Development of middle and upper atmosphere radar real-time processing system with adaptive clutter rejection

Atmospheric radars have the ability to continuously observe the height profiles of wind velocity vectors, across a wide height range, with high temporal resolution. They have been used for research, such as atmospheric gravity waves and meteorological phenomena, as well as for weather forecasting. For atmospheric radars, strong clutter echoes from surrounding hard targets, such as mountains or buildings, are the major source of interference. As they utilize very weak scattering from radio refractive index fluctuations produced by atmospheric turbulence, even weak echoes from low-level sidelobes become a serious problem. In order to reject or suppress clutter echoes, it is effective to use the norm constrained-directionally constrained minimization of power (NC-DCMP) method, which creates a null toward the direction of the clutter, while maintaining the main lobe shape. We successfully implemented the NC-DCMP adaptive processing in the real-time processing system of the middle and upper atmosphere radar. This study demonstrates the effectiveness of real-time processing of the clutter rejection. The primary advantage is enabling the estimation of wind velocity profiles in real time and the reduction of the amount of recorded data. The improvement of the wind estimation accuracy, especially for vertical flow, was confirmed from observation data recorded over a long period.