Sensor tracks forest fires from space

Scientists at NASA have created a new orbiting sensor that can spot the heat from fires and help firefighters plan their attack against fires.

The sensor, called the Moderate Resolution Imaging Spectroradiometer (MODIS), rides aboard NASA’s Terra satellite and detects infrared heat emitted by fires on the planet below.

MODIS data can be quickly transformed into ‘Active Fire Maps’ that show where wilderness fires are raging and where they’re heading.

‘Active Fire Maps offer the potential for understanding the ‘big picture’ when working on resource allocation decisions,’ said Alice Forbes, deputy director of Fire and Aviation Operations at the US National Interagency Fire Centre.

The Terra satellite, which carries MODIS, circles the Earth from pole to pole in an orbit that allows the sensor to image most of our planet’s surface every day. The polar orbit keeps Terra in a constant alignment with the Sun.

Each pixel in a MODIS image covers 250-1000 metres on the ground (depending on the frequency of light considered). This resolution is considered adequate for providing rough maps of large fires as a square pixel 1000 metres long covers about 250 acres, and forest fires often burn tens of thousands of acres at a time.

Because of MODIS’s coarse resolution, Active Fire Maps will be used to formulate broad strategies, not to make detailed decisions about on-the-spot tactics. Tactical decisions require more detailed aerial photographs or imagery from satellites like Landsat, which has pixels that are 15-30 metres in size.

When MODIS looks down on Earth it senses both visible light and thermal infrared (IR) radiation emitted by hot objects. MODIS can also sense the temperature on the ground.

‘We are developing a unique capability to show the intensity of the fire. We can measure something about its heat level even through intervening smoke, to a reasonable degree,’ said Vince Salomonson, the MODIS science team leader at the Goddard Space Flight Centre.

To the human eye, thriving forests appear green while the charred areas after a fire look black.

But MODIS sees much more than simply ‘green’ or ‘black’ because it is a spectrometer and as such senses many colours spanning the visible and IR portions of the electromagnetic spectrum.

When light (visible light or IR radiation) bounces off trees or other objects, the molecules at the objects’ surfaces leave their ‘fingerprints’ imprinted in the reflected spectrum.

By looking at such spectra, forest managers can track the recovery of an area after a fire, because the spectral fingerprint of an area initially evolves as weeds and grasses, then small trees, then large trees.

NASA anticipates that in the future MODIS maps and other Terra-derived data will help teams of scientists rehabilitate burned areas.

They will use burn severity maps – derived from satellite and ground measurements – to prevent further erosion, soil loss and adverse impacts to water quality.