Satellite Detected Waters Extent and Evolution in Maroantsetra area, Analanjirofo region, Madagascar

This map illustrates satellite-detected flood waters extent and evolution between 08 and 10 March 2017 over Maroantsetra area, Analanjirofo region in Madagascar as detected by TerraSAR-X radar images acquired on 10 and 08 March 2017. Between 08 and 10 March 2017 and within this map extent, waters receded from about 4,270 ha of lands. Many areas within this zone remain affected and ~6,230 ha of lands were still flooded on the 10 March 2017 whereas ~10,500 ha of lands were flooded the 08 March 2017. It corresponds to about 40% decrease. It is likely that flood waters have been systematically underestimated along highly vegetated areas along main river banks and within built-up urban areas because of the special characteristics of the satellite data used. This is a preliminary analysis and has not yet been validated in the field. Please send ground feedback to UNITAR UNOSAT.

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Date of Dataset Mar 13, 2017
Expected Update Frequency Never

UNOSAT datasets and maps are produced using a variety of methods. In general, analysts closely review satellite imagery, often comparing two or more images together, and determine notable changes between the images. For damage assessments, refugee or IDP assessments, and similar analyses, these changes are then manually documented in the vector data by the analyst. For flood extractions, landcover mapping and similar analyses, a variety of automated remote sensing techniques are used to extract the relevant information which is then reviewed and revised as necessary by the analyst. In all cases, resulting data is then loaded into a standardized UNOSAT geodatabase and exported asshapefiles for dissemination.

Caveats / Comments

This is a preliminary assessment and has not yet been validated in the field. It is important to consider the characteristics of the source imagery used in the analyses when interpreting results. For damage assessments it should be noted that only significant damage to the structural integrity of the buildings analyzed can be seen in imagery, while minor damage such as cracks or holes may not be visible at all. For flood extractions using radar data it is important to note that urban areas and highly vegetated areas may mask the flood signature and result in underestimation of flood waters. Users with specific questions or concerns should contact to seek clarification.