It is probable that Congress will require oceangoing ships in US ports to use Differential GPS (DGPS) and electronic charts once DGPS is available on all coasts of the US, which is currently scheduled for completion by the end of 1996. The type of electronic chart currently envisaged, the Electronic Chart Display and Information System (ECDIS) under development by the IMO & IHO, is unsuitable for those ports which are entered through long dredged channels – a category that includes Houston, Gramercy and New Orleans, the three ports which handled the most foreign tonnage in 1991. A different type of electronic chart has been in daily use in such channels, with microwave positioning, since 1984; the combination of DGPS with such a software package has been called an Electronic Navigation System (ENS) and differs from ECDIS in that the ENS is designed to supplement the published chart, not replace it. The paper suggests that the utility of ECDIS would be enhanced if its specifications were modified to allow the entry of the data files used by the ENS, thus giving ECDIS a similar capability for blind navigation in confined waters. Standardization of the current data format would also permit alternative versions of ENS to be developed.

Civil aviation authorities have a requirement for the application of devices which are capable of determining the geometric height of aircraft above flight level 290 with a high degree of precision. These devices, called height monitoring units (HMUS), should pave the way for a safe and expeditious introduction of reduced vertical separation of 1000 ft above flight level 290.

In this paper the design philosophy as well as the prototype development of such a device, which is called the dual-synchronized autonomous monitoring system (DAMS), are outlined. This device operates fully independently of any airborne equipment such as secondary surveillance radar transponders.

The configuration basically consists of two standard marine radars with both axes of revolution situated in a horizontal plane. With this configuration it is possible to determine the trajectory of an aircraft and, in particular, the geometrical height above ground level within typical radar slant range coverage of some 18 km. The basic application of this equipment will be in the field of height monitoring of aircraft targets in environments with reduced vertical separation standards of 1000 ft above flight level 290, but a wider application of this concept is foreseen for local precision tracking of aircraft targets.

The ship domain is a very important and useful concept in marine traffic engineering. It has been widely used in traffic simulation models, for encounter criteria, traffic lane design criteria, VTS planning, risk assessment, collision avoidance, and for other applications.

Dr Y. Fujii, Dr E. M. Goodwin and Dr T. G. Coldwell have done a lot of work on this subject. The differences between their ship domain concepts are described in the second part of this paper. In the third part, the authors have used a new branch of social psychology – the theory of Proxemics – to analyse the factors which affect the ship domain, and point out that the basis of producing ship domains is in the field of Proxemics. Finally, in the fourth part of this paper, some problems in ship domains are analysed.

The Global Positioning System (GPS) is a cheap, accurate (±100 m), satellite-based position fixing system. These qualities suggest that it might be used in the identification of marine radar targets. The first application of such a system on any scale will probably be as part of a Vessel Traffic Service (VTS) and here GPS would seem to be ideally suited. Vessels entering the VTS control zone would need to be fitted with GPS interfaced with either a dedicated VHF receiver or a ‘guard’ channel on their normal receiver A VTS radar operator needing to identify an echo would work out the echo's position from the radar range and bearing and transmit that position as the interrogating signal. Only the vessel in the control zone with that position (derived from its GPS interface) would respond with its identity. There would thus be no possibility of interference between responses or garbling that can be a problem in interrogation systems based on secondary radar. Even if the VTS had several radars, these could easily be synchronized to prevent simultaneous interrogations. However, outside VTS zones there is a clear need for a universal identification system that would allow any ship to identify any other. It would be unfortunate and wasteful if a system developed for VTS was found to be unsuitable for this general application. This note will therefore discuss the adequacy of GPS as the basis of a universal marine identification system.

There was an error in Mr Richard Trim's paper, ‘Some causes of problems in the observation of standard racon marine beacons when observed by means of standard marine navigation radars’, which was published in the May 1993 issue of the Journal of Navigation. Section 3, paragraph 4 of page 276 should read:

‘A third and very important cause of radar received-signal differentiation arises if a widely used form of automatic anti-sea-clutter processing is employed, since part of this processing is to differentiate the radar-received video so as to remove the d.c. term in the sea clutter echoes as part of the Constant False Alarm Rate (CFAR) processing. When such automatic sea clutter supression facilities are in operation, the gain level applied to the radar receiver video amplifier has an adaptive signal superimposed upon it which, while slow acting, generally follows the shape of the clutter returns on the received signal video, while being largely unaffected by the wanted echo returns such as those from ships, navigation marks, coastlines, etc. This effect may be reduced in the case of the very latest radar designs’.