Leap Second effect on Topcon GNSS Products - December 31, 2016

Leap Second effect on Topcon GNSS Products, and how to prepare for the event. 

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Leap Second effect on Topcon GNSS Products - December 31, 2016

International Earth Rotation and Reference Systems Service (IERS) announced there will be an extra second added to the end of this year, so clocks will read 23:59:60 on December 31, 2016. Such leap seconds are occasionally needed to ensure Coordinated Universal Time (UTC), the official measure of time, stays in sync with changes in the Earth’s rotation.  Additional details can be found here.

We have been working hard to provide a firmware solution assuring Topcon receivers are not impacted.  Without this firmware update users may experience issues acquiring or sustaining a fixed solution.  In some cases position solution may resolve itself after a new almanac & ephemeris are downloaded however we strongly recommend you provide your customers a firmware update.

This leap second addition is global, effecting all GNSS receivers and should be addressed as quickly as possible.  Please take the time to download the latest firmware for your GNSS receivers, by registering your receivers to activate the Firmware Download button on their respective product page(s).   

Firmware fix available for the following GNSS Receivers:

Firmware fix available for the following GNSS Boards:

Details of the upcoming event:

  • A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) in order to keep its time of day close to the mean solar time, or UT1. Without such a correction, time reckoned by Earth's rotation drifts away from atomic time because of irregularities in the Earth's rate of rotation.
  • Global Positioning System (GPS) time, is the atomic time scale implemented by the atomic clocks in the GPS ground control stations and the GPS satellites themselves. GPS time was zero at 0h 6-Jan-1980 and since it is not perturbed by leap seconds GPS is now ahead of UTC by 17 seconds.
  • The GPS constellation shares the same time scale with Galileo, BeiDou and QZSS constellations.
  • The GLONASS constellation is the only GNSS constellation that is synced with UTC time (UTC +3 hours – Moscow Time).  As a result, when GPS (or any other constellation) is used in combination with GLONASS the leap second correction is used to reference GPS and GLONASS data to the same time scale.
  • Upcoming leap seconds are typically announced months in advance by the International Earth Rotation and Reference System Service (IERS) in Paris, France, and the next leap second will be inserted on December 31, 2016, at 23:59:60 UTC.

GPS Navigation Message Update

  • Since GPS  time is continuous, and does not synchronize with UTC, a leap second correction is broadcasted by the satellites within the navigation message, and as of Jan 1, 2017, the updated message will broadcast as follows:


Before the leap second

GPS-UTC = +17s (i.e., GPS is ahead of UTC by seventeen seconds)


After the leap second

GPS-UTC = +18s (i.e., GPS is ahead of UTC by eighteen seconds)


GPS Almanac Update

  • GPS satellites also broadcast the following leap second information in their ALMANAC:
    • Current leap second correction
    • Future leap second correction
    • Date that the future leap second correction will be valid
  • The updated navigation messages and ALMANAC ensure that systems relying on GNSS timing information remain up to date with the latest UTC time.


Firmware Update Required for Topcon Receivers

  • Topcon’s GNSS firmware versions 4.7p2 and 5.1 have been modified to correctly interpret the updated messages and ALMANAC, in order to apply the leap second, precisely at 23:59:60 UTC on 31st December 2016.
  • Firmware versions 4.7p2 and 5.1 were tested with data recorded from previous leap second events, to verify that the improvements made properly manage the leap second event. 


For uninterrupted operation, the following steps are required ahead of the leap second rollover:

  • Install firmware version 4.7p2 or 5.1 (depending on your receiver model) as listed above


  • If receiver has been operating for less than 24 hours, update the Receiver ALMANAC:
    • Use TRU to Clear NVRAM1 by selecting Factory Reset in the Tools menu, (or alternatively sending the GRIL command ‘init,/dev/nvm/a’)
    • Allow receiver to operate without interruption for 20 minutes
    • Reconfigure receiver for its intended use

1The Clear NVRAM operation will return all receiver parameters to their default values.  Almanacs and ephemeris data will be erased.  This operation does not delete any raw data files stored in the receiver’s memory.

What if I cannot update the firmware?

  • The following information and instructions pertain to both base and rover receivers.
  • As of January 1, 2017, the receiver(s) will not operate properly if GLONASS is enabled
  • To operate using GPS only, DISABLE GLONASS tracking and positioning on the receiver(s).
  • If the receiver does not have an updated almanac after the event, and you are experiencing positioning degradation, update the receiver ALMANAC as follows:
    • Use TRU to clear NVRAM by selecting Factory Reset in the Tools menu
    • Allow receiver to operate without interruption for 20 minutes
    • Reconfigure receiver for its intended use
  • Once the ALMANAC has been updated, on January 2, 2017 GLONASS can be re-enabled.

Most common symptoms if firmware is not updated:

  • Users may observe continuous float, standalone or invalid solutions.  Users may see larger than normal fluctuations in position.
  • Real time correction output may be adversely affected for base receivers. This will impact any rover receivers using affected correction data and their ability to compute or maintain a continuous fixed position; even if the rover’s firmware has been updated. 
  • Raw data will not be affected by the leap second event, however:
    • GLONASS data may be offset by 1 second
    • RINEX output files may include incorrect leap second offset values.
  • Removal of GLONASS data from position computations, in both real time and post-processing, will resolve issues.  GLONASS can be re-enabled on January 2, 2017.

How long will symptoms persist?

  • If a receiver has been updated to firmware 4.7p2 or 5.1 and an up to date almanac has been downloaded, receivers will work without interruption during the leap second event.  This is typical for receivers that are: 
    • In continuous operation
    • Turned on for 24 hours prior to the event to download a new almanac without user intervention
    • Turned on prior to the event and forced to download a new almanac through a Clear NVRAM/Factory Reset operation.
  • If a receiver has been updated to firmware 4.7p2 or 5.1 but a recent almanac has not been downloaded prior to the event, users may observe symptoms for a short period of time.  This will be resolved once a new almanac is downloaded.
    • Approximately 20-30 minutes after a Clear NVRAM/Factory Reset is performed.   
    • If a Clear NVRAM is not performed, almanac data should update itself approximately 4 hours after the event.
  • If a receiver has not be updated to firmware 4.7p2 or 5.1, symptoms may persist for up to 24 hours after the leap second event.   Receivers should correct themselves and return to normal operations on January 2, 2017.  Users may improve receiver performance with the following actions:
    • Update the receivers almanac
    • Turn off GLONASS in positioning

Additional Note:

If your GNSS product is not listed above, there is not a new version of firmware available to properly mitigate the upcoming leap second event. It is recommended that users collect an up to date almanac prior to the event and turn off GLONASS until January 2, 2017.