Inter-calibration of the SEVIRI VIS0.6 channel with MODIS Aqua, using Deep Convective Clouds as transfer targetsSébastien Wagner, Tim Hewison

1: EUMETSAT, Eumetsat-Allee 1, D-64295 Darmstadt, GermanyPlease send questions and comments to sebastien.wagner@eumetsat.intNOAA Satellite Conference, College Park, MD, USA, 8-12 April 2013

CONTEXT:

1.Past and current geostationary imagers: no on-board calibration for the Solar Reflective Bands.

Calibration exclusively based on vicarious approaches using various target types (e.g. deserts, clouds, oceans, Moon).

2.Constellation of geostationary satellites do not see the same targets (in particular deserts and oceans)

Data sets harmonization and comparability are challenging.

SCOPE:

Comparability : achievable through the use of a common reference instrument on-board a polar satellite

Which reference for Solar Reflective Bands? GSICS recommendation = MODIS/Aqua

Which targets? In order to reduce uncertainties inter-calibration over similar targets with well characterized radiative properties such as Deep Convective Clouds

Which method? Implementation of the algorithm developed by Doelling et al. (2011), applied to the VIS0.6 channel, available on the Spinning Enhanced Visible and Infrared Imager (SEVIRI) aboard the Meteosat-8, - 9 and -10 satellites with MODIS-Aqua.

GSICS UsersGOS

Level 1b/c Data(Radiances)

Corrections

Statement of Needs

SCOPE CMNWP centresDevelopers of Lev2/3 products...

RSB:Inter-calibration

with MODIS using DCCs RSB:

Inter-calibration with ROLO using

the Moon

Absolute calibration

MODIS Aqua (01/04/2010 – 13:00) SEVIRI Met-9 (01/04/2010 – 12:57)

Test

on

the

view

zen

ith

angl

e

Missing DCCS due to test on VZA

Met-9/SEVIRI 10.8m

Aqua/MODIS 11m

Example of DCCs tracking with MODIS and SEVIRI as implemented

MODIS Aqua DCC radiance – 0.6 m

SEVIRI Met-9 DCC counts – 0.6 m

Derived gain for Julys

2008

2009

2011

20102012

What was wrong???

Shift in the PDFs + double peaking for 07/2008

Shift in the PDFs

-2.8%1.7 %

1.2 %

-5.7 %

Preliminary results for a few cases... as shown in September 2012

• Standard uncertainty u / mean < 0.2% with Sampling problem but not only...

• MODIS PDF derived dynamically (in parallel with SEVIRI PDF) wrong!

MODIS PDF to be derived for a time interval in early years of operations

• Implementation of the ADM correction• Angle calculation• Correction calculation

• Other reasons?

nsu /

NEW RESULTS AFTER LATEST DEVELOPMENTS... STILL NOT SATISFYING!

Before ADM correction After ADM correction

Shifted distributions!

MODIS radiances

COMPARISONS OF THE PDFS BEFORE AND AFTER ADM CORRECTIONS

GOS = Global observing SystemRSB = Reflective solar bands

GOS Level 1 b/c producers, in charge of the data absolute calibration

GSICSCorrections (inter-calibration, tie to common reference(s)). For Reflective Solar Bands, current activities include inter-calibration with MODIS using

Users Provide feedback on data usage, data quality and accuracy

PROVIDING CORRECTIONS TO ENSURE COMPARIBILITY AND HOMOGENEITY:

Govaerts, Y. M. and M. Clerici (2004). "Evaluation of radiative transfer simulations over bright desert calibration sites." IEEE TGRS 42(1): 176-187.

Govaerts, Y. M., M. Clerici, Clerbaux N. (2004). "Operational Calibration of the Meteosat Radiometer VIS Band." IEEE TGRS 42(9): 1900-1914.

Govaerts, Y. M., and Clerici, M. (2004). “MSG-1/SEVIRI Solar Channels Calibration Commissioning Activity Report” (EUMETSAT).

