Keynote2

Dive ofAUV "r2D4" to "The Great Dodo Lava Plain"in the Rift Valley of the Central Indian Mid-Ocean Ridge System

Tamaki UraInstitute of Industrial Science, The University of Tokyo

4-6-1 Komaba, Meguro, Tokyo 185-8505 Japanuragiis.u-tokyo.ac.jp

2). The team consists of four sub-groups; i.e. AUV,1. AUV "r2D4" chemistry, bathymetry, and rock sub-groups. The aim

of the AUV "r2D4" was to survey the rift valley usingThe Autonomous Underwater Vehicle "r2D4" (cf. its side scanning Sonar (100 kHz and 500 kHz), which

Fig. 1), constructed in 2003, is a cruising type AUV is associated with an interferometry Sonar, referring theweighing 1,600 kgf with a length of 4.4 m. "r" standsfor "ridge system" which can be seen as one of the lastfrontiers of our planet, "2" the second project, "D" East 65' 66depth, and "4" 4,000m depth rating. The lower case .................

letter "r" indicates that the vehicle is smaller than thefirst vehicle of the project the "R-One Robot" whichwas developed in the 1 990s and was capable of one-daycruising. It is fitted with a side scanning sonar, aninterferometry sonar, a CTDO, and an in-situ chemicalanalyzer "GAMOS" for measurement of manganeseconcentration. The AUV "r2D4" has previously beendeployed off Sado-ga-shima Island along a fault line inthe Sea of Japan (2003), over Kuroshima Knoll (2003),North West Rota 1 Underwater Volcano (2004) where it

Fig. 1 AUV "r2D4"tconstructed in 2003. x(

Underwater Crater (2005), and demonstrated high 66Oesperformance in autonomy and reliability in hostile Fig. 2 Central Indian Mid-Ocean Ridge East ofenvironments. Rodrigues

bathymetry data measured by the R/V Hakuho-maru(20 kHz). The AUV "r2D4" should carry and operate

2. Cruise to the Central Indian Mid-Ocean Ridge a set of CTDO measurement systems, the GAMOS, andSystem a 3-D magnetometer for the other sub-groups.

Unfortunately, the R/V Hakuho-maru is not equippedThe team, whose chief scientist is Prof. Kensaku with an ROV, so "'r2D4" was the only underwater

Tamaki, was organized to explore Segments 15 and 16 vehicle for this deep sea survey.of the Central Indian Mid-Ocean Ridge System (cf. Fig.

1-4244-1208-O/07/$25.OO ©C2007 IEEE. 3 UTO7+SSCO7, Tokyo, Japan, 17-20 April 2007.

Table 1 Dives in the rift valley of the Central Indian Mid-Ocean Ridge

No. Date Location Latitude Longitude Start of Dive End of Dive Dive Time Max. Depth28 2006.12.09 South of Seg.15 19:58:15S 66:09:03E 11:09 14:58 3:49 2,16029 2006.12.11 Roger Plateau 19:33:45S 65:50:38E 10:38 16:32 5:53 2,70130 2006.12.16 Roger Plateau 19:30:15S 65:48:09E 8:03 15:10 7:07 2,51031|2006.12.17 Roger Plateau 19:32:17S 65:48:32E 8:12 14:35 6:22 2,40232 2006.12.19 Dodo LavaPlain 18:21:22S 165:20:46E 7:321 16:06 8:331 2,701

0 Start The R/V Hakuho-maru left Port Louis in Mauritius.:l . jSUrfatba. . on 7th December 2006 for the NH06-4 Leg 3 cruise,

stayed around the rift valley of Segments 15 and 16until 21st December, and returned to Port Louis on the23rd.

The AUV "r2D4" performed 5 dives during thecruise as shown in Table 1. The first dive was carried

i___ l Ioutto test the complete system. Then, we deployedS 9 3B .#29 I "r2D4" for survey of "Roger Plateau (tentative name)"at 19_34S 65_5IE. The AUV "r2D4" performed three

I separate dives as shown in Fig. 3, and found someanomalies in the concentration of Manganese, but

source of these anomalies.hn.~ ~~~ ~ ~ ~ ~ ~ ~ ~~ ~3 Div to LaaPli

Fig. 3 Trajectories of r2D4 around the Roger 3. Dive to Lava PlainPlateau The second area is a narrow gorge in the middle

of segment 16. Figure 4 shows the dive plan for the#32 dive denoted by waypoints and tracklines, designedin order to take side scan images of the axis of the riftvalley covering almost all of the flat area. The divewas planned taking into consideration a maximum 300m error in position estimation and the maximumoperation time of 10 hours. At the center of the gorge,three track-lines can cover the full width of the bottom,

_a rtO(Cart which is about 3 km. The lowest height from the bedbetween waypoints was carefully selected as 60 m to

ft _A get clear side scan images, which can be obtained bytaking advantages of the AUV's stable motion.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~t tu]gtXt11!1 .t011T°-

