Borstad Associates Ltd. - CSA Outreach Test & Conditions

CSA Outreach Test & Conditions

Example Projects

It has been stated earlier that:

Satellite imagery can be obtained free of charge from a number of Canadian and U.S. web sites; and
Image products useful to the watershed manager can be produced without recourse to complex image analysis programs.

To test these two statements, a number of projects were undertaken to:

Acquire and print a satellite image of a southern Ontario watershed that looks like a colour air photograph and shows a level of detail equivalent to a 1:50,000 topographic map.
Overlay the image with various line maps, including catchment areas, streams, municipal boundaries, roads and, if it is feasible, to add highway numbers and stream names.
Acquire and print older satellite images from the early 1980’s, early 1990’s and compare them with the most recent image to illustrate changes in land use patterns throughout the watershed over the past 20 years.
If possible, make a three-dimensional model of the watershed that can be viewed from different angles on the computer.
Automatically calculate changes in the extent of built-up areas, agricultural land and in such natural features as forest cover.

The conditions under which the tasks were to be carried out included:

Sources for free data had to be used (if data had to be purchased, the source and cost was recorded)
Data sets had to be available for all of Canada (exceptions to be noted)
Georeferenced (i.e. spatially located) raster (e.g. satellite imagery) and vector (e.g. roads or streams) data sets had to be compatible with one another (e.g. map projections)
The programs used had to be commonly available (e.g. Jasc Paint Shop, Adobe PhotoShop, Corel PhotoPaint)
Where specialised programs (e.g. viewers capable of merging raster and vector data sets) were needed, an Internet search was made for freeware or the cheapest available software for each task were to be used (the price of all programs to be recorded)

To simplify the tasks, it was decided to concentrate on the use of imagery from the U.S. Landsat series. The sensor of interest, the Thematic Mapper (TM), is a multi-spectral scanning radiometer that was carried aboard Landsat-4 and subsequent satellites in the series. The TM sensor provides nearly continuous coverage from July 1982 to the present with a 16-day repeat cycle. The TM image consists of seven spectral bands with a spatial resolution of 30 m for bands 1 to 5 and 7. Resolution for the thermal infrared (band 6) is 120 m and for the panchromatic band 8 it is 15 m. The approximate scene size is 170 x 183 km. TM scenes available to the general public have undergone both radiometric and geometric correction, and a limited number of scenes have been further processed to using ground control points and corrected for parallax errors due to local topographic relief. The images available from the Canada Centre for Remote Sensing (CCRS) are displayed on a Universal Transverse Mercator (UTM) projection that is same as that used in the Canadian 1:50,000 topographic map series. The latest in the series is Landsat-7 that has an upgraded TM sensor, ETM+.

Landsat was designed for land cover mapping and the first satellite was launched in 1972, with Landsat-5 and –7 still operational today. The Canada Centre for Remote Sensing (CCRS), a branch of Natural Resources Canada, has received Landsat data for all of Canada since 1972 at its ground stations located in Cantley, Quebec and Prince Albert, Saskatchewan. Archived data now exist for most parts of Canada.

Among the possible con’s of using satellite imagery are the varying degrees of processing of the archived data. The most recent data have been geo-referenced (i.e. can be located on the Earth’s surface using a standard projection system such as UTM), and are in format that can be read using standard software, such as Jasc Paint Shop Pro or Corel Photo-paint. Older data have generally been corrected for the position and attitude of the satellite (Level 1G) and are in HDF format, but the results have not been correlated with ground control points with a known geographic position. Nevertheless, the positions of features are rarely out by more than 100 m. However, these older data sets require more specialised programs than Paint Shop or Photopaint.

“High speed” Internet connections with typical transfer rates of 116 KB/s were used to down load data from FTP sites. A single Landsat-7 band is about 55 MB and took about 6 minutes to download from GeoGratis. A CanImage 9.2 MB zipped file containing an RGB Landsat-7 image corresponding to a 1:50,000 NTS map area took about 1.5 minutes to down load.

Adobe SVG Viewer is a required plugin to the web based displays used in Projects 2 and 3. The browser will automatically recognize if this plugin is not already installed on the user's computer and prompt for the installation. The only input required from the user is to accept the installation and download everything else is automatic.