reading Sentinel-3 SRAL files fails

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hproe
Posts: 504
Joined: Sat Nov 27, 2010 3:46 pm

reading Sentinel-3 SRAL files fails

Post by hproe »

Hi -
IIRC in the past (~2018) it was possible to read/display netCDF files from Sentinel-3 SRAL instruments, in particular display of SWH tracks. With recent nigthtlies reading fails, in that it requests corrections via the widget 'Non-Compliant NetCDF Tool'. Panoply is just fine with these files. Find attached a sample of the files.
best, HP
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enhanced_measurement (5).nc
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bobc
Posts: 987
Joined: Mon Nov 15, 2010 5:57 pm

Re: reading Sentinel-3 SRAL files fails

Post by bobc »

Hi HP,

I'm replicating that this file is giving the Non-Compliant NetCDF Tool window at Add Source. I went back several McV versions and I'm getting this same result all the way back to version 1.3:
  • Nightly (2021/11/15)
  • Core 1.8 (release date - 2018/12/04)
  • Core 1.7u1 (release date - 2018/01/25)
  • Core 1.6 (release date - 2016/07/18)
  • Core 1.5 (release date - 2015/05/01)
  • Core 1.4 (release date - 2013/09/17)
  • Core 1.3 (release date - 2013/05/30)
I ran the file through a CF-Compliance checker and there are 5 errors in the file. According to the output of the compliance checker, the following variables must be of type byte, short or int:
  • total_electron_content_01
  • waveform_20_ku
  • waveform_20_c
  • waveform_20_plrm_ku
Additionally, the waveform_qual_ice_20_ku variable has an attribute error "flag_meanings present, but no flag_values or flag_masks specified".

Where exactly did you get this file from? I see you can download Sentinel-3 data from the Copernicus Open Access Hub, but the filenames are quite different and we don't support all of those data files. As for Sentinel data, we support Sentinel-5 Precursor TROPOMI data in the nightly builds as a gridded data source, though I would need to do more testing/experimenting with data from other Sentinel satellites to verify their statuses.

I'll experiment a bit with NcML and let you know if I'm able to get your data to load.

Thanks,
Bob Carp
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bobc
Posts: 987
Joined: Mon Nov 15, 2010 5:57 pm

Re: reading Sentinel-3 SRAL files fails

Post by bobc »

Hi HP,

I figured it out. This isn't a gridded netCDF file (which McV tries to load the data as), but a point netCDF file. Through the General>Files/Directories chooser, select "netCDF/GEMPAK Point Data files" from the Data Type dropdown, select your file, and click Add Source. From working with this data in the past, you'll likely already be familiar with the following steps to create a display, but I'll add it for completeness:

Each data point is its own timestep. Because of this, attempting to create a display with the data source in its initial form will lead to 1985 timesteps. You can bin the points together into one timestep by double-clicking on the name of the data source on the left side of the Field Selector tab of the Data Explorer to open the Properties window for the data source. From here, I adjusted the Time Binning settings at the bottom of the Properties tab to:
- Bin Size: 1 day
- Round To: 1 hour
You could modify these values if you are looking to display a loop and not the entire swath at once.

From here, you can select your gridded field and display type. You will likely want to experiment with different options in the Grid Parameters tab to get McIDAS-V to plot a swath roughly fitting to the data points. As a quick test with the rad_water_vapor_01_ku variable, I set the following:
Spacing: Degrees
Grid Size: 0.05 x 0.05
Passes: 2
Search Radius: 1
Gain: 1

These values, with the Image Display display type, produce a narrow strip of data in the display that follows along the path of the data. To verify the display was correct, I overlaid the Image Display with a Point Data Plot of the Point Data field which doesn't use any gridded interpolation to create the display.

Please let me know if you have any other questions about this.

Thanks again,
Bob
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