GeoBase in Action
GeoBase orthoimages: a Québec-wide result
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Figure 1: SPOT orthoimage coverage for Canada
Dissemination of free geospatial data via the GeoBase Web portal greatly facilitates territorial knowledge and development. This is particularly true for hard to reach remote areas. Orthoimages generated by the SPOT 4 and SPOT 5 satellites, covering over 95% of the Canadian landmass, are a useful and profitable source of information for organizations making use of geomatics and remote sensing. Where the various departments and agencies of the Québec government are concerned, such orthoimages represent a gold mine of information to help them accomplish their mandates, both current and future, in terms of managing Québec's natural resources and territory. Among the end uses for such imaging are:
- Updating hydro reservoir and forest cover mapping (forest fires, harvesting, epidemics);
- Preparing field trips for the mining and forestry sectors;
- Analyzing and interpreting satellite imaging for the mapping phase of the Ecological Reference Framework;
- Interpreting information on the structure and organization of topography, vegetation, geomorphology and hydrography.
The SPOT mosaic below covers the entire province of Québec. It was produced in 2011 for the Québec Department of Natural Resources and Wildlife (MRNF). It provides a global image of the province based on imaging taken from 2005 to 2010, depending on scenes. In the future, this data layer will enable comparisons in connection with potential changes to the landmass. This mosaic is routinely used as a base layer for the geomatics projects of the departments and agencies. In combination with other sources of existing geographical information (1:200,000 BDTQ data, 1:50,000 scale CanVec and NTDB data, Landsat imagery, etc.), it enables furthering geographical knowledge for purposes of landmass management as well as providing an overall view of Québec.
Figure 2: SPOT mosaic for the province of Québec
The mosaic is the product of integrating panchromatic and multispectral true-colour SPOT orthoimages. Enhancement is performed in two phases: radiometric calibration based on ecological regions as defined by the Québec Department of Sustainable Development, Environment and Parks, followed by application of a colour-enhancement filter. The resulting high-quality imaging has a spatial resolution of 10 metres. In total, 917 scenes (425 SPOT 4 and 492 SPOT 5) were used, with selection biased toward the more recent images, those without cloud or fog cover. In some instances, it was necessary to avoid snow-covered areas or frozen lakes which occur in northern Québec, for scenes captured in June or July. A file containing the forms that localize the boundaries of each scene and the relevant metadata is included in the mosaic.
Figure 3: Index of scenes for the province of Québec
Image processing and enhancement, as well as false-colour conversion processes were developed jointly with MRNF and Groupe Système Forêt.
Despite the size of the file (9 Gigabytes), the new image-compression formats and processes (ECW, MrSID, JPG2000, etc.) enable use of large files without loss of efficiency in refresh times, which are of the order of one second. Such technological advances facilitate simplified use and management of matrix-based spatial data, such as the SPOT mosaic, which would not have been as easy a few years ago.
Figure 4: SPOT mosaic for Montréal Region