How to interpret aerial photographs

Photo interpretation is the art of identifying visible details from their images on a photographic print. The best aid to this is the stereoscope. However it is easy to become skilled in this work by examining single photographs.

A reading glass will help a great deal. Skill will come by examining all types of photographs and comparing them with maps or, best of all, with the ground itself. Start with prints with a scale of 1:20 000 or larger.

Interpretation requires the study of three things: i) tone, 2) light and shadow, 3) shape and size.

Tone. A large amount of light reflected from an object results in a white object on the print, and no light results in a black object. In between these two extremes are all the shadows of gray.

This shade of gray of an object is known as the tone of the image. The less light reflected the darker will be the shade of gray, or the darker the tone,

Light and shadow. When studying the photographs always remember about the source of light and have the shadows on the print fall toward you.

This puts the light in the same position the sun was in when the picture was taken.

This is very important when studying relief.

Shadows often give the shape and size of an object that appears on a photograph. The top of a square building would look the same if it were one-story or ten-story building; but the shadow would be much different.

Shape and size. Man-made features are usually bounded by straight or curved lines, while natural features usually have irregular edges. It is important to keep the scale in mind when studying the shapes and sizes. A light square image may represent a building on a 1: 4,800 print. But the same size of square may represent a cultivated field in a 1: 20,000 print.

A s s i g n m e n t s

1. Comprehension questions:

1.With what print shall we start photo interpretation? 2. What does photo interpretation consist of? 3. When is the tone of the image darker? 4. What is important for studying relief? 5.What is characteristic for natural features on photoes?

2 .Describe applications of a reading glass.

3. Give a short summary of the text.

4.

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