Air Photography (Aerial Photography)
The image obtained by means of balloons, aircraft and any other celestial platform is called aerial photography.
Atmosphere based platform; A helicopter or aircraft is used for a stationary or moving base in the atmosphere. The field of aerial photography developed with the use of cameras and aircraft. Air photography has grown rapidly in the field of remote sensing due to its use as an aircraft platform, as it can accommodate larger automatic cameras and is easier to control.
The high and long flight capability of the aircraft also makes it an ideal platform, aircraft like MiG and Jaguar have proved to be more useful for this, as they can easily fly at altitudes of 30,000 to 50,000 m.
Properties of air photography
- Aerophotography provides more innovative information about the physical and cultural landscapes of an area. The new to new topographic map of an area is also often older than the aerial photograph of that area. Therefore, air photographs are used to obtain new information.
- In any topographical map made on the prevailing scales, all the small details of the surface cannot be displayed simultaneously, on the contrary, in the air photograph, even the smallest details of the surface are marked. Air photographs are used to obtain more innovative information.
- The heights of trees, buildings, pillars and chimneys, etc. are not marked in topographic maps, whereas in aerial photographs, a particular height (from the shadow of that detail) can be found.
- It is very difficult to map inaccessible areas with survey equipment, but aerial photography makes this task very easy. Air photographs are used to obtain information about inaccessible areas.
Defects of aerial photography
Inconsistency of scale: -
The scale is the same everywhere in the map, so the distance between any two points can be measured accurately by the scale in each part within the prescribed limits of the map, whereas in air photographs, the height of the surface can be measured. Differences and positional errors resulting from the inclination of the camera and the aircraft result in scale inconsistencies, i.e. the scale of one part of the air photographs differs from the scale of the other part.
Difficulty of Interpretation:-
The details of the surface in the air photograph are seen from an unusual point of view, so practice and experience are required to interpret it correctly. On studying the merits and demerits of air photographs, we come to the conclusion that the map is a clear and almost pure but old picture of the surface, whereas the air photograph presents such a new picture full of details of the surface, which should be read with special care. Requires practice and experience. Some distortions are inherent in air photography, so it is beneficial to use both these methods together.
Types of Air Photography
There are two main types of air photographs:- (1) oblique photographs and (2) vertical photographs.
(1) Oblique photograph
To take oblique photographs, the camera placed in the aircraft is fixed towards the ground and aimed in the direction, so that the side views of the surface details are visible in the photographs, thus these photographs are taken from a high tower or mountain. They are like photographs taken from the top.
(2) Vertical Photograph
The pictures taken vertically downward with the camera in an aircraft flying horizontally are called vertical photographs.
# Trimetrogon photo - In the Trimetrogon method, there are actually three cameras working at the same time. One camera takes vertical photographs and side cameras take oblique air photographs up to the horizon. In this way, in the Trimetrogon method, the entire area from the right horizon to the left horizon is marked.
# Convergent Photography - Two cameras are used in the aircraft to capture photographs by convergent method, which take two different oblique photographs of the same area. In photography, two photographs of an area taken by different cameras at the same time are obtained.
# Photomosaic - Often in a single aerial photograph, only a part of the surface is pictured, so to see a large area, such as the whole part in one picture, all the aerial photographs of that area are pasted together correctly. This group photograph is called the photomosaic of the air photograph.
Use of Aerial Photography Methods;
- Before taking photography, the time of flight and the weather should be considered.
- Lighting - Special care is taken of light in photography, so 1-2 o'clock is considered to be the best time for photographing air. In the air photographs taken in the morning or evening, long shadows of the surface details are marked.
- Weather - Although aerial photography is a quick medium of surface information and photography is necessary only when it is needed, but generally choose the weather according to the purpose of the survey. For example, spring is good for taking photographs of deciduous forests, similarly the crop season is chosen for photographs of crop fields.