Prediction and verification of regional evaporation duct and microwave path loss
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摘要: 蒸发波导对近海面电磁波传播有重要影响，区域蒸发波导及微波路径损耗预报对评估海上雷达、通信、侦察等电磁系统的性能至关重要. 本文基于美国国家环境预报中心的GFS预报产品和NAVSLaM蒸发波导预测模型，对我国南海海域进行了大面积蒸发波导预报，利用欧洲中期天气预报中心发布的ERA5再分析数据进行了对比，并结合电磁波传播抛物方程模型开展了微波在蒸发波导信道中的路径损耗预报；然后利用在南海北部的路径损耗测试链路，对预报结果的准确性及时效性进行了验证. 再分析数据对比及海上试验验证结果表明，基于GFS数据开展的蒸发波导层中路径损耗预报，除个别异常点外，预报的路径损耗与实测值趋势相同，在前24 h结果与实测值较为吻合，误差在5~10 dB，可以用于大面积蒸发波导层中路径损耗的预报. 另外，试验发现，降雨会导致预报结果与实测数据有很大的误差，在进行电磁波传播计算时，应充分考虑雨衰、海面粗糙等海洋环境.Abstract: Evaporation duct plays an important role in electromagnetic wave propagation near the sea surface, and the prediction of regional evaporation duct and microwave path loss is very important for evaluating the performance of electromagnetic systems such as radar, communication and reconnaissance at sea. Firstly, based on Global Forecast System (GFS) prediction products and NAVSLaM evaporation duct prediction model, a large area evaporation duct prediction in the South China Sea is carried out in this paper. The reanalysis data of ERA5 published by European Centre for Medium-range Weather Forecasts (ECMWF) are compared. Then, combined with the parabolic equation model of electromagnetic wave propagation, the path loss prediction of microwave in evaporation duct channel is carried out. Finally, the prediction results are verified by the path loss test link in the northern part of the South China Sea. The verification results show that the path loss prediction in evaporation duct layer based on GFS data is in good agreement with the measured values, and in the first 24 hours, the error is less than 5−10 dB, which can be used to predict the path loss in large area evaporation duct layer. There is a large error between the forecast results and the measured data, which is caused by rainfall. When calculating electromagnetic wave propagation, the marine environment such as rain attenuation and rough sea surface should be fully considered.
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图 1 基于GFS数据的蒸发波导及路径损耗预报方法
Fig. 1 Evaporation duct and path loss prediction method based on GFS data
图 2 起始时间为2021-04-07T00:00南海气象参数24 h预报结果
Fig. 2 24 hour forecast results of atmospheric factors in the South China Sea from 2021-04-07T00:00
图 3 起始时间为2021-04-08T00:00南海气象参数24 h再分析结果
Fig. 3 Reanalysis results of atmospheric factors in the South China Sea for 24 h from 2021-04-08T00:00
图 4 南海0~72 h EDH预报结果
Fig. 4 0−72 h evaporation duct height forecast results of the South China Sea
图 5 南海0~72 h EDH再分析结果
Fig. 5 0−72 h evaporation duct height reanalysis results of the South China Sea
图 6 南海0~72 h蒸发波导信道路径损耗预报结果
Fig. 6 0−72 h evaporation duct channel path loss forecast results of the South China Sea
图 7 南海0～72 h蒸发波导信道路径损耗再分析结果
Fig. 7 0−72 h evaporation duct channel path loss reanalysis results of the South China Sea
图 9 2021-04-07T00:00—2021-04-17T00:00预报路径损耗与实测路径损耗对比
Fig. 9 Comparison of predicted path loss and measured path loss from 2021-04-07T00:00 to 2021-04-17T00:00
表 1 提取的GFS数据参数
Tab. 1 Factors from GFS products
气象参数 高度 空气温度/℃ 2 m 海表温度/℃ 表面 相对湿度/% 2 m 大气压/ hPa 表面 风速分量v/(m·s−1) 10 m 风速分量u/(m·s−1) 10 m 
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表 2 蒸发波导信道路径损耗计算参数
Tab. 2 Evaporation duct channel path loss calculation parameters
参数 取值 中心点坐标 (114°E，18°N) 距离 300 km 角度范围 0~360° 频率 8 GHz 天线高度 5 m 极化方式 水平极化 环境信息 GFS预报数据
（2021-04-08T00:00起0～72 h）ERA5再分析数据
（与GFS数据时间对应）
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表 3 测试系统配置
Tab. 3 Experimental configuration
参数 取值 输出功率 10 W 发射/接收天线类型 全向天线 发射/接收天线增益 7 dB 天线高度 4 m 电磁波频率 9.100 5 GHz 极化方式 垂直极化 低噪声放大器增益 32 dB 线损等损失 5 dB
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