SCR 3-0001

SCR 3-0001: Time Standards (Z, UTC, GMT)

Priority: medium

Problem Summary

Questions surrounding the inconsistent use of the “Z” time zone indicator and the possible differences between the civil time at Greenwich (the “Z” time zone), “Greenwich Mean Time” (defined differently on land and sea), and Coordinated Universal Time (the appropriate time system for astronomy) have arisen periodically throughout the history of the Planetary Data System. The issue has come to the fore as part of serious efforts to support correlative searches based on recorded START_TIME.

Anne Raugh undertook the task of researching the differences between the above-mentioned time standards, the results of which were presented at the July 2002 Technical Session. The consensus of the technical group at that time was that the PDS documents should be modified to clearly state that UTC is the preferred time standard for fields such as START_TIME, and that a “Z” suffix on a time string indicates the civil time zone at Greenwich, England and is not synonymous with “UTC”.

This SCR presents the list of specific changes identified in the PDS standard documentation set, and notes one issue of PDS time zone notation that remains outstanding.

Working Group

A. Raugh (lead) R. Simpson

Originator: A. Raugh

Standards Change Request

22002-11-12A. RaughTEXT


Supplementary Material


StatusDateTaskResponsible PartyResponse
SUBMITTED 2002-10-24
IN_PROGRESS 2002-11-14
DRAFT 2003-01-29
APPROVED 2003-04-17
RELEASED 2003-08-01


The Management Council voted to APPROVE the SCR with a final vote of 12-0-0. The vote took place by email ending Apr. 22, 2003.

NodeRepresentativeVersion 2
ATMLyle Huberyes
GEOEd Guinnessyes
IMGSue LaVoieyes
NAIFBoris Semenovyes
PPIRay Walkeryes
RINGSMark Showalteryes
RSDick Simpsonyes
SBNMike A’Hearnyes
PDS-PMLaverne Hallyes
PDS-PSReta Beebeyes
PDS-PESteve Hughesyes
CN-MLRon Joyneryes