1. An imaging spectroradiometer, comprising: a light collector, including a lens which produces a two-dimensional viewed image of a scene, means for spectrally filtering a repeating sequence of spectral images from the viewed image over a preselected spectrum of wavelengths, the means for spectrally filtering including means for repeating the spectral imaging of the scene over the preselected spectrum at a preselected sequence repetition frequency; a normally closed optical gate which receives the sequence of spectrally filtered images from the means for spectrally filtering and controllably opens at a preselected time to pass an image of a preselected wavelength from the sequence of spectral images, and a detector which receives the image of preselected wavelength from the optical gate and produces an electronic signal of an amplitude of each of a plurality of pixels; and an image processor operating substantially in real time, comprising a memory which temporarily stores the electronic signals produced by the detector as a plurality of pixelated electronic images, each image corresponding to an amplitude of the scene viewed at one of the preselected wavelengths, means for correcting the amplitudes of the pixels of the electronic images responsive to preselected systematic sources of error and means for calibrating the amplitudes responsive to the optical properties of the light collector, producing a corrected and calibrated electronic image, and means for mathematically correlating the corrected and calibrated electronic image with a preselected response function to produce an electronic image of a preselected spectral characteristic.