Data-driven decisions

Time-crucial flood monitoring using publicly available imagery

Apr 07, 2017

During natural disasters, the ability to quickly gain a real-time view of the impact is crucial for fast, targeted response and recovery. Publicly available data makes it possible for anyone – amateurs and professionals – to analyse and view areas affected by these events.

Following the devastating floods in the Tweed Shire of NSW, I wanted to see the scale and extent of the damage caused.

During heavy rain and cloud cover, it is often hard to get any imagery.

Fortunately, Synthetic Aperture Radar (SAR) imagery came to my rescue. SAR imagery can be acquired day and night and even in times of cloud and rain. I quickly scrambled to find any public available SAR imagery over the area I was interested in. Fortunately, Sentinel-1 Satellite had captured a SAR image over the area on April 2, around the time when the flood was at its peak.

I downloaded data for the most recent image available at the time from the Copernicus site  and imported and analysed the Sentinel-1 radar imagery using ENVI SARscape.

To provide some context to my analysis, I also downloaded freely available optical Landsat Operational Land Imager data from the United States Geological Survey site. Although there weren’t many cloud-free images, I found one that was acquired on February 1, 2017.

With ENVI and ENVI SARscape I extracted the extent of the flood boundary – including areas that were flooded as well as areas that were very wet and waterlogged – and displayed this over the Landsat imagery and base maps in ArcGIS Pro.

Flooding caused by the aftermath of Tropical Cyclone Debbie was the worst in 43 years. We can’t prevent disasters, but we can take steps to minimise the impact.

The flooded areas are shown in blue and the Landsat imagery is displayed in the background with a false colour band combination that shows vegetated areas in green.

Tweed Shire flood image

I can easily see the impact of the flood and how information from this simple analysis could be useful to authorities in response and recovery efforts.

Most of the flood impact is immediately to the south of Lismore and west of the town of Buckendoon. Unfortunately, no SAR imagery had been acquired over an area immediately to the east, so I could not show the impact of the floods on that section of the map.

Although the data used for this quick analysis is free, the technology can be utilised to create more precise commercial-grade products that can convey more detail.

For example, the flooded areas could be overlaid with property boundaries to show exactly which properties were impacted by flooding. This would require a timely acquisition of higher resolution SAR imagery, near real-time processing and dissemination of the information using image analysis and GIS software tools like ENVI SARscape and Esri’s ArcGIS Online.

By combining GIS technology with publicly available data, disaster recovery stakeholders at every level can create and share maps that drive accurate, timely responses.

Find out more about GIS in emergency services, or call 1800 870 750 to speak to a specialist consultant.