Error using ocssw calibration on VIIRS

[slsmit34]

Hello,
I know I have asked many l2gen questions in the past week, so thank you in advance for your patience.

I am currently trying to run l2gen on L1A VIIRS-SNPP data (scene: SNPP_VIIRS.20230712T180000.L1A.nc). I am starting by running calibrate_viirs on the L1A scene to generate L1B. To do this, I did

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install_ocssw -t V2024.6 --viirsn --viirs_l1 --install_dir /path/l2gen/ocssw

which installed folders viirsj1 and viirsn files to /ocssw/var, viirs to /ocssw/share, and viirs_l1_benchmark to /ocssw. It also output the following:

downloaded_ocssw.PNG (34.42 KiB) Not viewed yet

However, I get this error when running calibrate_viirs:

calibrate_viirs_error.PNG (81.24 KiB) Not viewed yet

By the way, polar_wander.ascii does exist in my directory /ocssw/var/viirsn and has a size of 2.2MB.

Thank you!
Best,
Sami

[OB ODPS - towens]

Are you setting the correct environment?
export OCSSWROOT=path_to_your_ocssw_directory
export OCVARROOT=$OCSSWROOT/var

We stage the operational GEO files so you don't have to make them.
Replace "L1A" with "GEO" in the filename.

Tommy

[slsmit34]

Hi Tommy,
Thanks. So if I am understanding correctly, I can download the GEO file and use that as a parameter for l2gen? Do I still need to generate L1B with calibrate_viirs then? Can I just generate an l2 directly from l1a with a command like this:

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"l2gen ifile={l1a_file} ofile={output_name} geofile={geo_file}"

Is there a need to use getanc or calibrate_viirs then?

Best,
Sami

[OB ODPS - towens]

Yes, to make an L2 file you should provide the ancillary data. We make an L1B file from the L1A and GEO and then pass the L1B to l2gen.
I think l2gen has the code to make L2 directly from L1A and GEO but I will defer to one of our SeaDAS experts on running that...

Tommy

[OB.DAACx - SeanBailey]

Yes, l2gen can take a VIIRS L1A file as input (performing the calibration on-the-fly), but the VIIRS geolocation and calibration programs share code, so if you are unable to process the geoocation, you will likely have issues calibrating - either with calibrate_viirs or l2gen.

Sean

[slsmit34]

Thanks all for the support.
So the process to go from L1A to L2 includes two steps, each with ifile, ofile, and geofile:

• 1. calibrate_viirs create L1B: ifile=[VIIRSN.L1A.nc] l1bfile_mod = [VIIRSN.L1B.nc] (ofile and geofile are not valid params https://seadas.gsfc.nasa.gov/help-8.1.0/processors/ProcessCalibrate_viirs.html)
  2. l2gen create L2: ifile=[VIIRSN.L1B.nc] ofile = [VIIRSN.L2.nc] geofile=[VIIRSN.GEO.nc]

Is this correct? I'm not sure where getanc goes in this process.

[OB.DAACx - SeanBailey]

Yes, that is the process. The getanc call goes before l2gen to identify (and download) the ancillary inputs to the l2gen process. BTW, calibrate_viirs can output three different files, thus in place of ofile it uses l1bfile_[img,mod,dnb].

BTW, the calibrate_viirs code includes the bits of the geolocation code necessary to do the calibration, so a geofile is not required as input...which is why I said in my previous post that if geolocate_viirs fails due to an incorrect configuration or missing LUTs, calibrate_viirs is also likely to fail.

Sean