ROV Exploration Hydro Thermal Vent Sites

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Robotic Oceanographic Exploration of Hydrothermal Vent Sites

On The Mid-Atlantic Ridge At 37 North 32 West

R. Bachmayer, S. Humphris, D. Fornari, C. Van Dover, J. Howland, A. Bowen, R. Elder,

T. Crook, D. Gleason, W. Sellers, and S. Lerner1

1 The authors gratefully acknowledge the support of the National Science Foundation under Grant number OCE-9505579 and OCE-9627160. The authors were members of the

engineering and scientific staff of the 1996 Lucky Strike Cruise. Humphris and Fornari were the cruise chief scientists, and are with the WHOI Department of Geology and

Geophysics. Van Dover is with the the West Coast National Undersea Research Center at the University of Alaska, Fairbanks. Bowen, Elder,Crook, Gleason, Howland, and

Lerner are with the WHOI Deep Submergence Laboratory. Bachmayer is with the Department of Mechanical Engineering, Johns Hopkins University. Support for Bachmayer was

provided by the National Science Foundation under grant number BES-9625143 held by Louis Whitcomb. WHOI contribution number XXXX.

Abstract

This paper reports results from an oceanographic

expedition to hydrothermal vent sites at the "Lucky

Strike" segment (37N 32W) of the Mid-Atlantic Ridge

during summer 1996 with the Jason/Medea, Argo II, and

DSL-120 underwater robotic systems. This deployment is

used to discuss and illustrate how novel underwater robots

dramatically enhance and augment, but do not replace,

conventional field methods of deep-ocean oceanographic

science, and to illustrate the capabilities and limitations ofpresent day underwater robotic systems.

1. Introduction

The last decade of research has seen underwater robot

technology evolve from fragile laboratory engineering

prototypes into mature field tools for oceanographic

science. These new robot systems provide unprecedented

techniques for oceanographers to explore the world's

oceans. Since 1985 when the ARGO robot system was

used to discover the wreck of the H.M.S. Titanic in the

North Atlantic, robots have explored hydrothermal vent

fields in both the Atlantic and Pacific Oceans, conductedmid-water acoustic, biological, and physical-

oceanography experiments, and performed under-ice

surveys in both the Arctic and Antarctic Oceans.

The underwater robot systems which are used

successfully for scientific research appear to share several

distinguishing features. First, the engineering research

teams developing these robots work in close collaboration

with practicing Oceanographers (Biologists,

Geophysicists, Marine Chemists, and Physical

Oceanographers) to design systems capable of performing

the surveying, sampling, and manipulation tasks essential

to quantitative oceanographic science. These robots are

designed to support a great variety of oceanographicinstrumentation, to navigate precisely, and to provide

comprehensive multi-modal data-collection to produce

first-quality scientific data-sets. Second, the robotics

research teams actively collaborate with ocean scientists

to deploy their robots to conduct research on

oceanographic expeditions. Lessons learned in the field

are used to improve the design of these robots, and to the

design subsequent generations of robotic systems. Third,

these robotic systems are designed to perform tasks that

are expensive, impractical, or not feasible with other

oceanographic field methods such as manned

submersibles, SCUBA, surface acoustics, satellite remote

sensing, and cable sampling.

The goal of this paper is to elucidate the role ofunderwater robotics in the context of deep-ocean scientific

research, to illustrate the capabilities of present-day

systems, and to identify engineering research problems

that currently limit the performance of operational

underwater robot systems in scientific missions.

2. Deep-Ocean Scientific Field Research:

Past, Present, and Future

Two different approaches have traditionally been used for

observations and sampling of the seafloor beyond the

continental shelf. The first involves lowering different

types of instrument packages (to collect acoustic and/orphotographic imagery) or sampling devices (to collect

geological or biological samples) to the seafloor on the

end of a wire from a surface ship. Much of the early

seafloor observational research was conducted in this way,

and this approach still provides an efficient and relatively

inexpensive method of investigation that is best suited to

completing scientific objectives that require sampling over

large areas. However, there are a number of limitations

associated with these techniques. For example, a camera

sled has to be recovered in order to retrieve the

photographic film, which then must be processed,

reviewed and co-registered with the navigation from the

tow in order to geodetically locate features of interest. Adredge haul of rocks provides samples of the types of

material present along a given track, but the geologic

relations between seafloor features and their different

lithologies are lost.


