UHF Wind Profiler

1280-MHz Active Array Radars for Lower Atmospheric Wind Profiling

NARL has developed two L-band radars for Lower Atmosphere Wind Profiling (LAWP) and precipitation studies. These radars operate at 1280 MHz and employs the Doppler beam-swinging (DBS) technique for measuring the wind vector. Refractive index variations in the atmosphere act as tracers (targets) for the radar and provide the echo. Principal objectives of this radar are (i) measurement of height profile of atmospheric wind vector, (ii) characterization of atmospheric turbulence, and (iii) characterization of atmospheric convection and precipitation events causing rain fall. The radar has been configured and demonstrated with an active array, first of its kind in its class of atmospheric radars. A simplified active array configuration is adopted to make the radar simple, compact, rugged and low cost. In this configuration, a modified version of the two-dimensional Butler multi-beam forming matrix feeds the solid-state transmit-receive modules energizing the individual microstrip patch antenna elements of a planar array. The received atmospheric echoes are processed with a state-of-the-art direct IF digital receiver/processor comprising powerful signal processing & data processing algorithms. The configuration adopted here significantly improves the radar performance due to the active array nature in which the feed loss factors are totally eliminated. It makes the radar very compact by allowing smaller antenna when compared to the conventional radar for a given performance level. Two systems have been developed; one transportable radar with 1.4-m size 8x8 array and one fixed radar with 2.8-m size 16x16 array. The photographs of these two radars are shown in figure-1. Transportable radar is deployed initially at NARL and later at IGCAR, Kalpakkam, for air pollution studies. Fixed radar system is being operated at NARL for continuous atmospheric probing. Important features of the radar system include: Indigenous First of its kind in India Simplified active array scheme High- temporal and range resolution Planar microstrip patch array Compact in size Solid-state transmit-receive modules Transportable and fixed versions 2-D Passive beam forming Networks Continuous operation capability Direct IF digital Receiver and DSP Low cost Pulse-compression schemeAdvanced data processing

Figure-1: Photographs of Transportable Radar (left) and Fixed Radar (right).

Figure-2: Wind comparison of Transportable radar and GPS Sonde.

Figure-3: T-Radar observations during precipitation on (a) 31 March, (b) 19th May Laila Cyclone (White patches are the gaps in the data due to power failure) and (c) 5th July 2010.

Figure-4: Height coverage performance of T-Radar for the month of May.

Figure-5: Comparison of winds observed by the Main Radar and GPS Sonde on 3 August 2010 at 17:00 Hrs (left) Scatter plot comparing winds observed by LAWP and GPS Sonde during the month of April 2011 (right panel).

Figure-6: Diurnal variation of horizontal wind vector on 19 May 2012.

Figure-7: Observations of atmospheric precipitation event made with main radar on 15 April 2011.