基于SAR图像的海洋锋检测方法

海洋锋区中存在温度等海洋环境参数的跃变,影响声波在海洋中的传播,从而影响各种水声设备的使用,确定海洋锋的高精度位置在渔业和军事方面具有重要的应用价值,但目前大多数海洋锋检测技术难以实现全天时全天候高精度的海洋锋位置检测。文中简要介绍了利用遥感数据检测海洋锋的主要方法,理论分析了基于合成孔径雷达(SAR)图像的海洋锋检测方法的可行性。利用ENVISAT卫星搭载的合成孔径雷达(ASAR)图像,对海南岛东部海洋锋进行了检测,检测结果表明基于SAR的海洋锋检测方法能很好地保留锋线细节信息。对比红外融合SST数据海洋锋检测结果,证明了该方法的有效性。最后总结出基于SAR图像的检测方法的优势,该方法为现有基于红外SST数据的海洋锋检测方法提供了参考补充。     

一种基于Canny和数学形态学的海洋锋检测方法

MODIS遥感影像中海洋锋呈现明显的弱边缘信息特征。为有效获得海洋锋信息,首先应用调整后的Canny边缘检测算法,获取海洋锋初步检测结果,然后基于数学形态学二值重构及击中击不中算法,对检测出来的海洋锋进行再处理,确保了海洋锋的连续性及定位准确性。试验结果表明了该算法在海洋锋检测上的有效性与实用性。     

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。     

一次典型层积云发展-消亡过程对东海黑潮海洋锋响应的个例研究

基于ERA5再分析资料和卫星观测资料,本文揭示了2010年3月9—11日一次层积云发展-消亡过程中东海黑潮海洋温度锋对其的影响机制。研究发现,在层积云的发展阶段,海洋锋通过垂直混合机制影响层积云;而在维持阶段,海洋锋通过气压调整机制影响层积云;在消亡阶段,海洋锋对云的影响较弱。进一步研究表明,海洋锋能影响层积云的垂直结构,在维持阶段层积云的云底/顶高度在冷(暖)洋面下降(抬升),这对应于海洋锋强迫出的下沉(上升)气流。该结果说明东海黑潮海洋锋对大气行星边界层和层积云的垂直结构具有不可忽视的影响。     

海洋锋现象及其对水声传播的影响

为了研究海洋锋对声传播的影响,借鉴黑潮引起的台湾海峡南部海洋锋的历史水文观测资料,提出并建立了适合描述台湾海峡南部海洋锋的数学模型及其声速表达式。通过与实测资料对比,建立的海洋锋模型能准确反映客观实际情况,表现出较好的效果。同时,在借鉴了前人研究经验的基础上,采用Argo实测资料,建立了台湾海峡南部海洋锋的数学模型及其声速表达式,利用MMPE水下声场模型进行了海洋声场数值模拟试验,对目标海区典型的声场结构进行了声线路径模拟和传播损失的计算仿真,并将实验结果通过与前人进行的实际大洋声场实验的结果比较,证实了本文的模拟结果是准确可信的,提高了水声数值模拟试验的准确有效性。     

黄海西部春季海洋锋及其与渔业的关系

海洋锋是一种海洋学特征。作者根据1960—1981年的资料,用温、盐指标依聚类方法分析研究了该海区的环流结构和水团的混合带,最后定出了海洋锋的位置。本文还描述了春季黄海中的海洋锋的分布及特征,及其与鹰爪虾、鲅鱼、鲐鱼洄游规律和渔场的关系。     

海表温度与地转流融合的黑潮斜压性锋检测方法

由黑潮形成的海洋锋斜压性强,对海洋中的声传播带来极大影响,从而对各种依赖声学性质的海洋探测设备的使用造成极大影响,确定黑潮斜压性锋的位置和强度对海洋渔业和军事应用具有重要的意义。通过对海表温度梯度数据和地转流数据的分析,将海表温度梯度与地转流进行融合,从而检测黑潮流边缘的大温度梯度海洋锋。通过对实际数据的试验,说明了融合算法的原理、算法步骤和黑潮斜压性锋检测结果。试验数据表明,文中提出的融合算法能够很好地检测黑潮斜压性锋位置,同时提取其强度,与采用海面温度或地转流数据单一数据源检测相比,文中所述的方法检测位置准确,虚警率低,与文献报道的黑潮位置更为吻合。     

