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Quality indicators in an operational precipitation product

IPWG meeting 4Beijing, 13-17 October 2008

Presented by: Thomas HeinemannMeteorological Operations DivisionEUMETSAT

thomas.heinemann@eumetsat.int

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Overview

1. News from METOP/HRPT

2. The Multi Sensor precipitation Estimate (MPE), a real-time precipitation algorithm

3. Why shall we provide quality information4. The MPE quality indicators (QI)5. How useful are the MPE QIs

6. Outlook

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News from METOP-A HRPT

• METOP-A was launched on 19 October 2006 • LRPT direct data transmission was not activated• HRPT direct data transmission service failed soon after

activation• Root cause was heavy ion radiation causing the failure of a

component of the AHRPT Solid State Power Amplifier (SSPA)• To minimise the risk of failure to the HRPT-B unit a "partial"

HRPT service in those areas where the risk of damage from heavy ions is reduced, has been implemented. 

• For southbound passes over Europe and the North Atlantic, HRPT side B will be activated starting around 60°N.

• First activation was on 29 September 2008  (2 month trial)

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MPE: a real-time precipitation algorithm

• Combines passive microwave from polar orbiting satellites with IR data from geo-stationary satellites.

• Algorithm is based on the classical blending approach.

• Instantaneous rain rate data are produced every 15/30min in original Geo-satellite pixel resolution (MET-7 INDOEX, MET-8 RSS, MET-9 0°) in the operational environment of the MSG groundsegment.

• Processing is done in near-real time mode with a time delay of < 10 minutes between image acquisition and data dissemination.

• Data are provided on the internet and via EUMETCAST in GRIB-2 data format and in addition visualised on the EUMETSAT web-page.

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MPE: a real-time precipitation algorithm

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In large areas of the world methods based on ground measurements or polar orbiting satellite products cannot fulfil the NRT requirements and a dense radar network is not available ( Africa, Asia !!!)

NRT or RT precipitation data are essential for:

• Short term weather forecasts and nowcasting• Operational short term hydrological and acricultural applications

Photos: WFP

Who are the (designated) users of real-time precipitation algorithms ?

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Why (still) a blending algorithm ?

EUMETSAT ‘s and its users requirements for the rain-rate algorithm are:

1. To provide a real-time product in high temporal and spatial resolution.

2. To use a scientifically mature algorithm which has been proven to work operationally.

• Most other algorithm types cannot be used in real-time.• Other real-time algorithm’s are either very similar to the used one

or still in development phase.

But tests with other algorithms were done: Hydro-estimator implemented for South Africa, CMORPH version

tested, co-operation with H-SAF and NOAA …

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MPE and Hydro-Estimator in South Africa

MPE results (left) and Hydroestimator results (right) of the instantaneous rain rate (mm/hour) based on the 10:00 UTC MSG image of 6 November 2007.

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MPE validation by the European PEHRPP site

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MPE validation by the European PEHRPP site

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CMORPH

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Courtesy: Chris Kidd

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Why (quantitative) quality indicators?

• Users trust data only if they have a clear vision how accurate they are.

• Most algorithms perform in some conditions better than in others (especially combined algorithms).

• Algorithm developers have more a-priori information available and know their algorithm better than the users.

• Many algorithms depend on the results of previous data analysis (eg. cloud mask). The quality of the previous steps affects the quality of the final product.

• All this information should be provided to the users.• Different applications need different QI’s!

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Continuous re-adjustment of LUTs as source for MPE quality indicators

Blending principle:Co–located microwave rain-rates and IR brightness

temperature for a specific region and time-span are used to derive a monotonic relation between IR BT and rain rate.

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Definition of MPE QIs

QI1 := Correlation coefficient between MPE rain-rates for the co-located IR data and the microwave data rain-rates

QI2 := Standard deviation between MPE rain-rates for the co-located IR data and the microwave data rain-rates

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MPE Correlation QI

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MPE standard deviation QI

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Test strategy for QIs

Purpose : Test if MPE rain-rates in areas with high QI are really better.

Method: Compare MPE rain rates ffrom the real-time algorithm with microwave rain-rates.

Precondition: None of the microwave rain rates used for the comparison are included in the co-locations.

Limitation: Not a real validation of rain-rates but of the matching-algorithm.

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Correlation QI for 0.25° cell size

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Correlation QI for 5° cell size

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Histogram of QI1, January

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Histogram of QI1, July

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Summary

• EUMETSAT committed to continue the operational service for a disk-wide real-time rain-rate product

• The current algorithm should be updated to a mature, state-of-the-art algorithm which fulfils the requirements.

• The EUMETSAT Hydrology SAF is developing additional algorithms for various applications

• Effective and adapted Quality Indicators are essential for the optimal application of precipitation products, especially in models.

• The MPE QIs based on the co-location statistics are useful indicators to identify the areas where the MPE algorithm should not be used.