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A time delay and integration or time delay integration (TDI) charge-coupled device (CCD) is an image sensor for capturing images of moving objects at low light levels. The motion it can capture is similar to that captured by a line-scan CCD which uses a single line of photo-sensitive elements to capture one image strip of a scene that is moving at a right angle to the line of elements. A line-scan CCD needs to have high light levels, however, in order to register the light quickly before the motion causes smearing of the image. The TDI CCD overcomes this illumination limitation by having multiple rows of elements which each shift their partial measurements to the adjacent row synchronously with the motion of the image across the array of elements. This provides high sensitivity for moving images unobtainable using conventional CCD arrays or single-line-scan devices.
The TDI CCD improves upon the single-line-scan system by adding the photocharges of its multiple lines.