Shortwave Array Spectroradiometer-Hemispheric (SAS-He): Design and Evaluation

Abstract

Abstract. A novel ground-based radiometer, referred to as the Shortwave Array Spectroradiometer-Hemispheric (SAS-He), is introduced. This radiometer uses the shadow band technique to report total irradiance and its direct and diffuse components frequently (every 30 sec) with continuous spectral coverage (350–1700 nm) and moderate spectral (~2.5 nm ultraviolet/visible, and ~6 nm shortwave-infrared) resolution. The SAS-He’s performance is evaluated using integrated datasets collected over coastal regions during three field campaigns supported by the U.S. Department of Energy’s (DOE’s) Atmospheric Radiation Measurement (ARM) Program, namely (1) Two-Column Aerosol Project (TCAP; Cape Cod, Massachusetts), (2) Tracking Aerosol Convection Interactions Experiment (TRACER; in and around Houston, Texas), and (3) Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE; La Jolla, California). We compare (i) aerosol optical depth (𝐴𝑂𝐷) and total optical depth (𝑇𝑂𝐷) derived from the direct irradiance, (ii) the diffuse irradiance and direct-to-diffuse ratio (𝐷𝐷𝑅) calculated from two components of the total irradiance. As part of the evaluation, both 𝐴𝑂𝐷 and 𝑇𝑂𝐷 derived from the SASHe direct irradiance are compared to those provided by collocated Cimel sunphotometer (CSPHOT) at five (380, 440, 500, 675, 870 nm) and two (1020, 1640 nm) wavelengths, respectively. Additionally, the SAS-He diffuse irradiance and 𝐷𝐷𝑅 are contrasted with their counterparts offered by a collocated Multi-Filter Rotating Shadowband Radiometer (MFRSR) at six (415, 500, 615, 675, 870, 1625 nm) wavelengths. Overall, reasonable agreement is demonstrated between the compared products despite the challenging observational conditions associated with varying aerosol loadings and diverse types of aerosols and clouds. The 𝐴𝑂𝐷- and 𝑇𝑂𝐷-related values of root-mean-square error are within the expected measurement uncertainty of 𝐴𝑂𝐷 (0.01–0.02).