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NASA and NOAA Missions for Monitoring Global Fires
Different satellites provide observation and measurement capabilities for monitoring different fire characteristics: areas that are dry and susceptible to wildfire outbreak, actively flaming and smoldering fires, burned area, and smoke and trace gas emissions. Several satellite systems are currently available for fire monitoring with different capabilities in terms of spatial resolution, sensitivity, spectral bands, and times and frequencies of overpasses.
Fires vary widely in size, duration, temperature, and in the tropics, where it is moist and humid, fires have a strong diurnal cycle. No one system provides optimal characteristics for fire monitoringmulti-sensor data fusion is needed to optimize the use of current systems.
Flown on NOAA Polar Orbiting Environmental Satellites, the Advanced Very High Resolution Radiometer (AVHRR) measures electromagnetic radiation (light reflected and heat emitted) from our planet. AVHRR was originally intended only as a meteorological satellite system but it does have applications for fire monitoring. AVHRR remotely senses cloud cover and sea surface temperature, enabling its visible and infrared detectors to observe trends in vegetation, clouds, shorelines, lakes, snow and ice. The visible bands can detect smoke plumes from fires as well as burn scars. The thermal infrared band can detect actual hotspots and active fires. Its ability to detect fires is greater at night, since the system can confuse active fires with heated ground surfaces, such as beach sand and asphalt.
Active fire mapping on a global scale using a single satellite system has been coordinated by the International Geosphere Biosphere Program (IGBP) using AVHRR data for 1992-93 from international ground stations.
In addition, a small number of countries have developed their own regional AVHRR satellite fire monitoring systems using direct read-out; e.g., Brazil, Russia, and Senegal. Research groups have provided regional examples of trace gas and particulate emissions from fires for Brazil, Southern Africa, Alaska.
The Geostationary Operational Environmental Satellites (GOES) house a five-channel (one visible, four infrared) imaging radiometer designed to sense radiant and solar reflected energy from sample areas of the Earth. They are stationed in orbits that remain fixed over one spot on the equator, providing continuous coverage of one hemisphere. GOES satellites aquire images every 1530 minutes, at up to 1km resolution in visible light, for the detection of smoke, and 4km resolution in thermal infrared to directly detect the heat of fires.
The Landsat series of Earth-observing satellites monitor characteristics and changes on the surface of the Earth at high resolution (up to 15m per pixel). The original missions (1970s early 1980s) used the Multispectral Scanner (MSS) which was only capable of detecting scars. Current Landsat series satellites use the Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) to provide land surface information. The seven bands (eight on Landsat 7's ETM+) monitor different types of Earth resources over a wide area (81 North and 81 South Latitude). The thermal band enables the system to detect "hotspots." Landsat 7 provides impressive high-resolution images but only infrequently, revisiting an area every 14 days.
The Total Ozone Mapping Spectrometer (TOMS) is a measuring device that provides data regarding ozone levels. Measured in Dobson Units (DU), TOMS produces a complete data set of daily ozone levels around the world. This instrument is the first to show aerosols (airborne dust and smoke particles) over land. It also provides the ability to distinguish aerosols that absorb light from aerosols that reflect it. TOMS makes 35 measurements every 8 seconds, each covering 50-200 kilometers wide on the ground. Close to 200,000 daily measurements cover almost every spot on the Earth except for areas near the poles. These data make it possible to observe a variety of Earth events including forest fires, dust storms and biomass burning.
The Tropical Rainfall Measuring Mission (TRMM) carries a high-resolution sensor similar to AVHRR, called the Visible and Infrared Scanner (VIRS), which is capable of spotting active fires as well as evidence of burn scars. It has five bands from visible to thermal infrared (.6312µm) and provides 2km resolution. TRMM's primary purpose is to measure rainfall over both land and oceans from 30° South to 30° North Latitude. TRMM is unique in that previous satellites tended to show the tops of clouds whereas TRMM instrumentation allows a look into the cloud itself. In addition to its other sensors, TRMM carries LIS, the Lightning Imaging Sensor. LIS provides information on both cloud to cloud and cloud to ground lightning strikes around the world. The imager is capable of locating and detecting ninety percent of lightning strikes in the world. This information can help identify areas that may be particularly susceptible to wildfire outbreaks.
In late 1999, NASA launches the first in a series of new Earth remote sensors that will bring dramatically improved capabilities for global monitoring of fires. The Earth Observing System's flagship spacecraftTerra (formerly named EOS AM-1)will carry a payload of five sensors that, collectively, greatly expand scientists' capacity for near-real-time fire monitoring, while more accurately measuring emission products. The Terra spacecraft will fly in a near-polar orbit, crossing the equator in the morning when cloud cover is at a minimum and its view of the surface is least obstructed. Subsequently, in 2000, the Aqua (formerly EOS PM-1) spacecraft will launch into a near-polar orbit crossing the equator in the afternoon, to observe the daily variability of surface features.