基于光学浮标的赤潮生消过程半分析监测方法

赤潮爆发时水体叶绿素a质量浓度升高,引起浮游植物吸收系数、光束总吸收系数等水体固有光学性质(IOP)的变化,并导致水体表观光学性质(AOP)的改变。海洋光学浮标可实现水体表观光学性质的定点连续时间序列观测,基于此发展相应的模型方法有望实现赤潮生消全过程的监测。利用一次赤潮生消过程的海洋光学浮标数据,发展了一种赤潮半分析监测方法。该方法首先由光学浮标数据得到的水体光谱漫衰减系数Kd(λ)和遥感反射率rrs(λ),结合经验确定的水下光场平均余弦进行水体光束总吸收系数a(λ)的半分析估算,然后再半分析反演浮游植物吸收系数aph(λ)和叶绿素a质量浓度。经检验,该方法估算a(675),aph(675)和叶绿素a质量浓度的中值相对误差分别为8.6%,34.9%和38.9%。将本方法与半分析方法(QAA)和统计回归方法进行了对比分析,本方法的优势在于反演精度较高,所采用的经验参数大都源自辐射传输理论计算、不依赖于浮标数据且对反演结果的影响有限。

A Semi-Analytical Monitoring Method During the Process of Red Tide Based on Optical Buoy

Chlorophyll a mass concentration will increase when red tide breaks out. It causes the changes of waters inherent optical properties (IOP), such as phytoplankton absorption coefficients and beam total absorption coefficients, which lead to the changes of waters apparent optical properties (AOP). Optical buoy can realize continual observation of apparent optical properties in situ, so it is hopeful to monitor red tide by developing corresponding method based on optical buoy′s data. A semi-analytical monitoring method is developed for red tide by using optical buoy′s data obtained during the process of red tide. First, beam total absorption coefficients are retrieval from diffuse attenuation coefficient and remote sensing reflectance, which are calculated from optical buoy′s data, and combined with experiential underwater downwelling average cosine. Then phytoplankton absorption coefficients and chlorophyll a mass concentration are retrieved. The median relative errors of beam absorption coefficients, phytoplankton absorption coefficients and chlorophyll a mass concentrations estimated by the semi-analytical method are 8.6%, 34.9% and 38.9%, respectively. Compare with quasi-analytical algorithm (QAA) and statistical method, the advantages are that the retrieved results are better and all experiential parameters are from radiative transfer calculation, which don′t depend on buoy′s data and have limited effect on the results.