Manifestation specifics of hydrodynamic processes in satellite images of intense phytoplankton bloom areas

The paper summarizes the results of the long-term complex satellite monitoring of the Black and Baltic seas. Data from synthetic aperture radars (SARs) constitute the experimental basis for the investigation of satellite. In addition to radar data, the data of the visible and infrared bands from MODIS Terra/Aqua, MERIS Envisat, Landsat series sensors are used. The features of the manifestation of hydrodynamic processes, submesoscale eddies in particular, in satellite radar and optical images in a period of intense phytoplankton bloom are discussed. A relationship is established between the intensity and duration of the phytoplankton bloom in the regions of observation and the frequency of the appearance of long-lasting wakes behind moving ships in SAR images. These wakes appear as long narrow bright bands of enhanced backscattered signal extending for tens and sometimes hundreds of kilometers. It is proposed to consider the wakes of this type as indicators of the areas and duration of intense phytoplankton bloom. Satellite observations over the Black and Baltic Seas conducted for more than ten years have shown that long-lasting ship wakes are influenced by powerful jet streams, such as those associated with the passage of eddies that leads to shifts and deformations. By comparing the true route of a ship with its wake in the satellite image, it is possible to obtain detailed information about the parameters of currents.     

东海黑潮锋面涡、暖丝和暖环

本文根据1989年4月10～21日在东海东北部的海洋调查资料以及1989年4月10日和16日的卫星红外影象分析了黑潮锋面涡、暖丝和暖环的特征.结果表明,出现在这里的锋面涡约以30cm/s 的速度随黑潮主干移动,在锋面涡的冷中心区陆架混合水插入同时,下层的高营养水上升,从而造成高生产力区.黑潮暖丝携带约4×10~6m~3/s 的输运量以50 cm/s 的速度逆黑潮西行,然后暖丝可能沿陆架坡转向北,或可能顺时针旋转形成暖环.     

Satellite observations of synoptic eddies and the geostrophic circulation of the Sea of Japan waters

Currents and eddies in the Sea of Japan are investigated on the basis of shipboard multiyear averaged hydrologic measurements over 1925–2005 and satellite images over 1988–2002. The schemes of geostrophic currents are constructed and the positions of quasi-stationary eddies on the sea surface are determined. It is shown that eddy formations are concentrated along jets of the main currents. A construction of the scheme of surface currents with consideration for eddies is attempted.     

On the influence of the freshwater supply on the Baltic Sea mean salinity

The sensitivity of the Baltic Sea mean salinity to climatic changes of the freshwater supply is analyzed. The average salinity of the Baltic Sea is about 6‰. The low salinity is an effect of a large net freshwater supply and narrow and shallow connections with the North Sea. As a result of mixing in the entrance area, a large portion of the outflowing Baltic Sea water returns with the inflowing salty water and thus lowers the salinity of the Baltic Sea deep-water considerably. This recycling of the Baltic Sea water is a key process determining the salinity of today's Baltic Sea. The sensitivity of this recycling, and thus of the Baltic Sea salinity, to climatic changes in the freshwater supply is analyzed. A simple model is formulated for the variations of the Baltic Sea freshwater content. Historical data of the freshwater supply and the salinity in the Baltic Sea are used in the model to achieve an empirical expression relating variations of the recycling of Baltic Sea water to the variations of the freshwater supply. The recycling is found to be very sensitive to the freshwater supply. We find that an increase of freshwater supply of 30% is the level above which the Baltic Sea would turn into a lake. Recent climate modeling results suggest that river runoff to the Baltic Sea may increase dramatically in the future and thus possibly put the Baltic Sea into a new state.     

利用NOAA卫星图像和水文资料研究东海水文的变化

本文利用ＮＯＡＡ卫星图像处理结果与同期水文观测资料，对东海表层水团的分布和转移特征作了初步分析。结果表明，东海表层水温的分布与结构同该海区的水团和环流发展相联系，水团消长和东海冬季高密水核心上层环流的发展可诱导长江口外混合水向外海扩散，表层水块的移动速度可达２６ｃｍ／ｓ，与动力学估算和同期漂移浮标所得的结果一致     

基于合成孔径雷达的长江口海表流场反演

Range Doppler velocities derived from the Envisat advanced synthetic aperture radar（ASAR） wide swath images are analyzed and assessed against the numerically simulated surface current fields derived from the finite volume coastal ocean model（FVCOM） for the Changjiang Estuary. Comparisons with the FVCOM simulations show that the European Space Agency（ESA） Envisat ASAR based Doppler shift anomaly retrievals have the capability to capture quantitative information of the surface currents in the Changjiang Estuary. The uncertainty analysis of the ASAR range Doppler velocity estimates are discussed with regard to the azimuthal and range bias corrections, radar incidence angles, inaccuracy in the wind field corrections and the presence of rain cells.The corrected range Doppler velocities for the Changjiang Estuary area are highly valuable as they exhibit quantitative expressions related to the multiscale upper layer dynamics and surface current variability around the East China Sea, including the Changjiang Estuary.     

