A new solar irradiance reference spectrum

The accuracy to which top-of-atmosphere incident total solar irradiance is known would suggest that it does not contribute to the uncertainty in the surface radiative budget. However, the spectral distribution of spectral solar irradiance (SSI) is less well known than the integrated or total solar irradiance (TSI). Uncertainties in specific spectral bands are important when interpreting surface and airborne measurements because of the spectral dependence of scattering and absorption processes in the atmosphere. Thus, the need for standard and accurate solar irradiance spectra is of critical importance for computational radiative transfer applications in climate research and for validation and calibration applications in remote sensing. We describe the development of a new solar reference spectrum for radiation and climate applications. This spectrum relies to a large extent on data from the Solar Irradiance Monitor (SIM) flying on the Solar Radiation and Climate Experiment (SORCE). Recent progress on SIM characterization and data analysis will be discussed. Our approach is to make reference spectra adaptable to wide range of applications and models which may require, for example, variable spectral resolutions and spectral ranges. Very high resolution spectral structure is incorporated through the application of the Solar Radiation Physical Modeling (SRPM) project. We anticipate that these new spectra will be available in MODTRAN5 and later versions and fully adaptable to a wide variety of high and low resolution radiative transfer models.