When the summer feels like it's the hottest ever, it's facts and data from Europe's Copernicus Program that tell us whether we're just delusional from the heat or actually onto something.

What exactly is the Copernicus program?

Copernicus is an Earth observation system made up of a fleet of European satellites, known as the Sentinel satellites, and "in-situ” instruments — on the ground, at sea and in the air — that gather free, publicly available data.

A lot of this information is used to monitor the environment — by tracking rising sea levels, air pollution and visibility, melting polar ice, the ozone hole, extreme weather events and natural disasters, for example.

It's also used for humanitarian reasons, such as monitoring the displacement of people and refugees. For commercial and other purposes, it's used for monitoring marine transportation routes, military movements, security, agriculture, traffic and urbanization.

You mentioned open data. How much data?

All told, the space and in-situ components deliver 16 terabytes of data every day. As of 2023, the European Space Agency says 705,000 users have downloaded a combined 550 petabytes of data. That's a lot of photos!

What do the satellites do?

Sentinel 1 is a constellation of two polar-orbiting satellites that uses radar technology to observe land and oceans. It tracks floods, oil spills, earthquakes and volcanoes, records the movement of glaciers and detects ships. Radar technology is especially helpful for monitoring situations or locations where the view is obstructed by clouds.

Sentinel 2 is also a constellation of two satellites, but one that uses optical imagery. It tracks coastal erosion, agricultural crops, the build-up of algal blooms, deforestation, urbanization and, famously, penguin colonies.

Sentinel 3 observes the oceans and El Nino events. It can also measure ground temperature — useful for forecasting and monitoring wildfires and heat waves — as well as cyclones and hurricanes.

Sentinels 4 and 5 will provide atmospheric data. They have yet to be launched.

Meanwhile, Sentinel-5P (precursor) tracks gases, including methane emissions, sulfur dioxide from volcanoes and desert dust. This satellite notably tracked the spread of nitrogen dioxide, a dominant air pollutant, during COVID-19 lockdowns.    

Sentinel 6 uses a radar altimeter to measure variations in global sea levels. It maps 95% of the planet's ice-free oceans every 10 days.

Expansion missions over the coming years will enhance the fleet with complementary technological capabilities. One of those missions is CO2M: Copernicus Anthropogenic Carbon Dioxide Monitoring, which will aim to track the effectiveness of measures to decarbonize Europe and meet national emission reduction targets.

What do Copernicus' in-situ components do?  

We get the best use out of the Sentinel satellites when the information they gather is combined with data collected by other instruments or sensors.

The in-situ component of the Copernicus network includes sensors on river banks, tall towers, weather balloons, airplanes and vessels floating in the ocean, like ships, floats and buoys. Drones also collect images. 

Some of this data is known as geospatial reference data — it can be used to provide background geographic information, such as maps and boundaries, which is then used to complement, calibrate and verify the satellite data to ensure a complete package of consistent data over time.

Sounds great — where's the catch?

Copernicus aims to help in emergency situations, although natural extreme weather events like floods or landslides that leave populations asking, "Why didn't we see that coming?" do still happen occasionally.

But one of the core ambitions of the program has always been the long-term monitoring of Earth and the effects of our human existence on the planet — and whether and how we are driving its decline.

Edited by: Clare Roth