Doelling D. et al. (2011), “ATBD for Deep Convective Cloud technique of calibrating GEO sensors with Aqua-MODIS for GSICS”, https://gsics.nesdis.noaa.gov/pub/Development/AtbdCentral/GSICS_ATBD_DCC_NASA_2011_09.pdf.

• Satellite : MET-9 (0.0 Lat / 0.0 Lon)• Band : VIS 06

1. DCC identification• Time: for MET-9 (0.0 Lat / 0.0 Lon) 11:00 < t < 14:00• Geometry:

• Lat / Lon between 0.0 and +/- 20.0 degrees (with respect to the SSP)• SZA and VZA < 40 degrees

• DCC identification threshold using the MODIS 11m band and SEVIRI 10.8 m (BT<205K)

• Spatial homogeneity (over boxes of pixels in the “11 m” BT + in the “0.6 m” radiances)

2. Conversion from counts to overhead sun + spectral transformation to account for Spectral Response Function differences between MODIS and SEVIRI• Use of an Angular Distribution Model (Hu model, Hu et al. 2004)• Use of correction factors as given by the GSICS ATBD (Doelling et al, 2011)

3. Construction of the Probability Density Functions on a monthly basis4. Derivation of the gain from the calibration equation:

Main steps of the method as in Doelling et al, 2011

THE GOS BOX AT EUMETSAT FOR RSB: THE SEVIRI SOLAR CHANNEL CALIBRATION SYSTEM• Developed and implemented in 2002/2003 (Govaerts et al. 2004)• System in place for SEVIRI (Met-8, Met-9 and Met 10) BUT ALSO for MVIRI (Met-2 till

Met-7)• Vicarious calibration:

Reference = RTM simulations of Top-Of-Atmosphere radiancesEvaluated against well-calibrated polar-orbiting instruments (SeaWiFs, ATSR2, AATSR, VEGETATION, MERIS)Comparison with TOA measured signal

• 2 target types used for comparison:1. Desert bright targets (18 targets)2. Dark sea targets (9 targets) (checking purposes)

THE GSICS BOX : INTERCALIBRATION WITH MODIS/Aqua USING DEEP CONVECTIVE CLOUDS

USE OF DEEP CONVECTIVE CLOUDS AS CALIBRATION TARGETS

TWO-FOLD APPROACH:

1. Implementation of an inter-calibration algorithm based on the use of DCCs for VIS06

2. Development of a vicarious calibration algorithm to be added to the current SSCC system (absolute calibration + drift monitoring)

0.99/9

. KKGainSBAFAqua NadirEquivMetMetAquaMET

NadirEquivRadiance

• Implementation of the GSICS ATBD still on-going:• Requires further checks and debugging as some issues still to be solved (in particular

implementation of the Angular Distribution Model)• Uncertainty analysis still missing

• Limited to the MET-09/SEVIRI VIS06 band

• FUTURE WORK:Validation against D. Doelling results (by the end of June) Generation of a GSICS product (demonstration dataset) for MET-9 (end 2013 – early 2014) Generation of validation datasets for GSICS community Integration of the algorithm in the monitoring processing chain (MET-8, 9 and 10) Reprocessing of the past data:

MFGs (in particular MET-7) MSGs (MET-8 and 9)

• Once problems are solved Development of a vicarious calibration algorithm to be added to the current SSCC system (absolute calibration + drift monitoring)

CONCLUSIONS

Possible reasons for bad results and solutions...

MODIS reference radiance derived from a PDF covering 07/2002 – 02/2003

MET-9 PDF built independently

LATEST DEVELOPMENTS

• Still large variability in the gain time series• Potential seasonal cycle (even though

more gains should be derived over a longer period)

• Problem seems to be with the ADM correction (introduces a shift in the radiance and count distributions) Implementation of the ADM to be revisited