南海真光层深度的遥感反演

海水真光层是指海洋浮游植物进行光合作用的水层,海水真光层深度的反演有利于对海洋初级生产力的估算。介绍了真光层深度的遥感反演算法,并根据实测资料,通过经验拟合得到南海海水真光层深度与海水漫衰减系数Kd(490)的关系:zeu=2.784/Kd(490)。经过与实测资料的对比发现,与其它通过叶绿素估算真光层深度的算法相比,本算法的精度明显提高。利用遥感估算的Kd(490)数据计算2003年南海的真光层深度,结果表明,南海陆源营养成分的输入以及南海环流是影响南海真光层变化的主要因素。     

基于GOCI静止水色卫星数据的长江口及邻近海域Kd(490)遥感反演及其在机载激光测深预评估中的应用

长江口水下三角洲地形地貌对于长江口航道安全、生态环境、海岸带工程等均具有重要意义,本次研究拟采用世界上第一颗静止水色卫星GOCI(Geostationary Ocean Color Imager)开展长江口Kd(490)的季节和潮汐变化规律研究,以期为采用机载激光测深提供预评估信息。研究得到结论如下:长江口及邻近海域水体为典型的二类水体,悬浮泥沙含量最高可由杭州湾内几千mg/L迅速降低至10 mg/L以下,因此,分段式的漫衰减系数反演算法适用于研究区域;Kd(490)反演结果表明长江口及邻近海域的Kd(490)值的季节变化特征表现为冬高夏低,春秋居中,长江冲淡水流量和季风是影响其季节变化的主要因素,而在一个潮周期内,Kd(490)值总体表现为低潮期低于高潮期,悬浮泥沙浓度和潮水的潮位是长江口及邻近海域的Kd(490)值的重要影响因素;研究指出,长江口及杭州湾内激光可探测深度约在5~22 m范围内,夏季退潮低潮位最适合激光雷达观测。由此可见,GOCI 8景/d,1景/h的分辨率可以实现Kd(490)的动态变化监控,而且可以实现在相同潮位下更为合理地描述Kd(490)值的季节变化,为机载激光雷达探测的进一步开展提供了技术支持。     

Characteristics of Kd （490） around Nansha Islands in the South China Sea

The diffusion attenuation coefficient for downwelling irradiance, Ka(490), is an important optical parameter of seawater. The optical property, Kd(490), around Nansha Islands in the South China Sea was analyzed based on optical data profiles measured with SPMR (SeaWiFS Profiling Multichannel Radiometer) and SMSR ( SeaWiFS Multichannel Surface Reference ) instrument in April and May, 1999. The results show that Kd(490) is closely correlated with chlorophyll-a concentration, Ccgka, and that the vertical distribution of Kd(490) shows the strong stratification of the water column in this area. Kd(490) has a similar vertical co-variation as KL(490), the diffusive attenuation coefficient for upwelling radiance.Both coefficients increase with depth in the upper layer, where KL(490) is greater than Kd(490); and after a depth, approximatively at the chlorophyll maximum, they decrease with depth, with the former being smaller than the latter.     

长江口邻近海域冬季漫衰减系数及其遥感反演

利用2012年和2013年冬季长江口邻近海域的实测数据,分析了该区域漫衰减系数光谱特征,490nm波段向下漫衰减系数(Kd(490))的空间分布及影响因子,建立了该研究区域新的冬季漫衰减系数反演模型,并建立了研究区域内Kd(490)与有效光合辐射衰减系数(Kd(PAR))的关系。结果表明:长江口邻近区域Kd490值随着离岸距离的减小逐渐增大,最大值达到了1.8m-1,杭州湾邻近区域情况类似,舟山岛附近出现了Kd(490)的最大值2.8m-1。总悬浮物对Kd(490)的影响较大,悬浮物浓度与Kd(490)相关度大于0.86。黄色物质和叶绿素a对其影响较小,与Kd(490)相关度均小于0.25。本文建立了三波段遥感反射率与Kd(490)的反演模式:lg[Kd(490)]=a[Rrs(590)/Rrs(510)]+b[Rrs(670)/Rrs(510)],对比反演与实测结果显示:均方根误差为0.098m-1,平均相对误差为12.43%,决定系数为0.916;光合有效辐射衰减系数(Kd(PAR))与Kd(490)的关系:Kd(PAR)=0.495exp(0.8602Kd(490))-0.2217,对比反演与实测结果显示:均方根误差为0.102m-1,平均相对误差为14.62%,决定系数为0.927。     

