Scanners, such as those on the Landsats (MSS and TM) were the prime Earth-observing sensors during the 1970s into the 1980s. But these instruments contained moving parts, such as oscillating mirrors that were subject to wear and failure (although remarkably, the MSS on Landsat 5 continues to operate into 1999 after launch in March of 1984). Another approach to sensing EM radiation was developed in the interim, namely the Pushbroom Scanner, which uses charge-coupled devices (CCDs) as the detector.
CCD detectors are now in common use on air- and space-borne sensors (including the Hubble Space Telescope which captures astronomical scenes on a two-dimensional array, i.e., many parallel rows of detectors). The first airborne pushbroom scanner to be used operationally was the Multispectral Electro-optical Imaging Scanner (MEIS) built by Canada's CCRS. It images in 8 bands from 0.39 to 1.1 µm (using optical filters to produce the narrow band intervals) and uses a mirror to collect fore and aft views (along track) suitable as stereo imagery.
The German Aerospace Research Establishment (DFVLR) developed the first pushbroom scanner to be flown in space. The Modular Optico-electronic Multispectral Scanner (MOMS) was aboard Shuttle Mission STS-7 and STS-11 in 1983 and 1984. It uses two bands, at 0.575-0.625 and 0.825-0.975 µm, to produce 20 m resolution images. The MOMS image below is an area of farmland in Zimbabwe:
MOMS-2 was flown on STS-55 in May of 1993. It has four multispectral channels (13 m resolution) and a panchromatic band (4.3 m), and is in stereo mode. Here is a panchromatic image of a city on the western shore of the Persian Gulf (locus incertae; probably in Qatar):
The first use of CCD-based pushbroom scanners on an unmanned Earth-observing spacecraft was on the French SPOT-1 launched in 1986. (Page 3-2 describes the SPOT system, which is operated as a commercial program; 4 SPOTS have now been launched) An example of a SPOT image, from its high-resolution video (HRV) camera, covering a 60 km section (at 20 m. spatial resolution) of the coastal region in southwest Oregon, is the next image we show. Note that scan lines are absent, because each CCD element is, in effect, a tiny area analogous to a pixel.
False color composites are a standard product from SPOT. Here is part of a SPOT image taken in 1994 of developing farmland west of Miami, FL and near the edge of the Everglades, in which a new housing development has been put in since the mid-80s.
The third image is a panchromatic image (with 10 meters resolution) showing the edge of Orlando, Florida, including its airport.
Like Landsat, the SPOT satellites are widely used. The above only highlights the basic program. For more details, hit on the SPOT Image Internet home page.