Main results of Sea-Level CCI phase-1cci.esa.int/sites/default/files/content/docs/CollocationCCI_Main... · 1 CLS, 2LEGOS, 3 NERSC, 4University of Hamburg, 5 LOGICA,6 DTU, 7 NOCS,8IsardSat,

CCI Collocation meeting | 4-6 Feb 2014, ESRIN, Frascati, Italy

ESA’s Sea Level Climate Change Initiative

M Ablain1 , G. Larnicol1, A. Cazenave2, Y Faugère1, J. Johannessen3, D. Stammer4, G. Timms5, P. Knudsen6, P. Cipolini7, M. Roca8, S. Rudenko9, J.

Fernandes10, M. Balmaseda11, T. Guinle12, J. Benveniste13

1 CLS, 2LEGOS, 3 NERSC, 4University of Hamburg, 5 LOGICA,6 DTU, 7 NOCS,8IsardSat,

9GFZ, 10 University of Porto, 11 ECMWF, 12 CNES, 13ESA

Main results of Sea-Level CCI phase-1


•  Objectives of this presentation is to answer the two following questions :

1.  Which improvements have been done during phase 1 ?

2.  Why do we have to continue on phase 2 ?

1) Development and selection of new algorithms

2) Sea Level ECV products and assessment

3) Definition of user requirements and description of error budget

Outlines



•  The Altimetric system is complex : it integrates other sub-systems as complex as the altimetric system itself.

Altimetry System : Altimeter, radiometer

Precise Orbit Determination

Geodetic fields and processes (Geoïd, MSS ,

GIA, ..) Oceanic processes

(Tides, Sea state, …)

Atmospheric fields (pressure, wind, wet

troposphere)



Precise Orbit Determination

•  The consequences are : ⇒ The Sea-level calculation is composed of many components : ⇒  Several standards exist for each component

∑=

−−=N

iiCorrectionRangeOrbitSSH

0

The evaluation of sea-level calculation performances needs to evaluate a lot of algorithms/corrections

Altimetry System : Altimeter, radiometer

Oceanic processes (Tides, Sea state, …)

Atmospheric fields (pressure, wind, wet

troposphere)

Geodetic fields and processes (Geoïd, MSS ,

GIA, ..)

•  The Altimetric system is complex : it itegrates other sub-systems as complex as the altimetric system itself.


•  News algorithms and altimeter corrections have been developed and tested: -  they come from Sea Level CCI partners but also from external projects or studies

SL-CCI new algo/corrections: - New Orbit solutions (GFZ) -New instrumental corrections (CLS/isardSAT) -New wet Tropo corrections (University of Porto) -New atmosphercical correction with ERA-interim (CLS) - New ionospheric corrections (CLS) -New algorithms to merge altimeter mission together (CLS)

External projects and studies: - Jason-2 reprocessing (SALP project / CNES) - Envisat reprocessing (FPAC/ESA/CNES) : -  New orbit solutions (POD group) -  New tidal models (R.Ray, CNES/LEGOS/CLS) -  Mean Sea Surface (DTU, CNES/CLS) - ERS-1/ERS-2 reprocessing (REAPER project / ESA)

Validated within the

SL-CCI project


42 RRDP reports were produced


•  lt consists in comparing the new algorithms with the reference ones : - using a common set of validation diagnoses for all the algorithms

- using validation diagnoses dedicated for climate scales

- using the same altimeter data base

- producing validation reports separating the spatial and temporal climate scales


A formal validation protocol was developed within the SLCCI project in order to validate and estimate the performances of new altimeter standards at climate scales.


Impact of new SL-CCI correction in SSH calculation in comparison with the reference one (AVISO standards,…)

Climate

Applications Temporal Scales For 1 mission (Envisat, ERS,

Jason, T/P,…)

Global Mean Sea Level

Long-term evolution (trend)

Inter annual signals (> 1 year)

Annual and semi-annual Signals

Regional Mean Sea Level



Mesoscale Signals < 2 months



Impact of new SL-CCI in SSH calculation in comparison with AVISO standards

Climate

Applications Temporal Scales For 1 mission (Envisat, ERS,

Jason, T/P,…)


