大连港外海域船舶尾迹光学特征研究

通过大连港外海上实验测量船舶含气泡尾迹表观光学特征(如离水辐亮度、遥感反射率),分析了尾迹气泡对极度混浊的Ⅱ类水体海水表观光学特征的影响.实验结果证明:无论在可见光还是近红外波段,尾迹气泡都增强了海水表观光学量,如"耘海"船尾迹遥感反射率在可见光波段相对背景海水提高了50%,在近红外波段相对提高了159%.数据分析结果表明在此种水体中,气泡使得尾迹海水水色变黄,而不是在Ⅰ类水体中使水色变绿.随着观测点在尾迹中的位置靠近目标船,气泡数密度不断增加,遥感反射率也随之增强.     

西沙群岛附近海域船舶尾迹水体遥感反射率特性的实验测量与分析

利用海上实验现场测量船舶的尾迹气泡群对西沙群岛附近海域一类水体海水光学特征(例如归一化离水辐亮度、遥感反射率)的影响,为通过星载光学传感器遥感获取船舶尾迹信息提供理论依据。实验证明,在可见光和近红外波段,船舶含气泡尾迹不仅在幅度上、也在谱形上改变海水遥感反射率,作为结果,尾迹气泡使得海水变得更绿;同时,随着观测点在尾迹中的位置距目标船的接近,气泡密度不断增大,反射率也随之增强。     

2003年春季长江口海域黑水现象研究

长江口海域处于东海大陆架,水深较浅,受长江、钱塘江入海径流及潮汐搅拌的影响,水体浑浊度高,属于典型的二类水体。在浑浊二类水体由于水体中悬浮颗粒的散射作用,离水辐亮度通常较大洋清洁水体的大。通过分析2003年春季黄海、东海二类水体光学试验数据和同时段SeaWiFS卫星遥感数据,发现在长江口东南海域有一个归一化离水辐亮度极小的黑水区域,它在412~670nm波长的归一化离水辐亮度均小于0.5mW/(cm2·μm·sr)。利用现场实测的水体固有光学特性参数(色素吸收系数、非色素颗粒吸收系数、黄色物质吸收系数、颗粒散射系数、颗粒后向散射系数等)和水色要素浓度数据,分析了长江口海域黑水现象的机制,结果表明,长江口外黑水现象主要是由于水体后向散射系数值极小引起的,而造成颗粒后向散射系数值极小的原因主要有两种,一是颗粒物含量低,二是颗粒后向散射率的值小。黑水区浮游植物色素吸收所占的比例较高,大粒径的有机颗粒(浮游植物)导致黑水区域的颗粒后向散射率的值偏小。长江口海域黑水是在特定的颗粒物低含量及颗粒后向散射率极小的条件下出现的光学现象。     

船舶尾迹与尾迹气泡光学遥感研究

通过研究船舶航行产生的三类尾迹(表面波尾迹、湍流尾迹、内波尾迹)形成机制,以及深入分析尾迹的微波、热红外、声学以及光学特性以及尾迹气泡相关特征,从理论上寻求星载光学传感器探测舰船尾迹的适用性依据,满足充分挖掘卫星遥感监测海洋应用能力的目的。结论认为现实条件下运用星载合成孔径雷达最适合监测船舶尾迹,星载热红外传感器不适合探测船舶尾迹,而星载光学传感器作为一种重要的补充手段有着独到的优势。     

由现场离水辐亮度估算黄海透明度几种方法的比较

本文根据黄海现场离水辐亮度及遥感反射比,采用４种统计算法估算海水透明度。前２种算法中海水透明度作为因变量,两不同波段辐亮度之比及两辐亮度之和与第三者之比分别作为自变量,进行一元回归分析,前者相关系数ｒ＾２为０．９３３５。后者相关系数ｒ＾２为０．９４８３。第３种算法中,所有波段的遥感反射比做因子分析形成的主因子作为自变量,透明度作为因变量进行多元回归分析,子样全相关系数ｒ＾２为０．９６４９。第４种算     

