Arial photogram try induces the use of photographs taken in a systematic manner from the air they are then controlled by lend survey and measured by photogrametric techniques. Since the First World War the terrestrial photographic surveying has been replaced by aerial photographic surveying or aerial surveying for most of survey work due to development of aero plane.
- The survey work can be carried out with great speed.
- It can be used with great success for other purposes such as classification of land an soil, geological and archeological investigations etc.
Aerial surveying is a highly technical and specialized work and most be carried out by skilled, specially trained and experienced personal. It is mainly made by government organization i.e survey of Pakistan depth.
Aerial survey consists of 4 parts.
- Ground ControlL
- Compilation of Map
Equipments of aerial survey are:
- An aeroplane
- An aerial camera
- Aaccessories required for interpretation and plotting
Air survey camera:
- Principal components of an aerial survey camera are.
- Lens (most important part)
To control the interval of time that the light passes through the lens. The shutter of a modern air camera is capable of speeds ranging from 1/50 sec to 1/2000 sec
The range is commonly b/w 1/100 sec to 1/1000 sec
- Diaphragm: The diaphragm control the physical opening of the lens and therefore the amount of light passing to the lens.
- Filter: To reduce the effect of haze and distribute light uniformly over the format and also protects the lens form flying particles in the atmosphere.
- Camera Cone: To support the lens-shutterciaphram assembly with respect to the focal plane and prevent stray light form striking the film.
- Focal plane: surface on which the film lies when exposed.
- Fiducially marks: (not shown in the figure) 4 to 8 in no define the photographic principal point.
- Camera body: To house the drive mechanism, flattens the film and advances to b/w expose.
- Magazine: It hold the supply of exposed and unexposed fill
A levees vial (level Tube) attached to camera helps keep the optical axis of the camera nearly vertical inspire of any slight tilt of an air craft.
The value of the focal length determined accurately through the calibration for each camera. The most common focal length for aerial cameras is 6//(152mm)
Format size 9 Inc x 9 inch
(Negative) (230 mm x 230 mm)
Aerial cameras may be
- Single lens camera
- Multiple lens camera