Aerial photographs are photographs taken from a distance, from an airplane for example. Cameras on airplanes are the simplest and oldest form of aerial sensors used to monitor features of land surface. The spectral resolution of cameras is usually very coarse, which makes aerial photography more useful when finer spatial data are more important than spectral information. Aerial photography is therefore useful for purposes requiring a finer scale, such as areas ranging from a few hundred to a few thousand hectares (Das and Ravindranath 2006).
Successive photographs along a flight strip include overlapping of up to 60% and create stereoscopic areas. This overlapping area can be used to form stereo pairs, and hence three-dimensional images. Structures such as forest tree species and their age and health or agricultural crops and agroforestry systems can be revealed from aerial photography with some training.
The materials required for using this technique include aerial photographs, a georeferenced map and plastic film.
Step 1: Find several points that are visible both in the map and the aerial photograph. Step 2: If the photograph does not have a scale, calculate it with the use of the photograph and map information. This is required if land area is to be estimated. Calculate the distance between two points in the map. Calculate the distance between the same two points in the aerial photograph.
Scale = Ground(m) Photograph(m)
Step 3: Do visual interpretation of the land-use systems of interest on an overlaid plastic film.
Step 4: Calculate the land areas of selected land-use systems. Aerial photography can be scanned and used digitally in a GIS.
126.96.36.199 Merits and Demerits of Aerial Photography
• High resolution
• Easy to interpret visually
• Good for land areas that are inaccessible or large
• May already be available for the required area, even in a time series
• Suitable for project development and monitoring phases
• For some area, availability of aerial photographs is limited and the cost is high
• Absence of georeferencing makes digitalization difficult
• Includes tilts and errors
• If not available, it requires a relatively long time to obtain the photographs
• Not appropriate in rugged terrain
• If there are multiple land units far apart, more images are required
• Different stages of vegetation growth/degradation can be difficult to distinguish
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