针对我国新一代地球同步气象卫星 FY-4的预期发射和数据应用,本文借助与 FY-4卫星成像仪类似的 Meteosat-8卫星的 SEVIRI仪器数据资料开展先期研究,建立了一种部分云覆盖条件下红外辐射传输模型,模拟了不同大气条件、火山灰云高度、有效云量和观测天顶角情况下卫星观测的红外通道的亮度温度的变化。美国标准气候态大气廓线和火山灰区实时大气廓线两种模拟结果都表明,模型模拟的 8.3～9.1.m,9.8～11.8.m,11～13.m,12.4～14.4.m的入瞳亮度温度对云高度、有效云量较为敏感,基本呈线性相关;卫星天顶角对模拟的辐射亮温的影响相对较小。通过不同大气廓线状态和火山灰云发射率情景下的测试结果表明,只有同时考虑大气条件和火山灰云通道发射率的差异后,模式才能够较好地模拟出火山爆发情景下火山灰云中酸性物质在 11.m和 12.m的反吸收特性。与大气条件相比,通道的发射率差异对火山灰云的遥感建模更为重要。因此,可在传统的分裂窗通道的基础上,通过热红外多通道亮温及亮温差异信息联合反演火山灰云高度和有效云量等因子,提高部分覆盖下火山灰云的微物理参数的反演精度。本研究为建立基于我国新一代静止气象卫星 FY-4数据的火山灰云浓度定量反演模型提供了理论基础。

Based on instrument spectral response characteristics of Meteosat-8 SEVIRI which is adopted as a proxy of the FY-4 Imager which will be launched next year, an infrared radiative transfer model under partially cloud-covered is established. Observed brightness temperatures of SEVIRI infrared spectral bands (with 8.3-9.1.m, 9.8-11.8.m, 11-13.m and 12.4-14.4.m, respectively) under different atmospheric conditions, volcanic ash cloud heights, effective ash cloud emissivity and observation zenith angles are simulated. We found that no matter whether under U.S. standard atmosphere or in-situ atmospheric condition, the simulated brightness temperatures always show high sensitivity to cloud heights and effective ash cloud emissivity. The relationship between simulated brightness temperatures and cloud heights, effective ash cloud emissivity is nearly linear. However, the effect of satellite zenith angle on the simulated brightness temperatures is relatively small. Further simulation tests under both different atmospheric profiles and volcanic emissivity conditions demonstrate that only when the atmospheric effect and channel emissivity are all taken into account, the mineral particles’ reverse absorption effect in 11μm and 12μm in a volcanic eruption scenario can be simulated. Compared with the atmospheric conditions, the channel emissivity difference is more important for radiative modeling the ash cloud. Therefore, based on the traditional split-window temperature difference method, the joint use of multi-channel thermal infrared brightness temperature information can improve the retrieval accuracy of volcanic ash height and effective ash cloud emissivity under partial cloud-covered conditions. This study provides a theoretical basis on the establishment of quantitative volcanic ash inversion model for China’s new generation geostationary meteorological satellite FY-4.