Biooptical characteristics of the surface layer of the Baltic,Norwegian, and Barents seas in summer 2014–2016 from shipboard and satellite data

The article presents the results of shipboard and satellite measurements in the surface layer of the Baltic, Norwegian, and Barents seas during legs from the Baltic to the White Sea in June–August 2014–2016. Special attention is paid to marine phytoplankton blooms of cyanobacteria in the Baltic Sea and coccolithophores in the Barents Sea. No blooms were found in the Norwegian Sea. The efficiency of combined application of in situ and satellite optical methods for studying the parameters of phytoplankton blooms is shown.     

Peculiarities of distribution of oil polution in the Southeastern Baltic by satellite data and in situ measurements

The results of satellite monitoring of oil pollution of the sea surface and field measurements of the concentration of oil products in the water column and bottom sediments for the first time allowed the establishment of a relation between the surface pollution from ships and the general characteristics of spatial and temporal distribution of oil products in the Southeastern Baltic Sea. Areas with increased concentrations of oil products in the surface and bottom layers were determined in the southeastern Baltic Sea. The basic directions of pollution spread, which are consistent with the main direction of annual mean transport of substances in the Gdansk Basin, are determined.     

Deviation of mean sea level from the mean geoid in the transition area between the North Sea and the Baltic Sea

The mean sea level along the coasts of the Skagerrak, the Kattegat, and the Danish Straits—i.e., the transition area between the North Sea and the Baltic Sea—has been computed geodetically. The basis consists of mean sea level data from Denmark, Norway, and Sweden in various more or less inappropriate height systems. These are transformed and unified into a common height system relevant for oceanographic purposes to show the deviation of the mean sea level (1960) from the mean geoid, with Normaal Amsterdams Peil (NAP) as zero. The geodetically determined mean sea surface is compared with oceanographic model results for parts of the area. Among other findings, the outflow of low‐salinity water from the Baltic Sea, as well as its separation from high‐salinity North Sea water along the Kattegat‐Skagerrak front are clearly revealed.     

Validation of Marine Geoid Models by Profile-wise GNSS Measurements on Ice Surface

Ship-board global navigation satellite system (GNSS) measurements are widely used to determine sea surface heights, marine geoid validation, and/or satellite altimetry calibration. However, the use of a vessel could be complicated near coastal areas due to shallow water. Therefore, in the area of sea ice formation, GNSS measurements on the ice surface could be a viable alternative to vessel-borne surveys. Importantly, the ice-covered water is not affected by short-term winds, which otherwise could have systematic influence on the instantaneous sea surface topography. This study tackles methodology and validation of marine geoid models by profile-wise GNSS measurements on ice in an archipelago of the Baltic Sea. The GNSS measurements were carried out on the three ice roads with total length 48 kilometers. The along-route standard deviation between the gravimetric geoid model and profile-wise GNSS heights remained within ±2.1 centimeters.     

Bayesian classification of the ice cover of the Arctic seas

A classification of sea ice in the Arctic by age (multiyear; first-year; and first-year deformed ice, nilas, etc.) is developed based on the Bayesian approach using satellite radar data and taking into account regional peculiarities of these types of ice for different sectors of the Arctic. Estimations of a priori probabilities for each ice type, which are required for the use of the Bayesian classification, are obtained by the analysis of ice charts in the Arctic seas developed at the AARI in 2008–2013 using satellite data. A posterior probabilities are estimated visually by an expert. Types of sea ice distinguished by the expert on satellite images make it possible to create sample values of the radar-scattering cross section (RSCS). Examples of the proposed Bayesian classification of ice in the Laptev Sea according to Envisat satellite data are given.     

