A fast method for simulating observations of polarized light emerging fromthe atmosphere applied to the oxygen-A band

Polarimetry of the atmosphere as a function of wavelength can provide valua ble information on atmospheric aerosol and cloud properties. In particular, information can be obtained from polarization observations in wavelength r egions where molecular absorption is prominent. Simulation of such observat ions is, however, extremely time-consuming when using line-by-line radiativ e transfer calculations. To address this problem, a fast method to simulate such observations was developed, using the adding-doubling method which is especially suited for polarized light, and the correlated k-distribution ( ck) method. The part dealing with the ck-method was extended to include ins trumental spectral response functions as well as the spectral distribution of the incident solar flux. In our calculations, we used spectral response functions representative for the GOME instrument on board the ERS-2, and fo cussed on the O-2-A band. We present the calculated radiance and the degree of linear polarization of light emerging at the top and at the bottom of a n atmosphere that contains molecules as well as aerosol particles and that is bounded below by a Lambertian reflecting surface. Because the cli-method is an approximative method, special attention is paid to the errors in the degree of linear polarization of the emergent light resulting from the cor relation assumption used in the ck-method. It appears that the errors in th e polarization are in general smaller than the errors in the radiances. For the O-2-A band, the errors in the polarization are less than 0.25% for the reflected light and less than 0.05% for the transmitted light. This shows that our fast method can be used to simulate polarization observations in t he O-2-A band accurately. (C) 1999 Elsevier Science Ltd. All rights reserve d.