A system for measuring atmospheric attenuation of radiation comprises at least one vehicle, a radiation source and a radiation detector configured to measure the radiation from the source. The system further comprises means for precise positioning of the vehicle. The vehicle may be a drone (D) and/or a rover (R) and they may be autonomous or remotely controlled. The radiation detector is mounted on the drone and the radiation source is mounted on the rover (or vice versa), and the system is configured such that the atmospheric attenuation of the radiation can be measured over several distances and elevation angles. Such a system is optimally suited to performing all the measurements necessary for monitoring atmospheric attenuation at a central tower concentrated solar power plant.