Damage Assessment in An Emergency Situation

Whenever a natural disaster hit certain territory critical information over the affected area is urgently required in order to help first responders plan emergency response efforts on the ground. See how Pléiades could help in terms of emergency response planning and rapid damage assessment after a natural disaster hit the French territory of New Caledonia

Challenge

On 21 and 22 November 2016, the worst natural disaster in recent history hit the French overseas territory of New Caledonia. Several days of exceptional rainfall caused deadly flooding and two devastating landslides in the Houaïlou district, 235km from the capital Noumea. In just one hour, the discharge of the Néaoua River rose from tens of cubic metres per second, to 600m3 per second causing the worst flooding in living memory and scouring or silting up nearly 10% of the surface of the agricultural plain.

Around a hundred landslides combined, forming mudslides in small catchment basins, engulfing ten homes and leaving eight people missing. In such an emergency situation, critical information over the affected area was urgently required in order to help first responders plan emergency response on the ground. Equally, accurate and very fresh imagery was also immediately needed to further understand the impact of the event and assess the damages caused by the disaster.

Mud slides caused by flooding - Illustration case study

Solution

Relying on Airbus’ satellite constellation’s high reactivity, Pléiades satellites were tasked with the highest priority over the town of Houaïlou in order to collect two 50cm products of the affected area, with minimum cloud cover and an acquisition angle compatible with the operational needs of the project. The images were delivered very shortly after the tasking activation to perform change detection analysis.

Landslides caused by torrential rainfall and flooding

With the Help of Our Reseller

Airbus Defence and Space’s reseller in the Pacific, the INSIGHT team, carried out automatic processing of the Pléiades data in order to extract and understand the changes which had taken place. In order to qualify the field data more precisely, the change detection solution, using Pléiades 50cm products, uses a number of information enhancement techniques:

A co-registration phase that allows perfect superposition of the images used.

A change detection phase, which involves three main steps:

  • The Magnitude Difference, which is the conventional method for change detection, taking into account the time lapse between the two images and apparent changes in vegetation.
  • The Principal Component Analysis (PCA), which is used for more detailed characterisation of the changes on the ground.
  • The Subtractive method, which enables further details to be determined, though it is heavily influenced by shadows on the vegetation.

Finally, the results were concatenated and vectorised for direct integration into the GIS of the Conservation International NGO. All of these processing operations and quality control checks were made available to Conservation International by INSIGHT just 24 hours after Airbus Defence and Space delivered the source data.

Pléiades image of Houaïlou district in New Caledonia

Benefits

Timely and reliable insights provided to local entities allowing a clear understanding of the situation.

  • Rapid access to critical information resulting from Pléiades’ unrivalled responsiveness combined with INSIGHT’s reactivity.
  • Clearer understanding of the impact of the rainfall on the ground and precise insights over the area affected by the disaster, due to accurate and reliable change detection based on Pléiades 50cm products.
  • Precise information thanks to the excellent geometrical accuracy of Pléiades imagery and clearer assessment of the variability of the vegetation cover due to high quality Near-Infrared (NIR) products.
Landslides in the Houaïlou district following extensive rainfalls

Organisation Involved

INSIGHT, reseller of Airbus products and solutions in the South Pacific.

Partnering with indigenous groups globally, Conservation International pair local expertise with long-term financial support to make a lasting impact.

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