Clementine Ultraviolet/Visible CCD Camera (UV/Vis)

Description

The Ultraviolet/Visible camera (UV/Vis) was designed to study the surfaces of the Moon and the asteroid Geographos at five different wavelengths in the ultraviolet and visible spectrum. The Geographos rendezvous was cancelled due to equipment malfunction. This experiment yielded information on the petrologic properties of the surface material on the Moon, as well as giving images useful for morphologic studies and cratering statistics. Most images were taken at low Sun angles, which is useful for petrologic studies but not for observing morphology.

The sensor consisted of a catadioptric telescope with an aperture of 46 mm and fused silica lenses focused onto a coated Thompson CCD camera with a bandpass of 250-1000 nm and a six-position filter wheel. The wavelength response was limited on the short wavelength end by the transmission and optical blur of the lens, and on the long end by the CCD response. The CCD was a frame transfer device which allowed three gain states (150, 350, and 1000 electrons/bit). Integration times varied from 1 to 40 ms depending on gain state, solar illumination angle, and filter. The filter center wavelengths (and bandpass widths (FWHM)) were 415 nm (40 nm), 750 nm (10 nm), 900 nm (30 nm), 950 nm (30 nm), 1000 nm (30 nm), and a broad-band filter covering 400-950 nm. The field of view was 4.2 x 5.6 degrees, translating to a cross-track width of about 40 km at a nominal 400 km lunar altitude. The image array was 288 x 384 pixels. Pixel resolution varied from 100-325 m during a single orbit mapping run at the Moon. At Geographos the pixel resolution would have been 25 m at the 100 km closest approach, giving an image size about 7 x 10 km. The camera took twelve images in each 1.3 s image burst, which occured 125 times over the 80 minute mapping span during each five hour lunar orbit. The Moon's surface was covered completely during the two month lunar mapping phase of the mission. The dynamic range was 15,000. The signal-to-noise ratio varied from 25--87 depending on the surface albedo and phase angle, with a relative calibration of 1% and an absolute calibration of 15%.