Extraction Of Chlorophyll Fluorescence From The Water-leaving Radiance Of Algae-containing Water Based On The Polarization Technique

In the water of over-nutrition,planktonic algae will propagation abusively,while chlorophyll occupies a stable percentage in planktonic algae cells,therefore the concentration of chlorophyll[Chl]is an important parameter in reflecting the extent of water over-nutrition.After chlorophyll molecules within the planktonic algae cells absorb light energy,they will release energy in the form of chlorophyll fluorescence emission,for this reason,the chlorophyll fluorescence could be an important parameter for estimating the[Chl]approximately.Extract the chlorophyll fluorescence accurately would be of great importance for further detecting the[Chl]and monitoring water resources and environment protection.At the air-water interface,the sunlight will be scattered by atmospheric particles(especially molecules),aerosol,hydrosol and the sea surface,these process will change the polarization state of the light.The scattered and reflected light is partially polarized and containing the information which could reflect the intrinsic quantity of the particles.The elastic scattering of light by particles in water produces partially polarized light,in contrast,the fluorescence of chlorophyll in planktonic algae yields totally unpolarized light,these properties can be used to separate the fluorescent signals from the water-leaving radiance,allowing the determination of the chlorophyll concentration.But for coastal waters,the approach feasibility is still unclear,based on this,using the alga Aureococcus anophagef.ferens,Prorocentrum micans and Amphidinium carterae Hulburt we perfonned a polarization experiment in the laboratory with a combination of a field spectroradiometer and a polarizer,measurements were collected using two different observation modes.The results indicate that,fluorescence extraction using the measurement mode 2 is reliable with incident angles ranging from 30° to 60°,the efficacy of extraction was best at an incident angle of 45°.For algae-containing water with different concentrations of chlorophyll,the results were more satisfactory with high concentrations of chlorophyll compared with low concentrations.For algae-containing water with different concentrations of inorganic particles,the fluorescence peak will decrease while the concentration increase,but the retrieval result is still reliable when the concentration up to 3×105 mg/rm3.For algae-containing water with surface wind,the chlorophyll fluorescence extraction remains accurate despite the divergence effects of surface waves.We also conducted field measurement on the coastal water of Qin Huang Island,the results shows that the polarization methods is still applicable.The study proves that the polarization method is also applicable for complex water condition,this method could be very useful for detecting the[Chl]and harmful algae blooms in a remote sensing approach.In addition,in-situ data of costal suspended particle material water show a negative correlation between the DOP of upward polarization radiance and remote sensing spectra reflectance,which imply that the DOP of upward polarization radiance has the similar detection capability to retrieval optically active marine components compared with remote sensing reflectance.