Tilt flag/identification in SeaWiFS L1b data (via l1bgen)?

[amsayer]

Hi all,

I've been running l1bgen to convert SeaWiFS GAC L1a data to L1b (I don't need L2 data, just the L1b, hence l1bgen not l2gen). I'd like to be able to identify scan lines during which the spacecraft is tilting, so I can have a way to mask them out later (in case they give me trouble down the road).

From my reading around the forum and product documentation, I know that the L1a data include flags to identify when the tilt is ongoing, but these aren't included in the L1b output from l1bgen, and I don't see there's an option to do so. So I had thought that my easy option seems to be just to take the tilt SDS from the navigation_data group in the L1bs, and do a simple check to say if this changes between two scan lines then mark these lines as 'tilted' data. (The only downside is that the scan lines before the tilt starts and after it ends would then be thrown away, but I can live with that.)

I was wondering if that sounds sensible to you, or if there's an easier way I'm missing? For storage purposes I don't want to assume I will keep both L1a and L1b around so trying to use only the information provided within the L1bs.

Thanks,

Andy

[fredoceansips]

Hi Andy,

What you propose will work reasonably well, but you can simplify this with the knowledge that the static tilt values are 19.820 and -19.925 (these are set in the navigation parameter file).  So any tilt angles between those values can be safely treated as occurring during the tilt change.

Fred

[amsayer]

Thanks, Fred! Yes, that's a better solution. I'll do it that way.

Andy

[OB.DAAC - SeanBailey]

...or exclude data with the NAVWARN flag set in the l2_flags.  During the tilt, it is set.
(Yes, NAVWARN is one of the select few l2_flags set by l1bgen).

Sean

[amsayer]

Aha! Even better. :) Thanks! I scanned the flags for a tilt but it didn't click that NAVWARN would cover that. Mea culpa, I should read more closely!

Andy