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 Indo-Gangetic 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 pre-lockdown 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.

中文翻译：

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在 COVID-19 引起的封锁期间减少卫星图像中的大气影响

由于大气分子和气溶胶对太阳光的散射和吸收，卫星图像的质量受到影响。气溶胶是悬浮在大气中的小颗粒，会影响空气质量。大气气溶胶的浓度和特性因地而异。气溶胶是形成雾霾的主要成分，因此是造成卫星图像质量下降的原因。在印度新型冠状病毒病大流行 (COVID-19) 全国封锁期间，印度-恒河平原的印度北部城市的气溶胶水平显着降低。在本文中，对印度北部不同城市的 Sentinel-2A/2B 卫星图像的图像质量进行了分析，分析了在锁定前和锁定期间气溶胶对图像清晰度和表面反射率值的影响。通过图像中的功率谱、梯度和反射率值来评估图像的图像质量。据观察，由于大气中气溶胶水平的降低，卫星图像的清晰度在锁定期间有所增加。蓝色波段的功率谱值从 5%（最小）增加到 12%（最大），绿色波段从 4%（最小）到 10%（最大），以及 1.7%（最小）到 6封锁期间印度-恒河平原主要城市的卫星图像中红色波段的百分比（最大值）。