Representative Terrestrial Solar Brightness Profiles

Solar thermal energy systems often use optical imaging concentrators. The image size and shape produced in the focal plane of the concentrator system depends on the solar brightness distribution. Therefore, the forward scattering of solar radiation by the Earth’s atmosphere modifies the solar brightness distribution and creates a circumsolar aureole. The circumsolar ratio, the energy contained in the solar aureole compared to total energy, can impact the performance of these concentrating systems. Based on about 2300 sunshape measurements from sites in France, Germany, and Spain made with a camera system developed by the German Aerospace Center (DLR), average solar brightness profiles with a circumsolar ratio of about 0%, 5%, 10%, 20%, 30%, and 40% were generated. These profiles are compared to the measurements taken by the Lawrence Berkeley Laboratory (LBL) in the late 1970s and a commonly used limb-darkened solar brightness profile, as known from astronomy. A statistical analysis gives information on the frequency of occurrence of each of the average profiles. The profiles combined with the statistical weight should offer a numerical database for calculating the influence of variable conditions of the sunlight scattering on solar concentrating systems. Furthermore, a single average profile was calculated from the DLR data.

Representative Terrestrial Solar Brightness Profiles

Solar thermal energy systems often use optical imaging concentrators. The image size and shape produced in the focal plane of the concentrator system depends on the solar brightness distribution. Therefore, the forward scattering of solar radiation by the Earth’s atmosphere modifies the solar brightness distribution and creates a circumsolar aureole. The circumsolar ratio, the energy contained in the solar aureole compared to the total solar energy, can have an impact on the performance of these concentrating systems. Based on about 2300 sunshape measurements from sites in France, Germany and Spain made with a camera system developed by the German Aerospace Center (DLR), average solar brightness profiles with a circumsolar ratio of about 0%, 5%, 10%, 20%, 30%, and 40% were generated. These profiles are compared to the measurements taken by the Lawrence Berkeley Laboratory (LBL) in the late 1970’s and a commonly used limb-darkened solar brightness profile, as known from astronomy. A statistical analysis gives information on the frequency of occurrence of each of the average profiles. The profiles combined with the statistical weight should offer a numerical database for calculating the influence of variable conditions of the sunlight scattering on solar concentrating systems. Furthermore, a single average profile was calculated from the DLR data.

Shallow seismic reflection section—Introduction

For those interested in shallow seismic reflection (SSR) techniques, this special issue of Geophysics is likely to serve as a useful reference for years to come. The idea for this issue grew out of discussions that took place at the Shallow Seismic Reflection Workshop at the Lawrence Berkeley Laboratory, California, in September 1996. The content of those discussions is the subject of a published report elsewhere (Steeples et al., 1997). Several workshop participants and their colleagues contributed to the papers in this issue as authors and as reviewers. The articles include case histories, novel uses of the SSR technique, state‐of‐the‐art planning considerations for 3-D SSR surveys, and some examples of problems unique to SSR surveying.