Mesoscale eddies in the area of peter the great bay according to satellite data

We have studied the characteristics of mesoscale eddies in the Peter the Great Bay and the adjacent area of the northwestern Sea of Japan. The characteristics were determined using infrared images (NOAA/AVHRR satellite data) for July–October periods of 2000–2004. It is established that anticyclonic eddies are always present in the indicated area, since they have been identified on 85% of the available cloudfree images. Characteristics of 43 anticyclonic eddies have been determined. Their diameters vary from 20 to 110 km, with the most probable sizes within 20–60 km. The typical eddy lifetime varies from 3 to 30 days. However, some medium-sized eddies (40–60 km) have been observed for a longer time (up to 40–60 days) and large eddies (60–110 km in diameter) remained for up to 1–2 months. Eddies drift southwestward and southward along the continental slope at a typical speed of 3–6 cm/s. There are interannual variations in the vortex structure of water flows in the area studied, which are manifested by the presence of a single large eddy occupying a large part of the bay in some years (2000, 2002, and 2003) or by the formation of several smaller eddies (2001 and 2004). The eddies contain warmer and less saline shelf waters (compared to the surrounding water) and transport it in their cores over quite a long distance. Thus, eddies are an essential element of the process of the intermediate low-salinity water-mass formation in the Sea of Japan. In addition, eddies play important role in the cross-shelf water exchange, providing rapid ventilation of the coastal zone and determining the variability of the biological processes.     

Model study of the upper circulation in the Sulu Sea and its relation to the South China Sea circulation

According to the satellite remote sensing monthly mean sea surface temperature data from 1998 to 2002, it is shown that, the Sulu Sea is dominated by a cold eddy both in summer and winter. A coupled single-layer/two-layer model is employed here to study the summery and wintry characteristics and dynamic mechanism of the upper circulation in the Sulu Sea. According to the numerical experiments, it is found that, due to the local monsoon stress cud, the upper circulation in the Sulu Sea is dominated by a weak anticyclonic eddy in summer and a strong cyclonic eddy in winter. Once there is a large outflow via the Sibutu Passage flowing out of the Sulu Sea in summer, the upper circulation in the Sulu Sea may be dominated by a cyclonic eddy instead of the normal anti- cyclonic one. Moreover, in summer, the water exchange between the Sulu Sea and South China Sea via the Mindoro and Balabac Straits might have some effect on the separation position and strength of the northward western boundary current next to the Indo - China Peninsula in the southern South China Sea.     

Causes of different impact of Major Baltic Inflows on cod reproduction in the Gotland Basin of the Baltic Sea

The impact of the Major Baltic Inflows (MBIs) of 1976, 1993, and 2003 on cod reproduction in the Gotland Basin of the Baltic Sea is considered based on calculations of the eastern Baltic cod egg abundance and offspring survival indices. The reproductive success (1976–1977) was defined by the elevation of the 11 psu isohaline and deepening of the 2 mL/L isooxygene surface, which provided the formation of a water layer suitable for cod spawning at a depth of 90–130 m. Prerequisites of the appearance of the reproductive layer in 1976–1977 were a previously high salinity level and penetrating two successive MBIs in one year. The cause of the weak MBI impact in 1993 was the previous salinity minimum; in 2003 it was rapid oxygen depletion due to an increase in temperature. As a result of their weaker influence, small and fragmented cod spawning biotopes appeared in the Gotland Basin.     

2009-2010年冬季南海东北部中尺度过程观测

根据南海北部陆架陆坡海域2009-2010年冬季航次的CTD调查资料,发现西北太平洋水在上层通过吕宋海峡入侵南海,其对南海东北部上层水体温盐性质的影响自东向西呈减弱趋势,影响范围可达114°E附近。入侵过程中受东北部海域反 气旋式涡旋(观测期间,其中心位于20.75°N,118°E附近) 的影响,海水的垂向和水平结构发生了很大变化,特别是涡旋中心区域,上层暖水深厚,混合层和盐度极大值层显著深于周边海域。该暖涡在地转流场、航载ADCP观测海流及卫星高度计资料中均得到了证实。暖涡的存在还显著影响了海水化学要素的空间分布,暖涡引起的海水辐聚将上层溶解氧含量较高的水体向下输运,使次表层的暖涡中心呈现高溶解氧的分布特征。     

The impact of salt water inflows on the distribution of polycyclic aromatic hydrocarbons in the deep water of the Baltic Sea

