The detector in this instrument is a micro-machined thermopile array having about 20,000 elements. We arranged these elements in a unique geometrical pattern that provides excellent measurement accuracy, but eliminates outputs due to the inevitable thermal gradients that are generated within the instrument. The 20,000 elements were interconnected to provide only 16 outputs, for low complexity and high reliability of the electronics. Redundancy was designed into the array, so that broken elements would not disable the instrument.