Development and operation of a real-time imaging spectroradiometer

摘要

Many imaging applications require quantitative determination of a scene's spectral radiance. This paper describes a new system capable of near real-time spectroradiometric imagery. Operating at a full-spectrum update rate of 30 Hz, this imager is capable of collecting a 20 point spectral image from 400 nm to 700 nm, with a 10 nm bandwidth, over an image of 256 $MUL 192 pixels. At a slightly reduced update rate of 20 Hz, 30 point spectra can be collected. A slower update version is available with extended coverage to 900 nm. Although this full scene information is available, to make such a tremendous amount of data more manageable, internal processing electronics compute in real time the tristimulus integrals X, Y, and Z; along with standard RGB, these colorimetric integrals are available either as tristimulus values, or as chromaticity coordinates x, y, and Y. To allow the imager to simulate sensors with many different spectral responses, any arbitrary response function may be loaded into the imager including delta functions to allow single wavelength viewing. Understanding that some applications may require better spectral resolution than 10 nm, a separate processing section allows resolution enhancement to about 1 nm with 1,000 point spectra available from 256 pixels throughout the scene. These enhanced spectra are available at a .3 Hz update rate, limited by the readout rate of the imaging array. The luminous dynamic range of the instrument is about 1 cd/m$+2$/ to 10$+5$/ cd/m$+2$/. The unique challenges of design and calibration are described. Pixel readout rates of 30 MHz, for full frame readout rates of 600 Hz present the first challenge, with the processing rate of 300$PLU million integer operations per second presenting the second. Spatial and spectral calibration of 50,000 pixels and 2,000 spectral positions mandate novel decoupling methods to keep the required calibration memory to a reasonable size. Large luminous dynamic range also requires care to maintain precision operation with minimum memory size.