臭氧是地球大气中一种重要的痕量气体,在光化学反应和气候变化中都扮演着非常重要的角色。高光谱红外卫星可以观测到较高垂直分辨率的大气臭氧信息,但是由于热红外受大气温度影响较大,臭氧反演精度会有所下降。为此详细讨论和分析了温度对臭氧吸收光谱和权重函数的敏感性,以及对臭氧反演精度的影响。首先利用逐线积分辐射传输模型LBLRTM,分别模拟计算了六种不同标准大气模式下,1K的随机温度误差对大气透过率和辐射值的影响,发现1 K温度随机误差和臭氧浓度5%~6%的变化引起的辐射值变化量一致。接着利用CRTM辐射传输模型,针对搭载于美国对地观测卫星Suomi NPP(National Polar-orbiting Partnership)平台上的CrIS(Cross-track Infrared Sounder)红外高光谱观测数据,计算了1K的随机温度误差对大气臭氧权重函数的影响,并计算了由1K温度误差所导致的热红外高光谱资料大气臭氧廓线反演误差,结果显示CrIS对于臭氧的敏感区位于10~100 hPa之间,且1K的温度误差和6%的臭氧浓度变化引起的权重函数变化量相当。最后以CrIS作为实验数据,在最优估计法框架下,通过特征向量统计法获取臭氧廓线的先验知识,并将大气温度廓线和大气臭氧廓线都作为未知量,进行同步迭代反演。将反演结果和配对的世界臭氧紫外数据中心WOUDC的站点数据进行比较,发现在反演中加入大气温度廓线进行同步迭代后,反演结果有显著提高,尤其在平流层与真值几乎一致,最大相对误差不超过20%,在对流层反演结果相对较差,最大相对误差不超过50%,优于欧洲中期天气预报中心ECMWF(European Center for Medium-range Weather Forecasting)臭氧模式数据集ERA-Interim。
英文摘要:
Ozone is a particularly critical trace gas in the Earth's atmosphere, since this molecule plays a key role in the photochemical reactions and climate change. The TIR measurements can capture the variability of ozone and are weakly sensitive to the lowermost tropospheric ozone content but can provide accurate measurements of tropospheric ozone and higher vertical resolution ozone profiles,with the additional advantage that measurements are also possible during the night. Because of the influence of atmospheric temperature, the ozone profile retrieval accuracy is severely limited. This paper analyze and discuss the ozone absorption spectra and weighting function sensitivity of temperature and its influence on ozone profile retrieval in detail. First, we simulate the change of atmospheric transmittance and radiance by importing 1 K temperature uncertainty, using line-by-line radiative transfer mode under 6 different atmosphere modes. The results show that the transmittance change ratio for 1 K temperature variation was consistent with the transmittance change ratio for 5%~6% change of ozone density variation in all layers of the profile. Then, we calculate the change of weighting function by a temperature error of 1 K,using the Community Radiative Transfer Model (CRTM) for the Cross-track Infrared Sounder (CrIS) on the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite and calculate the corresponding change of retrieval result. The results demonstrate that CrIS is sensitive to Ozone in the middle to upper stratosphere, with the peak vertical sensitivity between 10 ~100 hPa and the change of weighting function for 1 K temperature variation was consistent with 6% change in the ozone profile. Finally, the paper retrieves ozone profiles from the CrIS radiances with a nonlinear Newton iteration method and use the eigenvector regression algorithm to construct the a priori state. In order to resolve the problem of temperature uncertainty and get high accuracy ozone profile,atmospheric temperature profile and ozone profile are simultaneously retrieved. Comparison of the CrIS retrieved ozone profile with high-vertical-res-olution ozonesonde profiles provided by the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) and ERA-Interim ozone profiles indicated that the retrieved ozone profiles are in good agreement with the ozonesonde profiles, and a notable improvement in this algorithm than the retrieval without atmospheric temperature profile,are also better than the ECMWF model profiles. The relative differences are less than 20% for the stratosphere and 50% for the lower troposphere.