Describing Visual Air Quality Is A Complex Issue Depending On:

1. Describing Visual Air Quality Is AComplex Issue Depending On: • characteristics of observer • optical characteristics of target • illumination of scene • optical properties of atmosphere, ambient aerosols and gases

2. Monte Carlo Radiation Transfer ModelTo Model Sky Radiance NS • backwards photon trajectory • multiple scattering, spherical geometry • Lambertian surface reflection • ANY complex inhomogeneous distribution of wave-length dependent scattering and absorbing gases, aerosols or clouds

4. Sky Radiance Measurements 5O Azimuth & 1O Elevation

7. Input 35 mm Color Slide • Digitize into three color (RGB) files; • calibrate with density vs. exposure data from manufacture; • Mask to get distance (r) to each picture element (pixel);

10. Estimating Radiance From Digitized Slide • Exposure (E) = light intensity x time • all picture elements (pixels) exposed for the same time • thus, exposure can be used as a surrogate for radiance: E = f(density)

14. Input 35 mm Color Slide • estimate sky radiance with Monte Carlo model and calibrated sky pixels from base slide; • estimate extinction (bext) on day slide was taken; • invert equation to calculate inherent radiance: NO = (Nr - NS(1-T)) / T

15. Model New Image Extinction • MIE model to get aerosol optical properties: phase function and single scattering albedo; • generate model geometry assigning spatial distribution of aerosol; • use Monte Carlo model to estimate new sky radiance;

17. Model New Image Extinction • assume inherent radiance is unchanged with changing extinction levels; • use equilibrium radiance model to get new image radiances: Nr = NOT + NS(1-T) • output new image.

19. Seeing is a psychophysicalphenomenon not easily modeled or reproduced by any process that is strictly physical in origin.

20. Requirements For Match • Spectral Sensitivities • Color Gamuts • Dynamic Range

22. Dynamic Range • Human visual system: 10,000 : 1 • Projected slides: 500 : 1 • Best Computer Monitor: 200 : 1 • Reflection Prints: Highest Quality 50 : 1 Newspaper 15 : 1

23. Projected 35 mm Slides Advantages • Best Color Saturation and dynamic range. • Proven to be valid representations of actual scenes for judgments of perceived scenic beauty, landscape preferences and visual air quality. • Can easily design survey to include preview images, control scenes and multiple visual air quality scenarios

24. Slides vs. Onsite Judgments

25. Projected 35 mm Slides Disadvantages • Must be viewed in darkened room. • Respondents must be brought to central facility. • Slides degrade rapidly with projection time.

26. Degradation of 35 mm slides

27. Reflection Prints Advantages • Easily transportable so can be brought to respondents. • Do not degrade as fast as 35 mm slides. • Have been used in most previous CV studies of visibility benefits.

28. Reflection Prints Disadvantages • Limited dynamic range means small changes in visual air quality cannot be presented. • Must use small focal length lens and large print size to mimic onsite field of view. • Difficult to efficiently present multiple visual air quality levels with prints.

29. Visibility Modeling Software • Aerosol • PLUVUE • WinHaze • VisualHaze

30. Aerosol

31. WinHaze

32. WinHaze • Small image files: 900 x 600 pixels; • Sky radiances calculated from fit to thousands of full Monte Carlo runs using a standard rural aerosol model; • All base images have same Rayleigh sky • Does not account for color shifts due to absorbing aerosols or gases; • Optimized for viewing on CRT monitors only; • IS FAST and simple to run.