Satellite detected water extent over Gujba LGA, Yobe state, Nigeria as of 18 Jul 2022

Name: Satellite detected water extent over Gujba LGA, Yobe state, Nigeria as of 18 Jul 2022
Creator: United Nations Satellite Centre (UNOSAT)
License: http://www.opendefinition.org/licenses/cc-by-sa

✦ DISCOVERED BY ORIONAIUnited Nations Satellite Centre (UNOSAT)WaterNigeria

Nigeria

About this dataset

**UNOSAT code: FL20220721NGA** This map illustrates satellite-detected surface waters in Gujba LGA, Yobe state, Nigeria as observed from a Sentinel-1 image acquired on 18 Jul 2022 at 18:22 local time. Within the analyzed area of about 1,040 km2, about 22 km2 of lands appear to be flooded. Based on Worldpop population data and the detected surface waters, about 1,400 people are potentially exposed or living within/close to flooded areas. This is a preliminary analysis and has not yet been validated in the field. Please send ground feedback to United Nations Satellite Centre (UNOSAT). Important note: Flood analysis from radar images may underestimate the presence of standing waters in built-up areas and densely vegetated areas due to backscattering properties of the radar signal.

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.

Related datasets

Satellite detected water extents between 13 and 17 October 2022 over Nigeria

**UNOSAT code FL20221019NGA** This map illustrates cumulative satellite-detected water using VIIRS in Nigeria between 13 to 17 October 2022 compared with the period from 08 to 12 October 2022. Within the cloud free analysed areas of about 890,000 km², a total of about 30,000 km² of land appears to be affected. In the analysed areas, 738 health facilities and 1,424 schools are identified to be within or close to a flooded zone. In comparison with the period between 08 to 12 October 2022, water extent appears to have decreased of about 1,000 km². Based on Worldpop population data and the maximal flood water extent ~6,660,000 people are potentially exposed or living close to flooded areas amongst the 204 million people living in the analysed zone. This is a preliminary analysis and has not yet been validated in the field. Please send ground feedback to the United Nations Satellite Centre (UNOSAT).