37GHz和94GHz的大气微波衰减比较分析

Analysis of the Atmospheric Attenuation at 37 GHz and 94 GHz

毫米波更接近云粒子的尺度,因此毫米波及短厘米波段雷达已被应用于云层的探测,美国与加拿大的云卫星计划(CloudSat)将要上3mm云雷达(CPR),如何与已在天上的TRMM/PR结合,获得从薄云到浓厚云的垂直结构信息,是一个值得关注的课题。但是,毫米波云雷达探测,必须考虑的问题之一是大气衰减订正。主要比较分析了在37GHz和94GHz大气的衰减特性,目的是对星载94GHz云雷达进行大气的衰减订正。计算分析了在不同云、大气条件下37GHz和94GHz的大气衰减,得出如下结论:1大气气体的微波吸收在测云波段产生明显的衰减,其中水汽衰减效应变化很大;即将上天的空间94GHz测云雷达必须有水汽衰减订正方案。237GHz和94GHz雷达测云,由于大气和云衰减不同和雷达反射率的很大差异,导致雷达回波信号强弱不同。3对云层较薄、含水量较少的云,在不计雷达参数的情况下,37GHz雷达回波信号不如94GHz测云雷达,也就是说94GHz对薄云有更强的探测能力;对云层较厚、含水量大的云,由于强衰减的作用,94GHz雷达回波信号小于37GHz雷达。4从大气衰减的不利因素方面考虑,空间94GHz雷达测高层薄云的效果最好;测低层薄云时需要考虑气体衰减订正;因浓厚云的强衰减作用,探测其中下部的能力大大减弱,不仅要进行衰减订正。

Millimeter-wave is close to the size of cloud particles, so millimeter-wave radar has now been constructed and operated for cloud observations. In the CloudSat Mission there will be a 3-millimeter cloud profile radar (CPR). It is very interesting to investigate the combination of CloudSat/CPR with TRMM/PR which has been in space to get the information of the vertical structure of clouds from thin to thick clouds. Thereinto, the correction of attenuation is a big problem in millimeter-wave cloud radar detection. A study of the characteristics of atmospheric attenuation at 37 and 94 GHz is presented in this paper. The primary aim of this study is to provide some basic information to the atmospheric correction for 94 GHz cloud radar. The atmospheric attenuation at 37 and 94 GHz have been calculated and analyzed in different cloudy atmospheres. The feasibility of performing the correction is discussed on the basis of dual- or triple- wavelength transmission and backscattering measurements.