Atmospheric Pollution variation

Pollution refers to the introduction or presence of a substance which has harmful effects on the environment. Pollution can be both naturally (e.g. as a result of a volcanic eruption) or artificially produced (e.g. as a consequence of human industrial activity). Among the many substances that are considered as pollutants, the ones that have the largest effect on the health of the population and nature are Nitrous Oxide (NO2), Ozone (O3), Nitric Acid (HNO3), Sulfur Dioxide (SO2), and aerosols or particulate matters (PM). These pollutants are the ones are most present in the atmosphere and its presence causes severe health problems in the population worldwide.

Satellites  have greater coverage than fixed pole stations and, because of this,  they are more suited to regional measurements of the atmospheric  composition. While fixed stations measure the air quality with greater  accuracy at lower altitudes, satellites are able of measuring larger  areas at different altitudes and thus, generate an atmospheric map of air quality and pollution.

Satellite observation data can be used to measure the presence of pollution in the different layers of the atmosphere throughout the world and how the composition of the atmosphere varies during the year with the different seasons. Comparing the data obtained pre and post pandemic will give us a strong indicator of how the human activity (industry) and land-based movement (traffic) has been affected by the COVID-19. In addition, the data will show the effect of the policies the different countries have had in response to the pandemic.

There are several projects currently working on measuring the Air Quality and composition of the atmosphere.

• The European Union’s Earth observation programme runs the Copernicus Atmosphere Monitoring Service (CAMS) project, in collaboration with the ESA and EUMETSAT, among others. In this project, the main satellites being used are the Sentinel family (https://www.copernicus.eu/en).
• Another project, run in collaboration between NASA and JAXA, is the A-Train constellation family: a constellation of, currently, four earth observation satellites (OCO-2, GCOM-W1, Aqua and Aura) which combine their observations to build high definition three dimensional images of the Earth’s atmosphere. In this mission, the Aura satellite studies air quality, the ozone layer, and Earth’s climate (https://www.nasa.gov/mission_pages/aura/main/index.html).

During the past months, most countries have had to implement severe restrictions in human activity and movement, with some countries declaring a total lockdown. As a result of this, most non-essential businesses have stopped operating (while some still continue to be inoperative) and movement of people has been significantly reduced. The reduction of human activity caused by the COVID-19 has had a positive effect in the Earth’s atmospheric composition and, Earth observation satellites have detected a decrease in the pollution emissions worldwide. This reduction has been most significant in large cities, highly industrialised, that have been most severely affected by the pandemic such as China, Italy or Spain.

Night-time light brightness

Nighttime light (NTL) observation data provides a measure of artificial night lighting  brightness on the earth’s surface, as seen from space. Although  observation of NTL can be achieved by conventional panchromatic imaging,  more specialised sensors augmented by post-processing algorithms are  able to produce datasets with wider usefulness. For example, imagers  with high-sensitivity sensors and high spatial resolution, such as the  Chinese panchromatic JL1-3B satellite and cubesat LJ1-01, with spatial resolutions of 0.92m and 130m respectively. Data  from LJ1-01 is available freely, however data from JL1-3B is only  available on a commercial basis (Zhao et al).

The  current state of the art in NTL data is provided by the NASA Black  Marble product, containing imagery obtained by the visible-infrared  VIIRS instrument onboard the Suomi National Polar Partnership satellite,  coupled with data from Landsat-8, Sentinel-2 and other earth observing  satellites. VIIRS has a minimum spatial resolution of 375m and a  very-sensitive low-light Day/Night frequency band. Uncorrected nightly images are available, as well as monthly and annual cloud-free and moonlight-corrected composites (NASA Black Marble).

Regarding  the use of NTL data in observing the effect of the COVID-19 pandemic on  human movement, we expect that a comparison of previous data to data  obtained during the pandemic will reveal that established seasonal  patterns in NTL change are broken, with reduced NTL brightness along  roads and at popular tourist destinations and increased brightness in  rural areas as people move away from large cities.

NTL  can be a reliable proxy for socioeconomic activities such as population  density and human movements, including road traffic. NTL  data has previously been used to study seasonal epidemics such as  measles through the estimation of population density fluctuations (Bharti et al).

Unfortunately,  it was not possible to validate our assumptions regarding observable  changes using the nightly imaging available at EOSDIS Worldview, mainly due to cloud coverage and inconsistent image exposure. Attempts to recreate published images of the Wuhan lockdown effects on road traffic were also unclear. Additionally, the in-flight calibration of the sensor and the continuously improving image quality make it hard to objectively compare data from different years.

Visual variation in human related infrastructure and movement

This parameter is chosen as it is the most distinct change that can be observed using earth observation satellites. However, care must be taken when drawing conclusions as a visual change may not only be associated with a change due to the pandemic but as a result of many factors like seasonal changes. Hence data for the other variable factors will need to be collected and used when drawing a meaningful conclusion.

What will be measured?

We  will be able to track vehicle influxes into a city centre, how often  there are traffic jams, how the city traffic changes throughout the year  and distinguish between pattern changes due seasons and hence use  machine learning to differentiate between changes due to a pandemic and  those that occur annually.

This  can be extended to the shipping industry especially in the vicinity of a  port, and aircraft on the ground can also be monitored using the same  techniques.

Using  the above satellites, the concentration of people in a city can also be  measured using a chorographical method as the resolution of the  satellite allows this to be achieved as its resolution is 0.31 m.

Advantages

1. Easy to understand the theory and the hypothesis of the change
2. May not be difficult to set up an algorithm to observe seasonal changes and compare them to a change due to a pandemic
3. Use a satellite already in orbit reduce environmental impact like space debris.

Limitations to this method

1. May need to use a private sector satellite which may be expensive
2. May need loads of data from previous years that may not be available
3. A lot of storage space needed.
4. Limited down link capacity.

Equipment required

There are 2 satellites currently in orbit that can be used for this mission.

1. WorldView-3 Satellite Sensor (0.31m) (WorldView-3 Satellite Sensor | Satellite Imaging Corp, 2017)
2. SuperView-1 Satellite Sensor (0.5m) (SuperView-1 Satellite Sensor | Satellite Imaging Corp, 2017

Variation in commercial aviation and passenger maritime industries

The work carried out using this parameter includes contrasting air traffic and shipping traffic pre-pandemic data (late 2019-early 2020) with current data in order to show how COVID19 has affected these two industries. This analysis also includes explanation of key events represented in these  sets of data which are related to the different actions taken by  governments during the evolution of the pandemic. The data used to carry out this analysis has been obtained by software (FlightRadar24 and MyShipTracking) that uses Satellite Navigation Systems to provide active tracking of aircraft and ships in these industries.

An example of a satellite constellation that provides aircraft tracking is the Iridium constellation which has been fitted with ADS-B transponders. These  transponders are the ones that allow the FlightRadar24 software to  actively track all aircraft flying around the world with significant  accuracy. This system also allows aircraft to be tracked in remote  places of the world where there are no local radar stations near the  designated flight path (patches of the Indian Ocean and the Pacific  Ocean).

The  shipping industry also has its specific Navigation satellites that  allow live tracking of large vessels and their specific cargo (oil,  cargo, LNG or passengers). An example of a satellite that aids ship  navigation in the European region is EGNOS. These satellites allow software such as MyShipTracking or MarineTraffic to actively track ships all around the world.

This parameter has been chosen because the most common policies adopted by governments to contain the spread of the disease directly affect it. Most countries have imposed nationwide lockdowns and closure of borders, these actions have virtually put the commercial aviation industry and the passenger maritime industry in temporary hibernation due to the large risk of infection they possess as a consequence of their global nature.