Principles of Image Interpretation

Visual image interpretation is a fundamental process that is often the first step in obtaining site-specific information from traditional aerial photographs, single band, and composite band satellite images. Interpretation skills are necessary in order to effectively complete many studies involving Earth system processes and ensuing environmental issues. Interpreting an image begins as a visual process consisting of an ordered sequence of steps including: detection, recognition, identification, classification, and analysis. When viewing an image, one first detects the presence or absence of a number of spatial objects in the scene. The brain presumably has some stored experience that enables an interpreter to recognize (to generalize spatial entities by sorting them into general feature classes.) objects based upon some measure of learned knowledge; for example, an ability to recognize water from land. Further thought enables one to identify (to refine the identity of feature classes) water as having different physical properties such as variances in color, tone (lightness/darkness), and perhaps patterns such as flow lines indicating movement and direction. The variations in these properties are next classified (categorizing objects or areas by specific criteria through a more formal process of discrimination.) either by manually drawing boundaries between these visual properties, or by running computer driven classifiers (software algorithms). Once the image has been classified, an analysis may seek to answer any number of questions.