Using High Dynamic Range Photogrammetry for Luminance Mapping the Sky and the Sun

摘要

Accurate and efficient measurement of the luminance distribution of the sky and the sun is very important for daylight harvesting. The conventional way to measure the luminance of the sky is to use a luminance meter or a sky scanner. The measurement resolutions of the two instruments are very low (1 degree for LS-100 luminance meter and 11 degree for a typical sky scanner). Neither of the two methods is able to measure the high luminance of the sun (1.6 × 10~9) and its corona. In addition, the sky scanner measures only 2/3 of the celestial hemisphere. This study used the recently developed high dynamic range (HDR) photogrammetry for luminance mapping the sky and the sun. This paper introduced a camera-array-based measurement technology and a luminance replacement method to measure the luminance distribution of the entire celestial hemisphere. Two Canon EOS Rebel T2i cameras each fitted with a Sigma 4.5mm circular fisheye lens were set up for the measurement of the sky and the sun, respectively. The luminance data, together with the three dimensional XYZ coordinates were extracted from the HDR images using HDR photogrammetry. The measurement results of the luminance distribution of the sky and that of the sun were combined together to form the luminance distribution of the entire celestial hemisphere. Then, an experiment was carried out in the Clinton State Park at Lawrence, Kansas to validate the measurement method, and the preliminary results of the experiment were discussed. The measurement protocol was also introduced. It was shown that our method might be applicable to the measurement of the luminance distribution of the sky and the sun, and could contribute to climate-based daylight modeling research studies.