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Agenda Platforms Group : USL – NMFD 0900   Introduction and Autosub6000         Steve McPhail

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

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Agenda Platforms Group : USL – NMFD 0900   Introduction and Autosub6000         Steve McPhail

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  1. 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

  2. Platforms Group in USL The Team: Steve, Peter, Miles, James, Maaten... Autosub6000 The Oceans 2025 Projects Long Range AUV Air Deployed Sensors 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 £k Year

  4. First Sea Trials of Autosub6000 The latest in the Autosub AUV Series Stephen McPhail

  5. . 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.

  6. The Team …. Dave White (Sea Systems) MaatenFurlong Mick Minnock CPO -Sci Steve McPhail Colin Morice (PhD Student) James Perrett Miles Pebody Mark Squires Peter Stevenson

  7. SPECIFICATIONS of Autosub6000 • 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

  8. 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

  9. 47 50 N 47 30 N 47 00 N 11 30 W 11 00 W 10 30 W 10 00 W 5 4000 m 4100 m 3 4200 m 4300 m 4 4400 m 4500 m 6, 7 2 4600 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. OPERATING AREAS 8 • 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.

  10. Launch ..

  11. We weren’t alone …. Ben Teresa John

  12. We weren’t alone …. Steve Mac Chris Balfour “TINY”

  13. 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 ? ?

  14. 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

  15. 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 ?

  16. However ….. Refraction effect is surprisingly insignificant  Systematic errors .. Sound speed, depth error, can be solved for given the that there are many (e.g. 100) measurements. 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 …

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

  18. Simulation “Results” 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 rms Results: RMS Horizontal radial error 3.3 m Mean horizontal radial error 0.39 m Time to do a run 42 minutes

  19. 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 . Practical 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)

  20. 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

  21. Pre and post positioning uncertainty 600 m 4 m

  22. 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 ..

  23. AUTO-TERCOM How to maintain Navigation accuracy over an area survey “TERCOM fixes” at each track intersection • Navigation error reduces from Proportional to distance travelled (800 km) • To Proportional to Radial distance travelled from fix. (e.g. 5 km)

  24. 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 ..

  25. F() Buoyancy  Lift Speed  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 - Elevation (m) 2500 m - 4000 m - 4556 m - 0 1 2 3 4 5 6 7 8 Elapsed time (Hrs)

  26. dz dt Buoyancy 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. Buoyancy Measurement –A better method • In practice – (near) “free ascent” method worked better…. • 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 ..

  27. 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.

  28. 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

  29. 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) ….

  30. Geometry of the two boxes run (ship position at 0,0) Range circles @ : 450, 600, 800, 1200, 2000 m Analysis of results • 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 )

  31. 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.

  32. Discovery Trials September 2007 20th September to 4th October (14 days). Falmouth to Falmouth Operating Areas 1 50⁰ N 49⁰ N 8 48⁰ N 5 3,4 6,7 47⁰ N 2 10⁰ W 9⁰ W 8⁰ W 7⁰ W

  33. Practical results Our real time USBL tracking was not quite so neat …(uncorrected at present for fish attitude and ships position) but adequate for the purpose .. Screen photo of Linkquest tracking output

  34. 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. Range Vs Speed

  35. Discovery Trials September 200720th 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.

  36. Navigation, Tracking and Telemetry DVL , INS and GPS We are developing algorithms, which, for area surveys, will maintain GPS level of accuracy over several days. Linkquest Tracklink10000 USBL/ coms Used for tracking, monitoring, AUV navigation and control. Working on a scheme to overcome the “initialisation problem” using this system.

  37. 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

  38. Charging in situ in 5 hours from fully exhausted 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.

  39. AUTOSUB6000 : Trials in September 2007 The Very Long Range AUV: 2012 AUTOSUB6000 and the Very Long Range AUV Steve McPhail. Underwater Systems Laboratory, NMFD Steve McPhail 6/2/2007

  40. Very Long Range AUV • 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. 500 kg Long Range AUV 1 W sensor power • Key to long range is slow speed and limiting the sensor and control power. Autosub3

  41. 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

  42. Very Long Range AUV - User Requirements ? Size? Speed ? Sensors ? Sensor Power ? Range ? Depth ? Endurance ? Navigation Accuracy ? Unit Cost ? Battery Cost ? Many or few ? Communications ?

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