CASI Multispectral Imagery

Compact Airborne Spectrographic Imager is a multispectral pushbroom system that acquires data in visible and near infrared (VNIR) light. Unlike camera systems that generally acquire data in three (red, green, blue) or four (red, green, blue and near infra-red) bands, the CASI splits light into several discrete bands, up to 288, although approximately 20 are more normally captured. It is capable of collecting data in discrete areas of the electromagnetic spectrum and can target key wavelengths that allow information about ground characteristics and ground cover type to be inferred. For example, the CASI can target the precise wavelengths of chlorophyll absorption or the algae fluorescence peak. CASI data have been acquired on a project basis, so there are not extensive datasets. These datasets have generally been acquired where the limited spectral information in aerial photography would not be sufficient to map a specific variable, such as a specific vegetation type or biomass. CASI data are supplied in time-stamped GeoTIFF format as 5km by 5km tiles of the image mosaic. The tiles consist of a series of image layers representing discrete wavelengths. There has been no image balancing or atmospheric correction applied to the flight lines. Hence, lighting differences maybe apparent in the image mosaics. There are ways of mitigating against these effects, for instance applying band ratio techniques. CASI data should be used within either GIS or specialist image processing software for best results. Please refer to the metadata index catalgoues for the survey date captured, spatial resolution of the imagery and number of wave bands present in the data.