missing 'time' data in SWOT_L2_LR_SSH_BASIC

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madelinedm
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Joined: Tue Jan 16, 2024 1:22 pm America/New_York
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missing 'time' data in SWOT_L2_LR_SSH_BASIC

by madelinedm » Tue Jan 16, 2024 1:38 pm America/New_York

Hello, I used the podaac data downloader to download a large number of files from SWOT_L2_LR_SSH_Basic. I am using MATLAB ncread to open and read in the files, and many of them have the _FillValue in the 'time' variable, which MATLAB replaces with NaN.

A few of the 147 granule files that have missing 'time' are:
SWOT_L2_LR_SSH_Basic_536_014_20230529T232701_20230530T001116_PIB0_01.nc
SWOT_L2_LR_SSH_Basic_536_016_20230530T010736_20230530T015329_PIB0_01.nc
SWOT_L2_LR_SSH_Basic_536_018_20230530T024948_20230530T033542_PIB0_01.nc
SWOT_L2_LR_SSH_Basic_536_020_20230530T043208_20230530T051755_PIB0_01.nc
SWOT_L2_LR_SSH_Basic_536_022_20230530T061507_20230530T070253_PIB0_01.nc
SWOT_L2_LR_SSH_Basic_536_024_20230530T075621_20230530T084613_PIB0_01.nc
SWOT_L2_LR_SSH_Basic_537_006_20230530T162718_20230530T171759_PIB0_01.nc
SWOT_L2_LR_SSH_Basic_537_008_20230530T181017_20230530T190035_PIB0_01.nc
SWOT_L2_LR_SSH_Basic_537_010_20230530T195140_20230530T204246_PIB0_01.nc
SWOT_L2_LR_SSH_Basic_537_012_20230530T213352_20230530T221928_PIB0_01.nc

Two questions:

1) Is this consistent with the data as recorded, or is this possibly a sign of a corrupt file download or problem with ncread?
2) If this is the correct data, can I use the start and end times in the filename to assign times to the data in the files, or are they irregularly sampled?

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madelinedm
Posts: 2
Joined: Tue Jan 16, 2024 1:22 pm America/New_York
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Re: missing 'time' data in SWOT_L2_LR_SSH_BASIC

by madelinedm » Tue Jan 16, 2024 4:27 pm America/New_York

Update: I tested opening the files with python's netCDF4 package, and I am now seeing that in the files that MATLAB's ncread was returning 'time' as all NaNs, the 'time' variable is masked for only a portion of the times. When the mask=True, the underlying time data is '0'. I looked at the 'ssha_karin_2_qual' variable at these times and it is full of the number 2751463680, which does not appear to be one of the quality flags.

How can I interpret these data points?

PODAAC - celiaoued
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Re: missing 'time' data in SWOT_L2_LR_SSH_BASIC

by PODAAC - celiaoued » Mon Jan 22, 2024 4:37 pm America/New_York

Hello,

Please see the latest L2_LR_SSH Product Description Document at this page: https://podaac.jpl.nasa.gov/swot?tab=datasets-information&sections=about%2Bdata

I believe the description of the quality flags under section 4.1.3, and especially Appendix B will help you. The flags are in binary.

With your example of 2751463680, it is less than 2^31. Since integers equal to or greater than 2^31 indicate bad/invalid values, and 2751463680 is less than 2^31, then I believe 2751463680 is the sum of more than one flag. Viewing 2751463680 in binary would allow you to see which flags sum up to 2751463680. Hope this helps!

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