Aerial Photography
Introduction
• Aerial Photography is defined as art, science and
technology of taking aerial photographs from an
air-borne platform
• Aerial photographs are taken from aircraft to capture
series of images using a large roll of special
photographic film
• The film is processed and cut into negatives. The
common sizes of negatives are 23 x 23 cm
• The basis of aerial photography is light sensitive
chemicals in the film emulsion
• These chemicals may react to ultraviolet, visible
and near infra-red portions of the spectrum from
0.3 µm to 0.9 µm wavelength.
Geometric Characteristics of Aerial Photographs
• Optical axis: is a line passing through the camera lens and
being at right angle to the camera film
• Principal Point : The foot (point) of the perpendicular drawn
from the camera lens center on the photo plane
• Vertical axis: is a line passing through the camera lens and
perpendicular to the ground surface
• Nadir Point: is the point on the terrain vertically beneath
the center of the camera lens.
• Flight height : height of the lens above sea level at the instant
of exposure.
Uses of Aerial Photographs
• Topographical Mapping
• topographical mapping on scales 1:10000,1:25000,1:50000 are being done photogrammetrically
• Geological Mapping
• Civil Works
• Forest Evaluation
Types of Aerial Photograph
• There are three important parameters that govern the classification:
• I.
Position of the camera axis
• II. Scale
• III. film used
Based on Position of the camera axis
1. Vertical Aerial Photograph
2. 2. Oblique Photography
Vertical Aerial Photograph
• The camera axis generates Vertical (90° or nearly) angle with
the ground or the earth surface (looking straight down )
• Allowable tolerance is usually + 3° from the vertical axis to
the camera axis
• used in cartography and photogrammetry.
1. It covers a relatively small area.
2. The shape of the ground area covered on a single vertical
photo closely approximates a square or rectangle.
3. Distance and directions may approach the accuracy of maps
if taken over flat terrain.
4. Relief is not readily apparent.
Oblique Photography
1.
Low Oblique Aerial Photography
• photograph taken with the camera axis inclined between 15° and
30° less than 30° from the vertical
1. horizon is not visible.
2. The ground area covered is a trapezoid, although the photo is
square or rectangular.
3. No scale is applicable to the entire photograph, and distance
cannot be measured.
4. Parallel lines on the ground are not parallel on this photograph;
therefore, direction (azimuth) cannot be measured.
5. Relief is detectable but distorted.
High Oblique Aerial Photography
• taken with the camera inclined about 60° or
more from the vertical
1.horizon is visible, covers a very large area.
2. The ground area covered is a trapezoid
3. Distances and directions are not measured on
this photograph
4. Relief may be quite detectable but distorted