How to download global VIIRS L1A and geo data?

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yang16
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How to download global VIIRS L1A and geo data?

by yang16 » Mon May 23, 2022 9:22 am America/New_York

Hello~

I want to download global VIIRS L1A and geo data from the NASA Ocean Color L1 & 2 brower. But the ordered data only included L1A data. I found that if the data I downloaded no need order, I could download both L1A and geo data. So I wonder how to access global VIIRS L1A and geo data?

Thank you.
Elaine

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Re: How to download global VIIRS L1A and geo data?

by OB ODPS - towens » Mon May 23, 2022 2:00 pm America/New_York

If you are not requesting regional extracts then you will get only the list of matching L1A file names returned,

That same list can then be used to get the GEO files by replacing the string "L1A" with "GEO-M" in the file name in the URL.

Tommy

yang16
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Re: How to download global VIIRS L1A and geo data?

by yang16 » Mon May 23, 2022 10:15 pm America/New_York

Hello Tommy,

Thank you for your reply. The URL I used to download VIIRS L1 data did not include L1A. For example: https://oceandata.sci.gsfc.nasa.gov/cgi/getfile/requested_files_1.tar?h=ocdist305&p=/data1/a000d322b38f2e67/requested_files

All the L1A files are in the folder of requested_files_1.tar. I tried to replace the folder name with L1A file name, but the revised URL could not be opened.

So could you explain more details about how to access GEO data?

Thank you.
Elaine.

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Re: How to download global VIIRS L1A and geo data?

by OB ODPS - towens » Tue May 24, 2022 9:26 am America/New_York

That is an extracted order. You can generate a geolocation file from the extracted L1A using SeaDAS.

See:
https://seadas.gsfc.nasa.gov/help-8.2.0/processors/ProcessGeolocate_viirs.html

Tommy

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Re: How to download global VIIRS L1A and geo data?

by yang16 » Wed May 25, 2022 11:50 am America/New_York

Hello Tommy,

Thank you for your reply. I tried to download DEM files for VIIRS from the NASA OBPG server, but I did not figure out how to register for "samoa.gsfc.nasa.gov". So could you tell me how to register for this server?

In addition, I think it is easier to use your first approach. Could you tell me what is the URL and how to get it?

Thank you.
Elaine.

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Re: How to download global VIIRS L1A and geo data?

by OB ODPS - towens » Wed May 25, 2022 12:47 pm America/New_York

When you place your order, if you select "do not" extract my files, you will be presented with a list of URLs to download. That is where you can substitute GEO-M for L1A to get the GEO files. I passed your samoa question to our web admins.

Tommy

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Re: How to download global VIIRS L1A and geo data?

by OB.DAAC - amscott » Wed May 25, 2022 5:22 pm America/New_York

You don't need to register for samoa access. The GEO file will be created in SeaDAS when you follow the steps on the page Tommy supplied.
You can generate a geolocation file from the extracted L1A using SeaDAS.

See:
https://seadas.gsfc.nasa.gov/help-8.2.0/processors/ProcessGeolocate_viirs.html

yang16
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Re: How to download global VIIRS L1A and geo data?

by yang16 » Thu May 26, 2022 8:13 am America/New_York

Hello Tommy,

Thank you for your reply. I selected "Do not" extract my order when ordered data, but the URL included in the http_manifest.txt file stilled did not contain "L1A":
https://oceandata.sci.gsfc.nasa.gov/cgi/getfile/requested_files_1.tar?h=ocdist309&p=/data1/f0f0c271ef862168/requested_files
Do you know what happened?

Thank you for passing my samoa question to your web admins. They told me to creat Geo files using Seadas following the page you supplied: https://seadas.gsfc.nasa.gov/help-8.2.0/processors/ProcessGeolocate_viirs.html
According to that page, DEM files from the NASA OBPG FTP server are required. However, your web admins said that I did not need to register for the samoa access. If so, I cannot get the DEM files.

By the way, I could generate Geo files without DEM files using Seadas. But those Geo files were different from that downloaded directly from the L1 & 2 browser. So I think DEM files are necessary when generate Geo files.

I am sorry that I could not generate Geo files with either of your methods. Could you give me more hints?

Thank you in advance.
Elaine.

yang16
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Re: How to download global VIIRS L1A and geo data?

by yang16 » Thu May 26, 2022 8:20 am America/New_York

Thank you for your reply. According to the page provided by Tommy, DEM files from the NASA OBPG FTP server are required to generate Geo files from L1A files. However, if I do not register for the samoa access, I cannot get the DEM files.

In addition, I could generate Geo files without DEM files using Seadas. But those Geo files were different from that downloaded directly from the L1 & 2 browser. So I think DEM files are necessary when generate Geo files.

Thank you.
Elaine.

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Re: How to download global VIIRS L1A and geo data?

by OB.DAAC - SeanBailey » Thu May 26, 2022 8:28 am America/New_York

Elaine,

The documentation on the "ProcessGeolocate_viirs" page needs to be updated (thanks for alerting us to that discrepancy). The required DEM files are no longer distributed using the samoa FTP server (it, in fact, no longer serves as an FTP server - as we no longer support FTP distribution). When you install the processing components of SeaDAS (OCSSW) and select VIIRS as a sensor you wish to be able to process, the installer will pull the required software and support files - including the DEM files.

As for the files in your extracted order request (f0f0c271ef862168), those were Level 2 files, which include the geolocation information internal to the netCDF file, so no need to generate a GEO file from a L1A file.

Sean

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