Research On Remote Sensing Monitoring Of Turbidity And Chlorophyll-a Concentration In Urban Lake

Water is the source of life,and lakes are an important part of inland water.With the increasingly serious problems of water pollution in inalnd lakes,water quality monitoring has become an important issue to be solved for the sustainable development of social economy.Conventional water quality monitoring methods can not meet the requirements of real-time,large-scale,and high-dynamic water quality assessment and monitoring,while satellite remote sensing approaches can monitor water quality changes and dynamic distribution in a large range,and make up for the shortcomings of conventional observation methods.Therefore,selecting high spatial and temporal resolution satellite remote sensing data and taking the advantages of multi-source remote sensing data can effectively improve the remote sensing monitoring capacity of inland lake water quality.Based on the satellite-ground joint method,Landsat and Sentinel series multi-source satellite remote sensing data,combined with the field measured data,the inversion model of turbidity and chlorophyll-a concentration was established,and the long-term water quality monitoring of Liangzi Lake and East Lake was carried out.The water quality of Liangzi Lake and East Lake from 2000 to 2019 was obtained.At the same time,the variations of water quality of Liangzi Lake and East Lake during the 2019Wuhan Military Games(October 18-27,2019)was analyzed.The dynamic change of water quality and its influencing factors were evaluated from the perspective of long-term and short-term respectives.This study foucus on:(1)Retrieval of turbidity and chlorophyll-a concentration in Liangzi Lake and East Lake based on multi-sensor satellite dataBased on Landsat-5/TM,Landsat-7/ETM+and Landsat-8/OLI surface reflectance products,Sentinel-2/MSI after atmospherically corrected by the software(Acolite)provided by Nature Remote Sensing and Ecosystem Modelling team,and Sentinel-3/OLCI data after atmospheric correction by the SNAP provided by European Space Agency(ESA).After reducing the discrepencies of radiometirc and spectral differences,combined with field automatic observation station and field measured turbidity data,a turbidity model for Liangzi Lake and East Lake is built with a determinat coefficient(R~2)of 0.88,and root mean square error(RMSE)of 5.07 NTU,and a chlorophyll a concentration model with a R~2 of 0.79,and a RMSE of 1.46μg/L.(2)Analysis of turbidity variations and temporal and spatial distributions of Liangzi Lake and East Lake from 2000 to 2019Based on the turbidity distribution maps retrieved by Landsat series images from2000 to 2019,Normalized Difference Vegetation Index(NDVI)data and the meteorological data(rainfall and wind speed),the annual variation characteristics and spatial distribution pattern of turbidity in Liangzi Lake and East Lake are analyzed,and the factors influencing the variation of turbidity are discussed.It is found that the turbidity in Liangzi Lake and East Lake is about 2%annual growth rate from 2000 to2007 NTU.From 2007 to 2010,turbidity maintains a reduction rate of 4 NTU per year.From 2011 to 2019,turbidity is maintained at a rate of 1 NTU reduction per year.Moreover,the decrease of NDVI may cause the increase of turbidity in Liangzi Lake,and the turbidity of East Lake may also be affected by other human activities.(3)Analysis of turbidity and chlorophyll-a concentration in Liangzi Lake and East Lake during the 2019 Wuhan Military GamesBased on Landsat and Sentinel satellites and in-situ turbidity and chlorophyll-a concentration measurements,high-resolution turbidity and chlorophyll-a concentration time series products are derived.The water quality changes of Liangzi Lake and East Lake during the 2019 Wuhan Military Games are analyzed,and the water quality status during the preparation of Wuhan military games is evaluated.The results showed that the military games did not cause the changes of turbidity and chlorophyll-a concentration in the surrounding waters,and it was carried out in an environment-friendly state.Based on the multi-source satellite remote sensing data,the water quality of Liangzi Lake and East Lake involved in the 2019 Wuhan Military Games is evaluated comprehensively from the perspective of long-term and short-term,which is helpful to better understand and monitor the water quality changes and serve the government’s decision-making.