Direct normal irradiance is the component of solar radiation exploited by concentrating solar power plants. However, solar radiation reflected by heliostats can be partially extinguished on its way to the receivers in solar power tower plants. These energy losses are accentuated with the distance travelled by the light. The growing development of solar power tower plants has highlighted the interest in determining this phenomenon. This paper presents the results of a six-month intercomparison campaign of the two most promising extinction measuring systems. The system developed at Plataforma Solar de Almería (SE Spain) is based on a direct measurement methodology by using two digital cameras. The second system indirectly estimates the extinction from forward-scatter meter (FSM) measurements. Two FSMs were used in this study. Both FSMs provided the same Meteorological Optical Range (MOR) trends, with differences into declared error margins. A selected number of days corresponding to medium to high aerosol loads have been used to assess the performance of both types of systems. Results show that, in these days, the atmospheric extinction coefficient values derived from the two-camera system were on average 2.1 times higher than those determined with the FSMs. Semi-empirical and empirical corrections for the aerosol spectral characteristics and for the content of water vapour in the atmosphere have been applied to the FSM measurements so that both systems provide similar values of horizontal attenuation.

直接法向辐照度是聚光太阳能发电厂利用的太阳辐射的组成部分。然而，由定日镜反射的太阳辐射在到达太阳能发电塔式发电厂的接收器的途中可能会被部分熄灭。这些能量损失随着光行进的距离而加剧。太阳能发电塔式发电厂的不断发展凸显了确定这一现象的兴趣。本文介绍了对两个最有希望的消光测量系统进行的为期六个月的比对活动的结果。Plataforma Solar de Almería（西班牙东南部）开发的系统基于使用两个数码相机的直接测量方法。第二个系统通过前向散射仪 (FSM) 测量间接估计消光。本研究中使用了两种 FSM。两种 FSM 提供了相同的气象光学范围 (MOR) 趋势，但在声明的误差范围内有所不同。对应于中高气溶胶负载的选定天数已用于评估两种类型系统的性能。结果表明，在这些日子里，由双摄像头系统得出的大气消光系数值平均比用 FSM 确定的值高 2.1 倍。对气溶胶光谱特性和大气中水蒸气含量的半经验和经验修正已应用于 FSM 测量，以便两个系统提供相似的水平衰减值。对应于中高气溶胶负载的选定天数已用于评估两种类型系统的性能。结果表明，在这些日子里，由双相机系统得出的大气消光系数值平均比用 FSM 确定的值高 2.1 倍。对气溶胶光谱特性和大气中水蒸气含量的半经验和经验修正已应用于 FSM 测量，以便两个系统提供相似的水平衰减值。对应于中高气溶胶负载的选定天数已用于评估两种类型系统的性能。结果表明，在这些日子里，由双摄像头系统得出的大气消光系数值平均比用 FSM 确定的值高 2.1 倍。对气溶胶光谱特性和大气中水蒸气含量的半经验和经验修正已应用于 FSM 测量，以便两个系统提供相似的水平衰减值。