Old leapsec.dat file on Ancillary site

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jessica.braun
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Joined: Wed Oct 20, 2021 11:16 am America/New_York

Old leapsec.dat file on Ancillary site

by jessica.braun » Wed Oct 20, 2021 11:19 am America/New_York

Hello,

We routinely grab the utcpole.dat and leapsec.dat file from:

https://oceandata.sci.gsfc.nasa.gov/Anc ... UTs/modis/

We noticed the leapsec.dat file has not updated since 9/26. Is there an ongoing issue with updating this file?

Thanks,
Jess Braun

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OB.DAAC - SeanBailey
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Re: Old leapsec.dat file on Ancillary site

by OB.DAAC - SeanBailey » Fri Oct 22, 2021 7:03 pm America/New_York

Jess,

The file is not old. In fact, there hasn't been a leap second since 2017. The reason the file is regularly updated is because the SDPTK code used by the MODIS geolocation code checks the time stamp in the header of the file (a timestamp it adds to the file) and will stubbornly refuse to work if it is more than 3 months "old". Personally, I think it's an unnecessary check, but did ensure that a current leap second file was in place (leap seconds are only ever added in January or July, so not sure why 3 months was picked...).

The file on our site is less than a month old. Check back next week and you may find it magically has a new date (but the data - aside from the header line - will be identical). We don't updated it more frequently than monthly - unless there's a leap second to add ;)

Regards,
Sean

gnwiii
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Re: Old leapsec.dat file on Ancillary site

by gnwiii » Mon Oct 25, 2021 8:40 am America/New_York

unless there's a leap second to add
or, thanks to global warming, subtract! Adding a second is simpler than subtracting, as you don't get the same time twice when adding, so it will not be surprising to see some problems with subtracting a leap second.

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