It is an interline CCD with progressive scanning and can be cooled to −20°C by Peltier element. The camera is shown in Fig. 4. It was filled with dry nitrogen gas to protect for wet air to condense on the CCD surface. The Peltier element is cooled by circulating water. A signal processing circuit was also produced to digitize the video signal with 12 bits resolution, control exposure time from 0.1 ms to 351 s, accumulate frame images up to 65535 times. Double sampling method was adopted and a PCI interface board was developed to transfer the stored image data in the system to a personal computer.