A SIMPLE AND EFFICIENT APPROACH FOR COARSE SEGMENTATION OF MOROCCAN COASTAL UPWELLING

International audienceIn this work, we aim to develop a simple and fast algorithm using conventional methods in images segmentation for the automatic detection and extraction of upwelling areas, in the coastal region of Morocco, from the sea surface temperature (SST) satellite images. Our approach is based on the evalua- tion and comparison between two unsupervised classification methods, Otsu and Fuzzy C-means, and explores the appli- cability of these methods to our classification problem. The latter consists in coarse detection of the main thermal front that separates coastal cold upwelling waters from the remain- ing ocean waters. The algorithm has been applied and val- idated by an oceanographer over a database of 66 SST im- ages corresponding to southern Moroccan coastal upwelling of the years 2004, 2005, 2007 and 2009. The results indicate that the proposed algorithm revealed is promising and reli- able on different upwelling scenarios and for a wide variety of oceanographic conditions

An Efficient Tool for Automatic Delimitation of Moroccan Coastal Upwelling Using SST Images

International audienceAn unsupervised classification method is developed for the coarse segmentation of Moroccan coastal upwelling using the Sea Surface Temperature (SST) satellite images. The algorithm is started with the generation of c-partitioned labeled image using Otsu's method for the purpose of finding regions of homogenous temperatures. Then two well-known validity indices are used to select the c-partition which best reproduce the shape of upwelling area. A region-growing algorithm is developed that is used to remove the noisy structures in the offshore waters not belonging to the upwelling area. The algorithm is used to provide a seasonal variability of upwelling activity in the southern Moroccan Atlantic coast using 70 SST images of the years 2007 and 2008. The performance of the proposed methodology has been validated by an oceanographer, showing its effectiveness for automatic delimitation of Moroccan upwelling region

A Simple Tool for Automatic Extraction of Moroccan Coastal Upwelling from Sea Surface Temperature Images

International audienceThis work aims at automatically identify and ex- tract the region covered by the upwelling waters in the costal ocean of Morocco using the well known region-growing segmen- tation algorithm. The later consists in coarse segmentation of upwelling area which characterized by cold and usually nutrient- rich water near the coast. The complete system has been validated by an oceanographer over a database of 30 Sea Surface Tem- perature (SST) satellite images of the year 2007 obtained from Advanced Very High Resolution Radiometer (AVHRR) sensor onboard NOAA-18 satellite serie, demonstrating its capability and effectiveness to reproduce the shape of upwelling area

On Detectability of Moroccan Coastal Upwelling in Sea Surface Temperature Satellite Images

International audienceThis work aims at automatically identify the upwelling areas in coastal ocean of Morocco using the Sea Surface Temperature (SST) satellite images. This has been done by using the fuzzy clustering technique. The proposed approach is started with the application of Gustafson-Kessel clustering algorithm in order to detect groups in each SST image with homogenous and non-overlapping temper-ature, resulting in a c-partitioned labeled image. Cluster validity indices are used to select the c-partition that best reproduces the shape of upwelling areas. An area opening technique is developed that is used to filter out the residuals noise and fine structures in offshore waters not belonging to the upwelling regions. The de-veloped algorithm is applied and adjusted over a database of 70 SST images from years 2007 and 2008, covering the southern part of Moroccan atlantic coast. The system was evaluated by an oceanographer and provided acceptable results for a wide variety of oceanographic conditions

Robust Detection of the North-West African Upwelling From SST Images

International audienceAnalysis and study of coastal upwelling using sea surface temperature (SST) satellite images is a common procedure because of its coast effectiveness (economic, time, frequency, and manpower). Developing on the Ekman theory, we propose a robust method to identify the upwelling regions along the northwest African margin. The proposed method comes to overcome the issues encountered in a recent method devoted for the same purpose and for the same upwelling system. Afterward, we show how our method can serve as a framework to study and monitor the spatio-temporal variability of the upwelling phenomenon in the studied region

Detection of Moroccan coastal upwelling using sea surface chlorophyll concentration

International audienceThe aim of this work is to automatically identify and extract the upwelling area in the coastal ocean of Morocco using the satellite observation of chlorophyll concentration. The algorithm starts by the application of FCM algorithm for the purpose of finding regions of homogeneous concentration of the chlorophyll, resulting in c-partitioned labeled images. A region­ growing algorithm is then used to filter out the noisy structures in the offshore waters not belonging to the upwelling regions. The proposed methodology has been validated by an oceanographer and tested over a database of 166 weekly Sea Surface chlorophyll data. The region of interst cover the southern part of Moroccan atlantic coast spanning from the years 2007 to 2012

Automatic Detection of Moroccan Coastal Upwelling Zones using Sea Surface Temperature Images

International audienceAn efficient unsupervised method is developed for automatic segmentation of the area covered by upwelling waters in the coastal ocean of Morocco using the Sea Surface Temperature (SST) satellite images. The proposed approach first uses the two popular unsupervised clustering techniques, k-means and fuzzy c-means (FCM), to provide different possible classifications to each SST image. Then several cluster validity indices are combined in order to determine the optimal number of clusters, followed by a cluster fusion scheme, which merges consecutive clusters to produce a first segmentation of upwelling area. The region-growing algorithm is then used to filter noisy residuals and to extract the final upwelling region. The performance of our algorithm is compared to a popular algorithm used to detect upwelling regions and is validated by an oceanographer over a database of 92 SST images covering each week of the years 2006 and 2007. The results show that our proposed method outperforms the latter algorithm, in terms of segmentation accuracy and computational efficiency

