Wake Measurements with Lidar

Since its emergence in the mid-2000s, Doppler wind lidars specifically developed for the wind industry were used for a number of different types of applications including field experiments that were focused on studying wind turbine wakes. Wake flows are to be considered as complex flows and represent for this reason a specific challenge to a remote-sensing lidar instrument. There are various approaches to overcome this challenge including the combination of certain lidar scan strategies and model assumptions as well as the application of more than one lidar device with overlapping planes or intersecting beams, respectively. The flexibility lidar technology offers is directly linked to the need for validating a specific measurement strategy in a particular situation. A respective framework is proposed with the definition of lidar use cases. Beside a comprehensive introduction to lidar measurement principles and strategies, that are relevant for the measurement of wake characteristics, and the use case concept, we give an overview about published wake measurement campaigns. The listed field experiments are categorized with respect to the applied types of lidar instruments and measurement strategies as well as the studied wake features.When considering the limitations the technology may have in particular situations carefully and assessing the measurement uncertainties in a sufficient way, lidars can be very powerful tools for studying wake flows as well as for quantifying specific wake characteristics.