在97.8GHz处测量地球大气的不透明度

RADIOMETER MEASUREMENT OF TERRESTRIAL ATMOSPHERIC OPACITY AT 97.8 GHz

用研制的全自动辐射计在97．8GHz上测量南京市内大气的不透明度以及这种不透明度随时间的变化．辐射计记录大气在不同天顶高度的辐射温度，由此测出天顶方向的大气不透明度。在56小时的测量时间内，取得了1400多组数据，拟合得到了在观测时段内天顶方向的大气不透明度在0．2至0．7之间，典型值为0．4，表明测试地点的大气条件允许进行3mm波段的射电天文观测．由于在工作频段内大气不透明度的主要来源是对流层水汽的吸收，测量的不透明度可用来直接反映大气内水汽的含量，并实时校准大气吸收．

An experiment was made in Nanjing city to measure the terrestrial atmospheric opacity and its variation by using a tipping radiometer at 97.8 GHz. The radiative temperatures at different zenith distances were recorded with a period of 1 minute and the zenith opacities were derived. More than 1400 data sets were obtained over 56hours of measurement. The zenith opacities were found to be in the range of 0.2 to 0.7 with a typical value of 0.4, indicating that the millimeter-wave radio observation is feasible under the atmospheric condition at the testing site. Since the opacity at the working frequency is mainly due to the absorption of tropospheric water vapor, the measured opacity is used to give a direct estimate of the precipitable water vapor content and to provide a reference for real-time calibration of the atmospheric attenuation.