The Four- and Five-Band Multispectral Scanners for Landsat

The earth resources sensing Multispectral Scanner (MSS) for the Landsat satellite has two versions; one with four spectral bands from 0.5 to 1.1 um, and one with five bands, the added band being 10.4 to 12.6 pri. This paper describes optical design and performance. The instrument uses a flat, object-space scanning mirror of near linear motion, with a sensitive optical position monitor to detect mirror angular position. The 22.9-cm aperture telescope images the scene on an array of fiber optics, which dissect and transmit the scene energy to photomultiplier tubes detecting in Bands 1, 2, and 3, and silicon photodiodes detecting Band 4. Band 5 energy passes the fiber optic assembly and is reimaged on a radiatively cooled mercury cadmium telluride (HgCdTe) detector. Bands 1 through 4 are calibrated by an internal lamp and by the sun. Band 5 employs an internal blackbody and a cold refer-ence which is a self-view of the detector. The orbiting four-band scanner is furnishing data registered to better than 50-m band-to-band and resolving 80-m repetitive pattern over a 185-km swath width from 907-km altitude. Over a year's time, radiance measurements have shown less than 2% variation.