Observed Differences Between Imaging Nephelometer Scattering Measurements and AERONET Retrievals During the Discover-AQ Field Missions

Abstract:

Aerosols, clouds, and their interaction play a central role in the climate of our planet. Satellite remote sensing allows for global measurements of aerosol radiative properties; however high confidence in these measurements, and their corresponding retrieval algorithms, requires in situ validation. The Laboratory for Aerosols, Clouds and Optics (LACO) at the University of Maryland, Baltimore County (UMBC) has developed the Imaging Nephelometer, a uniquely accurate instrument concept for the measurement of in situ optical scattering properties.

Imaging Nephelometers provide measurements of the scattering coefficient, phase function and polarized phase function over an angular range of 3 to 177 degrees with an angular resolution better than one degree. The first of these instruments, the Polarized Imaging NEPHelometer (PI-NEPH) has taken part in five airborne field experiments and shown high accuracy in a wide variety of validation studies. In 2014 the open path, Open Imaging NEPHhelometer (OI-NEPH), was constructed at UMBC. This instrument provides measurements that are free from size biases introduced by a sampling inlet as well as changes in hydroscopic growth resulting from relative humidity changes.

This presentation will provide an intercomparison between the aerosol properties that are measured and retrieved by LACO Imaging Nephelometers and the corresponding remote sensing retrievals obtained during the California and Colorado DISCOVER-AQ field experiments. The primary goal of this work will be to compare the scattering-weighted, column-averaged in situ phase functions measured by Imaging Nephelometers with the corresponding phase function retrievals performed by collocated AERONET (AErosol RObotic NETwork) sun photometers. These comparisons will include profiles with a wide range of aerosol loadings, including cases with low optical depth where the AERONET retrieval is less frequently evaluated and the quality of the resulting products is not well known.