Satellite remote sensing technology strengthens the defense line for water quality safety in Taihu Lake.

With the development of industry and commerce, dense population, and rapid urbanization, the environmental burden on my country's water resources is increasing year by year. As a large-scale and efficient means of Earth observation, satellite remote sensing technology can play an important role in water quality monitoring, obtaining more accurate and comprehensive water quality results.

Water quality remote sensing monitoring concept

Water quality remote sensing monitoring refers to the technology of obtaining water quality information over a large area by using the relationship between spectral characteristics and pollutant concentrations in water bodies, through experience or model inversion.By studying the relationship between satellite remote sensing data and measured water quality data, an inversion model for water quality parameters can be constructed. Remote sensing monitoring can acquire information on water quality parameters exceeding standards, offering advantages over traditional ground-based monitoring, such as wider coverage, time and labor savings, and ease of long-term dynamic monitoring.

Water quality remote sensing monitoring principle

The principle of water quality remote sensing monitoring is to analyze the absorption and scattering of light of specific wavelengths by water quality parameters in the water body based on the different spectral characteristics of pure water and polluted water bodies, and then invert the concentration of each water quality parameter in the water body.Besides the pure water itself, there are three main types of substances that affect the spectral characteristics of water: yellow substances, phytoplankton (chlorophyll a), and total suspended solids. Water radiance contains water color information, and it is primarily used for water quality remote sensing inversion, which yields water quality remote sensing monitoring parameters: chlorophyll a concentration, suspended solids concentration, and transparency. By inverting the results, remote sensing monitoring of water quality changes can be achieved.

Satellite remote sensing technology assists in the monitoring of water quality in Taihu Lake.

In May 2007, a large-scale cyanobacteria bloom occurred in Taihu Lake, causing severe pollution of the lake and triggering a water supply crisis for nearly 2 million residents in Wuxi City. The national and local governments have attached great importance to the issue of Taihu Lake water pollution control, and as of 2020, nearly 1,800 pollution control projects have been implemented.

Satellite remote sensing technology has the advantages of wide coverage and high timeliness, and can provide a reliable technical means for monitoring water changes over large areas.Satellite remote sensing technology can be used to monitor algal blooms in Taihu Lake over a long period of time, effectively provide early warning of disasters, and provide data support for subsequent environmental governance. 

Changes in the Water Quality Index of Taihu Lake by Xi'an Institute of Optics and Precision Mechanics CAS Aerospace Science and Technology Group Co.,LTD

Recently, based on existing research, CAS Xi'an Optics & Aerospace Technology Co., Ltd. extracted the spatiotemporal distribution of cyanobacterial blooms in Taihu Lake from clear-sky images taken on similar dates (August 26, September 6, and August 24) between 2021 and 2023. The Fauna Index (FAI) was used to extract the cyanobacterial blooms in Taihu Lake, utilizing the strong absorption of water in the red, near-infrared, and short-wave infrared bands to ultimately construct a FAI extraction model.

The extraction results show that, after a long period of treatment, the cyanobacterial bloom in Taihu Lake has changed from a large-scale outbreak in 2021 to a small-scale phenomenon in 2023, with its area decreasing and its harmfulness gradually decreasing. 

By leveraging the wide coverage and stable information acquisition capabilities of satellite remote sensing, it is possible to monitor the entire process of water quality changes in Taihu Lake. This allows for a comprehensive and objective understanding of the actual water quality and eutrophication situation before and after pollution control in Taihu Lake, providing technical means for timely problem detection and preventative measures. This not only saves significant manpower, material resources, and financial resources, but also helps environmental protection departments efficiently grasp and monitor the real-time status of the aquatic ecological environment.