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Aerial Photographs

General Information

What is aerial photography?

Aerial photography is the acquisition of a vertical image with a specialize camera installed on board of an airplane, equipped for this type of work.

Airborne acquisitions are always performed in such a manner that two consecutive photographs have a side and forward overlap. These overlaps enable a three dimensional (3D) observation of the territory, with the help of a specialized tool. The optical phenomenon, which makes it possible to see in 3D, is called the stereoscopy.


In order to obtain a three dimensional view of a covered territory, part of the photographed land on one image has to be also present on the next image, this is what is called overlap.


As the airplane flies, the photographed area, which is showed on two consecutive aerial photographs, that is the forward overlap, provides a view of the territory photographed at two different angles. When looking at this part of the photographs with the help of a specialize tool, such as the stereoscope, it is possible to view the landscape (relief) because it appears in three dimensions.

The raw image, as it is acquired on board the airplane, can be processed and printed on paper film or diapositive; and is then called an aerial photograph.

When the image is digitalized and corrected so as to eliminate the imprecision resulting from the airplane position in flight and the distortion due to the ground relief, it is called an orthophotograph. Every orthophotograph is georeferenced, which means that it has location geometrical properties identical to those of a map.

Why use aerial photographs?

An aerial photograph is rich in information. It is possible to pinpoint, amongst others, rivers, ponds, paths and clearings, which are not shown on a map. It is also possible to recognize cuttings and burns, as well as determine changes and types of vegetation. However, the incontestable advantage of aerial photography remains in the possibility of obtaining a three dimensional view of the territory, thus the relief, by stereoscopy.

The orthophotograph is halfway between the aerial photograph and the topographical map. It offers the aerial photograph’s details and richness, combined with the geometrical precision of a map. Because it is georeferenced, geographical information such as hypsometry (relief representation), toponymy (places names: lakes, rivers, road network) and territorial limits (administrative, recreational and protected).

By nature, aerial photographs and orthophotographs present a global view of the territory at a given time. This is why we use them to obtain information about the past and also to plan projects.

Which field of activity uses the aerial photographs?

Return to the past...
Aerial photographs can be use as a record. Indeed, it allows a return in the past by photo-interpreting an image taken a few years back.

Here are some examples of the use of past aerial photographs by various field of activity:

  • Legal field;
  • Land Development field;
  • Security field.

In the legal field...
When the land of an estate is the subject of a dispute, older aerial photographs are often used to obtain information regarding its state or its limits prior to the modifications that caused the dispute. In such a case, the photographs become very reliable supporting elements to establish a proof.

In the land development field...
Older aerial photographs are often used to restore places as they were in the past. Aerial photographs will then serve in the preparation of the core elements for urban development guiding plans.

In the field of security...
Aerial photographs can help in evaluating the scale of a natural disaster’s damages.

  • The Saguenay’s flooding
  • The ice storm

Evolution witness...
Aerial photography, when taken in an urban area, can demonstrate the stages of urbanization or its sprawl by juxtaposing images taken at different times.

Here are application examples for various activity fields:

  • Land development field;
  • Forestry field

In the land development field...
Aerial photography provides information on urban evolution in time.

In the forestry field...
Aerial photography provides information on urban evolution in time.

A vision of the future...
Aerial photographs can be used to analyze research sites or plan major projects.

Here are project planning examples:

  • Civil engineering field;
  • Agricultural field.

In the civil engineering field...
Aerial photographs are used in the search for implementation sites (plants, damps, ports, etc.) or to prepare network pre-projects (roads, railroads, canals, energy transportation lines, piping, etc.). They can also be transformed in orthophotographs so as to take measurements, add information layers, plan and, even, produce project models.

In the agricultural field...
Aerial photographs are used to forecast yield, evaluate crop insect, illness and flooding damages, evaluate ground water balance, discover oversalting areas, etc. They provide a reliable agricultural potential forecast.

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