With the development of sophisticated airborne photographic systems, most aerial photographs today are made by photo-configured aircraft, such as the F-14 Tomcat with the Tactical Air Reconnaissance Pod System (TARPS). The role of the Photographer's Mate in aerial photography evolves less flying as a crew member and increased responsibilities in a ground-support function. Even with this changing role, you may be called upon from time to time to make hand-held vertical photographs and oblique photographs from airplanes and helicopters. This aerial photography could include such assignments as gunnery exercises, refueling at sea, publicity photography, construction progress, accident investigation, ship identification, display pictures, mapping, aerial motion-media work, and so on. As a knowledgeable PH you may also have to train non-photographic personnel in the operation of cameras and picture-making techniques for antisubmarine warfare and maritime surveillance photography.

Aerial photographs are taken from a variety of altitudes. The altitude ranges are defined as follows: Low altitude: 0 to 1,500 feet

Medium altitude: 1,500 to 10,000 feet High altitude: 10,000 feet and above

As a Photographer's Mate, your aerial photographic assignments are normally accomplished from low to medium altitudes.

CATEGORIES OF AERIAL PHOTOGRAPHY

Three basic categories of aerial photography are in use today: vertical, oblique, and air-to-air. The vertical and oblique categories are broken down further into types of aerial photography. The three basic categories are discussed first.

VERTICAL PHOTOGRAPHY

Vertical aerial photography is accomplished with the camera held or suspended in the aircraft, so it points directly downward with the optical axis of the lens perpendicular to the ground fig 4-1 . At the moment of exposure, when the camera is level and the film is parallel to the ground, the result is a photograph, for all practical purposes, with a uniform scale. However, if the aircraft is climbing, diving, banking, or the camera is tilted for any other reason at the moment of exposure, the resulting photography does not have a uniform scale. It is always important in vertical aerial photography to hold the camera in a true vertical position. The angle between the camera axis (or optical axis) and the true vertical position is called the TILT ANGLE; straight down, perpendicular to the ground, is 0 degrees, and straight out, parallel to the ground, is 90 degrees fig. 4-2 . The purpose of vertical aerial photography is to show details clearly of ground objects at a uniformly accurate scale. In peacetime, these aerial photographs are valuable for mapping and for planning locations of buildings, streets, runways, docks, and other similar projects. During wartime, vertical aerial photography is valuable for a variety of military purposes, such as determining enemy location, strength, and capability.

The entire view of a vertical image is not perfectly vertical because only the very center of the image area is taken straight down. A building in the center of a vertical image shows only the roof, but a building near the edge shows part of the sides in addition to the roof. Although this slight change in the viewing angle from center to edge of the image is undesirable when you try to match prints for laying strips or mosaics, it does provide the necessary differences in photos for stereo viewing.

Most vertical aerial photography is performed with photo-configured aircraft. It is possible, however, to make hand-held vertical photographs from planes and helicopters.

OBLIQUE PHOTOGRAPHY

An oblique aerial photograph is made with the camera directed out and down at an angle from the aircraft (not straight out and not straight down). For accuracy, the amount of the oblique angle is stated in degrees. The angle between the camera axis (or optical

Figure 4-1-Vertical photograph.

Figure 4-2. -Tilt angle.

axis) and the horizontal is called the CAMERA DEPRESSION ANGLE; straight out, parallel to the ground, is 0 degrees, and straight down, perpendicular to the ground, is 90 degrees fig 4-3. Oblique images may be anywhere between 0 and 90 degrees, do not have a uniform scale, and are divided into two subcategories-high oblique and low oblique. The horizon is visible in high obliques but not in low obliques. This can be remembered easily by thinking high sky, low no.

Here again, as with vertical photographs, oblique photographs can be made with photo-configured aircraft or with a hand-held camera.

High-Oblique Photography

High-oblique photography is accomplished at a camera angle that shows the horizon at about a 30-degree camera depression angle (fig 4-4). It resembles the view a pilot sees when approaching the target. High-oblique photographs are useful in guiding pilots toward a photographic target, a bombing target, or a helicopter landing site. High-oblique photographs are also used for orientation purposes because large areas are covered. A high-oblique photograph is particularly suitable for pictorial and illustrative purposes because it provides a true perspective view of land surfaces. It is easier for a person on the ground to locate and identify objects in a high-oblique photograph than in a low oblique or vertical photograph.

Low-Oblique Photography

Low-oblique photography does not show the horizon fig 4-5. It is made with a camera depression angle of about 60 degrees. A low-oblique photograph covers a relatively small area. The subjects in a low-oblique photograph look more familiar than in a vertical photograph-as if you were viewing them from the top of a tall building. A low-oblique photograph is normally used for identification purposes, and for that reason, a large image of the target is necessary.

You may at first come to the wrong conclusion, because of their names, that high- and low-oblique photographs are made from high and low altitudes, respectively. This is not the case. The aircraft altitude is not a determining factor in whether an oblique is classified as high or low. Remember, the horizon is the determining factor; high sky, low no. As a matter of fact, most high-oblique photographs are made from a

Figure 4-4-High-oblique aerial photographs.

Figure 4-5.--Low-oblique aerial photographs.

relatively low altitude and low-oblique photographs from a relatively high altitude.