Atmospheric correction algorithm for POLDER data.Case study: DAISEX 1999 campaign

This paper presents an algorithm to correct the effects of the atmosphere of POLDER hyperspectral and multiangular reflectance, paying particular emphasis to the aerosol effect. The data were acquired during the European Space Agency campaign DAISEX-99. The algorithm is based on the inversion of measured reflectance in two steps. First, we invert the POLDER reflectances to determine the three parameters of a bidirectional reflectance distribution function (BRDF) of the surface. These values are the first guess of the surface parameters for the second step. In the second step, we invert again the reflectance to obtain three surface parameters and four aerosol variables, in rural sites, and five variables in the rest. The aerosol variables are the particle density of the basic aerosol components: water-insoluble, water soluble and soot particles, sea-salt in accumulation mode and sea-salt in coarse mode. Thus, the algorithm output is the content of some aerosol basic components and the BRDF parameters of the surface. Applying the Mie scattering theory we have obtained the aerosol optical depth (AOD) of the retrieved aerosols and compared it with the values obtained from ground-based solar irradiance extinction measurements. The available information about the aerosols coming from airmass backtrajectories and isobaric maps provides a boundary condition for the inversion. Using this information we show that the AOD values are closer to the measured values and thus the performance of the algorithm is betterl.