GEOMAR Landers as Long-TermDeep-Sea Observatories Applications and Developments of Lander Technology in Opera-tional Oceanography

By Dr. Olaf PfannkuchePrincipal Scientistand Dr. Peter LinkeSenior ScientistGEOMAR Research Center for

Marine Geosciences Kiel, Germany

Landers, as autonomousinstrument carrier systems,

are used to study processes at thebenthic boundary layer. They areusually deployed on the seafloorat depths of several hundred to6,000 metres beyond the reach ofremote sensing and conventionalsystems.

After reaching the seafloor in afree-fall mode, an onboard com-mand system starts the deep-seaexperiment. At the end of themission an acoustic commandreleases the ballast weights, andthe lander rises by the virtue ofits positive buoyancy to the seasurface.

The first steps toward thedevelopment of successful deep-sea autonomous vehicles weretaken in the United States in thelate 1970s by the development ofthe free vehicle grab respirome-ter (FVGR)1 and ManganeseNodule Project (MANOP) Lan-der.2

The first German lander sys-tem was successfully deployed ata 4,500-metre depth in 1986.3 Inthe early 1990s, there werealready about 30 lander systemsin operation.4 Also in the 1990s,the technological lead of interna-tional lander development shiftedto Europe, which was benefiting

A fleet of six GEOMAR modular landers lined up for deployment.

Reprinted from Sea Technology

System (GML) is based on a tripod-shaped universal platform that can beeasily dismantled for transport, pro-vides a flexible float arrangement andan open instrument platform to carry awide range of scientific payloads. Theframe is made of stainless steel or tita-nium, the later version for long-termendurance in corrosive environmentsand weight reduction. The GML car-ries a floatation unit with up to 33 17-inch glass floats. Some of these floatsare used as instrument housings for anArgos beacon and for the power sup-ply (NiCd batteries with up to12V/56Ah) for the various instru-ments. Three stacks of iron squares(150 kilograms each) are used as bal-last weights. They are released by

from the European Union Marine Sci-ence & Technology (MAST) Pro-grammes, specifically theAutonomous Lander Instrument pack-ages for Oceanographic Research(ALIPOR) Programme.5

GEOMAR Lander SystemLander systems are now used as

platforms for a wide spectrum ofoceanographic applications. Theymust work autonomously for periodsof up to six to 12 months. Thisrequires robust design and manufac-turing as mechanical and electronicssystems must withstand worldwidetransportation in containers anddeployment from an arbitrary ship tothe deep ocean at pretty rough seastates. Once on the seafloor, the sys-tems must work without human input.Instruments and software systemsmust be robust because system crash-es, similar to those one may haveexperienced with a desktop PC, cannotbe tolerated.

GEOMAR Research Center forMarine Geosciences has 10 years ofexperience working with the designand manufacture of deep-sea landersin close cooperation with local small-and medium-sized enterprises. Thecenter presently operates a suite of sixmodular design landers as a universalinstrument carrier for benthic bound-ary layer observatories.

The GEOMAR Modular Lander

paired acoustic transponder releasersupon acoustic command. For spottingand recovery, the lander is equippedwith a radio beacon, strobe light andflag.

To facilitate the recovery procedure,a small float with a six-metre-longfloating recovery line is releasedsimultaneously with the ballastweights which can then be salvaged tolift the floating lander from the seasurface onboard with the ship’s crane.The float is retained in a small con-tainer during deployment to preventinterference with instrumentation.

Another modular feature lies in theuse of a universal microcontrollerboard based on the Infineon C164CIcontroller. The design goal has been tocome up with an easily programmable,flexible platform with decentralised

(Left) A sketch of the GML-configuration with floats,ballast and launchingdevice. The central plat-form potentiates the incor-poration of a large spec-trum of scientific payload.

(Bottom) The launcherconnected to (1) the ves-sel’s cable, (2) carrying thetelemetry, (3) the electricrelease, (4) the survey, (5)the down-looking videocamera and (6) the flood-light.

design to minimise the effect of fail-ures of single components, low powerconsumption, timed control of DC-motors and enough memory to be usedas dataloggers. The solution was asmall printed circuit board (PCB) thatcarries a commercial microcontroller-board and some relay-based driversfor the various DC-motors. Standard-ized and exchangable motors are usedfor any mechanical movement on thelanders. They deliver a transistor-tran-sistor logic (TTL) signal that corre-sponds to their revolution. This signalis galvanically isolated and evaluatedby the microcontroller board. Theshaft of the motor is sealed by a spe-cially developed O-ring construction.The PCB is mounted in a titanium

The launcher carries up to two video cameras, a surveycamera in the front and a downward-orientated camerashowing the lander during deployment. Both cameras andfloodlights can be switched on and off with a PC-controlledtelemetry surface unit. Additionally, the launcher isdesigned to carry a scanning sonar with online data trans-mission to the surface to scan a broader field for acousticobjects (e.g., precipitates, clam fields, gas emissions, obsta-cles) than can be obtained by the video cameras.

