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Re: UTC - GPS Time
From: James H. Maynard
Date: 1996 Jun 26, 01:43 GMT
From: James H. Maynard
Date: 1996 Jun 26, 01:43 GMT
In article 6BT8FkgxonB@gps_gear.mayn.de, guido@gps_gear.mayn.de (Guido Lenz) said: > >Does anybody have the exact time delay in GPS to UTC time? I >heard rumours of about 11 seconds, but from experience this >seems to be 11.21 seconds. Does anybody have exact data? > >Best regards >Guido >-- >And in the end, it's not the years in your life that count. It's >the life in your years. -Abraham Lincoln > > GPS time is currently FAST (that is, ahead) of UTC time by exactly 11 seconds. The number of seconds by which the GPS time for a given event is greater than the UTC time for that event is the same as the number of leap seconds that have been inserted into the UTC time scale since the GPS time scale began at 1980-01-06 00:00:00.0 UTC. Leap seconds are inserted as necessary to keep UTC in reasonably close agreement with the time scale that uses the rotating earth as a clock. Each time a leap second is inserted into the UTC time scale, the difference between the GPS time and UTC time increases by one second. Therefore, (GPS time) - (UTC time) = (number of leap seconds), where (GPS time) and (UTC time) are the readings on the two time scales for the same event, and (number of leap seconds) is the number of leap seconds that have been inserted into the UTC time scale since zero hours, zero minutes, zero seconds UTC on Sunday, the 6th of January, 1980. I don't know when the next leap second will be inserted, as the International Earth Rotation Service has not yet promulgated that information. Tyhpically, leap seconds have been inserted from a year to a year and a half apart. They are usually inserted at the very end of June or of December, UTC, but if necessary to insert one sooner, the IERS might choose the end of March or of December. Jim Maynard, K7KK -- Salem, Oregon, USA jmaynard@teleport.com (Home), iim1jhm@iim.ups.com (Work) "Every vessel shall at all times maintain a proper lookout...." (COLREGS Rule 5) From mail Mon May 19 13:40 EDT 1997 Received: from dg-webo by wellspring.us.dg.com (5.4R3.10/dg-gens08) id AA06612; Mon, 19 May 1997 13:40:47 -0400 Received: from gw-ronin.mv.net by dg-webo.webo.dg.com (5.4R3.10/dg-webo-v1) id AA02049; Mon, 19 May 1997 13:40:42 -0400 Received: (from root@localhost) by gomoku.ronin.com (8.6.9/8.6.9) id MAA14546 for navigation-outgoing; Mon, 19 May 1997 12:27:54 -0400 Received: from dub-img-3.compuserve.com (dub-img-3.compuserve.com [149.174.206.133]) by gomoku.ronin.com (8.6.9/8.6.9) with ESMTP id MAA14535 for; Mon, 19 May 1997 12:27:44 -0400 Received: by dub-img-3.compuserve.com (8.6.10/5.950515) id MAA10674; Mon, 19 May 1997 12:27:11 -0400 Date: Mon, 19 May 1997 12:23:36 -0400 From: Pierre H Boucher Subject: [Nml] GPS Satellites Not 2000 Compliant? To: "(inconnu)" Message-Id: <199705191223_MC2-16E1-6F1A@compuserve.com> Sender: owner-navigation@gomoku.ronin.com Precedence: bulk Reply-To: Pierre H Boucher Errors-To: owner-majordomo@RONIN.COM Content-Type: binary Content-Length: 2261 David Deratzian wrote : >Has anyone heard that the GPS satellites are not year 2000 compliant? >This was suggested to me recently. Anyone know if it is true? The following was a Notice to Mariners issued by the CCG L3182/96 LAURANTIAN REGION GPS SYSTEM TIME ROLLOVER WARNING TO THE USER GPS system time will roll over at midnight 21-22 August 1999. In fact, GPS accounts for time using a Week Number and the number of seconds in that week. It counts weeks using a starting point of midnight (0000) on the evening of 5 january 1980/ morning of 6 january 1980 (UTC), and has increase its count by 1 for each week since then. Both week and seconds are broadcast as part of GPS message provided by satellites and are used by receivers in their computations. The GPS Week Number field message can only provide for numbers up to 1024 wich means that, at completion of week 1023, the Week Number will roll over from 1023 back to 0: Week beginning at midnight (0000) on : GPS Week Number satellites broadcast : 08 August 1999 1022 15 August 1999 1023 22 August 1999 0 29 August 1999 1 It will be the responsability of the user to account for this changeover, the satellites themselves will simply start broadcasting the new Week Number. How it will affect your particular GPS unit will depend on what brand and model of receiver you have. Some receivers may merely display inaccurate date information, but other may also calculate incorrect navigation solutions or might stop providing positions. If the roll over hasn�t been taken into account during the conception of your GPS receiver, the unit might have problems. Some units will require a software update. Mariners should ask the manufacturer or distributor of the receiver wheter this change will affect their equipment. ------------------------------------------------- Pierre Boucher N CPS code 16-32 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-= =-= TO UNSUBSCRIBE, send this message to majordomo@ronin.com: =-= =-= navigation =-= =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=