Infrared Aerial Surveying

the survey of terrain from the air with invisible infrared rays. A distinction is made between infrared surveying in the near infrared region of the spectrum (0.8–1.1 microns [μ]), which is done directly on infrachromatic aerial photographic film in daylight, and photoelectronic infrared photography in the far infrared region (1.2−25.0 fi, with operating intervals of 2–5, 8–10, and 14−15 μ.), which is done both in daytime and nighttime using special surveying cameras that record the thermal radiations from the earth’s surface and convert them into luminous images, which are automatically copied from the screen of a cathode-ray tube onto photographic film. With both types of infrared surveying the pictures produced are similar to the black-and-white aerial surveys obtained from ordinary panchromatic aerial photographs with visible light.

Because of the peculiarities of spectral reflection from objects in the infrared region, infrared photographic surveys are effective in reproducing shorelines and swampy areas, in interpreting the composition of mixed forests and crops, and in identifying local objects from the photographic images of their shadows. The photoelectronic infrared surveys provide an effect that is important when mapping volcanic and hydrothermal phenomena or underground and forest fires; they have potential for the study of ice and water masses (with separation according to temperature characteristics, impurities, and so on) and in interpreting certain kinds of rock and hydrographic networks under the cover of trees and shrubs, as well as buildings, pipelines, and other structures that can be distinguished from one another by their thermal properties. According to international terminology the first type of surveying is called IR photography; the second, IR imagery.