Still a strong Rayleigh signal after Rayleigh correction

Optical Toolbox
#1

Dear Marco,

I’ve found that the BRR reflectances I obtain from SNAP might have still a strong Rayleigh signal. I get this idea (which might not be accurate) by comparing with a home made processor I’ve been working on.

As a first “evidence”, let me show you the blueish foreground I get in the RGB composite from SNAP RC reflectances:

RCReflectanceSnapVsHomeMade01.png1855×1001 1.11 MB

As a second “evidence”, observe that in all pins (last figure) I get a strong blue signal difference which seems to match quite well a Rayleigh reflectance functional type (sort of lambda^-4). Might there be an issue here? Or it’s me that haven’t interpreted thr rBRR magnitude as I should have done?

RCReflectanceSnapVsHomeMade02.png1855×1001 358 KB

Any reply will be useful. Thanks a lot!!

Juancho Gossn

The result of Rayleigh Correction
#2

Can you tell us which product (file name of the product) you have used? Then we can replicate what you have done.

Do you use the latest version? you can check by going to Help -> Check for Updates

#3

Hi Marco,

Sorry for my late reply. This is the product I’ve used:

S3A_OL_1_EFR____20170814T131014_20170814T131314_20170814T151131_0179_021_095_3600_MAR_O_NR_002

Yes, I’m using the latest version. I’ve created the BRR product via Optical -> Preprocessing -> Rayleigh-Corrected (or similar) and used the BEAM output.

Thanks!
Juancho

#4

Hi Juancho

Thank you for detailed information.
I would like to know how to perform Rayleigh correction for OLCI in BEAM.

Regards,
Bi

#5

It’s not possible in BEAM. BEAM does not support OLCI.
SNAP is the successor of BEAM. As said on the entry web page of BEAM, it is not further developed.
So you should SNAP.

#6

Thank you!

#7

Hi marco and bishun,

Yes, I meant that I used the BEAM-DIMAP output for the Rayleigh corrected product, using SNAP. Find attached a picture to clarify what I mean.

So, any idea of what could be the problem with the Rayleigh signal remaining after the Rayleigh Correction?

#8

We have tested the Rayleigh Correction implemented in SNAP under the Optical/Preprocessing plugin.
The results, using the processing parameter “Compute bottom of Rayleigh reflectance bands”, were highly satisfactory - the selected S-3 OLCI L1 scenes were largely corrected and improved. See an example below for the region of Chile.

Rayleigh_beforeafter_Chile.jpg790×572 170 KB

This was performed using SNAP v.5 and was also succesfully reproduced with SNAP v6.0.

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#9

Hi David,

thanks for this investigation and feedback. Why was the processing with SNAP 6 not successful? To which Thread are you referring?

#11

Hi marco

I tried again with v.6 and a different scene, and it works.
I amended my previous post, all good.

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