A Colorized Sub-aperture Image (CSI) is a Capella Spotlight mode collection processed to accentuate manmade objects, angular features, and objects in motion in a scene with vivid colors.
During the Spotlight data acquisition, the satellite’s antenna beam is focused on a point of the earth for an extended period—tens of seconds. In data processing, this long synthetic aperture is divided into a set of up to 5 single-look sub-apertures generated from different squint angles across the duration of the collection.
In CSI processing, each sub-aperture is progressively colorizes using a cool-warm colormap and combines them into a 3-band detected image. Manmade features, even those partially obscured by vegetation, will typically reflect strongly from a single sub-aperture and thus ‘pop’ out in a single color of the CSI image, as seen in the example below.
Objects in motion will render as a rainbow, representing the displacement of the object in each sub-aperture, with blue indicating the first sub-aperture and red indicating the last sub-aperture. Features such as tree canopies or brush generally reflect energy equally in all sub-apertures and will render grayscale.
Capella’s CSI is geocoded, terrain-height corrected, and delivered as a GeoTiff so that it can be combined with other geospatial data and viewed within a wide range of geospatial software.