Satellites contribute to pollution control of plateau lakes

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A series of Chinese earth observation satellites have played an important role in monitoring, evaluating and forecasting pollution in lakes on the plateau in southwest China's Yunnan Province.

Plateau lakes are mainly fed by rainfall so the replacement period of lake water is long, which means the lakes lack the ability for effective self-purification and their ecological environment is fragile. One of three famous plateau lakes in Yunnan Province, Erhai Lake is key to ecological protection and curbing pollution in China, say environmental experts.

Erhai Lake sits at the watershed of the Lancang, Jinsha and Yuanjiang rivers. It belongs to the Lancang-Mekong River water system. The drainage area is 2,565 square km.

"Previously, we used traditional physical and chemical methods, as well as foreign satellite data to monitor the water quality of Erhai Lake. The monitoring area was limited, and it took too much time, manpower and resources. And the monitoring results were incomplete," said Zhang Zhenyu, of the Erhai Lake research team at Shanghai Jiao Tong University.

China began to construct the High-resolution Earth Observation System in 2010, aiming to provide all-weather, round-the-clock global coverage by 2020. With the network of Gaofen observation satellites, China has had an increasingly clearer view of the planet. Data from the Gaofen satellites has been widely used in more than 20 industries across China.

"Since the China-developed Gaofen satellites were launched, especially the Gaofen-5 hyperspectral satellite, China's dependence on foreign remote-sensing satellite data has greatly reduced," Zhang said.

"By combining a variety of satellite data, timely water quality dynamic monitoring is possible, and water quality changes can be presented in a timely and efficient way."

Zhang recalled how Erhai Lake was once mainly monitored manually and researchers had to take samples by boat, which meant the time that every sampling point was taken differed greatly and they couldn't monitor the whole lake in real time.

"By analyzing the Gaofen satellite data, we can now provide a basis for the government to control cyanobacterial blooms in Erhai Lake," he said. "The satellite data is also used to evaluate the effect of protection measures.

"Gaofen satellites can also monitor coastal conditions such as changes to lake shorelines and illegal construction, providing evidence for law enforcement and inspections," he added.

"We're going to establish an environmental monitoring, evaluation and trend-forecasting system by combining Gaofen remote-sensing data and ground-based monitoring data to help control pollution caused by excessive construction and agricultural development."

Since 2016, high-resolution images from Gaofen-1 and Gaofen-4 have also been used to monitor cyanobacterial blooms in Dianchi Lake, Yunnan Province, said Wu Yong, an engineer of the Environmental Monitoring Center in Kunming, capital of Yunnan Province.

"The Gaofen satellite images could help us monitor the evolution and spread of the cyanobacterial blooms in Dianchi Lake, and allow us to predict algae blooms," Wu added. 

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