Effect of mountain clutter on a VHF (206.5 MHz) wind profiler in the central Himalayas

A modern, indigenously developed VHF ( 206.5 + 2.5 MHz) wind-profiler radar, operating in the Himalayan region, was installed at Aryabhatta Research Institute of Observational Sciences (ARIES) near Nainital, Uttarakhand (29.4N; 79.5E; 1793 m amsl) India. This profiler was named the Aries ST RADar (ASTRAD). The profiler was installed within a 30 m χ 30 m two-story building for better utilization of available space on a hilly terrain, surrounded by high-rise mountains. In an innovative way, 12 clusters of 49 elements were placed on the rooftop with the required precision in forming a quasi-circular aperture. Activation and integration of the clusters of the system progressed with extensive calibration of each individual transmitting/receiving module (TRM) connected with each antenna. During activation, the presence of a strong central patch in the Doppler-spectrum-like clutter, close to 0 Hz, was encountered. Based on experiments, it became clear that the reflected strength of the RF signal in the VHF band was significant due to the mountain terrain. A metal fence 3.5 m-4 m height was designed and installed at the perimeter of the rooftop to minimize the strength and to gain improvement in the detectability of the weak backscattered atmospheric signal. In this article, technical details of the system and design steps of the fence that led to overcoming the issue of clutter are summarized.