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Agenda

Platforms Group : USL – NMFD

0900   Introduction and Autosub6000         Steve McPhail

0905 Autosub6000 Sea Trials Steve McPhail

0950   Autosub6000 on JC027                      Dr Russell Wynn (G&G)

1000   Long Range AUV (LRAUV)             Dr Maaten Furlong, Dr Miles Pebody

1020   Science Application for LRAUV    Dr Richard Lampitt (OBE*)

1030    Air Deployed AUVs:                          Peter Stevenson

1045     Closing Q and A   

1100 Coffee Ocean Biogeochemistry and Ecosystems

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Platforms Group in USL

The Team: Steve, Peter, Miles, James, Maaten...

The Oceans 2025 Projects

Other Work : Autosub3 Support (10 person months over next year).

Sea trials in June.

Cruise to Pine Island Glacier Jan 2009 on RV N B Palmer

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Projected Relative Spend in Oceans 2025

Year

£k

First Sea Trials of Autosub6000

The latest in the Autosub AUV Series

Stephen McPhail

Objectives of the sea-trails on Discovery

Standard AUV Stuff … Navigation .. ..Control …Launch and recovery .. Speed Performance … Acoustic telemetry….

Interesting issues specific to deep AUV

Buoyancy Change for deep dive

Navigation: A solution to the initial position problem ?

Energy: Field test the new Rechargeable batteries.

.

The Team ….

James Perrett

Miles Pebody

MaatenFurlong

Peter Stevenson

Steve McPhail

Mick Minnock CPO -Sci

Dave White (Sea Systems)

Colin Morice (PhD Student)

Mark Squires

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5.5 m long, 0.9 m Diameter

1500 kg dry weight

Range : 330 km at 1.6 m s-1 (up to double in future)

6000 m Depth Capability.

Navigation using Doppler, USBL, and INS. Aim to achieve and maintain GPS accuracy over several days without a position fix.

Battery recharge time of 5 hours from totally exhausted.

Payload space of 0.5 m3

Up to 250 W available for sensors.

Typical sensors: Multibeam, Sub bottom, Cameras, Chemical

SPECIFICATIONS of Autosub6000

Key to the Range / Depth performance of Autosub6000

Lithium Polymer Pressure Balanced Batteries

Up to 12 battery packs, each of 5 kW hr can be fitted within the centre section of Autosub6000.

Charge in 5 hours

11 30 W 11 00 W 10 30 W 10 00 W

47 50 N

47 30 N

47 00 N

2

5

3

6, 7

4

4100 m

4500 m

4400 m

4200 m4300 m

4600 m

4000 m

Figure1 . Map of the Ausub6000 trial operating area. The first mission (Mission 1) was carried out in Falmouth bay. The last (Mission 8 – Navigation trials), was carried out in water depth of 150 m near the top of the Whittard canyon.

Fortunately we had some good quality multibeam charts … (thanks to Alan Evans and Veerle Huvenne)

1st Mission was in Falmouth bay (50 m deep).

2nd was in 4700 m of water

Last was in 150 m of water for navigation calibration.

OPERATING AREAS

8

11

Launch ..

We weren’t alone ….

Ben Teresa John

We weren’t alone ….

Chris Balfour Steve Mac

“TINY”

6 km

AUV Navigation: Problem 1: The Initial Position Problem

On the surface the AUV can get GPS fixes

Near (within 200 m) of the seabed the AUV can dead reckon navigate with good accuracy using its Doppler Velocity Log (DVL ) and Gyro compass

But during the descent - the AUV navigation effectively drifts with the currents - it could drift by hundreds of metres

?

?

Multiple Ranges measured by acoustic transponder as AUV circles

6 km

1 km

The Solution

As the AUV circles at depth (bottom tracking ) under the ships position ..

Get many ranges from the ship mounted interrogator to the acoustic transponder on the vehicle

Combine Ranges, AUV’ s navigation and Ships positions, to yield a single, high quality position fix for the AUV

Multiple Ranges measured by acoustic transponder as AUV circles

6 km

1 km

But …But ….