与南沙深水区温跃层有关的海水平均温度的分布特征

在确定温跃层三要素（深度（上界深度）、厚度和强度）及测站温度垂直最大梯度的基础上,分别计算了南沙深水测站（水深大于１０００ｍ）在温跃层上界深度范围内的平均温度、温跃层下界渡以下自３００ｍ层至８００ｍ层之间的平均温度。分析表明,在温跃层上界深度范围内,海水平均温度的水平分布明显显示出低温海水自南沙的西北部向东南部缓慢推进之势,似是东北季风驱动的结果。温度垂直梯度越大,它在垂直方向上阻碍上层海水的热量     

水下辐照度分布的异常尖峰现象及其机理初探

简述了水下辐照度异常尖峰分布现象和它的主要特征，根据海水光学参数的关系及水下总辐射的指数衰减方程导出了上行和下行辐照度垂直分布的三参数模型，该模型包括三个参数：海水体吸收系数ａ（ｚ）、后向散射系数ｂｂ（ｚ）和平均余弦的初始边界μ，（０）。利用该模型对几种典型水体中辐照度垂直分布的模拟结果与海上实测结果很一致。在模拟计算基础上，分析讨论了异常尖峰的产生机制。     

水下辐照度分布的异常尖端现象及其机理初探

简述了水下辐照度异常尖峰分布现象和它的主要特征，根据海水光学参数的关系及水下总辐射的指数衰减方程导出了上行和下行辐照度垂直分布的三参数模型，该模型包括三个参数：海水体吸收系数α（ｚ）、后向散射系数ｂｂ（ｚ）和平均余弦的初始边界μ（０）。利用该模型对几种典型水体中辐照度垂直分布的模拟结果与海上实测结果很一致。在模拟计算基础上，分析讨论了异常尖峰的产生机制。     

西北太平洋低纬度区域海水中溶解氨基酸的分布及组成研究

本文对2018年秋季西北太平洋低纬度区域上层海洋(5~200 m)中溶解氨基酸(THAA)的分布和组成进行了研究。结果表明,该海域表层海水中THAA的浓度范围为0.40~0.97μmol/L,平均浓度为0.58±0.14μmol/L;5~200m垂直断面上THAA的平均浓度为0.59±0.16μmol/L,范围为0.30~1.05μmol/L。调查海域内THAA浓度明显低于中国近海,在5~200m内的垂直分布基本表现出随深度增加而增加的趋势。将表层和垂直水体中的THAA分别与DOC、Chla等环境因子进行相关性分析,结果显示均无显著相关性。西北太平洋低纬度区域海水中的优势氨基酸是天冬氨酸(Asp)、谷氨酸(Glu)、丝氨酸(Ser)、甘氨酸(Gly)、苏氨酸(Thr)和丙氨酸(Ala)。基于氨基酸的碳归一化产率(THAA-C%)、降解因子(DI)值,表明该海域表层海水中的有机质降解程度较高,且随深度的增加而降低。     

分层水体对表层辐照度比影响的蒙特卡罗分析

众多海洋观测数据表明,在真光层深度范围内,海水固有光学特性和光学有效组分的剖面分层分布是广泛存在的,而很多遥感反演模型的建立基于均一分布假设,尤其是在经验模型的建立中,往往只利用某一深度或各深度平均的光学有效组分浓度与水体光谱的统计关系。文章通过模拟平静水面水下光的辐射传输,分别研究了叶绿素、无机悬浮物浓度垂直分布结构对水下辐照度比的影响,并对比了两类分层水体权重函数等效浓度计算式及相应水下辐照度比,结果表明,对于分层水体,透射深度和层化强度是影响等效浓度值计算误差的主要因素,透射越深,表层层化越强,水体层化对水下辐照度比的影响就越大,但其计算误差也越大。Gondon等效浓度计算结果比较接近实际值,而Zaneveld计算式则高估了分层水体的等效浓度值。     

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。     

Characteristics of water masses and bio-optical properties of the Bering Sea shelf during 2007–2009

