A strip is a series of overlapping exposures matched together to form one long picture. A strip is used when your assignment calls for photographing long, narrow targets, such as railroads, highways, coastlines, rivers, and mountain ridges. You may hold the camera at any angle to make a strip; however, exposures made with the camera pointing straight down from the aircraft join together better and have the most consistent scale. A strip comprised of oblique views is called a PANORAMIC.

One long, continuous picture, made from a number of photographs, requires the images to be matched carefully so one picture ends where the next begins. Because the camera is in a different position for each exposure, a perfect match is impossible. But, by overlapping exposures and using only the central area of each picture, you can obtain a near-perfect result.

Once a strip is started, photographing it is a mechanical job because the aircraft flies at a constant speed and at a constant altitude. You should not alter the camera angle while exposing a strip, and you should make the exposures at regular intervals. Thus the longer the strip, the more an automatic camera system is preferred. The camera-to-scene distance must remain constant while you are making the strip. The smallest change in distance changes the image size and makes matching adjacent exposures extremely difficult, if not impossible.

MOSAIC PHOTOGRAPHY

Large land areas are photographed in strips that overlap sideways. The strips are pieced together to form one large composite picture, called a MOSAIC. When photographing for mosaic purposes, you should keep the camera the same distance from the scene throughout the photographing evolution. Mosaics are usually produced from vertical photographs made by aircraft with an automatic camera system.

STEREO PHOTOGRAPHY

Two pictures of the same subject, photographed properly, can provide a stereoscopic or threedimensional effect. The two pictures are called a STEREO, a STEREOPAIR, or a STEREOGRAM. The word STEREOGRAM indicates that the two pictures are mounted and ready for stereo viewing.

The primary purpose of stereo aerial photography is to provide measurements, such as height and depth, and detect features that are not visible in a regular photograph. Photo interpreters (Intelligence Specialists) are trained in stereo techniques to detect these fine points. Stereo photographs are produced by making two pictures of the same subject from slightly different positions. When the pictures are made from the same position, the two are identical and there is not a stereo effect. A very small shift in the camera position, between exposures, produces a very shallow stereoscopic depth. As you increase the shift in camera position between exposures, the apparent depth of the stereoscopic view increases. When the stereo effect is exaggerated-so hills appear steeper and depressions appear deeper than they really are-the effect is called HYPERSTEREOSCOPY. The terms inverted stereo, pseudo ,stereo, and reverse stereo refer to the effect of interchanging the position of the pictures, causing hills to appear as valleys and valleys to appear as hills.

RECONNAISSANCE PHOTOGRAPHY

Another aspect of aerial photography that you should be concerned with is reconnaissance photography. The Navy performs aerial reconnaissance photography of enemy territory to observe enemy defenses, troop concentrations, troop movements, enemy strength, and so on. Aerial reconnaissance photography may also include taking images over friendly territory, both ours and our Allies. This is discussed further in the TARPS section of this chapter.

CARTOGRAPHIC PHOTOGRAPHY

Cartographic photography is accomplished for the purpose of making charts and maps. Usually several strips are flown over known landmarks that are used as reference points or ground-control points. Cartographic photography always has vertical views but may include oblique views that are made simultaneously to produce horizon-to-horizon coverage along the flight line.

AERIAL PHOTOGRAPHIC SYSTEM

An aerial photographic system may simply be the same hand-held camera you use on the ground, or it may be a complex, pilot-controlled electronic system, such as TARPS. The following discussion is only a brief overview of TARPS along with a brief explanation of aircraft cameras and associated equipment. Hand-held systems are addressed later in this chapter under the heading "Shooting Hand-held Aerial Photography."