Planetary Data System
Engineering Node

PDS3 Standards: Individual Issue

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:

Version Date Author(s) Format Note
2 2002-11-12 A. Raugh TEXT


Supplementary Material:


Status Task ResponsibleParty Response
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.

Node Representative Version 2
ATM Lyle Huber yes
GEO Ed Guinness yes
IMG Sue LaVoie yes
NAIF Boris Semenov yes
PPI Ray Walker yes
RINGS Mark Showalter yes
RS Dick Simpson yes
SBN Mike A'Hearn yes
PDS-PM Laverne Hall yes
PDS-PS Reta Beebe yes
PDS-PE Steve Hughes yes
CN-ML Ron Joyner yes