How long is the sun duration in a street canyon?-Analysis of the view factors of street canyons

Sun duration is the best proxy for solar radiation, which has important effects on different aspects, including street thermal environments and solar energy utilization in urban areas. This study develops a method for efficiently calculating the sun duration using Baidu Street View (BSV) images and view factors (VFs) at a low cost in a wide range of spaces. We map the VFs and sun duration within the Third Ring Road of Beijing using the proposed method. The results show that the average daily sun duration in the study area (5.64 h) is approximately 40% of the theoretical sun duration, and the sun durations vary greatly among different built environments and roads of different grades and different directions. The spatial distributions of the sun duration and sky view factor (SVF) in the study area are significantly similar. Greening vegetation and buildings block 41% and 19%, respectively, of the typical sun duration. VFs determine the final characteristics of the sun duration in a street canyon. Hence, accurately quantifying the sun durations of street canyons in a wide range of spaces is helpful for understanding and predicting the thermal environments of street spaces and effectively supplementing and enriching current research on the spatial characteristics of urban thermal environments. The study will greatly improve our understanding of the interactions among radiation, human health and urban thermal environments, making it more convenient for urban planners and meteorologists to study urban street spaces and environments.