The hydrographic and bio-optical properties of the Bering Sea shelf were analyzed based on in-situ measurements obtained during four cruises from 2007 to 2009. According to the temperature and salinity of the seawater, the spring water masses on the Bering Sea shelf were classified as the Alaskan Coast Water, Bering Sea Shelf Water, Anadyr Water, Spring Mixed Layer Water, Remnant Winter Water, and Winter Water, each of which had varying chlorophyll a concentrations. Among them, the highest chlorophyll a concentration occurred in the nutrient-rich Anadyr Water ((7.57±6.16) mg/m3 in spring). The spectrum-dependent diffuse attenuation coefficient (K_d(λ)) of the water column for downwelling irradiance was also calculated, exhibiting a decrease at 412–555 nm and then an increase within the range of 0.17–0.48 m–1 in spring. Furthermore, a strong correlation between the chlorophyll a concentration and the attenuation coefficient was found at visible wavelengths on the Bering Sea shelf. Spatially, the chlorophyll a concentration was higher on the northern shelf ((5.18±3.78) mg/m3) than on the southern shelf ((3.64±2.51) mg/m3), which was consistent with the distribution of the attenuation coefficient. Seasonally, the consumption of nutrients by blooms resulted in minimum chlorophyll a concentration ((0.78±0.51) mg/m3) and attenuation coefficient values in summer. In terms of the vertical structure, both the attenuation coefficient and the chlorophyll a concentration tended to reach maximum values at the same depth, and the depth of the maximum values increased as the surface temperature increased in summer. Moreover, an empirical model was fitted with a power function based on the correlation between the chlorophyll a concentration and the attenuation coefficient at 412–555 nm. In addition, a spectral model was constructed according to the relationship between the attenuation coefficients at 490 nm and at other wavelengths, which provides a method for estimating the bio-optical properties of the Bering Sea shelf.     

Variation of diffuse attenuation coefficient of downwelling irradiance in the Arctic Ocean

The diffuse attenuation coefficient(Kd) for downwelling irradiance is calculated from solar irradiance data measured in the Arctic Ocean during 3rd and 4th Chinese National Arctic Research Expedition(CHINARE), including 18 stations and nine stations selected for irradiance profiles in sea water respectively. In this study, the variation of attenuation coefficient in the Arctic Ocean was studied, and the following results were obtained. First, the relationship between attenuation coefficient and chlorophyll concentration in the Arctic Ocean has the form of a power function. The best fit is at 443 nm, and its determination coefficient is more than 0.7. With increasing wavelength, the determination coefficient decreases abruptly. At 550 nm, it even reaches a value lower than 0.2. However, the exponent fitted is only half of that adapted in low-latitude ocean because of the lower chlorophyll-specific absorption in the Arctic Ocean. The upshot was that, in the case of the same chlorophyll concentration, the attenuation caused by phytoplankton chlorophyll in the Arctic Ocean is lower than in low-latitude ocean. Second, the spectral model, which exhibits the relationship of attenuation coefficients between 490 nm and other wavelength, was built and provided a new method to estimate the attenuation coefficient at other wavelength, if the attenuation coefficient at 490 nm was known. Third, the impact factors on attenuation coefficient, including sea ice and sea water mass, were discussed. The influence of sea ice on attenuation coefficient is indirect and is determined through the control of entering solar radiation. The linear relationship between averaging sea ice concentration(ASIC, from 158 Julian day to observation day) and the depth of maximum chlorophyll is fitted by a simple linear equation. In addition, the sea water mass, such as the ACW(Alaskan Coastal Water), directly affects the amount of chlorophyll through taking more nutrient, and results in the higher attenuation coefficient in the layer of 30–60 m. Consequently, the spectral model of diffuse attenuation coefficient, the relationship between attenuation coefficient and chlorophyll and the linear relationship between the ASIC and the depth of maximum chlorophyll, together provide probability for simulating the process of diffuse attenuation coefficient during summer in the Arctic Ocean.     

Remote sensing and surface POC concentration in the South Atlantic

Several SeaWiFS products have been compared with shipboard data to assess the possibility of using remote sensing to estimate particulate organic carbon (POC) concentration in surface waters. Transmissometer data were collected during six South Atlantic Ventilation Experiment (SAVE) hydrographic expeditions conducted between November 1987 and March 1989 from R/V Knorr, and Melville. A total of 361 beam attenuation profiles were made with a SeaTech transmissometer interfaced with a CTD/rosette. In order to calculate the POC concentration from transmissometer profiles, a regression between beam attenuation and POC for open Atlantic Ocean waters derived from our research in the North Atlantic (North Atlantic Bloom Experiment, NABE) and enhanced by data from the Bermuda Atlantic Time Series Station (BATS) was applied. The profiles were processed and examined as vertical sections of the surface 250 m. The data were collected in two successive years, during the same season, which allowed us to compile a combined data set over the austral summer for examination. Beam attenuation/POC concentrations were integrated down to one attenuation depth with the intent of making comparisons with satellite optical data. No satellite optical data were available for 1987–1989, so the only option was to compare our integrated data with SeaWiFS-derived variables from later years averaged over the same season as SAVE data. Analysis of four SeaWiFS products acquired from 1997 to 2002 demonstrated very low variations from year to year for seasonally averaged data, suggesting that making comparisons of the beam attenuation/POC fields with averaged satellite optical products from later years is a valid (though not optimal) approach for this area. The highest correlation between beam attenuation/POC concentration and remotely derived products was found with normalized water-leaving radiance at 555 nm. Other SeaWiFS-derived variables—chlorophyll concentration, diffuse attenuation coefficient at 490 nm and integral chlorophyll (integrated over one attenuation depth)—were also compared but showed a slightly less satisfactory correlation.     

