A telescope on the side of the spinning satellite is focused on the earth disc and causes a .8 km x .8 km area of the earth to fall on each sensor through a mirror assembly. As the satellite spins, the 8 sensors see 8 lines of image across the earth disc, one line per sensor with each line being .8 km high. After each rotation of the satellite the scan mirror assembly is stepped so that light from the next eight parallel adjacent lines are swept out in the west to east direction. This process continues until the earth has been scanned from pole to pole. 1800 steps of the mirror are required to form a complete image of the earth.
Light falling on each sensor represents individual picture elements or pixels.
To create the image then, pixels in the horizontal direction are obtained from the satellite spin and pixels in the vertical direction are obtained from the stepping of the vertical scan mirror. The mirror reflects the incoming light from the telescope on the light sensor elements. The output of each sensor is referred to as a channel. Thus there are eight channels of visible data. When stimulated by incident radiation from visible light, each channel responds with an output which is then analog to digital converted to a numerical value for transmission back to earth as raw data.