Single field-of-view sounder atmospheric product retrieval algorithm: establishing radiometric consistency for hyper-spectral sounder retrievals

The Single Field-of-view (SFOV) Sounder Atmospheric Product (SiFSAP) retrieval algorithm has been developed to address the need to retrieve high spatial resolution atmospheric data products from hyper-spectral sounders and ensure the radiometric consistency between the retrieved properties and measured spectral radiances. It is based on an integrated optimal estimation inversion scheme that processes data from the satellite based synergistic microwave (MW) and infrared (IR) spectral measurements from advanced sounders. The retrieval system utilizes the principal component radiative transfer model (PCRTM) which performs radiative transfer calculations monochromatically and includes accurate cloud scattering simulations. SiFSAP includes temperature, water vapor, surface skin temperature and emissivity, cloud height and microphysical properties, and concentrations of essential trace gases for each SFOV at a native instrument spatial resolution. Error estimations are provided based on a rigorous analysis for uncertainty propagation from the Top-Of-Atmosphere (TOA) spectral radiances to the retrieved geophysical properties. As a comparison, the spatial resolution for the traditional hyper- spectral sounder retrieval products is much coarser than the native resolution of the instruments due to common use of the ‘cloud clearing’ technique to compensate for the lack of cloud scattering simulation in the forward model. The degraded spatial resolution in traditional cloud-clearing sounder retrieval products limits their applications for capturing meteorological or climate signals at finer spatial scales. Moreover, rigorous uncertainty propagation estimation needed for long-term climate trend studies cannot be given due to the lack of direct radiative transfer relationships between the observed TOA radiances and the retrieved geophysical properties. With advantages of the higher spatial resolution, the simultaneous retrieval of atmospheric, cloud, and surface properties using all available spectral information, and the establishment of ‘radiance closure’ in the sounder spectral measurements, the SiFSAP provides additional information needed for various weather and climate studies and applications using sounding observations. This paper gives an overview of SiFSAP retrieval algorithm, and assessment of SiFSAP atmospheric temperature, water vapor, clouds, and surface products derived from the Cross-track Infrared Sounder (CrIS) and Advanced Technology Microwave Sounder (ATMS) data.

单视场（Single Field-of-view, SFOV）探测器大气产品（SiFSAP）反演算法，旨在满足从高光谱探测器反演高空间分辨率大气数据产品的需求，并确保反演属性与实测光谱辐射亮度间的辐射一致性。该算法基于集成最优估计反演方案，可处理卫星搭载的协同式微波（Microwave, MW）与红外（Infrared, IR）先进探测器的光谱测量数据。本反演系统采用主成分辐射传输模型（Principal Component Radiative Transfer Model, PCRTM），该模型以单色模式执行辐射传输计算，并包含精准的云散射模拟模块。SiFSAP可在仪器原生空间分辨率下，为每个单视场提供温度、水汽、地表表皮温度与发射率、云高与微物理属性，以及关键痕量气体浓度等参数。其误差估计基于从大气层顶（Top-Of-Atmosphere, TOA）光谱辐射亮度到反演地球物理属性的严格不确定性传播分析完成。相较而言，传统高光谱探测器反演产品的空间分辨率远低于仪器原生分辨率，这是由于传统方法普遍采用"云清除"技术，以弥补正演模型中云散射模拟的缺失。传统云清除探测器反演产品的空间分辨率退化，限制了其在捕捉更精细空间尺度气象或气候信号中的应用。此外，由于观测的大气层顶辐射亮度与反演的地球物理属性间缺乏直接辐射传输关联，长期气候趋势研究所需的严格不确定性传播估计无法实现。凭借更高空间分辨率、利用全部可用光谱信息同步反演大气、云与地表属性，以及在探测器光谱测量中建立"辐射闭合"等优势，SiFSAP可为各类利用探测观测的气象与气候研究及应用提供所需的额外信息。本文概述了SiFSAP反演算法，并评估了基于跨轨红外探测器（Cross-track Infrared Sounder, CrIS）与先进技术微波探测器（Advanced Technology Microwave Sounder, ATMS）数据得到的SiFSAP大气温度、水汽、云与地表产品。