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A considerable advance was made with the increasing use

of submersibles for deep-sea research [2,7,8]. These allow

one or two scientists per dive to make direct observations

of seafloor features and their geologic and tectonic

relationships, and to make real-time sampling decisions.

Every sample, whether geological or biological, is

therefore precisely located on the seafloor relative to itswell-characterized geologic setting or ecological habitat.

In addition, dexterous manipulative capabilities of

submersibles, and their capacity for large payloads, enable

researchers to deploy and service instruments and

experimental equipment on the seafloor at precise

locations. Several submersibles, operated by different

countries, have been used routinely for oceanographic

research for many years. For instance, the DSV Alvin,

operated by the Woods Hole Oceanographic Institution,

has now completed over 3000 dives, with a >95% success

rate over the last 10 years. Although considerably more

expensive than instrument deployments from surface

ships, studies from submersibles have been fundamental indiscovering unique geological, geochemical and

biological phenomena and furthering our understanding of

many important seafloor processes.

The latest technological developments in fiber-optics and

robotics, and their application to deep-sea investigations,

have added additional capabilities that complement the

two approaches described above and provide new

strategies for carrying out deep submergence research

programs [1,6]. The use of fiber-optic cable to transmit

data - with both towed instrument packages and remotely-

operated vehicles (ROVs) - allows scientists on board a

surface ship to view, and react to, sensor data and acoustic

and video/photographic imagery in essentially real-time.

Real-time capabilities permit nested survey strategies, in

which data collected at a broad scale with one vehicle can

be used immediately to plan smaller-scale surveys during

the same cruise. Nested surveys are especially important

when working in logistically remote situations where

staging expenses prohibit timely return to a site.

For example, during a recent cruise to the Lucky Strike

hydrothermal field located on a Mid-Atlantic Ridge

seamount near 37 17N, scientific goals included placing

the hydrothermal activity within the context of the

structural geology of the region (on the order of several

km2) as well as study of the biological and chemicalcharacteristics of the hot springs themselves (at a scale of

m2). This kind of effort requires a nested survey approach.

Image Credit: S. Humphris and Dan Fornari/WHOI 1996

Figure 1: Bathymetry of the Lucky Strike segment of the Mid-Atlantic

Ridge at 37N 32W obtained by the Authors in Summer 1996 using the

SeaBeam 2100, the R.V. Knorrs hull mounted multi beam depth

profiling system

The DSL-120 sidescan sonar system was first used to

collect 120 kHz sonar data (in 1 km swaths) and co-

registered bathymetry over a 26 km-long portion of the riftvalley to investigate relations between crustal accretion

processes at the segment-scale. This was followed by

more detailed investigation of the summit of the seamount

using the ARGO-II optical/acoustic imaging system to

collect high-resolution acoustic and photographic imagery

to establish the geotectonic setting and distribution of

hydrothermal vents. Based on these data, several

hydrothermal sites were then selected for detailed imaging

and collection of samples using the ROV Jason. The

creative use of this combination of vehicles proved very

powerful in terms of achieving the scientific objectives of

the cruise. The large amounts of data that were collected

at a variety of scales provided both synoptic overviews aswell as detailed, high resolution observations.

An added advantage of data transmission from a mapping

vehicle or an ROV to the surface is the ability for several

scientists to simultaneously make observations and

participate in the real-time decision-making process,

rather than one or two scientists in a submersible working

in isolation. This is particularly helpful during field


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programs that are multidisciplinary, such as studies at

hydrothermal sites on mid-ocean ridges. Having

geologists, chemists and biologists "present" at all times

allows the work to proceed along a strategy based on

integrated interpretation of all the data. Observations can

be made by the appropriate specialists and directly entered

into a computer logging program as the work proceeds.This has two effects: it results in more consistency in the

description of seafloor features and biological organisms

than is achieved by a number of different scientists who

each participate in perhaps two to four dives during a

submersible dive series; and, second, the database

constructed in real-time can be used for preliminary

mapping of major geologic units and biological

communities within a short period of time following

collection of the data and merging of the navigational

information. Sample collection and experimental

manipulations are also optimized by the "presence" of

multiple scientists. The appropriate specialists can select

their own sampling sites and can direct the experimentalor sampling procedures, thus avoiding others having to

take this responsibility.

