Study On Absorption Properties Of Ocean Color Constituents In The Typical Subtropical Bay

Phytoplankton,non-algal particle and CDOM absorption,the important inherent optical properties of waterbody,is the basic parameter for the establishment of biological-optical water color remote sensing inversion model.Xiamen Bay and Sansha Bay are two typical subtropical bays located in the central and northern coastal areas of Fujian Province.Xiamen Bay is adjacent to the mouth of Jiulong River and is significantly affected by rivers.There is a high density of aquaculture in Sansha Bay,and there is a high occurrence of algal blooms outside the Bay.As things stand,it is necessary to understand the distribution characteristics of the inherent optical parameters of secondary waterbodies such as offshore estuary to evaluate and construct an effective regional water-color inversion algorithm and promote the application of satellite remote sensing products in the operational monitoring of offshore estuary.Based on the field measurements of bio-optical data,this paper analyzes the spatial and temporal distribution characteristics of three absorption coefficients of phytoplankton,non-algal particles and CDOM in these two typical bays.The similarities and differences of absorption coefficients of phytoplankton,non-algal particles and CDOM of different waterbodies are compared,and the factors influencing the spatial and temporal distribution characteristics and differences are preliminarily discussed,its research results are as follows:(1)The absorption of total particulate matter in Xiamen Bay is dominated by nonalgal particles,and the absorption of phytoplankton is dominant only around 665nm.Also,the absorption of ad(443)by non-algal particles was the highest in the Jiulong River Estuary,followed by the western sea area,and the lowest in Tong ’an Bay and the southeastern sea area.And the distribution of aph(443)and ag(443)was the highest in Jiulong River Estuary,and lower in the waters around Xiamen Island.In addition,both ad(443)and ag(443)decreased with the increase of salinity,and there was a significant correlation between them and salinity.As such,the optical properties of the main water-color components of waterbody in Xiamen Bay are significantly affected by the runoff of Jiulong River.(2)The absorption of non-algal particles and CDOM of Xiamen Bay decreased exponentially with the increase of wavelength,this is comparable to the Sd and Sg averages obtained for most Category 2 waterbody bays.The Sd of Jiulong River Estuary is slightly higher than that of other subdivisions of Xiamen Bay,while the Sg is lower than that of other subdivisions.There is no significant absorption peak of phytoplankton absorption spectrum aph at 443nm,and only one absorption peak at 675nm is caused by Chlorophyll a absorption.(3)The light absorption of each waterbody component in Xiamen Bay has obvious seasonal variation characteristics,with the highest values of ap(443)and ad(443)in autumn,followed by summer and winter,and the lowest values in spring.And ag(443)is higher in summer and autumn,but lower in winter and spring.aph(443)is the highest in summer,followed by winter and lowest in spring and autumn.Besides,ad(443)is significantly correlated with TSM in summer,autumn and winter.Moreover,the annual changes of aph(443)and aph(665)were quite consistent with the changes of Chl.The statistics showed that aph(443)and Chl,aph(665)and Chl were significantly positively correlated with each other in each season,and aph(665)was more strongly correlated with Chl.(4)The optical absorption of different waterbody components in Sansha Bay and its adjacent waters has obvious spatio-temporal characteristics.Among the absorption of total particulate matter in Sansha Bay,the absorption of non-algal particles from the December and May trips was absolutely dominant,and the proportion of>in most bands was 90%.The seasonal variation characteristics of ad(443)and ap(443)were similar,that is,the highest in winter and the lowest in summer and spring.Different from Xiamen Bay,ad(443)has no significant correlation with salinity,but has a significant negative power correlation with Chlorophyll a.In Sansha Bay,aph(443)and ag(443)had the same seasonal variation trend,so to speak,the maximum was in summer,followed by winter and the minimum was in spring.In summer voyages,aph around 675nm accounted for more than 80%of ap.In May,the average absorption spectra of phytoplankton outside Sansha Bay are very similar to those in July,and aph and Chl are significantly higher than those in the same period.What’s more,aph(665)in Sansha Bay showed a significant linear correlation with Chl,R2 as high as 0.9223,while ag(443)showed a significant negative correlation with salinity.Furthermore,the different culture types exert certain effects on optical absorption and Chlorophyll concentration distribution of each component of waterbody.The highest values of aph(443)and Chl were found in asparagus culture area,while the lowest values were found in large yellow croaker culture area and abalone culture area.Also ag(443)and ad(443)have similar distribution characteristics.