Modeling optical contrast for thin organic films on the sea surface

A continuation of the work dedicated to the study of slicks and film formations on the sea surface is presented. A vector model for the calculation of reflected radiation by the wavy sea surface with respect to the contribution of upwelling radiation from under the sea surface (the second type of waters) is described briefly in [5]. This work contains an analysis of numerical calculations according to the developed procedure and the search for optimal conditions of slick detection. The best conditions for detecting slicks on the sea surface are reached when a P-polarization component of reflected radiation is recorded. In this case, the value of contrast between a slick and a clean surface is 30% higher on average than in recording a contrast without using a polarization filter and is 50% higher than in the case of recording a contrast with a filter oriented to the maximum transmission of S polarization component of reflected radiation. It is shown that, under clear sky conditions, the optimal condition for recording slicks on a sea surface is videotaping in the plane of solar vertical at viewing angles sliding towards the sea surface and when a polarization filter that identifies the Р polarization component of sea radiation is used. In contrast, under overcast sky conditions, it is best to perform observations in the plane that has a wind velocity vector.     

Estimation of underwater scattering radiances up to the third order

Vertical distribution of underwater scattering radiances of the first, the second and the third order is estimated by the Jerlov's method. In the estimation the volume attenuation coefficient and the volume scattering function are assumed to be constant in near surface layer, and the sky radiation separated from solar radiation to be a parallel beam and to fall into the sea in the vertical direction only.In the zenith direction the second scattering radiance is more intense than the first scattering radiance in near surface layer. As for the total radiance which is a sum of radiances up to the third order, the zenith radiation is largest, the nadir radiation is moderate and the horizontal radiation is least.     

Determination of the variance of rough water surface slopes by the distortion of Snell’s circle boundary

We studied the opportunities of diagnostic of the wind roughness by distortions of Snell’s circle boundary images, i.e., images of the sky observed from underwater through a rough water surface. Models of random realization and statistically average image of Snell’s circle which takes into account various condition of illumination (overcast sky, clear sky and isotropic distribution of sky radiance) have been developed. Formulas for definition of slope variance of the sea surface by distortion of Snell’s circle boundary for one-dimensional roughness have been received. Dependence of accuracy of definition of slope variance on time of image averaging, depth of receiver diving, wind speed, range of waves forming the roughness, have been analyzed by the method of computer modeling. It has been shown on the basis of numerical calculation and experimental data that waves with length from millimeters to meters can be shown in the image of Snell’s circle depending from depth of receiver diving, receiver resolution and water turbidity.     

可见光波段海面目标物的光谱对比度──Ⅰ．理论基础

对海面目标物的目视观察，其能见距离与观测方向、海面背景光谱辐射、目标物固有光谱辐射和大气分子及气溶胶的光学参数等因素有密切关系。本文从理论上分析各种因素的影响，特别是研究了海面背景辐射对目标物光谱对比度的作用。推导出不同观测方向下目标物光谱对比度的计算公式。作为例子，给出海面上黑色物体的光谱对比度公式，也给出海面目标“被隐蔽”的条件。     

海冰对北极海冰边缘区大洋光学观测的影响评估

Diffuse attenuation coefficient(DAC) of sea water is an important parameter in ocean thermodynamics and biology, reflecting the absorption capability of sea water in different layers. In the Arctic Ocean, however, sea ice affects the radiance/irradiance measurements of upper ocean, which results in obvious errors in the DAC calculation. To better understand the impacts of sea ice on the ocean optics observations, a series of in situ experiments were carried out in the summer of 2009 in the southern Beaufort Sea. Observational results show that the profiles of spectral diffuse attenuation coefficients of seawater near ice cover within upper surface of 50 m were not contaminated by the sea ice with a solar zenith angle of 55°, relative azimuth angle of 110°≤φ≤115° and horizontal distance between the sensors and ice edge of greater than 25 m. Based on geometric optics theory, the impact of ice cover could be avoided by adjusting the relative solar azimuth angle in a particular distance between the instrument and ice. Under an overcast sky, ice cover being 25 m away from sensors did not affect the profiles of spectral DACs within the upper 50 m either. Moreover, reliable spectral DACs of seawater could be obtained with sensors completely covered by sea ice.     

Diagnostics of the mesoscale water exchange on the basis of statistical characteristics of the distribution of normalized radiance

A new approach is suggested for the diagnostics of manifestations of water exchange in the field of normalized radiance and automation of the analysis of digital images of the water surface. The approach is based on the application of a set of statistical characteristics of a radiance relief as an integral indication of local inhomogeneities in the water medium and provides for the estimate of these characteristics over small regions (frames) of the basin studied using multispectral information. Using the example of the SeaWiFS scanner data on the evolution of an eddy dipole in August 1998 in a study region with a size of 160 × 160 km in the northwestern part of the Black Sea, it was shown that the estimates of a number of statistical characteristics of spectrally different radiance reliefs found in the frames with a size of 40 × 40 km significantly depended on the presence of fragments of an eddy dipole or other structures in these frames. A set of such characteristics made possible reliable differentiation of radiance reliefs by the degree of randomness, by the orientation of the inhomogeneities that form the relief, and by other properties caused by the variability of the light scattering and light absorbing admixtures in the sea medium in the course of the water exchange. The approach does not require any preliminary information about the object of observations. It is promising in the basins with moderate water transparency and vertical inhomogeneity of the upper layer available for remote profiling.     

