A new automatic oceanic mesoscale eddy detection method using satellite altimeter data based on density clustering

The mesoscale eddy is a typical mesoscale oceanic phenomenon that transfers ocean energy. The detection and extraction of mesoscale eddies is an important aspect of physical oceanography, and automatic mesoscale eddy detection algorithms are the most fundamental tools for detecting and analyzing mesoscale eddies. The main data used in mesoscale eddy detection are sea level anomaly(SLA) data merged by multi-satellite altimeters' data.These data objectively describe the state of the sea surface height. The mesoscale eddy can be represented by a local equivalent region surrounded by an SLA closed contour, and the detection process requires the extraction of a stable closed contour structure from SLA maps. In consideration of the characteristics of mesoscale eddy detection based on SLA data, this paper proposes a new automatic mesoscale eddy detection algorithm based on clustering. The mesoscale eddy structure can be extracted by separating and filtering SLA data sets to separate a mesoscale eddy region and non-eddy region and then establishing relationships among eddy regions and mapping them on SLA maps. This paper overcomes the problem of the sensitivity of parameter setting that affects the traditional detection algorithm and does not require a sensitivity test. The proposed algorithm is thus more adaptable. An eddy discrimination mechanism is added to the algorithm to ensure the stability of the detected eddy structure and to improve the detection accuracy. On this basis, the paper selects the Northwest Pacific Ocean and the South China Sea to carry out a mesoscale eddy detection experiment. Experimental results show that the proposed algorithm is more efficient than the traditional algorithm and the results of the algorithm remain stable. The proposed algorithm detects not only stable single-core eddies but also stable multi-core eddy structures.

Statistical characteristics and thermohaline properties of mesoscale eddies in the Bay of Bengal

The statistical characteristics and vertical thermohaline properties of mesoscale eddies in the Bay of Bengal are studied from the view of satellite altimetry data and Argo profiles.Eddy propagation preferences in different lifetimes,eddy evolution process,and geographical distribution of eddy kinetic properties are analyzed in this area.Eddies exist principally in the western Bay of Bengal,and most of them propagate westward.There is a clear southward(equatorward)preference for eddies with long lifetimes,especially for cyclones.Moreover,the eddies in different areas of the bay show different north-southward preferences.Evolution of eddy kinetic properties with lifetime shows that eddies have the significant three-stage feature:the growth period in the former one-fifth lifetime,the stable period in the middle two-fifth to four-fifth lifetime,and the dying period in the last one-fifth lifetime.Large-amplitude and high-intensity eddies occur only in the relatively confined regions of highly unstable currents,such as the East Indian Coastal Current and eastern Sri Lanka.Based on Argo profile data and climatology data,the eddy synthesis method was used to construct three-dimensional temperature and salt structures of eddies in this area.The mean temperature anomaly is negative/positive to the cyclonic/anticyclonic eddies in the upper 300×10^(4)Pa,and below this depth,the anomaly becomes weak.The salinity structures of positive anomalies inside cyclonic eddies and negative anomalies inside anticyclonic eddies in the Bay of Bengal are not consistent with other regions.Due to the special characteristics of the water mass in the bay,especially under the control of the low-salinity Bay of Bengal water at the surface and the Indian equatorial water in the deep ocean,the salinity of seawater shows a monotonic increase with depth.For regional varieties of temperature and salinity structures,as the eddies move westward,the temperature anomaly induced by the eddies increases,the effecting depth of the eddies deepens,and the salinity structures are more affected by inflows.In the north-south direction,the salinity structures of the eddies are associated with the local water masses,which comprise lowsalinity water in the northern bay due to the inflow of freshwater from rivers and salty water in the southern bay due to the invasion of Arabian Sea high-salinity water from the north Indian Ocean.

Intuitionistic Fuzzy Petri Nets Model Based on Back Propagation Algorithm for Information Services

Intuitionistic fuzzy Petri net is an important class of Petri nets,which can be used to model the knowledge base system based on intuitionistic fuzzy production rules.In order to solve the problem of poor self-learning ability of intuitionistic fuzzy systems,a new Petri net modeling method is proposed by introducing BP(Error Back Propagation)algorithm in neural networks.By judging whether the transition is ignited by continuous function,the intuitionistic fuzziness of classical BP algorithm is extended to the parameter learning and training,which makes Petri network have stronger generalization ability and adaptive function,and the reasoning result is more accurate and credible,which is useful for information services.Finally,a typical example is given to verify the effectiveness and superiority of the parameter optimization method.