But isn’t the geometry terrible for this ??

Position errors are very sensitive range measurement errors … as shown , 1m of range error gives ..12 m of horizontal error..

What about sound speed ? (0.01% needed?)

What about refraction ?

What about depth sensor error, and pressure to depth conversion?

What about the fish vertical movement ?

However …..

1)Refraction effect is surprisingly insignificant

2)Systematic errors .. Sound speed, depth error, can be solved for given the that there are many (e.g. 100) measurements.

3)Fish vertical movement causes a random errors … (is averaged out significantly)

Horizontal error vs offset angle for “worst case” constant 0.017 ms-1 sound velocity gradient.

4) And fish vertical movement can be measured… and we did …

Maths is pretty simple

The implementation is a minimisation problem based on Pythagoras’s famous equation (X2 + Y2 + Z2 = R2)

Pythagoras 569 BC – 475 BC

22( - )

2( - )

2( - )

2-((1 . )

1

xSHIP xAUVj j

ySHIP yAUVj j

zSHIP zAUVj j

R j

N

j

Xerr

Yerr

Zerr

K)

Find a solution for Xerr, Yerr, Zerr, K to minimise ξ.

Maths

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Simulation results suggest that GPS quality or better fixes can be obtained within 40 minutes for an AUV circling at 6000 m depth

Monte – Carlo simulation for AUV output of position errors. 1000 runs

Setup:

Sound speed error 0.2% AUV depth sensor error 10 m Range noise 1.0 m rms Fish Motion (uncorrected) 1.0 m rmsResults:RMS Horizontal radial error 3.3 m Mean horizontal radial error 0.39 mTime to do a run 42 minutes

Simulation “Results”

AUV spiralled down to 4556 m

Autosub6000 then ran a square box around the centre position (while we collected range and position data).

After 20 minutes we repeated this box (to check the repeatability of the method)

Practical results

Figure 3: 3D Navigation plot for the first deep Autosub6000 mission. The AUV spiraled down to 4556 m depth, and then, after receiving a “continue” command sent by acoustic telemetry, executed a 1 km side box .

-1000-500

0500

1000

-1000

0

1000

-1000

0

1000

2000

3000

4000

5000

Y position (East) [m]X position (North) [m]

Dep

th [m

]

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Results of range only navigation processing

Results are consistent to within RMS radial error of 3 m , over two consecutively run boxes and varying the number of points used from 20 to 160.

i.e. the method looks robust , and should give GPS quality fixes or better with the AUV at deep depths.

For future missions we will use the acoustic communication system to send the navigation correction to the vehicle

Solutions for positions for the two boxes run (solid for box two). Higher numbers are for more data used (5 , and 10 are for all the data used). As a comparison the 50% horizontal radial accuracy (4m) of standard GPS is superimposed

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600 m

4 m

Pre and post positioning uncertainty

Problem 2: How to maintain Navigation accuracy over an area survey

So we can fix the AUV position at the start of the run …..

But what about the inevitable dead reckoning drift … maybe a few hundred m over the course of a long mission ?

A promising technique, where the AUV has a multibeam sonar, and the seabed is not completely flat, is a simple adaptation of Terrain Contour Mapping (TERCOM - which has been around for a long time - and is a very simple algorithm).

The difference is that we do not need to have a terrain map to start with – I’ll call it AUTO-TERCOM ..

AUTO-TERCOM How to maintain Navigation accuracy over an area survey

Navigation error reduces from Proportional to distance travelled (800 km)

To Proportional to Radial distance travelled from fix. (e.g. 5 km)

“TERCOM fixes” at each track intersection

Buoyancy Change ..the worrying unknown

Buoyancy change as the vehicle dives is caused by the vehicle parts compressing at a different rate to seawater as the pressure increases.

