Current status of the remote sensing ocean observing system

Transcription

1 Current status of the remote sensing ocean observing system Pierre-Yves Le Traon Ifremer & Mercator ocean with contributions from G. Dibarboure, Y. Faugere, M.H. Rio, B. Chapron, J. Johannessen, L. Santolieri, F. Gohin, D. Antoine, N. Reul, J. Font, G. Lagerloef, C. Donlon, P. Le Borgne, M. Martin The role of satellites for operational oceanography and main requirements Where are we now? Progress over the last 5 years Altimetry, SST and Ocean Colour Other techniques (Sea Surface Salinity, Sea Ice, Scatterometry, SAR) Conclusions/prospects

2 Satellites and operational oceanography Unique contribution of satellites Provide key parameters (sea level and ocean currents, SST, ocean colour, sea ice, waves) needed to constrain global/regional/coastal ocean models through data assimilation and/or to validate them Data are also directly used for some applications (e.g. marine safety, pollution monitoring, water quality) Global, real time and high space and time (repeat) resolution, Need to be complemented by in-situ observing system (an integrated observing system)

3 Satellite observing systems and operational oceanography: main (today) requirements Core operational satellite observations required for global, regional and coastal ocean monitoring and forecasting systems Sea level, SST, Ocean Colour, waves, sea ice and winds = backbone prognostic quantities in operational oceanography. Data needed to constrain and validate ocean models. Data also needed for applications. SSS needed on the longer run Continuity International cooperation (virtual CEOS constellation) Specific requirements : AATSR-class SST needed as part of combined satellite/in situ SST measurement system to give highest absolute accuracy. A microwave SST satellite is required. 3-4 altimeters minimum required: only plausible way to initialise ocean mesoscale. Need long term series of Jason satellites (climate reference) Ocean colour increasingly important : global and coastal (at least 2 satellites) Surface winds (2 scatterometers) SAR for waves, sea-ice characteristics and oil slick monitoring (2 satellites)

4 Satellite altimetry and the altimeter constellation : the today vision One of the most important satellite techniques for operational oceanography. 3 to 4 altimeters (virtual constellation) needed with one very precise long time reference (Jason series). Much better understanding of the value of multiple altimeters and importance of mesoscale variability. Better understanding of errors through extensive validation and intercalibration exercices. Stronger requirements from real time applications (e.g. surface currents). Kinetic Energy from a SSALTO/DUACS altimeter map Operational oceanography now uses high resolution models with data assimilation: 1/12 (global), 1/36 (regional), < 1 km (coastal) (e.g. MyOcean). This poses (much) stronger requirements for an altimeter constellation. Degradation of results when an altimeter fails. Mercator global 1/12 model with multiple altimeter data assimilation

5 From Dibarboure

6 SSALTO/DUACS Homogeneous, inter-calibrated and directly usable high quality altimeter data from all altimeter missions Along-track & gridded products in near real time and delayed mode. Global and Regional (e.g. Arctic, marginal seas) products. New and improved products (e.g. MSLAs, MDTs). Products tailored for data assimilation. Daily products, timeliness improved ESA CCI / Climate products 60 years of data - 9 satellites Short time scale to include new missions (e.g. Alti-Ka). (AVISO WWW site)

7 Contribution of each satellite in the DUACS High resolution mapping (DFS) in 2013 Faugère et al., 2013 Jason-2 Jason-1G Cryosat-2 Altika 01/13 03/13 05/13 07/13 Constellation requirements: 3 satellites minimum in real time for mesoscale Alti-Ka ingested operationally in Duacs early July 4 month after launch => good timing (a few days after J1 loss), thanks to CNES/SALP experts efficiency in the Cal/Val phase. HY2 would become critical if one of the three altimeter mission fails. Sentinel-3 is needed.