近岸浑浊水体大气校正算法研究进展

大气校正问题是海洋光学遥感的关键技术问题之一。精确的大气校正是实现高精度水色信息反演的前提。I类水体的大气校正算法发展相对成熟,其假设近红外(NIR)波段离水辐亮度为零,从而将NIR波段的大气程辐射外推至可见光(VIS)波段求出离水辐亮度实现大气校正。但是,II类水体由于受到悬浮物(TSM)和黄色物质(CDOM)的影响,其大气校正相对复杂。文中概述了国内外近岸浑浊水体大气校正算法的研究现状及应用效果,总结了各种算法的特点、优势和局限性。文中还提出了浑浊水体大气校正研究需要解决的关键问题,并展望了该领域未来的发展趋势和方向。     

基于S2000光谱仪的小型海面高光谱辐射计的研制

将普通的小巧型S2000光谱仪组装改造成用于海面测量的高光谱辐射计,安装在船只等移动平台上进行原位测量,可以获得向下辐照度和向上辐亮度的实验数据.阐述了整体设计思路,说明了其光路结构,光学采集单元分为光谱辐照度光学探头和光谱辐亮度光学探头.叙述了通过机械结构的调整来更准确地测量离水辐亮度,并给出了基于计算机进行显示和存储的编程软件.此系统获得的试验测量结果可以为海洋学研究提供充分的现场光学数据,有一定的实用价值.     

由现场离水辐亮度估算黄海透明度几种方法的比较

本文根据黄海现场离水辐亮度及遥感反射比,采用４种统计算法估算海水透明度（Ｓｅｃｃｈｉ　Ｄｉｓｃ　Ｄｅｐｔｈ）。前２种算法中海水透明度作为因变量,两不同波段辐亮度之比及两辐亮度之和与第三者之比分别作为自变量,进行一元回归分析,前者相关系数ｒ２为０．９３３５。后者相关系数ｒ２为０．９４８３。第３种算法中,所有波段的遥感反射比做因子分析形成的主因子作为自变量,透明度作为因变量进行多元回归分析,子样全相关系数ｒ２为０．９６４９。第４种算法中,遥感反射比作为自变量,透明度作为因变量进行逐步回归分析,复相关系数ｒ２为０．９８１５。计算结果表明,多元统计分析的估算精度高于一元回归分析。     

由TSRB辐射计数据估算海面离水辐亮度的经验方法

为建立基于经验统计的TSRB辐射计数据估算离水辐亮度的方法,利用SeaBASS数据库中640多个现场测量的辐亮度和辐照度光谱剖面数据,建立向上辐亮度衰减系数K_(lu)的经验算法.此算法为幂指数形式,输入变量为水下0.65 m的向上辐亮度(490 nm)与海面上向下的辐照度(555 nm或665 nm)之比(即为TSRB直接测量的两个参数).当水体较清时,输入为蓝绿波段之比,当水混浊时,采用蓝红波段之比.获得了K_(lu)后,海面以上的辐亮度(离水辐亮度)由z=0.65 m处的辐亮度外推获得.初步的检验结果表明,该方法对一类和二类水域都有很好性能,且算法实现简单,运行速度快.     

黄东海表观光学量与固有光学量经验模式研究

表观光学特性和固有光学特性是海洋光学研究领域的两大主要研究内容。文中通过2003年黄东海试验和2007年908专项海洋光学调查所获取的表观光学参数中的遥感反射率Rrs(λ)、水下遥感反射率rrs(λ)、海水透明度Zs、下行辐照度漫衰减系数Kd(490)、固有光学参数中的后向散射系数bb(λ)和水体吸收系数a(λ),建立了区域性、季节性的表观光学量和固有光学量之间的经验模式,并对模式进行了误差分析和改进。     

水下光辐射测量的阴影效应及其校正方法研究

用后向Monte Carlo模拟方法计算多仪器水下光学系统测量水体向上辐亮度和辐照度时由测量系统阴影导致的误差,给出了这种误差与入射太阳光相对于仪器的水平方位角之间的关系,给出了测量船对测量的影响与入射太阳光天顶角之间的关系.提出了一种辐亮度仪器自阴影误差的多光谱校正方法,模拟结果表明校正后误差小于5%.     