The Autosub6000 is usually ballasted at about + 10 kg buoyant (only 0.3% of its displacement)

The biggest area of doubt surrounded the syntactic foam for the vehicle buoyancy

We (Peter Stevenson ) made some measurements on thermal and compressive moduli of the materials…

But not possible to be sure enough about the full scale changes ..

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Great Caution needed for the first dive .. Started with 20 kg buoyancy (2 x more than usual).. Small Wings helped the vehicle fly. (Also 20 kg of abort ballast)..

Vehicle dived spiralling down then circled at 1000 m depth.

…waiting

By acoustic telemetry were able to read the vehicle pitch, stern plane angle and speed ….

And calculate the buoyancy

All looking Ok .. We would send an acoustic command to continue the mission (down to 2500 m ..etc ..)

If not it times out and would surface ..

In practice , the speed measurement was inaccurate due to poor backscatter for the ADCP in deep water …..

1000 m -

4000 m -

2500 m -

4556 m -

0 1 2 3 4 5 6 7 8Elapsed time (Hrs)

Speed

Buoyancy

Lift

F()

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Buoyancy Measurement –A better method

In practice – (near) “free ascent” method worked better….

Buoyancy

dz dt

Drag

Figure 2: The vertical ascent speeds during Mission #6, run alternately at 300 W and 10 W propulsion power. From this data we can calculate the depth dependant buoyancy variation and vehicle drag.

7000 7500 8000 8500 9000 9500 10000

0

1000

2000

3000

4000Aut

osub

6000

's D

epth

[m]

7000 7500 8000 8500 9000 9500 10000-2

-1.8

-1.6

-1.4

-1.2

-1

filte

r ve

rtic

al v

eloc

ity [

m]

Mission Time [s]

Key to the success of this method is that the vertical speed dz/dt can be measured very accurately.

Results show increase in buoyancy from 20 kg at surface to 26 kg at 4500 m.

..acceptable ..

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Summary

AUV ran for 60 hours, 278 km in 8 deployments.

The vehicle dives, controls and navigates as planned.. reliability looks good.

Linkquest Acoustic Coms and USBL worked well

Buoyancy change is quantified and tolerable

Range Only Navigation tested .. Looks very promising method of fixing the position of the AUV on the seabed.

McPhail, S. D., M. Pebody, “Range Only Navigation of a Deep Dived AUV”, Submitted to IEEE Journal of Oceanic Engineering, Jan 2008.

Longer Term Plans for Autosub6000

Develop and Implement AUTO-TERCOM using EM2000 data - eventually in real time.

Guided by Oceans 2025 proposal, and driven by Scientific Requirements ...

Develop Capability for the vehicle to get safely closer to the seabed, eventually with hovering and landing capability - opening prospect of sampling and interactions ….

Develop Real Time “intelligent” capabilities ..e.g. Find the source of a chemical signal ….

Have it used by marine scientists

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This Year – Short term plans for Autosub6000

Integrate EM2000 Multibeam Sonar - about 2 km2/hour survey at 4 m resolution

Increase battery capacity from 2 to 6 batteries - giving 48 hour, 300 km endurance.

Develop the Range Only Navigation – Implemented in “near real time” (AUV gets position correction update).

All this in time for James Cook Cruise 026, August 2007. (Russell Wynn) ….

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Two box runs were run at 4500 m deep with 20 minutes gap between. Each took 1 hour.

The data was analysed by progressively adding data according to the range circles shown , and solving for position of the AUV.

The idea was to see how sensitive the position output was to “bad geometry” and fewer measurements (20 to 160 )

The geometry was never “good” (ship was not in the centre of a closed box )

Analysis of resultsGeometry of the two boxes run (ship position at 0,0)

Range circles @ : 450, 600, 800, 1200, 2000 m

Autosub6000 in Oceans 2025

Bring it online as a the world’s most capable deep AUV, serving present and future science needs:

Overflow and exchanges across sills, abyssal circulation + mixing, Southern Ocean Mixing processes, ocean ridge, marine census, canyons and sea-mounts, ocean margins benthic communities,

gas hydrate surveys ..

