Improving accuracy of global positioning

Global satellite positioning systems suffer from radio beam ‘bending’ errors due to localised weather conditions (e.g. water vapour). Current techniques reduce errors from weather conditions from 30m to less than 1m. High accuracy applications, such as surveying, require that accuracy be improved even further to below 1cm.

The patented (WO 2004/095055) technology provides tropospheric delay correction values for use in GPS receivers to improve their accuracy. The system reduces the impact of these short-term delay values by updating the prior tropospheric delay zenith values (ZTD) within the GPS receivers with correction data derived from Numerical Weather Predictions (NWPs), produced by weather forecasting service providers. The ZTD correction values can be compressed and transmitted to the GPS satellite constellations using a novel (and simple) grey-scale image (JPEG2000) technique, covering the regional weather variations, on a global basis. These only require a small upward link (to the satellite) at a transmission data rate in the range of 25-500 bits/sec.