Typical Operations on Aerial Image Data

Hardcopy aerial photography began in a hot air balloon near Paris around 1858 (Downs, 1999). Since then, the science of photogrammetry has developed. This science involves taking accurate measurements from photographs to determine size and to map objects in an image. Many industries utilize methods of photogrammetry. A forester, for example, can measure the height and diameter of a  tree in his or her district by interpreting aerial photography. Other types of measurement include area, distance, terrain elevation, and geographical location.

One of the most common initial operations on digital aerial imagery is called image enhancement. This refers to using digital image processing techniques to make the image more attractive and pleasant to the human eye. This has been going on in photo labs for over a century. It does not make the data any better, but rather, makes it aesthetically more pleasing in appearance, and therefore easier to interpret.  A wide variety of methods are available to accomplish this in various ways. Some of the most common methods are: rescaling the brightness values, contrast enhancement, image sharpening, and image merging.

Another procedure applying to hardcopy photographs is photomosaicing. A photomosaic is a reproduction of a series of adjacent photos fastened together so that a single, larger image is formed. This technique is effective for producing large format photos with a maximum amount of detail. All of these procedures can also be accomplished with softcopy images using digital image processing.

Image 23: Landsat 7 Image of the southern coast of Louisiana (USGS)

New techniques in digital image processing allow scientists to extract specific information from aerial images. For example, computers can convert digital image information into a photographic representation showing productive soils for farming (Downs, 1999). This is done by interpreting information from special remote sensors that detect soil characteristics, like moisture level, and then conducting digital image processing.

Georeferencing is another exercise with softcopy data. Essentially, georeferencing takes a digital image and “ties” it to the ground. In other words, coordinates are assigned to the photographs that indicate where the image lies on the earth’s surface. A georeferenced image is important for making accurate maps.

There is specific equipment used for most of these operations with aerial image data. For instance, all softcopy data operations call for sophisticated and powerful software packages, along with modern hardware, to process and store large amounts of information.