Along track scanner, also known as a pushbroom scanner, is an optoelectronic device that obtains images with a multispectral imaging system. The scanners are used for passive remote sensing. It records electromagnetic energy that is reflected (e.g., blue, green, red, and infrared light) or emitted (e.g., thermal infrared radiation) from the surface of the Earth. The scanners are mounted on space- or aircrafts.
A two-dimensional image is created (line by line) by exploiting the platform motion along the orbital track. The data are collected along track using a linear array of detectors arranged perpendicular to the direction of travel. The array of detectors are pushed along the flight direction to scan the successive scan lines, and hence the name pushbroom scanner.
There are no moving parts on a pushbroom sensor, hence, the scanning speed can be increased compared to across track systems. A longer dwell time over each ground resolution cell increases the signal strength (high radiometric resolution, no pixel distortion). Additionally, finer spatial and spectral resolution can be achieved as the size of the ground resolution cell is determined by the Instantaneous Field of View (IFOV) of a single detector. The systems are designed for high-resolution imaging. However, a very large number of detectors is needed for high resolution images. It is a complex optical system. In addition, the pushbroom scheme requires a wide Field of View (FOV) optics system to obtain the same swath as for a corresponding whiskbroom (across track) scanner. It has narrow swath width.
The detector arrays with such a line-scanning pushbroom system are usually of the type Charge-Coupled Device (CCD).
The MultiSpectral Instrument (MSI) on board the Sentinel-2 satellite (Copernicus mission) uses a pushbroom concept.
Multispectral imaging systems building the final image (line by line) exploiting the platform motion along the orbital track. No rotating mechanical part required, usually based on a CCD matrix (high spectral resolution but just up to 1 micrometer), e.g. Sentinel-2 MultiSpectral Instrument (MSI), Sentinel-3 Ocean and Land Colour Imager (OCLI).