Reduction of Atmospheric Effects in Satellite Images During the COVID-19 Induced Lockdown
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RESEARCH ARTICLE
Reduction of Atmospheric Effects in Satellite Images During the COVID-19 Induced Lockdown Ashish Joshi1 • Shefali Agrawal2 • Prakash Chauhan3 Received: 25 June 2020 / Accepted: 17 September 2020 Ó Indian Society of Remote Sensing 2020
Abstract The quality of satellite images is affected due to the scattering and absorption of sunlight by atmospheric molecules and aerosols. Aerosols are small particles suspended in the atmosphere which affects the air quality. The concentration and characteristics of the atmospheric aerosols can vary from place to place. Aerosols are major constituents for the formation of haze and thus responsible for degradation in the satellite images. During the novel corona virus disease pandemic (COVID-19) countrywide lockdown in India, aerosols level significantly lowered in the north Indian cities in the IndoGangetic plain. In this paper, an analysis of image quality was done for Sentinel-2A/2B satellite images for different north Indian cities with respect to the impact of aerosols on image sharpness and surface reflectance values during the prelockdown and lockdown period. The image quality of the images was evaluated through the power spectrum, gradient, and reflectance values in the image. It was observed that the sharpness of the satellite images increased during the lockdown period due to the reduction in aerosols levels in the atmosphere. There was an increase in the power spectrum values from 5% (minimum) to 12% (maximum) in the blue band, 4% (minimum) to 10% (maximum) in the green band, and 1.7% (minimum) to 6% (maximum) in the red band in the satellite images of major cities in the Indo-Gangetic plain during the lockdown period. Since haze is an additive component in the images, thus it was also observed that surface reflectance values had decreased in visible bands for the features which have low surface reflectance values like water (30%), vegetation (21%) and barren land (17%) and surface reflectance values had increased in visible bands for the features which have high surface reflectance values like building (19%) during the lockdown period. Keywords Power spectrum COVID-19 Surface reflectance Sentinel-2A/2B AOD Lockdown
Introduction & Ashish Joshi [email protected] Shefali Agrawal [email protected] Prakash Chauhan [email protected] 1
Geospatial Technology and Outreach Programme Group, Photogrammetry and Remote Sensing Department, Indian Institute of Remote Sensing, Indian Space Research Organisation (ISRO), Dehradun, India
2
Geospatial Technology and Outreach Programme Group, Indian Institute of Remote Sensing, Indian Space Research Organisation (ISRO), Dehradun, India
3
Indian Institute of Remote Sensing, Indian Space Research Organisation (ISRO), Dehradun, India
Sharpness in the image can be defined by the frequency content in the image. Aerosols, major contributors in the haze, generally reduce the sharpness in the image (Kopeika et al. 1998; Yoram 1984). India observed the nationwide lockdown from 25/03/2020 due to COVID-19 pande
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