Effects of image quality, size and camera type on forest light environment estimates using digital hemispherical photography

Digital hemispherical photography is an effective device for estimating the light environment beneath a forest canopy. In this study, the effects of different image quality, size and camera type on the light environment estimates using digital hemispherical photography were examined. Using two digital cameras, Coolpix 900 and 990, with the exclusive fish-eye converter FC-E8, we took hemispherical photographs of all selectable combinations of image quality and size in 15 stands with various light environments, and then estimated the gap fraction and canopy openness. The estimates made using the two cameras did not differ with the image quality. By contrast, the estimates made with Coolpix 900 differed in image size, but not those made with Coolpix 990. These results suggested that the basic-quality and full-size image was adequate for Coolpix 900, whereas the basic-quality and VGA-size was the optimum combination for Coolpix 990. Comparison of the best combination images between two cameras showed that the Coolpix 900 produced significantly higher gap fraction and canopy openness than Coolpix 990. It is therefore necessary to state clearly the type of camera used in further studies, so that the results obtained from a different camera could be compared. In conclusion, although digital hemispherical photography would be a convenient means for estimating light environments, we should pay attention to the effects of image size and camera type presented in this study.