Kate pictured with large mooring float.

Recovering a mooring of any significant size essentially amounts to getting it to the surface and picking it up with a ship using a crane. Recall that one of the key items contained on the mooring is the acoustic release. The release is essentially a chain link that opens up when it receives a particular acoustic waveform placed into the water.

An acoustic release with integrated beacon.

Many, such as the one Kate is using, also send out a beacon or “ping” when acoustically interrogated. So, to recover a mooring, one steers the ship to the GPS location closest to where the mooring was deployed, places the appropriate set of tones in the water which will induce the release to start sending beacon tones and release the mooring from the anchor, and then home in on the mooring’s location using the beacon. At this point, the mooring can be reached at the surface, and only the anchor remains at the bottom.

To physically perform the recovery on a big ship such as Healy, a rigid inflatable boat (RIB) is dispatched from the recovering ship to find the top float(s). Of course, if the top float(s) ascended under a blanket of sea ice, there are more details to handle, but we didn’t have to deal with this particular problem on this cruise. We avoided it by electing not to recover a particular mooring on the first day and coming back later to recover it (when the ice had moved on).

Rigid inflatable boat (RIB) used to recover moorings.

The small boat will locate the mooring by looking for the float(s). Floats are typically painted in colors or contained within painted containers that are relatively easy to see, even in poor weather conditions (e.g., optic yellow or orange). One of the more common float arrangements is to strap together a collection of glass spheres each of which provides a certain amount of buoyancy and can resist the high pressures of submergence at depth. Such spheres can also be used to house instruments. Floats for less extreme depths, made of plastic or foam materials, can be used for applications involving less pressure (foam compresses at high pressure and loses its buoyancy; glass does not). In some applications the float is allowed to bob around on the water surface (called a “surface expression”), but in cold areas such as the arctic this can be a problem because floating ice can damage a float or, worse, carry off the entire mooring.

Once the small boat operators get a hold of the recovery line attached to the float, they maneuver to the stern of the recovering ship and connect the recovery line to the ship’s crane line. At this point, the small boat gets out of the way so the ship’s mooring crew on deck can recover the mooring. This is accomplished by winching in the line and moving the A-frame, which is a large metal inverted-U-shaped hoist attached to the ship. It is operated by hydraulic lifters and is used to position moorings or other equipment beyond the stern of the ship over the water.

Crane and A-frame used to hoist mooring (floats and audio recorder are visible).

Deploying a mooring, or re-deploying a mooring, involves placing the mooring into the water top-to-bottom (there are other ways, but all the moorings deployed on this cruise were done top-to-bottom), with the recovery line first and anchor last.

Mooring with acoustic release, audio recorder, CTD and float ready for deployment; the recovery line and its floats are already in the water.

If the mooring is sufficiently small (like Kate’s) it is possible to lay the entire mooring out on deck ahead of time.

Kate awaits the ship to be positioned for the next deployment. The full mooring is visible on deck.

First, the top float(s) are placed in the water, then the instrument(s), then any additional floats and finally the anchor. The anchor is placed in the water by careful use of the ship’s crane. It may be partially lowered into the water and released at just the right time so as to land on the ocean floor at the desired location. After the anchor is released, it sinks to the bottom pulling the rest of the mooring along with it. It is thus possible to see the primary float(s) rapidly approaching the stern of the ship until they are pulled below the surface.

Anchor weights are deployed by the winch. John holds a line that when pulled releases the weights from the crane.

Although the recovery and deployment of moorings may seem conceptually simple, there are many details to get just right. Errors in mooring design or deployment execution could mean a costly waste of ship time, a loss of data or equipment, or possible injury to the scientists or crew. This is true of most heavy work on ships, but is exacerbated when working in the Arctic due to the hostile conditions. For this set of scientists and crew, mooring recovery and deployment is conducted by the Woods Hole Oceanographic Institution’s Mooring Operations Engineering and Field Support Group, led here by John Kemp, a legend in the “mooring community.”

Emblem of WHOI Mooring Ops.

John Kemp, WHOI’s expert at mooring design/recovery/deployment.

Although I personally lack the level of sea experience this crew has by many orders of magnitude, I have been around ships and small boats for most of my life, and I can appreciate a virtuoso at getting work done at sea, and John is definitely one.

