The instrument carried aboard the satellite which views the earth. Examples are AVHRR, CZCS, SeaWiFS and MODIS. Typically the scanner is simultaneously sensitive to a number of parts (bands) of the visible and infra-red spectrum. It will rotate, scanning the earth directly underneath the satellite (the sub-satellite point) from left to right. The data will then be transmitted to earth as one scan-line, typically 1000 to 2000 points across, each point having values for the parts of the spectrum seen. By the time the scanner comes back to the start the satellite will have progressed so a different part of the earth is seen. See also Sensor.