Quality of real time altimeter products
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Quality of real time altimeter products impact of the delay G.Larnicol, G. Dibarboure, C.Boone, CLS Space Oceanography Division Ananda Pascual, IMEDEA(CSIC-UIB), Spain Pierre-Yves Le Traon, IFREMER, Brest, France. Context. Overview of SSALTO/DUACS products. Global products Regional products:

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Quality of real time altimeter productsimpact of the delay G.Larnicol, G. Dibarboure, C.Boone, CLS Space Oceanography DivisionAnanda Pascual, IMEDEA(CSIC-UIB), SpainPierre-Yves Le Traon, IFREMER, Brest, France


Context

Overview of SSALTO/DUACS products

Global products

Regional products:

Mediterranean sea:

standard processing refined

for Med sea

European Shelves:

Products dedicated to

regional applications

provision of tide, inverse

barometer, HF signals

information

Sampling : Along-trackGridded fields

Content : sea level anomalyabsolute sea level (MDT+SLA)


Context

Research activities (science review)

Global products

Regional products:

Mediterranean sea:

standard processing refined

for Med sea

European Shelves:

Products dedicated to

regional applications

provision of tide, inverse

barometer, HF signals

information

(Ducet et al. 2000)

Sampling : Along-trackGridded fields

Content : sea level anomalyabsolute sea level


Context

Operational activities (Dombrosky review)

Global products

Regional products:

Mediterranean sea:

standard processing refined

for Med sea

European Shelves:

Products dedicated to

regional applications

provision of tide, inverse

barometer, HF signals

information

Sampling : Along-trackGridded fields

Content : sea level anomalyabsolute sea level


Assess the quality of NRT altimeter observing system

  • Main sources of errors in near real time:

  • Orbit error (POE  MOE)

  • minor error thanks to the long wave length

  • error correction procedure


Assess the quality of NRT altimeter observing system

  • Main sources of errors in near real time

  • Orbit error (POE  MOE)

  • minor error thanks to the long wave length

  • error correction procedure

  • Data availability

  • delay in the data delivery

  • number of missions available

June 21, 2006

Theory

real life !!


Délay IGDR

Dec 06

Jan 06

Anomalie IGDR

IGDR Nominal

Délai > 15j : désactivation automatique d’une mission

Livraison Météo (4 jours de retard sur toutes les missions)

Jason : SHM + Problème lecture mémoire

GFO : Problème batteries + WVR

ENVISAT : USO + SideB

Assess the quality of NRT altimeter observing system

  • Main sources of errors in near real time

  • Orbit error (POE  MOE)

  • minor error thanks to the long wave length

  • error correction procedure

  • Data availability

  • delay in the data delivery

  • number of missions available


Assess the quality of NRT altimeter observing system

  • Main sources of errors in near real time

  • Orbit error (POE  MOE)

  • minor error thanks to the long wave length

  • error correction procedure

  • Data availability

  • delay in the data delivery

  • number of missions available

  • Time window used for data selection in

  • the mapping since we need maps as recent

  • as possible in NRT


Assess the quality of NRT altimeter observing system

  • Main sources of errors in near real time

  • Orbit error (POE  MOE)

  • minor error thanks to the long wave length

  • error correction procedure

  • Data availability

  • delay in the data delivery

  • number of missions available

  • Time window used for data selection in

  • the mapping since we need maps as recent

  • as possible in NRT

  • Data and data processing

  • AVISO products

  • Period where 4 altimeters are available

  • Oct 2002- Oct 2003


0 5 10 (cm)

Impact of the satellite configuration (DT analysis)

Presented last year in Venice

Pascual et al. (GRL, 2006)

- 2 DT satellite configuration is a minimum

to provide a relatively good description of

Mesoscale activity

- 4 satellites configuration improved this

description and could be indispensable for

specific area (Med for instance)

0 10 20 (cm)

rms of sea level anomaly (SLA) estimated with 4 altimetric missions.

rms of SLA differences

between 4 and 2 satellites


0cm

10cm

Degradation of the NRT products (versus DT)

RMS of the differences between delayed and real time SLA Estimation done with 4 satellites configuration


Comparison with tide gauge data

Comparison with drifters data

Mean square differences between drifter and altimeter velocities (AVISO+ Ekman= SURCOUF)

Units are % of drifter variance.

Mean square differences between tide gauge and

altimeter sea level.

Units are % of tide gauge variance.

DAC = IB+MOG2D (Dynamic Atmos. Cor.)


Performance loss due to delay in the IGDR delivery

RMS of differences between “optimal” DT maps with degraded NRT maps (as a function of the number of days of delivery delay)

  • On going work : tested for Indian ocean and Gulf-stream region

  • Simulated NRT : DT with delay

  • The NRT maps are compared to “optimal” DT maps.

  • Results are the same for all areas and only the base variance is different.

  • Impact of the delay shows linear trend

2 missions1 unavailable

3 missions2 unavailable

3 missions1 unavailable

4 missionsBest NRT available


Performance loss due to delay in the IGDR delivery

  • Definition of a performance

    Indicator for NRT applications

  • The linear trend is used to define a NRT perfor-mance indicator. The RMS of the DT-NRT difference (additional NRT error) is normalized by the best and the poorest NRT results one could obtain in a nominal scenario.


Performance loss due to delay in the IGDR delivery

  • Performance of 3 satellites conf = 72%

  • Absence of GFO  loss of 25% performance

  • For a two satellite configuration, there is a 5% error increase per day of missing data

  • Only 4% for a three satellite configuration.

  • 10% error increase with delay of 2 satellite

Best NRT map (4 sat)

3 satellites

2 satellites

Poorest NRT map (1sat)


Conclusions

  • 2 DT satellites is the minimum to observe the mesoscale signal

  • 4 NRT satellites give same results than 2 DT satellites

     Need to have a at least 3 but preferably 4 satellites for operational applications

  • Data gaps and delivery delay cause a significant loss of accuracy on NRT maps. The IGDR delivery delay is critical for NRT applications, especially with fewer satellites

    Being able to process Real Time (<24h) altimeter products with an IGDR-like accuracy could improve the NRT accuracy by up to 25%  Ongoing work on DUACS

  • Continue the development of performance indicator.

    Refined the estimation by characterising the loss or the delay of Jason (reference mission)

  • Improvements not only come from additional missions and reduction of delay. It is also important to continue to improve the processing (geophysical corrections, dynamic atmospheric correction,etc…)


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