Remote Sensing

The image formation and viewing systems are composed of four basic components:

1. The image collection
2. The image sensitive
3. The image recording
4. The image viewing

A photographic image formation system has: (a) the camera lens to collect light rays reflected from illuminated object, (b) the unexposed film which is light sensitive material, (c) the exposed film which records the image, (d) the developed film or printed photographic paper which records and at the same time displays the image.

A video image formation system has: (a) the camera lens, (b) a CCD light sensitive array to sense the image and (c) a recording system (RAM, magnetic tape, CD, DVD), (d) the viewing system plays the recorded media and displays the video image on a TV screen.

Satellite images are obtained using all kinds of image formation systems including multispectral optical mechanical scanners and radar images.

Recorded image such as exposed film, video tape etc. usually is not visible and it is called latent image to make it visible it is necessary to use a viewing system.

Photographic development of the exposed film and printing images on paper are part of the viewing system.

Software and hardware devices that take images from media such as RAM, magnetic tape, CD, DVD etc and they assemble then on a TV screen or in paper print compose also image viewing systems.

The way an image formation and viewing system works can be visualized as follows:

Consider an object located in the geographical space and illuminated by a light source (instead of illumination could be radiation from the electromagnetic spectrum). There are two cases to obtain an image:

1. the object is composed of infinite number of points (analog image) each one of them reflecting light to all directions. Somewhere, in direct view with the object, an image collector is located (camera lens) which collects a cone of light rays from each object point and focuses them into a corresponding point in the image domain where the image sensitive material (image sensor) is located (unexposed film) and the latent image is formed and recorded. After the developing process the image is formed either in black and white form by giving a gray scale value to each image point (gray scale is formed by the total concentration of metallic silver over each point), or, by the component hue of three layers of colors (yellow, magenta, cyan – YMC) over the same point. A color photograph may also be considered as a three channel image.
2. the object is composed of finite number of points ordered in rows and columns (digital image or raster image), each point reflecting light to all directions. Somewhere, in direct view with the object, an image collector is located (camera lens) which collects a cone of light rays from each object point and focuses them into a corresponding point in the image domain where the image sensitive material is located (CCD array) and the latent image is formed and stored in a mass storage media such as RAM, magnetic tape, hard disk, CD-ROM etc. The focussed radiation to form the image point can feed one sensor cell for black and white image (single channel image) thus one gray scale value is recorded, or, could feed an array of sensor cells (multichannel or multispectral image) each one of them being sensitive to specific band of wavelengths of the electromagnetic spectrum, thus an array of gray scale values for the same image point is recorded. To view such recorded image it is necessary to run appropriate software which takes the image values from the mass recording media, assembles them in corresponding rows and columns, gives them a color value from a color palette and prints them either in a TV screen or in a hard copy.
   

© 1999 TRIANET, Program of the European Union Socrates-Comenius
Last update on 04.05.1999 by Markus Zapke-Gründemann