1/16 Report on Seaglider Pilot Training Seaglider ... - Ifremer

Context 

<strong>Report</strong> on 

Seaglider Pilot Training 

Seaglider Fabrication Center 

School of Oceanography 

University of Washington 

Seattle, 7-11/01/08 

T.Terre IFREMER - LPO 

1/<strong>16</strong> 

Seaglider Pilot Training 5-12/01/08 

Changde 04/04/2008 

Participants : 

Fritz Stahr, Seaglider Fabrication Center (SFC) General Manager, 

Dan Hayes, Grigoris Konnaris, Tommys Eleftheriou, Oceanography Center, 

Cyprus 

Thierry Terre, IFREMER, LPO, Brest. 

Contacted persons : 

Charlie Eriksen, Mike Johnson, Kirk O’Donnell, Bill Fredericks, Karl Kunckle 

Within the European Gliding Observatories (EGO) (4), informal observatory gathering several 

European laboratories including LPO, we aim to maintain and increase our glider experience. 

The opportunity arises in the frame of a collaborative effort with the Oceanography Center (OC), 

University of Cyprus (D. Hayes) and LOCEAN (P.Testor). 

OC has recently acquired 2 Seagliders developed by the School of Oceanography (SOO), 

University of Washington (UW) and built by the Seaglider Fabrication Center (SFC), a SOO unit. 

OC offered us an access to the Seaglider training with an agreement of our side to put our 

experience with gliders to help in the first deployment of those gliders offshore Cyprus. Those 

deployment should arise during next spring according to the current Seaglider delivery schedule. 

The Seaglider is one of the 3 gliders together with Spray (SIO) and Slocum (WRC) which are 

currently commercialized. Having gained some experience with Spray and Slocum during 

numerous deployments carried out within the frame of MFSTEP and MERSEA, we were willing 

to pursue the mastering of this technology through the knowledge of this 3 rd instrument.

Schedule 

Figure 1 – Location of the training places. Document SFC 



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07/01 The day is dedicated to the presentation of the participants, SFC and Seaglider 

characteristics and piloting. 

Figure 2 – Description of Seaglider components. Photo SFC



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The Seaglider has been developed under the direction of Professor Charlie Eriksen, School of 

Oceanography (SOO). SFC has been created to built the gliders and insure the Seaglider service 

(maintenance, ballasting, batteries replacement, …) both for UW internal needs (SOO and APL 

(Applied Physics Lab)) researchers and for external needs (others research centers, US Navy, 

…). It concerns four persons and 2 students jobs. Fritz Stahr is SFC General Manager and the 

teacher for the training session with help of course documents (1) and diaporama (2). 

The Seaglider characteristics in shape are close from the others ~2m, ~50 kg but this is not 

surprising as it was a constraint in the Office of Naval Research glider call. Its peculiarity resides 

in its shorter wings span ~1m versus ~2m. 

Its main difference is the search for a shell having the same compressibility as the seawater. The 

goal was to minimize the energy consumption by avoiding spending energy to compensate the 

buoyancy variation due to the pressure case compression. After the experiment return, the gain is 

estimated to be ~10 %. 

The standard embedded sensors are a Seabird CTD, identical to the Slocum or Spray one, a 

Seabird oxygen sensor, a Wet Labs fluorimeter and a Wet Labs backscatterer. Facing some 

troubles with the oxygen sensor, some Seagliders are equipped with an Aandreaa oxygen optode 

too. 

The electric power is supplied by primary lithium batteries. The proof autonomy is 6 months and 

eventually 7 months ( 1 time). 

The Seaglider communicates through an Iridium satellite link using a data mode. The piloting is 

done with files exchanges (data and commands). 

08/01 The morning is dedicated to the Seaglider assembly from the components as it will be 

delivered. The shipping will be composed of 3 boxes : 

- Box 1 : forward part with the electronics, wings, fin and antenna 

- Box 2 : aft fiberglass fairing which includes some sensors 

- A support for handling and deployment.



Changde 04/04/2008 

Photo 1 – Two Seaglider components : the aft fairing ; back, the forward part. (Photo OC) 

All 3 parts require to be assembled and a detailed procedure is provided with the delivery. The 

assembly steps are simple with very little tools (1 screwdriver and 1 pliers). The only delicate 

point concerns the antenna connector with an O-ring which can easily slip out and be lost. It is 

mandatory to check the O-ring during the assembly steps. 