Primary Analysis of Oceanic Mesoscale Eddies Observation Abilities by Sentinel-3A SRAL

In this study,the north-western Pacific Ocean of Kuroshio region is selected as the experimental area to analyze the mesoscale eddies observation abilities of Sentinel-3 A SRAL,including the independent detection abilities of Sentinel-3 A SRAL and the improvement of mesoscale eddies detection abilities by data fusion with other satellite altimetry data.The Sentinel-3 A SRAL data are mapped by the spatial-temporal objective analysis method to the sea level anomaly grid data.The mapping errors are analyzed by the comparisons between the grid data of different combinations and along the ground track of Jason-2/3.The independent detection abilities of Sentinel-3 A SRAL are analyzed by the comparison between the grid data and the AVISO MSLA data.On the other hand,through the multi-satellite data fusion of different combinations of Sentinel-3 A altimeter and other satellite altimeters such as Jason-2/3,the mesoscale eddies detection was performed based on the merged sea level anomaly data and the addition of Sentinel-3 A SRAL data for the improvements of mesoscale eddies detection abilities by multi-satellite altimeters are concluded.It is concluded that Sentinel-3 A SRAL has good abilities of mesoscale eddies detection as the combination of Jason-2 and Jason-3,and it is better than that of single altimeter of Jason-2 or Jason-3.

Identification and census statistics of multicore eddies based on sea surface height data in global oceans

This study produced a statistical analysis of multicore eddy structures based on 23 years’ altimetry data in global oceans. Multicore structures were identified using a threshold-free closed-contour algorithm of sea surface height, which was improved for this study in respect of certain technical details. Meanwhile a more accurate definition of eddy boundary was used to estimate eddy scale. Generally, multicore structures, which have two or more closed eddies of the same polarity within their boundaries, represent an important transitional stage in their lives during which the component eddies might experience splitting or merging. In comparison with global eddies, the lifetimes and propagation distances of multicore eddies were found to be much smaller because of their inherent structural instability. However, at the same latitude, the spatial scale of multicore eddies was found larger than that of single-core eddies, i.e., the eddy area could be at least twice as large. Multicore eddies were found to exhibit some features similar to global eddies. For example, multicore eddies tend to occur in the Antarctic Circumpolar Current, some western boundary currents, and mid-latitude regions around 25°N/S, the majority(70%) of eddies propagate westward while only 30% propagate eastward, and large-amplitude eddies are restricted mainly to reasonably confined regions of highly unstable currents.

Preliminary results of the global ocean tide derived from HY-2A radar altimeter data

The HY-2A satellite,which is equipped with a radar altimeter and was launched on August 16,2011,is the first Chinese marine dynamic environmental monitoring satellite.Extracting ocean tides is one of the important applications of the radar altimeter data.The radar altimeter data of the HY-2A satellite from November 1,2011 to August 16,2014 are used herein to extract global ocean tides.The constants representing the tidal constituents are extracted by HY-2A RA data with harmonic analysis based on the least squares method.Considering tide aliasing issues,the analysis of the alias periods and alias synodic periods of different tidal constituents shows that only the tidal constituents M_(2),N_(2),and K_(2)are retrieved precisely by the HY-2A RA data.The derived tidal constants of the tidal constituents M_(2),N_(2)and K_(2)are compared to those of tidal gauge data and the TPXO tide model results.The comparison between the derived results and the tidal gauge data shows that the RMSEs of the tidal amplitude and phase lag are 9.6 cm and 13.34°,2.4 cm and 10.47°,and 8.1 cm and 14.19°for tidal constituents M_(2),N_(2),and K_(2),respectively.The comparisons of the semidiurnal tides with the TPXO model results show that tidal constituents have good consistency with the TPXO model results.These findings confirm the good performance of HY-2A RA for retrieving semidiurnal tides in the global ocean.

Shallow sea topography detection using fully Polarimetric Gaofen-3 SAR data based on swell patterns

Compared to single-polarization synthetic aperture radar(SAR)data,fully polarimetric SAR data can provide more detailed information of the sea surface,which is important for applications such as shallow sea topography detection.The Gaofen-3 satellite provides abundant polarimetric SAR data for ocean research.In this paper,a shallow sea topography detection method was proposed based on fully polarimetric Gaofen-3 SAR data.This method considers swell patterns and only requires SAR data and little prior knowledge of the water depth to detect shallow sea topography.Wave tracking was performed based on preprocessed fully polarimetric SAR data,and the water depth was then calculated considering the wave parameters and the linear dispersion relationships.In this paper,four study areas were selected for experiments,and the experimental results indicated that the polarimetric scattering parameterαhad higher detection accuracy than quad-polarization images.The mean relative errors were 14.52%,10.30%,12.56%,and 12.90%,respectively,in the four study areas.In addition,this paper also analyzed the detection ability of this model for different topographies,and the experiments revealed that the topography could be well recognized when the topography gradient is small,the topography gradient direction is close to the wave propagation direction,and the isobath line is regular.