Abstract
ABSTRACT A demanding challenge in atmospheric research is the night-time characterization of aerosols using passive techniques, that is, by extracting information from scattered light that has not been emitted by the observer. Satellite observations of artificial night-time lights have been used to retrieve some basic integral parameters, like the aerosol optical depth. However, a thorough analysis of the scattering processes allows one to obtain substantially more detailed information on aerosol properties. In this letter, we demonstrate a practicable approach for determining the aerosol particle size number distribution function in the air column, based on the measurement of the angular radiance distribution of the scattered light emitted by night-time lights of cities and towns, recorded from low Earth orbit. The method is self-calibrating and does not require the knowledge of the absolute city emissions. The input radiance data are readily available from several spaceborne platforms, like the VIIRS-DNB radiometer onboard the Suomi-NPP satellite.
Highlights
Determining the aerosol properties at night-time is an essential step for a better understanding of aerosol dynamics, with direct applications to the study of planetary atmospheres, the characterization of potential candidate sites for astrophysical observatories, and light pollution research
Artificial night lights of cities and towns offer a permanent set of light beacons distributed worldwide, whose observation from Earth orbiting platforms has been shown to be useful to determine some basic integral properties of the aerosols contained in the air colum, as e.g. the aerosol optical depth (Choo and Jeong 2016; Johnson et al 2013; McHardy et al 2015; Wang et al 2016; Zhang et al 2008, 2019)
We demonstrate in this work that the diffuse atmospheric scattered radiance distribution around urban nuclei detected by on-orbit radiometers at night-time contains useful and retrievable information about some key aerosol properties, like the columnar number size distribution function
Summary
Determining the aerosol properties at night-time is an essential step for a better understanding of aerosol dynamics, with direct applications to the study of planetary atmospheres, the characterization of potential candidate sites for astrophysical observatories, and light pollution research. Night-time imagery contains additional useful information, among other the angular dependence of the signal produced by the artificial light scattered by the atmosphere, that can be measured in clear and moonless nights by observing the radiance received at the satellite from directions corresponding to Earth pixels with no light sources, preferably located in the vicinity of urban nuclei with sharp geographical borders. This scattered light appears in the satellite images as a diffuse glow surrounding the city areas, blurring the city
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