Ocean classification of dynamical structures detected by SAR and spectral methods

We discuss a taxonomy of different dynamical featuresin the ocean surface and provide some eddy and frontstatistics, as well as describing some events detected byseveral satellites and even with additional cruise observationsand measurements, in the North-west MediterraneanSea area between 1996 and 2012. The structureof the flows are presented using self-similar traces thatmay be used to parametrize mixing at both limits of the Ross by Deformation Radius scale, RL. Results showthe ability to identify different SAR signatures and at thesame time provide calibrations for the different local configurationsof vortices, spirals, Langmuir cells, oil spillsand tensioactive slicks that eventually allow the study ofthe self-similar structure of the turbulence. Dependingon the surface wind and wave level, and also on the fetch.the bathimetry, the spiral parameters and the resolution of vortical features change. Previous descriptions did not includethe new wind and buoyancy features. SAR imagesalso show the turbulence structure of the coastal area andthe Regions of Fresh Water Influence (ROFI). It is not eworthytt such complex coastal fielddependent behavioris strongly influenced by stratification and rotation of theturbulence spectrum is observed only in the range smallerthan the local Ross by deformation radius, RL. The measuresof diffusivity from buoy or tracer experiments areused to calibrate the behavior of different tracers and pollutants,both natural and man-made in the NW MediterraneanSea. Thanks to different polarization and intensitylevels in ASAR satellite imagery, these can be usedto distinguish between natural and man-made sea surfacefeatures due to their distinct self-similar and fractal as afunction of spill and slick parameters, environmental conditionsand history of both oil releases and weather conditions.Eddy diffusivity map derived from SAR measurementsof the ocean surface, performing a feature spatialcorrelation of the available images of the region are presented.Both the multi fractal discrimination of the localfeatures and the diffusivity measurements are importantto evaluate the state of the environment. The distributionof meso-scale vortices of size, the Ross by de for mationscale and other dominant features can be used to distinguishfeatures in the ocean surface. Multi-fractal analysisis then very use full. The SAR images exhibited a largevariation of natural features produced by winds, internalwaves, the bathymetric distribution, by convection, rain,etc as all of these produce variations in the sea surfaceroughness so that the topological changes may be studiedand classified. In a similar way bathimetry may bestudied with the methodology described here using thecoastline and the thal wegs as generators of local verticalvorticity.Peer ReviewedPreprin

Multiscale analysis of SAR from the earth surface

The use of Synthetic Aperture Radar (SAR) to investigate the earth’s surface provides a wealth of useful information. Here we will discuss some recent fractal and multi-fractal techniques used to identify oil spills and the dynamic state of the Ocean as well as the mountain structures in the solid earth. It is important both in the Ocean and in the Atmosphere to be able to parametrize mixing at the Rossby Deformation Radius scale (i.e. most energetic eddy scale) to aid in the prediction of pollutant dispersion. Results presented here aim to identify different SAR signatures and at the same time provide calibrations for the different local configurations that allow to predict the behaviour of different tracers in the sea surface, in the atmosphere or in the earth. We also compare different SAR images of the Eastern Pyrenees, evaluating the changes in structure as a function of average height. The multiple correlations between HH HV VV polarizations and the images are used to calculate the fractal dimension with the Box-Counting method. The distribution of the boxes is accomplished systematically for each SAR intensity level, ρ the intersection of these boxes with the images gives N(ρ) boxes with a non void intersection, which may be compared with the standard multifractal formalism.Postprint (author’s final draft

Turbulent structure in environmental flows: effects of stratification and rotation

