Watching Earth from Space: Climate Change and Natural Disasters

Remember from Grade 6

In Grade 6 you learned that satellites take pictures and measurements of Earth, that Canada's RADARSAT Constellation Mission monitors ice, oceans and disasters, that SCISAT measures gases in the upper atmosphere, and that satellite data needs ground checks and local knowledge (like the SmartICE program in Nunatsiavut). In Grade 9 you will learn how satellites gather this data and evaluate how much it really helps.

A question to start

In the record-breaking Canadian wildfire season of 2023, smoke from fires drifted over Toronto, Ottawa and even across the Atlantic. Firefighters and forecasters needed to know where fires were burning, where the smoke was going, and which communities to evacuate, sometimes across areas the size of a province. How could anyone see all that at once? From space.

Orbits for different jobs

Satellites are placed in different orbits depending on their job:

• Low Earth orbit (LEO): a few hundred to about 2000 km up. Close enough for detailed images. The International Space Station orbits about 400 km up and circles Earth about every 90 minutes.
• Polar orbit: a satellite passes over (or near) the poles while Earth rotates underneath, so over a few days it can image the whole planet. Many Earth-observation satellites, including RADARSAT, use this kind of orbit.
• Geostationary orbit: about 35 786 km above the equator. The satellite circles once per day, the same rate Earth turns, so it stays above the same spot. Weather satellites here watch storms develop over a whole hemisphere, minute by minute. Communication satellites use this orbit too.
• Navigation satellites (GPS and similar systems) orbit about 20 000 km up so that several are always visible from anywhere on Earth.

How satellites 'see': remote sensing

• Passive sensors record energy coming from Earth: sunlight reflected by land, water, ice and clouds, and infrared (heat) given off by the surface. Infrared sensors can detect wildfire hot spots. Different surfaces reflect different wavelengths, so healthy plants, burned forest, water and snow look different in the data.
• Active sensors send their own signal and measure what bounces back. Radar satellites, like Canada's RADARSAT Constellation Mission, send microwave pulses. Microwaves pass through clouds, smoke and darkness, so radar can see Earth day and night in any weather. This is very important in Canada, with its long, dark Arctic winters and cloudy skies.
• Altimeters time radar or laser pulses to measure the height of the ocean surface or ice sheets very precisely.
• Gravity satellites measure tiny changes in Earth's gravity to track where water and ice mass are being lost or gained.

What satellites tell us about climate change

• Temperature: satellites measure the temperature of the land, oceans and atmosphere around the whole planet.
• Sea ice: satellites have tracked Arctic sea ice since the late 1970s and show that the area of ice left at the end of summer has declined over that time.
• Ice sheets and glaciers: gravity satellites (such as NASA and Germany's GRACE missions) showed that the Greenland and Antarctic ice sheets are losing ice.
• Sea level: satellite altimeters show that the global average sea level has been rising by a few millimetres per year, and faster in recent decades.
• Greenhouse gases: satellites such as NASA's OCO-2 measure carbon dioxide across the globe. Canada's SCISAT has measured gases in the upper atmosphere, including ones that affect the ozone layer, since 2003.
• Snow and permafrost: satellites show changes in snow cover and in ground movement over thawing permafrost.

What satellites tell us about natural disasters

• Wildfires: infrared sensors detect hot spots; images map burned areas and smoke. Canada is developing WildFireSat, a planned satellite mission designed specifically to monitor wildfires (a contract to design and build the satellites was awarded in 2025, and launch is planned for about 2029).
• Floods: radar maps flooded areas through clouds, so emergency crews know which roads and homes are under water.
• Hurricanes and storms: geostationary weather satellites track storms as they form and move, giving people time to prepare.
• Earthquakes and landslides: radar images taken before and after can measure ground movement of just millimetres to centimetres.
• Sharing: through the International Charter 'Space and Major Disasters', space agencies, including the Canadian Space Agency, provide satellite data free of charge to countries struck by major disasters.

Other phenomena

Satellites also track ocean currents, algae blooms in lakes (including the Great Lakes), crop health, deforestation, air pollution and migrating animals fitted with tracking tags.

Evaluating satellite data

Satellite data is powerful, but it has limits:

• Resolution: some sensors cannot see small details, such as a single small fire under trees.
• Gaps in time: a satellite in low orbit passes over a place only at certain times.
• Calibration: measurements must be checked against ground, ship and aircraft measurements.
• Interpretation: data needs trained people (and increasingly AI systems, which must themselves be checked) to turn numbers into useful knowledge. AI can quickly scan images for fire, flooding or ice changes, but it can miss unusual events or produce false alarms.
• Local knowledge: people who live on the land notice changes that satellites miss. Programs like SmartICE combine Inuit knowledge, local sensors and satellite data.
• Cost and access: satellites are expensive, and not every community has the internet access or training to use the data.