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Surface Mapping of Earth-like Exoplanets using Single Point Light Curves

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Measuring overcast colors with all-sky imaging.

Raymond L Lee¹

¹Mathematics & Science Division, United States Naval Academy, Annapolis, Maryland 21402, USA. raylee@usna.edu

|November 28, 2008

Summary

Digital sky imaging reveals consistent patterns in overcast colors and spectra. A new semiempirical model explains these findings, offering insights into light scattering and absorption in clouds.

Area of Science:

Atmospheric optics
Radiative transfer theory

Background:

Overcast skies exhibit complex color and spectral properties not fully understood.
Existing atmospheric models (LOWTRAN7, MODTRAN4) fail to capture observed overcast spectral patterns.

Purpose of the Study:

To investigate the angular details of overcast colors and visible spectra using digital sky imaging.
To develop and validate a model explaining observed overcast spectral characteristics.

Main Methods:

Calibrating a CCD camera with a fisheye lens using a spectroradiometer for accurate all-sky spectral mapping.
Analyzing chromaticity data from time-averaged overcast images using histograms and averaged curves.
Developing a semiempirical model based on the radiative transfer equation.

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Main Results:

Digital sky imaging produced colorimetrically accurate all-sky maps of overcast spectra.
Consistent, unexpected patterns were observed in time-averaged overcast colors.
The developed semiempirical model successfully explained these patterns, unlike established models.

Conclusions:

Digital sky imaging is a viable tool for studying overcast spectral properties.
The semiempirical model provides valuable insights into radiative transfer within and below overcast conditions.
Observed spectral patterns are a direct consequence of light absorption and scattering processes in clouds.