Social approach and the Radar Images in the management of the flooding risk in the Danube Delta

The flooding areas, as well as the duration of the floods, have an essential role in the populating and ecology of the humid areas. The possibility of shaping the potential of the floods and of mapping the flooding area, the time and intensity of the phenomenon in different medium conditions is primordial to the understanding of the dynamics of the deltaic systems, as well as the durable management of these areas. The first objective of this paper is to evaluate the capacity of some radar images to detect the flooding areas from the Danube Delta. Different images that have been acquired in C band (? = 5,6 cm), at VV polarization by the ASAR sensor onboard the European ENVISAT satellite were chosen for this study due to their capabilities to discriminate between the soil surfaces with different moisture content and degree flooded areas. These images had been registered before the floods in Spring 2006 (19/04/2006), during the floods (01/05/2006) and after that (08/05/2006). Also, we used images acquired one year later at the same period (13/06/2007). A double fusion of information/images is offered, on the one hand, a fusion among the three images from 2006 and on the other hand, among the three plus the image from 2007. The social approach of the risk problem of flooding in a deltaic medium constitutes the second "chapter" of this paper. An analysis of the perception of flooding risk in the Danube Delta was proposed at different levels : the people's, the authorities' and the scientists' perception. These inquiries have as a main objective to measure the people's awareness towards this phenomenon as well as the culture of the flooding risk. 80 % of the population affected by these floods (2006) were inquired (through semi-direct inquiries and discussions).Les zones inondables et la dur?e des inondations ont un r?le essentiel dans le peuplement et l'?cologie des zones humides. La possibilit? de modeler le potentiel d'inondation et de cartographier la zone inond?e, la dur?e et l'intensit? sous diff?rentes conditions environnementales est essentielle pour la compr?hension de la dynamique des milieux delta?ques, ainsi que pour la gestion durable de ces espaces. Le premier objectif de cette contribution est d'?valuer la capacit? de toute une s?rie d'images radar ? d?tecter les zones inond?es et inondables du Delta du Danube. Des images acquises par le capteur radar ASAR (Advenced Synthetic Aperture radar) ? bord du satellite europ?en ENVISAT, operant en bande C (? = 5,6 cm) et en polarisation VV (polarisation verticale ? l'?mission comme ? la r?ception), ont ?t? choisies pour cette ?tude vu leur capacit? ? identifier les caract?ristiques et les degr?s d'humidit? du sol (tout en sachant que la r?ponse d'un radar sur une zone inond?e peut-?tre tr?s diff?rente de celle d'un sol humide). Ces images ont ?t? prises avant les inondations du printemps 2006 (le 19/04/06), pendant (le 01/05/06) et apr?s (le 08/05/2006), et l'ann?e suivante (le 13/06/2007). Une double fusion des donn?es est propos?e, d'une part, les trois dates de 2006 et, d'autre part, les m?mes dates de 2006 avec l'unique date de 2007. L'approche sociale du risque d'inondation en milieu delta?que constitue le deuxi?me volet de cette contribution. Une analyse de la perception du risque en milieu delta?que a ?t? men?e ? plusieurs niveaux : perception de la population, perception des autorit?s et celle des scientifiques. Ces sondages ont pour objectif de mesurer l'?tat du niveau de sensibilisation et de culture de risque ? inondation ? de la population. 80 % de la population affect?e par ces inondations ont ?t? enqu?t?s (par des enqu?tes semi directives et des entretiens).