Clutter suppression for high-resolution atmospheric observations using multiple receivers and multiple frequencies



[1] Range imaging (RIM) was developed in 1999 to improve range resolution by transmitting multiple frequencies. Since then, the capability of RIM for resolving fine atmospheric layer embedded in the conventional range gate has been demonstrated by a number of VHF and UHF atmospheric radars around the world. Nevertheless, like conventional radar, RIM is susceptible to clutter contamination that is contributed from antenna sidelobes. This work addresses this important issue in RIM for the first time by capitalizing the capability offered by multiple receivers and multiple frequencies with the goals of maintaining resolution gained by RIM and simultaneously, suppressing clutter contamination. Two techniques are developed where multi-receiver signals from the same frequency are initially combined using Fourier or Capon beam-forming for clutter suppression, and subsequently, these combined signals from multiple frequencies are processed using RIM for resolution enhancement. The two techniques are abbreviated by FB-RIM and CB-RIM. The mathematical representation of FB-RIM and CB-RIM is derived. Moreover, the 3-D atmospheric radar imaging (AIM) is applied to the multi-receiver and multi-frequency signals to image in the vertical direction. The feasibility of the three techniques is demonstrated and their performances are compared using both simulations and real data collected by the Middle and Upper (MU) radar in Japan. The FB-RIM, which is similar to the conventional RIM, has the best performance of reconstructing a single thin layer embedded within the radar volume with high temporal resolution, but is prone to the contamination of moving clutter. On the other hand, although CB-RIM and AIM retrieve the thin layer with slightly degraded performance, the clutter contamination can be significantly suppressed. Furthermore, for most cases AIM provides comparable or better performance of both layer reconstruction and clutter mitigation compared to CB-RIM.