the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Towards Gridded Nighttime Aerosol Optical Thickness Retrievals Using VIIRS Day/Night Band Observations Over Regions with Artificial Light Sources
Abstract. Using observations from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band (DNB), we examined the feasibility of developing a gridded nighttime aerosol optical thickness (AOT) data set based on the spatial derivative of measured top-of-atmosphere attenuated upwelling artificial lights at night (ALAN) over the US, Middle-East and Indian Subcontinent regions for 2017. We also studied the potential of using NASA’s standard operational Black Marble nighttime lights product suite (VNP46) for estimating the spatial derivatives of surface artificial light emissions, that is one of the key lower boundary conditions for the retrieval process. Sensitivity of nighttime aerosol retrievals to observing conditions and different methods of estimating the spatial derivative of surface artificial light emissions were also explored. Root-Mean-Square Errors (RMSEs) of ~ ~0.15 and ~0.18 and correlations of ~0.8 and ~0.6 were found between VIIRS nighttime AOT and Aerosol Robotic Network (AERONET) nighttime and daytime data, respectively, suggesting that the proposed gridded nighttime AOT retrievals have reasonable skill levels for potential data assimilation, air quality and climate studies of significant events. We also found that NASA Black Marble products can be used to estimate the spatial derivative of surface artificial light emissions for nighttime AOT retrievals over regions that are not frequently contaminated by aerosol plumes, such as the USA. This study demonstrated the feasibility of constructing a gridded nighttime AOT data, using artificial lights, for monitoring of nighttime aerosol events over large spatial and temporal domains. Given the deployment of VIIRS instruments (currently in orbit and forthcoming) on board the NOAA Joint Polar Satellite System series satellites, this study can be viewed as a precursor for gridded nighttime AOT retrievals at both regional and global scales in the future. We also show that the use of the NASA Black Marble products, which would greatly save processing time of this method, is challenging over regions with frequent aerosol pollution such as the Indian Subcontinent and further exploration is required.
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RC1: 'Comment on amt-2024-181', Anonymous Referee #1, 19 Dec 2024
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2024-181/amt-2024-181-RC1-supplement.pdf
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RC2: 'Comment on amt-2024-181', Anonymous Referee #2, 23 Dec 2024
This study utilizes VIIRS DNB day-night band data to investigate the spatial derivative of upward atmospheric layer attenuation and artificial light at night (ALAN) over the United States, the Middle East, and the Indian subcontinent in 2017. It explores the feasibility of developing a gridded nighttime aerosol optical thickness (AOT) dataset. Additionally, the study evaluates the potential of using the NASA standard Black Marble nighttime lights product suite (VNP46) to estimate the spatial derivative of surface artificial light emissions, and discusses the sensitivity of nighttime aerosol retrieval to observational conditions as well as the application of different methods for estimating the spatial derivative of surface artificial light emissions. The research validates the retrieved AOD by comparing it with ground-based AOD data from AERONET sites and satellite-based AOD products, such as MODIS AOD and MISR AOD. There are certain aspects/details that require further clarification from the authors, and I have listed them in my comments below:
1. The selection of aerosol types has a certain impact on the inversion accuracy. In this context, aerosol plumes in the Indian subcontinent primarily consist of a mixture of polluted haze, smoke, and pollutant aerosols (Line 224). How is this mixed aerosol type (aerosol composition) defined?
2. The lunar AERONET AOT data at 440, 675, 870, 1020, and 1640 nm (Line 152). Why was the 700 nm value not obtained by fitting the 675 nm and 870 nm bands for the analysis in Figures 4-7?
3. Please discuss the influence of lunar radiation on the AOD nighttime inversion results in Section 4.5.
4. The 6S model requires satellite surface reflectance data as input, but the method for calculating the surface reflectance from VIIRS DNB remote sensing imagery is not explained.
Citation: https://doi.org/10.5194/amt-2024-181-RC2
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