Aerial Shots of Istavrit Visual Solutions – 5

Basic Elements of Air Photo Interpretation

Novice photo interpreters often encounter difficulties when presented with their first aerial photograph. Aerial photographs are different from “regular” photos in at least three important ways:

  • objects are portrayed from an overhead (and unfamiliar) position.
  • very often, infrared wavelengths are recorded, and
  • photos are taken at scales most people are unaccustomed to seeing

These “basic elements” can aid in identifying objects on aerial photographs.

  • Tone (also called Hue or Color) — Tone refers to the relative brightness or color of elements on a photograph. It is, perhaps, the most basic of the interpretive elements because without tonal differences none of the other elements could be discerned.
  • Size — The size of objects must be considered in the context of the scale of a photograph. The scale will help you determine if an object is a stock pond or Lake Minnetonka.
  • Shape — refers to the general outline of objects. Regular geometric shapes are usually indicators of human presence and use. Some objects can be identified almost solely on the basis of their shapes.
    • the Pentagon Building
    • (American) football fields
    • cloverleaf highway interchanges
  • Texture — The impression of “smoothness” or “roughness” of image features is caused by the frequency of change of tone in photographs. It is produced by a set of features too small to identify individually. Grass, cement, and water generally appear “smooth”, while a forest canopy may appear “rough”.
  • Pattern (spatial arrangement) — The patterns formed by objects in a photo can be diagnostic. Consider the difference between (1) the random pattern formed by an unmanaged area of trees and (2) the evenly spaced rows formed by an orchard.
  • Shadow — Shadows aid interpreters in determining the height of objects in aerial photographs. However, they also obscure objects lying within them.
  • Site — refers to topographic or geographic location. This characteristic of photographs is especially important in identifying vegetation types and landforms. For example, large circular depressions in the ground are readily identified as sinkholes in central Florida, where the bedrock consists of limestone. This identification would make little sense, however, if the site were underlain by granite.
  • Association — Some objects are always found in association with other objects. The context of an object can provide insight into what it is. For instance, a nuclear power plant is not (generally) going to be found in the midst of single-family housing.