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).     

Method for estimating admixture content in seawater using operative spectrophotometry

The paper discusses spectra of the radiance coefficient of the sea surface measured in the open ocean and in coastal waters, and different kinds of these spectra corresponding to the water types are revealed. The focus is the method of measuring the radiance coefficient from a moving ship with a hyperspectral spectrophotometer. The results of studying a water area of Russia’s Black Sea coast at river mouths are presented. A new calibration method that can process measurement results taking into account the impact of cloudiness and wind has been proposed and tested. The concentrations of the main admixtures in natural seawater in the studied water area are estimated according to the obtained spectra; these estimates are compared to the results of direct analysis of water samples. It has been shown that the method of remote measurement of the sea radiance coefficient from on board a ship makes it possible to obtain operative maps of the spatial distribution of the main seawater admixtures.     

用陆地卫星─5近红外图像观测胶州湾海况

对海洋上空卫星测得的近红外波段辐射所反映的信息进行理论分析，表明卫星近红外波段图像上反映的是海况信息。1986年11月5日陆地卫星TM6图像显示胶州湾海表温度的波状分布，TM2，TM3，TM4波段彩色合成图显示胶州湾的悬浮泥沙含量分布和泥沙运动。TM4图像显示在海洋波动和风力作用下的海况，并用实测潮汐资料、气象信息解译胶州湾海况。在胶州湾中、西部，悬浮泥沙含量较高，而TM4波段辐射值较低，图像阴暗，较高的泥沙含量并没有提高TM4波段的辐射值。胶州湾东部，悬浮泥沙含量较低，而TM4波段辐射值较高，图像明亮。TM4波段辐射值并不反映泥沙含量和海底深度，它们仅提供海洋表面粗糙度或海况信息。     

直接同化卫星辐射数据的黄海海雾数值试验研究

基于中尺度大气模式WRF及其3DVAR.模块,采用循环3DVAR数据同化方案,针对6次明显的黄海海雾过程,实施了一系列直接同化ATOVS卫星辐射数据数值试验.在试验中设计了不同化任何观测数据、仅同化GTS常规数据、仅直接同化辐射数据,同时同化二者,以及同化不同疏密程度辐射数据的对比研究方案.利用地面水平能见度与卫星云图对模拟的海雾雾区进行了评估,并比较了各种同化方案所形成初始场的差异.对试验结果的统计分析表明:同化试验较好地再现了影响海雾的天气系统,模拟雾区与实际观测较为吻合,并且初始温度场和湿度场对比不同化任何观测数据的试验有明显的改善;仅同化辐射数据的结果略优于仅同化常规数据的结果,疏化或者只同化海上辐射数据几乎不影响模拟的雾区,但却可以大幅节约计算资源;同时同化常规数据与辐射数据的结果为单独同化它们所得结果的综合体现,总体效果最好.     

Determination of wind roughness characteristics based on an underwater image of the sea surface

The opportunities of diagnosing wind roughness with the help of underwater vision systems have been investigated. The model of the rough sea surface image observed from under water under conditions of natural illumination has been developed. It has been shown that the statistical processing of the image of a solar path which is formed as a result of light refraction at randomly irregular air-water interface allows one to define not only the slope variance and the curvature variance of the surface, but also the coefficient of spatial correlation of slopes. The algorithms for defining of characteristics of wind roughness on the basis of images of underwater solar path and the results of their testing using the data of numerical and natural experiments are given. It was found that waves of very small amplitude images with high contrast near borders of the Snell’s circle (the underwater image of the sky).     

Spectral radiometric measurements of the temperature and radiation capacity of a rough sea surface

The results of radiometric remote simultaneous field measurements of the temperature and radiation capacity of the upper layer of the sea-surface temperature film 0.2 mm thick are presented. The measurements were conducted in the presence of wind waves and were characterized by an increased accuracy, which was achieved owing to the use of measurements of the intensity of radio radiation from the surface illuminated by radiation of a specified varying power. In our experiment, this illumination was provided by the radio radiation of the atmosphere, whose radiance temperature varies significantly, depending on the frequency at the slope of the absorption band of molecular oxygen (52.5–56 GHz). As a result, the radiation capacity and temperature of the skin layer were determined from the correlation dependence between the radiance temperatures of the surface and atmosphere measured by a radiometer-spectrometer in a number of channels separated in frequency. The radiance temperatures of the sea and atmosphere were measured at four frequencies of the 5-mm spectral range (53–55 GHz) on a vertical polarization. For absolute measurements, a calibration method was developed on the basis of a blackbody disk and two reflecting mirrors with the same solid angles. The measured values of the radiation capacity are variable and substantially smaller than the theoretical values determined by the models accepted for the permittivity of water and sea roughness. A possible cause of this can be the change of the permittivity of water in a thin surface layer of the temperature film (0.2 mm) due to the concentration of gases dissolved in water and surface-active substances within this layer.     

