Wind Turbines Focusing with Spaceborne SAR via Multi-Frame ISAR Imaging

This work puts forward a technique for focusing wind turbines observed with spaceborne synthetic aperture radar (SAR). As the fast rotations of the blades along with their significantly large sizes result in severe defocusing, proper approaches are needed to achieve well-focused images, with the goal of supporting the monitoring of such infrastructures, mostly located in remote areas. To this purpose, a multi-frame refocusing procedure is here developed, comprising the focusing of consecutive sub-apertures, the alignment of the images over a common reference plane, and their noncoherent combination. Notably, the approach also provides in output an estimation of the wind turbine rotation rate, which can also enable more advanced (but more computationally expensive) focusing tools like the back-projection algorithm. Imaging results and performance analysis of the rotation rate estimation are provided using simulated data.