getting numeric chlorofil A color as CVS file

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cahitmuderris
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Joined: Thu Sep 02, 2021 3:56 pm America/New_York

getting numeric chlorofil A color as CVS file

by cahitmuderris » Thu Sep 02, 2021 4:50 pm America/New_York

Hi there,

You have big chlorophyl-a datasets obtainable from MODIS Terra and Aqua L3 (global view) for almost a 20-year period. But the spatial resolution of them is too coarse to study (4 km).

you present it as an NC file (pixelmap). When I open it with SEADAS I am facing a pixelation problem (pls see attachment).

(Note: I know at the moment, via Hawkeye sat., it's possible to obtain OC maps with significantly higher resolution but the problem is about the lack of dataset dating 2020 before.)

How can I get numeric chl-A data [as lat, long, chl-A (mg/L)] for MODIS Terra and Aqua L3. I will use it as comma-separated value (csv format) and planning to import it into QGIS for interpolating it conveniently to create maps with higher resolution (but of course with lower reliability due to this process) ?

Is it rational? Any idea or evaluation will make me glad,

Many thanks,

Kind Regards,

Cahit
Bioengineer
Ocenographer
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GES DISC - jimacker
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Re: getting numeric chlorofil A color as CVS file

by GES DISC - jimacker » Thu Sep 02, 2021 5:47 pm America/New_York

Hello,
It is possible to convert a netCDF file to a CSV output file using the free software NASA Panoply. The How-To document linked below describes how to use a Giovanni output file in netCDF, convert it to CSV with Panoply, and then make a lat,lon,value list with Excel.

https://disc.sci.gsfc.nasa.gov/informat ... nd%20Excel

Giovanni uses the ocean color MODIS-Aqua files at 4km resolution, but this procedure should work for 1km data files as well, which can be downloaded from the OBDAAC. The procedure may not work for a full global file due to Excel limitations, so a subset file may be best.

Please reply if you have additonal questions.

cahitmuderris
Posts: 4
Joined: Thu Sep 02, 2021 3:56 pm America/New_York

Re: getting numeric chlorofil A color as CVS file

by cahitmuderris » Thu Sep 02, 2021 6:13 pm America/New_York

thanks for the reply,

As you indicated limiting the area via subset files is important to not overwhelm with huge data in Excel.

I am working in the context of the Marmara Sea (roughly 41 N - 40 S - 26 W - 29 E)
using "find swaths" button to limit the data but still facing data of much larger area.

How can I cut (remove/edit) a netCDF file after downloading via "find swaths-step". Giovanni is able to do this as well?

Regards,

GES DISC - jimacker
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Re: getting numeric chlorofil A color as CVS file

by GES DISC - jimacker » Fri Sep 03, 2021 11:02 am America/New_York

I am not sure how to edit a netCDF file in the manner you mention. I would suggest using the Black Sea region in the Level 1&2 browser (OBDAAC). I hope they included the Sea of Marmara in that region.

Giovanni will provide output for a subset area defined by a bounding box, which can be created on an interactive map or defined with geographic coordinates. Note that Giovanni only has the 4km Level 3 data, 8-day and monthly.

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