This study presents an analysis of the spectral characteristics of remote sensing reflectance(Rrs)in northwestern South China Sea based on the in situ optical and water quality data for August 2018.Rrswas initially di...This study presents an analysis of the spectral characteristics of remote sensing reflectance(Rrs)in northwestern South China Sea based on the in situ optical and water quality data for August 2018.Rrswas initially divided into four classes,classes A to D,using the max-classification algorithm,and the spectral properties of whole Rrs were characterized using the empirical orthogonal function(EOF)analysis.Subsequently,the dominant factors in each EOF mode were determined.The results indicated that more than 95%of the variances of Rrs are partly driven by the back-scattering characteristics of the suspended matter.The initial two EOF modes were well correlated with the total suspended matter and back-scattering coefficient.Furthermore,the first EOF modes of the four classes of Rrs(A-D Rrs-EOF1)significantly contributed to the total variances of each Rrs class.In addition,the correlation coefficients between the amplitude factors of class A-D Rrs-EOF1 and the variances of the relevant water quality and optical parameters were better than those of the unclassified ones.The spectral shape of class ARrs-EOF1 was governed by the absorption characteristic of chlorophyll a and colored dissolved organic matter(CDOM).The spectral shape of class B Rrs-EOF1 was governed by the absorption characteristic of CDOM since it exhibited a high correlation with the absorption coefficient of CDOM(ag(λ)),whereas the spectral shape of class C Rrs-EOF1 was governed by the back-scattering characteristics but not affected by the suspended matter.The spectral shape of class D Rrs-EOF1 exhibited a relatively good correlation with all the water quality parameters,which played a significant role in deciding its spectral shape.展开更多
Colored dissolved organic matter(CDOM)is an important optically active substance in marine environment.Its biochemical conservatism makes it an important indicator to offshore pollution process.Monitoring the content,...Colored dissolved organic matter(CDOM)is an important optically active substance in marine environment.Its biochemical conservatism makes it an important indicator to offshore pollution process.Monitoring the content,composition,and diffusion process of CDOM is a good approach to analyze the terrestrial input,optical properties,and ecological environment of offshore areas.The spatiotemporal characteristics of CDOM around the Leizhou Peninsula were analyzed based on field observation data collected in the autumn 2020 and spring 2021,and an empirical inversion model of the ag(355)(absorption coefficient at 355 nm)and spectral slope(Sg)(g stands for gelbstoff/gilvin,which is called CDOM)based on Sentinel-3A ocean and land color instrument(OLCI)images was constructed.The results show(1)the order of average ag(355)value around the Leizhou Peninsula was east coast(0.503/m)>Qiongzhou Strait(0.502/m)>west coast(0.365/m);(2)the best band combinations of CDOM inversion in spring and autumn were(B4+B11)/B3 and(B7-B1)/B6(B stands for the band of spectral images),and the final inversion results are close to the measured results,indicating that the model has good accuracy;(3)the S_(g)value of the CDOM absorption spectrum was fitted to the hyperbolicexponential model.The fitting accuracy of the model was higher than those of the exponential model and the hyperbolic model,and the best S_(g)inversion model was constructed by selecting Sg(275-295)and Sg(250-295)in spring and autumn;(4)the spatial distributions of ag(355)and S_(g)were inverted,and CDOM in the waters around the Leizhou Peninsula originated from terrestrial organic matter carried by coastal aquaculture zones and runoff in the northeast Zhanjiang and the northern Beibu Gulf.展开更多