After we assist to the very first tuning of the Seaglider attitude in salt water. These very first 

tunings are the reference state : pitch and roll attitude, weight in water, communication and 

surface position to well expose the double functions antenna (GPS + Iridium).

Photo 2 – Tuning of Seaglider attitudes in a salt water pool. (Photo OC) 



Changde 04/04/2008 

Once the mass distribution inside the glider is set to find the right attitudes, we went through the 

checking list before the deployment. The glider is set outside with a clear sky view for good GPS 

and Iridium reception. During those tests, the iridium connection required several tries before a 

successful connection. 

Then we went through the steps for the next day with deployment of 2 gliders at Kayak point (see 

Figure 1). The Seaglider deployment requires both an onboard and an onshore team except if a 

good internet connection is available on board. 

09/01 The sea trial area for SFC Seagliders is located in Puget Sound at Kayak point county park, 

Port Susan. The depth is around 150 m in the south part but very shallow (~10m) with mud 

bottom in the northern part. This is an area with relatively low traffic but very stratified in density 

with up to 10 density units between surface and bottom. The glider must be able to deal with such 

density gradient by adjusting its volume.



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Photo 3 - Seagliders in their cradles during checks before déploiement. (Photo OC) 

The in-situ team is at Kayak Point at10 :50. Two gliders will be deployed but only one (SG141) 

for the training purposes, the other one is on test for an operational cruise. During checks, the 

Iridium connection is again a bit difficult to establish for SG141. The glider is deployed at 12:05 

and it has a good attitude at surface, the antenna mast is well above the sea level. At 12:53, the 

first dive starts, the estimated return time on surface is 13:30. At 13:29, the in-situ team see it at 

surface. The first communication is set at 13:32 but is interrupted very shortly. It turns out that 

this glider has very likely an Iridium communication problem (modem, antenna ?) as the second 

glider is doing very fine in communicating. During the very first dives, the glider parameters like 

pitch, roll and oil volume to pump are tuned. The first parameter to adjust is pitch for the dive 

angle and then we try to minimize the pumped oil volume. Among the plots proposed from the 

guidance and control software are curves helping to adjust those parameters. Still with the 

communication difficulties, the glider was able to send only 2 dives data from the 5 dives of the 

afternoon. The steering of the glider with a waypoint toward south is therefore not possible and 

the glider drift northward in the shallow water area under conjugated actions of both wind and 

tidal current. The weather conditions are not that good too and the wind is quite strong and the 

sea is rough. The in situ team is on its way back, the recovery is planned for the next day. 

10/01. The Seaglider managed to dive and have a few successful connections during the night. 

But it stayed a long time on surface and drifted a lot northward and is now in the very shallow 

area. During its last dive, it stayed on the bottom (11 m) for a while, up to the maximum allowed



Changde 04/04/2008 

dive time, before surfacing. The data indicate too a potential failure of the compass or bad 

compass calibration coefficients. 

The in situ team left to the field for the recovery. As the communication are working badly, there 

is no GPS position available. As the Seaglider is not equipped with an Argos beacon, the only 

remaining system for localization is an acoustic transponder in the glider nose. Checking the 

activity on the device associated to the modem called by the glider, we were able to indicate to 

the field team the glider surfacing for a visual search. The acoustic search is problematic as the 

acoustic propagation conditions in shallow water with a glider at surface are difficult. At the end, 

the glider is seen at surface and put on board 

Lessons from this deployment are that very early in the checking procedure the Iridium link was 

suspicious and that a compass problem emerged too. The weak communication link would have 

indicated to cancel the deployment but we ignore it for some reasons. The antenna tuning on the 

Iridium frequency is likely to be the cause. The compass showed a problem too either due to an 

hardware failure and/or to a wrong calibration coefficients set. 

11/01 The first morning is dedicated to a debriefing of the previous days together with the 

general philosophy of the Seaglider piloting. A presentation of the incoming experiment in the 

Cyprus area is made by Dan Hayes showing meteorological and oceanographical characteristics 

of the planned experiment area.

Remarks 

Mechanical characteristics 



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The isopycnal shell with a fiberglass fairing is the main innovation of this glider. The wings 

position located in the aft and the relatively small wing span are another innovative features. 

There is no external moving part outside like Spray. The maximum diving depth is 1000 m. 

