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

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

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

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


Context

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


Context

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 !!


Context

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


Context

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


Context

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


Impact of the satellite configuration dt analysis

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


Degradation of the nrt products versus dt

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 drifters data

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

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 delivery1

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 delivery2

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

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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