Unusual rainfall events caused severe flooding in rural and urban areas of New South Wales and southeast Queensland during the austral summer of 2022. A recent study published in Remote Sensing uses brightness images of the VIIRS night light to map the extent of flooding in Brisbane and assess change. in the energy utilization for the flood effect.
Study: Assessing the impacts of the 2022 floods in Queensland by combining optical radar and daylight and nighttime imaging data. Image credit: Alex Cimbal/Shutterstock.com
The researchers established the Normalized Difference Inundation Index (NDII) using a new spectral measurement based on variations in NIR reflectance due to sediment-laden flood waters. They used images from Planet-Scope before the floods and peak floods to map the flooded areas. Planet-Scope mapping of inundated areas was derived from Capella-Space X/HH-band imaging radar data collected on the maximum inundation date.
The use of a single-date radar image partially scattered by the tree canopy and the SAR aspect angle that prevents the satellite from observing flooded streets contribute to omission inaccuracies. The researchers were able to locate grid cells where electricity use was influenced by flooding using VIIRS night-light images.
Remote sensing technology for flood detection
Mapping damage caused by severe events is now common practice. These events are natural disasters such as fires, earthquakes, floods, volcanic eruptions or man-made disasters.
Flood remote sensing mapping is used to map flooded areas with high spatial resolution optical images as the most successful method. Remote sensing is also used to map flood damage to buildings and properties, with imaging radar data being the most effective method.
Because of its ability to penetrate cloud cover and dense forest, imaging radar is best suited for mapping the flooded area.
Data sets available for flood events
The International Charter for Space and Major Disasters, which will have 17 founding members by 2022, was founded in 1999 to provide emergency assistance to nations in need. A total of 405 activations out of 765 activations worldwide are associated with flooding, demonstrating the severity, frequency and social effects of flooding.
MODIS-NRT-FLOOD, which has a spatial resolution of 250 m, and the UNO-SAT Flood Portal, which provides flood vector maps for selected flood situations using different satellites, are two sets of flood data accessible worldwide. The Dartmouth Flood Observatory used MODIS imagery to create maps of 913 significant flood events between 2000 and 2018. These datasets are available in the Global Flood Database on Google Earth Engine. A new flood water fraction product based on the VIIRS sensor with a spatial resolution of 375 m is also accessible.
Limitations of current datasets for flood events
Flood mapping is one of the main focuses of the European Union’s new Copernicus Emergency Management Service (CEMS).
MODIS and VIIRS flood products are based on optical imagery and coarse spatial resolution. Cloud cover affects their mapping, making them insufficient for short-term and relatively minor urban flooding.
Fusion of imaging and optical radar sensors for better flood mapping
The European Union’s Sentinel-1 SAR satellites can provide flood map outputs with a spatial resolution of 20 m. Fusion of image and optical radar data can improve the mapping of surface-referenced water covers to improve flood mapping products. Temporal return time is crucial for mapping flooded areas because flooded areas often only remain under water for a few hours or days (apart from seasonal floodplains).
Development of optical and radar sensors with night light imaging for flood mapping
In Australia, the Water Observation from Space product provides annual water cover mapping based on the Landsat image collection. This product, while admirable, is not suitable for mapping areas that were briefly underwater due to the relatively short Landsat review time. Voluntary passenger imagery taken from aircraft can be used as an additional source for flood mapping, but this is not a practical option.
A suitable method for tracking human activity from space is remote sensing of nighttime light, which is also used to track how natural and human disasters affect energy availability.
Levin et al. demonstrated the collective use of night-time light imagery and high-resolution daytime spatial optical imagery to assess the effect of flood events in northern New South Wales (NSW) and southeast Queensland (SEQ), Australia. This was due to the limitations of currently available flood products. The researchers used VNP46A1’s VIIRS Black Marble nighttime product to analyze how flood events affected nighttime artificial lights.
Search Found
Flooding is a frequent and essential threat both internationally and in Australia. Flood monitoring in urban environments presents unique challenges that require frequent sensor checks (at least twice daily) due to the shorter duration and geographic extent of flood episodes.
The effects of flooding on energy access can be tracked using VIIRS nighttime luminosity imagery. In this research, the researchers showed that a multi-sensor strategy is useful when dealing with complicated natural disaster situations because multiple sensors validate each other and track various elements of unfolding events.
reference
Levin, N. and Phinn, S. (2022) Assessing the impacts of the 2022 floods in Queensland by combining optical radar and day and night light imaging data. Remote Sensing, 14(19), article 19. https://www.mdpi.com/2072-4292/14/19/5009/htm
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