融合scSE模块的改进Mask R-CNN海洋锋检测方法

海洋锋是重要的中尺度海洋现象,具有数据量小、目标小、弱边缘等特性。针对实际检测任务中弱边缘、小目标海洋锋的检测精度低、错检及漏检率高等问题,融合scSE (spatial and channel Squeeze&Excitation)空间注意力模块构建了一种改进的Mask R-CNN海洋锋检测模型。该方法首先对Mask R-CNN骨干网络结构进行改进,采用scSE模块引导的ResNet-50网络作为特征提取网络,通过加权策略对图像通道和空间位置进行特征突出,提升网络对重要特征的提取能力;其次,针对海洋锋目标边缘定位不准确的问题,引入IoU boundary loss构建新的Mask损失函数,提高边界检测精度。最后,为验证方法的有效性,从训练数据和实验模型上,分别设计多组对比实验。实验结果表明,相比传统Mask R-CNN、YOLOv3神经网络及现有Mask R-CNN改进网络,本文方法对SST梯度影像数据集上的强、弱海洋锋检测效果最好,定位准确率（IoU,Intersection-over-union））及检测精度（mAP,Mean Average Precision）均达0....     

黄海西部沿岸锋多年平均特征统计分析

根据黄海1939-1999年海洋实测数据集和2010年黄海成山头附近海域海试资料,统计分析了黄海西部沿岸锋温度分布结构、平均强度、宽度、位置分布等特征。实测数据统计分析结果表明,黄海西部沿岸锋具有明显的季节变化特征:春季开始形成并逐步加强,夏季处于强盛期,秋季海洋锋逐渐减弱,冬季相比秋季略有增强的趋势,初春季节海洋锋消亡。海试资料表明2010-08该锋位于20m等深线以西5nmile至以东30nmile之间的海域,且位于40m等深线以西20nmile至以东20nmile之间的海域。     

海洋锋信息产品制作方法研究

根据海洋要素梯度统计结果、区域环境特征、实际业务需求及海洋锋影响等,研究了海洋锋诊断阈值和分级,定义了海洋锋各个特征信息,制作了西北太平洋海洋锋二维、三维特征信息产品和声传播损失信息产品。     

海洋锋区的一种声速计算模式及其在声传播影响研究中的应用

利用穿过海洋锋区断面的实测CTD数据,确定了锋面的宽度、所在的位置以及陡度等特征参数,建立了海洋锋区声速计算理论模式。结果表明,此模式可以用来描述选定断面的锋面特性。将理论计算结果与实测数据进行比较,二者符合较好。进而利用二维PE模型,研究了通过海洋锋面的声传播特性。结果表明,在声源深度为50m和发射频率为150 Hz的情形下,对不同接收深度,有锋面与无锋面时传播损失的差别最大约为20 dB左右。     

Plankton distribution associated with frontal zones in the vicinity of the Pribilof Islands

We studied the effect of four types of fronts, the coastal front, the middle front, the shelf partition front and the shelf break front on the quantitative distribution and the composition of plankton communities in the Pribilof area of the eastern Bering Sea shelf in late spring and summer of 1993 and 1994. The coastal fronts near St. Paul and St. George Islands and the coastal domains encircled by the fronts featured specific taxonomic composition of planktonic algae, high abundance and production of phytoplankton, as well as large numbers of heterotrophic nanoplankton. The coastal fronts also were characterized by high values of total mesozooplankton biomass, high concentrations of Calanus marshallae, as well as relatively high abundances of Parasagitta setosa and Euphausiacea compared to surrounding shelf waters. We hypothesize that wind-induced erosion of a weak thermocline in the inner part of the coastal front as well as transfrontal water exchange in subthermocline layers result in nutrient enrichment of the euphotic layer in the coastal fronts and coastal domains in summer time. This leads to prolonged high primary production and high phytoplankton biomass. In this paper a new type of front—the shelf partition front located 45–55 km to the north-east off St. Paul Island—is described, which is assumed to be formed by the flux of oceanic domain waters onto the shelf. This front features a high abundance of phytoplankton and a high level of primary production compared to the adjacent middle shelf. Near the southwestern periphery of the front a mesozooplankton peak occurred, composed of C. marshallae, with biomass in the subthermocline layer, reaching values typical for the shelf break front and the highest for the area. High abundance of phyto- and zooplankton as well as heterotrophic nanoplankton and elevated primary production were most often observed in the area adjacent to the shelf break front at its oceanic side. The phyto- and mesozooplankton peaks here were formed by oceanic community species. The summer levels of phytoplankton numbers, biomass and primary production in the shelf break frontal area were similar to those reported for the outer and middle shelf during the spring bloom and the coastal domains and coastal fronts in summer. In the environment with a narrow shelf to the south of St. George Island, the mesozooplankton peak was observed at the inner side of the shelf break front as close as 20 km from the island shore and was comprised of a “mixed” community of shelf and oceanic species. The biomass in the peak reached the highest values for the Pribilof area at 2.5 g mean wet weight m⁻³ in the 0–100 m layer. Details of the taxonomic composition and the numbers and production of phytoplankton hint at the similarity of processes that affect the phytoplankton summer community in the coastal domains of the islands, at the coastal fronts, and at the oceanic side of the shelf break front. The middle front was the only one that had no effect on plankton composition or its quantitative characteristics in June and July. Location of a variety of frontal productive areas within 100 km of the Pribilof Islands creates favorable foraging habitat for higher trophic level organisms, including sea birds and marine mammals, populating the islands.     

