Deep inside a concrete-filled pit just outside Munich, Germany, researchers are taking some of the best measurements ever of Earth鈥檚 motion. They are using huge, red lasers set 15 metres below Earth鈥檚 surface to get data that could help make GPS navigation more precise.
GPS uses measurements from satellites which have to be calibrated with measurements of Earth鈥檚 orientation in space, which is constantly changing. 鈥淚f we don鈥檛 measure it, our GPS location that we have in our car and our phone would be off by dozens of metres within a couple of weeks,鈥� says Heiner Igel at Ludwig Maximilian University in Munich.
Igel and his colleagues that can take faster and more precise measurements of the planet鈥檚 rotation and movement than other methods. The apparatus is made up of four so-called ring lasers. Each of these consists of two laser beams that shine in concrete vacuum tubes and travel in opposite directions around a triangular path.
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At each corner of the triangle, the beams are bounced in a new direction by 鈥渟upermirrors鈥�, which are far more reflective than any you would find in everyday life.
Without the planet鈥檚 rotation, the two opposing beams in each ring laser would match up exactly because they would each follow precisely the same path. But because Earth is rotating, that isn鈥檛 quite the case.
鈥淏y the time the light goes around at a speed of 300,000 kilometres per second, the mirrors have moved very, very slightly,鈥� says Igel. 鈥淭he light that goes in the same direction as the rotational motion has a slightly longer path because its mirror has moved away, and the beam that goes the other way around has a shorter path because its mirror moved towards it.鈥�
By measuring the differences between the two light beams in each of the ring lasers, the researchers reconstructed Earth鈥檚 movement extremely accurately. This will help improve navigation and could also be useful in understanding our own planet, its motion and its interior dynamics, Igel says.
