大气波导模拟分析及雷达资料三维插值处理

【作者】 何宇翔；

【导师】 顾松山；

【作者基本信息】 南京气象学院 ， 大气物理学与大气环境， 2003， 硕士

【摘要】 在利用雷达进行探测时，经常会发现一些电磁波的异常传播现象。其中一种显著的现象是：在一定的气象条件下，在大气边界层尤其是在近地层中传播的电磁波，受大气折射的影响，其传播轨迹弯向地面，当曲率超过地球表面曲率时，电磁波会部分地被陷获在一定厚度的大气薄层内，就好像电磁波在金属波导管中传播一样，称为大气波导传播，形成波导传播的大气薄层称为大气波导层。 由于大气的折射率与大气压力、温度和水汽分压有关。本文在讨论折射率与气象因子之间的关系的基础之上，大气波导进行了分类。在此基础之上，介绍了波导传播的波长(频率)范围和最小发射角。 用球面分层的假定，用分步积分的方法，进行了射线模拟追踪，分别模拟了一层、两层、三层模式。结果与实际观测到的波导传播时的回波结构相同，说明，根据不同的大气层结，利用电磁波的波导传播的射线追踪方法可以基本上确定电磁波的传播轨迹。在雷达探测中可以利用此方法，初步确定雷达回波中哪个地区会出现陷获折射回波，为进一步分析从雷达回波反演大气层结提供了可能。 在雷达二次产品处理算法中，讨论了一种新的三维插值，比以往在显示每一个雷达二次产品时，都作一次插值相比，这种方法既节省了总的机时，也提高了每个产品的显示速度，在讨论这种方法后，用几个产品的实例，说明了这种方法是可行的，并且还讨论了等值线的生成原理，在“雷达二次产品处理平台”下，开发了Visual C++实现程序。更多还原

【Abstract】 The speed of a radio wave in the atmosphere is determined by the dielectric property of the air. This property depends on the pressure, temperature and humidity of the air. In general as we move upwards through the atmosphere the pressure decreases and temperature falls. This means that the dielectric property changes with height and allows a slight increase in the speed of a radio wave as we move upwards through the atmosphere. This in turn means that if a radio wave moves away from the earth at an angle less than 90 degrees, then the upper part of the wave travels faster than the lower part. Therefore even under normal conditions this can in effect bend, or refract, the wave back down to earth.Tropospheric ducting occurs when we get a sharp rate of change in the dielectric constant as we move upwards through the atmosphere. This occurs when we get a rapid increase of temperature and a rapid decrease in humidity (dew-point) with height.In terms of deriving the maximum trapped-wavelength and the critical emitting angle of elevation for electromagnetic wave which can forms duct propagation and introducing the four kinds necessary condition for electromagnetic wave to form duct propagation, Under these conditions we now have the radio wave bent back towards the earth. However, the radio wave can then reflect back of the earth and become refracted again to return earthwards once more. This can sometimes occur a number of times with little attenuation but some fading. The result can be long distance reception of radio waves that would normally have been far beyond the radio horizon.The equations for ray tracing were given, simulating and tracing electro-magnetic wave duct propagation using spherical layered atmosphere mode, This method is very useful for analysis of radar echo distribution and confirm relation of stratification of atmosphere and ray duct propagationIn the process of studying radar second product, introduce a new 3-D interpolation method. Outcome of this method can suit all kinds of density product. And use some of the products to test its feasibility. On the base of the method, studied the 2-D isoline of the echo top etc and carry it out with Visual C++.更多还原