How We Do It
CHS has channelled its in-depth knowledge and extensive expertise into the development of new technologies and scientific procedures – today offering everything from three-dimensional views of Canada’s seabeds to real-time updates on water levels in the St. Lawrence River.
How we develop our nautical charts
We’ve come a long way from our hydrographers lowering lead lines – lead weights attached to a line – into the water to measure its depth. This slow method, which could not provide continuous, gap-free coverage of the water bottom, has given way to the echo-sounder which measures depths by bouncing sound waves off the seabed. By measuring the length of time it takes for the echo to return, hydrographers can calculate the distance to the sea bottom.
Surveys done this way follow pre-planned lines along which the surveying vessel steers. How closely the lines are spaced depends on the complexity of the seabed. In hazardous waters, complete coverage of the bottom is required.
Hydrographers must know exactly where the vessel is when each sounding is made in order to indicate depths at the correct locations on charts. In the past, the main tool for determining the vessel's position was a hand-held instrument called a “sextant” which was used to measure angles. The sextant has largely been replaced with the tools of our modern age - computers, satellites, multibeam acoustics, and electronic charts.
A significant advance in determining a ship’s position is the Global Positioning System (GPS) which allowed us to achieve an accuracy of plus or minus 20 metres (95% of the time). The differential GPS (DPS) has since allowed CHS to achieve an even greater accuracy of plus or minus three metres.
Along with water depths, our hydrographers also measure tides and other changes in water level. CHS has installed permanent water-level gauges along Canada's coasts and larger inland waterways to monitor tidal- and water-level data. Two CHS gauges on the West Coast are part of an international warning system for tsunamis – dangerous ocean or tidal waves triggered by earthquakes or seabed eruptions.
CHS hydrographers also obtain the positions of all buoys, lighthouses, and other fixed or floating navigational aids as well as the position of landmarks, natural or man-made, which mariners use as reference points.
When the survey work is completed, our multidisciplinary hydrographers combine the measurements with shoreline and other topographical data, changing them to the required scale for a navigational chart. From this mass of material, the information most critical to safe navigation is selected and enhanced and CHS charts are created, in both digital and paper formats.
Navigation in the digital era
With the addition of Electronic Navigational Charts (ENCs) and raster electronic charts to its library, CHS has tripled the size of its traditional product line. Burned to CD-ROMs, these ENCs run on onboard computers and allow for onscreen navigation. A pioneer in this area, Canada has one of the largest ENC portfolios in the world.
Electronic charts have the potential to provide more information than their paper cousins. For example, they can reveal multi-dimensional views of waterways, showing the shape and the depth of the lake or sea floor and revealing alternative points of view. They can even capture relatively small-scale attributes such as the height, length, age and ownership of a specific wharf – at the click of a computer mouse.When combined with GPS, radar, ship course, speed and draft in an Electronic Chart Display and Information System (ECDIS), the Electronic Navigational Chart (ENC) becomes part of a powerful system that allows mariners to know their ship’s position instantly and accurately and to be warned of dangerous situations. The magnitude and demands of today's ships have made accurate and timely hydrographic information more vital than ever.
'Seeing' into the oceans (multibeam systems)
Canada is a world-renowned leader in multibeam systems modeling technologies. Oceans modeling and remote sensing provide multidimensional, real-time information about water, sea floor, coastal and bank conditions in waterways such as the St. Lawrence River.
Multibeam imagery allows fishers to view the seabed and target specific species. This is important for environmental reasons – for example, scallop fishers can reduce the area of seabed they disturb with their rakes since they know which seabeds are most likely to contain scallops.
The ability of multibeam systems to produce an aerial photograph-like image of the seabed has led to a demand for multibeam mapping to support other applications such as mapping pipeline and cable routes, proposed marine protected areas, and fishing grounds.
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