Remote Sensing and Natural Disasters

Some Important Needs Remain

By Dr. Ray Williamson

Images from satellites and the software used to analyze them have added an important set of tools to responders' ability to provide help and succor to victims of natural disasters. The earthquake that rocked Sichuan Province in China this May and the earlier tropical cyclone Nargis, which struck Burma's coastal regions, illustrated once again the power of this imagery to reveal the extent of damage. Nevertheless, much work still needs to be done to use the imagery effectively.

Immediately following the 7.9 Sichuan primary shock in May, Chinese officials activated the International Charter on Space and Major Disasters, requesting earthquake data from other members of the Charter to assist them in assessing the geographical extent of damage and to guide them toward areas of greatest concern. China's National Space Administration joined the Charter in 2007, after being the recipient of satellite-derived information during an earlier flooding disaster and seeing how useful it was.

In an ironic twist, the island of Taiwan, which the Peoples Republic of China claims as its own, even provided some of the first satellite data to the mainland. Taiwan operates FORMOSAT, a very capable multispectral satellite, which senses details as small as two meters in black and white and eight meters in color. These data were used to monitor possible flooding from lakes formed when massive landslides blocked some of the rivers in the Sichuan region following the earthquake.

Yet according to many who have assisted in the process of placing imagery into the hands of the disaster responders, the process of moving from raw satellite data to usable information in the hands of first responders is slow and cumbersome, despite the ready availability of satellite imagery from a number of sources. Countries generally lack the necessary institutional arrangements, interpretive capacity, and distribution mechanisms making it possible for the needed information to reach responders quickly and in a form that they can use effectively.

Even in the United States, with its robust commercial and governmental capacity for collecting and distributing imagery from satellite and aircraft platforms, the government is not fully prepared to distribute data or processed imagery to affected communities. Hurricanes Katrina and Rita proved that.

Shortly after the storms had struck, television and print media were full of overhead pictures of the disaster, some acquired by satellite, many more by aircraft. However, people in the local community charged with responding in times of natural disasters had a hard time getting what they needed to save lives and assess the extent of damage. Power lines were down, cell phones did not work, and in most cases, the only way to receive the necessary digital imagery was by hand delivery.

Yet, even if the data were delivered to offices that had the necessary digital tools to process them, they were seldom in a useable format, and they might also lack the necessary geo-registration to link them to the areas they imaged. As a result, the utility of the imagery was severely blunted.

In remote areas with few of the modern computer tools prevalent in the United States, the problem is even more serious, because first responders there generally need very simple paper maps with captions in the local language. Besides, computers are difficult to use in the field where adequate sources of electricity or protection from the elements seldom exist.

The International Charter—which was started in 1999 to provide satellite-derived information to States affected by severe natural disasters—has done a commendable job in tasking partner countries to provide satellite data to countries in need. However, the Charter still lacks the means and mechanisms to assure timely delivery of useful information to the affected areas. The supply chain is generally long and complex, and because disasters often strike with limited warning, delivering needed information quickly enough to disaster sites or even to crews heading into them is a huge logistical problem.

The international community needs to spend the money and time to develop ways to collect and deliver the needed information to first responders. This part of the job is not as sexy as collecting data from space, but is just as important in making sure that the many operating Earth observing satellites in the world can be used effectively to reduce the loss of human life.

Despite the growing pains we suffer in using satellite data to improve human security, we have become more aware than ever before of the direct human impacts of natural disasters. Increasingly, the media seek satellite imagery to illustrate the scope of these calamitous events and their effects on the local populations. High-resolution images, especially, have provided details that add important depth to the coverage.

In 1984, I led a study for the Congressional Office of Technology Assessment entitled "Newsgathering from Space," in which we explored the utility of satellite imagery to illustrate and lend greater depth to news coverage. As it turned out we were a few years ahead of our time. Imagery then was expensive and lacked sufficient resolution for the sort of visual appeal needed for most readers or TV viewers. Nevertheless, proponents of using satellite imagery in the media pressed on, using those images wherever possible. As satellite images became sharper and the media learned to be more effective in using them, they became important components of news coverage.

Since 1984, I have observed a steady increase in the use of satellite imagery in the media where details of the geographical context of the event can enhance understanding. I would argue that the public's appreciation of the power of imagery from satellites to inform understanding derives first from the heartbreaking coverage of hurricanes Katrina and Rita, and of course from the aftermath when property owners, friends and relatives began searching the Internet for details on the conditions of their loved ones, homes and businesses from their refuges far away from the damaged areas. Many of these pictures, collected either by satellite or by various aircraft, were only a few hours or days old.

Private industry has made significant contributions to vastly expanded awareness of satellite imagery including Google Earth, Microsoft Virtual Earth, and others. These powerful platforms for information about the Earth's surface have made it possible for millions of people around the world to get in touch with their surroundings better than ever before. A nonprofit organization called InSTEDD ( has been bridging the gap between raw data and useful data following the Myanmar cyclone and China earthquake in May. They are currently developing a free, open source software and services platform for early detection and more effective response to human-itarian crises and emerging infectious diseases. These companies have made the world much more transparent than ever before and created expectations that we will use even better the information that satellite imagery can provide to meet the enormous challenges posed by the effects of natural disasters.


Following the May 12, 2008 earthquake in China, landslides blocked the Jiangjiang River, creating swollen reservoirs that threatened to break and flood catastrophically. The largest of these lakes, Tangjiashan Lake, threatened roughly 1.3 million people.

On June 10, 2008, Chinese authorities announced that the landslide that created Tangjiashan Lake had been successfully breached, and the lake had safely drained. These natural-color images show changes in the Jiangjiang River—downstream from the lake.

The ‘before' image from June 8, 2008, shows the apparently slow-moving river, hampered by landslides both up- and downstream (river direction is from left to right).

The image on the right, from June 10, 2008, shows a swollen, faster-flowing river after the massive landslide upstream was breached. Compared to the image taken two days earlier, the river is wider, and it has submerged some land features along its banks. Its tan hue indicates that it carries a considerable amount of sediment.

Draining the lake sent floodwaters coursing into the city of Beichuan, which had been home to some 22,000 people before the earthquake struck. Having already experienced massive damages from the quake, the city was evacuated before authorities drained the lake on June 10.

As of June 10, 2008, more than 69,000 people had died in the Sichuan earthquake, and more than 17,000 remained missing.

Credit: Taiwan's Formosat-2 image, Dr. Cheng-Chien Liu, National Cheng-Kung University, and Dr. An-Ming Wu, National Space Organization, Taiwan. Caption by Michon Scott.

Ray A. Williamson, PhD, is editor of Imaging Notes and Executive Director of the Secure World Foundation, an organization devoted to the promotion of cooperative approaches to space security (

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