基于海色融合数据的东海黑潮锋面检测研究

海洋锋是典型的海洋中尺度现象之一。目前卫星遥感主要利用海表温度数据分析海洋锋,但由于西北太平洋海域夏季海表温度的趋同特性,不能进行有效的锋面监测;而不同水团所具有的生物光学特性往往是不同的,且不具有太阳辐射引起的显著性季节变化,因此海色资料也成为检测海洋锋的有效数据源。文中以东海黑潮为例,详细说明了基于叶绿素a浓度融合数据,采用梯度法进行海洋锋面检测的过程,通过比较不同季节不同梯度阈值得到的东海黑潮锋结果,从保持锋面的完整性及对零碎锋区的剔除效应方面,选取了不同季节较优的梯度阈值。总体来说,文中检测出的东海黑潮区域海色锋与海流黑潮强流区较吻合,12月至4月东海黑潮海色锋检测结果不如海温锋,而5-11月东海黑潮海色锋检测结果优于海温锋,特别是台湾以东黑潮区域,不论什么季节海温锋都没有体现,而海色锋始终很明显。利用文中提出的海洋锋检测算法、分析方法及选择的梯度阈值可以有效地检测东海黑潮区域的海洋锋面,结合海色锋和海温锋,可以监测分析东海黑潮强流区的时空变化。

Study on East China Sea Kuroshio Front Detection Based on Satellite Ocean Color Merging Data

Oceanic front is an important mesoscale phenomenon of oceanography and it is usually studied based on the analysis of sea surface temperature (SST). But SST over some sea areas, e.g. northwest Pacific, increases in summer because of intense solar radiation and heating, so SST gradient is not obvious in summer and not effective in the front analysis. The bio-optical properties of different water masses are different and their seasonal variation caused by solar radiation is not significant. The ocean color data, especially chlorophyll a concentration, can be used as an effective indicator of oceanic front analysis. Oceanic front extracted with chlorophyll a concentration can overcome the shortage of the SST front and improve the accuracy of ocean front detection. With the Kuroshio as an example, oceanic front detection algorithm is studied based on chlorophyll a concentration merging data. Through comparing different gradient thresholds of different seasons, the best gradient thresholds are selected from the aspects of maintaining the integrity of the front and the removal effect on the fragmented front over Kuroshio region. With the OSCAR current product as reference and compared with the SST front extracted, the ocean color front is worse from December to April but the ocean color fronts are better from May to November. Especially over the eastern region of Taiwan Island, the ocean color front is more obvious than SST front for the whole year. With the proposed front detection method and thresholds in this study, the spatial and temporal change of front over Kuroshio region can be analyzed by combining ocean color front and SST front.