二类水体颗粒吸收光谱两种测量方法的差异分析

Differences Between Two Methods for Particle Absorption Measurements in Case-2 Waters

对两种颗粒吸收光谱测量方法的差异性及在二类水体中的适用性进行了研究．通过理论推导指出．颗粒后向散射是T方法（Transmittance method）较T—R方法（Transmittance and Reflectance method）测量结果偏高的首要原因，并且其偏高程度同时取决于颗粒的后向散射和吸收性质；对福建沿岸典型二类水体同时采用两种方法测量的结果表明：与T—R方法相比．T方法测量所得总颗粒、非藻类颗粒、藻类颗粒的光学密度．在400～700nm波段的平均相对误差分别为38．5％、40．0％、33．1％．根据理论推导和实际测量分析结果，提出在中国近海二类水体中需采用T—R方法来替代T方法测量颗粒吸收光谱的建议．

There are two methods for absorption measurements of aquatic particles retained on glass-fiber filters,which are named as T and T-R method, respectively. The T-R method is modified from the T method by combining light-transmission and light-reflection measurements,so that the spurious contribution to the measured absorption generated by sample backseattering and multi-scat- tering between sample and filter may be removed. It is thus applicable to Case-2 waters with high suspended sediment content. In order to qualitatively and quantitatively evaluate how different these two methods are, we defined the differences between the optical densities measured by using the two methods as/XOD. On the basis of theoretical analysis,AOD is a function of sample absorption and backscattering properties,of which the backscattering properties dominate. Measurements using both methods were carried out on samples collected from turbid waters alongshore Fujian. The average error of the optical density （400- 700 nm） derived from T method relative to T-R method for total particles, phytoplankton and non-algal particles was 38.5 % ,40.0% ,and 33.1%, respectively. It is suggested to use T-R method in stead of T method for absorption measurements of aquatic particles in the coastal region of China Sea.