辽东湾MODIS生物光学算法研究(I) 算法适用性评估

辽东湾是典型的复杂二类水体,我们利用2002~2004年在辽东湾现场实测的叶绿素a数据(分光法、荧光法和HPLC法),以及水面之上法现场实测的离水辐射率和遥感反射率数据模拟的MODIS各相应波段值对MODIS海洋水色算法进行了评估。评估的MODIS生物光学算法有四个,即CZCS_pigm、chlor_MODIS、chlor_a_2和chlor_a_3算法。结果表明,两个一类水体生物光学算法(CZCS_pigm和chlor_MODIS)反演值与分光法和荧光法测试分析结果相比,算法均低估了叶绿素a浓度,与HPLC分析结果相比算法高估了叶绿素a浓度;两个二类水体算法(chlor_a_2和chlor_a_3)与所有叶绿素a分析方法相比,均高估了叶绿素a浓度。根据MODIS生物光学算法在辽东湾的具体表现,我们认为HPLC法分析的叶绿素a浓度更适合于作为海洋水色算法评估的现场检验依据。叶绿素a浓度的反演值和实测值之间较低的相关系数则显示MODIS两个一类水体算法所采用的波段比值不适合本海区。

MODIS Bio-optical algorithms in Liaodong Bay(I) Algorithms assessment

The data set from the field measurements was used to evaluate the performance of standard Moderate Resolution Imaging Spectroradiometer(MODIS) ocean color algorithms in the Liaodong Bay,which represents an example of optically complex Case 2 water.The data set includes chlorophyll a concentration(by spectrophotometer,HPLC and fluorescence),and spectrum data,Which were taken on 12 cruises between 2002 and 2004.The band radiance of MODIS were simulated,using the Normalized water-leaving radiances and remote sensing reflectance measured by above-water measurements.We compare the measured chlorophyll a with retrieved chlorophyll a from the MODIS standard pigment algorithms. We can draw a conclusion,CZCS_pigm and chlor_MODIS algorithms showed a systematic and overestimation in chlorophyll a retrievals to the experimental value measured from spectrophotometer and fluorescence,and underestimation to the HPLC method,chlor_a_2 and chlor_a_3 algorithms overestimation in chlorophyll retrievals to the all measurements.We also found that chlorophyll a obtained from HPLC may be more suitable to the ocean color algorithms evaluate and instu measurement base on our discussion.The lower correlation coefficient appears that the CZCS_pigm and chlor_MODIS using band is not suitable the discuss area.And new approaches for bio-optical algorithms are required in the Liaodong Bay.