Study on heterogeneous distribution of plankters at oceanic fronts

In this paper, I review my study on heterogeneous distribution of plankters at oceanic fronts, taking advantage of an opportunity awarded the Okada Prize 1989 of the Oceanographical Society of Japan. The main focus is on the formation and retention mechanisms of phytoplankton peak abundance at the Kuroshio Front, and the events observed at other oceanic fronts, such as the Oyashio Front, the Antarctic Polar Front and the Subtropical Convergence in the southern hemisphere are compared to those found at the Kuroshio Front.Phytoplankton standing stock was hign in the inner cold belt of the Kuroshio Front. Since the inner cold belt form from water masses entrained into the front from coastal and/or the Oyashio areas, one of the characteristics of the phytoplankton community is high contribution of microplankton fraction. Rising of isopleths of temperature and nutrient saltsetc. at the front suggested that upwelling event occurred along the front. Incubation experiments with nutrient addition showed it would flourish the entrained species but oceanic ones when upwelling occurred at the front.Zooplankton was strongly aggregated at the Kuroshio Warm-Core Ring Front, and the peak of abundance was spatially separated in each individual. I thought that biological processes, such as motility and prey-predator interaction, play an important role to control the aggregated patterns.Since the cabbeling event is expected at the Oyashio Front where the relatively cold and low-salinity Oyashio water faces the relatively warm and saline water of the perturbed area, it appears that the phytoplankton species having larger density than that of sea water sink down there. The mixture of sea waters on both sides of the front, however, may accelerate their growth by supply of some deficient element (s).I consider that raise of temperature is the most plausible factor to make phytoplankton peak abundance at the Polar Front. Experiments on board showed that raising temperature activates photosynthesis of antarctic phytoplankton. Phytoplankton standing stock and productivity were also high at the Subtropical Convergence.The primary object of this study is the biological role of oceanic fronts for fish ecology. I consider that concentrated phyto- and zooplankton communities at oceanic fronts support the energy of migrating fishes, and also support the survival of juvenile fishes just after hatching which are transported from coastal areas.     

我国周边海域典型海洋锋特征建模研究

基于海洋锋空间位置、水平分布结构和垂直扩展特征等时空特征参数,结合海洋锋空间结构几何模型,建立了区域海洋锋温盐三维结构快速重构特征模型,对黄海西部沿岸锋和东海黑潮中段锋锋区温度场进行了仿真计算,并与实测数据进行了比较分析,实验结果表明：仿真结果与实测数据符合较好,实验结果验证了特征模型的有效性和可推广性。海洋锋区声速具有明显的水平梯度变化,对声纳的水下探测和反探测产生显著影响,因此,需要建立实时估计获取锋区水下温、盐结构的方法。海洋锋特征模型能够快速有效地重构海洋锋区温度场,为实时获取海洋锋水下结构特征提供了方法。     

Crustal velocity structure off SW Taiwan in the northernmost South China Sea imaged from TAIGER OBS and MCS data

