机载测雨雷达两种反演方法的优化和综合利用的模拟研究

A Simulation Study of Two Algorithms Optimization and Application for the Airborne Rain Radar

由于机载雷达的天线不能做得太大,如果想获得一个较好的束向分辨率,就不得不使用X波段的频率,而该波段的电磁波穿过雨区时会受到衰减,直接利用视反射率进行降水反演就会产生很大的误差,因此,衰减效应必须进行校正。两种降水反演方法——立体雷达方法和双束算法,在实际的反演中各有优缺点。立体雷达方法对边界条件要求高,而双束算法在雨团中心雨强大处会有较大的误差。引入权重因子后的立体雷达方法双束算法(综合算法)能充分发挥两种方法的优点,从而更具适用性和准确性。

The airborne radars have good maneuverability and can easily follow the observed phenomena and allow scanning meteorological systems in place where ground-based radars are not easy to operate （i. e. oceans）. On the other side, the size of the airborne rain radars＇ antennas is difficult to be made large enough, so radars use an X-band frequency. However, the electromagnetic wave on the frequency is attenuated though rain, thus algorithm should be studied to correct for the attenuation effect. The dual-beam algorithm and the stereoradar analysis have obvious shortcoming in different conditions. The stereoradar analysis needs to get the required boundary conditions where the ＇true＇ reflectivity is known. And the dual-beam algorithm cannot provide reliable estimates for reflectivity at the cell center. It is an ideal means that the final result is composed of difference proportion of the dual-beam algorithm and the stereoradar analysis. The proportion of retrieval result by dual-beam algorithm is more than that by stereoradar analysis at the cell boundary. And the proportion of retrieval result by stereoradar analysis is more at the cell center. It is called the hybrid algorithm. In the hybrid algorithm, a normative weighting factor is used. It changes along with the PIA （Path-Integrated Attenuation） difference. The weighting factor has a very good corresponding relation with the rain rate. The factor is the maximum value when the rain rate is the minimum value. Then the factor reduces with the rain rate increasing. All algorithms are applied to a simulative rain system. The simulative system has two peak value areas, and has a minimum value area between the peak value areas. In order to be consistent with the actual situation, stochastic noise is used in the simulation field. The value of noise is between 5：0. 7 dB. The reflectivity estimated by the hybrid algorithm is more accurate than that estimated by stereoradar and dual-beam algorithms. The good result is gotten using the hybrid algorithm in the simulation field. The hybrid algorithm is of serviceability and accuracy.