1. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 E. Bösche 1, P. Stammes 2, R. Preusker 1, T. Ruhtz 1, J. Fischer 1 1 (Institute for Space Sciences, Free University of Berlin) 2 (Royal Netherlands Meteorological Institute, De Bilt, The Netherlands) Simulation of skylight polarization with the DAK model and comparisons with measurements

2. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Overview Introduction Mie-Simulations DAK-Simulations First comparison with measurements Outlook

3. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Introduction Radiative forcing by tropospheric aerosols depends on their optical properties like optical thickness, single scattering albedo and phase function. Basic idea: Spectral resolved VIS and NIR measurements of the diffuse sunlight at various directions in the suns principal plane with inclusion of polarization. Comparison of measurements and radiative transfer simulations Comparison allows to draw conclusions on: the size distribution, the refractive index and vertical distribution of aerosols. From the knowledge of the size distribution and the refractive index the single scattering albedo and the phase function can be derived.

4. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Mie-Simulations (1/4) First mie-calculations have been performed with the following standard input parameters: wavelength 675 nm real and imaginary part of the refraction index of 1.5 and 0.006 log normal size distribution with a sigma of 1.8 mode radius of 0.1 microns To analyse how sensitiv the mie calculations are to changes of one of these parameters, each parameter was changed in a certain range, while the rest of the parameters remaind constant. The mie simulations serve as input for the DAK-simulations

5. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Mie-Simulations (2/4) Mode radius variation

6. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Mie-Simulations (3/4) Abs(Im(m)) variation

7. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Mie-Simulations (4/4) Re(m) variation

8. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 DAK-Simulations (1/5) The DAK-simulations have been performed for multiple scattering and the following standard input parameters: a surface albedo of 0.15 an optical thickness of 0.39 a standard midlatitude atmospheric profile and the mie-aerosol (output of the mie-simulations) was put in the first layer (first one km) while varying the optical thickness the standard mie aerosol was used.

9. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 DAK-Simulations (2/5) Mode radius variation

10. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 DAK-Simulations (3/5) Abs(Im(m)) variation

11. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 DAK-Simulations (4/5) Re(m)

12. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 DAK-Simulations (5/5) Optical thickness variation

13. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Comparisons with measurements (1/5) For the first comparison of simulations and measurements data from the BBC2 campagne have been used, taken at Cabauw, 8 Mai 2003, the Netherlands. Measurement geometry: principal plane Wavelength: 675nm Sunelevation angle: 17.65 °

14. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Comparisons with measurements (2/5) FUBISS-POLAR scans, Cabauw, 08 May 2003FUBISS-POLAR zenith, Cabauw, 08 May 2003

15. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Comparisons with measurements (3/5)

16. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Comparisons with measurements (4/5) Mode radius variationAbs(Im(m)) variation

17. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Comparisons with measurements (5/5) Re(m) variationOptical thickness variation

18. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 OUTLOOK… Investigate the effect of different size distributions (e.g bimodal) Implementation of the k-distribution in DAK (O2A-Band) First sensitivity studies of radiance and polarization to aerosols in the absorbtion bands (O2A-Band) Sensitivity to aerosol optical thickness Sensitivity to aerosol altitude Sensitivity to aerosol size parameters Size distribution Effective radius Effective variance Sensitivity to aerosol refractive index Surface albedo effects Final aim: an retrieval algorithm for aerosol optical properties from polarization measurements.

19. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 ENDE

20. Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.2004 Measurement-equation... Interaction of a light wave with an optical unit (e.g. polarizer, lense or even a scattering particle) can be described by a linear transformation of the Stokes- Vector Negligence of the circular component V Supposition of an ideal sensor FUBISS-POLAR measures only intensities