and reliability, the future application of these for providing feedback
in real time can yield important advances in terms of safety and efficiency.
However, new and more sophisticated developments can give rise to new
and more sophisticated forms of error. Similarly, new computational algorithms may yield
errors with a low probability of occurrence and may go undetected unless a redundancy of
data sources is available, and are monitored. In many ways, the mariner's skill must
therefore proceed into the realm of quantitative evaluation in addition to the qualitative
evaluation to which mariners are accustomed. This has implications for the way in which we
train the mariner of the future.
The possibility of large errors from GPS in occasional circumstances
also raises the important question of whether a redundant position source is needed,
particularly in the vicinity of ports and harbours where position accuracy is on the one
hand critical, and on the other is compromised by the nature of the environment. To be
usuable it needs to have accuracies approaching those provided by the GPS system.
References
1. Mueller T., Loomis P., Sheynblatt U., "Wide Area DGPS Design
Issues Study", United States Coast Guard, 1995, p.44.
2. ibid.
3. Ackroyd N., Lorimer R., "Global Navigation", LLoyds,
London 1994, p.25.
4. Ashkenazi, V. et al "Wide Area Differential GPS: A performance
study", Journal of the Institute of Navigation, Vol.40 No.3, 1993, pp.297-319.
5. Ackroyd N., Lorimer R., "Global Navigation", LLoyds,
London 1994, p.145.
