Retrieving ocean surface current by 4-D variational assimilation of sea surface temperature images

In this article we propose a new method to estimate ocean mesoscale structures of the surface current velocity by processing sea surface satellite images. Assuming that the intensity level can be described by a transport-diffusion equation, the proposed approach is based on variational assimilation of image observations within a simple transport-diffusion model. This approach permits to retrieve the current velocity field from a sequence of satellite images. Results of processing synthetic data and real NOAA-AVHRR satellite images are presented and commented.     

Satellite observations of circulation features associated with a bowhead whale feeding ‘hotspot’ near Barrow, Alaska

Satellite images, along with oceanographic, meteorological, and whale aerial survey data, are used to illustrate aspects of ocean circulation associated with a bowhead whale feeding ‘hotspot’ near Barrow, Alaska. In response to weak winds, a strong front forms near the shelf-break along the southern edge of Barrow Canyon when the Alaska Coastal Current flows adjacent to the southern flank of Barrow Canyon or intrudes onto the western Beaufort shelf. This front is of particular local interest because it is indicative of aggregation and retention of zooplankton on the western Beaufort shelf and, as a result, is a locus for bowhead whales pausing to feed during their westward fall migration. Groups (4 or more individuals) of bowhead whales are primarily seen on the western Beaufort shelf following wind conditions that promote the formation of this front.     

A Lagrangian model for tracking surface spills and SaR operations in the ocean

An operational model for tracking surface objects in the ocean is presented. Contrary to most of traditional Lagrangian Particle Tracking Algorithms, the presented approach computes the probability density function from the final position of a set of neutrally buoyant particles deployed in the flow providing the area of accumulated probability. The model departs from daily predictions of ocean surface currents, winds and waves provided by an Operational Forecasting System, and integrates the Eulerian velocities to obtain the trajectory of each particle forward in time. A random walk term is added to simulate numerical diffusivity. Several tests are performed in order to determine the optimal numerical scheme as well as the computational time step. To show the performance of the model we simulate the trajectories of a set of SVP-drifters deployed in the Balearic Sea. For these experiments, the final position of the drifters laid within the modeled contour of 50% of accumulated probability for the first 24 h forecast.     

CFOSAT散射计几何定位验证与精度初步评估

采用STK软件对中法海洋卫星（CFOSAT）散射计几何定位算法进行了验证。针对CFOSAT散射计扇形波束扫描观测体制,分别就扇形波束扫描散射计几何定位原型算法、包含天线安装误差的完整几何定位算法利用STK进行了详细验证。结果表明了CFOSAT扇形波束散射计几何定位算法的准确性,与STK几何定位结果偏差在100 m以内。在此基础上,结合有源定标器实验数据,对CFOSAT实际观测数据几何定位参数进行了校正,给出了CFOSAT散射计几何定位精度的初步评估。     

浅谈《化学海洋学实验》教学改革

通过近几年在《化学海洋学实验》教学中的一些归纳和总结,为了提高学生的创新意识和动手能力,全面提高学生的综合素质,从实验教学课程的设计、教学方法的改革和考核方式等方面探讨《化学海洋学实验》教学改革的思路和方法。     

ARGO遥感数据结构分析及快速读取方法

支持ARGO 计划的地理信息系统平台能分析处理海量的海洋信息。但对ARGO 数据结构进行分析和读取方法介绍的资料文献很少。在开发自主的支持ARGO 数据的地理信息系统处理平台中, 读取ARGO 数据是一项最基本和重要的工作。在分析了ARGO 数据物理存储结构后, 给出了读取ARGO 数据的方法实例。     

Feasibility of the Zero-V: A zero-emissions hydrogen fuel-cell coastal research vessel

