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Preliminary Study on Millimeter Wave Attenuation Characteristics Combined with Wind Profiler
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摘要: 使用中国气象局大气探测综合试验基地35 GHz毫米波云雷达和L波段风廓线雷达2016年5月1日-7月31日在降水条件下的观测数据，根据不同观测模式下两部雷达得到的数据，计算在一定高度区间内不同下落速度的降水粒子反射率因子变化量，初步分析不同下落速度的降水粒子对毫米波衰减的影响。结果表明：在持续时间较长的层状云降水且降水粒子在雷达观测范围内均匀分布条件下，毫米波衰减与降水粒子下落速度呈近似线性关系，且毫米波经过的路径长度越长，衰减越大；毫米波在经过1110~2430 m，1110~3510 m的高度区间时，下落速度处于3.5~7.5 m·s-1之间的降水粒子对毫米波的衰减作用导致毫米波云雷达所测的等效反射率因子分别减小约1~7 dB和2~11 dB。Abstract: 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.
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图 1 ΔZw与Vr的关系
(a)1110~2430 m高度范围内风廓线雷达低模式, (b)1110~3510 m高度范围内风廓线雷达中模式
Fig. 1 Relation between ΔZw and Vr
(a)the low mode of wind profiler at height range of 1110-2430 m, (b)the medium mode of wind profiler at height range of 1110-3510 m
图 2 ΔZc与Vr的关系
(a)1110~2430 m高度范围内毫米波云雷达2 μs探测模式, (b)1110~3510 m高度范围内毫米波云雷达5 μs探测模式
Fig. 2 Relation between ΔZc and Vr
(a)2 μs detection mode of the millimeter-wave cloud radar at height range of 1110-2430 m, (b)5 μs detection mode of the millimeter-wave cloud radar at height range of 1110-3510 m
图 4 2016年6月20日17:30—20:00(a)以及2016年7月19日14:00—16:30(b)毫米波云雷达反射率因子
Fig. 4 Reflectivity factor observed by millimeter-wave radar from 1730 BT to 2000 BT on 20 Jun 2016(a) and 1400 BT to 1630 BT on 18 Jul 2016(b)
图 5 2016年6月20日18:51毫米波云雷达2 μs探测模式的功率谱(a)以及风廓线雷达低模式功率谱(b)
Fig. 5 Power spectrum observed by 2 μs detection mode of the millimeter-wave radar(a) and the low mode of wind profiler(b) at 1851 BT 20 Jun 2016
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