(Thanks to Dale Chayes (LDEO) and Kate Stafford (APL) for helpful comments on this article).

Placing a Mooring

Kate’s moorings, like most others, are constructed to be placed on the sea floor at a particular location and depth. Locating nearly anything on the surface of the Earth has become much easier with the widespread use of the Global Positioning System (GPS) and its relatives (assisted GPS, differential GPS, carrier-phase GPS, Real-Time Kinematic (RTK) GPS, etc). Knowing the depth (and associated bottom contours) at a point in the ocean is less straightforward, yet these details are important for designing and manufacturing moorings, as these details affect certain aspects of a mooring’s design such as the amount and strength of cable required, the weight of the anchor to be used, the amount of buoyance required, etc.

Ocean depths are typically measured with an echosounder (see below) and then recorded on bathymetric maps. Contour lines of the same depth are called isobaths. The map below indicates our ship’s cruise track, mooring deployment/recovery locations, geopolitical data, plus a number of isobaths (black lines) and bathymetric data (salmon-colored tracks).

Cruise track, made available to the science party underway, had a number of optional overlays. This shows the track, geopolitical map, bathymetric data, and mooring deployments/recoveries.

The bathymetric data used to create such maps are measured using either airborne platforms (e.g. satellites) or ships’ sonar systems. Healy has a multibeam sonar system. Using multiple sound beams allows the ship to map out more sea floor information per unit time than would a single beam.

In Healy’s multibeam, sound is emitted through hull-mounted projectors in the form of short acoustic “pings” (which sound a bit like bird chirps when you are on one of the lower decks– bring earplugs if you have to sleep there!). The pings are 12KHz acoustic waveforms that bounce off the sea floor and are picked up by an array of hydrophones (also mounted on the hull). The amount of time between when a ping is sent and when it is received gives an estimate of how long it takes sound to travel to the bottom and back. If the speed of sound in sea water is assumed to be 1500m/s, then the depth (in meters) can be estimated as (1500)(t)/2, where t is the time (in seconds) between the sending and receiving of the ping. However, this calculation really isn’t good enough. The reason is because the speed of sound in water varies based on a number of factors, including temperature, salinity and depth. So, data collected from onboard instruments: an expendable probe (see XBT, below), a CTD that is repeatedly cast into the water (see my previous dispatch that describes the CTD), and archived data, are used to form a sound speed profile which is then used as input to the ship’s SeaBeam 2112 control computer to make corrections to the simple formula above. Using all this information, while also taking into account motion of the ship itself when estimating the time between sent and received pings, the computer can form an accurate bottom map that is made available to anyone on the ship and also shared with others back on shore through one of the various archives at LDEO.

WHOI Mooring Ops. Engineering and Field Support Group logo.

As you can probably see, there is a considerable amount of subtlety in how this works inside the computer. For example, the ship may be experiencing rolling, pitching, or yawing. Movements such as these (especially roll and pitch changes) affect how the beams are reflected back to the hydrophones, and all this must be considered when creating an estimate of far away the bottom is and what features it has. In addition, the temperature of the water varies as a function of depth and can change over time. To determine the temperature/depth relationship at a moment in time, a device called an expendable bathythermograph (XBT) and/or a CTD (described last in my dispatch) is used (e.g., once daily or when the ship moves into an area with different ocean characteristics) to measure the temperature/salinity/depth profile.

An expendable bathythermograph sitting on its launcher.

An XBT looks like a small rocket that is launched by a fixed or hand-held launcher off the ship; the ship can be still or moving. The XBT itself remains attached to the launcher by means of a very fine 2-conductor copper wire that unspools as the XBT descends toward the sea floor. As it descends, it measures temperature while its depth is estimated using an assumed falling rate. The resulting information is displayed to the user and used in forming the sound speed profile for the multibeam echosounder (and for a few other things). To learn more about the finer points of estimating sound speed in water, this link provides a number of more detailed references as a starting point.

Mooring Technology

In oceanography, moorings are used to hold instruments in a fixed location and, typically, at a fixed pre-determined depth. I say “typically” because we shall in future dispatches see how some special instruments with limited but very useful mobility can be used to measure ocean characteristics at a range of depths over time. These designs can be somewhat more complicated to design and deploy.

