It is possible to measure solar insolation directly using a pyranometer or indirectly with hemispherical photos from beneath the forest canopy. These methods are feasible at a small scale, but often an assessment of the entire watershed is desired. Researchers evaluated two different methods for modeling solar insolation using remotely sensed airborne lidar data, which provides elevational data points that correspond with canopy cover and the ground surface. A raster model and an approach using lidar data to create synthetic hemispherical photos were compared to on-the-ground data, and both methods were found to be effective. The raster model of solar insolation derived from lidar data was applied throughout the watershed and provided a means to assess spatial patterns of solar inputs throughout the stream network. 

Richardson, J.J., Torgersen, C.E., Moskal, L.M., 2019, Lidar-based approaches for estimating solar insolation in heavily forested streams: Hydrology and Earth System Sciences, v. 23, no. 7, p. 2813-2822, https://doi.org/10.5194/hess-23-2813-2019.