[CF-metadata] How to define time coordinate in GPS?

From: Timothy Patterson <Timothy.Patterson>
Date: Mon, 27 Apr 2015 13:51:57 +0200

The OSTM/Jason-2 netCDF products added some attributes to their time variables to handle a similar situation.

When declaring time as ?seconds since a given epoch?, they also add an attribute ?tai_tuc_difference? which contains the number of leap seconds applied since that epoch.

In addition, when the data is an array of time values, because a leap second could conceivably be applied at a time within that array, there is also an attribute "leap_second" that contains the UTC time at which any new leap second is applied.

With this information, you have everything in the dataset to convert from UTC to TAI.

An example from the Jason User Handbook:

double time(time);
        time:long_name = "time (sec. since 2000-01-01)";
         time:standard_name = "time";
         time:units = "seconds since 2000-01-01 00:00:00.0";
        time:calendar = "gregorian";
        time:tai_utc_difference = [GA_TAI_UTC_DIF];
        time:leap_second = [GA_LEAP_TIME];
        time:comment = ? ?tai_utc_difference? is the difference between TAI and UTC reference time (seconds) for the first measurement of the data set. ?leap_second? is the UTC time at which a leap second occurs in the data set, if any. After
        this UTC time, the tai_utc_difference is increased by 1 second. ?

Regards,

Tim


__________________________________________________________________

From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Julien Demaria
Sent: Thursday, April 23, 2015 2:51 PM
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] How to define time coordinate in GPS?

Hi,

I need to define a time coordinate variable which use the GPS time referential instead of UTC, but I did not found how to specify this.
For the moment my variable look like this :

??????????????? int64 time_stamp(rows) ;
?????????????????????????????? time_stamp:standard_name = "time" ;
?????????????????????????????? time_stamp:units = "microseconds since 2000-01-01 00:00:00" ;
?????????????????????????????? time_stamp:_FillValue = -1L ;

Thanks in advance,

Julien

Any email message from EUMETSAT is sent in good faith but shall neither be binding nor construed as constituting a commitment by EUMETSAT, except where provided for in a written agreement or contract or if explicitly stated in the email. Please note that any views or opinions presented in this email are solely those of the sender and do not necessarily represent those of EUMETSAT. This message and any attachments are intended for the sole use of the addressee(s) and may contain confidential and privileged information. Any unauthorised use, disclosure, dissemination or distribution (in whole or in part) of its contents is not permitted. If you received this message in error, please notify the sender and delete it from your system.
Received on Mon Apr 27 2015 - 05:51:57 BST