A typical mooring is a collection of lines or cables with an attached set of instruments and floats, and a device called an acoustic release (“release” for short). At the bottom is a heavy weight (“anchor”) placed on the sea floor. The mooring design/deployment sheet for Kate’s mooring was designed at he University of Washington’s Applied Physics Lab and can be seen here.

Mooring with acoustic release, audio recorder, CTD (conductivity, temperature, and depth measurement instrument) and float ready for deployment; the recovery line and its floats are already in the water.

This mooring includes 3 meters of Amsteel line, a type of line with a very high strength-to-weight ratio. A Benthos 866A release combines the acoustic release and transponding functions together in one device (see below). (Teledyne-Benthos is one of several companies that make these types of devices).

An acoustic release with integrated beacon.

Kate’s recording instruments are Aural M-2 autonomous audio recorders made by the Canadian company Multi-Electronique. Each includes an HTI-96 hydrophone manufactured by High Tech Inc. that can measure sound in the 2Hz to 30KHz frequency range. The recorders can sample the signal from the hydrophone up to a rate of 32KHz at 16 bits per sample. Kate has set up the recorders to operate 10 minutes out of every half hour.

When one of Kate’s moorings is recovered, its year-long recording resides in a storage system within the instrument. The storage system includes both a flash based storage device as well as a conventional hard drive. The 64MByte flash device makes no sound when written to, so this is advantageous when measuring sound. The hard drive stores more information, but makes noise when operating that is detectable by the hydrophone. Thus, is it desirable to write data as it is recorded to the flash device and later, when the hydrophone is inactive, transfer the data to the hard drive for longer-term storage.

To power the system, the instrument includes 128 ‘D’ cell batteries. In its current configuration, the hard drive will fill up before the battery power is exhausted. Before the hard drive fills up (hopefully), the instrument itself must be retrieved in order to avoid losing data. This is one of the reasons for Kate’s work on Healy– to recover instruments deployed a year earlier and deploy new ones to last another year.

Moorings can be used for a variety of purposes, but for this cruise moorings are being used to keep acoustic and oceanographic sensors in place for some period of time (typically a year). Scientist Kate Stafford from the University of Washington’s Applied Physics Lab (APL) has a set of acoustic sensors forming a ‘hydrophone array’ that are to be recovered and (re) deployed later in the cruise.

Hydrophones are passive measuring devices– they do not emit any sound themselves, but instead convert acoustical energy in the water to an electrical signal. Kate analyzes the sounds or “vocalizations” of whales, bowhead and beluga whales in particular, using these instruments. Fixing a hydrophone array in place underwater for a relatively long period of time (a year) allows scientists to listen for the presence of cetaceans (whales, dolphins, and porpoises) from multiple locations, even in poor weather conditions.

Kate pictured with a large mooring float.

Detection Using Passive Hydrophone Arrays

Each hydrophone Kate uses sits inside an instrument that includes the hydrophone itself, a data recorder where the digitized audio samples are stored for later retrieval, and a pack of batteries to keep the whole instrument running for a year or more. These are the instruments that are attached to moorings that are deployed out at sea until they are recovered. When these types of instruments are placed sufficiently close together, more than one will pick up the same vocalizations or sound. When this happens it may be possible to locate and track a particular sound source (animal or otherwise) over time. When the instruments are used together in this way, they behave as an array, or group that is acting together cooperatively. Hydrophone arrays can also be used in estimating animal populations, although gaining high confidence using this approach is an ongoing challenge.

The hydrophone instrument.

When the data from Kate’s instruments is recovered, it can be processed in a number of ways. One way is to simply listen to the sounds on the recordings. A person with enough expertise in doing this can pick out some of the vocalizations and other sounds. As an example, you can listen to the recording of a beluga:

Beluga Whale Recording

A more quantitative approach involves taking the data and analyzing the frequency, timing and intensity (loudness) of particular sounds. A popular way of doing this is to visualize this information on a special kind of graph called a spectrogram. In this spectrogram of a beluga vocalization in the Beaufort sea, for example, the intensity of sound at a particular frequency at a particular time is indicated by the color (blue less intense; red most intense).