The weight (~52 kg) and overall length (~2m) are very close to the ones of others commercial 

gliders. 

Sensors 

The standard Seaglider sensors are a Seabird CTD without pump, a Seabird dissolved oxygen 

together with the Wet labs BB2F measuring both the backscattering and the chlorophyll 

fluorescence. We noticed that an Aanderaa optode has sometimes been added to complement the 

Seabird oxygen sensor. 

Photo 4 – Aanderaa and Seabird (red ribbon) oxygen sensors fixed on the rear top fiberglass fairing. The 

CTD is just in front of those 2 sensors. (Photo OC)

Sampling 



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The sampling can be adjusted for each sensor independently. The water column can be defined in 

several slices were the sampling can be adjusted too. 

This last function is not available on the other gliders. 

Constant W objective 

The main line to develop the Seaglider was to keep as constant as possible the vertical speed 

while minimizing the energy consumption during dives. The different vehicle controls ‘oil 

ballast, flying angle, attitude) are determined by the glider itself to keep the vertical speed close 

to the aimed value fixed by the pilot through a set of parameters (depth, diving time, waypoint). 

The motivation was to obtain a regular sampling on the full water column. However, this 

objective is quite difficult to fulfill in strong density gradients. 

For the 2 others gliders, the diving angle together with the volume variations are fixed. The 

vertical speed is then relatively variable during the diving time. 

Hydrodynamic model 

An hydrodynamic model has been built and check all along the Seaglider development. The 

model is based on 3 parameters : lift, drag, induced drag. The model is integrated in the glider 

software. An estimate of the glider speed is produced based on computed buoyancy and 

measured dive angle. The horizontal component is used to predict the next surface position and to 

deduce from the difference of the GPS position and estimate of integrated current along the 

trajectory. The vertical component together with the one deduced from the CTD pressure 

variation rate are used to adjust the glider volume. 

Spray and Slocum perform a dead reckoning navigation by using data from pressure, attitude, and 

heading vehicle sensors without hydrodynamic model. 

Mass distribution 

If the glider buoyancy is controlled by volume variations due to an exchange of oil between 

internal and external ballasts, their pitch and roll attitude is driven by moving mass(es) around 

the center of gravity. The Seaglider controls the displacements in translation and rotation of one 

mass, its batteries, to act on the dive angle and heading changes. 

If for all kind of gliders, the dive angle is always controlled by moving a mass in translation, the 

heading can be insured by an external moving fin like it is the case for Slocum. With such a 

device, the turning radius is smaller and the reaction time faster. In coastal area, that can be a 

great advantage. Spray drives 2 masses, one in translation and the other in rotation. 

It exists a precise description of the mass distribution for each Seaglider and it is kept in an Excel 

file. It proves to be useful for adjusting the weight to ballast.



Changde 04/04/2008 

This description is also available for Spray, not at this detailed level, but not for Slocum. 

Altimeter and bathymetry maps 

The Seaglider is equipped with an altimeter to navigate in shallow water. However due to the 

time response of the hydraulic pump, it is recommended to run the glider in water deeper than 75 

m. An alternative to the altimeter is to rely on embedded bathymetry maps. 

If Slocum is equipped with an altimeter, Seaglider is the only one using bathymetry maps. Spray 

has none of those functions. 

Navigation 

The development philosophy is also to transfer as much as possible decisions to the embedded 

computer. Emphasis has been done on guidance and control by implementing a Kalman filter. 

The Kalman filter predicts the next dive parameters (buoyancy, angle, bearing). The dive depth is 

determined too in conjunction with either the altimeter or the bathymetry map. But the pilot has 

always the ability to suppress this filtering 

Slocum and Spray are able to compensate the estimated integrated current i.e. to act only on the 

direction to follow. 

Modules electric consumption 

Another characteristic of Seaglider reside in the tracking of the electric consumption of every 

activity in the Seaglider. All basic glider activities are described in terms of consumption and 

memory of the cumulative consumption is kept. It allows to provide to the pilot a good estimate 

of the remaining energy. 

It is the only glider with such a function. Slocum, basically equipped with alkaline primary 

batteries has a voltage threshold to stop. For Spray, the proved autonomy is around 140 days for a 

cruise with most dives at 1000m. 

Ballasting philosophy 

It is a point on which every development team has proposed its own way but all proposed 

methods could be applied to every glider. 

