Positioning technologies

GPS

The U.S.-based Global Positioning System (GPS) is the most widely known satellite-based positioning system. Many people have their own GPS receiver in their car, in their boat—even on their smart phone. In the 1980s, a GPS receiver consisted of a large box, a separate antenna and source of power (e.g. batteries with solar panels). Today, a GPS wristwatch is hardly bigger than a regular wristwatch.

CHS uses a much more sophisticated version of the GPS than you find on your smartphone. It positions CHS vessels, both horizontally and vertically, to within a few centimetres, depending on which of the following technologies are used.

DGPS

Differential GPS, or DGPS, corrects errors that are inherent in the satellite broadcast GPS signal. In the marine environment, local-area DGPS corrections are broadcast from CCG radio beacons in most regions of the country. This technology isn’t available in the Arctic—yet.

SBAS

Differential GPS corrections may also be available over a wide area, called wide-area DGPS. One system that provides these corrections around the globe is the satellite-based augmentation system (SBAS). In Canada, the United States and Mexico, the SBAS, which was originally designed for air traffic use, is called a wide-area augmentation system.

Glonass

Russia has developed Glonass , the only system close to the capabilities of the GPS—so far. China, India and the European Union are all developing their own systems.

While Glonass may be seen as a competitor to GPS, in fact, the two complement each other. CHS has been upgrading GPS receivers to be fully Glonass compliant. This gives us an additional constellation of 24 positioning satellites. Access to more satellites means greater positioning reliability, especially in remote areas, like the Arctic.

GNSS

The suite of satellite-based positioning systems, together with the SBAS, is considered the global navigation satellite system.

RTK

RTK stands for real-time kinematic positioning. The position information is available at the time of collection (in real time) and the vessel is in motion (kinematic). Having the precise position of all measurements is critical for CHS navigational products. DGPS allows CHS to have real-time positioning within a few metres, or in ideal cases somewhat less than one metre.

But there are occasions when better positioning is needed—within 10 centimetres or even one to two centimetres, particularly in the vertical dimension. This type of precision can be achieved only by using sophisticated techniques—making measurements on the GPS carrier phase signal. To get this precision in real time, measurements must also be taken at a local shore-based GPS station (a reference station) and transmitted via radio modem to the vessel as it is collecting data.