Specifying radiometric performance of hyperspectral and conventional cameras: A minimal set of independent characteristics

Abstract

The radiometric performance of cameras is customarily characterized and specified in terms of component properties such as F-number and readout noise. This paper considers the camera as an integrated unit and derives characteristics suitable for specifying noise, throughput and saturation as determined from the overall input-to-output performance. A conventional model of signal and noise is reformulated into a simpler "equivalent camera" model with the same radiometric performance, constrained to have a lossless lens with detector-side pupil subtending 1 steradian, and a detector with a peak quantum efficiency (QE) of 1. The small parameter set of this model can then be determined with the camera treated as a "black box", relevant for verification of camera specifications. The net light collection of the real camera is expressed by the detector area of the equivalent camera, denoted A* , as well as the wavelength dependence of its QE, denoted η* (λ). The noise floor due to readout noise can be expressed for a particular camera as a noise equivalent spectral radiance (NESR). For comparison of cameras with different bandwidths, it is shown that a comparative figure of merit, which is also independent of integration time, is the "noise equivalent radiance dose" (NERD). For a hyperspectral camera, the model parameters can be determined with a simple broadband source, while cameras with broad spectral response require measurements with tunable monochromatic light. The treatment also applies to spectrometers. Reference is made to D*, a well-established figure of merit for detectors, and it is argued that A*,η* (λ) and NERD are analogous figures of merit for camera properties.