Clementine Long-Wavelength Infrared Camera (LWIR)

Description

The Clementine Long-Wavelength Infrared (LWIR) Camera was designed to image darkside features on both the Moon and the near-Earth asteroid 1620 Geographos in the thermal infrared spectrum, and to allow measurement of thermal properties of material on both bodies, from which an assessment of regolith characteristics can be made. The Geographos phase of the mission was cancelled due to equipment malfunction.

The LWIR camera consisted of a catadioptric lens with an aperture of 131 mm focused onto a mechanically-cooled (to 65 K) Amber HgCdTe focal-plane array (FPA). The FPA had a broad-band response from wavelengths of 8000--9500 nm. The focal length was 350 mm. The field of view was 1 x 1 degree, translating to a width of about 17.5 km at 1000 km distance. The image array was 128 x 128 pixels, with each pixel being 50 micrometers on a side, giving a pixel resolution varying from about 55--136 m/pixel. (At Geographos the pixel resolution would have been about 14 m for a 100 km closest approach, giving an image width of about 1750 m.) At the Moon, the camera was used primarily for nightside imaging near the poles, where it could take 660 images over a ten minute pass each five hour orbit. It was also used for selected high-resolution images in other areas. The camera imaged approximately 0.4% of the Moon's surface (both poles from 85--90 degrees) over the two month lunar phase of the mission. The nominal signal-to-noise ratio was 950, with a relative calibration of 1% and an absolute calibration of 30%, and a gain ranging from 0.5 to 36.