The polarized Sun and sky radiometer SSARA: design, calibration, and application for ground-based aerosol remote sensing

Abstract

Abstract. Recently, polarimetry has been used to enhance classical photometry to infer aerosol optical properties, as polarized radiation contains additional information about the particles. Therefore, we have equipped the Sun–sky automatic radiometer (SSARA) with polarizer filters to measure linearly polarized light at 501.5 nm. We describe an improved radiometric and polarimetric calibration method, which allows us to simultaneously determine the linear polarizers' diattenuation and relative orientation with high accuracy (0.002 and 0.1∘, respectively). Furthermore, we employed a new calibration method for the alt-azimuthal mount capable of correcting the instrument's pointing to within 32 arcmin. So far, this is limited by the accuracy of the Sun tracker. Both these methods are applicable to other Sun and sky radiometers, such as the Cimel CE318-DP instruments used in the AErosol RObotic NETwork (AERONET). During the A-LIFE (Absorbing aerosol layers in a changing climate: aging, LIFEtime and dynamics) field campaign in April 2017, SSARA collected 22 d of data. Here, we present two case studies. The first demonstrates the performance of an aerosol retrieval from SSARA observations under partially cloudy conditions. In the other case, a high aerosol load due to a Saharan dust layer was present during otherwise clear-sky conditions.

Ice crystal characterization in cirrus clouds II: radiometric characterization of HaloCam for the quantitative analysis of halo displays

“…The MIM rooftop platform hosts a cloudnet site (Illingworth et al, 2007) featuring operational measurements by a MIRA-35 cloud radar (Görsdorf et al, 2015), a CHM15kx ceilometer (Wiegner et al, 2014), and an RPG-HATPRO microwave radiometer. Further operational measurements are performed by a CIMEL sun photometer, which is part of the AERONET (Aerosol Robotic Network) network (Holben et al, 1998), as well as with the institute's own sun photometer SSARA (Sun-Sky Automatic Radiometer, Toledano et al, 2009Toledano et al, , 2011Grob et al, 2020). HaloCam observations ideally complement these measurements to retrieve information about ice crystal properties.…”

Investigation of Volcanic Emissions in the Mediterranean: “The Etna–Antikythera Connection”

“…Dust and volcanic ash, being both large non-spherical particles are difficult to distinguish based on lidar observations alone. Both aerosol species produce comparable values of their intensive optical parameters used for aerosol characterization (i.e., lidar ratio (S) and δ p , (see [94,95])).…”

Optomechanical Design and Application of Solar-Skylight Spectroradiometer

“…However, the instruments have to take a few seconds to traverse a filter wheel sequence while performing measurements, limiting their time resolution. In contrast to the CE318 radiometer, the multispectral sun-photometer (SSARA) manufactured at the Meteorological Institute Munich can measure the radiation of all channels simultaneously [ 11 ]. Owing to the design of their electronics, the channel amplifiers have a high time constant during scanning.…”