溪頭地區為典型的亞熱帶霧林帶，經常雲霧繚繞，雲霧除了可為森林生態系帶來水平降水的補充外，其遮蔽大量短波輻射入射量，成為霧林帶生態系保護傘的另一個重要功能。雲霧遮蔽了短波輻射的直接輻射射量，一部分反射回太空，另一部份則藉由散射輻射穿透雲層到達地面，成為霧林帶植物行光合作用的主要短波輻射量來源，然而雲霧及散射輻射的觀測相對少。本研究利用溪頭通量站的觀測資料， 探討溪頭地區散射輻射的特性，並建立推估模式，以供未來推估使用。研究結果顯示，溪頭地區的散射輻射為主要的太陽輻射來源，利用Liu和Jordan(1960)模式建立良好關係(R =0.89)，該關係在2013-2017年間的年際及季節性變動不大，可直接引用單一關係式利用全天光輻射量進行散射輻射量的估算。

Xitou is a typical subtropical cloud forest area, often surrounded by fog that brings additional horizontal precipitation to the forest ecosystem. Besides, the clouds obstruct a large amount of shortwave radiation. Some of the radiation is reflected back into the space; the rest penetrates the cloud layer to reach the ground by diffuse radiation, and becomes the main source of shortwave radiation for photosynthesis in cloud forests. Although fogs and clouds have been known to provide important function to the cloud forest ecosystem, observations of cloud and diffuse radiation are relatively rare. As a result, this study aims to understand the characteristics of diffuse radiation by using the observed data from the flux tower in Xitou, and to establish a model for future forecasting purposes. The results showed that diffuse radiation in Xitou is the main source of solar radiation. A significant relationship (R2 = 0.89) was established by using the model described by Liu and Jordan (1960), and the relationship remained similar across years and seasons from 2013 to 2017. This suggests that a single relationship could be used to estimate the quantity of diffuse radiation by using the amount of global radiation.