Analyzing colors and spectra of natural rainbows with hyperspectral imaging

Few colorimetric analyses of natural rainbows (i.e., bows seen in rain showers) have been published, and these are limited either to approximate techniques (colorimetrically calibrated red-green-blue (RGB) cameras) or to rainbow proxies (bows seen in sunlit water-drop sprays). Furthermore, no research papers provide angularly detailed spectra of natural rainbows in the visible and near-IR. Thus some uncertainty exists about whether the published spectra and colors differ perceptibly from those in natural rainbows. However, battery-powered imaging spectrometers now make possible direct field measurements of the observed chromaticities and spectra in such bows. These data (1) show consistent spectral and colorimetric patterns along rainbow radii and (2) let one subtract additively mixed background light to reveal the intrinsic colors and spectra produced by rainbow scattering in nature.