Preliminary Study on Millimeter Wave Attenuation Characteristics Combined with Wind Profiler

Millimeter wave is easily impacted by the attenuation of precipitation, and the energy of electromagnetic wave emitted by millimeter-wave cloud radar is often absorbed and scattered by the precipitation particles. Electromagnetic wave attenuation makes the radar echo intensity less than the actual echo intensity and affects the detection accuracy. However, wind profiler is invented to detect the turbulence of clear air and it can detect precipitation particles. For the L-band wind profiler with a wavelength of 220 mm, the attenuation caused by rainfall is negligible. Therefore, detection results of wind profiler can be considered as no attenuation. A millimeter-wave cloud radar is installed in Meteorological Observation Center of CMA, and its observations of precipitation are compared with data of an L-band wind profiler from 1 May 2016 to 31 July 2016. The millimeter-wave cloud radar has three kinds of pulse width (2 μs, 5 μs and 20 μs), and the wind profiler has also three detection modes (low, medium, and high). Because the temporal resolution of two radars is different, to make sure that the observation time are consistent and samples of data for analysis is sufficient, the difference of observation time for each group of data is set within 120 s. The data for comparison and analysis comes from 2 μs and 5 μs modes of millimeter-wave cloud radar, low and medium mode of wind profiler. Reflectivity factors are calculated using the power spectrum data of wind profiler and I, Q data of millimeter-wave cloud radar. The processing method of power spectrum and calculation method of reflectivity factor are also introduced. The relationship between the attenuation and the falling velocity of precipitation particles is initially analyzed.Results indicate that the attenuation of millimeter wave caused by precipitation is obvious. If precipitation particles are uniform in the range of radar observation, there is a positive correlation between the attenuation of the millimeter wave radar and the falling velocity of precipitation particles. And the longer distance the millimeter-wave travels, the greater the attenuation is. The variation of reflectivity factor caused by attenuation is about 1-7 dB, 2-11 dB when the falling velocity of precipitation particles is within the range of 3.5-7.5 m·s^-1 at the height range of 1110-2430 m, 1110-3510 m. Results are consistent under different detection mode of the millimeter-wave radar and the wind profiler.