Cooperative Institute for Research in Environmental Sciences

Science Rendezvous > 2009 Posters
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Angular Corrections to the Brewer Spectrophotometers of the U.S. EPA Neubrew Network Using the Direct-to-Diffuse UV Solar Irradiance Ratio (DDR) from Co-located Multi-filter Rotating Shadow Band Radiometer (UV-MFRSR)

K. Lantz¹,², P. Kiedron¹,², P. Disterhoft¹,²

¹ Cooperative Institute for Research in Environmental Sciences, University of Colorado-Boulder, Boulder, CO, 80309, ²NOAA Earth Systems Research Laboratory, 325 Broadway, Boulder, CO, 80305

UV Multi-Filter Rotating Shadowband Radiometers (UV-MFRSR) and Brewer spectrophotometers are located at six NEUBREW sites in the continental U.S. At one of the sites, there is also a UV Rotating Shadowband Spectrograph (UV-RSS). The UV MFRSR provides instantaneous total, diffuse, and direct solar irradiance in 7 2-nm wide channels in the UV region, where the UV-RSS gives instantaneous total, diffuse, and direct solar irradiance across the wavelength range from 290 - 400 nm. The spectral Direct to Diffuse Ratio (DDR) is a reflection of the local conditions and can be a wealth of information on the local atmosphere. The purpose of the work is to compare Direct to Diffuse Ratios (DDR) from UV-MFRSR measurements to DDR from the UV-Rotating shadow-band Spectrograph (UV-RSS) co-located at Table Mountain Test Facility (TMTF) 8-km outside Boulder, CO under a variety of conditions. An applicattion of the DDR is to correct the non-Lambertian angular response of the Brewer Spectrophotometer. Because of the angular response error, the Brewer spectrophotometer underestimates the UV solar irradiance, where the correction depends on the sky conditions that are reflected in the DDR. In this study, results from the fitting or parameterization of the diffuse and direct solar irradiance from collocated UV-MFRSRs are used to correct global horizontal solar irradiance from the Brewer spectrophotometers for the effects of non-Lambertian angular response. In the future, the DDR studies are expanded to look at the retrieval of aerosol optical properties in the UV.