Earth monitoring satellite system with combined infrared interferometry

Abstract

Apparatus for producing interferograms on array of light detectors is described in which light from a field of view is gathered by a concave Newtonian mirror, collimated by a Schwarzchild objective and directed along a first optical path having PEM's modulated so as to act like an interferometer between a pair of linear polarizers and a lens for imaging light passing through said polarizers onto the array. Scattergrams are produced on the array by a laser in a second optical path that includes a linear polarizer, a modulated PEM for producing light that is polarization modulated, optical elements for directing the circularly polarized light into the field of view of the Newtonian mirror, a modulator for causing the PEM's in the first optical path to elliptically polarize light and a device for extracting the first linear polarizer in the first optical path from that path. The distance between the apparatus and an area under examination is determined by turning on the laser, sinusoidally modulating the PEM in the second optical path, detecting the light modulated by that PEM so as to produce a first sinusoidal voltage, removing modulation from the PEM's in the first optical path and determining the phase difference of a second sinusoidal voltage produced by one light detector of the array and the first sinusoidal voltage.