Long-term evolution (trend) NO IMPACT

Inter annual signals (> 1 year) LOW IMPACT

Annual and semi-annual Signals STRONG IMPACT





Definition of the indicator value

Significant impact Low impact No impact detected

Trend >0.15 mm/yr Trend> 0.05 mm/yr Trend< 0.05 mm/yr

Amplitude> 0.5 mm Amplitude> 0.2 mm Amplitude< 0.2 mm

Amplitude> 1 mm Amplitude> 0.2 mm Amplitude< 0.2 mm

Trend > 0.5 mm/yr Trend> 0.1 mm/yr Trend< 0.1 mm/yr

Amplitude> 5 mm Amplitude> 0.5 mm Amplitude< 0.5 mm

Crossovers Variance differences > 1 cm²

Crossovers Variance differences > 0.2

cm²

Crossovers Variance differences < 0.2

cm²

+ -



ERS-1 ERS-2 EN T/P J1 J2 GFO

Orbit Reaper Reaper GDRD GDRD GDRD Major Instrumental correction

PTR

Sea State Bias 2007

Ionosphere Reaper Rep.

Wet troposphere

GPS-based

GPS-based

GPS-based

GPS-based

GPS-based

GPS-based

Dry troposphere Era Interim based

Combined atmospheric correction

Era Interim based

Ocean tide GOT 4.8 Solid Earth tide

Pole tide MSS DTU10 Merging algorithms New regional biases and monthly OI

Selection meeting outputs

Discussions & recommendations available on the SL CCI web site

New algo/corr applied in SL CCI

No change with respect to reference (AVISO products)



ERS-1 ERS-2 EN T/P J1 J2 GFO

Orbit Reaper Reaper GDRD GDRD GDRD Major Instrumental correction

PTR

Sea State Bias 2007

Ionosphere Reaper Rep.

Wet troposphere

GPS-based

GPS-based

GPS-based

GPS-based

GPS-based

GPS-based

Dry troposphere Era Interim based

Combined atmospheric correction

Era Interim based

Ocean tide GOT 4.8 Solid Earth tide

Pole tide MSS DTU10 Merging algorithms New regional biases and monthly OI

Selection meeting outputs

Discussions & recommendations available on the SL CCI web site

New algo/corr applied in SL CCI

No change with respect to reference (AVISO products)



Atmospheric corrections derived from ECMWF reanalysis (ERA-Interim): ⇒ very strong improvement on early altimetry years (1993-2000) : T/P, ERS1-ERS-2

Climate

Applications

Temporal Scales

For TOPEX, ER1 and ERS-2

Global Mean Sea

Level


Inter annual signals (> 1

year) Annual and semi-annual

Signals

Regional Mean Sea

Level


Annual and semi-annual

Signals


+

+

Evolution of the SSH error reduction thanks to the new DAC corrections



Climate

Applications

Temporal Scales

For TOPEX, ER1 and ERS-2

Global Mean Sea

Level


Inter annual signals (> 1

year) Annual and semi-annual

Signals

Regional Mean Sea

Level


Annual and semi-annual

Signals


+

+

Impact of the new DAC correction on the regional MSL trends between 1993 and 2005

Atmospheric corrections derived from ECMWF reanalysis (ERA-Interim): : ⇒ very strong improvement on early altimetry years (1993-2000) : T/P, ER1-ERS-2



Input data acquisi-on

Pre Processing Orbit, Instrum & Geophysical corr,

including CCI correc.ons

Mul-mission calibra-on Orbit / Long Wave Lenght Error

including the new CCI methodology

Mapping including including the new CCI methodology

Level 2 product

Indicators computa-on

•  7 missions (re)processed: (T/P, Jason1/2, ERS-1/2, ENVISAT & GFO) •  Period: [1993-2010]

•  50 years of data (re)processed

•  Based on SSALTO/DUACS infrastucture




¼° Gridded Monthly mean

Global MSL evolution SLCCI ECV release : V1.1 available via: http://www.esa-sealevel-cci.org/

Please contact us: [email protected]



SLCCI ECV release : V1.1 available via: http://www.esa-sealevel-cci.org/

Please contact us: [email protected]

¼° Gridded Monthly mean



•  External users have also uploaded the SL-CCI products :

⇒  NASA Earth Observatory (USA), U. Colorado (USA), University of Edinburgh (UK), Mercator Océan (France), IMEDEA (Spain), …

•  Products are used by the climate modelling group:

⇒  UoH (D.Stammer) : assimilation of sea-level ECV in model (along-track product) ⇒  ECMWF (M. Balmaseda) : assimilation of sea-level ECV in model (along-track product) and also the Global MSL indicator ⇒  NERSC (J. Johannessen) : comparison of sea-level ECV (grids) with model outputs ⇒  LEGOS (A. Cazenave) : use of sea-level ECV (grids + indicator) for closure budget studies

