1 Agenda Platforms Group : USL – NMFD 0900 Introduction and Autosub6000 Steve McPhail 0905Autosub6000 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 1100Coffee Ocean Biogeochemistry and Ecosystems

2 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

3 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 Maaten Furlong 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 m 3  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 W W W N N N , m 4500 m 4400 m 4200 m 4300 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)  1 st Mission was in Falmouth bay (50 m deep).  2 nd 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 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 (X 2 + Y 2 + Z 2 = R 2 ) Pythagoras 569 BC – 475 BC Find a solution for Xerr, Yerr, Zerr, K to minimise ξ. Maths

19 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 runs Setup: Sound speed error 0.2% AUV depth sensor error10 m Range noise1.0 m rms Fish Motion (uncorrected) 1.0 m rms Results: RMS Horizontal radial error 3.3 m Mean horizontal radial error0.39 m Time to do a run42 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.

21 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

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..

26 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 … m m m m Elapsed time (Hrs) Elevation (m)   Speed Buoyancy Lift F(  )

27 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.  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..

28 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

30 This Year – Short term plans for Autosub6000  Integrate EM2000 Multibeam Sonar - about 2 km 2 /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 (Russell Wynn) ….

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32  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 results Geometry of the two boxes run (ship position at 0,0) Range : 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 th September to 4th October (14 days). Falmouth to Falmouth Operating Areas 50 ⁰ N 10 ⁰ W 49⁰ N 48⁰ N 47⁰ N 9⁰ W 6,7 5 8⁰ W 7⁰ W 3,

35 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 th September to 4th October (14 days). Falmouth to Falmouth Provisional plan and objectives: II nitial on shelf water tests possibly in sheltered area. For tests of basic control and navigation, launch and recovery. TT rails between the 200 and 300 m contour on the shelf edge. To check limit of bottom tracked navigation. DD eep 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 I 2 C 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 ?