Detection of Moroccan Coastal Upwelling Fronts in SST Images using the Microcanonical Multiscale Formalism

International audienceNonlinear signal processing using the Microcanonical Multiscale Formalism (MMF) is used to the problem of detecting and extracting the upwelling fronts in coastal region of Morocco using Sea Sur- face Temperature (SST) satellite images. The algorithm makes use of the Singularity Exponents (SE), computed in a microcanonical framework, to detect and analyze the critical transitions in oceano- graphic satellite data. The objective of the proposed study is to develop a helpful preprocessor that transforms SST images into clean and simple line drawing of upwelling fronts as an input to a subse- quent step in the analysis of SST images of the ocean. The method is validated by an oceanographer and it is shown to be superior to that of an automatic algorithm commonly used to locate edges in satellite oceanographic images. The proposed approach is applied over a collection of 92 SST images, covering the southern Moroccan Atlantic coast of the years 2006 and 2007. The results indicate that the approach is promising and reliable for a wide variety of oceanographic conditions

Segmentation et classification des images satellitaires : application à la détection des zones d’upwelling côtier marocain et mise en place d’un logiciel de suivi spatiotemporel

The knowledge of the upwelling systems is very important for many applications in geophysical and oceanographic.The remotely sensed images acquired in real time allow to conduct continuous space maritime monitoring, especially in thermal and visible range, which provide information about the temperature distribution in the sea surface and the ocean colour. In this work, we are interested on the study of the upwelling phenomenon using the sea surface temperature images which is considered to be the origin of the formation of many ocean structures, such as thermal fronts, filaments, meanders and eddies. The main aim is to improve the visual interpretations of the satellite images made by the oceanographers. The proposed approach is based on the segmentation and detection of the thermal mesoscale structures in coastal upwelling waters using several methods in image processing and computer vision. In addition, the images processing methods based on the statistical physics and thermodynamics concepts were also used for the purpose of highlighting the turbulent and complex character of the marine phenomena. In this sense, the singularities points detected in infrared images, using the Microcanonical Multifractal Formalism, contain key information to understandingintermittencyandoceanicturbulence. A computational software system for the calculation of the upwelling index is made available for users in orders to extract and monitor the intensity and extension of upwelling along the Moroccan Atlantic coast. This application allows providing users continually by space synthetic products informing about environmental parameters and permitting to evaluate and to survey the coastal upwelling dynamic in space and time. Finally, a statistical study has been conducted in order to monitor the seasonal variability of the upwelling intensity along the Moroccan Atlantic coast by using well-established upwelling indices and consequently highlight the areas of highupwelling activity.La connaissance des systèmes d’upwelling est d’un grand intérêt pour nombre d’applications géophysiques et océanographiques. Les images satellites acquises en temps réel permettent d’avoir une surveillance continue de l’espace maritime, notamment dans le domaine thermique et visible délivrant des informations respectivement sur la distribution des températures à la surface de la mer et sur la couleur de l’eau. Dans ce travail, nous nous sommes intéressés à la caractérisation et l’étude du phénomène d’upwelling, à partir des images de température de surface de la mer, qui est à l’origine de la formation de nombreuses structures océaniques, telles que les fronts thermiques, les filaments, les méandres, et les tourbillons. Le but est d’améliorer les interprétations visuelles des images par des océanographes qui restent souvent subjectives. La démarche proposée consiste à relier les problèmes de détection des structures thermiques dans les eaux côtières d’upwelling à des concepts théoriques de traitement d’images et de vision par ordinateur. Il s’agit notamment d’utiliser des méthodes de segmentation. Par ailleurs, des méthodes de traitement d’images non linéaires, basées sur des concepts de physique statistique et de thermodynamique, ont été utilisées pour la mise en évidence de la turbulence océanographique caractérisant le régime chaotique des phénomènes complexes marins. Ainsi, les points de singularités détectés dans les images infrarouges, en utilisant le formalisme multifractal microcanonique, contiennent des informations clés à la compréhension de ces notions de turbulence et d’intermittence océanique. Ensuite, un applicatif de calcul d’indices d’upwelling est mise à la disposition des utilisateurs afin d’extraire et de suivre l’évolution de l’intensité et de l’extension d’upwelling sur la côte marocaine. Cet applicatif permet de suivre à la fois en temps réel et d’analyser les séries temporelles des variations de ce phénomène. Enfin, une étude statistique a permis de faire un suivi de la variabilité saisonnière de l’intensité de l’upwelling sur la côte atlantique marocaine tout en mettant en évidence les caractéristiques spatio-temporelles de ce phénomène via des indices établis à cet effet. Cette analysea permis de mettre en évidence les zones de forte activité d’upwelling et les poids des processus à l’origine du phénomène d’upwelling