max planck institut informatik
Realistic Solar Disc Rendering
Andrei Linţu, Jörg Haber, Marcus Magnor
In: WSCG'2005 Full Papers Conference Proceedings, 2005.
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This work concentrates on rendering the solar disc considering Rayleigh scattering, Mie scattering, absorption, and refraction. The atmosphere is modeled in layers, each layer having a set of individual optical properties. Based on different atmospheric temperature profiles and climates, the solar disc is rendered in realistic shape and color. In particular, we replicate optical phenomena such as the red and the green flash, limb darkening, and refractive distortions of the solar disc.
In order to achieve realistic renderings, the optical phenomena occurring in the atmosphere need to be considered. We take into account Rayleigh scattering due to air molecules as well as Mie scattering due to aerosols present in the atmosphere, thus obtaining a realistic color of the solar disc. To obtain the correct shape of the solar disc, we also model refraction, allowing us to trace rays correctly through the atmosphere. The atmosphere model used in our system is stratified, consisting of atmosphere layers located geocentrically around the surface of the Earth. The height of individual layers is chosen such that approximately the same amount of molecules is contained in each one of them. Our atmosphere model reaches up to a height of 35 km. A schematic description of the used model is depicted in the Figure below. To each layer we assign the relative humidity and optical parameters. If there is a temperature inversion present in the atmosphere, we can replicate different types of mirages.
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| Figure 1: Layered Atmosphere Model |
In Figure 2, the two possible cases of the intersection between the currently traced ray and the boundaries of an atmosphere layer are depicted. The expected trajectory of the ray is denoted as Path 1. However, if a thermal inversion is present, the ray can bend downwards following Path 2.
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| Figure 2: Possible Paths for a Given Ray of Light |
In the Figures below, sunset scenarios for different cilmate types are presented. For each situation the current aerosol distribution and air humidity is taken into account. In this case no temperature inversion layers in the atmosphere are considered.
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| Figure 3: City Sunset Landscape |
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| Figure 4: Sunset in a Maritime Climate |
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| Figure 5: Sunset in a Continental Climate |
The consequences of a temperature inversion layer close to the ground is depicted in Figure 6 This is the so called Omega Sunset, the form of the solar disc being reminiscent of the Greek letter Omega.
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| Figure 6: Omega Sunset |
In Figure 7, a green flash is replicated. The difference in altitude between successive renderings is below one arc-minute.
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| Figure 7: Green Flash |
The red flash is simulated in Figure 8. An atmosphere containing a weak inversion layer is used here to create a mock mirage for an observer situated at an altitude of 45 m above sea level.
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| Figure 8: Red Flash |
Note: All images presented in this paper have been generated using a discretization of N = 8 wavelengths in the range from 380 nm to 720 nm.
Demo Movie. (3.8 MB)