Typhoon is one of the frequent natural disasters in coastal regions of China.As shown in many studies,the impact of typhoons on the South China Sea(SCS)should not be overlooked.Super typhoon Rammasun(2014)was studied ...Typhoon is one of the frequent natural disasters in coastal regions of China.As shown in many studies,the impact of typhoons on the South China Sea(SCS)should not be overlooked.Super typhoon Rammasun(2014)was studied that formed in the northwestern Pacific,passed through the SCS,then landed in the Leizhou Peninsula.Remote sensing data and model products were used to analyze the spatiotemporal variations of the cold eddies,upwelling,sea surface temperature,mixed layer depth,rainfall,sea surface salinity,suspended sediment concentration,and surface-level anomaly.Results confirm the constant presence of upwelling and cold eddies in the southeast of Hainan(north of the Zhongsha Islands)and the southeast of Vietnam in July.In addition,we found the strengthening effect of super typhoon Rammasun on the upwelling and cold eddies in the SCS.The major reasons for the continuous decrease in sea surface temperature and the slow regaining of seawater temperature were the enhanced upwelling and vertical mixing caused by the typhoon.The increasing of the surface runoff in the Indochina Peninsula was mainly affected by the typhoon,with some contribution for the southeast of Vietnam’s cold eddy and upwelling.展开更多
Two kinds of regression equations are used to reproduce the sediment flux of the 26 small coastal watersheds in southeastern China.The first kind is the global equations suggested by Milliman and Syvitski(1992),Mulder...Two kinds of regression equations are used to reproduce the sediment flux of the 26 small coastal watersheds in southeastern China.The first kind is the global equations suggested by Milliman and Syvitski(1992),Mulder and Syvitski(1996),Syvitski et al.(2003),and Syvitski and Milliman(2007).The second kind is the modified equations revised by the characteristics of the coastal watersheds,including the drainage area,mean water discharge,and mean sediment discharge.Compared with the observations of the hydrometric stations,the global equations overestimate the sediment flux by 1–2 orders of magnitude.By using the modified equations,the accuracy of the estimated sediment flux is significantly improved,with the relative error in the range of 7%–24%.The reason for the overestimation mainly caused by different parameters’domain and regression coefficients between global rivers and study coastal watersheds.This study demonstrates that modification needs to be considered when using global regression equations to reproduce the sediment flux of the small coastal watersheds in southeastern China.展开更多
基金The Key Projects of the Guangdong Education Department under contract No.2019KZDXM019the Fund of Southern Marine Science and Engineering Guangdong Laboratory(Zhanjiang)under contract No.ZJW-2019-08+2 种基金High-Level Marine Discipline Team Project of Guangdong Ocean University under contract No.002026002009the Guangdong Graduate Academic Forum Project under contract No.230420003the"First Class"discipline construction platform project in 2019 of Guangdong Ocean University under contract No.231419026。
文摘This study presents an analysis of the spectral characteristics of remote sensing reflectance(Rrs)in northwestern South China Sea based on the in situ optical and water quality data for August 2018.Rrswas initially divided into four classes,classes A to D,using the max-classification algorithm,and the spectral properties of whole Rrs were characterized using the empirical orthogonal function(EOF)analysis.Subsequently,the dominant factors in each EOF mode were determined.The results indicated that more than 95%of the variances of Rrs are partly driven by the back-scattering characteristics of the suspended matter.The initial two EOF modes were well correlated with the total suspended matter and back-scattering coefficient.Furthermore,the first EOF modes of the four classes of Rrs(A-D Rrs-EOF1)significantly contributed to the total variances of each Rrs class.In addition,the correlation coefficients between the amplitude factors of class A-D Rrs-EOF1 and the variances of the relevant water quality and optical parameters were better than those of the unclassified ones.The spectral shape of class ARrs-EOF1 was governed by the absorption characteristic of chlorophyll a and colored dissolved organic matter(CDOM).The spectral shape of class B Rrs-EOF1 was governed by the absorption characteristic of CDOM since it exhibited a high correlation with the absorption coefficient of CDOM(ag(λ)),whereas the spectral shape of class C Rrs-EOF1 was governed by the back-scattering characteristics but not affected by the suspended matter.The spectral shape of class D Rrs-EOF1 exhibited a relatively good correlation with all the water quality parameters,which played a significant role in deciding its spectral shape.