Several series of experiments in stratified and in rotating/stratified decaying flows after a grid is used to stir the two layer stable fluid brine and fresh water set up. We measure by comparing the gained potential energy with the available kinetic energy AKE, the relative efficiency of mixing. The experiments in stratified rotating flows with grid driven turbulence were both periodic (quasi stationary) and non-monotonic (decaying) forcing. This thesis compares experimental, numerical and field observations on the structure and Topology of the Stratified Rotating Flows as well as their decay, the horizontal spectra changes appreciable with slopes from 1.1 to 5, but vorticity and local circulation, and also the initial topology and forcing of the flow. A detailed study of the vorticity decay and vortex and energy structure has been performed, the new results show that neither stratified nor rotating flows exhibit pure 2D structures. The work parameterizes the role of the Richardson number and the Rossby number, both in the experiments and in the ocean visualizations is very important. The conditions of vortex decay show the effects of the internal waves in the decay turbulent conditions both for stratified and rotating flows. The parameter space (Re,Ri,Ro) has been used to interpret many previously disconnected explanations of the 2D-3D turbulent behaviour. The comparison of numerical simulations with experiments has allowed implementing new theoretical aspects of the interaction between waves and vortices finding the surprising and very interesting result that these interactions depend on the level of enstrophy. This also leads to new ways of using multifractal analysis ad intermittency in ocean environmental observations. A large collection of SAR images obtained from three European coastal areas were used for routine satellite analysis by SAR and other sensors, which seem very important to build seasonal databases of the dynamic conditions of ocean mixing. The topology of the basic flow is very important and in particular the topology of the vortices and their decay which depends on ambient factors such as wave activity, wind and currents. We find more realistic estimates of the spatial/temporal non-homogeneities (and intermittency obtained as spatial correlations of the turbulent dissipation); these values are used to parameterize the sea surface turbulence, as well as a laboratory experiments at a variety of scales. Using multi-fractal geometry as well, we can establish now a theoretical pattern for the turbulence behaviour that is reflected in the different descriptors. Vorticity evolution is smoother and different than that of scalar or tracer density. The correlation between the local Ri and the fractal dimension detected from energy or entropy is good. Using multi-fractal geometry we can also establish certain regions of higher local activity used to establish the geometry of the turbulence mixing that needs to be studied in detail when interpreting the complex balance between the direct 3D Kolmogorov type cascade and the Inverse 2D Kraichnan type cascade

The structure of turbulent jets, vortices and boundary layer: Laboratory and field observations

The main aim of this work is research, understand and describe key aspects of the turbulent jets and effects connected with them such as boundary layer interactions or the effect of a 2D geometry. Work is based principally on experiments but there are also some comparisons between experimental and field results. A series of experiments have been performed consisting in detailed turbulent measurements of the 3 velocity components to understand the processes of interaction that lead to mixing and mass transport between boundaries and free shear layers. The turbulent wall jet configuration occurs often in environmental and industrial processes, but here we apply the laboratory experiments as a tool to understand jet/boundary interactions in the environment. We compare the structure of SAR (Synthetic Aperture Radar) images of coastal jets and vortices and experimental jets (plumes) images searching for the relationship between these two kinds of jets at very different Reynolds numbers taking advantage of the self-similarity of the processes. In order to investigate the structure of ocean surface detected jets (SAR) and vortices near the coast, we compare wall and boundary effects on the structure of turbulent jets (3D and 2D) which are non-homogeneous, developing multifractal and spectral techniques useful for environmental monitoring in space

Comparative detections of oil spill using multimode radarsat-1 synthetic aperture radar satellite data

Oil spill or leakage into waterways and ocean spreads very rapidly due to the action of wind and currents. The study of the behavior and movement of these oil spills in sea had become imperative in describing a suitable management plan for mitigating the adverse impacts arising from such accidents. But the inherent difficulty of discriminating between oil spills and look-alikes is a main challenge with Synthetic Aperture Radar (SAR) satellite data and this is a drawback, which makes it difficult to develop a fully automated algorithm for detection of oil spill. As such, an automatic algorithm with a reliable confidence estimator of oil spill would be highly desirable. The main objective of this work is to develop comparative automatic detection procedures for oil spill pixels in multimode (Standard beam S2, Wide beam W1 and fine beam F1) RADARSAT-1 SAR satellite data that were acquired in the Malacca Straits using three algorithms namely, textures using cooccurrence matrix, post supervised classification, and neural network (NN) for oil spill detection with window size 7 x 7. The results show that the mean textures from co-occurrence matrix is the best indicator for oil spill detection as it can discriminate oil spill from its surrounding such as look-alikes, sea surface and land. The entropy and contrast textures can be mainly used for look-like detections. The receiver operator characteristic (ROC) was used to determine the accuracy of oil spill detection from RADARSAT-1 SAR data. The results show that oil spills, lookalikes, and sea surface roughness are perfectly discriminated with an area difference of 20% for oil spill, 35% look–alikes, 15% land and 30% for the sea roughness. The NN shows higher performance in automatic detection of oil spill in RADARSAT-1 SAR data as compared to other algorithms with standard deviation of 0.12. It can therefore be concluded that NN algorithm is an appropriate algorithm for oil spill automatic detection and W1 beam mode is appropriate for oil spill and look-alikes discrimination and detection

