A Laboratory Experiment for the Statistical Evaluation of Aerosol Retrieval (STEAR) Algorithms

• Published in: Remote Sensing
• Main Authors: Doubovik, Oleg, Schuster, Gregory, Espinosa, W., Ziemba, Luke, Beyersdorf, Andreas, Rocha-Lima, Adriana, Anderson, Bruce, Martins, Jose, Dubovik, Oleg, Ducos, Fabrice, Fuertes, David, Lapyonok, Tatyana, Shook, Michael, Derimian, Yevgeny, Moore, Richard
• Other Authors: Laboratoire d’Optique Atmosphérique - UMR 8518 (LOA), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: aerosols; aerosol retrievals; AERONET; GRASP; [SDE]Environmental Sciences; Aerosol Robotic Network
• Online Access: https://hal.archives-ouvertes.fr/hal-03008692; https://hal.archives-ouvertes.fr/hal-03008692/document; https://hal.archives-ouvertes.fr/hal-03008692/file/remotesensing-11-00498.pdf; https://doi.org/10.3390/rs11050498

International audience We have developed a method for evaluating the fidelity of the Aerosol Robotic Network (AERONET) retrieval algorithms by mimicking atmospheric extinction and radiance measurements in a laboratory experiment. This enables radiometric retrievals that use the same sampling volumes, relative humidities, and particle size ranges as observed by other in situ instrumentation in the experiment. We use three Cavity Attenuated Phase Shift (CAPS) monitors for extinction and University of Maryland Baltimore County's (UMBC) three-wavelength Polarized Imaging Nephelometer (PI-Neph) for angular scattering measurements. We subsample the PI-Neph radiance measurements to angles that correspond to AERONET almucantar scans, with simulated solar zenith angles ranging from 50 • to 77 •. These measurements are then used as input to the Generalized Retrieval of Aerosol and Surface Properties (GRASP) algorithm, which retrieves size distributions, complex refractive indices, single-scatter albedos, and bistatic LiDAR ratios for the in situ samples. We obtained retrievals with residuals less than 8% for about 90 samples. Samples were alternately dried or humidified, and size distributions were limited to diameters of less than 1.0 or 2.5 µm by using a cyclone. The single-scatter albedo at 532 nm for these samples ranged from 0.59 to 1.00 when computed with CAPS extinction and Particle Soot Absorption Photometer (PSAP) absorption measurements. The GRASP retrieval provided single-scatter albedos that are highly correlated with the in situ single-scatter albedos, and the correlation coefficients ranged from 0.916 to 0.976, depending upon the simulated solar zenith angle. The GRASP single-scatter albedos exhibited an average absolute bias of +0.023-0.026 with respect to the extinction and absorption measurements for the entire dataset. We also compared the GRASP size distributions to aerodynamic particle size measurements, using densities and aerodynamic shape factors that produce extinctions consistent with our CAPS ...