Spectral and radiometric calibration of midwave and longwave infrared cameras

Abstract

Accurate spectral and radiometric calibrations of IR cameras are needed to interpret infrared imagery properly, to monitor camera performance over time, and to evaluate new imaging radiometers. In this paper, the physical basis for calibrating IR cameras is derived from first principles, and a laboratory setup used to perform both radiometric and spectral calibrations is described. The calibration procedures used with this setup are then demonstrated on a midwave IR focal plane array camera, a midwave IR scanned camera, and a longwave IR scanned camera. The system spectral response and radiometric response of each camera is given and analyzed. An error analysis of approximating a camera's spectral response by an equivalent top-hat responsivity is also given.

Verification of the Aerosol Emissivity Model, PILOT-EX

“…In all cases, the mathematical calculations were performed using the semi-analytical methods described in the SPIE (International Society for Optical Engineering) Handbooks [9] and are accurate to within 0.01percent for the range of temperatures shown. For ease of explanation we have assumed that the idealized instrument has been calibrated against a Blackbody target so that any instrumental artifacts are either compensated or otherwise removed [10]. Thus, with an instrument so calibrated, it is possible, in principle, to convert the measured signal to the target temperature using the inverse of eq.…”

“…(2) to insert the mass extinction coefficient [a=kabs+Gsca] and albedo [Oo,=csca/(kabs+osca)], and the second to replace the spatial variable, r, with the path optical thickness, r [=T(r,ro)]. Following conventional practice, we now define the optical thickness between any two points in terms of the concentration path integral as [note dT-'aC(r)dr]: r r (ro,r) = fdc' = fJcC(r')dr' (10) where it is understood that the integration proceeds along the straight line path connecting the two points r, and r.…”

Analysis of uncertainties in infrared camera measurements of a turbofan engine in an altitude test cell

“…This relationship can be easily derived by examining Kirchhoff's Law as he first recorded it in 1858 [16]: 25) where M (λ) is the exitance from a graybody source. From the Stefan-Boltzmann Law, Equation (2.25) then becomes 26) where it follows that α = .…”

“…Foremost, it accounts for the fact that detectors are not respon- Mermelstein, Snail, and Priest [25] derived the following experimental algorithm for measuring the normalized system spectral response, R * (λ) , for MWIR and 2-27 LWIR cameras:…”

Effect of Ambient Temperature on Calibration of Cooled Thermal Camera

“…These cameras measure the IR radiance of the object and derive the apparent temperature of the object using the calibration files provided by the manufacturer 1 . The calibration file is essentially created using a process where temperature reference is taken from a blackbody source 2 . Cooled thermal cameras are based on photon detectors and detector signal is proportional to number of incident photons per second from the sources as well as from the background 3 .…”