光谱仪测量离水辐射亮度的方法

概述了利用光谱仪在水面上方进行水表光学特性测量和基本原理与测量方法，以及处理和计算离水辐射亮度、归一化离水辐射亮度及遥感反射比等水表光学特性参数的主要方法。对1998年东海3个站点的测量数据进行了处理和分析，并与剖面法计算结果进行了比较。     

水下光谱辐射计光学特性的测试与分析

为适应高精度水下光学测量的需求，设计研制了多通道水下光谱辐射计。该辐射计可同步测量12波段的下行／上行光谱辐照度和7波段的上行光谱辐亮度。对该辐射计的主要性能指标，如余弦响应特性、浸没因子、光谱辐射精度、稳定性和重复性进行了室内测试和分析，用MonteCarlo方法模拟了阴影误差，给出并分析了现场实验数据及部分推导的物理量。结果表明，该光谱辐射计各波段的中心波长和带宽偏差小于1．6nm，稳定性优于5％，阴影误差可控制在5％之内，具有良好的余弦响应特性，满足当前定量化水色遥感现象光辐射测量的技术要求。     

On the possibility of mapping living corals to the species level based on their optical signatures

Several methods (Spectral Angle Mapper, first derivatives, spectral clustering) were used to test the possibility of discriminating live corals at the species level by using reflectance spectra obtained by close range underwater remote sensing. The Spectral Angle Mapper used with an in situ spectral library of 73 coral colonies recognised all corals correctly in an artificial remote sensing image created from the same coral spectra. The results did not change when “grey” noise was added to each pixel in the artificial image or when the artificial image was made from reflectance spectra modelled through a 5-m water column. The results showed that the within-species variability in optical properties of a set of four coral species, for which at least three different specimens were measured, was as high as between-species variability. Thus, it is highly unlikely that hard corals can be discriminated at a species level by means of remote sensing. Cluster analysis showed that it is difficult to recognise corals also at the genus level (Acropora vs. non-Acropora) based on their reflectance spectra. However, visual inspection of the coral spectra and clustering analysis suggest that it is possible to separate three main optical types of corals: green, blue, and brown corals. This may form the basis for an optical classification of corals that is more suited for remote sensing than traditional taxonomy.     

Phytoplankton,sediment and optical observations in Netherlands coastal water in spring

Factors controlling the dynamics of suspended particulate matter (SPM), its influence on sea-leaving radiance and in-water optical properties, and the consequences of optical variation for phytoplankton growth, were studied at the ‘Processes of Vertical Exchange in Shelf Seas’ (PROVESS) project's southern North Sea site during April 1999. The optical properties of Netherlands coastal water were not unexpectedly found to be primarily determined by suspended sediment (Case 2) and were classified as Jerlov type 7 ‘relatively turbid coastal water’. During the study period, vertical mixing periodically resuspended optically active particles from the bed fluff layer throughout the water column and into the near-surface layer. These particles influenced sea surface radiance reflectance, and the red/green ratio of radiance reflectance, both of which can be observed by remote sensing. Linear relationships between sea surface radiance reflectance and SPM concentration were primarily determined by the inorganic fraction, as organic SPM varied little in concentration throughout the cruise period. The inorganic fraction was an important scatterer of light at all wavelengths, whereas the organic fraction displayed a greater tendency for light absorption at shorter wavelengths. Although the euphotic layer (depth of 1% surface irradiance) was only 8–10 m deep, vertical mixing ensured that phytoplankton throughout the water column (∼18 m) had access to PAR in excess of the estimated compensation illumination.Growth rates of microplankton (which includes pelagic microheterotrophs as well as phytoplankters) were calculated using an algorithm from the PROWQM model. These ranged from 0.1 to 0.3 d⁻¹, and implied loss rates of 3–25% which were mostly attributed to mesozooplankton grazing. Estimated oxygen production, however, was in near equilibrium with oxygen demand observed in dark bottles, and implied a significant oxygen demand due to detrital respiration and nitrification. This was estimated as 3–6 mmol O₂ m⁻³ d⁻¹.In an order of magnitude timescale analysis, vertical mixing was found to be the single most important factor controlling the dynamics of SPM under mixed or stratified conditions. For a mixed water column microplankton aggregation and fluff layer resuspension also had the potential to redistribute material in the water column several times per day, whilst under stratified conditions horizontal exchange and inorganic particle sinking were more important. Resuspended material in a stratified water column remained below the pycnocline and had little impact on the near-surface layer optics. Other factors varied in importance with the level of stratification, which was recognised as a significant factor in determining the dynamics of SPM in this region of freshwater influence (ROFI).     