The whole system is towed approximately one metreabove the seafloor, and the height is adjusted by the winchoperator. For navigation purposes, a transponder is mount-ed close to the instrument on the cable using either longbase line or ultra-short base line navigation. The launcherenables accurate positioning on metre scale, soft deploy-ment, and instantaneous disconnection of the lander andlauncher by an electric release that is activated by electriccommand of the operator through the telemetry unit.

Scientific PayloadThe GML provides the platform for GEOMAR’s present

research activities, but carrying guest experiments from sci-entific partners is also common practice. The construction-al characteristics of the GML offer the potential for funda-mental and applied deep- water studies.

The present GML application addresses integrated benth-ic boundary layer current measurements, quantification ofparticle flux, quantification of gas flow from acoustic bub-ble size imaging, monitoring of mega-benthic activity, fluidand gas flow measurements at the sediment-water interface,biogeochemical fluxes at the sediment-water interface (oxi-

dants, methane, nutrients),experiments with deep-seasediment and organisms (foodenrichment, tracer addition,change of physical and chemi-cal environmental parameters)and gas hydrate stabilityexperiments.

The GML is employed bothas a carrier for commerciallyavailable oceanographicequipment in various configu-rations and GEOMAR-designed benthic observato-ries. Standard payload equip-ment includes acousticDoppler current profilers (75,300 and 1,200 kilohertz); cur-rent meters; conductivity, tem-perature, depth instruments; astereo deep-sea camera sys-tem; a multibeam echosounder; sediment traps (coni-cal and triplet cylinder); andsyringe water samplers.

A focus of GEOMAR obser-vatory development is benthic

pressure housing that has six to 12 connectors and is pres-sure-resistant down to 6,000 metres. The programs for themicrocontroller were written with a commercial C-compil-er. The code of the program can be transferred serially viaRS-232. The power consumption is kept very low by notusing stand-by modes; instead the complete system is pow-ered down and then restarted by a real-time clock alarm.The times of events are preprogrammed with a laptop com-puter and a Windows-based interface (in the lab or on deckof the ship). A magnetic “wizardstick” and a reed-switchfinally start the system.

Targeted Lander DeploymentLanders are typically deployed in the conventional free-

fall mode, where the lander is released from the ship at thesea surface. It will land on the seafloor depending on waterdepth and the ambient hydrographic regime in a radius ofhundreds of metres to more than a kilometre beneath theship’s position. This mode of deployment is still used forinvestigations on abyssal plains or other rather uniformseafloor settings.

However, many scientific objectives addressing specificgeomorphological features such as cold seeps, mud moundsor particular benthic communities require a targeted andsoft lander deployment. For these requirements, Dr. PeterLinke developed the concept of a targeted lander deploy-ment with a special launching device connected to theship’s coaxial or hybrid fibre optical cable. This launchercarries the telemetry, cameras, lights and an electric releaseto separate the GML from the launcher.

The bi-directional video and data telemetry providesonline video transmission, power supply and surface con-trol of various relay functions. At present, three telemetrysystems are used to deploy landers in various projects/set-tings from different research vessels. Whereas the coaxialtelemetry provides only black and white video transmissionfor one camera, the fibre optic telemetries provide twocolour video channels per laser module.

The biogeochemical observatory consisting of (1, 2) two cylindrical chambers with (3) anattached syringe water sampler, (5) the gas exchange system comprises the water reser-voir with (4) a syringe water sampler and (6) the gas exchange unit.

“In the future, landers will also be incorpo-rated as modules into glass-fibre opticalcable systems spanning whole continentalmargins. ”

and T. Viergutz) to measure and differ-entiate between gaseous and aqueousfluxes and the direction of very smallfluid flows from cold seep settings.Further Applications

With the growing need for long-term seafloor observatories, as pre-sently outlined in the European Un-ion’s European Seafloor ObservatoryNetwork programme,6 the lander willplay a vital role. Targeted deployedlanders with a wide range of instru-ments and sensors for physical, chem-ical, biogeochemical and biologicalparameters will be employed in a sin-gle autonomous mode in relativelyinaccessable terrains (high latitudes,central parts of the oceans, canyons,mid-ocean ridges, fracture zones).Typical observation periods will beone to two years. Bi-directional com-munication with the lander was recent-ly introduced by using an acoustic linkthrough a modem. The transmissionrates and data quality, however, arestill hampered by the baud rate of themodems.

