利用北冰洋多光谱数据计算光合有效辐射的研究

光合有效辐射（PAR）是重要的生物光学量，与海洋浮游植物的初级生产过程有密切联系。PAR通常由单波段的PAR传感器直接测量，也可以由多光谱数据计算。在极区用多光谱数据计算PAR不仅面对不同谱宽度的问题，而且还有海冰的影响。本文研究了4种可能导致PAR计算误差的主要因素。多光谱仪器避开了大气对太阳辐射的主要吸收带，用多光谱数据计算会对PAR高估。实测数据分析表明多光谱计算的PAR与高光谱数据的计算结果非常接近，误差在1%以内。用本文建立的拟合函数进行校正，校正后的结果与高光谱数据计算的结果达到同样的精度。计算PAR的衰减率要用到进入海水表面的PAR（PAR0），本文提出先确定表层衰减系数，再通过最小二乘拟合确定PAR0值，与水下观测数据有很好的衔接。海上同一站位不同时间的观测数据计算的PAR衰减系数相差很小，表明PAR的衰减系数是海水的光学性质，与辐射强度无关。在海冰覆盖的条件下，PAR的观测结果与无冰海水的PAR有明显差别。由于海冰选择性的吸收，穿透海冰进入海洋的PAR组分已经不同，海水对PAR的衰减系数也会相应变化。由此可以推断，不同海冰中成分的差别将导致进入海水中PAR的差别，影响PAR的衰减特性。通过本文的研究，解决了在极区用多光谱计算PAR的各种问题，使多光谱数据成为PAR的重要数据源。

CALCULATION OF PHOTOSYNTHETICALLY AVAILABLE RADIATION USING MULTISPECTRAL DATA IN THE ARCTIC

Photosynthetically Available Radiation (PAR) is an important bio-optical parameter related to marine primary production. PAR is usually measured by a single band sensor and can also be calculated by multispectral data. When the PAR is calculated by multispectral data in polar region, four factors are possible error sources. PAR could be overestimated as the wavelengths of multispectral instrument are usually chosen to evade main absorption zones of atmosphere. However, both PARs calculated by hyperspectral and multispectral data are consistent with the error less than 1%. By the fitting function proposed here, the PAR calculated by multispectral data has the same accuracy with that by hyperspectral data. To calculate the attenuation rate of the PAR needs PAR0, the PAR just under the surface. Here, an approach is proposed to calculate PAR0 by the best fit of the irradiance profile of 1-5 m with a content attenuation coefficient under surface. It is demonstrated by theory and data observed in different time at same location that the attenuation coefficient of PAR is independent of the intensity of radiation. But under sea ice, the attenuation coefficient of PAR is little bit different, as the spectrum of the light has been changed by selective absorption through the sea ice. Therefore, the difference of inclusions inside sea ice will result in different PAR, and impact the attenuation of PAR. By the results of this paper, PAR can be calculated reliably by multispectral data.