Comparison of film and digital hemispherical photography across a wide range of canopy densities

Hemispherical photography is a widely used method for assessing the light environment beneath forest canopies. As technology advances, digital photography is expected to increasingly replace conventional film photography for such work. However, in the absence of satisfactory comparisons between the two methods, caution is needed in the use of a digital camera for hemispherical photography. In this study, paired digital and film hemispherical photographs were taken in conifer plantations in southern and central Scotland, with a wide range of light environments. The analysis package Hemiview was used to calculate canopy openness, diffuse and direct transmittance, and leaf area index (LAI). There was strong positive correlation between the results from the two systems, with no systematic differences over a range of transmittance from 10 to 70%. Beneath very dense canopies (below 10% transmittance) the film camera is known to produce inaccurate values of transmittance, so the utility of the digital camera in these environments could not be ascertained. We concluded that using the cameras and analysis package described, film and digital hemispherical photography produce comparable results.