Concept information
Preferred term
CASI
Definition
- The Compact Airborne Spectrographic Imager (CASI) is an imaging spectrometer designed and built by Itres Ltd of Calgary, Canada, and is flown on aircraft. It works on the principle of a series of lines of charged coupled devices (CCDs) which each produce an electrical charge dependant upon the amount of light energy falling upon them. These are packed together into a 3 dimensional array made up of 288 x 512 CCDs. Upwelling light radiation from beneath the aircraft is focused onto the array by a compound lens. Light entering the system is split into a number of wavebands, each registering on a different CCD or row of CCDs. As the aircraft travels forward, light reflected from a succession of small areas fall onto the array and is split into its wavebands. The minimum size (pixel size) of the areas recorded in the routine coastal surveys was 8m x 8m. Other pixel sizes can be recorded by altering height, speed and the focal length of the lens. The CASI can be operated continuously in 2 modes and intermittently in a third. In the spatial mode, the CASI records data in up to 19 selected spectral channels from all the pixels across the swath. Waveband channels can be selected for specific environmental parameters (such as chlorophyll, vegetation, etc.). The CASI can also be used in the spectral mode, recording data from across the whole spectrum over 288 wavebands but only for a limited number of pixels across the swath. This mode also allows the collection of spatial mode data in a single waveband to aid in the location of the spectral data. Finally, the CASI can also be used in short bursts in an enhanced spectral mode to record up to 74 channels over a 300 pixel wide swath. This acts as a middle ground between spectral and spatial modes. A PCI image processing package reads and displays CASI data directly in full 16 bit resolution to produce high resolution images. [This description was obtained from the UK Environment Agency.] (en)
Broader concept
URI
https://gcmd.earthdata.nasa.gov/kms/concept/895234ca-e7fe-4343-ac53-52786aa0b811
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