Germany-based navigation specialist ChartWorld has taken advantage of bathymetry derived from multi-spectral satellite imagery to detect thousands of underwater objects. This information has been used to make hidden shoals visible to mariners and to transform what was a pilot project into a Global Service.
The accuracy of depth information in navigational charts can vary. Its quality depends on the age and accuracy of individual surveys. Remote areas tend to be surveyed less well and less frequently.
Mariners must take Category Zone of Confidence (CATZOC) into account when planning routes and when vessels are sailing with ECDIS/ENCs. An ECDIS displays CATZOC values assigned to geographical areas to indicate whether data meets a minimum set of criteria for position, depth accuracy and seafloor coverage. The Zone of Confidence (ZOC) value is dependent on the positional and depth accuracy of the survey.
By understanding the accuracy limitations of the underlying data in greater detail, the mariner can manage the level of risk when navigating in a particular area.But in recent years, several cases have been reported in which taking too little regard of CATZOC has contributed to groundings.
In the area researched (South-East Asia), during the pilot project conducted by ChartWorld and EOMAP (Earth Observations and Environmental Services, www.eomap.com), 4,724 shoals were detected. Out of 381 isolated dangers marked in ENCs, only 92 were able to be matched – others are potentially at another location.
ChartWorld has used the data to introduce a StayAway Service, integrated into CW’s Chart Information Overlay, CIO+. The overlay shows the real extent of underwater features, rather than showing them as points in ECDIS data. The service can be implemented for route planning and for ECDIS-alert functions, marked as “StayAway areas” that must be avoided.
So far, the StayAway service is available for two regions – the Caribbean and South-East Asia. Technical feasibility (water clarity) for other regions, such as the South Pacific, is currently being analysed. Other criteria are low CATZOC classification and the level of vessel-traffic density.