Spectrogram of beluga soundings in the Beaufort Sea.

By looking at the spectrogram or other types of graphs (or by using a computer program to do so), acoustic frequency patterns resulting from cetacean vocalizations (or boats, or the sounds of airguns used in seismic exploration, etc.) can be found.

For the interested reader, the analysis of hydrophone data is similar to both signal processing and image processing techniques. Common techniques include matched filters, band-limited energy summation and classification, image matching techniques on the spectrogram or time series, and other frequency-domain analysis techniques such as wavelet-based decomposition. A more detailed explanation of how this can be accomplished and why fixed passive arrays are useful for monitoring cetaceans is given in this paper.

The ultimate goal for much of the related science here is to estimate animal populations, which is important for both ecological understanding and policy-setting reasons. As suggested above, there are a number of factors posing challenges to doing this effectively using acoustic arrays. Animals may use different vocalizations at different points in time and these may vary in many ways (e.g., frequency, phase, amplitude, modulation, etc) based on its activity (e.g., feeding or seeking a mate). In addition, instruments are only capable of detecting a signal up to some distance (which depends on frequency), so forms of statistical inference must be employed in an attempt to estimate a population given a number of detections.

Necessarily, these are only estimates, but they are estimates based on measured data, and moored acoustic arrays offer some significant advantages for making such measurements versus the alternatives of visual observation from ships (or other platforms like airplanes, etc) or from towed hydrophones that only last a few days or weeks. Moorings last a long time and are relatively immune to poor weather so they can offer a richer data set on which to base estimates. Of course, they need to be designed, deployed, and recovered, which generally involves a ship such as HEALY…

Side view of Healy.

Coast guard H-65 helicopter carrying science party departs Barrow airport.

Equipped with a helmet and flight suit, we are given a flight briefing at the airport, focusing mostly on what to do if the helicopter should be forced into the water. Fortunately, the flight suits provide some floatation and cold protection and the trip is not long.

Co-chief scientist Harper Simmons from UAF/IARC dons flight helmet.

Scientist Matthew Alford wearing a flight suit.

In the helicopter (“hee-lo” as they say) we are led into the back and we strap in to a 5-point harness. We also plug the headphone-equipped helmet into the aircraft’s intercom system. The craft is operated by three “coasties” — the pilot, co-pilot and flight engineer. They all sit up front (and middle), and two of us, myself and co-chief scientist Harper Simmons sit in the back, secured to the aft cockpit wall. From this position it is hard to see much other than the backs of the flight crew or an occasional clump of ice visible through the windows.

Scientist’s-eye view of the flight crew.

Harper Simmons fills out a personnel log prior to take-off.

Chatter on the radio and a quick glimpse over the heads and shoulders of the flight crew reveal that we have arrived at the ship and been cleared to land. Touching down on the ship’s helipad, the ship is at “Flightcon-1″– no unnecessary personnel are permitted on the flight deck, and no hats are allowed (hats can get caught in helicopter rotors or engines). In addition, a rescue boat sits at the ready with the damage control (fire fighting) party. Fortunately, we don’t don’t require their assistance.

Helicopter arrival on the flight deck of Healy.

After stepping off the helipad, we are greeted by Dale Chayes from the Lamont-Doherty Earth Observatory (LDEO)… part of Columbia University. He directs arriving scientists into the hangar to be re-united with their luggage. There, we get a peek at the larger moorings that will be deployed later in the cruise.

Dale Chayes from LDEO directs arriving passengers to the hangar.

Large BS-4 (WHOI) mooring being stored in the hanger for later deployment.

Dale had invited me on my first trip on Healy in 2005 after I gave a talk at LDEO on Delay Tolerant Networking– my research area that is looking at communication in challenged and remote environments. Dale heads the science support crew that provides technical and computer help for the science party, technical institutional memory, and provides a channel to match terminology between the Coast Guard running the ship and the scientists running their instruments. The last time he was in San Francisco, together we met with Turing award winner Jim Gray to discuss how large data sets are handled. Sadly, Jim still remains lost at sea, having disappeared in his sailboat off the coast of California near San Francisco.