During TAiwan Integrated GEodynamics Research of 2009, we investigated data from thirty-seven ocean-bottom seismometers (OBS) and three multi-channel seismic (MCS) profiles across the deformation front in the northernmost South China Sea (SCS) off SW Taiwan. Initial velocity-interface models were built from horizon velocity analysis and pre-stack depth migration of MCS data. Subsequently, we used refracted, head-wave and reflected arrivals from OBS data to forward model and then invert the velocity-interface structures layer-by-layer. Based on OBS velocity models west of the deformation front, possible Mesozoic sedimentary rocks, revealed by large variation of the lateral velocity (3.1–4.8 km/s) and the thickness (5.0–10.0 km), below the rift-onset unconformity and above the continental crust extended southward to the NW limit of the continent–ocean boundary (COB). The interpreted Mesozoic sedimentary rocks NW of the COB and the oceanic layer 2 SE of the COB imaged from OBS and gravity data were incorporated into the overriding wedge below the deformation front because the transitional crust subducted beneath the overriding wedge of the southern Taiwan. East of the deformation front, the thickness of the overriding wedge (1.7–5.0 km/s) from the sea floor to the décollement decreases toward the WSW direction from 20.0 km off SW Taiwan to 8.0 km at the deformation front. In particular, near a turn in the orientation of the deformation front, the crustal thickness (7.0–12.0 km) is abruptly thinner and the free-air (?20 to 10 mGal) and Bouguer (30–50 mGal) gravity anomalies are relatively low due to plate warping from an ongoing transition from subduction to collision. West of the deformation front, intra-crustal interfaces dipping landward were observed owing to subduction of the extended continent toward the deformation front. However, the intra-crustal interface near the turn in the orientation of the deformation front dipping seaward caused by the transition from subduction to collision. SE of the COB, the oceanic crust, with a crustal thickness of about 10.0–17.0 km, was thickened due to late magmatic underplating or partially serpentinized mantle after SCS seafloor spreading. The thick oceanic crust may have subducted beneath the overriding wedge observed from the low anomalies of the free-air (?50 to ?20 mGal) and Bouguer (40–80 mGal) gravities across the deformation front.     

On the dynamics and effects of double-diffusively driven intrusions

Some of the characteristics of intrusive finestructure observed in oceanic fronts suggest that salt fingering is active in the intrusions. An extension of Stern's 1967 study of the stability of a thermohaline front to intrusive finestructure driven by salt fingers is presented to investigate this hypothesis. Intrusions are found to grow due to the salt finger induced density fluxes even in the presence of small scale momentum dissipation. The presence of this dissipation defines a fastest growing mode for the disturbance which has physical characteristics not unlike those observed in oceanic fronts. The model results do not agree well with the laboratory studies of intrusions. For many fronts, the model requires initial perturbations in the front which can support salt fingers. Linear internal waves are investigated to determine if they can provide the initial perturbation. It is shown that, away from the equator, the interaction between internal waves and intrusions is weak because of a mismatch of time scales. Finally, growing intrusions are shown to flux heat, salt and density across fronts. The senses of these fluxes are to run down the lateral gradients of many oceanic fronts.     

The dynamics of a bathymetrically arrested estuarine front

The mixing and circulation associated with a bathymetrically arrested estuarine front was studied using hydrographic and current data. A quasisteady front, exhibiting strongly convergent surface flows, is formed along the steeply sloping inner margins of the flood tide delta during each semidiurnal tide cycle. This front separates the brackish ambient water within a deep estuarine basin from the incoming oceanic tidal water. The position of the front is dependent on the local water depth and the difference in density between the two water masses. Beneath the surface there is an inclined frontal interface where static stability is very low and vertical mixing intense. A vertically integrated horizontal momentum equation was derived for flow in the upper layer and an estimate made as to the value of the associated entrainment coefficient.     

The features and generation of CWB near the South Shetland Islands in austral summer of 1987

-STD Data obtained from the Third Chinese National Antarctic Research Expedition from January to February 1987 in the region near the South Shetland Islands are used to investigate an oceanic front, continental water boundary (CWB), north of the South Shetland Islands. The characteristics of the CWB in surface and subsurface layers as well as deep layer are discussed respectively. The estimations of the geostrophic currents and the baroclinic deformed radius Rbc in this area show that the flow along the front is in the geostrophic equilibrium approximately, and the formation of the front is mainly due to the strong boundary current north of the South Shetland Islands. Its length along the front is estimated to be about 360 km and its width across the front is about 30 km.     

基于阈值区间的海洋锋面提取模型

A model （Bayesian oceanic front detection, BOFD） of sea surface temperature （SST） front detection in satel- lite-derived SST images based on a threshold interval is presented, to be used in different applications such as climatic and environmental studies or fisheries. The model first computes the SST gradient by using a Sobel algorithm template. On the basis of the gradient value, the threshold interval is determined by a gradi- ent cumulative histogram. According to this threshold interval, front candidates can be acquired and prior probability and likelihood can be calculated. Whether or not the candidates are front points can be deter- mined by using the Bayesian decision theory. The model is evaluated on the Advanced Very High-Resolution Radiometer images of part of the Kuroshio front region. Results are compared with those obtained by using several SST front detection methods proposed in the literature. This comparison shows that the BOFD not only suppresses noise and small-scale fronts, but also retains continuous fronts.