New technologies: Developments during WOCE and what the future might hold

1. New technologies: Developments during WOCE and what the future might hold WOCE Final Conference San Antonio, 18 Nov 2002 Uwe Send IfM Kiel

2. In 1983 the community set out to tackle a challenging task: “To provide a snapshot of the global T/S and absolute flow structure of the global ocean and to determine the components of variability” The purpose was to collect data for testing models useful for climate prediction and for providing a baseline for future observations. This needs global coverage since no ocean region is expected to have zero long-term influence in system or models. • This global vision and approach • was a drastic departure from focus on regional scale at the time • had only become realistic (and probably inspired) by recent advances in technology at the time, notably in satellite altimetry and model/computer development. • was destined to change our view of the ocean and our way of doing ocean research

3. At the beginning of WOCE a wide range of techniques already was available. The WOCE design WG´s were faced with the challenge to determine the right mix and scale of observing methods. • Needed to • pay attention to their abilities and limitations • exploit complementarities • study the feasibility of the task • recommend/foresee improvements to existing techniques • take into account developing technologies Many existing techniques were ultimately used in WOCE. All of them experienced large improvements or further developments:

4. Hydrography, higher accuracy, global standards transient tracers better techniques, smaller sample volumes current meter moorings more reliable, addition of ADCPs Molinari et al ´98

5. XBT´s from VOS routine operations, expanded networks surface met moorings flux reference measurements possible Surface drifters cheaper, smaller, longer life NTAS buoy (A.Plueddeman) (P.Niiler)

6. Shipboard ADCP leap forward due to improved navigation Subsurface Rafos floats commercialized, large-scale applications (Bower et al 2002) Satellite scatterometry winds now available globally

7. The only technique expected to provide true global coverage and reveal time variability of a range of ocean phenomena was altimetry. • Rationale: • cm-accuracy sea-surface height • geostrophic surface flow relative to geoid • heat storage from large-scale steric effect • variability from 20-10000km, 20days-10years After the success of SEASAT, the new planned altimetry missions were adusted to best complement the in-situ experiment. Topex/Poseidon (T/P) was essentially designed for WOCE. • Challenges and limitations: • geoid insufficient at <3000km • aliasing of tides at 62, 173,... days • aliasing of high-frequ. wind-forced variability • extrapolation to ocean interior • no coverage in polar (and ice-covered) regions • land motion of tide gauges for SL rise

8. Altimetry in WOCE was hugely successful in terms of results and insights. It changed our view of the ocean, and stimulated/enabled many new activities. Demonstrated the extremely active time-dependence of the circulation (barotropic, baroclinic current systems, eddy motions, etc) (C. Wunsch) Quantified SSH and slope variance on all space/time scales globally (D.Stammer)

9. Eddy contribution to meridional heat flux: • Other results/achievements: • open-ocean tides measured globally to 2-3cm • surface heat-flux estimates on basin-scales from storage • observation of interannual variability (ENSO, circumpolar wave, etc) • kinetic energy of geostrophic currents in agreement with moorings • eddy energy helped to demonstrate that models need 0.1° resolution • agreement of T/P currents and ADCP data to 3-5cm/s • global test of Rossby wave speeds • global SL rise (calibrated with tide gauges) accurate to 0.5mm/yr • transports of baroclinic current systems (variability) • drove advances in earth´s gravity field • drove most of the work in assimilation • many more..... (D. Stammer)

10. New development for WOCE : autonomous deep floats WOCE need: global field of the true (absolute) interior flow field The only method available was acoustically tracked floats (RAFOS), which require a network of sound source moorings. New approach: cycling autonomous floats located by satellites (ALACE) (R.Davis)

11. Deep floats: The low cost of RAFOS and ALACE floats made it possible to directly measure the basin-scale deep flow during WOCE: • provide (Eulerian) mean deep flow field at all locations • quantify eddy variability • provide reference level velocity for geostrophic flow • visualize transport patterns The objective of mean flow required minimization of eddy noise deep level. Need: 5year record in each 500km2 box  5000 float years in ice-free ocean.

12. Deep floats: In many regions, a statistically reliable description of deep flow can now be constructed: (R.Davis) Additional capability for T/S profiling added 1000´s of CTD profiles from regions not visited by ships (and during severe conditions)

13. Interesting discrepancy: Floats mostly remain in N.Atlantic subpolar gyre, but tracers clearly show export in boundary current. Consequence of non-lagrangian property of ALACE-type floats ? Profiling floats are NOT lagrangian, they provide only pieces of average velocity; RAFOS floats more closely lagrangian. (Zenk/Koltermann)

14. Deep floats: • Issues: • restricted to ice-free regions during WOCE and at present • sampling biases (diffusion bias, Stokes drift) • difficult to separate time and space variability • unique lagrangian nature of (RAFOS) data not exploited yet • desire to minimize surface interval

15. Tracer release techniques An important element of WOCE was the “control volume” concept, a successful implementation took place in the Brazil Basin. Objective: a detailed study of the deep flow and mixing processes A new technique for directly observing interior mixing processes were deliberate tracer releases (SF6) (J. Ledwell)

16. Tracer release techniques: Very large diapycnal diffusivities observed in deep Brazil Basin near MAR topography - sufficient to close budgets and consistent with accompanying turbulence measurements: (Polzin et al ´97) (Ledwell et al ´00)

17. Technological issues WOCE did not manage to solve: • CTD and water samples: Very time-consuming and inefficient to lower CTD/rosette on wire from expensive research vessels. Some efforts to speed this up did not lead to break-throughs (new sampler, “fast fish”) • Stability of conductivity sensors: Often, water samples are only required to calibrate conductivity. • Observations in ice-covered regions • Mooring technology:Did not change much during WOCE. Endurance of hardware and sensors limited to 1-2 years. No telemetry capability from deep sensors. • Satellite surface flux measurements:All 4 heat flux components are difficult to measure, total flux cannot meet research (or operational) requirements at present.