Needing :

Improved collision avoidance (getting in close)

More reactive control and sampling - automatically find maxima or sources of interesting signals

Improved and novel navigation techniques.

Discovery Trials September 2007

20th September to 4th October (14 days). Falmouth to Falmouth

Operating Areas

50⁰ N

10⁰ W

49⁰ N

48⁰ N

47⁰ N 9⁰ W

6,7

5

8⁰ W 7⁰ W

3,4

2

8

1

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Practical results

Screen photo of Linkquest tracking output

Our real time USBL tracking was not quite so neat

…(uncorrected at present for fish attitude and ships position) but adequate for the purpose ..

Range Vs Speed

Range versus Speed prediction for Autosub6000, with the maximum load of 12 batteries (the 2007 version will have 6 batteries).

This prediction includes no contingency, and is for a minimal sensor suit.

Discovery Trials September 2007 20th September to 4th October (14 days). Falmouth to Falmouth

Provisional plan and objectives:

Initial on shelf water tests possibly in sheltered area.

For tests of basic control and navigation, launch and recovery.

Trails between the 200 and 300 m contour on the shelf edge.

To check limit of bottom tracked navigation.

Deep water tests at 4500 m contour and beyond (at about 47.5 N, 11W).

The variation of buoyancy as the vehicle descends – Tentatively !

Reliable operation of the batteries, and charging system.

The range and accuracy of the tracking and telemetry system.

Bottom track (within 200 m ), in deep water.

Produce data for advanced positioning algorithm.

Navigation, Tracking and Telemetry

Linkquest Tracklink10000 USBL/ coms

Used for tracking, monitoring, AUV navigation and control.

Working on a scheme to overcome the “initialisation problem” using this system.

DVL , INS and GPS

We are developing algorithms, which, for area surveys, will maintain GPS level of accuracy over several days.

Data for this Navigation already obtained using Autosub3 in a Norwegian Fjord:

Autosub3 Diving in Sognerfjord (March 07)

Lawnmower pattern in 1.8 x 1km box repeated 15 X over 48 hrs

Water depth as measured by Autosub - Very little relief .. 2 m over 1 km line – Very challenging for TERCOM Navigation type approach

Pressure Balanced Li Po batteries

Developed at NOC. Extensively tested at 600 bar pressure

Each Battery is 5 kW hr, at nominal 58 volts

Monitoring via I2C bus for Currents, Voltages, temperature, oil level, leak.

Charging in situ in 5 hours from fully exhausted

AUTOSUB6000 and the Very Long Range AUV

Steve McPhail. Underwater Systems Laboratory, NMFD

AUTOSUB6000 : Trials in September 2007

The Very Long Range AUV: 2012

Steve McPhail 6/2/2007

Very Long Range AUV

Key to long range is slow speed and limiting the sensor and control power.

500 kg Long Range AUV

1 W sensor power

Autosub3

Based on a simple observation.

Gliders are AUVs - but they use a particular type of propulsion system - which isn’t particularly efficient + constrains the AUV to profiling.

We can develop a very long range AUV using a conventional propulsion system which overcomes these limitations.

Very Long Range AUV The proposition is simply that we can design an AUV which be of great interest to a wide variety of oceanographers, e.g.

Choke points, reciprocal runs e.g. Drake passage

Long transects, e.g. Ocean basin

Station keeping for very long periods (year or more) - especially where the mooring is vulnerable

Able to have the an operating range of 1000’s of km.

Essentially gives the endurance of a Glider, but without the drawbacks

0.5 m/s rather than 0.2 m/s (much less affected by currents) + can sprint.

Not constrained to profile - same as any AUV

Larger power available to sensors

Size?

Speed ?

Sensors ?

Sensor Power ?

Range ?

Depth ?

Endurance ?

Navigation Accuracy ?

Unit Cost ?

Battery Cost ?

Many or few ?

Communications ?

Very Long Range AUV - User Requirements ?