SAR Analysis of the ocean surface : aplication to the NW mediterranean marine pollution and dynamic features

The interaction between multiple scales in nature and mainly in turbulent flows produces fractals or multifractal structures. We use multi-fractal analysis to investigate the scales and influence of stratification in different types of surface eddies in the ocean, and specially, near the coastline. We will also show and discuss the structure and residence time in oil spills and slicks in the ocean surface. This method, of multifractal analysis on the intensity SAR signals, as an example will also be applied to experiments of unstable mixing fronts driven by Rayleigh-Taylor Instabilities. These hydrodynamic instabilities are a fundamental buoyancy or acceleration driven mixing process since they are the main causes of mixing and regulate for example the overturning process. A turbulent model is used in order to study the self-similar mixing process. The results are parameterized in terms of the Atwood number, which in terms of initial condition evaluation seems more convenient than using reduced gravity or buoyancy flux. The advance of the mixing front can be compared to several laboratory and field measurements, showing the effects of the initial perturbations and the two-dimensionality and boundary conditions of a model that combines 3 and 2 dimensional effects. The multi-fractal analysis reflects the flow conditions and allows us to understand further the mixing processes.Postprint (published version

Investigation of the microwave signatures of the Baltic Sea ice

It is essential for winter shipping in the Baltic Sea to get reliable and up-to-date information of its rapidly changing ice conditions. Spaceborne synthetic aperture radar (SAR) images are the only way to produce this information operationally in fine scale independent of daylight and nearly independent of weather conditions. Currently, classification algorithms for the RADARSAT-1 and ENVISAT SAR images utilize mainly the image structure and only limited information on sea ice geophysics and empirical statistics of backscattering signatures of various ice types are utilized. Therefore, interpretation of the classification results is often difficult. Both classification results and their interpretation should very likely improve with the addition of this information. Spaceborne microwave radiometer data are not suitable for the operational Baltic Sea ice monitoring aiding ship navigation due to their coarse spatial resolution, but they can provide an independent data source on the sea ice conditions for validation of the SAR classification algorithms. Both SAR and radiometer data based sea ice products can also be utilized in the geophysical studies of the Baltic Sea ice. In order to support development of operational classification algorithms for SAR and radiometer data, basic research on the microwave remote sensing of the Baltic Sea ice has been conducted in this work. The research work included the following topics: (1) statistics of C- and X-band backscattering signatures of various ice types, (2) statistics of L- and C-band polarimetric discriminants of various ice types, (3) radar incidence angle dependence of backscattering coefficient (σ°) in RADARSAT-1 SAR images, (4) dependence between standard deviation and measurement length for σ° signatures and its usability in sea ice classification, (5) comparison between SAR σ° time series and results from a thermodynamic snow/ice model, and (6) statistics of passive microwave signatures of various ice types. Additionally, a comprehensive literature review of the previous work on the microwave remote sensing of the Baltic Sea ice is presented. The main results of this work include the following. It is not possible to discriminate open water and various ice types using the level of σ°, co- or cross-polarization ratio, or standard deviation of σ°. C-band VH-polarized σ° at high incidence angle provides slightly better ice type discrimination accuracy than any other combination of C- and X-band radar parameters. VH-polarization is more suitable for estimating the degree of ice deformation than co-polarizations. Snow wetness has a large effect on the