Image Credit: S. Humphris and Dan Fornari/WHOI 1996

Figure 2: Electronic photograph of active hydrothermal vent at the

Statue of Liberty site at 37N 32W . This is one of approximately

24,000 still images obtained by the Authors in Summer 1996 using the

Argo II underwater robot.

The other important feature of the fiber-optic cable is the

capability to provide towed and remotely operated

vehicles with electrical power from the surface rather than

from subsea batteries built in the towed instrument

package or submersible. This means that lowerings can

last for many days with data being collected continuously.

This type of operation requires three teams of scientists to

provide direction and maintain the data and sample

collection process throughout each 24-hour period,

making it very people-intensive. For example, on the

Lucky Strike cruise mentioned above, the ARGO-II

lowering lasted five days, during which over 24,000

digital images of the seafloor (together with other

photographic and acoustic imagery) were collected.

For remotely operated vehicles, the extended on-bottom

time (compared with submersibles which have to be

recovered every 8-12 hours to recharge batteries and rest

personnel) is partially offset by two factors. First, in order

to move the ROV beyond its tether length (i.e. 35 m in the

case of ROV Jason mentioned above), coordinated and

sometimes time-consuming maneuvers of the ship are

necessary. Second, the small payload of current ROVs

relative to submersibles for instrumentation, sampling

devices, and samples results in the use of elevators to take

equipment/samples down to the bottom and return them to

the surface being a necessity for any sampling program.

Consequently, driving to the elevator site and transferring

equipment and samples can be time-consuming.

Although ROVs do not, as yet, have as great a payload

capability or the stereoscopic cognitive presence that

submersibles offer, they can carry out many of thetraditional tasks that submersibles have been used for in

the past, and they can remain submerged for long periods

of time transmitting vast amounts of data to the surface.

They also offer vastly increased performance in high

resolution sonar and image-based mapping investigations

of small areas compared to submersibles.

Over the past 25 years, we have learned a great deal about

what kinds of deep submergence capabilities are needed

to effectively address the next generation of inter-

disciplinary scientific questions that face the community

of deep-sea oceanographers. The suite of deep

submergence vehicles has been augmented considerablythrough fiber-optic technology and robotics, and new

approaches to carrying out field programs are beginning

to emerge. Scientists can now collect a variety of data

continuously and in real-time using towed vehicles over a

wide range of spatial scales, and use that information

almost immediately to direct their scientific research. The

synergy afforded by the utilization of the appropriate suite

of vehicles, combined with their creative application to

scientific problems, will have a major impact on future

approaches to deep-sea research and exploration.

3. Engineering and Operations: DSL-120,

Jason/Medea, and Argo II

This section gives an overview of the DSL-120,

Jason/Medea, and Argo II vehicles, material, and the

operations.


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3.1 DSL-120

The DSL-120, shown in Figure 3, is deep-towed sidescan

sonar platform designed for continuous operations down

to 6000 meters depth. It was developed by Dr. Kenneth

Stewart of the WHOI Deep Submergence Laboratory in

collaboration with the University of Washington.

DSL-120 is a 120kHz high-resolution swath bathymetric

(sidescan) sonar. The sonar is instrumented to detect both

magnitude and phase information of sonar pulses, and in

consequence can be used to generate highly accurate 3-D

bathymetric maps. The vehicle is neutrally buoyant, and is

connected to a 1000Kg depressor weight by a neutrally

buoyant tether 50m in length. The depressor weight and

vehicle are lowered on a 0.68 diameter main cable from

the traction winch of a surface ship. Vehicle depth is

controlled by varying the length of the main cable. Both

the main cable and tether provide power conductors as

well as optical fibers for data communication. The vehicle

is normally towed at approximately 2 km/h at an altitudeof about a 100-200m altitude above the seafloor. At this

height the sonar swath extends about 0.5 Km to either side

of the vehicle., and provides approximately 1 meter-

resolution bathymetry.

Photo Credit: Margaret Sulanowska/WHOI 1996

Figure 3: The DSL-120 deep-towed sonar vehicle being launched from

the deck of theR.V. Knorrin August 1996.

