MODIS-Aqua QL subscription gives QLP

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dem1
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MODIS-Aqua QL subscription gives QLP

by dem1 » Wed Feb 21, 2018 5:15 am America/New_York

Hi,

We try to download MODIS-Aqua QL L2 products (excluding QLP because we need to differentiate both) so we used the same logic than for VIIRS:
https://oceancolor.gsfc.nasa.gov/forum/oceancolor/topic_show.pl?pid=30985#pid30985
"If you set up a non-extracted subscription to the QL data, that subscription query will only return QL file names."
but it seems we only get QLP products, is it normal?
The subscription ID is 2044.

Thanks in advance,
Julien

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dem1
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MODIS-Aqua QL subscription gives QLP

by dem1 » Fri Feb 23, 2018 10:59 am America/New_York

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MODIS-Aqua QL subscription gives QLP

by OB.DAAC - SeanBailey » Fri Feb 23, 2018 4:08 pm America/New_York

Julien,

The post you reference is VIIRS specific.  For VIIRS, we receive the Level 0 data twice - once as a session-based file (i.e. ground station contact) and later as a time-based file (replayed as exact 2-hr chunks).  The session-based files receive the QLP designation and once the time-based version is available, it gets the QL designation.

When we implemented the revised calibration update procedure for MODIS-Aqua, we defined QLP for MODIS to be data generated with the as-available ancillary data.  Once the final coincident ancillary data are available, the data are reprocessed and considered QL until the revised calibration is available at which point the refined reprocessing is done.  So, for MODIS, the current QL is the equivalent to the previous definition of refined, while QLP is equivalent to the previous QL definition.   We chose to not offer three options for subscriptions, so the options are still refined or quicklook.   So, in short, yes, it is normal :grin:
Sean

dem1
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MODIS-Aqua QL subscription gives QLP

by dem1 » Mon Feb 26, 2018 7:12 am America/New_York

Sean,

OK I understand, and I have checked our other MODIS refined subscription and just realized that now it gets only "QL" files so we can use it to get them.
It is a bit misleading that MODIS and VIIRS QL products do not represent the same level of refinement and we have fallen in the trap :-)

Thanks,
Julien

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MODIS-Aqua QL subscription gives QLP

by OB.DAAC - SeanBailey » Mon Feb 26, 2018 7:52 am America/New_York

Perhaps, but whatever the QL designation, the data should be considered preliminary and used with caution....even refined doesn't guarantee "perfection"...
In the past (a pretty distant one now), it was possible -even likely- that climatological ancillary would be used in the QL file processing.  In our current processing stream, that is extremely rare, so the impact of the different QL flavors is lessened.
Sean

dem1
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MODIS-Aqua QL subscription gives QLP

by dem1 » Mon Mar 18, 2019 5:48 am America/New_York

Hi,

It seem that my subscription 1588 on MODIS Aqua refined L2 contains new files from 2016,2017,2018, example:
A2016359012500.L2_LAC_OC.nc
    :processing_version = "2018.0" ;
      :software_version = "9.3.0-V2019.0" ;
    :date_created = "2019-03-16T13:30:36.000Z" ;

Are you doing a reprocessing of MODIS-Aqua? My previous product has also the 2018.0 version but :software_version was "9.2.0-V2017.0.3" ;

And I used this subscription to get only QL products, following the logic explained in this thread, did you change something which explain that now I get also real RF products?

Thanks in advance,
Julien

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MODIS-Aqua QL subscription gives QLP

by OB.DAAC - SeanBailey » Mon Mar 18, 2019 7:56 am America/New_York

Julien,

We identified an issue with our L1A processing that affected a few granules per day.  The affected scenes were missing a single scan.
We corrected that processing problem and initiated a regeneration of the affected granules.  We also discovered that a few subscriptions
did not have a correct "look back" time entered in the database - so these if these regenerated L1s matched the subscription, they would be restaged.
We also fixed this - bu not before a few (or perhaps more than a few) slipped through.

Regards,
Sean

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MODIS-Aqua QL subscription gives QLP

by dem1 » Mon Mar 18, 2019 8:49 am America/New_York

Thanks Sean for the explanations,

For this granule I compared the chlor_a of the 2 versions of 2018.0 (9.3.0-V2019.0 vs 9.2.0-V2017.0.3) and found that the values are not exactly the same. Is it normal? Are the 2 versions scientifically equivalent?

Regards,
Julien

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MODIS-Aqua QL subscription gives QLP

by OB.DAAC - SeanBailey » Mon Mar 18, 2019 9:24 am America/New_York

They should be "scientifically equivalent".  You can compare the ancillary inputs and calibration LUTs used - likely some differences there will explain what you see.

Sean

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