In the second week of Photo Interpretation and Remote Sensing, we began looking more closely and analytically at aerial photos. By making use of some systematic and discriminating methods, it's possible to learn much more from air photos than we can with a more casual and cursory approach.
The top map to the left shows examples of different degrees of tone, or brightness along a gray-scale, and texture, in features in an aerial photo. Our tone scale has five classes: very light, light, medium, dark and very dark. It's important to use a scale like this in order to maintain consistency as we describe and identify objects on the ground.
The bottom map illustrates four different elements of image interpretation. Different objects on the ground have a variety of characteristics...some, such as cars and houses, are most easily recognized by their shape or size, others, such as a parking lot, by a distinctive pattern, and others, such as light poles, more by the shadow that they cast on the ground. Finally, some features, (such as the pier in this map) can be distinguished mainly by their association with certain other features (the ocean in this case.) An interpreter must keep all of these elements of interpretation in mind while working to identify objects from aerial imagery.
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