Analysis Options

Once the multiple dates of photography have been orthocorrected, there are few limits to analysis options. The imagery itself, with little or no analysis, may be sufficient for public awareness, although some interpretation is usually helpful. To detect and document spatially continuous changes over time, (e.g., vegetation cover), we have used a digital dot grid technique that provides percentage of cover by cover type for each cycle of imagery. For discrete feature changes, such as OHV trails, we have used two different techniques. Our first method used a digital grid that required the interpreter to simply click a cell of the grid if an OHV trail was in the cell. The grid was then put through a kriging process, and a map of OHV hot spots was created. The second method consisted of manually digitizing the trails as they were interpreted from the imagery. The kriging method has the advantage of being very fast. The digitizing method has the advantages of being simple, easily verifiable, and producing a map of actual OHV trails. In addition, it was a simple matter to construct graphs of the rate of change from the digitized trail’s attribute tables. These methodologies have worked well for us, but the optimum methodologies may yet be awaiting discovery.

Only the most basic interpretations should be attempted from the monoscopic imagery. Most interpretations should be accomplished in stereo, which allows users to visualize relief within the image and heights of features. This can be achieved using a stereoscope and the analog (hardcopy) imagery or digitally using commercially available applications.