The Ontario Ministry of the Environment, Conservation and Parks (MECP) distributes pre-processed regional meteorological data and terrain data as required under Ontario Regulation 419/05. Data are hosted on the MECP website.
Recently, MECP updated their database to distribute Canadian Digital Elevation Model (CDEM) data in GeoTIFF format, replacing the old ASCII-text Digital Elevation Model (DEM) tiles.
MECP Meteorological & Terrain Data Website
AERMAP, the terrain preprocessor for the U.S. EPA’s AERMOD air dispersion modeling system, has long been able to read and process digital terrain data in GeoTIFF format. To process the new CDEM files, follow the steps below.
Step 1: After setting up the model objects in your AERMOD View project, open the Terrain Processor.
Step 2: Set the Map Type drop-down menu to NED GEOTIFF.
Step 3: Use the Add button to select the GeoTIFF terrain file(s) as downloaded from MECP’s website.
Step 4: Click  to execute AERMAP.
Step 5: When AERMAP finishes, identify which objects you wish to import elevations for (sources, receptors, and/or buildings) and click Import.
Note: GeoTIFF terrain files take longer to process than ASCII DEM files. This is because the terrain data is embedded into the GeoTIFF image and must first be extracted before it can be processed.
AERMOD View presents two options to address these longer processing times:
1. AERMAP MPI – Lakes’ parallelized version of the AERMAP model reduces runtimes by running on up to 8 processors simultaneously where the native AERMAP executable only runs on a single processor.
You can select AERMAP MPI via the Preferences menu. See Modeling Tip: Run AERMAP MPI for Faster Terrain Processing.
2. Reduce the domain read by AERMAP to save processing time. See Modeling Tip: Defining Domain in AERMAP.
When the User-Defined Domain option is set in the Terrain Processor’s AERMAP tab, AERMAP’s calculations are limited to the extents defined by the Region to Import tab.
Reducing the domain and running AERMAP MPI will make processing run faster thus saving you time.
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