RUI: Spectral Imaging of Overcast Skies

United States Naval Academy- Do Not Use, Annapolis MD

Investigators

Abstract

The scientific objective of this research is to use newly available spectral imaging techniques to quantify and thus better understand overcasts' visible features. Such improvements will create new observational criteria for testing the realism of atmospheric radiative transfer models of overcasts' visible-wavelength spectral structure. The intellectual merit of the proposed research is that it would investigate overcasts in a fundamentally new way by complementing conventional spectroradiometry with high-resolution spectra extracted from digital images. This combination permits new kinds of analyses of overcasts' often rapidly changing features. Before now, studying the fine angular details of overcast radiance spectra has not been possible (and certainly not second-by-second), so the proposed research constitutes a wholly new method of atmospheric passive remote sensing. No comparable work exists for narrow field-of-view overcast radiances. The spectral structure of overcast radiances is useful in describing the spatial distribution of cloud optical depth and absorptivity. This in turn offers insights into details of the near-surface heat budget. With suitable data inversion techniques, various atmospheric scattering models will be tested to see how well they account for a given overcast's visible structure, including details seen through linear polarizers. Currently, no detailed observational study of overcast polarization seems to exist. Such wide-ranging observations can provide valuable new insights into everyday phenomena that are now thought to be well understood both theoretically and phenomenologically. The broader impacts of the study will be derived from benefits to science education and impacts on the general public. The digital imaging techniques developed for NSF-sponsored research will be translated into both daily classroom instruction and yearlong honors research projects for Naval Academy midshipmen. An improved understanding of the spatial and spectral distribution of overcast radiances has practical applications in many areas ranging from interior lighting and highway safety to plant growth and development. The principal investigator's presentations are apt to be a powerful recruiting tool for future atmospheric scientists and also for outreach to the general public.