Leap Second - What, Why?
As you celebrate the end of 2016 and the clock counts down this year New Year’s Eve – you’ll need to add one more second. International Earth Rotation and Reference System Service (ERS) 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. These leap seconds are occasionally needed to ensure Coordinated University Time (UTC), the official measure of time, stays in sync with changes in the Earth’s rotation.
UTC or Universal Coordinated Time is the combination of Universal Time (UT1) and International Atomic Time (TAI – in French – Time Atomic International – The Standards Bureau is in Paris, France).
UT1 (Universal Time), also known as Astronomical Time - is the time it takes for the Earth to rotate on its own axis. It is easy to come to the conclusion that the Earth’s rotation is constant. However, it actually fluctuates slightly due to a variety of reasons such as wind, the friction of tidal currents flowing along the bottom of the oceans, ocean currents in general, and the motions of the Earth’s fluid core. Currently, the length of a day is about 2 milliseconds (two one-thousandths of a second [0.002 of a sec or 2 milliseconds] in 200 years) longer than it was in the early 1800’s.
Who or what cares? GNSS systems care about UTC - because they use timing to calculate position.
The UT1 part of the UTC solution loses about 2 seconds per 1000 days in relation to the TAI.
International Atomic Time (TAI) is the second element of the UTC. TAI is the output of 200 highly precise [0.000000001 seconds – (known as a nanosecond) per day] atomic clocks worldwide. These clocks are very precise, even more precise than the rotation time of the earth.
To keep the UTC within 0.9 seconds of the UT1 - leap seconds are periodically added to the UTC. There have been 25 leap seconds added to the UTC since the current system began in 1972. They are applied on either June 30th or December 31st.
What does this mean for TOPCON GNSS Users?
Several of these leap seconds have occurred since Topcon has been utilizing GNSS for positioning solutions. Currently, Topcon has firmware upgrades available for the current GNSS receivers. However, many of the older units will not get a firmware upgrade for the upcoming leap second.
How will this affect your operation?
- It may cause you to have to clear the NVRAM on January 1st.
- It might take a bit longer to initialize.
- There might be a few older receivers that this leap second will cause to become inoperable.
It is hard to predict since there is a very precise oscillator (clock) on the GNSS boards that uses the UTC time signal from the satellites. If this oscillator, or clock, is close to the limits - then this one-second change could push it over the limit of functionality. If so, your system will not be able to initialize.
Our Solutions Center and team of experts are available to answer any questions you may have related to the leap second. Contact us via email or phone (877-90-RDOIC).