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Types of Aerial photographs:

Aerial photographs are of different types which are as follows:

A) Types of aerial photographs on the basis of orientation of camera axis:

i. Vertical photograph: An aerial photograph taken with the camera axis/optical

axis coinciding with the vertical to the ground is known as vertical photograph.

ii. Tilted photograph: An aerial photograph in which the camera axis is

unintentionally tilted by small amount (less than 3 °) from vertical/perpendicular

to the ground is known as tilted photograph.

iii. Oblique photograph: An aerial photograph taken keeping the camera axis

intentionally tilted from the vertical is known as oblique aerial photograph. The

amount of tilt ranges from 30° to 60 °. The advantage of oblique photographs is

that they cover large area and they also provide side view of features.

Oblique photographs are of two types

- Low oblique: Oblique photographs in which horizon is not seen. Tilt is 30°.

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Low oblique photograph

- High oblique: Oblique photographs in which horizon is seen. Tilt is 60°.

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High oblique photograph

B) Types of aerial photographs on the basis of angle of coverage:

i. Narrow angle photograph: Angle of coverage is less than 60°.

ii. Standard or Normal angle photography: Angle of coverage is of the order of

60°.

iii. Wide angle photograph: Angle of coverage is of the order 90°.

iv. Superwide of Ultrawide photograph: Angle of coverage is of the order of 120°.

C) Types of aerial photographs on the basis of special properties of films, filters and

photographic equipments:

i. Panchromatic: Records only single band data (visible region of spectrum).

ii. IR: Records only red and IR portions of EMS.

iii. Color: Records all reflections of visible portion in color or natural colors.

iv. Color IR: Records spectral colors and IR in combination resulting in false colors.

v. Thermal imagery: Records only thermal IR emissions of objects.

vi. Radar imagery: Records reflection of radar waves.

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vii. Spectrazonal: Records only selected part of the spectrum.

D) Types of aerial photographs on the basis of lens system:

i. Single lens photograph.

ii. Multiple lens photographs.

- Three lens photograph (Trimetrogon photograph).

- Four lens photograph.

- Nine lens photograph.

Types of aerial cameras:

1. Strip camera:

Strip camera uses a high-speed, low-altitude aircraft to take a continuous picture, rather than

using overlapping high-altitude photographs, as in conventional aerial photography. The shutter

of the strip camera is kept open throughout the flight while taking photographs.

Popular from the 1940's to 1970's, strip camera was once used internationally for aerial mapping

and surveys of highway degradation, but has been replaced by satellite photography, which is

less expensive.

2. Single lens/Frame camera:

Aerial mapping cameras (also called as metric or cartographic cameras) are single lens frame

cameras designed to provide extremely high geometric image quality.

These cameras consist of following three parts:

A) Magazine: Magazine consists of two reels namely – supply reel and take up reel. The supply

reel supplies film negative which is exposed on focal plane. The take up reel takes up the

exposed film.

B) Body: The camera body is the middle part of camera that consists of electrical drive

mechanism for advancing the film and flattening the film during exposure and for controlling the

shutter.

C) Lens cone assembly: The lens cone assembly includes – lens, filter, shutter and diaphragm.

The lens gathers the light and focuses it onto focal plane. The distance between focal plane and

the center of lens is known as focal length. The function of filter is to block the unwanted light.

The shutter open at the time of taking photograph while rest of the time it is closed. The opening

and closing of shutter is mainly controlled by using an automatic device known as

intervalometer. The diaphragm prevents the excess light from entering the camera. The optical

axis of camera is perpendicular to the focal plane and extends from the center of the camera lens.

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3. Panoramic camera:

In panoramic cameras the ground areas are covered by either rotating the camera lens or rotating

a prism in front of the lens (known as rotating lens assembly). The terrain is scanned from side to

side, transverse to the flight direction. The film is exposed along a curved surface and the angular

coverage can extend from horizon to horizon. Camera with a rotating prism design contains a

fixed lens and a flat film plane. Scanning is accomplished by rotating the prism in front of the

lens.

4. Multiband camera:

A multiband camera captures the photographs in different spectral regions of the EMS.

This allows in better identification of different terrain features. Such camera uses either a

multicamera array or mutilens camera system.

Multilens camera system

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Multi camera array comprising four 70 mm camera

5. Digital Camera: Digital cameras record electromagnetic radiation electronically rather

than using the photographic film. Instead of using film, digital cameras use a gridded

array of silicon coated CCDs (charge-coupled devices) that individually respond to

electromagnetic radiation. Energy reaching the surface of the CCDs causes the generation

of an electronic charge which is proportional in magnitude to the "brightness" of the

ground area. A digital number for each spectral band is assigned to each pixel based on

the magnitude of the electronic charge. The digital format of the output image is

amenable to digital analysis and archiving in a computer environment, as well as output

as a hardcopy product similar to regular photos. Digital cameras also provide quicker

turn-around for acquisition and retrieval of data and allow greater control of the spectral

resolution. Although parameters vary, digital imaging systems are capable of collecting

data with a spatial resolution of 0.3m, and with a spectral resolution of 0.012 mm to 0.3

mm. The size of the pixel arrays varies between systems, but typically ranges between

512 x 512 to 2048 x 2048.