In the hangar, we doff the flight suits so they can be given to the next set of helo passengers. I pick up my pager and information card and drop off my things in my stateroom. Everyone wears a pager on ship, as it’s nearly impossible to find anyone otherwise. The information card gives the number of the life raft you need to report to in case there is a reason to abandon ship. I arrived just in time for lunch, but about a third of the science party didn’t… they were delayed due to fog. Barrow is one of the foggiest cities in the country, and it’s not unusual to have flights (helicopter or otherwise) cancelled or delayed. If you intend to travel here, give yourself a day or two slack on either side.

Exploring the ship alone, I remember it is easy to get lost and that its time to switch to at least a semblance of nautical jargon. The “house” includes places to cook, eat, sleep, have meetings and drive the ship. Forward of the house, the fo’c’stle is the front deck of the ship, and is also nice place to use for photography, as we’ll see later. Aft of the house is the engine and lab spaces, the hangar and helipad, and the aft control room (“Aft Con”). Next to the science lab spaces is the aft outdoor workspace, containing winches and cranes to deploy and recover gear. On the starboard side is another, smaller winch system. Above it all is the “Aloft Con,” essentially the crow’s nest of Healy. Port is, of course, the left side of the ship and starboard is the right. The term starboard derives from the words “steer board”– years ago its was common to mount your boat’s steering board (modern equivalent of a rudder) on the right-hand side.

After the fog lifted, aviation operations continued once again. Repeated ringing of the ship’s bells indicated the arrival of our VIPs (known as ‘Distinguished Visitors’ or DVs). Our DVs included Michael Chertoff, the Secretary of Homeland Security, and the Commandant of the Coast Guard, Admiral Thad Allen. They were met by the commanding officer of Healy, Captain Frederick Sommer. I was also in the hangar when they arrived, and Admiral Allen said hello and shook my hand. A solid handshake… not surprising, as he is a solid-looking fellow. They would speak to the ship and its crew later in the evening.

The Secretary of Homeland Security, Michael Chertoff.

Admiral Thad Allen.

Commanding Officer of Healy, Capt Sommer.

While the captain was sequestered with the DVs in the wardroom, the flight deck was converted back for its normal deck use. The science party wasted little time during all of this. One of the first operations is to get a sample of water and ensure the instruments read true. This is accomplished using the starboard winch to cast a rosette into the water. The rosette has a (variable, usually 12 or 24) number of water sampling bottles attached to it. They are left open until the rosette reaches a certain depth (or set of depths). At specific points, an activator controlled by a terminal in Aft Con causes the bottles to close using the snap-action of attached springs. The commands given to the rosette are frequency shift keyed (FSK) signals that travel along the same cable that lowers and raises the rosette.

Converting the helipad back for ordinary deck use.

Rosette holding sampling bottles, CTD, and other instruments.

Wilken Von Appen secures the water sampling bottle on the rosette.

In addition to the bottles, the rosette has an instrument package attached to it at the bottom. The package includes a CTD, and several other instruments. The CTD measures conductivity, temperature, and depth. It is one of the most common oceanographic instruments used, and there are many models available. In this particular case, the data retrieved from the CTD can be compared against similar measurements made on-ship of the sampled water to ensure the CTD is operating correctly. CTD “casting” takes place regularly as the cruise progresses. Data from this CTD, as well as many other instruments permanently mounted in the ship, is made available to scientists over the ship’s local area (science) network. More details on the network later.

In the evening, the DVs addressed the crew (and the rest of us who wished to attend). They handed out various awards and promotions to the crew. Secretary Chertoff discussed the importance of the arctic to both science and the national interests of the United States, and Admiral Allen underscored some of the secretary’s comments, highlighting the deployment of the CG’s new “National Security Cutter,” Bertholf. There are plans to place three more of these cutters into service in the next several years. The Commandant went on to discuss some of the crew’s concerns regarding days between port calls, career advancement and other issues, such as a revised uniform for CG personnel.

Admiral Allen addresses the crew.

