Earthshots: Satellite Images of Environmental Change

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A nuclear accident devastated the region near Chernobyl, Ukraine, on April 26, 1986. These images show the area around the nuclear power plant three days after the accident, and then years and decades after the accident.

The Landsat 5 image from April 29, 1986, was the first civilian satellite image of the accident. The data from Landsat were used to help confirm that an explosion had happened at Chernobyl and that the plant had been shut down.

Map of the featured area.

Near the common borders of Ukraine, Belarus, and Russia, the Chernobyl Nuclear Power Plant lies near the Pripyat River at the northwestern end of a cooling pond. The pond is 12 km long; during normal operation the plant discharged warm water counterclockwise around the pond, taking in cool water near the north end. Just northwest of the plant is the city of Pripyat. The smaller town of Chernobyl lies south of the cooling pond.

The 1986 and 1992 images clearly show farm abandonment. Agriculture appears as a collage of bright green (growing crops) and tan (highly reflective bare ground). Many of these areas appear a flat gray-green in 1992, indicating natural vegetation that has taken over the abandoned fields. The 2011 and 2018 images show that this land change persists.

While the reactor was still on fire, all settlements within 30 km were evacuated, including Pripyat (1986 population 45,000), Chernobyl (1986 population 12,000), and 94 other villages (estimated total population 40,000). This area remains almost completely abandoned and is called the Chernobyl exclusion zone. The area is a mixture of former agriculture, forest, and marshland. It has been mostly free from human intervention since 1986.

Radiation contamination later forced abandonment even outside the 30-km zone. High levels of cesium-137 detected years later caused further abandonment. In all, more than 120,000 people from 213 villages and cities were relocated outside contaminated areas.

In 2011, the director of the Chernobyl power plant, Ihor Gramotkin, was asked when the area would again be inhabitable. He responded, “At least 20,000 years” (Harrell and Marson).

A closer look at the site of the power plant in the 1986 image shows a red spot near the location of reactor number 4. The high brightness of those pixels indicates a high temperature heat source. This heat source and darkened strip that extends to the west indicate an explosion, with the reactor still emitting high heat three days later.

The exclusion zone is not officially a wildlife preserve, but with virtually no human intervention in the 1,600-square-mile zone since the accident, wildlife is prospering. Studies with automated cameras have spotted bison, boars, wild horses, beavers, badgers, red foxes, deer, moose, and wolves. Gray wolves are especially abundant. The density of gray wolves there is higher than it is even in Yellowstone National Park.

If there are radiation effects on animal populations in the exclusion zone, they are overshadowed by the lack of human intervention in the zone. In short, animals are free to thrive when there are no humans hunting them, building on the land, or hitting them with cars.

The Landsat 5 image acquired before April 26 shows heated water being pumped from the plant into the adjacent cooling pond and circulating counterclockwise. Landsat 5’s thermal infrared band shows that heated water as orange, then gradually turning yellow then blue as it cools. But the image from April 29 indicates all the water in the pond is the same temperature, evidence the plant was not operating. As the first civilian satellite to image the disaster, Landsat 5 helped confirm the disaster had happened, and this was part of the evidence.

In just the past few years, the cooling pond by the former power plant began drying up. Satellite images clearly reveal a rapid decrease in water level.

Soon after the accident in 1986, radioactive material entered the pond from atmospheric fallout. The contamination went into the pond’s sediment and was shielded by the water. In 2014, the Ukraine stopped pumping water into the pond from the Pripyat River in order to save money. The consequence of this action could be to expose radioactive sediment to the air where it can be dispersed by the wind.

A temporary structure was quickly built over reactor number 4 to contain radioactive material. A more permanent solution was needed. About two decades in the making, a massive steel structure called the New Safe Confinement was built to seal in the site.

Segments of the structure were pre-assembled in Italy and shipped to Ukraine. To prevent exposure to radiation for the workers, the structure was erected 300 m away from the site. The framework was completed in 2014, and the entire structure was moved into place in November 2016. Notice the difference in its location between these 2015 and 2018 images from Sentinel-2.

Considered the world’s largest moveable structure, the new covering weighs 40,000 tons and is 843 feet across, 355 feet high, and 492 feet long. It’s tall enough for the Statue of Liberty to fit inside. At Sentinel’s 10-meter resolution, the huge structure appears as a bright set of pixels at the accident site.

The New Safe Confinement is expected to securely contain the radiation for 100 years.

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