Subject: [IGSMAIL-4717]: CGSIC: GPS NOTICE - Leap Seconds
From: "Diotalevi, Eugene PO" <[email-masked]>(by way of Ruth E. Neilan)
To: [email-masked]
Cc: [email-masked], [email-masked]
Date: Fri, 21 Nov 2003 11:37:11 -0800

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IGS Electronic Mail      21 Nov 11:37:12 PST 2003      Message Number 4717
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Author: Gene Diotalevi (via IGS Central Bureau)

Forwarded to IGSMail: http://igscb.jpl.nasa.gov/mail/mailindex.html

Good day all.

At approximately 00:00:00 GMT on 28 November 2003, some GPS receivers may
incorrectly assume that a change to the number of leap seconds separating
GPS system time from Coordinated Universal Time (UTC) has occurred.

The GPS navigation data message contains identifiers used by GPS receivers
to determine both the current GPS week number and the week number
corresponding to when a change to UTC will occur.  Due to the design of the
navigation message, however, both values are truncated.  Because of the
unprecedented length of time since the last leap second change, the 1999 GPS
epoch week rollover, and the truncated nature of both values, the truncated
week number representations in the navigation message will be the same
during the week of 28 November 2003.  Per ICD-GPS-200C, GPS users are
responsible for accounting for this truncation.

Some GPS receiver manufacturers have already identified receiver makes and
models that will experience an anomaly on 27-28 November (see below link to
Motorola Oncore Technical Application Note).  It is suggested that GPS users
consult with their receiver manufacturer to determine whether or not they
will be impacted.

MOTOROLA ONCORE TECHINCAL APPLICATION NOTE:
http://www.motorola.com/ies/GPS/docs_pdf/notification_oncore.pdf

Regards,

BM1 Gene Diotalevi
www.navcen.uscg.gov

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