Hyperspectral characterisation of natural illumination in woodland and forest environments

Conference item

Light in nature is complex and dynamic, and varies along spectrum, space, direction, and time. While both spectrally resolved measurements and spatially resolved measurements are widely available, spectrally and spatially resolved measurements are technologically more challenging. Here, we present a portable imaging system using off-the-shelf components to capture the full spherical light environment in a spectrally and spatially resolved fashion. The method relies on imaging the 4π-steradian light field reflected from a mirrored chrome sphere using a commercial hyperspectral camera (400-1000 nm) from multiple directions and an image-processing pipeline for extraction of the mirror sphere, removal of saturated pixels, correction of specular reflectance of the sphere, promotion to a high dynamic range, correction of misalignment of images, correction of intensity compression, erasure of the imaging system, unwrapping of the spherical images, filling-in blank regions, and stitching images collected from different angles. We applied our method to Wytham Woods, an ancient semi-natural woodland near Oxford, UK. We acquired a total of 168 images in two sites with low and high abundance of ash, leading to differences in canopy, leading to a total 14 hyperspectral light probes. Our image-processing pipeline corrected small (<3°) field-based misalignment adequately. Our novel hyperspectral imaging method is adapted for field conditions and opens up novel opportunities for capturing the complex and dynamic nature of the light environment.

Authors: Li, S; Steel, L; Dahlsjö, CAL; Peirson, SN; Shenkin, A

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Society of Photo-optical Instrumentation Engineers
• Host title: Proceedings of SPIE 11815, Novel Optical Systems, Methods, and Applications XXIV
• Journal: Proceedings of SPIE
• Volume: 11815
• Pages: 32-41
• Article number: 1181506
• Publication date: 2021-09-07
• Event title: SPIE Optical Engineering + Applications (2021)
• Event location: San Diego, California, USA
• Event website: https://spie.org/conferences-and-exhibitions/optics-and-photonics/program/conferences/optical-engineering--applications
• Event start date: 2021-08-01
• Event end date: 2021-08-05
• DOI: 10.1117/12.2595301
• EISSN: 1996-756X
• ISSN: 0277-786X
• EISBN: 9781510644694
• ISBN: 9781510644687
• Language: English
• Keywords: visualization; color vision; optical spheres; cameras; calibration; imaging systems; organisms; light; mirrors; vision; computational color vision; reflectivity; light sources and illumination; hyperspectral imaging; environmental sensing