Basics: Geographic Tech (1/2)

What Is Aerial Photography and How Does It Work?

Aerial photography is - as it sounds - the process of taking photographs from the air, but there is more to it than simply using a light aircraft or helicopter and flying up to take photographs. There are many elements to an aerial survey that must be considered to ensure that the data is useful enough to extrapolate whatever is being investigated. It is often difficult to see elements of the landscape on the ground, features can easily be missed, and what might seem like an insignificant bump from ground level can become more significant in a wider context ; some landscape types are difficult to access on foot so aerial photographs are vital to study and map them.

They have been used as a method of landscape studies for over a century, especially in archaeology and researchers have learnt much about the world around us; its applications today are broad and coupled with the growing technology of GIS (geographic information systems), the potential means that the method will not become obsolete any time soon. Aerial photographs are taken in two basic forms and both have different uses and applications: oblique and vertical. Even today in an age of high quality digital imaging, black and white images are preferred - partly because they are cheaper but also partly because the contrast of black, white and greys makes it easier to pick out features.

Look at the image below, of a greenway in Boston, USA. See which features you can make out. Think about which other features this image would not prove useful for.

Oblique

These images, such as the one above, are usually taken at an angle, typically 45 degrees but as they are often taken manually, they can be whatever angle gives the best view of the feature or landscape. The oblique image is primarily used in archaeology to take a wider context of a feature and the area around it, and also to give depth. Nearly always taken at a much lower elevation than the vertical image and in few numbers, its application is fairly limited and often taken for a specific purpose. There is a problem in perspective because the farther away a feature is, the smaller it will appear: nearer objects of comparable size appear larger than those that are farther away so it is often best to take a selection or to use a frame of reference on the ground for perspective purposes. These images are taken from small fixed-wing aircraft and helicopters and are perfectly suited for monitoring erosion of features and monuments throughout the year and over the course of many decades.

Taking a photograph straight down over a landscape is the more familiar form of aerial photograph. It is a plan view so there is no perspective to distort the image. This also means that it is difficult to read the lay of the land such as changes in height - though there is a work around to create 3D image through stereoscopic views, using a device to examine two at once. This usually gives a good impression of the variation in the elevation of land . They are taken at regular heights for consistency so it is easier to compare contexts of a landscape taken on the same day, or many years apart to examine development. Rarely used in archaeological applications except perhaps sometimes to find interesting earthworks and other sites that are easily missed on the ground, they cover a much wider area and focus on topography rather than specific details.