A computer-based processing system on board the surface

ship receives real-time telemetry from the vehicles via

optical fibers, displays the sidescan data in real-time, and

time-stamps the data to permit cross-referencing to vehicle

navigation data, and logs the data to disk and tape. These

data, including vehicle attitude, are then used to generate

high resolution backscatter and bathymetric maps in near-real-time.

3.2 Argo II

Argo II, shown in Figure 4, is an 2100kg ROV designed

to support acoustic and optical imagery at depths to 6000

meters. The original Argo was a coaxial camera platform

developed at the Deep Submergence Laboratory in the

early 1980s. In 1994 Argo II was constructed (using

Argo's original steel frame) as a next-generation

computer-controlled fiber-optic vehicle. It is negatively

buoyant, and normally lowered on a 0.68 cable from the

traction-winch of a surface ship. As with the DSL-120,Argo II's depth is controlled with the traction winch. The

main cable provides both power and fiber-optic data/video

connections to the surface ship. ARGO II is equipped with

two laterally mounted thrusters that enable the pilot to

remotely control the vehicle heading and lateral position

under joystick control. Argo II is normally towed at about

10m above the sea-floor at a speed of about 1km/h.


Figure 4: ARGO II in 1994 at 26N 44W being recovered on the deck

of theR.V. Knorrafter a five-day deployment at 3500 Meters depth onthe Mid-Atlantic Ridge.

Argo II is equipped with three Silicon Intensified Target

(SIT) b/w cameras, one color camera, one 35mm film

camera, and an electronic Still Camera (ESC). All

cameras can be viewed in real-time on the surface ship.

Illumination is provided by 2500 Watts of incandescent

flood lighting and four 800 Watt/second strobe lights. The

ESC produces 1024x1024x16-bit images of the seafloor.


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With altitude and position information, scientists use the

ESC images to construct mosaics of the sea-floor. The

vehicle can be equipped with a transmissometer, a

conductivity-temperature-depth (CTD) sensor, 3-axis

magnetometer, 100kHz (for obstacle avoidance) or

200kHz split-beam sidescan sonar, scanning pencil-beam

sonar, and a variety of additional scientific instruments.Analog, digital, and serial interfaces are provided to

support almost any possible science instrumentation

package. All data is time-stamped and logged in real-time

on the surface ship.

Argo II's navigation suite includes a fluxgate magnetic

compass, a heading gyro-compass, redundant roll and

pitch attitude sensors, attitude rate sensors, a pressure

depth sensor, and a 100kHz acoustic altimeter. The

vehicle's position is determined with a transponder-based

longbaseline (LBL) acoustic navigation system.

3.3 Jason/MedeaJason, Figure 5, is a 1200 kg ROV designed for 6000m

teleoperation. Jason is neutrally buoyant, and is connected

to a 1000kg depressor weight (Medea) by a neutrally

buoyant tether 35m in length. It is lowered on a 0.68

diameter main cable from the traction winch of a surface

ship. The depressor weight depth is controlled by varying

the length of the main cable with a ship-board traction

winch. Both the main cable and tether provide power

conductors as well as optical fibers for data

communication. Video images from Jasons cameras plus

video from Medeas black and white camera are up-linked

in real-time to a control room on the mother ship, where

they are viewed by a pilot who flies the vehicle remotely

under joystick control. Jason is fully actuated with 7

brushless DC thruster motors that enable the remote pilot

to freely maneuver Jason in 3-D with a top speed of about

2 km/h.

The Jason/Medea ROV system was developed at the

WHOI Deep Submergence Laboratory, and first deployed

in the Mediterranean in 1989. Since that time

Jason/Medea has been deployed on dozens of scientific

missions around the world. Like Argo II, the Jason/Medea

system became part of the Deep Submergence Operations

Group, a national research facility, in 1995.

In 1992, Jason was upgraded by researchers at the Deep

Submergence Laboratory with a new modern 32-bit

control system with extensive data processing and I/O

capabilities [4,6]. Jason and Argo II now share this

common computer control system. Jason supports the

entire suite of scientific and navigation instruments listed

for Argo II in the previous section. The custom on-board

computers, telemetry, and power electronics inhabit three

cylindrical titanium pressure housings with a 15cm

diameter and a length of 1m.