18 25SW0 3 0|l696i,~~~~~~~~~~~~~?Ot

|~ ~~ 270

2N 0 --- 3------- --+- ---------------------- ------------.--r------- ----

2E 0 ?42 64 -| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Time (Mauritius)Fig. 4 Plan for #32 Dive along the Great Dodo Lava of December, 2006

Plain

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The AUV "r2D4" descended to the east peak ofthe rift valley, at a depth of 2,400 m, near the center ofthe gorge. After calibrating the magnetometer byturning right and left several times, the AUV jumped offthe cliff to the bottom of 2,700 m deep gorge, cruisedover the bottom of the gorge for about 6 hours at 3.3 Vknots as shown in Fig. 5 and took side scan images ofthe bottom surface covering 25 km2.

Fig. 7 Close-up of the central part of the plain

MM~ ~ ~~~d~ gceRik At the north part of the plain, there is a small rock'Puce d named Dodo's Beak. When "r2)4" passed

over the rocks, it found significant anomalies in the-18 22 4 concentration of Manganese and turbidity. Based on

eth results of Tow-yo surveys that o owed,i wasStaim ~confirmed that there is hydro-thermal activity at Dodo's

beak.

4. Conclusions

D o~ Pta round Washboa ~ It shoul be emphasized that by onl onedieo"r2D)4", we recorded tremendous amount of high quality

FDt9Pat ocks K oil Ball data o the ri valey, whic cannot be ob ained byRo ~~other systems such as manned submersibles and ROVs.

-18 '26 its depth.We would like to visit the Great Dodo Lava Plain

again. For frequent visits and discussion, it is veryK convenient that the every specific feature has a name to

-18 '28~~ ~ ~ ~ ~ s ayFal identify it. Considering that the gorge r2D4 visited is

in the EEZ of Mauritius, we named it "the Great DodoLava Plain" since te Dodo, which went extinct in te17 century, is the symbol of Mauritius. Smfeatures in the valley are named as shown in Fig. 6,

6 ~ 65138 65 '20 65'22~ which include

Fig. 6 Side Scan Images of the Lava Plain, and Dodo Soccer Stadium,Names of Paticular Objects Dodo Play Ground, and

Dodo Skate Rink.Because of the increasing number of underwater

The images, as illustrated in Fig. 6, show that vehicles, we are able to visit the bottom of the Ocean

there is a wide region of very flat lava plain, which is 26 more frequently than ever expected so far. Therefore,km in length and has an average width of 2.7 km, i.e. 70 we need many names.km2 in area. Considering the configuration of thebottom, it is estimated that the bottom of the lava plain Acknowledgementha a det of 3,0 m. Cosqety throueo The total plan of NH06-4 Leg 3 cruise was madelava~ ~isetmtda'6k3 by Prof. Kensaku Tamaki supported by the Ocean

Research Institute (ORE) of the University of TokyoThpli isepnigb. .8c e er o and the Japan Agency for Marine-Earth Science and

can see in Fig. 7 some cracks on the surface Of the plain Tcnlg JMTC. M.KniNghsiocaused bytheexpansion. ~Mitsui Engineering and Shipbuilding Co., Ltd. and his

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colleagues prepared the hardware and software of"r2D4" for safe and reliable operation. Acoustic datacaptured by "r2D4" was analyzed by Prof. Akira Asadaof Institute of Industrial Science of the University andhis colleagues. The chemistry group, whose leadersare Prof. Toshitaka Gamo of ORE and Prof. KeiOkamura of Kochi University, analyzed data fromGAMOS and CTDO and advised the AUV Group onthe areas "r2D4"should visit. The bathymetry group,leaded by Prof. Kyoko Okino of ORE, showed us thenewest and the most precise data of the configuration ofthe sea floor and rocks. The rock group, leaded byProf. Yuji Orihashi of the Earthquake Research Instituteof the University of Tokyo, provided us with thecharacteristics of the material of the bottom.

Captain Fujio Inaba, his officers and crew playeda big part in the launching and recovery operation of thevehicle from a rolling ship, and significantly contributedto the success of the AUV's dives.

References1] T. Ura: "Construction of AUV R2D4 based on theSuccess of Full-Autonomous Exploration of TeisiKnoll by R-one Robot", AUV Show Case, UK, (2002.9),pp. 23-28

2] T. Ura et al: "Introduction to an AUV "r2D4" andits Kuroshima Knoll Survey Mission", Proc.OCEANS'04 (OTO'04), Kobe, Japan, (2004.11),pp.840-8453] K. Nagahashi et al: "Underwater VolcanoObservaiton by Autonomous Underwater Vehicle"r2D4"", Proc.OCEANS'05, Brest, France, (2005.6),CD-Rom4] T. Ura et al: "Dive into Myojin-sho UnderwaterCaldera", Proc OCEANS'06, Singapore, Singapore,(2006.5), CD-Rom

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