Hello. I am using Sentinel-3 OLCI L2 water products for a study. I am interested in the diffuse attenuation coefficient of downward irradiance at 490 nm. When I extract these values for my area of interest the values range from 0 to 10. Are these numbers real? The average Kd value for my area is 0.1 so I doubt these numbers are real. I have tried to find information about this but haven’t been able to. I figured to use only values from 0 to 1.
Actually, SNAP generates recommended masks for OLCI L2 products. See Sentinel-3 Recommended Flags. Also, for KD490.
Unfortunately, this mask does not consider the FAIL flag correctly.
If you combine the mask with the flag as follows, everything should be good.
WQSF_KD490_M07_RECOM && !WQSF_lsb_KDM_FAIL
I just tested. When only considering the flag WQSF_lsb_KDM_FAIL then only pixels <1 remain.
@TomBlock @diana_harosa It seems there is an issue with the recommended mask.
Marco from EOMasters - Mastering Earth Observation
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Dear all,
this issue is corrected in SNAP master. There were two errors involved in the problem stated by alligumo which are connected:
a) there was a bug in the mask expression, which is corrected now.
b) these masks are working differently than expected. All recommended masks for the L2 WFR data are invalid pixel masks. So, every pixel covered by the mask must be excluded from processing. I have updated the documentation to state that clearly.
Cheers,
Tom
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Thank you all for your timeliness with this issue.
To make sure I understood correctly, the issue was within SNAP and not the images?
and so when I extract Kd it already has all the masks it needs or is it necessary to use the WQSF_lsb_KDM_FAIL flag as a filter?
There is/was an issue in SNAP with the definition of recommended flags, but you should still make use of the WQSF_lsb_KDM_FAIL flag to filter your data. Flags are usually not automatically added because their usage varies from case to case.
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