Seaglider is ballasted with the objective to be neutral for the denser water i.e. the maximum depth 

for the deployment. Seaglider has a total oil volume of 800 cc but among them 650 cc are useful 

for the buoyancy, the remaining 150 cc are reserved for the glider attitude on surface. This 650 cc 

amount of oil allows to face density stratifications up to 10 units. 

Spray is ballasted to reach a weight of 250g with its minimum volume at surface i.e. in the less 

dense water when all the oil is inside. That weight would allow the glider to dive even in strong



Changde 04/04/2008 

stratified waters. Having an oil reserve of ~600 cc is quite sufficient to fight against that weight 

to climb. 

Slocum is ballasted to be neutral at surface with half its total oil volume of 550 cc pumped 

outside. The strategy is to be able to dive by pumping inside and to climb by pumping outside the 

entire or part of the 270 cc available for each way. 

Emergency devices and procedures 

There is no emergency devices on the Seaglider. Scenarios in case of problems are not too much 

developed : the glider try to climb to the surface, switch to an abort mode in which it tries to call 

its server. There is no ejectable weight nor Argos beacon to compensate for GPS, Iridium or 

antenna failure. The only device which could be used to localize the glider as last possibility is an 

acoustic transponder With acoustic replies and a triangulation it is possible to get a position. 

This system could be a good solution as far as the search area is rather well defined. Acoustic 

propagation conditions are an issue too specially with an instrument at surface or close to the 

surface. From F. Stahr, 45 gliders have been built by SFC, and 22 by research teams and around 

20 of them have been lost at sea (~30 %). 

Slocum and Spray have more scenarios to fight emergency situations in case of devices failure 

(GPS, Iridium, pump, leak, ..) : back to a predefined point with shallow dives, Argos beacon, 

weight ejection, …. The more equipped seems to be Slocum with more than 20 abort codes and 

appropriate responses. To the best of my knowledge, there are very little lost in the deep Slocum 

line (1 for ~20 gliders, ~5 %) and a bit more for the Spray (6 for ~30 gliders, ~20%). 

Communications 

Iridium is the communication link implemented on all the glider models. The antenna is a 

cylinder of around 10 cm which is tuned on both Iridium and GPS frequencies. It is located at the 

end of 1m mast at the rear of the glider. To have the antenna in the best working position, it must 

be as much vertical as possible. The glider take a pitch of ~75° by moving its batteries all the 

way forward. In addition a volume of 150 cc is pumped out to increase the buoyancy and have 

the mast well above the sea surface. In case of fresh water patch or weak salinity, it is possible 

that the antenna is not enough outside the water to have communications. The Iridium 

communication mode chosen is the data mode (versus message mode). 

Once again the solutions proposed by the different glider team differ. Slocum has a patch antenna 

located on top on the fin. When the glider is at surface an air bladder is inflated with the internal 

air to increase the position by ~20 cm above the sea surface. The data mode is retained too. 

Spray uses its wings as antenna. Each wing acts both as a GPS and Iridium antenna. At surface, 

the glider rolls by 90° by rotating a batteries pack to expose one of it wings outside water. The 

pilot can decide to use the wings in an alternate mode or always the same and switch to the other 

only in case of problem. Spray uses the Iridium message mode.

Compass 



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Photo 5 – Seaglider position at surface to get GPS fixes and communicate. (Photo SFC). 

We should note that according to the glider position at surface, the module attitude was required 

to work on large angle range. A solid-state module has been retained for that reason. The 

calibration is a delicate phase and we can rely on the auto-calibration procedure of this product. 

Spray and Slocum are equipped with a compass working on a smaller pitch angle range. They use 

the same module. The remark regarding the calibration applied here too. Slocum and Spray have 

an in-house calibration procedure to compensate the not reliable auto-calibration method. 

Piloting methods 

Seaglider piloting follows a fixed protocol which is based on file exchange between the glider 

and server. When the glider connect to its server, it first sends its GPS position and then it must 

receive a command file with a list of parameters and their values. Then, according to some 

specific files presence, directives regarding sensors, waypoints are sent. Once those operations 

succeed, the data are sent. After, extra commands can be sent for devices status for example. 

All the files must be ready before the glider arrives on surface. 

For Slocum, we do have directly an open console in the glider and all commands –including 

dangerous ones- can be send on line. It allows a strong interactivity and to decide in real-time of 

actions to execute. For Spray all the exchanges are done through mails. The interactivity is lost 

but the communications time are shorter and more secure.

