The satellite’s “eye” is the ruler

2022-05-01 0 By

Nansihu Lake, the largest freshwater lake in northern China, covers an area of 1,266 square kilometers and is responsible for flood control and storage, south-to-north water diversion, aquaculture development, shipping and transportation.On April 8, 2021, the Supreme People’s Procuratorate started a public interest lawsuit to file a case against the ecological environment damage in the Nansihu Lake basin.After 10 months, has the damaged ecological environment in nansihu Lake basin improved?The objective image and data are the yardstick to measure the effect of justice in handling cases.Recently, the reporter from space information innovation research institute, Chinese Academy of Sciences and Chinese environmental monitoring station to understand some case since the monitoring data of satellite remote sensing image faithfully records the far beyond the range of the ChaoRenYan observation nansi lake terrain information, the national environmental quality monitoring network data monitoring the change of water quality in different periods, with this time of year,You can clearly see the changes that have taken place in Nansi Lake.Space information innovation research institute, Chinese Academy of Sciences, entrusted by the Supreme People’s Procuratorate to the third party objective stance on nansi lake and the surrounding ecological environment for the continuous remote sensing monitoring, through to obtain image data processing, model of computing and information extraction, comparative analysis and historical traces, field inspection and investigation and follow up with dynamic display technology, such as effectiveness,The ecological environment clues, typical site evidence collection and treatment effect follow-up work were carried out for the “Nansihu” project.”Using satellite remote sensing data, according to different degree of eutrophication of water body, black smelly, suspended matter concentration change in the visible light and near infrared band show different spectrum characteristics, focus on observation and analysis of the nansi lake black smelly water index, the degree of eutrophication of water body, water suspended solids concentration of the three typical water quality indicators, reflect the nansi lake lake water quality situation from different dimensions,Compare the year-to-year changes.”Chinese Academy of Sciences space information Innovation Research Institute researcher Liu Shuo introduced.Observation, according to the calculation comparison from late October 2020 to 2021 in late October, nansi lake lake black smelly index is high, the high degree of eutrophication and high suspended solids concentration of water water water area were significantly reduced, and the black smelly index is low, the low degree of eutrophication and water suspended solids concentration of low water area were significantly increased.According to introducing, in the whole process of satellite remote sensing monitoring comparison, in order to ensure the objectivity of the nansi lake basin water, satellite remote sensing data contrast, for the same area, using the same kind of satellite data, the same phase, the same processing algorithms, a common data acquisition meteorological conditions, the method of “five one” the satellite remote sensing monitoring technology has carried on the strict constraints.At the same time, considering that the south-to-North Water Diversion project of 2020-2021 will be completed before flood, a large amount of external water will enter Nansihu Lake in the first half of the year;From June to September, it is in the rainy season, and a lot of rain water flows into Nansihu Lake in the flood season. In summer, vegetation is lush and cloudy, and there are many external barriers from space to water observation.Winter is the time when the lake is calm and impurities settle, and the water quality generally improves compared with other seasons.Therefore, the satellite observation of Nansihu lake was carried out in late October, when the water body was relatively stable and the weather was clear, the water grass gradually withered and the water body was relatively stable.”Satellite remote sensing monitoring shows that the overall water quality of The Nansihu Lake basin has improved significantly, and the pollution risks of key monitoring targets have been greatly reduced.”Liu Shuo said.The image reflects the objective change of visual effect level, and the water quality monitoring data from another side confirms the governance effect of Nansihu lake for a period of time.The reporter learned that according to the surface water environmental quality standards, the quality of water is divided into several grades from class ⅰ to class ⅴ, lower than class ⅴ for poor, is a severe pollution.Water environment monitoring indexes mainly include total phosphorus, ammonia nitrogen and permanganate index.Total phosphorus exceeds the standard mainly from non-point source pollution, ammonia nitrogen exceeds the standard mainly from domestic sewage, permanganate index exceeds the standard indicates that water is likely to be polluted by organic matter.According to the data provided by China Environmental Monitoring Station based on the National Environmental Quality Monitoring network, there are 5 monitoring points and 28 monitoring sections of 19 rivers entering the lake in nansihu Basin.Monitoring data showed that during the 13th Five-Year Plan period, the water quality of Nansi Lake was stable on the whole, but exceeded the standard in some areas and parts of the period, with prominent problems such as urban and rural non-point source pollution, cyanobacteria bloom and ecosystem imbalance.In August 2020, water quality from class ⅳ to worse than class ⅴ was found in several sections of the rivers entering nansihu Lake, with permanganate index and total phosphorus exceeding the standard “prominent”.Water pollution in flood season is serious and non-point source pollution is obvious.In August 2021, the Nansihu Lake project is in progress.The monitoring data showed that the water quality of the secondary dam at the lake point improved from class ⅴ to Class ⅲ, and the main improvement index was total phosphorus.Fourteen stations into the lake showed improvement or obvious improvement, and the main improvement indexes were total phosphorus and permanganate index.During the same period, the average daily concentration of total phosphorus in flood season of secondary dam water of Nansihu Lake decreased significantly compared with the same period of last year.Ammonia nitrogen and permanganate index showed a stable level without the large fluctuation before the project.The average daily concentration of total phosphorus in some sections of rivers entering the lake decreased significantly compared with the same period last year.Permanganate index concentration decreased year-on-year;The overall concentration of ammonia nitrogen did not change significantly.”After the project was registered, the water environment quality of nansihu Lake basin has gradually improved, and the main pollution indicators have decreased.The surrounding environment is cleaner and greener, and the project promotes the effect.”Li Wenpan, deputy director of water ecological environment monitoring room of China Environmental Monitoring Station, said.(Yan Jingjing)