Aerial Photos: Source Data Disrupted?

Aerial Photos:

Source Data Disrupted?

“Remember when seeing the Ellerslie grain elevator meant we were almost at Edmonton?” This question elicited the comment that Edmonton now seems to start shortly after you leave Nisku. Land changes over time. Landmarks, that guided journeys for decades, become impossible to trace. Traditional photos can capture specific moments in time but aerial photos can capture the exact locations of landmarks long erased from the landscape. They can bring the past and present together overlaying the current epoch with a historical one, and make it possible to determine the distance from a demolished elevator to a brand new downtown skyscraper. One can determine the height and other metrics of long gone buildings. With such visualization tools it can be like time travelling and seeing the layout of the past in context with the present. Thus, aerial photos are irreplaceable assets that governments have been collecting since planes first took to the sky.

Accordingly, the transition from film to digital capture of these images bears examination. Surveyed aerial photos are done to exacting standards to determine metrics that can be evaluated in terms how much uncertainty is present in the measurements made. Without the collection of necessary metadata regarding these images the validity of such measurements cannot be evaluated. Natural Resources Canada’s (NRCan) (2007) website states, “in 1925 the Interdepartmental Committee on Air Surveys (ICAS) and the National Air Photo Library (NAPL) were established were established to take charge of all federal non-military air-photo activities” (para. 4). However, industry has embraced a new format of collection and standards for archiving this new information are necessary to ensure this visual archive is usable by future generations. This report intends to look at how film is being replaced in aerial photography by digital collection and the risks and rewards associated with adopting this new methodology for collection.

Scope

Generally, for the purpose of this report scope was limited to a consideration of Canadian standards and practices. Consideration was given mainly to the collection of natural color imagery of a high resolution used for the purposes of creation of orthophotos used to make photogrammetric measurements. In contrast, parameters of imagery collected for the purposes of interpretation was largely overlooked as these variables increased the scope beyond this report. It is also important to acknowledge this report, was primarily concerned with types of imagery used with Geographic Information Systems and highlights some of the more common uses of aerial photography and the various types available.

Background

Regardless of the type of collection when an area of interest