Clocking smear analysis and reduction for multi phase TDI CCD in remote sensing system.

Clocking smear caused by charge transfer of time delay and integration charge coupled device (TDI CCD) is the natural component in remote imaging sensing system, and it could not be eliminated by traditional motion compensation schemes. After researching on the operation of a typical three phase TDI CCD, we give a thorough understanding on causes of clocking smear. Then an elaborate mathematical model describing the charge transfer procedure is developed, and the modulation transfer function (MTF) losses due to charge transfer is also presented, which shows that nearly one pixel smear will be introduced by traditional phase timing. Therefore we propose a novel charge transfer method, using which only 1/2ϕ pixel smear will occur within the imaging operation of a single TDI stage, where ϕ represents the number of timing phases. Finally, a series of image simulations are made for two, three and four phase TDI CCD in which clocking smear is caused by our and conventional charge transfer methods respectively. The experimental results confirm that image quality improvement can be achieved by our method.