Abstract: The invention provides an imaging spectrometer that provides a wide field-of-view camera and spectrometer for spectral imaging of a large two-dimensional area of the Earth's surface from an orbiting satellite or airplane. The wide field-of-view camera fore-optics includes spherical optical elements arranged monocentrically. The spectrometer includes an all-reflective coupling design that transfers the curved optical image to one or more compact imaging spectrometers. The spectrometers preferably comprise a spherical convex holographic grating and associated reflective optics for dispersing a collimated optical beam into its spectral components and focusing the spectral image onto a planar detector array. The instrument described herein is designed to operate in a "pushbroom" fashion, that is, the forward motion of the satellite or airplane generates the spatial dimension of the resulting image.

Abstract: The sun's energy is used in combination of movable and fixed diffuser plates, windows and apertures which are positioned in a series of test sequences (modes) for reflectance monitoring and calibration without the use of man-made sources. There are three embodiments, or implementations, of the invention--one embodiment uses two diffusers--a working diffuser and a secondary diffuser--the second embodiment uses three diffusers, a working diffuser, a secondary diffuser and a reference diffuser--and the third embodiment uses two diffusers--a working diffuser and a secondary diffuser, the latter also functioning as a cover for the working diffuser. The movable diffusers are mounted on rotatable cones and, in all embodiments, the sun is blocked from reaching the diffusers when not in use.