Evolution satellite detected water extent over Sanamxay District, Attapeu Province, Lao People Democratic Republic

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This map illustrates the evolution of satellite-detected surface waters in Sanamxay district, Attapeu province, as observed from the Radarsat-2 radar image acquired on 24 July 2018 and compared with a Radsarsat-2 image acquired on 10 July 2018. As of 10 July 2018, flooded areas and saturated soils were already visible, due to the heavy rains that happened previously to the collapse of the dam. As well, the reservoir controlled by the dam was full of water. As of 24 July 2018, an additional surface of 5,826 ha of inundated areas were detected, representing an increase of the surface waters of 66%, due to the collapse of the dam. At this date, the reservoir that was controlled by the dam has decreased in its size. Several villages and surrounding agricultural fields seems to be inundated. The villages of Ban Hinlat, Ban Thaseangchan, Ban Mai and Ban Samong-tai seems to be the most affected ones. It is likely that flood waters have been systematically underestimated along highly vegetated areas, along the main riverbanks and within built-up urban areas because of the special characteristics of the used satellite data. This is a preliminary analysis and has not yet been validated in the field. Please send ground feedback to UNITAR - UNOSAT.

Metadata

Source UNOSAT
Contributor
Date of Dataset Jul 26, 2018
Expected Update Frequency Live
Location
Visibility
Public
License
Methodology

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 unosat@unitar.org to seek clarification.

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