GPM微波成像仪资料同化对台风“麦德姆”路径预报的影响研究

基于中尺度数值模式WRF及其三维变分同化系统,自主构建了新的探测仪器GMI(Global Precipitation Measurement (GPM) Microwave Imager)的同化模块。本文以2014年太平洋台风季中台风“麦德姆”为例,实现了GMI资料在登陆台风中的有效应用。试验结果表明:晴空条件下GMI资料同化能够对模式背景场中的台风位置进行有效修正。与没有同化该资料的控制试验相比,同化GMI微波成像仪资料可以有效改进台风暖心结构的分析,同时使得台风涡旋环流结构增强,并进而提高了对台风路径的预报水平。     

大气对微波散射计回波信号衰减的修正方法研究

为了使微波散射计测得的海面后向散射具有足够的精度，必须考虑大气对微波衰减的影响。大气对微波的衰减可以用微波射计来测定。本文将估算晴空、云和降雨天气下的衰减系，讨论计算海面发射率及用微波辐射计剩余亮温估算散射计工作频率下大气衰减的方法。     

Reconstruction of the spectrum of the radiance coefficient from measurements at fixed wavelengths

A method permitting the complete ensemble of characteristics to be reconstructed from a few selected characteristics is suggested. Finding sets of characteristics which ensure a minimum error of reconstruction, as well as the reconstruction procedure itself, requires the invoking of information on the convariance relationships between the characteristics. The method has been applied to determine the wavelengths, optimal for the reconstruction of spectra of sea surface radiance coefficients in the western tropical Atlantic.Translated by Vladimir A. Puchkin.     

海面之上法中海面反射率和观测几何模拟研究

测量离水辐亮度的水面之上测量方法中最大的不确定性因素是太阳耀斑的污染和海面反射率的估算。文章根据Cox和Munk研究结果,利用大量随机数模拟海面波浪倾斜,估算不同仪器观测方向与风矢量几何以及不同仪器视场角下的海面反射率,并估算出不同太阳天顶角及相对风矢量方位角的太阳耀斑基本分布。     

基于GPS反射信号技术的渤海海冰实验

传统的海冰检测手段都存在着受天气影响或实时检测成本太高的缺点,为了更实时有效的检测海冰,减轻海冰灾害对于我国的影响,并达到防灾减灾的目的,本文研究了GPS反射信号(GPS-R)技术检测海冰的可能性。通过对2013年2月下旬在中国天津渤海湾的岸基架设GPS信号接收机所接收的观测数据进行分析,使用不同特性的反射海域(几乎全为海水或是海冰)的数据进行比对分析,其结果显示极化比值(反射左旋信号与直射右旋信号的比值)能够明显反演海冰密集度。本文首次将GPS-R技术应用于国内自主设计的渤海海冰检测实验中。     

太阳反射光对海洋水色卫星遥感的影响研究

海洋水色卫星遥感的关键是水色图像资料的利用率。受到太阳反射光的影响使图像饱和是水色卫星图像的主要噪声之一。笔者首先论述了卫星海洋水色遥感中到达水色扫描仪的太阳反射光（即太阳耀光）的辐射量计算模式；然后介绍了产生太阳耀光模拟图像的全过程，并对我国FY－1B、美国的SeaSTAR和台湾省的ROCSAT－1号卫星作了全轨道下的太阳耀光模拟图像；最后，讨论了影响太阳耀光的主要因素，同时提出了减小太阳耀光提高海洋水色卫星遥感图像利用率的建议。     

辽东湾冰季太阳辐射分析

利用渤海辽东湾ＪＺ２０－２石油平台上的气象和海冰观测数据,研究了冰季大气层和云层对太阳辐射的影响,结果表明,辽东湾冰季大气光学可取为０．８３,碧空、少云、多云阴天、雾天和雨雪等不同天气条件下的云量系数可分别取为０、３、６、８、９和１０。分析了冰水混合情况下海面对太阳辐射的反射情况;讨论了太阳辐射对冰面长波辐射和对流传热的影响。利用冰面太阳辐射的实测值和计算结果,对整个冰季内太阳辐射的规律进行了分析     

机载海洋激光雷达测量叶绿素a浓度、悬移质浓度和浅海深度的性能估计

以14:00时离水辐亮度作为背景光强度,模拟355nm激光雷达测量不同深度水层叶绿素a荧光的信噪比.分析体积衰减系数c、辐照度衰减系数k、散射系数b和透明度盘深度(SDD)的关系.最后模拟532nm激光雷达测量悬移质浓度的最大测量深度和误判率小于10%时的最大海底探测深度随SDD的变化.