Exploring wintertime canopy surface temperature dynamics in a sub-alpine spruce forest using thermal infrared imagery

Canopy surface temperature is a critical state variable of forest snow and land surface models. Affecting both radiative and turbulent fluxes, it plays a key role in modulating energy exchange between the atmosphere, the canopy air space and the underlying snowpack. As recent model developments are leaning towards increasingly detailed forest structure representations to resolve snow-vegetation interactions at the sub-tree scale, understanding spatial and temporal variations of canopy surface temperatures is gaining priority. We present a novel dataset of canopy surface temperatures from a sub-alpine forest stand in the Eastern Swiss Alps from ground-based thermal infrared imagery. To this end, we created ultrahigh-resolution composite panoramic images with a 360° view field, resolving horizontal and vertical canopy surface temperature variations for a range of canopy density and insolation regimes. In this manner, over 100 panoramic composites were collected over the entire winter season, providing new insights into the spatiotemporal dynamics of canopy surface temperatures. Repeated images at the same locations documented both diurnal cycles as well as the impact of varying meteorological conditions on canopy surface temperature distributions. Image time series following snowfall events further allowed us to track the detailed depletion dynamics of snow intercepted in the canopy and its correlation with solar exposure. These new data will be extremely valuable for informing and verifying forest snow model developments, especially those targeted at multi-layer canopy structure representations.