8 SSALTO/DUACS Absolute Dynamic Topography vs SST and Ocean Colour with (upper fig) and without Altika (lower fig) on 26/07/2013 ( C) (cm) (mg/m3) ( C) (cm) (mg/m3) Faugère et al

9 Geoid and Mean Dynamic Topography (MDT) SLA + MDT = ADT With GRACE and GOCE, one can now compute precise MDT that gives access to abolute dynamic topography (ADT). MDT = MSS Geoid. A major impact for operational oceanography. 100 km resolution from GOCE (Rio et al., 2013). Mean velocity in the Kuroshio from 2 years of GOCE data NEW : MDT from latest GOCE data and drifters (MDT CNES-CLS13) (Rio et al., 2013)

10 Altimetry for operational oceanography Summary & Issues Altimetry is vital for ocean analysis and forecasting and GOV. Multiple mission high resolution products are readily available (e.g. SSALTO/DUACS). Many improvements (timeliness, regional products, climate). New MDTs from GRACE and GOCE. A major impact for GOV / to be tested. Very strong complementarity with Argo. Altimeter constellation remains fragile (far from being optimal over the past couple of years). Need to ingest new missions as early as possible (e.g. Alti-Ka). Stronger requirements for high resolution. Need to progressively infuse new technology (e.g. SAR/altimetry, SWOT).

11 Sea Surface Temperature The importance of sea surface temperature (SST) as a variable for assimilation into ocean dynamical models: A key property influencing air-sea interaction processes. Provide a means to correct for errors in forcing fields (heat fluxes, winds). Characterises the mesoscale variability of the upper ocean (eddies, frontal structures) at very high resolution (a few km). Assimilation and validation. SST data are also often directly used for operational oceanography applications. SST data (as ocean colour) can also be used to derive high resolution velocity fields.

12 Mission of the Group for High Resolution Sea Surface Temperature: to provide operational users and a massive science community with the SST measured by the satellite constellation GHRSST provides a framework for SST data sharing, best practices for data processing and a forum for scientific dialog, bringing SST to the user. Group for High Resolution Sea Surface Temperature

13 L2P Common format with uncertainty N-17/18 AVHRR GAC (9km) AMSRE (25/12km) GOES-E/W (5km) N-17/18 AVHRR LAC (1km) MSG (5/10km) AATSR (1km)

14 OSTIA Global SST analysis The loss of AATSR as reference sensor AATSR data was used in addition to in-situ data in the reference dataset. The loss of AATSR in April 2012 degraded the accuracy w.r.t ARGO obs of the OSTIA analysis, both globally and across all regions. This degradation was due to the loss of the AATSR data in the bias correction rather than its impact via direct assimilation. Able to mitigate the loss of AATSR by using an accurate subset of MetOP AVHRR data based on satellite zenith angle in reference dataset. Interim solution until SLSTR data is available. Still problems with MetOP AVHRR at high Northern latitudes. Argo-minus-OSTIA stats for March 2012 Impact of reference data set for bias correction In-situ only subset METOP AATSR Global North Atlantic Tropical Atlantic South Atlantic North Pacific Tropical Pacific South Pacific Indian Ocean Southern Ocean From J. Roberts-Jones and M. Martin

15 SST for operational oceanography Summary & Issues Satellite high resolution SST observations are essential observations for GOV. Thanks to GHRSST, major improvements in data processing issues and use of different types of sensors have occurred. The GHRSST community continues to thrive and the Regional/Global Task sharing Framework is stable. Much work on the SST ECV through the ESA CCI. Considerable developments in the L4 activities. L2 and L3 data used operationally in many applications including GOV models. Major Challenges with the gap in dual-view infrared radiometry since the loss of AATSR on ENVISAT. The status of passive microwave SST is fragile (successor to GCOM-W not approved yet). Improved data assimilation schemes are still needed to make a better use of high resolution SST observation (e.g. diurnal cycle, mixed layer dynamics, mesoscale). High resolution SST data also provide unvaluable information on mesoscale and submesocale phenomena. There is still a lot to do to fully use the high resolution information content of SST observations in ocean models.

16 Ocean Colour Global monitoring of chlorophyll (phytoplankton biomass) Global distribution of chlorophyll Estimates of primary production Detection of plankton blooms Biogeochemical, carbon and ecosystem model validation. Potential for assimilation Measure optical diffuse attenuation coefficient Contribution to climate monitoring Role in CO2 air-sea gas exchange monitoring As a tracer of dynamical processes (mesoscale) Regional (shelf seas) monitoring of water quality Measurement of suspended sediment Measurement of dissolved organic material Used in conjunction with regional / coastal ecosystem models Detection of harmful algal blooms. Monitoring eutrophisation.

