about L2 Ocean Products

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tnonaka01
Posts: 4
Joined: Mon Oct 16, 2017 6:38 pm America/New_York

about L2 Ocean Products

by tnonaka01 » Mon Oct 16, 2017 6:53 pm America/New_York

We received the following comments:
"As an aside, the file in question does not have any valid SST retrievals over
the lake. The qual_sst flag indicates the data are all cloud covered."
I'd like to ask several questions.
1. SST data has already some null value in the Ocean area.
We first consider these areas are covered by cloud.
Will you inform me what is the definition of the null SST area?
2. We checked the "qual_sst", and the value of Suwa Lake is 3.
So it means "Bad Cloud/ice/or atmospheric correction failed",
according to table 1 of the following site.
https://oceancolor.gsfc.nasa.gov/atbd/sst/
We need to separate "cloud" and "ice", so we would use the "flags_sst".
Will you kindly inform me to separate the cloud pixel.
If the bit description is following, the pixels with more than 2^15 (=32768)
mean cloud?
https://oceancolor.gsfc.nasa.gov/atbd/sst/flag/
We checked the range of value.
"flags_sst" has two bands, the range of band 1 is from 0 to 537,920,320
(What does this value mean?), and band 2 is from -32,736 to 18,464.
Which band should we use?

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gfireman
Posts: 59
Joined: Thu Jan 07, 2010 2:59 pm America/New_York

about L2 Ocean Products

by gfireman » Tue Oct 17, 2017 11:10 am America/New_York

1.  For any product, when a pixel contains a null or fill value, it means that no meaningful value could be determined - for any of a number of reasons.  To find the reason in the case of SST, you will need to decode the corresponding flags_sst value using the table you mentioned: https://oceancolor.gsfc.nasa.gov/atbd/sst/flag/

2.  I don't believe our products distinguish between cloud and ice.  But yes, since CLOUD is flagged in bit 15, and 15 is the highest bit, any value >= 2^15 means a cloud pixel.

3.  There is only one flags_sst dataset, with no band dimension.
         short flags_sst(number_of_lines, pixels_per_line) ;

Perhaps the first "band" you mentioned is actually l2_flags?
        int l2_flags(number_of_lines, pixels_per_line) ;

Decode those values using l2_flags:flag_meanings, or the table at https://oceancolor.gsfc.nasa.gov/atbd/ocl2flags/
537920320 = 2^29 + 2^20 + 2^9 + 2^8 + 2^6, indicating that the flags HIPOL, MODGLINT, CLDICE, STRAYLIGHT, and COASTZ are set.

tnonaka01
Posts: 4
Joined: Mon Oct 16, 2017 6:38 pm America/New_York

about L2 Ocean Products

by tnonaka01 » Wed Oct 18, 2017 10:52 am America/New_York

Thank you for your reply.
I checked the value, and found that bit 15 was flagged in lake Suwa (inland water?) in all weather conditions.
Is it correct?

gfireman
Posts: 59
Joined: Thu Jan 07, 2010 2:59 pm America/New_York

about L2 Ocean Products

by gfireman » Wed Oct 18, 2017 11:22 am America/New_York

Bit 15 of which flag?
Our land/water mask flags only the largest inland water bodies.  At 15 sq km, Lake Suwa is probably flagged as land.
Our standard products do not attempt to process chlorophyll or SST over land.  Your best bet is to generate l2 products yourself, using the "proc_land=1" flag.

tnonaka01
Posts: 4
Joined: Mon Oct 16, 2017 6:38 pm America/New_York

about L2 Ocean Products

by tnonaka01 » Wed Oct 18, 2017 4:52 pm America/New_York

Thank you for your reply.
Bit 15 of SST Quality Flags.
https://oceancolor.gsfc.nasa.gov/atbd/sst/flag/

>Lake Suwa is probably flagged as land.


OK, but I confirmed the value of SST, it had some pixels of water temperature.
We wonder whether we can use it, or not.

>Your best bet is to generate l2 products yourself, using the "proc_land=1" flag.


Will you kindly inform me how to generate l2 product by myself?
You mean that we should use level 1 calibrate radiance data, and calculate SST value?

gfireman
Posts: 59
Joined: Thu Jan 07, 2010 2:59 pm America/New_York

about L2 Ocean Products

by gfireman » Wed Oct 18, 2017 5:13 pm America/New_York

Could you give us an example of a standard product, where SST_CLOUD is set where there are no clouds?

And, yes, I mean starting from calibrated radiance.
You may want to start with SeaDAS: https://seadas.gsfc.nasa.gov/

tnonaka01
Posts: 4
Joined: Mon Oct 16, 2017 6:38 pm America/New_York

about L2 Ocean Products

by tnonaka01 » Wed Oct 18, 2017 6:14 pm America/New_York

Thank you for your quick return.
The attachment of the file is possible?
And I mean SST (not SST_CLOUD) is set in Suwa Lake, though you mentioned that the small lake is
dealt as land.

>Our land/water mask flags only the largest inland water bodies.  At 15 sq km, Lake Suwa is probably flagged >as land. Our standard products do not attempt to process chlorophyll or SST over land.


gfireman
Posts: 59
Joined: Thu Jan 07, 2010 2:59 pm America/New_York

about L2 Ocean Products

by gfireman » Thu Oct 19, 2017 10:54 am America/New_York

Please just give us a file name.
Bit 15 of SST Quality Flags is SST_CLOUD, which you had said is set in Suwa Lake under clear conditions.

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