Study On The Mass-Specific Backscattering Of Suspended Particles In The Yellow And East China Sea Based On Mie Theory And Measured Data

The mass-specific backscattering coefficient of suspended particles(the ratio of backscattering coefficient to particle mass concentration,b_bp^*)in natural water is an important optical property reflecting important information such as particle composition and particle size.In this paper,based on Mie scattering theoretical simulation and in-situ data,the characteristics of mass-specific backscattering and its influencing factors in the nearshore water of the Yellow and East China Sea are systematically analyzed.This is of great significance for deeply understanding the backscattering characteristics of ocean water,and improving the quantitative accuracy of ocean color remote sensing.During the Mie scattering simulation,various organic algae and inorganic mineral particles with different physical and chemical properties were fully considered,and their differences in magnitude and spectral shape were compared and analyzed.Simulation study found that on the one hand,b_bp^*spectrum changes in the form of a power function with the increase of wavelength,and the spectral slope?has a significant positive correlation with the particle size distribution slope?.When?is greater than 4,?is approximately?-3.The selective absorption of particles on different wavelengths light makes the mass-specific backscattering fluctuate,which reduces the spectral slope value to a certain extent,and this effect is more significant when the particle spectrum is relatively flat.Therefore,when?is less than 4,?is less than?-3.On the other hand,it is found that with the increase of?,the b_bp^* magnitude increased exponentially.the average b_bp^* of mineral particles is about twice that of algae particles for the same?,and when?is 4,the average b_bp^* of mineral particles and algae particles at 532 nm are 0.00912�3.2*10^-3 m~2�g^-1 and 0.00409�0.48*10^-3m~2�g^-1,respectively.The lower b_bp^* value of algae particles can be explained by the lower real part of refractive index.In addition,the study also found that the increase of the lower limit of the particle size spectrum distribution will reduce both b_bp^* magnitude and the spectral slope,while the decrease of the upper limit will only lead to an increase in the magnitude.In-situ data in coastal waters of the Yellow and East China Sea shows that the spatial variability of b_bp^* is lower than the backscattering coefficient,indicating that b_bp^* weakens its dependence on particle load and thus reflect the difference of the particle composition and particle size distribution to a greater extent.In terms of spectral shape,with the increase of suspended particulate matter concentration,the measured b_bp^* spectral slope decreases and then tends to be stable.The spectral slope of nearshore water is lower than that of offshore water.When the organic particle mass concentration(POM)dominates the total particle mass concentration(SPM)(POM/SPM>0.7),the average mass-specific backscattering coefficient b_bp^*(532)is 0.00363 m~2�g^-1,while it is 0.00846 m~2�g^-1 when inorganic particles matter dominates(POM/SPM<0.2),and the latter is 2.3 times the former.The study found that the measured b_bp^* shows a decreasing trend in the form of a power-law function with the increase of POM/SPM,and with the increase of the proportion of inorganic suspended particulate matter,the dispersion of b_bp^* value increases.Combining Mie simulation result and in-situ data,it can be concluded that the range of particle size distribution slope?in our study is about 3.6 to 4.2,and?is about 3.9 for offshore waters dominated by organic particles.On the whole,variation of mass-specific backscattering coefficient of particulate matter is the result of the combined effect of various influencing factors.The increase in the load of inorganic mineral particles and the increase in the proportion of small particles will increase the b_bp^* magnitude.The size distribution and absorption of particles are the main reasons for the difference in spectral shape.