Survey platforms

Survey platforms used by the Canadian Hydrographic Service (CHS) include:

• surface vessels
• underwater vehicles
• aircraft
• satellites

Motion sensors are used to refine the data aquired.

Surface vessels

Surface vessels (ships, boats or launches) are the most common survey platforms used by CHS. Most of these vessels are owned and operated by the Canadian Coast Guard (CCG), but CHS owns some smaller vessels.

Underwater vehicles

Underwater vehicles are used in areas where surface vessels would be inefficient, unsafe or incapable of collecting good data. These vehicles may be semi-autonomous or may be completely autonomous. CHS uses remotely operated vehicles (ROVs), remotely operated from a ship via a tether, and autonomous underwater vehicles (AUVs) for the under-ice work that supports Canada’s UNCLOS claim. However, CHS still considers these vehicles developmental for routine data acquisition operations.

Aircraft

Aircraft—both airplanes and helicopters—are generally used to take CHS personnel to remote locations to install or service equipment. They can also be used for rapid bathymetry (depth) or topography (height) surveys, using light detection and ranging (lidar) equipment. Aircraft can cover large areas quickly and provide a safe alternative to small boats in rock-strewn waters exposed to ocean swells, However, both the aircraft and lidar equipment are expensive. These technologies provide the best possible interpretation of the high-water line and low-water line, the shape and nature of the foreshore, the shallow depths of the nearshore, and the low elevation heights of the near-shore. Some information is used to update charts, but it may also be used to identify key nearshore habitats, to assist in planning for spill response, as well as modelling for tsunami and storm surge responses.

Satellites

Satellites can also provide imagery or sea-surface height information that is useful to CHS. A satellite’s ability to revisit the same area repeatedly makes it useful in verifying recent changes, particularly to the shoreline—such as harbours—in areas of ongoing development.

Many satellites provide imagery or height data with high spatial resolution (small ground footprint or pixel size), broad spectral resolution (many frequency bands, which allows better discrimination of foreshore type and better ability to see into clear water) and good temporal resolution (frequent revisits, for example, to check on construction status of proposed facilities). All of these characteristics can be useful for CHS work in improving shoreline and offshore tidal modelling. Satellites that don’t rely on visual data (i.e., those that use radar) are useful for imaging shoreline areas through cloud cover or at night. This can be very useful for shoreline images at a particular stage of the tide. RadarSat II and TOPEX Poseidon are some of the satellites used by CHS, as well as other commercial satellites.

Inferring depths from satellite altimetry
The oceans cover about 71 percent of the Earth’s surface. Mapping these oceans using echosounders will take many centuries. In the deep ocean, it is possible to infer the depth of water by looking at the topography of the sea surface using satellite altimetry.

Motion sensors

Motion sensors measure all the motions of the sonar during transmission of each ping and receipt of each beam acquired from multibeam sonars. Hydrographers use these measurements to further refine the depth data.

Motion sensors are used for measuring roll, pitch, heave and heading. Inertial sensors measure accelerations and are used to determine spatial displacements, that is, heave, surge and sway. Gyroscopes measure angular rotations, for example, as a source of heading with respect to true north. These sensors are arranged in triads: that is orthogonal (at right angles) to each other in a 3-D reference frame, such as x, y and z axes.