Japan working on centimetre-precision civil GPS system

Japan is working on a Quazi-Zenith Satellite System (QZSS) that will work in conjunction with US GPS satellites to provide centimetre-precision location, timing and navigation services throughout the country.

GPS usability within built-up city areas, which can have lots of high-rise towers, is not always the best due to shadowing and blocking of the satellite signals. The QZSS will help overcome these drawbacks by providing an extra measure of precision.

The first QZSS satellite, QZS-1, was launched in 2010. Three more are planned for launch by 2017, with a further three to be added in subsequent years to give a constellation of seven. The Japanese government is providing US$500 million for each satellite, plus US$1.2 billion for the ground segment, which will include 1200 reference stations.

Those reference stations, the positions of which will have been accurately surveyed, will receive signals from each satellite and send timings to a master control centre. The control centre will process the data to precisely fix the satellite’s position in space and then transmit the data back to the satellite, which will in turn broadcast its signals to the end users’ equipment.

And it clearly works. Tests with QZS-1 have returned average on-the-ground precision of 2.9 cm vertically and 1.3 cm horizontally.

The system will find use in mapping, mobile navigation, surveying, emergency services, farming and disaster management.