Copernicus Sentinel-5P

Six Sentinel-5P data products are now available in the Esri  Living Atlas  and currently in beta release. These services provide timely observations of air quality and atmospheric pollutants for the planet, allowing for accurate weather prediction, improved aviation safety, modeling of health factors (UV exposure) a better understanding of the complex and dynamic chemical processes and reactions that occur in the atmosphere.

This powerful imagery also provides insight into current environmental issues from deforestation in the Congo Basin, to air pollution in the Himalayan foothills, or climate change globally. By exposing what cannot be seen with the naked eye in the atmosphere, Sentinel-5P imagery alerts to problems on the ground. These insights can inform land use, conservation, and climate policy decisions to reduce environmental degradation and improve human health.

• Launch: 13 October 2017
• Orbital Cycle: 16 days
• Orbits/Day: 14
• Orbits/Cycle: 227
• Altitude: 824 km
• Spatial Resolution: 5 km
• Operational Lifetime: 7 years

Sentinel-5P is the latest in a family of Copernicus Sentinel missions from a collaboration between the European Space Agency and European Commission. The first Sentinel mission, Sentinel-1, launched in 2014 to replace aging Envisat and ERS satellites. Earlier Sentinel satellites focus on land monitoring and marine observation through radar and optical imagery.

Sentinel-5P tests new atmospheric monitoring capabilities and is the first Sentinel mission to study air quality. Earlier satellites monitored the atmosphere, but these missions, NASA Aura and ESA Envisat, were either severely degraded or lost contact by 2017. Since Sentinel-4 and 5 required more time for development, Sentinel-5P launched as a precursor in 2017. Until Sentinel-4 is launched in 2024, Sentinel-5P will fill in, providing continuous data between earlier missions and more advanced satellites to come.

Each day of collection, Sentinel-5P level 2 data is cloud-optimized, regridded, and merged to a single level 3 GeoTiff. The package  HARP-Convert  merges and re-grids the level 2 data to keep only one grid per orbit. HARP-Convert converts to level 3 using the "bin_spatial" operation, spatially averaging values between overlapping scenes for each day of collection. Besides merging, HARP-Convert filters pixel values for quality, eliminating noise and invalid values in daily measurements. After merging, filtering, and re-gridding,  OptimizeRasters  then creates the daily level 3 cloud-optimized GeoTiff.

Using several shortwave infrared bands, Sentinel-5P senses and reports molecular concentrations typically in mols per square meter. For some molecules, concentrations can be quite high, but they may be removed from the atmosphere fairly quickly. For example, tropospheric ozone often exists in high concentrations but breaks down within hours.

High molar concentrations alone are not necessarily more hazardous, it depends on the toxicity of the particular molecule. Methane exists at such low concentrations that it's reported in parts per billion. Unlike other molecules measured by Sentinel-5P, methane can linger in the atmosphere for over a decade.

The sensor reports concentrations in "columns." Each column roughly spans the vertical distance between the sensor and the earth's surface. Most values report back as a concentration for the whole column, but others, such as NO ₂  and HCHO, can be isolated for just a tropospheric component. Over time, as the sensor matures, tropospheric-specific calculations may be possible for all molecules.

After its launch in October 2017, Sentinel-5P began gradually monitoring and reporting molecular concentrations and distributions starting with carbon monoxide and sulfur dioxide part way through 2018. Since then, the four subsequent molecules have come online.

Here are a few tips for getting the best out of the Sentinel-5P layers in ArcGIS Pro and ArcGIS Online.

#1: Default time window

By default, when you open a Sentinel-5P layer you see an average of the most recent seven days of imagery. This is because the layer already has a definition query applied where "Best < 8". If this definition query is removed, the layer would try to average a year's worth of data, significantly impairing performance. The default seven-day average smooths over one-day anomalies but still captures notable events in atmospheric chemistry.

#2: Mind the gaps

Near the equator, you may have noticed little cuts or gaps where there is no data between scenes. The default seven-day average mostly fills these gaps with data, but you may also notice some larger gaps in this story's animations. The missing swaths can appear for hours or days, and are primarily caused by satellite repositioning, instrument recalibration, or ground station errors.

To check your Sentinel time-series for missing data, open the layer in a web map, then change the Definition Query to the time window size you're interested in. Use the Show Table option in the layer drop-down to open the selection table to scan for missing days. In the example to the right, the image shows a gap in the last 14 records on May 8th.

#3: Creating animations

At the start of creating animations in ArcGIS Pro, remove the "Best < 8" query entirely, as this will interfere with the time slider and cause the layer not to draw. Instead of using a query, use the time slider to create a 2, 7, or more day window, filling in equatorial gaps and intermittent data drop-outs.

#4 Investigating specific timeframes

Say you want to see the atmospheric impacts of a specific wildfire since it first started blazing six months ago. Manipulating either the definition query or time slider can be used to see the specific dates. Using the definition query, you can specific "acquisition date" and pick a time frame. It is important to note that anything longer than a 30-day average will not be possible as this would impair performance. Once within the desired date range, the time slider can be used to toggle between times and assess atmospheric impacts.

