Chapter 5
Pre-processing Wan Bakx Ben Gorte Wim Feringa Karl Grabmaier Lucas Janssen Norman Kerle Gabriel Parodi Anupma Prakash Ernst Schetselaar Klaus Tempfli Michael Weir 5.1
Visualization and radiometric operations
This section explains the processing of raw remote sensing data and the basic principles of visualization of data. The production of images on a computer monitor or paper print-out has always been a prime concern of RS. We use images for inspecting raw data and for performing various data rectification and restoration tasks. Once data are corrected, we convert them once more to images and use these for information extraction by visual interpretation or to support digital image analysis. Many RS applications make use of multispectral data; to visualize them we have to rely on the use of colour. Section 5.1.1 explains how we perceive colour, which can help us to understand how to produce optimal images from multispectral data and how to properly interpret them. We try to build remote sensors SO that they faithfully image a scene, and we are increasingly successful in doing so. Consider as an example a vertical photograph (or nadir view) of high resolution from a space-borne sensor: it closely resembles a map of the scene and, if the scene was a city, urban planners would be able to readily recognize objects of interest. Taking a closer look, we know that RS images will be geometrically distorted as compared to a map. The degree and type of distortion depends on the type of sensor platform used. Geometrical correction of RS images will be treated in Section 5.3. In Chapter 2 you have learned that remote sensors measure radiances. The results of
167