基金Supported by the Key Projects of the Guangdong Education Department(No.2019KZDXM019)the Fund of Southern Marine Science and Engineering Guangdong Laboratory(Zhanjiang)(No.ZJW-2019-08)+3 种基金the High-level Marine Discipline Team Project of Guangdong Ocean University(No.002026002009)the Guangdong Graduate Academic Forum Project(No.230420003)the“First Class”Discipline Construction Platform Project in 2019 of Guangdong Ocean University(No.231419026)the Innovation Projects of Colleges and Universities in Guangdong Province(No.2021KQNCX028)。
文摘Colored dissolved organic matter(CDOM)is an important optically active substance in marine environment.Its biochemical conservatism makes it an important indicator to offshore pollution process.Monitoring the content,composition,and diffusion process of CDOM is a good approach to analyze the terrestrial input,optical properties,and ecological environment of offshore areas.The spatiotemporal characteristics of CDOM around the Leizhou Peninsula were analyzed based on field observation data collected in the autumn 2020 and spring 2021,and an empirical inversion model of the ag(355)(absorption coefficient at 355 nm)and spectral slope(Sg)(g stands for gelbstoff/gilvin,which is called CDOM)based on Sentinel-3A ocean and land color instrument(OLCI)images was constructed.The results show(1)the order of average ag(355)value around the Leizhou Peninsula was east coast(0.503/m)>Qiongzhou Strait(0.502/m)>west coast(0.365/m);(2)the best band combinations of CDOM inversion in spring and autumn were(B4+B11)/B3 and(B7-B1)/B6(B stands for the band of spectral images),and the final inversion results are close to the measured results,indicating that the model has good accuracy;(3)the S_(g)value of the CDOM absorption spectrum was fitted to the hyperbolicexponential model.The fitting accuracy of the model was higher than those of the exponential model and the hyperbolic model,and the best S_(g)inversion model was constructed by selecting Sg(275-295)and Sg(250-295)in spring and autumn;(4)the spatial distributions of ag(355)and S_(g)were inverted,and CDOM in the waters around the Leizhou Peninsula originated from terrestrial organic matter carried by coastal aquaculture zones and runoff in the northeast Zhanjiang and the northern Beibu Gulf.
基金Supported by the Key Projects of the Guangdong Education Department(No.2019KZDXM019)the Fund of Southern Marine Science and Engineering Guangdong Laboratory(Zhanjiang)(No.ZJW-2019-08)+1 种基金the High-level Marine Discipline Team Project of Guangdong Ocean University(No.002026002009)the“First Class”Discipline Construction Platform Project in 2019 of Guangdong Ocean University(No.231419026)。
文摘Typhoon is one of the frequent natural disasters in coastal regions of China.As shown in many studies,the impact of typhoons on the South China Sea(SCS)should not be overlooked.Super typhoon Rammasun(2014)was studied that formed in the northwestern Pacific,passed through the SCS,then landed in the Leizhou Peninsula.Remote sensing data and model products were used to analyze the spatiotemporal variations of the cold eddies,upwelling,sea surface temperature,mixed layer depth,rainfall,sea surface salinity,suspended sediment concentration,and surface-level anomaly.Results confirm the constant presence of upwelling and cold eddies in the southeast of Hainan(north of the Zhongsha Islands)and the southeast of Vietnam in July.In addition,we found the strengthening effect of super typhoon Rammasun on the upwelling and cold eddies in the SCS.The major reasons for the continuous decrease in sea surface temperature and the slow regaining of seawater temperature were the enhanced upwelling and vertical mixing caused by the typhoon.The increasing of the surface runoff in the Indochina Peninsula was mainly affected by the typhoon,with some contribution for the southeast of Vietnam’s cold eddy and upwelling.
基金The National Natural Science Foundation of China under contract Nos 41625021,41676079 and 41906021the Project of Enhancing School with Innovation of Guangdong Ocean University under contract No.Q18307the Program for Scientific Research Start-up Funds of Guangdong Ocean University under contract No.060302112010
文摘Two kinds of regression equations are used to reproduce the sediment flux of the 26 small coastal watersheds in southeastern China.The first kind is the global equations suggested by Milliman and Syvitski(1992),Mulder and Syvitski(1996),Syvitski et al.(2003),and Syvitski and Milliman(2007).The second kind is the modified equations revised by the characteristics of the coastal watersheds,including the drainage area,mean water discharge,and mean sediment discharge.Compared with the observations of the hydrometric stations,the global equations overestimate the sediment flux by 1–2 orders of magnitude.By using the modified equations,the accuracy of the estimated sediment flux is significantly improved,with the relative error in the range of 7%–24%.The reason for the overestimation mainly caused by different parameters’domain and regression coefficients between global rivers and study coastal watersheds.This study demonstrates that modification needs to be considered when using global regression equations to reproduce the sediment flux of the small coastal watersheds in southeastern China.