#5 Use ArcGIS Notebooks for deeper analysis

ArcGIS Notebooks provide advanced analysis options if you want to take Sentinel-5P data to the next level. At the bottom of this story, you'll find a video on how to use notebooks to investigate and probe deeper into these Sentinel-5P layers...

 Ozone (O ₃₎   most commonly exists in the stratosphere, between 15-30km above the Earth’s surface, with a primary benefit of shielding the planet and its inhabitants from harmful ultraviolet radiation originating from the Sun. This is the "good" version of Ozone and the reason why monitoring and protecting stratospheric Ozone is critical.

However, Ozone is also present closer to ground level in the troposphere, where it is a byproduct of reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. These reactions result in what we know as smog. Tropospheric ozone is thus considered "bad" ozone. Not only does it cause respiratory and other health issues when inhaled, but in the troposphere, ozone is also a greenhouse gas contributing to climate change.

Though a greenhouse gas in the troposphere, higher up in the stratosphere, ozone can help reduce the effects of climate change by reflecting solar energy. Holes in stratospheric ozone increase the amount of solar radiation reaching the Earth's surface, and heighten the risk of skin cancer, cataracts, and impaired immune systems. It wasn't until the 1970s that links were made between the expanding ozone hole over Antarctica and the common use of Chlorofluorocarbon propellants (CFCs) since the 1930s. While these were eventually outlawed, the damage will take many decades to repair, due to the long lifespan of the ozone-depleting chemicals. The ozone hole has slowly started to recover but fluctuates seasonally. It is typically most prominent from September through the end of the year and is best viewed on a map using a Polar projection. Wobbling and changing its extent daily, the hole still cumulatively covers much of Antarctica.

 Nitrogen Dioxide (NO ₂ )  primarily enters the atmosphere as a byproduct of the burning of fossil fuels – cars, trucks, ships, power plants, and off-road equipment.

Localized high temperatures can cause atmospheric nitrogen (N ₂ ) and oxygen (O ₂ ) to form NO and NO ₂  (collectively known as NOx). NOx interact with water, oxygen and other chemicals to form acid rain and “haze” over cities. NOx also contributes to nutrient pollution in coastal waters and has potentially dangerous respiratory effects. NOx contributions to climate change are complex. In direct effects, it acts as a greenhouse gas and can increase tropospheric ozone. Taking into consideration its indirect effects, however, NOx can react with OH radicals and  reduce  the greenhouse effect.

The abundance of NO ₂ , like many highly concentrated gases, can be a proxy for human activity, which typically fluctuates seasonally or by population distribution. Note the relatively consistent NO ₂  levels in China, Europe, the Middle East, and North America, and the seasonality of increased concentrations in Brazil, the Democratic Republic of Congo, and Angola.

The rapid reduction of industrial activity in response to the COVID-19 lockdowns early in the pandemic provide a unique opportunity to compare the "business as usual" state of the world to a global industrial machine that is effectively on life support. Using the swipe map, it's stunning to juxtapose the before and after emissions of NO ₂  across the globe.

 Formaldehyde (HCHO)  is found in the atmosphere as a byproduct of natural processes, like combustion from forest fires, and also from fuel combustion and anthropogenic incineration. It can also be formed through the reaction of volatile organic compounds (VOCs) with ozone. While rainfall removes formaldehyde from the atmosphere, it can also cause acid rain. It can break down in the lower atmosphere to formic acid (CH ₂ O ₂ ) and carbon monoxide (CO), which are also harmful. As a carcinogen, formaldehyde can be harmful at high levels.

In a year's worth of observations, high concentrations of formaldehyde spike over some of the world's densest forests: the Amazon and Congo Basin. There is some seasonal component to this; formaldehyde is removed from the atmosphere by rainfall, and therefore concentrations tend to peak in dry seasons. In fact, formaldehyde peaks over West Africa during its dry season in January. Precipitation shifts over 6-9 months, leading to formaldehyde concentrations over the Congo during its August-September dry season.

Similarly, the Amazon, especially on its southern and western fringes, sees some of the highest formaldehyde concentrations in the world. Often overlooked in comparison to large-scale, industrial agriculture in the Amazon, small-holder farms can also be  threatening  to the environment. These farms often employ slash-and-burn techniques to clear the rainforest. The widespread use of slash-and-burn can be seen through the Living Atlas Sentinel Explorer using high-resolution shortwave infrared imagery.

Compared to carbon dioxide,  Methane (CH ₄ )  is  25 times  as powerful at trapping heat in the atmosphere, though it remains in the atmosphere for less time. It occurs naturally and is generated by fossil fuel production, the decay of organic matter in wetlands (and permafrost melt in arctic, Greenland), and as a byproduct of digestion in ruminant animals (cows).

Methane is, after carbon dioxide, the most important contributor to the anthropogenically enhanced greenhouse effect. Roughly three-quarters of methane emissions are anthropogenic, and as such it is important to continue the record of satellite-based measurements. Sentinel-5P aims at providing methane column concentrations with high sensitivity to the Earth's surface, good spatio/temporal coverage, and sufficient accuracy to facilitate inverse modelling of sources and sinks.

