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MODIS fire alerts

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"There's a fire season somewhere in South Africa all the time,"says researcher Philip Frost of the South African Council for Scientific and Industrial Research (CSIR). During the summer, fires sweep over the Mediterranean landscape on the southwest coast, and the warm, dry winters in the northeast spur to the grass fires that consume the savannah. On top of a landscape that loves to burn, South African also has a subculture that views fire as a tool for everything from hunting and land management to encouraging rain. Fire is a daily problem in South Africa.

For Hein Vosloo, the frequent fires are Texas-sized headache. A specialist in the transmission division of South Africa, power company, ESKOM, Vosloo has to keep power flowing through the country's massive grid, and one of the top culprits in causing outages is fires. "If you look at South Africa," says Vosloo, "our power stations are typically in the northeastern part of the country, but on the other end, about a thousand miles away, we have Cape Town." In between the city of Cape Town and the power stations are about 28,000 kilometers of high-voltage power transmission lines, a network that is about the same size as the Texas power grid. When fire burns anywhere under this extensive network of lines, it creates a column of ionized air that can conduct electricity. If the flames are tall enough to create an ionized column that reaches the power lines, electricity arcs from the power lines to the ground like lightning. A safety breaker sees the drop in electricity flowing through the lines and opens, cutting off the flow of electricity and triggering a power outage called a line fault.  

"I remember in 2002 we had 35 line faults on one day. On that particular day, we lost our power supply to Cape Town because two of our major lines both went out as a result of two fires, which were 295 kilometers from each other. It was rather a rare occasion," says Vosloo. In a typical year, ESKOM has to find and fix between 70 and 150 line faults. With 28,000 kilometers of line to check for faults, the problem is time-consuming and expensive.

So when Frost arrived at Vosloo's office in April 2004 to propose a collaboration in building a satellite-based fire alert system, he found a ready supporter. "The idea from the beginning was to monitor the transmission lines around the country and use cell phone technology such as text messaging to immediately alert people whenever there's a fire, which will then give them the opportunity to do something about it," says Frost. Together, Frost and Vosloo convinced the managers at ESKOM to fund a fire alert system. "The fire season started in June, so we had 2-3 months to put it all together," Frost remembers, referring to the northern winter fire season that caused most of the outages. "We went for it."

Frost envisioned an early warning system that would locate fires in South Africa based on satellite data, and then automatically alert local officials with the fire's location and current weather conditions. The first and most important step in setting up such a system was getting the satellite data, and the data he wanted came from the Moderate Resolution Imaging Spectroradiometer (MODIS) flying on NASA's Terra and Aqua satellites.

Though other satellites were capable of monitoring fire, MODIS was the first specifically designed to detect fires, and as a result can see both smaller fires and a wider range of fires from cool grass fires to raging forest fires. Burning carbon particles both on the tiny soot particles in the flame and on the fuel itself emit a very specific wavelength of light, 3.8 to 4 microns, says Louis Giglio, the remote sensing scientist who, while on contract at NASA Goddard Space Flight Center, developed the process used to find fires in MODIS data. "Compared to everything else in the environment—the land surface and the atmosphere—nothing else emits nearly as much radiation (light) at that wavelength. So we look for this surplus of radiation at that wavelength," says Giglio. MODIS can detect very hot fires that are as small as 100 square kilometers, but a cool grass fire must be larger before MODIS can see it.

For Frost, MODIS had a second advantage: at the same time that it stores the data it is acquiring, MODIS also transmits the data, so anyone with a receiving antenna can have immediate access to it. For real time applications like fire monitoring, getting the data quickly is essential, and so Frost obtained funding from the Department of Agriculture to buy a direct broadcast. He then turned to NASA and the University of Maryland for help in developing a system that would automatically extract fire locations from the data fast enough to provide useful alerts to the power company.

At the University of Maryland, the Web Fire Mapper had long provided MODIS fire locations in an interactive online map. The system took its fire locations from the MODIS Rapid Response System, developed at NASA Goddard Space Flight Center to process MODIS images and fire locations within a few hours of acquisition. Seeing how difficult an online map might be to users who had slow Internet connections, Diane Davies, a research scientist at the University of Maryland, had been developing an email system that automatically notified subscribers when a fire was detected in their area of interest. Frost was aware of the system, and contacted Davies to find out how to replicate it. "We adapted our system to meet their needs, which included the text messaging. Technically, it's very similar to the email that goes out," says Davies.

"The first challenge was to set up a system like MODIS Rapid Response, but faster," says Jacques Descloitres, the developer of the MODIS Rapid Response System. "We successfully set up a version of the system that just ran fire data," says Descloitres. "ESKOM provided a map of their power grid. We wrote a code that determined how far the fire was from a segment of the power grid. If the fire got within 5 kilometers, an alert was triggered." When an alert is triggered, the system automatically sends a 40 character text message to the people responsible for that segment of the power grid.

In the meantime, Frost realized that he would need data from a second satellite to complement MODIS. "MODIS is a snapshot in time," says Frost. "It flies over for fifteen minutes at 10:00 in the morning and again at 3:00 in the afternoon, and then it's gone. It sees whatever fires are there at the time." Fires that cause power outages occur between 11:00 a.m. and 5:00 p.m., so MODIS may miss many of those fires simply because it only flies over once during that time period. Frost decided to integrate data from a geostationary weather satellite, METEOSAT, that provided data every 15 minutes. METEOSAT wasn't as accurate as MODIS, but what it lost in accuracy, it made up for in frequency. "We wrote a little software package that would automatically detect the fires [in METEOSAT data]," says Frost, "and Jacques integrated it into the alert service. We put it all together, started up the engine, and it worked." Over the next year, the alert system detected 65 percent of all fires that caused outages.

"What is particularly nice about this is all of our field staff have mobile phones," says Vosloo. They can be out in the field, away from their computers and still get the fire alert. "The system is set up so that a particular field personnel would only get the information that they would need for their lines. If they get a notification, they can phone the local land owner and inquire about the extent of the fire," explains Vosloo. "Then the person will say, 'don't worry, I'm just burning some old maize,' or sometimes they might say 'this is a fire, and it's running away, and we can't control it." 

If a fire is large and out-of-control near power lines, the field person notifies the national control center. If backup lines are available, the control center can then divert power away from the affected lines until the fire is controlled. Sometimes, lines aren't available because backup lines are already in use while main lines are being maintained. "Then we're sitting on a shoe-string situation," says Vosloo. "If you've got lines out, then sometimes you must just close your eyes and ride through it and hope it's not bad."

"One of the seven regions we have in Transmission reported that although they don't record these events, they can recall at least 35 cases during the last two fire seasons [2005 and 2006] where fire trips were prevented in their region. Considering that we experience between 75 and 150 fire faults per year on a national basis, this region has been very successful using the early warning system," Vosloo concludes.

Frost is now working to expand the reach of the alert system to local fire authorities in South Africa. (As Vosloo says, "We're not in the fire fighting business, we're the electrical utility.") Each community in South Africa has a fire protection association responsible for controlling fires. "We're trying to get each fire protection association on board so that whenever there is a fire in their region of interest, they will also be informed," says Frost. To promote fire awareness, he provides fire reports to the South African Broadcasting Corporation, which appear once a week on the weather report. "We show MODIS fires from the last 24 hours and try to do educational tips. It works very well. Most people have been very receptive to it," Frost says.

"I'm proud that the system actually works to the level that if were to be stopped now, I would have hundreds of people on my case asking where is the data," says Frost. "It's becoming part of people's lives, it's becoming routine, and that's great."