Assessing the Raspberry Pi as a low-cost alternative for acquisition of near infrared hemispherical digital imagery

Hemispherical imagery is used in many different sub-fields of climatology to calculate local radiation budgets via sky-view factor analysis. For example, in forested environments, hemispherical imagery can be used to assess the leaf canopy, (i.e. leaf area / gap fraction) as well as the radiation below the canopy structure. Nikon Coolpix cameras equipped with an FC-E8 fisheye lens have become a standard device used in hemispherical imagery analysis however as the camera is no longer manufactured, a new approach needs to be investigated, not least to take advantage of the rapid development in digital photography over the last decade. To this end, this paper conducts a comparison between a Nikon Coolpix camera and a cheaper alternative, the Raspberry Pi NoIR camera, to assess its suitability as a viable alternative for future research. The results are promising with low levels of distortion, comparable to the Nikon. Resultant sky-view factor analyses also yield encouraging results, but challenges remain to overcome small differences in the field of view as well as improving the present availability of bespoke fittings.