Retrieval of Atmospheric Parameters from Spectroscopic Observations using DOAS Instruments - RAPSODI

地球上的S大气受复杂的化学和动力学过程控制，对痕量气体和气溶胶的垂直分布的详细了解对于彻底了解大气系统至关重要。遥感测量非常适合于确定大气的垂直结构。地面、机载和卫星遥感测量提供了一种从远处测量大气成分的非接触方法。特别是，多轴差分光学吸收光谱(MAX-DOAS)是一种用于观测各种痕量气体和气溶胶垂直分布的通用且经济实惠的方法。在拟议项目的框架内，将开发一种新的反演算法，这将使人们能够充分利用散射和直射阳光的MAX-DOAS测量所包含的信息。与现有算法不同的是，DOA分析和轮廓检索将一步完成。直接从测量的光谱辐射中同时恢复气溶胶和痕量气体的垂直剖面，预计将导致总体信息量的显著增加。有关大气状况的额外信息将通过对宽带光谱结构的模拟和旋转拉曼散射(Ring Effect)的显式模拟获得，而宽带光谱结构在传统的DOAS应用中迄今被忽略。与辐射传输模型耦合的T矩阵和/或Mie模型将允许从太阳辐射测量中恢复气溶胶微物理特性，例如尺寸分布和复折射率，类似于现有的Aeronet太阳光度计测量算法。该算法将作为彻底评估MAX-DOAS测量关于痕量气体、气溶胶消光和气溶胶微物理性质的总体信息量的基础。将在本项目范围内设计和建造的一种新型极化MAX-DOAS(Pmax-DOAS)仪器的测量将进一步提高散射光测量的信息含量。在可旋转偏振滤光片的不同方向上的天光测量将允许重建斯托克斯矢量。对强度、痕量气柱和环效应的偏振相关测量将显著提高气溶胶和痕量气体反演的准确性。为了充分利用Pmax-DOA的信息量，反演算法将基于一个矢量化的辐射传输模型，该模型能够模拟完整的斯托克斯矢量。

The Earth s atmosphere is governed by complex chemical and dynamical processes, and a detailed knowledge of the vertical distribution of trace gases and aerosols is crucial for a thorough understanding of the atmospheric system. Remote sensing measurements are ideally suited for the determination of the vertical structure of the atmosphere. Ground-based, airborne and satellite borne remote sensing measurements provide a contact free method to measure the atmospheric composition from a distance. In particular, Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) represents versatile and cost effective method for the observation of the vertical distribution of a variety of trace gases and of aerosols. In the framework of the proposed project, a novel retrieval algorithm will be developed, which will allow for a thorough exploitation of the information contained in MAX-DOAS measurements of scattered and direct sunlight. In contrast to existing algorithms, DOAS analysis and profile retrieval will be performed in a single step. This simultaneous retrieval of vertical profiles of aerosols and trace gases directly from the measured spectral radiances is expected to lead to a significant increase in the overall information content. Additional information on the state of the atmosphere will be gained from a simulation of the broadband spectral structure, which has so far been ignored in traditional DOAS applications, and from an explicit modelling of rotational Raman scattering (Ring effect). A T-Matrix and/or Mie model coupled to a radiative transfer model will allow for a retrieval of aerosol microphysical properties, such as size distribution and complex refractive index, from solar almucantar measurements, similar to existing algorithms for Aeronet sun photometer measurements. This algorithm will serve as the basis for a thorough assessment of the overall information content of MAX-DOAS measurements with respect to trace gases, aerosol extinction and aerosol microphysical properties. Measurements by a novel Polarimetric MAX-DOAS (PMAX-DOAS) instrument, which will be designed and built in the scope of this project, will yield a further enhancement of the information content of scattered light measurements. Skylight measurements at different orientations of a rotatable polarising filter will allow for the reconstruction of the Stokes vector. Polarisation-dependent measurements of the intensity, trace gas column and Ring effect will significantly increase the accuracy of aerosol and trace gas retrievals. In order to fully exploit information content of the PMAX-DOAS, the retrieval algorithm will be based on a vectorised radiative transfer model, which enables the simulation of the full Stokes vector.