You might be familiar with all sorts of photography taken with regular cameras. You come across these photographs all the time that gives you the same view of the subject as your eyes. In basic terminology, you get the horizontal perspective of all the subjects being photographed.
But what you are missing out is the ‘bird’s eye view’. Suppose if you want to look at the subject from above, then you most probably have to place yourselves somewhere in the air. So that when you look down you can see a whole new perspective.
This different perspective is what most people don’t know about. It is a view which you can only experience via aerial photographs. It is termed as aerial because it gives a perspective from above like air.
These photographs are usually taken with the help of aircraft and helicopters using a precision camera. These aerial photographs act as indispensable tools in many aspects especially in the interpretation of landscapes, topographical mapping, etc.
This is why today we are going to take an in-depth look into this genre of photography:
What is aerial photography?
We are going to first begin with a glossary to make you understand some basic terms:
- Aerial Camera: It is a type of a precision camera which is specially designed for usage in aircraft. It is specifically built to capture aerial photographs from far above.
- Aerial Film: This is a roll film which features high sensitivity, dimensionally stable emulsion support, and high intrinsic resolution power.
- Aerial Photography: This is an art and science of taking aerial pictures from an airborne platform. It is a genre of photography used for topographical mapping and interpretation.
- Aerial Photograph: Any photograph which is captured from an airborne platform with the help of a precision camera.
- Fiducial Marks: these are Index marks that are rigidly connected at the central edges of the body of the camera. If the film is exposed, you can see the marks visible on its negative.
- Forward Overlap: This is the common area in the two successive pictures taken in the flight direction. It is mostly stated in %.
- Image Interpretation: The method of identifying the subject in the image and assessing their relative significance.
- Nadir Point: It is the foot of the perpendicular from the center of the camera lens on the ground plane.
- Principal Point: It is the foot of the perpendicular from the center of the camera lens on the photo plane.
- Principal Distance: It is the perpendicular distance from the perspective center to the photograph’s plane.
- Perspective Centre: It is the point of origin of the bundle of rays of light.
- Photogrammetry: It is the science of taking accurate measurements from aerial photographs.
Where are AERIAL PHOTOGRAPHS used?
Aerial photography has two main uses. The first and foremost use is in topographical mapping and the other one is in image interpretation. These two are independent sciences but are related. Their combined usage has led to the development of photogrammetry.
What is Image Interpretation?
It is the science of assessing images of objects and estimating their comparative importance. The rules of image interpretation are used to gain qualitative information from the aerial results such as usage of the land, soil types, topographical forms, etc… An expert interpreter can use aerial pictures to study any changes in land-use.
What is Photogrammetry?
Photogrammetry is the science of making accurate measurements through aerial photographs. The rules of photogrammetry facilitate reliable measurements linked with length, height, and breadth of aerial pictures. Thus, it can be utilized as a data source for gathering, producing and updating maps of topographic nature.
What are the advantages of AERIAL PHOTOGRAPHY?
There are many advantages of aerial photographs as compared to ground-based observation but the four major ones are:
- Improved vantage point: the results gained from aerial pictures provides a bird’s eye view of large areas. This enables users to view and discover the features of the earth surface in spatial context rather than just horizontal perspective provided by regular images.
- Broadened Sensitivity: The film sensitivity utilized in capturing aerial photographs is comparatively a lot more sensitive than human eyes. Our eyes can only perceive visible regions of the electromagnetic spectrum from 0.4 to 0.7 µm. While the aerial films can detect them from ranges of 0.3 to 0.9 µm thanks to enhanced sensitivity.
- Time freezing ability: Aerial pictures provide users with a record of the surface features at an instant. These moments of exposure have time-freezing abilities and can, therefore, be used as historical records.
- Three Dimensional Perspective: Aerial results usually feature uniform exposure interval which enables users to obtain a stereo pair of photographs. With these pairs of photographs, you can get three-dimensional views of the surface captured.
What are the types of AERIAL PHOTOGRAPHS?
Aerial photographs can be classified into four types based on either the position of the camera axis, scale, angular extent of coverage and the film used. We are going to shed light on 2 of these classifications:
Types of Aerial Photographs Based on the Position of the Camera Axis:
- Vertical Photographs
- Low Oblique
- High Oblique
Types of Aerial Photographs Based on Scale:
- Large Scale Photographs: Scale is larger than 1: 15,000
- Medium Scale Photographs: Scale ranges between 1: 15,000 and 1: 30,000
- Small Scale Photographs: Scale is smaller than 1: 30,000
Difference between a map and an aerial photograph:
A map and aerial photograph are not the same. A map can’t be directly traced from an aerial photograph. The reason behind this is that both have different planimetry thus the perspective of an aerial photograph and a map can never be the same.
The differences in their projection are given in the table below. Even aerial photographs taken vertically do not have a consistent scale expect if they are captured on flat terrain. That is why to use Aerial photographs as map substitutes they first need to be transformed from the planimetry view from a perspective view. Such transformed results are called orthophotos.
|It is a central Projection||It is an orthogonal Projection|
|An aerial photograph is geometrically incorrect. The distortion in the geometry is minimum at the center and increases towards the edges of the photographs||A map is a geometrically correct representation of the part of the earth projected|
|The scale of the photograph is not uniform||The scale of the map is uniform throughout the map extent|
|Enlargement/reduction does not change the contents of the photographs and can easily be carried out.||Enlargement/reduction of the maps involves redrawing it afresh|
|Aerial photography holds good for inaccessible and inhospitable areas||The mapping of inaccessible and inhospitable areas is very difficult and sometimes it becomes impossible|
All in all, this technique of photographing from above has become very significant. It is being used to capture many types of Earth surfaces, their features, atmosphere, and hydrosphere. Be it with cameras mounted on rockets, aircraft, spacecraft, or Earth-orbiting satellites, aerial photographs are being highly used for the provision of info for numerous purposes.
They are becoming popular in the military and reconnaissance as well. In the mapping of terrestrial features, the aerial picture remains at the top as their overlapping series make the preparation of contour maps and three-dimensional models possible.
So in topography, hydrology, soil, geology, vegetation, ocean currents, meteorology, aerial photography can never be forgotten. Moreover, its wings have also spread in assessing cloud patterns for weather forecasting thanks to orbiting satellites and expert interpretation.
So it’s high time the world realizes its benefits and aerial photography gains the popularity it deserves!