Radiant energy detection system

Claim 1

In a radiant energy system for discriminating between radiation from a target and ambient radiation, the combination of: optical receiver means comprising an optical objective for focusing the said radiation originating from an observed field, an optical splitter device for producing two optical channels, a first optical filter in a first of said channels having a pass-band corresponding substantially to the said target radiation spectrum, a second optical filter in the second of said channels having a pass-band corresponding to a portion of the said ambient radiation spectrum and outside the target spectrum and optical attenuating means for balancing the ambient radiation levels in the two channels; reticle means for modulating the focused radiation by means of grids comprising, in a plane, transparent zones separated by opaque zones said grids being moved substantially in the focal plane of said optical objective in a direction transverse to that of the optical axis of said objective; photodetection means behind said reticle means for detecting the modulated and filtered radiation and a circuit for processing the detected signals; the said optical splitter device producing in combination with said objective two images of the said field, one for each channel, which are staggered in the plane of the grids in the said direction by an amount substantially equal to the diameter of the target image, the dimension of the said zones in this direction being a multiple of and at least equal to this diameter.