Natural disasters can turn normal daily lives into nightmares in an instant. Sadly, they have become increasingly severe and more frequent in recent years. Owing to large-scale global climate change, flooding is one disaster scenario that is becoming all too common.
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One study from Nature estimated that the total number of people affected by floods increased from 58 million to 86 million between 2000 and 2015, meaning the percentage of the world’s population exposed to flood risks increased by 20-24%.
In Japan, where I live, severe flood damage occurs almost every year. In order to minimize the damage caused by disasters and save as many lives as possible, it is essential to be vigilant at all times and to take urgent action when appropriate. Disasters can occur at any time of the day or night or over a long period of time, as in the case of torrential rains. Traditionally, optical sensors are used as part of early warning systems, but they are not as effective in darkness or under thick cloud cover as they are during daytime. But there is a solution, and it comes in the form of synthetic aperture radar (SAR) satellites.
A SAR satellite fires microwaves at an observation target and receives microwaves bounced back from the target. Although SAR satellites have been used to image wide, disaster-stricken areas and assess the current situation, their development has been limited due to their high cost. However, technological innovation in the past few years has led to the downsizing of SAR satellites (to the 100 kilogram class compared to the 1,000-2,000 kilogram class for conventional SAR satellites), and the prospect of reducing the cost of development and manufacturing per satellite has led to the birth of many private startups.
Typhoon Hagibis
SAR satellites can provide situational awareness and support for identifying flooding and large structural damage. Using flood damage assessment (FDA), a rapid analysis of the flood extent and depth of Typhoon Hagibis, which hit Koriyama City, Japan in October 2019, was conducted. SAR imagery and data can be effective in providing accurate flood depth measurement and damage mapping techniques in near real time anywhere in the world.
Typhoon Hagibis formed off the eastern coast of the Mariana Islands on October 6, 2019, and made landfall in Japan on October 12. It struck the Japanese archipelago while maintaining a very large force and caused widespread heavy rains, high waves and storm surges. With a minimum pressure of 915 hPa and a maximum wind speed of 162 miles per hour (mph), the total damage in Japan is said to have amounted to 1.86 trillion yen.
Sentinel-1 SAR satellite data (observed at 11:42 p.m. UTC on October 12, 2019) was used to assess the floods around Abukuma River, which caused great damage to the Tohoku region. The flooded area at the time of imaging was approximately 26 kilometers, of which more than half was estimated to have been flooded at a depth of 1.8 meters or more. If we assume that more than half of the flooded roads and buildings had a depth of 1.8 meters, we can estimate that more than 1,800 kilometers of roads and 6,800 buildings were severely damaged.
Supporting Relief Efforts
SAR satellites can monitor the ground surface regardless of weather and time of day and have a broad range of applications. For example, governments and municipalities will be able to prioritize relief activities in the affected areas by gaining near real-time understanding of the situation through SAR satellite observations. In the private sector, insurance companies will be able to receive near real-time data on the extent and depth of flooding in the affected areas, which will improve the efficiency of on-site surveys for assessing insurance claims and thus speed up the payment of insurance claims to disaster victims.
Through these analyses, we are able to see and understand the world in a way that we could not see or understand until now, providing detailed detection of changes in near real time that can be updated every few hours. We’re confident that SAR satellites will become a new option in crisis/disaster management, by providing necessary information to the people who need it most, now.
Akifumi Sumiya is vice president of the marketing and sales department at Synspective. He is responsible for leading operations to build out scalable processes of satellite solutions, as well as product manager of its flood damage assessment (FDA) service. Prior to his role at Synspective, Akifumi led the growth of new services at medical IT startup companies and worked in consulting and electrics. He has a master’s of business administration from Aoyama Business School in Japan.