Salt-water inflows into the Baltic Sea are important events for renewing the deep and bottom waters of the deep basins of the Baltic Sea. These events occur only at irregular intervals. The last strong event was in January 1993 followed by minor inflows in winter 1993/1994. As a result of these inflows, the deep water of the central Baltic basins was completely renewed.Based on extensive observations of polycyclic aromatic hydrocarbons (PAHs) in water, fluffy layer material and surface sediments between 1992 and 1998, the transformation of PAHs and the modification of their distribution in the Baltic deep water is discussed in connection with the spreading of the inflowing highly saline and oxygen-rich water along its pathway from the sills into the central basins. In the course of the inflows in 1993/1994, the PAH concentration in the deep water of the different basins increased significantly. The concentrations were elevated, at least by a factor of 2 and as much as seven to eight times (for the four-ring PAHs) compared to the previous and the following years. Two hypotheses for the causes were discussed: the inflowing salt water may have entrained more highly polluted surface water in the western Baltic Sea, or it may have entrained contaminated fluffy layer material or sediment particles along the route of transport.     

Application of Web-GIS and Geovisual Analytics to Monitoring of Seabed Evolution in South Baltic Sea Coastal Areas

Regular surveys of coastal zone seabed deliver important information about geomorphologic processes such as silting of waterways. The recent introduction of the Sentinel series of sensors has allowed for the use of satellite sensing for shallow bathymetry morphology monitoring. In this context, this article presents a dedicated Geographic Information System for Baltic Sea shallow water depth monitoring on the basis of Sentinel-2 imagery. The system employs Geovisual Analytics for differential analysis of bathymetry changes as well as monitoring the visibility of known wrecks in the coastal waters of Southern Baltic Sea. Results are verified with regard to known changes in shallow water bathymetry between 28 June 2015 and 3 March 2017.     

Variability of Sea Surface Heights in the Baltic Sea: An Intercomparison of Observations and Model Simulations

Sea level changes in the Baltic Sea are dominated by internal, short-term variations that are mostly caused by the ephemeral nature of atmospheric conditions over the Baltic area. Tides are small and their influence decreases from western parts of the Baltic Sea to the Baltic Proper. Superimposed to the large short-term sea level changes (up to few decimeters from day to day) are seasonal and interannual variations (centimeters to decimeters). This study focuses on the comparison of sea surface heights obtained from observations and from a high resolution oceanographic model of the Baltic Sea. From this comparison, the accuracy of the modeled sea surface variations is evaluated, which is a necessary precondition for the further use of the oceanographic model in geodetic applications. The model reproduces all observed Baltic sea level variations very reliably with an accuracy of 5 to 9 cm (rms) for short-term variations (up to 2 months) and 8 cm (rms) for long-term variations (>2 months). An additional improvement of the model can be attained by including long-period sea level variations of the North Sea. The model performs well also in the case of extreme sea level events, as is shown for a major storm surge that occurred at the southern coast of the Baltic Sea in November 1995.     

卫星遥感预测南黄海盆地油气远景

为了预测南黄海盆地油气远景,利用卫星遥感对东海陆架盆地进行海面温度测量。东海陆架盆地已知油气远景区与卫星热红外温度异常区具有原地重复性,与水气界面CH4含量曲线及海底化探异常吻合程度很好。南黄海盆地卫星遥感海面温度异常区沿南北向 (123o30′) 呈带状分布,与航磁解释出的南北向分布的东部鼻状隆起吻合较好。由于温度异常区主要分布在南黄海盆地东部鼻状隆起的南北端,故推测东部鼻状隆起的南北端具有较好油气远景。     

The behavior and the role of the anti-cyclonic eddy in the Kuroshio large meander development

The processes underlying the development of the Kuroshio large meanders that occurred in 1986 and 1989 are investigated using a satellite SST data set and hydrographic data. In both processes visible on the satellite SST images, a round-shaped, lower SST region with a diameter of about 200 km is found to the east of the Kuroshio small “trigger” meander (Solomon, 1978) until the region became extinguished near theEnshu Nada. The lower SST region can be interpreted as an anti cyclonic eddy, mainly because of the existence of a warm water mass in the subsurface layer of this region. The warm water mass is characterized by a constant temperature of 18–19°C, the maximum thickness of which is about 400 m. The satellite images show that the eddy is closely related to the Kuroshio path transforming into a shape like the letter “S”. This means that the eddy plays an important role in the development of the Kuroshio large meander since this, too, tends to follow an “S”-shaped path. Added to this, the subsurface layer structure of the eddy is similar to that of the warm water mass offShikoku. This similarity, together with the eddy behavior visible on the satellite SST images, implies that the examined eddy corresponds to the warm water mass offShikoku. In other words, the warm water mass offShikoku can be advected near to theEnshu Nada when the Kuroshio large meander occurs.