NASA scientists have developed an amazing stopwatch which can measure a fraction of a billionth of a second. This would be wonderful as it can precisely measure heights of glaciers, forests, sea ice and rest of the surfaces of the Earth.
The engineers at NASA’s Goddard Space Flight Centre in the US built the timer for the Ice, Cloud and land Elevation Satellite-2 (ICESat-2). This will be launched in 2018 and the new timer will use six green laser beams to measure height.
With the help of this stopwatch’s precise time measurements, scientists can calculate the distance between the satellite and the Earth below and from there scientists will manage to record the exact height measurements of the surfaces of the planet.
ICESat-2’s deputy project scientist, Tom Neumann said, “Light moves really, really fast, and if you’re going to use it to measure something to a couple of centimetres, you’d better have a really, really good clock.”
If the stopwatch kept time even to a highly accurate millionth of a second, the ICESat-2 could only measure elevation to within about 500 feet. Scientists would not be able to tell the top of a five-story building from the bottom.
That does not cut it when the goal is to record even subtle changes as ice sheets melt or sea ice thins.
To reach the needed precision of a fraction of a billionth of a second, engineers had to build their own series of clocks on the satellite’s instrument, the Advanced Topographic Laser Altimeter System or ATLAS.
The stopwatch depends on the laser pulse, where out of many photons some are assigned to start the pulse detector triggering the timer.
Researchers will measure heights to within about two inches because of this time accuracy. Deputy instrument system engineer with the ATLAS instrument, Phil Luers said, “Calculating the elevation of the ice is all about time of flight.”
ATLAS pulses beams of laser light to the ground and records the expected time of returning photons. Actually, photons from the Mount Everest will come sooner than the Death Valley as the distance is less from the Mt. Everest.
When combined with the speed of light, it tells researchers how far the laser light travelled. This flight distance, combined with the knowledge of exactly where the satellite is in space, tells researchers the height of Earth’s surface below.
The clock comprising a GPS receiver which counts each seconds giving information about satellite time and an ultrastable oscillator that in fact divides and counts 10 nanoseconds in each GPS-derived second. Then those 10 seconds are divided to reach hundred picoseconds measurement.
Inputs taken from PTI