18. Lessons and Achievements of WOCE observing techniques • First 3-D view of the global ocean structure • Demonstration that the long-term global observations required for climate studies are feasible • Requires ongoing technological developments and integration of a variety of techniques • The implementation needs the determination and commitment of the global community • An efficient infrastructure is required for data management and dissemination • Joining forces with the biogeochemical community has a high pay-off for both (e.g. JGOFS sampling from WOCE cruises) “Through WOCE, the observation of the global ocean came of age, and wenow have the tools and understanding to address & observe global issues.”

19. Developments for the near future Satellite gravity missions: GRACE and GOCE will deliver geoid with 1cm accuracy above 100km scale. Also mass field (bottom pressure) of ocean above these scales. Helps to distinguish SL changes due to steric and mass anomalies. Sea surface salinity from space: SMOS satellite mission scheduled for 2006. Wide-swath Ocean Altimeter: replace altimeter data along line with a200km wide swath  complete ground coverage every 5 days

20. Developments for the near future SEAGLIDER (C.Eriksen) • Autonomous gliders (battery power): • use buoyancy change like floats to glide at inclined paths of 20° • horiz. speed up to 25cm/s • can do sections or profiles in fixed location (“virtual moorings”) • operating ranges of up to 7000km • deployment from “shore” • multidisciplinary sensors feasible • Autonomous gliders (thermal power): • energy for pumping from ocean thermal contrast • projected range of up to 30,000km SPRAY (R.Davis) • Two-way & high-rate satellite communication: • enables control of gliders (and floats) • minimizes surface time & energy consumption • adaptive sampling • Acoustic UW telemetry: • low-power & high-rate allows long-term bottom deployments

21. (N. Hogg) Developments for the near future Ice-sensing floats: Detect ice and store data/navigate acoustically • Sensor stability: • Salinity from floats and for long-term moorings feasible now, better than 0.01psu. • Bottom pressure better than 1cm, telemetry “eliminates” drift. • Moorings: • profiling vehicles • 5-year development (Ultramoor) • telemetry underwater (acoustic/inductive) and above (satellite, capsules) • increasing # of interdisciplinary sensors

22. Developments for the near future Interdisciplinary sensors: For autonomous moored applications, sensors for many variables are available now CO2 sensor (M. DeGrandpre) 14C Primary Production Measurements(C. Taylor) Optical (Dickey) and O2 sensors (Wanninkhof) • New sound sources: • Prototype new design that can • serve both tomography and • Rafos signals • high power • high bandwidth • high efficiency • simple and affordable

23. Developments for the near future Data management systems and structures: WOCE has demonstrated the importance and feasibility of data assembly, quality control, data archiving and user-friendly dissemination structures. Argo is implementing this with modern techniques (S.Pouliquen)

24. Where should we go • Ultimate goal: • Develop techniques for implementing an ocean observing system that is • global • multidisciplinary • truly integrated • resolves all space and time-variability of interest (build in flexibility) • user-friendly • cost-effective • providing data publicly and in real-time • can evolve with technological advances and new demands danger to “freeze” functioning operational systems

25. Where should we go Minituarize sensors: • Biogeochemical sensors that are small, low-power, “dry” (optical, acoustic, chips) MEMS chip Optical O2 sensor • meteorological sensors that can be submerged • acoustic receivers/amplifiers/clocks for tomography and rafos signals Micro-humidity sensor (JPL)

26. Where should we go 3rd generation autonomous vehicles (symbiosis of glider, float, AUV) : • ability to travel long distances to mission area and back to shore base (propelled or glider mode) • choice of going into float mode, glider mode (sections) or mooring mode • long endurance (thermal or solar power) • option to receive sound signals for tracking (Rafos), e.g. under ice, and tomography • flexible choice of sensors • ability to collect ml water samples and bring home for analysis Autonomous surface craft should also receive more attention

27. Where should we go Multidisciplinary moorings for - high-frequency observations - strong current regimes - process studies - heavy/large sensors - reference sites - sound sources • long-life, advanced telemetry, expendable? • docking of gliders for calibration and to return samples • self-calibrating sensors • deployable from VOS ?

28. Integration: Expand the satellite network Complete and maintain the ARGO network; gradually enhance/replace with 3rd generation vehicles Implement the pilot timeseries network and sustain it; gradually add sound sources to provide distributed signals

29. Integration: • develop data merging, assimilation, forecasting techniques for the integrated system • recognize and exploit common users and needs of research and operational networks • ensure multi-use of sensors and platforms • implement data assembly, quality control, dissemination infrastructure • establish international coordination/management structure The WOCE vision led to a demonstration of global ocean observations. We now need the determination and commitment to take the steps beyond.