In addition, Jason supports a variety of instruments not

supported on Argo II including a pan/tilt camera platform

and a 300kHz ultra-high accuracy acoustic navigation

system. The vehicle is passively stable in roll and pitch;

position and heading are actively controlled degrees of

freedom. It can be operated in either open-loop or fully

closed-loop positioning modes.

Jason is equipped with a custom-designed 5-axis robotic

arm that is teleoperated by the pilot. This arm, coupled

with the vehicles high maneuverability, enables Jason to

perform a huge variety of scientific tasks such as water-,

plankton-, rock-, sediment core-, and biological sampling,

and collecting temperature data.


Figure 5: JASON, a 6000 meter underwater robot for oceanographic

research developed and operated by the Woods Hole Oceanographic

Institution.

3.4 Elevator System

ROV operations make it possible to stay underwater for

extended periods of time, resulting in a large quantity of

data transmitted up the cable. Jasons manipulative

capabilities permit the use of a variety of sampling tools

and collection of a large number of samples. Tool and

sample storage on Jason quickly become limiting during

extended deployments. When the vehicle's maximum

payload capacity is reached, samples and/or tools must be

off-loaded into an independent vehicle deployed on the

work site, the elevator, Figure 6. The elevator serves as adelivery truck for Jason. An elevator consists out of a

basket equipped with five 17'' glass flotation spheres and

one 17'' acoustic transponder. The device is simply

released from the surface ship with an anchor hanging 6-

7m below it. After the elevator is filled with samples and

tools by Jason, the anchor release is triggered acoustically

from the surface ship. During the summer 1996 cruise,

eight elevators were deployed at various locations. As the


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elevator ascent and descent trajectory is not actively

controlled, it takes a considerable amount of experience --

and luck -- to place it close to the desired location.


Figure 6: An elevator being deployed fromR.V. Knorr.

3.5 Operations and Material

Jason/Medea, Argo II, and the DSL-120 are normally

deployed from a dynamically-positioned surface ship such

as the 3000 ton R.V. Knorr, Figure 8. The vehicles are

connected to the ship via custom-manufactured "main

cable" with a diameter of 0.68, a length of 9km, and a

strength of 200kN. Inside the triple-layer tension elements

of the cable are 3 copper conductors and 3 optical fibres.

The copper conductors supply the vehicle with about

20kVA of electrically isolated 1800 Volts AC power at

400Hz from a Jetway-power supply. On the vehicles the

400Hz AC is transformed and rectified to supply the on-

board 120V DC supply bus. One of the three optical fibersis reserved for digital data telemetry from the vehicles.

The other two fibers provide four video channels. The

capacity of a single fiber is 1.2Gbits/sec, and at present

the digital data telemetry rate is about 125Mbits/sec.

This type of cable must be spooled and stored with near-

zero residual tension. The 24500kg DYNACON cable

handling system consists of three main parts: a drum with

cable (13200kg), a level-winder unit (1100kg), and

tractionwinch unit (10200kg). The unit is able to spool

18000kg at a speed of 35 meters/minute or the normal

4500kg operating load at a maximum 120 meters/minute.

One of the major operational concerns during a cruise is

spare parts. There are no parts vendors at sea and,

accordingly, a huge inventory of spare parts must be

carefully maintained by the operational personnel. One 20'

shipping container contains nothing but gear and spares.

Another 20' shipping container has been modified to

contain a fully equipped workshop. This "tool van" holds

all the necessary tools to maintain and repair the vehicles

and associated equipment.

Two 20' shipping containers "control vans" were specially

modified to bolt-together to form a portable "mission

control center" for conducting vehicle operations. The

DSL crew can install the entire system on a surface ship in

about 3 days. Once installed, operations are conducted by

4 people in the control van in close collaboration with the

officers and crew on the ship's bridge. The pilotteleoperates the robotic vehicle and remotely operates its

on-bord equipment. The navigator monitors the vehicle

acoustic navigation and pilots the surface ship via closed-

loop dynamic positioning. The engineerkeeps track of all

the life functions of the vehicles and instruments and

assists the pilot. These three individuals coordinate their

efforts to collect scientific data and samples under the

direction of the chief scientist. On a long duration cruise

the vehicles are typically operated 24 hours a day by three

complete crews of operational personnel.

