Coastal Surveying of Depths with EGNOS to Enhance Charts

The accuracy of nautical charts is highly dependent upon accurate surveys being carried out, and as the sea bed is often soft sand or mud that moves with time, these need to be repeated periodically.

Unfortunately hydrographic offices are generally tasked to concentrate on the main routes for large commercial shipping, and have limited budgets, which mean that many coastal areas that are frequented by leisure and small commercial craft are inadequately surveyed.

This results in a greater likelihood of damage to vessels, injuries and pollution due to vessels going aground. The lack of up-to-date survey data also impacts other areas, such as the monitoring of silting or movements of the sea bed and the availability of data for engineering projects, such as outfalls, or offshore tidal or wind energy schemes. Although surveys can be specially commissioned for engineering activities such as these, this is a very expensive process, and the costs are often hard to justify, especially early on in the project when multiple possible sites may be being examined.

Description 

A key part of the project is in recruiting the data loggers. To help with this, a consumer brand, TeamSurv, is being developed to attract and enrol loggers in the trial areas in the UK, France and Lithuania (see www.teamsurv.eu). They will be able to log data either by using software on their computer, or a hardware logger will write data to a USB memory stick, and then once ashore uploads the logged data to the project servers via the Internet.

The logged data is collated into the server, where it is processed to correct for height of sea level and other corrections. The complete data set is then processed to produce the final survey data - first of all carrying out an error analysis to assess the quality of each data item, and then combining them into a model of the sea bed.

Both the use of crowd sourcing for marine charts and the processing of the data logged are innovative aspects of the project. In addition, a quantitative analysis of the benefits of EGNOS to positioning in the marine sector will be obtained, compared against both differential and unassisted GPS.

The resultant data can be viewed on the web, rendered via a Web Map Server, and it should also be available in a number of formats such as S-57 and S-100, ISO 19100, and through the INSPIRE directive.

Objectives

CoSuDEC brings together a number of developments to overcome the paucity of data and the high costs of commissioning custom surveys. First, with the enhancements to GPS accuracy, especially when augmented with the use of EGNOS, positional accuracy of a general navigation GPS is adequate for IHO (International Hydrographic Organisation) Level 1 surveys for harbours and coastal areas. Secondly, crowd sourcing can be used by getting the many leisure and workboats in an area to log data that can be then collated and processed. By combining data from a large number of vessels, it can be treated statistically to remove any rogue readings, and generally to enhance the accuracy of the depth readings, so again Level 1 standards can be achieved.

This will allow cost-effective gathering of data that can then be processed to provide input to downstream users such as chart publishers or GIS users, as well as being made available to the data loggers themselves to recompense them for their efforts.