This lecture discusses the principles and applications of meteorological radar and lidar technologies. It begins with an overview of the OPERA project, which centralizes radar data across Europe, highlighting the differences in radar types and their operational frequencies. The instructor explains various sources of uncertainty in radar measurements, including attenuation due to precipitation, interactions with terrain, and vertical variability of precipitation. The lecture also covers the advantages of polarimetric radar, which provides additional information about hydrometeors by measuring different polarizations. The discussion extends to lidar technology, detailing its operational principles, including elastic and Raman lidar, and its applications in atmospheric studies, forestry, and archaeology. The instructor emphasizes the importance of understanding these technologies for accurate meteorological observations and environmental monitoring, concluding with a summary of key concepts and their implications for hydrological applications.