二类水体表观光学特性的测量与分析--水面之上法方法研究

水体光谱特性的测量与分析是海洋水色遥感的基础工作之一。水体光谱特性包括两个方面：表观光学特性和固有光学特性。现场直接获取表观光学特性有剖面法和水面之上法。在多次现场试验的基础上,主要针对二类水体从误差来源的角度来对水面之上法进行方法研究。同时,借鉴一类水体水面之上法的多种数据处理方法,对二类水体水面之上法的数据处理方法进行探讨。     

An overview of remote sensing of chlorophyll fluorescence

Besides empirical algorithms with the blue-green ratio, the algorithms based on fluorescence are also important and valid methods for retrieving chlorophyll-a concentration in the ocean waters, especially for Case II waters and the sea with algal blooming. This study reviews the history of initial cognitions, investigations and detailed approaches towards chlorophyll fluorescence, and then introduces the biological mechanism of fluorescence remote sensing and main spectral characteristics such as the positive correlation between fluorescence and chlorophyll concentration, the red shift phenomena. Meanwhile, there exist many influence factors that increase complexity of fluorescence remote sensing, such as fluorescence quantum yield, physiological status of various algae, substances with related optical property in the ocean, atmospheric absorption etc. Based on these cognitions, scientists have found two ways to calculate the amount of fluorescence detected by ocean color sensors: fluorescence line height and reflectance ratio. These two ways are currently the foundation for retrieval of chlorophyl l - a concentration in the ocean. As the in-situ measurements and synchronous satellite data are continuously being accumulated, the fluorescence remote sensing of chlorophyll-a concentration in Case II waters should be recognized more thoroughly and new algorithms could be expected.     

卫星海洋水色遥感的辐射模式研究

海洋水体向上的辐射由水中多种成分的浓度所决定，同时辐射的强度十分微弱并随着时间和空间在变化。因此，海洋水色遥感需要从水体和大气辐射传递机理出发，研究到达卫星遥感器的辐射模式，以达到模拟仿真卫星水色遥感图像和卫星图像质量预测的目的。本研究通过叶绿素、悬浮泥沙和黄色物质等海洋水色的主要因子，分别从可见光波段和荧光波段对辐射的贡献出发，发展了海洋水体离水辐射率模式。在卫星水色遥感机理的基础上，同时运用Iqbal，Gordon和Sturm等的大气程辐射模式和太阳耀光模式，使卫星海洋水色遥感的辐射模式系统化，模拟仿真了我国1990年9月3日发射的FYIB卫星两个海洋水色通道的全轨道辐射图像，同时利用从德国柏林大学气象中心接收到的1990年9月23－25日卫星图像进行验证。结果认为，本文所发展的模式可应用于卫星图像质量的预测和水色信息的提取。     

Optical water type discrimination and tuning remote sensing band-ratio algorithms: Application to retrieval of chlorophyll and Kd(490) in the Irish and Celtic Seas

This paper assesses the feasibility of applying remote sensing algorithms based on blue/green reflectance ratios to Case 2 waters. Two algorithms from the SeaDAS (NASA) image processing package, OC4v4 for surface chlorophyll concentration, Chl, and K(490) for the attenuation coefficient for downward irradiance at 490 nm, K_d(490), were investigated using an extensive set of observations from the Irish and Celtic Seas. In situ data from a profiling radiometer were used as inputs for the algorithms to avoid uncertainties in atmospheric correction procedures, and direct measurements of Chl and K_d490 and were used for validation purposes. The standard versions of the algorithms performed poorly: OC4v4 generally overestimated Chl (with a very low coefficient of determination), and K(490) progressively underestimated K_d490 for values greater than 0.3 m⁻¹. A two-step procedure for level 2 product generation was therefore devised in which the numerical coefficients of OC4v4 and K(490) were tuned for the two optical water types known to occur most frequently in this region (McKee, D., Cunningham, A., 2006. Identification and characterisation of two optical water types in the Irish Sea from in situ inherent optical properties and seawater constituents. Estuarine, Coastal and Shelf Science 68, 305–316) by statistical regression on a data set of 102 stations from the Irish and Celtic Seas. The water types were distinguished by the magnitude of their normalised water leaving radiance signals at 665 nm, nL_w(665), and appropriate versions of the tuned algorithms applied to each water type. When this procedure was tested on an independent data set of 19 stations from the Bristol Channel, Chl values were recovered with an RMS error of 0.36 mg m⁻³ and K_d(490) values with an RMS error of 0.095 m⁻¹. The identification of water types from water-leaving radiance signals, and the application of band-ratio algorithms tuned for specific water types, may therefore provide a simple means of improving the quality of remote sensing products in optically complex shelf seas.