Abstract: A detection assembly is disclosed for an infrared monitoring system, comprising a strip of elementary infrared detectors for analyzing the background of a scene. The elementary detectors are image formation detectors having sensitive areas smaller than the optical spots produced by the hot objects to be detected. The assembly comprises circuitry adapted for grouping together the image formation detectors virtually into virtual monitoring detectors having sensitive areas adapted to said optical spot, the grouping together circuitry comprising circuitry for summation in elevation of p contiguous intermediate image formation detectors at the pitch of q detectors with overlapping of p-q intermediate detectors from one monitoring detector to the next and circuitry for summation in relative bearing of r image formation samples at the pitch of s samples with an overlap of r-s samples from one monitoring pixel to the next.