Next up is the “in-brief,” where new arrivals learn about basic procedures on the ship. Much of it is also covered in the “Welcome Aboard” document allegedly present in everybody’s cabin. For those having never had the experience, it is during the inbrief where a new arrival experiences the donning of an arctic water survival suit more affectionately known as a “gumby suit,” given the way one appears when wearing it. These are not easy to get in to or remove, nor easy to maneuver in when on. However, they are supposedly effective in keeping you alive for at least a few tens of minutes should you fall into the icy water of the arctic. Attached one finds a mirror and whistle– used to signal for help.

Teacher John Peterson dons a gumby suit.

A typical day aboard Healy starts at about 0700, when breakfast is served. For most of the crew, the day ends about 1800. After dinner movies and other entertainment may be available. For the science party, however, hours can be extremely long. Working until 0300 or 0400 is not terribly unusual, and all-night sessions are not unheard of. Of course, being light effectively all day can encourage one to work longer than they might otherwise. It’s something to avoid if you intend to stay alert and safe.

Winding up the first day on Healy, I recall from my last time here that the fo’c’stle affords a nice view of the sea (and ice, if present), and is a nice spot for taking pictures. Phil and I proceed forward and begin some photography and videography. We run into Holly and Kjetil, both from the MIT/WHOI joint graduate program, who have also discovered the views.

Scientist Holly Dail poses on the fo’c'tle.

Kjetil Vage poses on the fo’c'tle.

There is also some nice ice with blue pools floating by. Although pools are fairly common, this piece has a larger than average number. Shortly after, we spot a baby seal on the ice– the first noteworthy wildlife we have seen since coming aboard. It is a bit far off, so the photo is not a close-up. The seal appears to be seeking its mother; we expect her to not be far off, but never see her.

Drift ice with numerous blue pools.

Seal on the ice.

As the arctic “summer sunset” draws near, I think of how difficult a life it must be in the arctic, but how beautiful, important, and unique it is.

The nearest we have to sunset in this part of the arctic in summer.

The emergency escape card on the Boeing “Combis” 737 aircraft. Cargo travels first class.

When winter temperatures can reach -50F, cars need to be plugged in overnight to keep them warm enough to start.

There are a handful of research activities happening in Barrow, and scientists are in no short supply. At the cafeteria joining the Barrow Arctic Research Consortium (BASC) and the I?isa?vik College, it is not unusual to overhear or join in on a conversation about methane flux at one table while at another the finer points of the year-round hunting season are reviewed in Iñupiaq. The diversity is palpable — some of the most important scientific questions affecting our planet are being asked in a setting shared with some of its most ancient inhabitants.

It takes time to unload the planes at the Barrow airport, affording an opportunity to get to know others that may well become your colleagues. In this case, it was a research team from UC Berkeley lead by Robert Rhew, Bob Reiss (a writer doing an article for Outside magazine), Phil and our driver, Scott.

Scott.

After the 20 minute drive on the dirt road (the only kind of road in Barrow) leading from the airport to BASC, one is assigned a room and meal card. Accommodations are basic… “dormitory style.” It was too late for dinner at BASC, so hooking up with our new colleagues from the Univ. of Colorado and Berkeley we were able to dine at Pepe’s– the northernmost Mexican restaurant in America… in a dry town that’s definintely NOT south of the boarder.

All roads in Barrow are dirt roads, but some have a nice view.

Our accommodations in Barrow.

Walking the 200 or so yards to visit the new $60M+ BASC building, Phil and I we were squawked at by a fairly rare Parasitic Jaeger (also known as Arctic Skua or more formally Stercorarius parasiticus). This is the first noteworthy wildlife encounter.

A Parasitic Jaeger.

Science and native culture are not the only concerns in Barrow. There is a national government presence as well. The new BASC building is currently being shared with the US Coast Guard. The CG provides support for its traditional mission areas (navigation aids, border security, oil spill response, fishery enforcement, and search/rescue), in addition to its science support of resources such as the icebreakers. The warming of the arctic poses new concerns for the USCG and its parent, the Department of Homeland Security (DHS)… less ice means more navigable water. More navigable water means more work for DHS. This is enough of a concern they have coined the term ‘Arctic Domain Awareness’, and the Secretary of DHS has come to Barrow to see how its working. As fate would have it, he was closer than I had really realized…