Radiant energy detection system for suppressing the effects of ambient background radiation

Claim 1

IN A RADIATION DETECTION SYSTEM IN WHICH RADIANT ENERGY IS RECEIVED FROM A TARGET HAVING A GIVEN SPECTRAL DISTRIBUTION ALONG WITH AMBIENT BACKGROUND RADIATION HAVING A SPECTRAL DISTRIBUTION WHICH DIFFERS SUBSTANTIALLY FROM THE SPECTRAL DISTRIBUTION OF RADIANT ENERGY RECEIVED FROM SAID TARGET, THE COMBINATION OF AN OPTICAL SYSTEM FOR COLLECTING RADIANT ENERGY EMANATING FROM A VOLUME OF SPACE ENCOMPASSED BY A PREDETERMINED FIELD OF VIEW, A FIRST RADIATION SENSITIVE CELL, A FIRST OPTICAL FILTERING MEANS FOR PASSING RADIATION COLLECTED BY SAID OPTICAL SYSTEM TO SAID FIRST CELL WITHIN A FIRST SPECTRAL BAND, A SECOND RADIATION SENSITIVE CELL, A SECOND OPTICAL FILTERING MEANS FOR PASSING RADIATION COLLECTED BY SAID OPTICAL SYSTEM TO SAID SECOND CELL WITHIN A SECOND SPECTRAL BAND ENCOMPASSING THE FIRST SPECTRAL BAND, SUBTRACTION MEANS COUPLED TO SAID FIRST AND SECOND RADIATION SENSTIVE CELLS FOR DEVELOPING A SIGNAL REPRESENTING RADIATION INCLUDED IN SAID SECOND SPECTRAL BAND FALLING OUTSIDE OF SAID FIRST SPECTRAL BAND ONLY, AND MEANS FOR SUPPRESSING THE EFFECTS OF BACKGROUND FROM THE SIGNAL PROVIDED BY AT LEAST ONE OF SAID RADIATION SENSITIVE CELLS IN ACCORDANCE WITH THE SIGNAL PROIVDED BY SAID SUBTRACTION MEANS.