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 as downloaded from MECP’s website .
Step 4: Click the Process + Run AERMAP 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 as outlined in our archived Modeling Tip.
2. Reduce the domain read by AERMAP to save processing time. AERMAP’s domain settings were discussed in our recent Modeling Tip.
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.