17 Use of OC data in the MyOcean Modelling Forecasting Centers MyOcean MFC RT MFC Biochemical products (Analysis and/or Forecasts) Assimilation in BGC models Validation of BGC forecasts Multi-years MFS BGC products (10-12 Hindcast or Reanalysis) Assimilation in BGC models Validation of BGC forecasts V0 V2 V3 V0 V2 V3 V0 V2/V3 V4 V0 V3 V4 GLOBAL O O O X X ARTIC O O O X X X X X BALTIC O O O O X X NWS O O O O O X O X X X IBI X Med O X X O X X O X X X O X BS X X X X X X no use of OC data in assimilation and/or validation systems with OC data assimilation and/ or use of OC in the validation system V0: April 2009; V2: April 2012 V3: April 2013; V4: April 2014 Increasing use of OC data in MFC modelling assimilation and validation. High quality of OC data is cruicial. From L. Santolieri

18 Ocean colour for operational oceanography Summary & Issues Ocean colour is now more and more used for operational applications (e.g. water quality, eutrophisation, HAB). Essential observations for GOV. Reduced number of OC missions has been a major issue (e.g. from April 2012 to May 2013 only MODIS data were ingested in the MyOcean OC TAC). Progress in data access, data processing and data assembly systems (role of IOCCG akin to GHRSST). Assessment of the uncertainties associated with ocean colour products and improvement of OC data accuracy are required by users communities. Higher resolution and specialized OC products are required to monitor the coastal environment and to contribute to coastal management. Need to enlarge the bio-geochemical variables available from in situ observing system (for Cal/Val and to complement OC data in data assimilation systems) (e.g. Bio-Argo). The potential of OC data to calibrate or improve biogeochemical models is considerable but development lags behind other remote sensing techniques. A challenging and high priority research topic for operational oceanography.

19 New : Sea Surface Salinity from Space Two complementary missions L-band radiometer (f = 1.4 Ghz) SMOS launched in 2009 Synthetic Aperture Radiometer => resolution 40km, precision 1 psu. SSS accuracy: psu over 200km x 200 km and days Aquarius launched in 2010 L-band radiometer and scatterometer Aquarius SMOS Complementarity with Argo Issues : accuracy, error characterisation Assimilation tests : starting but challenging Planning for future missions SSS annual mean (Sept 2011 Aug 2012)

20 SMOS : cross-frontal exchanges of salt in the Gulf-stream area Reul et al., 2013

21 Community Uptake Challenge We have a growing archive of 10-day SSS data sets from SMOS and Aquarius: UNIQUE! The ocean community needs to fully invest in the critical assessment and application of the data A major challenge is to develop the SSS applications community to take full benefit of SMOS and Aquarius SSS data to demonstrate its utility. We cannot hope for future missions if we cannot (after 4 years) demonstrate that SSS (an essential climate variable) is being used widely. A challenge for GOV.

22 Ice measurements from satellites Ice drift Sea-ice concentration (microwave) Sea-ice type (microwave, scatterometer, SAR) Sea-ice drift (microwave, scatteromer, SAR) Sea Ice thickness (altimeter) (Cryosat, Icesat) Operational ice monitoring from SAR Ice concentration

23 Wind stress and scatterometry Scatterometry Eddy-scale provided by scatterometers is not retained in NWP analyses Direct observations of wind stress also better represent ocean/wave/atmosphere coupling (stability, role of currents and waves on wind stress). Need to develop the use of scatt products for ocean analysis and forecasting. (from Stoffelen)

24 Surface roughness from SAR Wave field Oil spill Wind field Current front Internal waves and ship ASAR MDT+SLA HYCOM w/assim and Sea ice New : Ocean surface currents from SAR (Doppler shift) From Johannessen

25 Conclusions/perspectives Status of satellite observing system (virtual constellations) for our key core variables was not optimal (high risk, degraded performance). Ensuring a long term optimized high resolution satellite observing system remains a challenge. Evolution and science infusion (e.g. SAR/altimetry, OC/Geo, SWOT, SSS). The critical role of international cooperation (GOOS, CEOS, GEO) and well organized and very active scientific community (e.g. OST-ST, GHRSST, IOCCG). In-situ data mandatory to complement satellite observations. The potential of satellite observations is not and will not be fully realized without an adequate and sustained in-situ observing system. Improvements of models and data assimilation techniques and development of applications/services (a GOV legacy) have resulted in a much better use of our satellite observing capabilities. Advances in data assimilation needed to better take into account observations. Use of new theoretical frameworks to better exploit high resolution information. Need to develop further OSE/OSSE activities (GOV Task Team). Essential to define needs, quantify impacts and to improve data assimilation systems.