As methane exists in such low concentrations, methane is the only molecule reported in parts per billion (ppb) a ratio of methane to other molecules in the absence of water vapor. Because there may be so little methane in a given area, the sensor may pick up noise when detecting it, resulting in some quirky distributions. Below, we take a tour of notable methane concentrations globally.

 Carbon monoxide (CO)  is a poisonous gas with harsh consequences for global climate change and acute human health. At high levels, carbon monoxide poisoning can be lethal and sends hundreds of thousands of Americans to the hospital yearly. The greatest contributors of carbon monoxide are automobiles, fossil fuel-burning machinery, and fires. Unlike other gases, carbon monoxide does not have a direct effect on global temperatures. However, carbon monoxide is an indirect contributor to climate change. Through atmospheric chemical reactions, carbon monoxide can convert to methane, carbon dioxide, and tropospheric "bad" ozone – all major greenhouse gases.

Carbon monoxide can also form from the breakdown of formaldehyde in the lower atmosphere. As such, its geography and concentrations are often similar to that of formaldehyde. Like formaldehyde, a year's worth of carbon monoxide observations shows large concentrations around the Amazon and Congo. Like the Brazilian Amazon, much of the Democratic Republic of the Congo has been degraded through slash and burn agriculture. Sentinel shortwave infrared imagery below shows the scale of the burns in near Kabinda, DRC that contribute to high carbon monoxide levels.

 Sulfur Dioxide (SO ₂ )  is the most abundant pollutant in the troposphere, originating from the burning of fossil fuels (75-85% of contribution), plus coal-powered generators, boilers, petroleum refining, paper manufacturing, and metal smelting (15-25%). Volcanic eruptions are also natural contributors of sulfur dioxide in the atmosphere (20 to 25 million tons a year, collectively), where it can combine with water to form sulfuric acid aerosols and cause respiratory issue at high levels. Sulfur dioxide is especially harmful to plant life since it can react to form acid rain disrupt photosynthetic processes.

While the background signal of SO ₂  emissions is fairly constant across the globe when animated over a year, volcanic events bookend 2022 with enormous plumes coming from several notable eruptions. In January, Volcán Wolf offshore of Ecuador erupted, followed a week later on January 15th by the explosively violent Hunga Tonga eruption in the South Pacific, sending volcanic gases, ash, and over 50 million tons of water vapor into the atmosphere. On November 27, Mauna Loa, dormant since 1984, came back to life and erupted for 12 days, closing out a very active year of Pacific Ocean volcanism.

The submarine eruption of Hunga Tonga may have been  the most impactful natural climatic event of the last 30 years , and we will be studying its effects for decades to come. Sending metric megatons of sulfate aerosols into the atmosphere, the water vapor alone is estimated to have increased the stratospheric water mass by 13%, warming the surface climate. At the same time, the increase in sulfate aerosols contributes a global cooling effect, resulting in a complicated mix of opposing-forces and interactions. As we continue to monitor the impacts of this historic eruption on the gaseous chemistry and particle microphysics in the stratosphere, the improved observational data provided by Sentinel-5P (and soon, Sentinel-5) will be critical in its understanding.

In fact, volcanic eruptions have had massive impacts on the temperature of the planet due the cooling effect of sulfur dioxide. Known as the "year without a summer," 1816 was one of the coldest years on record with summer snowfalls and famine across the world. The previous year, Mount Tambora erupted, releasing up to 120 million tons of sulfur dioxide (25-300x more than Hunga Tonga). The cold and hazy skies lingered for over a year. In Caspar David Friedrich's Two Men by the Sea painted in 1817, sulfuric ash is clearly visible in the afternoon sky. This painting reminds us of the tremendous effect gases and aerosols have on the climate. Sentinel-5P's ability to monitor greenhouses gases will be hugely important going forward as week seek to limit emissions and slow warming.

Monitoring atmospheric gases is important to understand our progress towards climate targets. Radiative forcing is used to measure the balance of energy entering or leaving earth's atmosphere. When energy entering exceeds that of energy leaving, warming occurs (greenhouse effect) and some gases are responsible for most of this warming. Sentinel-5P monitors methane and tropospheric ozone concentrations, important contributors to climate change. Unlike carbon dioxide, methane has a shorter lifespan, so monitored reductions in methane could be beneficial in the near term. Sentinel-5P also monitors sulfur dioxide, which has a negative radiative forcing because it reduces the greenhouse effect by reflecting more of the sun's energy back to space. Since molecules like methane and sulfur dioxide all play a role in climatic changes, Sentinel missions can help to monitor their concentrations and track progress.

Overall, the sentinel missions serve as a power monitor of the "pulse" of the atmosphere. Through it, we gain valuable insight into hazardous pollution, environmental degradation, and even climate indicators.

Do you want to know how to use Sentinel-5P layers in combination with other Living Atlas layers to better understand the natural and anthropogenic impacts on the atmosphere? Click on the card below to view the presentation on Raster Analytics by Esri's Lain Graham at the 2023 FedGIS Conference in Washington, D.C.: