Composite Generation for visual analysis, colour composites make fullest use of the capabilities of the human eye. Composite generation ranges from simply selecting the bands to use, to more complicated procedures of band combination and associated contrast stretch.

Contrast stretch is the procedure by which the input digital number range for an image, which tends to spans only a narrow range of values, is increased to include a larger part of the available digital number. Therefore contrast manipulation procedures are vital for most visual analyses.

Digital Elevation Model or DEM is a digital map of elevation data. These maps, a type of DTM (Digital Terrain Model), are raster data meaning that they are made up of equally sized gridded cells each with a unique elevation. The figure below shows a representation of DEM data. Each grid cell has an elevation association with it.

DEM data representation
Source: http://www.ems-i.com

Digital Filtering is one of the most interesting features of digital analysis. These filters can be used to provide edge enhancement, which will improve the image by removing the haze but will also isolate lineaments and directional trends

Electromagnetic Radiation is energy that travels at the speed of light, transmitted by oscillating electric waves.

Elimination Key is prepared in such a way that the interpretation proceeds step by step from the general to the specific eventually leading to the elimination of all features or conditions except the one being identified. Often elimination keys take the form of dichotomous keys, where the interpreter makes a series of choices between two alternatives eventually eliminating all but one possible answer.

MSS (Multispectral scanner) are systems that acquires data at the same time from different wavebands.

Photogrammetric Measurement of photographic images for the purpose of extracting useful information, particularly for the creation of accurate maps.

Photogrammetrists study photogrammetry science - making accurate measurements from photographs. Applies principles of optics and knowledge of interior geometry of the camera used. Necessary to have detailed knowledge of cameras and the circumstances under which they are used. Photographs for photogrammetry are normally prepared on glass plates as more stable and do not change with temperature/humidity. Its most common use has been in the production of hardcopy topographic maps. Today photographic processes used extensively to produce a range of GIS data products such as precise raster image backdrops for vector data and digital elevation models.

Pushbroom system is a system that uses an array of several tiny detectors, each of which measures the reflectance of an individual ground-sampling cell

Raster An image which is scanned with an optical scanner to convert graphics to computer-readable form. Spatial data is recorded in narrow strips across the data surface thereby producing a raster format. This can be seen from the outline map below:

Source: Lillesand and Kiefer (2000) p 48

Selective Key gives numerous example images together with supporting text. In using this key the interpreter selects an example that best resembles the feature or condition they are studying.

Spatial resolution is a measure of how much detail can be observed within an image.

Spectrum The several coloured and other rays of which light is composed, separated by the refraction of a prism or other means, and observed or studied either as spread out on a screen, by direct vision, by photography, or otherwise.

Stereopairs two photographs of the same area, which are overlapped and viewed through a stereoscope to produce a three-dimensional picture.

Stereoscope is the piece of equipment used to view aerial photographs in three-dimensions. A Pocket Lens Stereoscope is shown below:

Source: Lillesand and Kiefer (2000) p 202

Stereoscopic Viewing A single vertical aerial photograph is a two-dimensional representation of the three-dimensional landscape. Humans due to their binocular visual capabilities are able to assimilate three-dimensional information. Two adjacent photographs (a stereopair) can be viewed by using a stereoscope with the left eye observing the left photograph and the right eye the right photograph giving the three-dimensional effect.

Vector images represent polygonal boundaries as lines and represent lines as a sequence of very short line segments which can be represented by an ordered sequence of points defining the line segments. This can be seen in the example map below:

Source: Lillesand and Kiefer (2000) p 48