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VIIRS chlor_a noise/dropout lines

Posted: Wed Jul 05, 2017 5:18 pm America/New_York
by oceani
Dear OCG,

I imagine this is not the first time this question has been submitted, however, I ran a search and did not find the answer.  Can you please point me to the discussion(s) on the noise or dropout lines I am seeing in the VIIRS chlor_a level 2 data?  I am seeing these artifacts when using our in-house software and in SeaDAS.  I do not,however see these lines in your browse images and other sources of VIIRS data.  Any answers/direction on how to 'remove' these lines will be much appreciated.



VIIRS chlor_a noise/dropout lines

Posted: Wed Jul 05, 2017 7:41 pm America/New_York
by gnwiii
Look at SDRs and the “Bow-tie Effect" in Beginner Guide to VIIRS Imagery Data (PDF).  You can just use the NASA OBPG software or update your in-house software.

VIIRS chlor_a noise/dropout lines

Posted: Thu Jul 06, 2017 1:26 pm America/New_York
by fredoceansips
The referenced presentation has a lot of useful information, but is not entirely correct regarding the bowtie pixel deletion.

The figure shown on p. 12 is correct.  The pixels in the areas shown in red are actually deleted by the VIIRS instrument, not the SDR software.  The packets that are created by VIIRS, and then transmitted by the spacecraft to the ground, do not contain data for these pixels.  This is done to reduce the VIIRS downlink data volume.

The term "pixel trim" is used by IDPS to represent two different kinds of pixel deletion.  There additional pixels in the bowtie overlap region that are not processed to EDR products by the IDPS software, beyond those already affected by the bowtie deletion.  There are separate fill values defined for these two conditions in the IDPS data products.  IDPS refers to these as "onboard pixel trim" and "onground pixel trim" in their documentation. 

The OBPG VIIRS data products do not perform the "onground" pixel trim; however, the instrument bowtie-deleted pixels will appear as missing in the full-resolution products.  The browse products are subsampled so as to avoid the bowtie-deleted pixels.


VIIRS chlor_a noise/dropout lines

Posted: Thu Jul 06, 2017 2:56 pm America/New_York
by oceani
Thanks to both of you.  Very helpful.