, which provides a profile of the sub-bottom (the first dozen or so meters below the seafloor) from which the types of sediment can be inferred.

Captain Desjardins (left) prepares to draw transect lines
according to Dr. Silver’s plans.

 

First step of the project was to meet with the captain on the bridge to go over the plan. I was excited to see a paper chart out, ready for the captain to draw the transects by hand using measuring tools such as triangles and a divider. The approach angles and switchbacks desired by the scientists were drawn on the chart for the use of the bridge officers who drive the boat.

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Computer tech Dan Yang fires an XBT from the back deck of the Sally Ride.

 

The computing resources technician onboard, Daniel Yang, was in charge of making sure the instruments are functioning properly and that all the data is collected. He also fired off an XBT (expendable bathythermograph) at least once per day. XBTs consist of a copper wire connected to a temperature probe that sinks at a known rate. Temperature data is relayed up the wire to a computer as the probe sinks to the bottom of the ocean, and a sound-speed profile is calculated. Sound doesn’t travel through seawater at the same speed at all depths and temperatures, so an understanding about the profile at that location on that day needs to be factored into the multibeam data in order for it to be accurate.

Grad student Joel Edwards points out a feature, shown by color gradients,
shown on a monitor connected to one of the multibeam echo sounders.

Dr. Silver, Joel, and Dr. Bruce Appelgate (Director of Ship Operations and Marine Technical Support at SIO, but also a geology and seafloor mapping geek) stood watches just like the crew (two 4-hour shifts) so that someone was always in the computer lab as the monitors updated with data in real time.

SIO’s research vessels are all equipped with multibeams, which are running most of the time the ships are offshore. The cruises I go on are usually focused on the hydrography (chemical properties of seawater) but every step of our journey is usually mapped as well. Sometimes other scientists onboard are using that information, but even if that’s not the case the data is shared and adds to the ever-growing database of detailed seafloor maps.

Mapping added about two days to the travel time, but was a fun distraction from what would have otherwise been a dead-head transit. And it was appropriate that Dr. Silver was aboard as well; he was also onboard the Melville as a postdoc in 1967 for that ship’s first transit to its home port of San Diego. Hopefully he’s the good luck charm that ensures a research vessel’s long and productive life at Scripps Institution of Oceanography.


Homeward Bound

 

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R/V Sally Ride’s lines were cast off and we got underway at 10am

This morning the R/V Sally Ride left San Francisco after a short port call that included nearly 800 people touring the ship. Next stop is our home port of San Diego!

In the few hours since leaving the bay, we’ve spotted dozens of whales (humpbacks and blues) and dolphins (Risso’s and right whale).

San Francisco was absolutely lovely, especially being docked so close to the Bay Bridge with its night-time light display. But it’s also lovely now, with nothing on the horizon and just a quiet grey ocean all around us.

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Bay Bridge night display
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Risso’s and right whale dolphins feed together off the coast

 

 

 

 

 

 

 


Gearing up for Science!

The first science verification cruises (SVCs) scheduled on the R/V Sally Ride are fast approaching. September will be the month to test out various winches, wires, and pretty much every other system in the lab spaces onboard to make sure everything’s ready for the ship to enter full service at SIO. Dr. Bill Hodgkiss will be the chief scientist for the first SVC, which means he will make up the science plan and work with the captain and restech (marine research technician) to execute that plan in a safe and effective manner. We just had the pre-cruise meeting, which takes place at least a month in advance of every cruise on any of the ships in the SIO fleet. We went over the specific plan, which equipment will be used, how many people will be needed to operate it, what the expectations of the crew will be, and any other ideas that needed to be discussed. Present at this meeting were two restechs, the port captain and engineer, chief scientist and a few people from his lab, as well as the ship’s captain and chief engineer (via phone from Anacortes). I was there as well, as I will be sailing on the cruise to document it for posterity, and hopefully can be of some use as a technician as well.

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Sally Ride’s first SVC will take place in the Santa Barbara Channel, the waterway between the Northern Channel Islands and mainland California. It will take us about 24 hours to get there from San Diego. This area is a popular shipping lane; the nearby Ports of Los Angeles and Long Beach combined are the 9th busiest cargo port in the world. Ship traffic in busy areas is regulated just like street traffic when you’re driving. As you can see in the below figure showing the density of ship traffic, it is organized into well-used traffic lanes, just like we’re used to on freeways. The blue area in between the southbound and northbound traffic is called the separation zone and acts as a barrier, like the freeway median. The R/V Sally Ride will loiter in that area and carry out basic seawater measurements (conductivity, temperature, depth) in the water column, while the deployed instruments collect data.

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Shipping lane traffic density data from www.marinetraffic.com

Every registered ship in the world has a unique tracking identifier, called automatic identification system (AIS), that relays the ship name, location, course (direction of travel), and speed to nearby ships. There is a screen on the bridge that shows these – on ocean crossings, it’s a big event when one pops up. I know I’ve gotten excited to see a ship on the radar and through the porthole after weeks of no other signs of human life outside ourselves. In those circumstances it’s often a car or other cargo carrier headed between two busy ports. In this instance the AIS map will likely be crowded, with dozens of ships within the screen’s ~20 mile radius. The AIS data will be matched up later to the noises recorded by the deployed instruments.

Dr. Hodgkiss is a professor at Scripps, as well as at the Jacob’s School of Engineering on the main UCSD campus. His lab group at the Marine Physical Laboratory (MPL) designs acoustic devices that can be deployed below the surface of the ocean.

Diagram of the 32-hydrophone array to be deployed from R/V Sally Ride.

Anchored by a 1,000-pound train wheel, a string of acoustic equipment will be lowered to the ocean floor. The depth in this area is in the 500-580 meter range, and each array is assembled to stay as close to the seafloor as possible to avoid too much side-to-side movement in the currents. A total of 32 hydrophones are connected in a line, collecting data at various depths and over a range of frequencies. Large floats are included near the top of the mooring string in order to keep the array as straight in the water column as possible. After a week in the ocean, the instruments will be recovered. A signal is sent from the ship, and the line detaches at the release point just above the anchor. The floats are enough the bring the entire string to the surface, and a flashing beacon activates, making it relatively easy for the ship to find.

 

 

 

The yellow ellipsoid floats that will be attached to the acoustic array,
with a technician for scale. Photo courtesy of the Hodgkiss lab.

Verification cruises like this one are a great opportunity to get important science done while also testing out the ship’s systems and operations – everything from the climate control in the labs to the winches used to lower equipment to the bottom of the ocean. There’s a lot to be done still before the ship is fully operational, but a successful first scientific verification cruise will be a big step in that direction. Wish us luck, and follow along in future posts!