Earthdata Forum

Hello,

I am using SeaBASS dataset for SST, MODIS Aqua, R2018.
I have 3 questions:
1) How are the BT in the MWIR/LWIR corrected? Can you point me to the appropriate atmospheric correction document for these specific bands please?
2) When using night data (flagged as night), I have an issue at isolating clear sky matchups. The CLDICE flag returns 50 000 cloudy pixels over the 12 million matchups available at night, while it returns 5 million cloudy pixels for daylight matchups. Is there an issue at identifying clouds during the night, does the method differ from daylight? Maybe I missed something.
3) What algorithm is used? Because I use the R2018 reprocess of MODIS Aqua, I downloaded the data in 2021. I am uncertain if the SST4 and SST algorithms come from Kilpatrick et al. (2015) or from the latest formula described in Luo et al. (2019).

Thanks in advance

Hi,

The SST product you downloaded should be the most recent R2019 version.
Here is the document about it:
https://oceancolor.gsfc.nasa.gov/reprocessing/r2019/sst/

Details about the algorithms used in SST:
https://oceancolor.gsfc.nasa.gov/atbd/sst/
https://oceancolor.gsfc.nasa.gov/atbd/sst4/
https://oceancolor.gsfc.nasa.gov/atbd/sst_triple/

Please check these documents and see if you can find the answers for your questions. Let us know if you need more help.
Guoqing

Thank you for the answer, I now understand 1) and 3).
However for my 2nd question, I am still a bit lost.
Any thoughts about why I fail at identifying clear sky pixels at night?

Cheers

Hello, my question is still up, if someone can please get in touch with me to unlock the situation? I can provide more details if required.

The CLDICE flag is an ocean color flag, not a SST flag. Cloud masking is entirely different for SST (and differs a bit between day and night). For SST, unless you have a reason to do otherwise, you should use the quality flags (qual_sst) for selecting good quality SST retrievals. There is an flags_sst array with bits set for various conditions. These are combined into the qual_sst flag, for which 0=Best; 1=Good; 2=Questionable; 3=Bad

For more details, see:

https://oceancolor.gsfc.nasa.gov/atbd/sst/flag/

Sean

I understand now. I was using l2flags because I included visible bands along with IR/MWIR/LWIR to try to improve retrievals over noisy matchups. But I guess I will switch to qual_sst.

Thanks for the details!