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/MOTION - Leap Second Advisory Note

MOTION - Leap Second Advisory Note

The advisory note describes the forthcoming introduction of the next leap second which occurs on the 31st December 2016.

UTC background

Historically, time was defined in terms of the rotation of the Earth, known as mean solar time. The reason for using leap seconds is that we currently measure time with stable atomic clocks but the rotation of the Earth has been slowing down. Therefore the time measured by the rotation of the earth has been accumulating a delay with respect to atomic time standards. UTC (Coordinated Universal Time) is measured by atomic clocks, and kept synchronised with mean solar time by introducing a leap second whenever necessary.

The GPS epoch was January 6 1980 and was synchronised to UTC. GPS time is a ‘pure’ atomic time scale that is not adjusted to account for leap seconds. At the time of writing, GPS time was ahead of UTC by 16 seconds.

In order to relate GPS time to UTC, a set of UTC corrections are available from every tracked satellite as part of the navigation message broadcast. For continuously tracked satellites, it will take a minimum of 12.5 minutes to gather an updated data set. This includes the current leap second time difference between GPS time and UTC, as well as information on pending leap seconds.

The IERS has announced that the next leap second will be introduced on 31st December 2016.

MOTION Sensors

UTC correction parameters are maintained in memory, however this only includes UTC offset but does not include pending leap second information.

If the receiver is running continuously at least 12.5 minutes immediately before the impending leap second, at midnight on 31st December 2016, the leap second will be introduced to all outputs at midnight.

If the receiver is not running at midnight on 31st December it will update the UTC offset the next time it receives the UTC offset information, this may be up to 12.5 minutes after a cold start. Once the receiver has received the UTC offset information it will apply it after every cold start.

The MOTION Control software has been updated to apply the UTC offset to the display data even if the correct UTC offset has not yet been received. The MOTION Control version which has the leap second change is the current release V2.5 and can be downloaded from the Coda Octopus website.

The CodaOctopus F175, F180® and F180R series of receivers will not require a firmware update.

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If you have any further question on this, please contact our Support Team.

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