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Drift scan is a relatively low-cost technique for surveying a portion of the sky using a CCD, e.g., with amateur equipment. It can be effective in identifying movement of observed objects such satellites or minor planets.
The technique has the advantage that the telescope remains stationary. It is a method of scanning the sky as it passes through the field of view, the particular technique being that extraction of data from the CCD is synchronized with the rate at which a pixel of the CCD moves to new positions on the celestial sphere. The telescope and CCD must be oriented so as to allow such a set-up. The technique is very effective with portions of the sky near the celestial equator, where the image can drift across the CCD pixels in a regular pattern, making the process of producing the image trivial. The product of such a drift scan is an image consisting of an east-west strip across the sky.
The term drift scan is also used for such observations synchronized with the Earth's rotation, but not specifically using the synchronized unloading of a CCD as described above. It is also used for rotations other than Earth rotation such as a rotating space observatory (e.g., Gaia).