σ° statistics. Notably, when snow cover is wet then the σ° contrasts between various ice types are smaller than in the dry snow case. Incidence angle dependence of the C-band HH-polarized σ° was derived for level ice and deformed ice. It is utilized in the operational SAR classification algorithms developed by Finnish Institute of Marine Research. The method for deriving the σ° incidence angle dependence is applicable for any SAR sensor. There is a large variation of level ice σ° with changing weather conditions. A 1-D high-resolution thermodynamic snow/ice model generally helps to interpret changes in the σ° time series. The modeled snow and ice surface temperature, cases of snow melting, and evolution of snow and ice thickness are related to the changes in σ°. It was found out that the standard deviation of σ° for various ice types depends on the length of measurement. This may be utilized in the SAR image classification. It is not possible to resolve concentrations of thin new ice and all other ice types combined in the Baltic Sea using radiometer data as has been done for the Arctic seasonal ice zones.Talvimerenkulku Itämerellä tarvitsee luotettavaa ja ajantasaista informaatiota Itämeren nopeasti muuttuvista jääoloista. Synteettisen apertuurin tutkan (SAR) kuvat ovat ainoa tapa tuottaa operatiivisesti tarvittavaa jääinformaatiota riippumatta päivänvalon määrästä ja lähes riippumatta sääolosuhteista. RADARSAT-1 ja ENVISAT SAR-tutkakuvien luokittelualgoritmit perustuvat tällä hetkellä lähinnä kuvien rakenteeseen, eikä merijään geofysiikkaa ja empiiristä tilastotietoa eri jäätyyppien sirontavasteista hyödynnetä kuin rajallisesti. SAR-kuvien luokittelutulosten tulkitseminen on siten usein vaikeaa. Sekä itse luokittelutulokset, että niiden tulkinta parantuisivat, jos luokittelualgorimit hyödyntäisivät edellä mainittua tietoa. Satelliittiradiometrien kuvat eivät sovellu Itämeren jään operatiiviseen monitorointiin niiden karkean spatiaalisen resoluution vuoksi. Niillä kuitenkin voitaisiin validoida SAR-kuvien luokittelualgoritmeja, koska ne ovat SAR-kuvista riippumaton datalähde Itämeren jääoloista. Tässä työssä on suoritettu seuraavaa perustutkimusta Itämeren jään mikroaaltokaukokartoituksessa, minkä tarkoituksena on tukea SAR- ja radiometrikuvien operatiivisten luokittelualgoritmien kehitystyötä: (1) eri jäätyyppien C- ja X-kanavien sirontakertoimien (σ°) statistiikka, (2) eri jäätyyppien L- ja C-kanavien polarimetristen diskriminanttien statistiikka, (3) σ°:n mittauskulmariippuvuus RADARSAT-1 SAR-kuvissa, (4) σ°:n keskihajonnan ja mittausmatkan välinen riippuvuus ja hyödyntäminen jäätyyppiluokittelussa, (5) SAR-kuvien sirontakerroinaikasarjojen vertailu merijään termodynamiikkamalliin, ja (6) eri jäätyyppien kirkkauslämpötilojen statistiikka. Työssä saavutettiin seuraavia merkittäviä tuloksia. Eri jäätyyppien ja avoveden luokittelu ei ole mahdollista käyttäen sirontakerrointa, yhdensuuntais- ja ristipolarisaatiosuhdetta tai σ° keskihajontaa. C-kanavan VH-polarisaation σ° suurella mittauskulmalla luokittelee eri jäätyypit hieman paremmin kuin mikään muu C- ja X-kanavan tutkaparametrikombinaatio. Merijään deformoitumisasteen estimointiin sopii paremmin VH-polarisaation σ° kuin yhdensuuntaispolarisaation. Lumipeitteen kosteudella on suuri vaikutus sirontakerroinstatistiikkaan; erityisesti, kun lumipeite on märkä on sirontakerroinkontrasti eri jäätyyppien välillä pienempi kun lumipeite on kuiva. C-kanavan HH-polarisaation σ°:n mittauskulmariippuvuus määritettiin tasaiselle ja deformoituneelle jäälle. Mittauskulmariippuvuuden laskentamenetelmää voidaan käyttää mille tahansa SAR-tutkakuvalle. Muuttuvat sääolosuhteet aiheuttavat suuria muutoksia tasaisen jään σ°:ssa. Merijään termodynamiikkamalli yleensä auttaa selittämään muutoksia σ°:n aikasarjassa. σ°:n muutokset ovat yhteydessä termodynamiikkamallilla laskettuihin lumen ja jään parametreihin. σ°:n keskihajonnan havaittiin riippuvan etäisyydestä. Tätä riippuvuutta voitaneen hyödyntään SAR-kuvien luokittelussa. Itämerellä satelliittiradiometridatalla pystytään määrittämään vain merijään kokonaiskonsetraatio, toisin kuin arktisten merien kausiluontoisilla merijääalueilla, missä myös eri jäätyyppien konsentraatioiden määrittäminen on mahdollista.reviewe