A study is presented to determine the technical, regulatory, and economic feasibility of a coastal research vessel (named the “Zero-V”) powered solely by hydrogen fuel cells. Feasibility is examined in the context of science mission profiles of particular significance in coastal oceanography that require a modern, capable, general-purpose coastal research vessel. These missions translate into the primary Zero-V vessel requirements against which technical feasibility is assessed. Hull form analysis indicated a trimaran design enables a vessel that can meet all of the space and volume requirements as well as for fitment of the machinery, service, and control spaces necessary for operation of the vessel. To meet speed and range (endurance) requirements, the vessel needs to be constructed of aluminum to reduce weight. The beam (56 feet), length (170 feet) and draft (12 feet) of the vessel enable it to dock at all primary ports of call. With 1800 kW of installed proton exchange membrane (PEM) fuel-cell power for primary propulsion, the cruising speed is 10 knots. With 10,900 kg of consumable LH₂ stored in two LH₂ tanks, the range of the vessel is 2400 nautical miles, with an endurance of 15 days. Both the greenhouse gas (GHG) and criteria pollutant (NO_x, HC, PM₁₀) emissions were estimated based on a complete “well-to-waves” (WTW) analysis. Using renewable hydrogen, the annual WTW GHG emissions predicted for the Zero-V are 91.4% less than those from an equivalent vessel running on conventional diesel fuel. Analysis of the WTW criteria pollutant emissions show that hydrogen PEM fuel-cell technology can reduce these emissions below stringent U.S. Environmental Protection Agency (EPA) Tier 4 marine diesel engine emissions limits regardless of whether the hydrogen is made using natural gas or renewable methods.The capital construction cost is estimated to be ~ $79 M, not unreasonable when compared to other modern diesel-fueled research vessels of similar size and capabilities. The operations and maintenance (O&M) costs of the Zero-V were estimated to be 7.7% higher than operating the equivalent diesel-fueled vessel at the assumed fuel prices for LH₂ made from steam reforming of fossil natural gas. The approach to safety for the Zero-V is described in terms of the arrangement of hazardous areas on the vessel. Regulatory review of the vessel design by the United States Coast Guard (USCG) and the Class society DNV GL found no fundamental or “show-stopping” design concerns that would prevent eventual deployment of the Zero-V. Overall, this study found it feasible from technical, regulatory, and economic perspectives to design, build and operate a coastal research vessel powered solely by hydrogen fuel cells.     

Illustrative Visualization of Mesoscale Ocean Eddies

Feature‐based time‐varying volume visualization is combined with illustrative visualization to tell the story of how mesoscale ocean eddies form in the Gulf Stream and transport heat and nutrients across the ocean basin. The internal structure of these three‐dimensional eddies and the kinematics with which they move are critical to a full understanding of ocean eddies. In this work, we apply a feature‐based method to track instances of ocean eddies through the time steps of a high‐resolution multi‐decadal regional ocean model and generate a series of eddy paths which reflect the life cycle of individual eddy instances. Based on the computed metadata, several important geometric and physical properties of eddy are computed. Illustrative visualization techniques, including visual effectiveness enhancement, focus+context, and smart visibility, are combined with the extracted volume features to explore eddy characteristics at different levels. An evaluation by domain experts indicates that combining our feature‐based techniques with illustrative visualization techniques provides an insight into the role eddies play in ocean circulation. The domain experts expressed a preference for our methods over existing tools.     

Visualization and Analysis of Eddies in a Global Ocean Simulation

We present analysis and visualization of flow data from a high‐resolution simulation of the dynamical behavior of the global ocean. Of particular scientific interest are coherent vortical features called mesoscale eddies. We first extract high‐vorticity features using a metric from the oceanography community called the Okubo‐Weiss parameter. We then use a new circularity criterion to differentiate eddies from other non‐eddy features like meanders in strong background currents. From these data, we generate visualizations showing the three‐dimensional structure and distribution of ocean eddies. Additionally, the characteristics of each eddy are recorded to form an eddy census that can be used to investigate correlations among variables such as eddy thickness, depth, and location. From these analyses, we gain insight into the role eddies play in large‐scale ocean circulation.     

Mediterranean Balloon Experiment: ocean wind speed sensing from the stratosphere, using GPS reflections

The MEditerranean Balloon EXperiment (MEBEX), conducted in August 99 from the middle-up stratosphere, was designed to assess the wind retrieval sensitivity of Global Navigation Satellite Systems Reflections (GNSSR) technology from high altitudes. Global Positioning System reflected signals (GPSR) collected at altitudes around 37 km with a dedicated receiver have been inverted to mean square slopes (MSS) of the sea surface and wind speeds. The theoretical tool to interpret the geophysical parameters was a bistatic model, which also depends on geometrical parameters. The results have been analyzed in terms of internal consistency, repeatability and geometry-dependent performance. In addition, wind velocities have been compared to independent measurements by QuikSCAT, TOPEX, ERS/RA and a Radio Sonde, with an agreement better than 2 m/s. A Numerical Weather Prediction Model (NWPM, the MM5 mesoscale forecast model) has also been used for comparison with varying results during the experiment. The conclusion of this study confirms the capability of high altitude GPSR/Delay-map receivers with low gain antennas to infer surface winds.