Application of Vertical GPS Positioning on Shipboard

On 2 May 2000 (04:07, UTC), GPS users in single point positioning mode faced a new era of the system, without the application of S/A (Selective Availability). This was due to the change of the US Government policy on the application of the GPS after the IOC (Initial Operational Capability) declaration on 8 December 1993. Deregulation of GPS was brought forward 6 years ahead the initially planned date of year 2006. Deregulation of S/A has improved the accuracy of single point posi­ tioning considerably. Accordingly, the three-days measurement from 21 to 23 July 2000, at the Tokyo site, using a MX9112 GPS receiver, and an elevation mask of 5 degrees, showed a deviation of 10.7 m (2drms, 95 per cent).