The data collected by the CCGS Amundsen (and other platforms) is presented in the form of basemaps, with each map covering 15' of latitude and 30' of longitude. Data are gridded at a resolution of 10 metres. For perusal via the web portal, images are created in which depths are colour coded (based on the range of depths in the mapsheets) and the terrain is sun-illuminated. Grid files are available for download in ESRI grid format (.flt and .hdr files for each mapsheet, downloaded as a zipped .tgz archive file).
Map Projection
A Lambert Conformal Conic projection (with two standard parallels) is used for the ArcticNet Basemap series of mapsheets. In order to minimize distortion in the areas of most interest, the standard parallels were specifically chosen to follow the two major east-west channels through the Northwest Passage (Parry Channel and Queen Maud/Coronation Gulf). The projection parameters are as follows:
1st Standard parallel: 70°
2nd Standard parallel: 73°
Origin latitude: 70°
Origin longitude: -105°
False easting: 2,000,000 metres
False northing: 2,000,000 metres
Datums
Horizontal datum: WGS84 (G1150)
Vertical datum: soundings are reduced to mean sea level (MSL) using the WebTide tidal prediction models.
Misc. Processing Details
Since time is at a premium while underway, there are often cases where long transits are undertaken with little or no sound speed profiles collected. On the other hand, some oceanographic sections sampled by the Amundsen provide very dense sound speed information throughout the watercolumn. In sections where the watercolumn is poorly sampled, the 1/4 ° World Ocean Atlas (2001) climatology is used as a source of sound speed.
