Study of aerosol properties using polarization: Model development, simulation, validation and retrieval.

摘要

Aerosol properties are important in global climate change studies. Although progresses have been made during recent years, our understanding levels in these fields remain low due to lack of adequate observations.; This study developed an integrated High Spectrum resolution Vector Radiative Transfer Model (HSVRTM) for retrieving aerosol properties using polarization data, which will be available from the Aerosol Polarimeter Sensor (APS) on Glory and NPOESS. The special feature of this model is that this model incorporated the line by line radiative transfer model (LBLRTM) and the HITRAN (HIgh resolution TRANsmission) data which enable this model to calculate the gas absorption in detailed lines as well as calculate the aerosol absorption. This model is used to calculate the polarization caused by the absorption and scattering of gas and aerosol particles in the atmosphere. HSVRTM can calculate the absorption and scattering caused by relatively large aerosol particles with size up to 2.1 mum. The model is validated with data measured [Aben et al., 1999] by using the broad-band spectral Global Ozone Monitoring Experiment Bread Board Model (GOME BBM). The model is also used to successfully simulate observed sky light polarizations. Excellent agreement of the calculated results from the HSVRTM and from other models in the literature demonstrated the accuracy of the developed model. Therefore HSVRTM is also used to build the look up table (LUT) to retrieve the aerosol properties, i.e., effective radius (reff) and imaginary refractive index (mi).; The relationship between aerosol microphysical characteristics, i.e., reff, veff, mr, mi and phase matrix that is closely related with aerosol scattering and polarization properties is studied in detail. From our study it is found that the phase function (P11) will increase (decrease) with the increase of aerosol effective radius (reff), the linear degree of polarization -100P21/ P11 is highly related with reff, veff, mi and mr.; Using the HSV-RTM model, the sensitivity of polarization retrieval to two important factors, surface reflectance and aerosol optical thickness, were also studied. It is found that the uncertainty in the aerosol optical thickness and surface reflectance introduced error into the final retrieval results. Sensitivity studies not only demonstrated the advantage of retrieval aerosol property using polarization, but also found that aerosol vertical distribution could be distinguished using high spectral resolution polarization measurements at the oxygen A band.; This study exhibited the high possibility and potential of using polarization to retrieve aerosol properties and aerosol vertical distributions.