Changes in transparency of Lake Chagan and its surrounding lakes from 1984 to 2019 based on remote sensing
Water clarity is an important indicator for assessing eutrophication in lakes or reservoirs.Traditionally,water clarity is determined in the field using Secchi disk depth(SDD),which is time consuming,labour intensive and not suitable for large scale water clarity assessment.Water clarity is mainly determined by non-algal particulate matter,algal abundance and colored dissolved organic matter(CDOM)in the water column,which can be monitored by optical remote sensing.In this study,eight cruises were conducted over Lake Chagan in 2004-2009 and in situ measured SDD were determined.Correlation analyses between in situ meas-ured SDD and Landsat calibrated top-of-atmosphere(TOA)reflectance were performed to determine the best band or band combi-nations.Based on the in situ measured SDD and TOA pairs,we developed an algorithm based on the ratio of red and blue bands and the average of red,green and blue,e.g.AV(B3,Bl),to estimate the SDD in Lake Chagan.High model calibration accuracy was achieved,with lower RMSE and MAPE for model validation.The algorithm was applied to Landsat images to derive SDD distri-bution maps from 1984 to 2019.The Landsat-derived results indicate that the SDD in Lake Chagan ranges from 1.0 cm to 63.0 cm with an annual mean of 17.6 cm,with a significant increasing trend during 2002-2019 with an increasing trend of 2.3 cm/10 a.The annual mean values of the SDD variation dynamics in Lake Chagan went through two phases.From 1984 to 2001,the SDD showed no obvious trend,and then it showed a significant increasing trend.Our analysis showed that the SDD in Lake Chagan had some relationship with wind speed,precipitation and the normalized difference vegetation index(NDVI).The changes in water transparency in Lake Chagan were monitored by remote sensing on a long time scale,and the characteristics and rules of the chan-ges were analyzed to provide a scientific basis for ecological management in the Lake Chagan Basin.
万方数据
维普
