A thermal energy imaging system includes an optical system for focusing thermal energy emanating from a scene on an array of bulk semiconductor photodetectors. The detector array outputs electrical signals representative of the impinging thermal energy, a video electronic circuit and a pseudo ac coupling circuit interconnecting the detector array and video electronic circuit for reducing the required dynamic range of the video electronic circuit. The pseudo ac coupling circuit includes first and second electrical paths to an sychronous clamp. The first path includes a switch to the synchronous clamp; the second clamp includes first and second integrator circuits and a switch; the switch is connected to the synchronous clamp. The synchronous clamp includes an amplifier, capacitor and grounded switch. When the switch of the first electrical path is open and the switch of the second electrical path and synchronous clamp are closed, line picture element signals are voltage averaged and stored on the capacitor of the synchronous clamp. When the switch of the first electrical path is closed and the switches of the second electrical path and synchronous clamp are opened, the stored average voltage is combined with the line picture element signals to the video electronic circuitry for noise reduction. The first and second integrators comprise switched capacitors with the first integrator voltage averaging preselected portions of a line of picture element signals and the second integrator voltage averaging the average voltage of the portions of picture elements to provide a voltage average for a line of picture elements.
An imaging sensor for scanning an image in an object space is disclosed. The imaging sensor comprises a first and second plurality of infrared detectors. Also provided is a reflecting means for reflecting a predetermined portion of the object space on the first plurality of infrared detectors during first portion of the scanning cycle. The reflecting means is further able to reflect the predetermined portion of the object space on the second plurality of infrared detectors during the second portion of the scanning cycle. In a further embodiment, the orientation of the detectors permits each of the detectors to be calibrated with respect to another of the detectors by a sequential comparison of the outputs of pairs of the detectors whose fields-of-view overlap.