In the future, landers will also beincorporated as modules into glass-fibre optical cable systems spanningwhole continental margins. Whilelarge glass-fibre optical cable net-works represent a major investmentand remain stationary for decades, lan-der clusters connected by optical cablerepresent a cheaper and highly mobilealternative. Such networks can bemoved and used in a task force modefor current problems such as globalchange and environmental monitoring.Clustered lander systems should trans-mit data to the surface and further bysatellite link to the shore. The landerarrays can consist of diverse lander-types for scientific observation, powersupply and garage-types for smallautonomous (AUVs and crawlers) andtethered vehicles (ROVs).

AcknowledgementsThe development of the GML and

associated scientific modules wasachieved by the dedicated support ofthe members of our working group,namely the project engineers V. Nup-penau, F. Appel, A. Cremer, M. Poser,M. Pieper; the technicians A. Petersen,

chamber systems to measure materialfluxes and fluid flows at the sediment-water interface and to perform in-situexperiments with deep-sea benthiccommunities. Benthic chambers(squared or cylindric) are supported bya stainless-steel frame that is mountedto the GML platform. Each chamberrepresents an autonomous modulewith its own control unit and powersupply with rechargeable NiCd batterypacks integrated into a glass sphere.Chambers are driven into the sedimentby a motor approximately two hoursafter reaching the seafloor. Afterimplementation of the chamber, thetop lid is closed. At the end of eachincubation, a shutter is closed by a sec-ond motor in order to retrieve the sed-iment. Once the shutter is closed, thechamber is slowly withdrawn from thesediment by the first motor, and thelander can be called back to the sur-face. All maintenance-free drive unitsare standard DC motors in stainless-steel pressure housings.

Recent development toward a bio-geochemical observatory (BIGO) in acooperative project with the TechnicalUniversity of Hamburg-Harburg (withProf. G. Gust) will employ a “Gustmesocosm” as a chamber lid. This stir-ring device either reproduces theambient outside current regime oralters bottom shear stress for experi-mental designs.

In order to record long-term vari-ability of benthic turnover in semi-closed chamber systems, it is of cru-cial importance to maintain the oxy-gen supply at natural levels and toavoid severe oxygen depletion. Thus,to compensate for the total oxygenconsumption of the enclosed sedimentcommunity, a gas exchange systemwas developed. This system facilitatesa controlled oxygen transfer from areservoir containing oxygen-saturatedseawater into the benthic chamber. Aparticle and fluid injector is employedfor experimental designs to add organ-ic substances and liquid or particulatetracers. This approach represents amajor step toward the development ofdeep-sea experiment systems andfrom stationary to dynamic benthicchambers.

Another novel development withinthe long-term observatory for thestudy of control mechanisms for theformation and destabilisation of gashydrates (LOTUS) programme is theFluid Flux Observatory, which wasdesigned by the Technical Universityof Hamburg-Harburg (by S. Gubsch

W. Queisser; and the scientists Dr. U.Witte and Dr. S. Sommer. This workhas been funded by the German Feder-al Ministry of Education and Research(BMBF) as part of the projects BIO-C-FLUX, BIGSET, TECFLUX andLOTUS, and by the European Unionas part of the project ALIPOR.

This is publication GEOTECH-29of the progam GEOTECHNOLO-GIEN of the BMBF and the DeutscheForschungsgemainschaft (DFG).

ReferencesFor a full list of references, please

contact the author Olaf Pfannkuche atopfannkuche@geomar.de. /st/

“Lander systems are now used as platforms for a wide spec-trum of oceanographic applications.”

Olaf Pfannkucheobtained his master’sdegree in biology in1973 and his Ph.D.in 1977, both at theUniversity of Ham-burg. Since 1993 heworked at GEO-MAR. Pfannkuche has a record of 25 yearsof scientific work in the deep sea and par-ticipated in more than 50 sea-going expe-ditions. His research activities deal withcarbon cycling, benthic ecology, biogeo-chemistry of cold seeps and marine gashydrate deposits, risk assessment of min-ing activities and waste disposal in thedeep sea. He, together with Peter Linke,received the K.E.R.N Award for the devel-opment of advanced lander technology in2001.

Peter Linke is amarine biologist andstarted his scientificwork in 1985 on ben-tho-pelagic couplingwithin the Sonderfor-schungsbereich 313at Kiel University.There he got his Ph.D. in 1989 and joinedGEOMAR in 1993 as a senior scientist toinvestigate the biogeochemical processesthat are associated with fluid flow phe-nomena at various subduction zone andhydrothermal vent settings. He worked asprincipal investigator in several EuropeanUnion projects and various nationallyfunded projects. He, along with ErwinSuess, Gerhard Bohrmann, Jens Greinertand Dirk Rickert, received the Philip Mor-ris Award for research on marine gashydrates in 2001.