Satellite Detected Surface Waters Extent and Evolution in Niamey, Niger

✦ DISCOVERED BY ORIONAIUnited Nations Satellite Centre (UNOSAT)Imagery and land coverNiger
Niger

About this dataset

This map illustrates the satellite-detected surface waters extent and evolution over Niamey and surroundings in Niger as observed from the Sentinel-1 images acquired on 14 and 26 August 2017. Within the analysed area, an increase of surface waters extent was observed from the 26 August 2017 image: ~7,870 ha of surface water were observed the 14 August 2017 and reached ~10,210 ha the 26 August 2017. All over the analysed zone, it corresponds to an evolution of about 30%. In Niamey an increase of water surface of 320 ha was observed corresponding to an evolution of ~20% by comparison to the surface water detected on 14 August 2017. This is a preliminary analysis and has not yet been validated in the field. Please send ground feedback to UNITAR - UNOSAT.

Documentation

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. 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 unosat@unitar.org to seek clarification.

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