•  In phase 2, the objective is to increase the user number


•  The regional Mean Sea Level trends have been significantly improved : ⇒  differences in the range +/- 2 mm/yr at local scales ⇒  these differences are significant since regional Mean Sea Level trends are ranging between +/- 10 mm/yr from 1993 onwards

Improvements of SLCCI project on regional MSL trends

Regional MSL trends from SLCCI project

1993-2010



•  Interesting results of SL-CCI ECV products via sea level budget studies (LEGOS) at inter-annual scales :

⇒  Differences between other international groups have been analyzed ⇒ Better coherence between the SLCCI GMSL and the mass + steric components



•  ECV assessment by climate users:

- Validation of SL-CCI ECV products with models => performed by D. Stammer (University of Hamburg), M. Balmaseda (ECMWF), J. Johannessen (NERSC)

ECV CCI V1.0 – Ref (AVISO) Orca 1 Model - Ref (AVISO)

By M. Balmaseda (ECMWF)

-5 mm/yr + 5 mm/yr -10 mm/yr + 10 mm/yr



Spatial Scales Temporal Scales User Requirements


(10-day averaging)

Long-term evolution (> 10 years )

0.3 mm/yr

Inter annual signals (< 5 years)

0.5 mm over 1 year

Periodic signals (Annual, 60-days,…)


(2x2 deg boxes and 10-day averaging)


1 mm/yr

Inter annual signals (> 1 year) Periodic signals (Annual, 60-days,…)

•  Users requirements have defined separating spatial and temporal scales



Spatial Scales Temporal Scales User Requirements


(10-day averaging)


0.3 mm/yr


0.5 mm over 1 year


Not defined




1 mm/yr


Not Defined


Not Defined

•  Users requirements have defined separating spatial and temporal scales



Spatial Scales Temporal Scales User Requirements Altimetry errors


(10-day averaging)


0.3 mm/yr < 0.5 mm/yr


0.5 mm over 1 year < 2 mm

over 1 year


Not defined Annual < 1 mm 60-day < 5 mm




1 mm/yr < 3 mm/yr


Not Defined


Not Defined Annual < 1mm 60-day < 5 mm

•  Error characterisation of altimetry measurements at climate scales (Ablain et al, 2012)



Spatial Scales Temporal Scales User Requirements Altimetry errors


(10-day averaging)


0.3 mm/yr < 0.5 mm/yr


0.5 mm over 1 year < 2 mm

over 1 year


Not defined Annual < 1 mm 60-day < 5 mm




1 mm/yr < 3 mm/yr


Not Defined Not evaluated


Not Defined Annual < 1mm 60-day < 5 mm

•  Error characterisation of altimetry measurements at climate scales (Ablain et al, 2012)



4) Conclusions

•  Although ECV sea-level is a mature variable, a lot of improvements were made : ⇒  Improvement of user requirements for Sea Level at climate scales

⇒  homogenization of altimetry databases for all the altimeter missions

⇒  reduction of altimetry errors at climate scales

⇒  development of a formal validation protocol to select the best altimeter corrections ⇒  better characterisation of altimetry errors at climate scales

⇒  assessment of Sea-Level ECV products by climate users

⇒  publication of several peer-review papers

1. Which improvements have been done during phase 1?


4) Conclusions

•  Although a lot of improvements were made, the user requirements are not reached

⇒  Many external corrections still must be evaluated (altimetry system is complex)

⇒  Continue to improve the algorithms/corrections within the CCI project : e.g. : Arctic area and coastal areas could be improved.

⇒  Refine the user requirements at climate scales

⇒  Continue to better describe the altimetry errors

⇒  Increase the length of time series and provide ECV products more regularly (to reduce the gap with the present date)

⇒  Integrate new altimeter missions (Cryosat-2, Sentinel-3, SARAL/Altika, Jason-3)

⇒  Improve the link with users

2. Why do we have to continue on phase 2 ?

Documents

Main results of Sea-Level CCI phase-1cci.esa.int/sites/default/files/content/docs/CollocationCCI_Main... · 1 CLS, 2LEGOS, 3 NERSC, 4University of Hamburg, 5 LOGICA,6 DTU, 7 NOCS,8IsardSat,