title: Passive infrared sensors: limitations on performance.
abstract: The performance of passive sensors for surveillance, radiometry, spectroscopy, astronomy is analyzed using idealizations of engineering features. Sensors are characterized by a finite number of degrees of freedom in each of two angles, wavelength, and time. An optimum number of degrees of freedom is found to sense a target field in four dimensions. Degrees of freedom are quite freely interchangeable between dimensions of different kinds. An optimum number of output states is related to the sensing or measurement requirment. An optimum weighting is found for averaging degrees of freedom into output states. Simple equations relate performance to an index of cost. Examples apply the results to estimate limits to sensor performance for several applications.
authors.forename: J A
authors.initials: JA
authors.lastname: Jamieson