Photo Credit: Louis Whitcomb/WHOI 1996

Figure 7: Control Van: The mission control for ROV operations. From

left to right are stations for the Engineer, Pilot, and Navigator.

3.5 Navigation

Science is based on reproducible results. The physical

location of surveys and sampling operations must be

carefully documented in a standard international

geographical coordinate system. For land-based and air-

based operations, the U.S. sponsored Global Positioning

System (GPS) provides an inexpensive and highly precise

radio-frequency based system for documenting scientific

survey and sample operations. In the ocean, however,

normal radio-frequency waves do not propagate and,

accordingly, GPS and other radio-frequency navigationsystems are inoperable. Military submersibles commonly

employ inertial navigation systems (INS) for absolute 3-D

navigation, but the high cost of these systems has

precluded their widespread use in underwater robotic

vehicles. Acoustic time-of-flight navigation is the most

commonly employed technique for absolute 3-D

navigation of underwater robotic vehicles.


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Two types of acoustic navigation systems are commonly

used and commercially available. Long Baseline (LBL)

acoustic navigation systems operate at frequencies around

10kHz over baselines of the length of about twice the

water depth. Ultra Short Baseline (USBL) acoustic

navigation systems typically operate at frequencies from

100kHz to 1MHz and deliver a range resolution of acouple of centimeters. Due to the attenuation of high

frequency sound in water, the range of USBL is limited to

a few hundred meters. Update rates for both types of

systems are limited by the speed of sound in water, about

1500 meters per second, which determines the travel time

of an acoustic pulse.

For the large scale operations of the 1996 Lucky Strike

deployments, LBL navigation was used exclusively. The

LBL navigation systems components are (i) seafloor based

transponders, (ii) relay-transponders on the vehicles, (iii)

transducers on the vehicles, (iv) hull-mounted transducers

onboard the surface ship, and (v) a highly accurate GPS

(differential GPS or military P-code GPS) onboard the

surface vessel.

Photo credit: WHOI 1994

Figure 8: The R.V. Knorr, a 3000 ton oceanographic research vessel

operated by the Woods Hole Oceanographic Institution for the scientific

community.

LBL navigation works on the principle that distances

between any two transponders can be computed directly

from the time-of-flight of an acoustic pulse traveling

between the two transponders. The actual acoustic

interrogation pattern can be surprisingly complex in a

LBL deployment of, for example, three simultaneously

moving vehicles. When the position of anchored

transponders is known, as well as the sound-velocity

profile (sound-velocity versus depth), then the relative

position of the vehicles in the transponder network can be

computed. The accuracy of LBL navigation can be asgood as +/-2m with a 1km baseline. When the terrain is

not flat, the transponders are moored above the sea-floor

on long tethers to reduce acoustic shadowing due to the

terrain, although this makes the system susceptible to

currents (tidal currents) that perturb the transponder

positions.

In order to determine a bottom-moored transponder's

position, a net survey has to be performed. This is done

by driving the surface vessel through the net while

interrogating all transponders. The resulting round-trip

acoustic travel times are recorded along with the ships

trajectory as reported by the GPS. Using this data the

actual transponder coordinates can then be estimated.

During the mission the position fixes for the subsea and

surface vehicles (as well as other information) is made

available on the logging computer and shipboard

computer network.

4. Conclusion

Useful underwater robotic systems for ocean science are

designed specifically to perform a scientifically essential

data collection or sampling task that is infeasible with

existing oceanographic techniques, or to improve upon

existing techniques by providing an economy, efficiency,

or accuracy that justifies their use. In addition, most

successful underwater robotic systems can simultaneously

accommodate an ever-changing assortment of on-board

scientific instruments. In order to achieve these goals, it is

essential that the engineering research teams collaborate

closely, both in the laboratory and the field, with

practicing ocean scientists.

The engineering development of Argo II, Jason/Medea,

and the DSL-120 has been driven by the goal of

producing first-quality scientific data sets and samples.

