Hemispherical Photographs at Remote Camera Stations on Moscow Mountain in Latah County, ID, USA (6/2/21-11/2/21)
Description
We took hemispherical photographs (hemiphotos) at each camera station to estimate incoming shortwave radiation. We used a Canon EOS 70D SLR camera with a Sigma 8mm circular fisheye lens. We took hemiphotos on days with little to no wind or precipitation and early in the morning (5AM – 7AM), late in the evening (7PM – 9PM), or on overcast days to maximize the contrast between sky and vegetation. We took hemiphotos in June - July 2021, but nine camera sites were re-photographed in October 2021 due to poor quality of initial photographs. Overstory deciduous vegetation is rare at the study site, so summer changes in canopy cover are negligible. At each camera site, we placed the DSLR camera with attached lens on a tripod and levelled it to point directly up into the canopy. One set of hemiphotos was taken at the tree to which the camera was mounted, and a second was taken 5 m into the camera viewshed. We took photographs at multiple exposures using the auto-exposure bracketing settings of the camera. We analyzed hemiphotos using Hemisfer software. We selected the hemiphoto with the best exposure for each location at a camera site. We manually selected threshold values and adjusted color-weighting when needed to distinguish sky pixels from vegetation pixels in each image. Hemisfer then classified sky and vegetation pixels in the photograph using the threshold, overlaid a solar path onto photographs based on input georeferencing information and photograph orientation. We set Hemisfer to calculate hourly direct and diffuse shortwave radiation throughout time assuming 50% cloud cover. Hemisfer also output a count of sky and vegetation pixels in the image which we used to calculate percent vegetation cover. Photographs were analyzed using the attributes listed in the .csv file (this dataset) in Hemisfer software.