基于机载LiDAR测深水体波形的漫衰减系数提取方法

漫衰减系数是一个重要的海洋光学参数,能够为水体环境变化、水质分析以及水产养殖等方面提供基础性数据。针对目前船载实地测量效率与分辨率低、卫星遥感反演精度与分辨率较低的局限性,本文提出一种基于机载LiDAR测深水体波形的漫衰减系数提取方法。该方法首先通过分层异构模型的机载LiDAR波形分解算法得到水体散射回波,利用激光在水体中的衰减特性,构建漫衰减系数提取模型,最终获取大面积水域漫衰减系数的空间分布。采用西沙甘泉岛与江苏连云港两个航次的实测数据对所提算法进行了验证,本算法无需每个测深点的水底底部回波强度和深度即可反演得到漫衰减系数,并且在浑浊水域也可取得较好的效果,表明在中国近海利用机载LiDAR测深系统能够有效获取高精度的漫衰减系数。     

黄海、东海二类水体漫衰减系数与透明度反演模式研究

黄海、东海是典型的二类水体区域,总悬浮物含量高,水体光学特性复杂.利用2003年春秋季黄海、东海水色联合试验中获取的高质量现场实测数据,建立了由遥感反射比反演水体在490nm波段的漫衰减系数和海水透明度的统计反演模式.这两种模式皆采用490,555,670nm三个波段的组合,漫衰减系数的反演值和实测值的相关系数为0.96,平均相对误差为17.2%;透明度的反演值与实测值的相关系数为0.95,平均相对误差为16.8%.对两种反演模式对遥感反射比输入误差的敏感性进行了分析,结果表明反演模式对±5%的遥感反射比输入误差导致490nm波段的漫衰减系数反演误差最大为27.3%,透明度最大误差为22.7%,并利用2003年春秋季同一海区的实测数据对模型进行了检验,漫衰减系数的平均相对误差为25.0%,透明度的为16.5%.给出了412,443,510,520,555,565nm各波段的漫衰减系数同波段490nm的漫衰减系数之间的关系,结果表明,在400~600nm波段中的每一个波段的漫衰减系数与490nm波段的漫衰减系数的相关性较高,相关系数都超过了0.98.这样利用建立的各波段漫衰减系数关系模型可以从一个已知波段的漫衰减系数反演出其他任何波段的漫衰减系数,这就在水色反演和应用中大大减少了未知因子的个数.     

基于人工神经网络的海水漫射衰减系数的遥感反演方法

利用NOMAD数据集建立了基于人工神经网络的漫射衰减系数Kd490的反演算法。该人工神经网络是3层的反向传输神经网络。其结构为输入层有4个节点,它们分别对应4个波段443,490,555,665 nm的遥感反射比,隐含层有10个节点,输出层1个节点对应于漫衰减系数Kd490。利用另一独立的现场测量数据集(COASTLOOC)印证该反演算法的性能。结果表明,该研究建立的反演算法的性能明显好于业务化SeaWiFS算法,略好于Lee等人的半分析算法。     

Preliminary optical classification of lakes and coastal waters in Estonia and south Finland

A preliminary optical classification of lakes in Estonia and south Finland which can also be used for small bays of the Baltic Sea is elaborated. The classification is based on the optical properties of water (diffuse attenuation coefficient, diffuse reflectance) and parameters that are routinely monitored in water bodies (Secchi depth, concentration of chlorophyll-a, total suspended matter and yellow substance). The data complex used for our classification covers different types of water ecosystems (ranging from oligotrophic to hypertrophic) and the variability of water constituent concentrations in the ice-free period in Estonia and south Finland. Using cluster analysis, we found 5 optical classes of waters: clear (C), moderate (M), turbid (T), very turbid (V) and brown (B). There is satisfactory correspondence between class of water, shape of diffuse attenuation coefficient and diffuse reflectance spectra and trophic state of the lakes.