This would not have been possible without the close

collaboration with and feedback from ocean scientists who

are willing to explore new and unorthodox methodologiesof subsea scientific research. These robotic systems were

engineered (and re-engineered) from unreliable laboratory

prototypes into stable operational platforms for deep-

ocean scientific research. This ongoing engineering

research and development effort has been informed by the

harsh reality of ongoing successes and failures in field

operations. In the example of Jason/Medea, the result is

that almost none of the components and sub-systems

comprising these vehicles is "original equipment", most

having been replaced by improved designs that can

survive and function in the field. This underwater robot

engineering effort has benefited enormously from lessons

learned byAlvin's engineering team during their 25 yearsof pioneering deep-ocean research. The ongoing

collaboration under the Deep Submergence Operations

Group continues to be highly productive.

A huge variety of problems remain to be solved. The need

for more accurate and reliable subsea navigation methods

is acute. While long baseline acoustic navigation is likely

to remain the standard methodology for large scale survey


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operations, significant improvements are needed in the

range, sensitivity, and accuracy of LBL instrumentation.

Novel hybrid navigation methodologies incorporating

technologies such as LBL, ultra-short baseline acoustic,

doppler acoustic, optical, and inertial navigation hold

promise of dramatically improving operational navigation

capabilities.

Our inability to automatically control the position of

underwater vehicles with sufficient accuracy limits the

operational scope of both tethered and untethered

underwater robotic vehicles. A variety of open issues in

the dynamical modeling and control of both vehicles and

their actuators have yet to be resolved. Improved

navigation, noted above, is an essential antecedent to

improved closed-loop vehicle control. Our ability to

reliably manipulate subsea objects and perform tasks with

on-board robot arms remains primitive. Moreover,

improved vehicle control performance and manipulation

capability is essential to the development of the next

generation of untethered robotic vehicles. These

untethered vehicles are presenting novel engineering

challenges due to their inherent power and telemetry

constraints.

The enormous multi-modal data sets generated by

underwater vehicles (often amounting to Terra-bytes of

data) present unique data-processing challenges. The data-

set generated during a typical deployment might include

still film images, digital electronic images, video, several

different types of sonar data, navigation data, data from

perhaps dozens of scientific instruments, and actual

physical samples. New computational tools for accessing,

integrating, searching, and visualizing these data sets willdramatically increase their utility and dissemination

among ocean scientists.

Acknowledgments

Captain A. D. Colburn, the officers, and crew of the

R.V.Knorr provided enthusiastic and highly professional

support during the 1996 Mid-Atlantic Ridge operations.

Louis Whitcomb encouraged the writing and submission

of this paper. The authors are grateful for their

contributions. We wish to acknowledge the generous

support provided to the National Deep Submergence

Facility at WHOI by the National Science Foundationunder Grant number OCE-9627160, the U.S. Office of

Naval Research, and the National Oceanic and

Atmospheric Administration. The cruise was funded by

NSF Grant number OCE-9505579 (to D. Fornari and S.

Humphris).

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Laboratory, Woods Hole Oceanographic Institution,

Woods Hole, MA, USA, August 1996.

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Transponders are tuned such that they all listen to the

same frequency (usually 9kHz) and respond on an

individual frequency that allows the operator to

distinguish between different returns.

A typical navigation cycle in the relay-mode can be

described as following: Suppose the relay transponder on

the vehicle is tuned to listen to 8kHz and answers on9kHz. The surface ship sends out a 8kHz ping and listens.

The relay is triggered and responds at 9kHz, which is also

the calling frequency for the transponders. The ship has

heard the 9kHz answer of the vehicle as well as it hears all

the responses of the transponders. Suppose the position of

the individual transponders is known as well as the sound-

velocity profile (sound-velocity versus depth) then the

relative position of the vehicle in the transponder net is

determined using the rms of the computed positions.

Successful technology is most rapidly and effectively

developed

Methods evolve out of experience as tools evolve out of

needs. The needs of ocean sciences to learn more about

the oceans enhanced the development of the deep diving

submersibles like Alvin. Engineers learned a lot from

Alvins success. This experience was transferred into the

development of the vehicles described above. The close

cooperation with scientists during and after the

development of the Jason/Medea, Argo and DSL-120

proved its value. The scientists interest in getting most

out of an available tool together with flexible platforms

like Jason/Medea guarantee continuous development and

steady improvements that will finally result in a new

generation of vehicles. The described cruise showed thepower and correctness of this approach.

Documents

ROV Exploration Hydro Thermal Vent Sites