Understanding the aerosol information content in multi-spectral reflectance measurements using a synergetic retrieval algorithm
Abstract. The multi-wavelength SYNergetic AErosol Retrieval algorithm SYNAER (Holzer-Popp et al., 2002) is used to retrieve aerosol parameters from the Advanced Along Tracking Scanning Radiometer (AATSR) and the Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY). An information content analysis (Holzer-Popp et al., 2008) was performed to quantify the number of independent pieces of information can be retrieved from the combined reflectance measurements of aerosols by both instruments. In particular, the capability of SYNAER to discern various aerosol types is assessed. The focus of this work is further placed on an information content analysis with emphasis to the aerosol type classification. This analysis is applied to synthetic reflectance measurements for 40 predefined aerosol mixtures of different basic components, given by sea salt, mineral dust, biomass burning and diesel aerosols, water soluble and water insoluble aerosols. The range of aerosol parameters considered through the 40 mixtures covers the natural variability of tropospheric aerosols. In this work the capability of the multi-wavelength algorithm to discern aerosol types is investigated. After the information content analysis performed in Holzer-Popp et al. (2008) there was a necessity to compare derived degrees of freedom with retrieved aerosol optical depth for different aerosol types, which is the main focus of this paper. This information content depends on the aerosol optical depth, the surface albedo spectrum and the observation geometry. This theoretical analysis is performed for a large number of scenarios with various geometries and surface albedo spectra for ocean, soil and vegetation. When the surface albedo spectrum and its accuracy is known under cloud-free conditions, reflectance measurements used in SYNAER is able to provide for 2 to 4 degrees of freedom that can be attributed to retrieval parameters: aerosol optical depth, aerosol type and surface albedo.