Landsat turns 50: How satellites have changed the way we see and protect the natural world


By conversation

Fifty years ago, American scientists launched a satellite that radically changed the way we see the world.

It captured images of the Earth’s surface in exquisite detail, showing how wildfires burned landscapes, how farms obliterated forests, and many other ways humans were changing the face of the planet.

The first satellite in the Landsat series was launched on July 23, 1972. Eight more followed, providing the same views to track changes over time, but with increasingly powerful instruments. Landsat 8 and Landsat 9 are orbiting the planet today, and NASA and the US Geological Survey are planning a new Landsat mission.

Images and data from these satellites are used to track deforestation and changing landscapes around the world, locate urban heat islands and understand the impact of new river dams, among many other projects. Often the results help communities respond to risks that may not be evident on the ground.

Here are three examples of Landsat in action, taken from the archives of The Conversation.

Amazon Change Tracking

When work began on the Belo Monte Dam project in the Brazilian Amazon in 2015, indigenous tribes living along the Great Bend of the Xingu River began noticing changes in the river’s flow. The water they depended on for food and travel was disappearing.

Upstream, a new canal would eventually divert up to 80% of the water to the hydroelectric dam, bypassing the bend.

The consortium that operates the dam argued that there was no scientific evidence that the change in water flow harmed fish.

But there is clear evidence of the impact of the Belo Monte Dam project – from above, write Pritam Das, Faisal Hossain, Hörður Helgason and Shahzaib Khan of the University of Washington. Using satellite data from the Landsat program, the team showed how the dam has dramatically altered the hydrology of the river.

“As scientists who work with remote sensing, we believe satellite observations can empower people around the world who face threats to their resources,” Das and colleagues write.

It’s hot in town – and even hotter in some neighborhoods

Landsat’s instruments can also measure surface temperatures, allowing scientists to map street-by-street heat risk in cities as global temperatures rise.

“Cities are generally hotter than surrounding rural areas, but even within cities, some residential neighborhoods get dangerously hotter than others a few miles away,” writes Daniel P. Johnson, who uses satellites to study the climate. urban heat island effect at Indiana University.

Neighborhoods with more sidewalks and buildings and fewer trees can be 10 degrees Fahrenheit or warmer than greener neighborhoods, Johnson writes. It found that the hottest neighborhoods tend to be low-income, have a majority of black or Hispanic residents, and have been subject to redlining, the discriminatory practice once used to deny loans to racial minority communities and ethnic.

“Within these ‘micro-urban heat islands,’ communities can experience scorching conditions long before authorities declare a heat-related emergency,” Johnson writes.

Knowing which neighborhoods face the highest risk allows cities to organize cooling centers and other programs to help residents manage the heat.

The Making of Ghost Forests

Satellites that scan the same areas year after year can be crucial for spotting changes in hard-to-reach regions. They can monitor snow and ice cover and, along the Atlantic coast of the United States, endangered wetland forests.

These eerie landscapes of dead tree trunks, often whitewashed, have earned the nickname “ghost forests”.

Emily Ury, an ecologist now at the University of Waterloo in Ontario, used Landsat data to track changes in wetlands. She then zoomed in with high-resolution images from Google Earth – which includes Landsat images – to confirm they were ghost forests.

“The results were shocking. We found that over 10% of the forested wetlands in Alligator River National Wildlife Refuge [in North Carolina] has been lost for the past 35 years. This is federally protected land, with no other human activity that could kill the forest,” Ury writes.

As the planet warms and sea levels rise, more salt water reaches these areas, increasing the amount of salt in the soil of coastal forests from Maine to Florida. “Rapid sea-level rise appears to be exceeding the ability of these forests to adapt to wetter, saltier conditions,” Ury writes.

Many other stories can be found in Landsat images, such as a glimpse into the effects of war on Ukraine’s wheat crop and the spread of algal blooms in Florida’s Lake Okeechobee. Countless projects are using Landsat data to track global change and eventually find solutions to problems, from deforestation in the Amazon to the fires that put Alaska on pace for another historic fire season.


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