GIS and Graphics Processing
The animations were created from gridded climate estimates previously developed at the Spatial Climate Analysis Service, Oregon State University. The PRISM grids for Alaska consist of monthly raster datasets for mean daily minimum temperature (tmin), mean daily maximum temperature (tmax), and mean total precipitation, as well as grids for mean annual temperature and total annual precipitation. The grids represent long-term average monthly climate normals for the years 1961-1990.
The PRISM model ("Parameter-elevation Regressions on Individual Slopes Model") is essentially a sophisticated interpolation routine with weighted regression of various environmental parameters to spatially distribute climate parameters across complex terrain. The model takes into consideration the effects of elevation, topographic exposure (aspect), coastal proximity, inversions, and other factors. The temperature grids are based on 406 point measurements; the precipitation grids are based on 544 point measurements. The grids were peer-reviewed prior to release, and have been approved by the USDA NRCS and the US National Climatic Data Center. For more information, see:
To access the Alaska PRISM grids for your own purposes, please see The Climate Source, the distributor of the PRISM data products.
Standard vector and raster techniques using a Geographic Information System (GIS) were used in processing the PRISM grids. The initial PRISM grids have a geographic projection and WGS84 datum, with grid cell resolution of 2.5 arc minutes. The first step was to import the ASCII integer grids into ArcInfo v. 8.3 as floating-point grids in °C for temperature and mm (water equivalent) for precipitation. Mean temperature grids were created by averaging the tmin and tmax grids. The monthly grids were then projected to Alaska Albers, WGS84, oversampled slightly to a grid cell resolution of 2 km, and clipped to the state outline (excluding areas west of 180°W). A variety of other steps were taken, including creation of the percent precipitation grids. Additional statewide framework layers (towns, rivers, glaciers, lakes, DEM, etc.) were compiled with the same projection, datum, extent, and resolution.
GIS and graphics programs were then used to create the animations. In ArcMap v. 8.3, separate map layouts were created for each month, with creation of annual and custom color scales. The maps were then exported as .tif files at 960 x 720 resolution (equivalent to 2.8 km per pixel). The .tif files were imported into QuickTime Pro v. 6.5 as an image sequence, and exported as QuickTime .mov files (with video compression and "best" quality). The .tif files were also converted to .jpg files and imported into PowerPoint as an additional option for presentation.
The 3D fly-through visualizations were created as part of the EarthSLOT project. Peter Prokein and Matt Nolan (University of Alaska Fairbanks) used TerraBuilder to render the temperature and precipitation .mpt files. The fly-through environments were then finalized in TerraExplorer Pro as .fly files. For the 3D movies, routes were exported from TerraExplorer Pro as uncompressed .avi movies, then exported from QuickTime Pro as mpeg4 .mov movies.