Handling 



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Seaglider is delivered with a cradle which could be used for deployments. With wheels its use 

would be easier. The exposed components (antenna mast and wings) are dismountable et can be 

fixed at the very last time to minimize floor space requirement…and risk to break them.. The 

rear rudder is mechanically design to support the glider weight and offers another way to deploy 

and recover the instrument. 

Maintenance 

Photo 6 – Deployment with cradle (left ) or with the rear rudder (right). Photo SFC 

Seaglider maintenance requires the same operation than the other ones : batteries replacement, 

hydraulic check, sensors calibration, compass calibration, …SFC can perform these operations in 

about one month 

Delivery time 

At present time, SFC can produced 5 gliders a month and the delivery time is around 15 to <strong>16</strong> 

months. 

License 

SFC will pursue its activity but licensing for the Seaglider fabrication with a private company is 

in process.

Seaglider 6000m 



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UW pursues the Seaglider 6000m project. Up to now, the point was to make the same shell but 

for 6000m. Difficulties in the fabrication process of the shell in composite material is the main 

blocking point. Various tries to produce this shell shape have all crushed during the pressure 

tests. Now, there are plans to change the shape to the more classical cylindrical one. 

Conclusions 

The glider concept described by Stommel in his visionary paper in 1989 has been developed by 3 

institute/company which are now in state to have commercial instrument available. From the 

same common characteristics proposed and sponsored by the Office of Naval Research, the 3 

groups ended with projects and instruments showing some differences on all the functions to 

realize. The only common constants are the GPS and Iridium technologies but for those functions 

the choice is rather small even no choice at all. The CTD sensors are the same too but used in a 

pumped or unpumped mode. 

All these instruments share the same problems (equilibrium, ballasting, communications). Each 

group proved to be innovative in various domains (shell, antenna, mass displacements, …). Every 

vehicle presents advantages and disadvantages. Slocum from its modular conception had 

numerous leaks but appears to be maybe the most secure with the smaller loss rate. Spray offers 

the best rate of success in communications but suffers of a weakness in mass rotating mechanism. 

Seaglider appears as the best internally described (hydrodynamic model, mass distribution energy 

consumption) but the security and emergency devices are a weak point which could explain his 

higher loss rate. 

On these 3 models, we can feel the different approach in the conception. Slocum was an engineer 

driven project headed by Doug Webb. Modular, science bay for the sensors load independent 

from the remaining instrument, simple (cylindrical shape, cart) and open (software) are the basic 

ingredients. The current developments concern mainly the thermal version which will get the 

diving energy from the temperature gradient between surface and dive depth.. 

Spray is issued from Russ Davies team with their experience in SOLO floats. The idea was to 

transfer the science data in the most efficient and simple way as possible. We could say it is a 

data driven project. The data transmission through mail do not require any specific equipment as 

a simple mail address is enough. The antenna function located in the wing is rather floor space 

consuming and make it delicate to handle sometimes. We do not have information regarding 

development around Spray. 

Seaglider is a project driven by a scientist too who imposed as a guideline to collect data at a 

constant vertical speed. It’s a data driven project too. The glider is very well described and that 

information is used to maximize the glider autonomy at sea. To add new sensors would be 

probably not that easy but it is already well equipped. To pilot that instrument request the



Changde 04/04/2008 

knowledge of a relatively large number of files with their functions and format. The current 

development concerns the very deep version at 6000m. 

We should note that under the impulse of ONR, a common pilot interface is under development. 

That would be a definitive advantage for experiment involving different types of gliders. 

The proposed training address only the pilot view including deployment and recovery. But not at 

all the maintenance. For an operational use, I think that a training for maintenance would be very 

useful. 

Photo 7 – Different kind of gliders in which one can add the Slocum 1000 m version. (Photo SFC)

Documents 

1 Seaglider Pilot Training document 

2 Seaglider Pilot Training diaporama 

References 

3 Stommel H., The Slocum Mission, Oceanography, April 1989 

Documents on Internet 

4 Site EGO https://www.locean-ipsl.upmc.fr/gliders/EGO/ 

5 Site LPO http://www.ifremer.fr/lpo/gliders 

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1/16 Report on Seaglider Pilot Training Seaglider ... - Ifremer

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