Study On Variation In Chlorophyll A Concentration And Its Influencing Factors Of Jiaozhou Bay Based On Long Term Remote Sensing Images

With the state’s attention to marine blue economy and marine ecological environment,the rational use and protection of marine resources has become particularly important.In recent years,more and more technologies and methods of ocean monitoring have been developed.With the rapid development of water color remote sensing,it has become an important method to monitor the marine ecological environment.The application of remote sensing makes up for the shortcomings of traditional investigations and can achieve long-term and wide-range monitoring.Chlorophyll a in seawater is an important indicator of marine ecological environment.Therefore,the study of long-term monitoring of chlorophyll a concentration has important ecological significance.Jiaozhou Bay is a typical semi-enclosed Bay and mother bay of Qingdao.It is important to study the changes of its ecological environment for rational utilization of resources and protection of the environment in the bay.Based on the measured chlorophyll a concentration and synchronous Landsat images,a remote sensing inversion model for chlorophyll a concentration in Jiaozhou Bay was established.Through the correlation analysis of each band and band combination of Landsat image and chlorophyll a concentration,36 sensitive band combinations were selected as inversion variables.The quantitative relationship between each sensitive variable and chlorophyll a concentration was studied by using neural network method and regression analysis method,and the inversion model was finally established.Through the verification of the measured data,it is found that the inversion model has high accuracy(r=0.73,RMSE=0.69),and can be used for monitoring chlorophyll a concentration in Jiaozhou Bay.Based on the above remote sensing inversion model,the distribution map of chlorophyll a concentration in Jiaozhou Bay was retrieved using 338 Landsat images from 1986 to 2017,and the spatial and temporal(inter-annual,seasonal and monthly)variation characteristics were analyzed.The spatial distribution of chlorophyll a is very uneven,with obvious regional characteristics,generally showing the characteristics of high northwest and low southeast,and higher near coast than far coast.The concentration of chlorophyll a in Jiaozhou Bay showed an overall upward trend from 1986 to 2017.It was the smallest in 1998 and the largest in 2017.It fluctuated periodically and changed slightly before 2011.After 2011,the concentration of chlorophyll a increased significantly and continued to increase.From the seasonal point of view,the four seasons of last spring,summer,autumn and winter showed the trend of decreasing initially,then rising,with the highest in spring and the lowest in autumn.The change trend of monthly mean is consistent with seasonal change trend.From January to December,the whole trend shows a downward trend.The concentration of chlorophyll a reaches its maximum in March and minimum in August.Based on the study of spatial and temporal distribution,this paper analyzed the influencing factors of spatial and temporal variation of chlorophyll a concentration in Jiaozhou Bay from two aspects of natural factors and human activities.The results showed that the chlorophyll a concentration in Jiaozhou Bay was mainly affected by precipitation,wind speed and net discharge of Dagu River,the temperature had little effect on it,while the sea surface temperature had a slight effect.Human activities,such as the construction of sea-crossing bridge and the change of land use and landscape pattern in Jiaozhou Bay Basin,have a great impact on it.