Clementine Ultraviolet-Visible Camera (UVVIS)

The UVVIS camera has a catadioptic telescope using fused silica lenses focusing onto a metachrome-coated CCD imager. Active wavelength response is limited on the short wavelength end by the transmission of fused silica and the optical blur of the lens. Wavelength response on the long end is limited by the response of the CCD. Six spectral bands can be selected from a filter wheel which is controlled through the same serial-addressable synchronous interface (SASI).

The Thomson focal plane array (FPA) used is a frame-transfer device, accomplishing electronic shuttering by rapidly shifting the active pixel area into the storage area, pausing for the (13-bit programmable) integration time, then rapidly shifting the captured image into a storage buffer from which the image is read out. Post-FPA electronics allow three gain states followed by 5 bits of offset that span 248 counts in the analog regime to augment the basic 8-bit A/D conversion. Gain is A/D digitization noise limited, so proper exposure is critical. Working against the day side of the Moon as a target, typical integration times were as short as several milliseconds in the lowest gain state (1000 electrons/bit) near sub-solar illumination points at the brighter spectral bands, increasing to 40 msec near the polar regions in the mid-gain setting for the weaker 415 and 1000 nm spectral bands.