Update 1: The Crisis Map below was produced pro bono by Tonkin + Taylor so they should be credited accordingly.
Update 2: On my analysis of Ovalau below, I’ve been in touch with the excellent team at Tonkin & Taylor. It would seem that the few images I randomly sampled were outliers since the majority of the images taken around Ovalau reportedly show damage, hence the reason for Tonkin & Taylor color-coding the island red. Per the team’s explanation: “[We] have gone through 40 or so photographs of Ovalau. The area is marked red because the majority of photographs meet the definition of severe, i.e.,: 1) More than 50% of all buildings sustaining partial loss of amenity/roof; and 2) More than 20% of damaged buildings with substantial loss of amenity/roof.” Big thanks to the team for their generous time and for their good work on this crisis map.
Fiji recently experienced the strongest tropical cyclone in its history. Named Cyclone Winston, the Category 5 Cyclone unleashed 285km/h (180 mph) winds. Total damage is estimated at close to half-a-billion US dollars. Approximately 80% of the country’s population lost power; 40,000 people required immediate assistance; some 24,000 homes were damaged or destroyed leaving around 120,000 people in need of shelter assistance; 43 people tragically lost their lives.
As a World Bank’s consultant on UAVs (aerial robotics), I was asked to start making preparations for the possible deployment of a UAV team to Fiji should an official request be made. I’ve therefore been in close contact with the Civil Aviation Authority of Fiji; and several professional and certified UAV teams as well. The purpose of this humanitarian robotics mission—if requested and authorized by relevant authorities—would be to assess disaster damage in support of the Post Disaster Needs Assessment (PDNA) process. I supported a similar effort last year in neighboring Vanuatu after Cyclone Pam.
World Bank colleagues are currently looking into selecting priority sites for the possible aerial surveys using a sampling method that would make said sites representative of the disaster’s overall impact. This is an approach that we were unable to take in Vanuatu following Cyclone Pam due to the lack of information. As part of this survey sampling effort, I came across the United Nations Office for the Coordination of Humanitarian Affairs (UN/OCHA) crisis map below, which depicts areas of disaster damage.
I was immediately struck by the fact that the main dataset used to assess the damage depicted on this map comes from (declassified) aerial imagery provided by the Royal New Zealand Air Force (RNZAF). Several hundred high-resolution oblique aerial images populate the crisis map along with dozens of ground-based photographs like the ones below. Note that the positional accuracy of the aerial images is +/- 500m (meaning not particularly accurate).
I reached out to OCHA colleagues in Fiji who confirmed that they were using the crisis map as one source of information to get a rough idea about which areas were the most affected. What makes this data useful, according to OCHA, is that it had good coverage over a large area. In contrast, satellite imagery could only provide small snapshots of random villages which were not as useful for trying to understand the scale and scope of a disasters. The limited value added of satellite imagery was reportedly due to cloud cover, which is typical after atmospheric hazards like Cyclones.
Below is the damage assessment methodology used vis-a-vis the interpret the aerial imagery. Note that this preliminary assessment was not carried out by the UN but rather an independent company.
- Severe Building Damage (Red): More than 50% of all buildings sustaining partial loss of amenity/roof or more than 20% of damaged buildings with substantial loss of amenity/roof.
- Moderate Building Damage (Orange): Damage generally exceeding minor [damage] with up to 50% of all buildings sustaining partial loss of amenity/roof and up to 20% of damaged buildings with substantial loss of amenity/roof.
- Minor Building Damage (Blue): Up to 5% of all buildings with partial loss of amenity/roof or up to 1% of damaged buildings with substantial loss of amenity/roof.
The Fiji Crisis Map includes an important note: The primary objective of this preliminary assessment was to communicate rapid high-level building damage trends on a regional scale. This assessment has been undertaken on a regional scale (generally exceeding 100 km2) and thus may not accurately reflect local variation in damage. I wish more crisis maps provided qualifiers like the above. That said, while I haven’t had the time to review the hundreds of aerial images on the crisis map to personally assess the level of damage depicted in each, I was struck by the assessment of Ovalau, which I selected at random.
As you’ll note, the entire island is color coded as severe damage. But I selected several aerial images at random and none showed severe building damage. The images I reviewed are included below.
This last one may seem like there is disaster damage but a closer inspection by zooming in reveals that the vast majority of buildings are largely intact.
I shall investigate this further to better understand the possible discrepancy. In any event, I’m particularly pleased to see the UN (and others) make use of aerial imagery in their disaster damage assessment efforts. I’d also like to see the use of aerial robotics for the collection of very high resolution, orthorectified aerial imagery. But using these robotics solutions to their full potential for damage assessment purposes requires regulatory approval and robust coordination mechanisms. Both are absolutely possible as we demonstrated in neighboring Vanuatu last year.
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