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What are the main differences between MEGS C2 and C2R(BEAM)?
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What are the main differences between MEGS C2 and C2R(BEAM)?
meris c2r algorithm megs
4/22/13 10:45 AM
Dear forum,

I am looking to untie the knot regarding the main differences between MEGS C2 and C2R(BEAM). This is a follow up of an ODESA posted question.

http://www.odesa-info.eu/forum/viewtopic.php?f=13&t=143&sid=a6eb63fc218f14d5dda9cfcb74db6776

The answer from ACRI team was:

"the case2 algorithm implemented in MEGS8 comes from a C2R code provided by Roland Doerffer and distributed as a binary code in ODESA. It is based on this ATBD https://earth.esa.int/instruments/meris/atbd/abtd_2.25_v1.0.pdf.

I see these possible differences with the BEAM implementation:
Pre-correction: smile and gaseous correction of the MEGS code (see DPM); I don't know what they are in BEAM
Some physical constants: e.g. the solar flux at theoretical wavelengths
The "angular correction": Roland did originally include some corrections for angular convention in the radiative transfer modelling; but it was not consolidated and not documented in the ATBD so we removed it for MEGS. I don't know if these corrections are activated in the BEAM version.
Some tuning in the BEAM version? The original code included some tuning of the TOA signal at 412nm, also removed."

Can you comment on the latter implementation in BEAM?
Are there any other differences not related to the implementation described above? specially when it comes to derive the water products?
With regards,

Jose
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RE: What are the main differences between MEGS C2 and C2R(BEAM)?
4/26/13 10:08 AM as a reply to Jose M. Beltran.
Hello Jose,

I don't know the differences between MEGS C2 and the C2R, because I don't know MEGS. I can just try explain what is done in the C2R.
I guess that the main difference is in the AC part before it comes to calculating the water products.

In the C2R a correction of the satellite zenith is done before is handed over to the neural net. And some adaptations of the RLws (dividing by PI if necessary and computing the log of them, etc.).

As from reading the post in the ODESA forum I think the most questions are already clarified.

best wishes
Marco
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