Why gelbstoff absorption coeff. at 443 nm

Optical Toolbox
#1

s3-(OLCI) cr2cc processor retrieves one of the IOPs(gelbstoff absorption coeff. at 443 nm, units /m). My question is that, why not gelbstoff absorption coeff. at 400/412 nm have been chosen as standard product of s3-olci instead of 443nm (since gelbstoff absorption is stronger towards blue/uv). Is there any technical /scientific reason for that?

Another question is that when I processed (using CR2CC) and generated rhown in coastal waters of India I observed that rhown is varying at only third and fourth decimal places (first and second decimal place remain constant in rhown) while going from coast to open ocean for say more than 100/150 pixels? Is it possible that coastal and open ocean water rhown value remain same & do not vary upto first or second decimal place. Please correct/guide me if I am processing wrong somewhere.

#2

The band at 443 nm was chosen only for normalisation. for all IOPs, which are computed using the neural network. Chlorophyll has here its maximum absorption. If you need the absortption at another wavelength you could use the spectral coefficients which were used in the bio-optical model and re-calculate the absorption coefficient for this wavelength. Note: 2 different coefficients are used for ag (gelbstoff) and ad (detritus).
If you need these coefficients, let me know. We have to find out, which version of the C2RCC you are using, because these coefficients have changed meanwhile.

The question of the normalised reflectance: please let me know date and location of the scene, so that I can check this myself.
Roland

#3

Thanks Roland for your quick response. I am computing gelbstoff absorption coeff. at 412 nm for Indian coastal waters (off Gujarat state of India; it’s northeast Arabian Sea coastal waters, if you see it in Arabian Sea map)using CR2CC data. please send me the spectral coefficient and the bio optical model from which it can be computed.

2- normalised reflectance is of 30 January 2019 of the same area. please find attached file for scence complete id:
(upload://1q9fGB82Of4SErAiNHGuTDgxMnx.jpeg)
I am using default cr2cc parameters for water processing. Do I have to tune TSM factor bpart, bwit and CHL exp and CHL factor according to my coastal waters? If yes then please send any document for guiding the adjustment factors in these paramters.

Please let me know that you got the uploaded jpeg file or not for scence complete identification, which I am trying to process. My email is sahayarvind@gmail.com
you may send an email also to me.

#4

Please stick around in the forum so we other can also benefit from your discussion.
And I think the upload of the image did not work.

#5

Am I not writing in forum?
The image of 30 January 2019 again I processed for normalised reflectance, it is giving correct values; I think earlier there had been some file writing problem in my system folder.

How to take a ploygon subset of CR2CC processed normalised reflectance? Is there any video link etc. for making a polygon subset from main image?

#6

You do, but you mentioned also communication via email. That’s why asked you to stay in the forum.

There are multiple ways of doing a subset.
if you want to do on a batch of products you find here a discussion which can help you:

You can also use the graph builder. Or you just use the subset operation. But there you can only specify the corner coordinates of your area. This would be done with the options too, because the image needs to be rectangular at the end.

#7

Thanks marpet. With graph builder and importing shape file in graph builder I could do subsetting according to my Region of Interest (ROI) and could analyse the data very fast.

#8

how can I use cr2cc processor in graph builder and subsequently use it in batch processing after loading graph builder file? Not able to find cr2cc processor in graph builder?

#9

Sure, we would stick in the forum so that others can also be benefited instead of on emails.

1 Like
#10

C2RCC is not available in the graph builder, they are not compatible with each other.
You need to create the graph XML file manually. Or you can create the part without C2RCC in the graph builder and then add it later to the stored file.
The batch processing also struggles sometimes with optical data even when not using C2RCC.
If you want to do batch processing I would suggest that you follow this guide: https://senbox.atlassian.net/wiki/spaces/SNAP/pages/70503475/Bulk+Processing+with+GPT

#11

Thanks a lot marpet for your quick reply and guidance regarding batch processing.

#12

Hi marpet
I am analyzing two parameters using Analysis–> Scatter plot. Can I change the one of the axis to logarithmic axis?

#13

No this is not possible. But you can export the data and use it in Excel for example

image
image1206×585 68.3 KB

#14

Thanks Marpet. Thought need not go to excel, will do it in snap only.But now I am doing in the same way in excel only!

#15

Hi marpet,
Hope you are doing good. I am using c2rcc processor (want to change the flag). In this connection I would like to understand that what is the meaning of the following flag (default in c2rcc processor)

!quality_flags.invalid && (!quality_flags.land || quality_flags.fresh_inland_water)

#16

C2RCC will be applied when your data is not flagged as invalid AND (is not land OR is fresh_inland_water)

1 Like
#17

Thanks a lot.

#18

Can I get the documentation on IOP bio-optical models used in c2rcc processors. I want to know the apig, adet and agelb models, so that I can tune these models according to bio-optical parameters in our waters! Do I have to write some script for changing those parameters or i can do it in c2rcc processor?

#19

The ATBD for MERIS 4th reprocessing is linked in the help.

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image773×801 65.5 KB

The ATBD for OLCI will also be linked in the next release.
You can access it already here:

And this is the direct link to the MERIS ATBD.

The bio-optical model didn’t really change and is actually also the same for Sentinel-2 data.

C2RCC Output Parameters---Rrs & Rhown
#20

Thanks. Will go through it.