Rationale

• Heritage
• Intent
• Relevance

Heritage

Satellites have a role to play in detecting, monitoring and characterizing fires. There are satellite systems currently in orbit that provide information on different fire characteristics: location and timing of active fires, burned area, areas that are dry and susceptible to wildfire outbreaks, and pyrogenic trace gas and aerosol emissions. These satellite systems have different capabilities in terms of spatial resolution, sensitivity, spectral bands, and times and frequencies of overpasses, but none of the sensing systems prior to MODIS included fire monitoring in their design.

Combining multiple satellite products that provide synthetic information on different fire characteristics and developing multi-sensor algorithms is needed to optimize the use of the current sensing 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. The AVHRR was originally intended only as a meteorological satellite system but it does have applications for fire monitoring. The 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 middle-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 was first 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 acquire images every 15-30 minutes, at up to 1 km resolution in visible light, for the detection of smoke, and 4 km 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 15 m 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) satellite carries a sensor similar to the AVHRR, called the Visible and Infrared Scanner (VIRS), which is capable of detecting active fires as well as evidence of burn scars. It has five bands from visible to thermal infrared (0.63 - 12 µm) and provides 2.1 km resolution. The primary purpose of the TRMM instrument suite is to measure rainfall over both land and oceans from 38 degrees South to 38 degrees 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 the Lightning Imaging Sensor (LIS). The 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.

Intent of the MODIS Fire and Thermal Anomalies Products

The intention of the MODIS fire team is to provide global change researchers with global  time-series of fire data. In particular these products are aimed at supporting the modeling of trace gas and particulate emissions.

First order estimations of trace gas and particulate emissions from biomass burning involve multiplying the area burned by the amount of fuel consumed taking into account the emission factors for the gases and particulates (Crutzen and Andreae 1990). More detailed estimates account for other controlling variables such as wind speed, fuel moisture content and fire intensity. Reporting of national estimates of anthropogenic trace gas emissions are a requirement of the Framework Convention on Climate Change and the IPCC provides guidelines for these emissions calculations (Callander 1995). For many parts of the world however, national emissions estimates from biomass burning are based largely on expert opinion or summary statistics and the resulting accuracies are largely unknown.

The IGAC-BIBEX program has contributed significantly to our understanding of biomass burning emissions and the methods and data needed for improved emissions calculations e.g. (Kaufman et al. 1992, Ward et al. 1996, Scholes et al. 1996, Delmas and Guenther 1998).

Synoptic fire information derived from satellites provides a source of information for augmenting available national fire statistics. Satellite detection of active fire occurrence has been used to identify the timing and location of fires and have been used for example in emission product transport studies. The first global data set of annual satellite fire distributions was developed directly as a contribution to BIBEX (Stroppiana et al., 1999). Since that time both polar orbiting and geostationary satellite systems have been used to provide other fire information (Prins et al. 1998, Elvidge et al. 1996, French et al. 1996).

Automated algorithms for direct estimation of burned area are currently under development with the intent of providing direct input to emissions modeling (Roy et al. 1999). Satellite based techniques for direct estimation of emitted energy, fire intensity, atmospheric aerosol loading and vegetation recovery are also under development. As in most cases the data products are to be used in numerical modeling, there is a need to provide a quantitative assessment of their accuracy. For satellite products, validation using independent data sources needs to be undertaken to determine product accuracy.

New satellite systems are planned for launch, which will improve our current fire monitoring capability, e.g. Kaufman et al. (1998). The requirements for these systems come in part from the experience gained from the BIBEX experiments. The satellite fire research community is working to secure the necessary long-term fire observations from the next generation of operational satellite systems, such as the U.S. National Polar Orbiting Environmental Satellite System (NPOESS).

With the operational availability of satellite derived fire information on the location and timing of fires, area burned it will be feasible to run an improved class of models to estimate emissions on an annual basis. These improved models will require ground based estimates of emission factors and modeled estimates of fuel load and fuel consumed for a given year, rather than representative values for a given vegetation type and. As new satellite information become available on fire intensity, emitted energy and fuel moisture content, these first order emissions estimates can be improved. Providing robust models that can be used for operational generation of annual emissions estimates and developing approaches to validate them, provides the next challenge for the fire and global change research community.

The MODIS fire team will make a contribution to the Global Observation of Forest Cover (GOFC) project, an operational pilot project for the Committee on Earth Observation Satellites.

Relevance to Global Change Issues

Impacts on Atmospheric Chemistry

Vegetation burning is recognized as an important contributor to global climate change because of its potential to modify atmospheric composition and chemistry (Crutzen et al., 1979; Crutzen and Andreae, 1990; Cicerone, 1994; Helas and Pienaar, 1996; Levine et al., 1996; Scholes et al., 1996; Lobert et al., 1990; Lobert et al., 1999). A number of interdisciplinary, international scientific initiatives , such as STARE (Southern Tropical Atlantic Regional Experiment), TRACE-A (Transport and Chemistry near the Equator), SAFARI-92 (Southern African Fires and Atmosphere Research Inititiative), SAFARI-94, EXPRESSO (Experiment for Regional Sources and Sinks of Oxidants), SCAR-B (Smoke Clouds Aerosols and Radiation) and SCAR-C conducted under the International Global Atmospheric Chemistry (IGAC) programs Biomass Burning Experiment (BIBEX), have dealt with different aspects of the role of fires in diverse ecosystems, e.g., savannas, temperate ecosystems and boreal forests, on atmospheric chemistry and climate (Andreae, 1998). Several recent and ongoing projects are aimed to characterize and quantify pyrogenic emissions and assess their consequences on the regional and global atmospheric chemistry and climate and the resulting feedbacks between terrestrial ecosystems and the atmosphere. These include LBA (The Large Scale Biosphere-Atmosphere Experiment in Amazonia) currently underway in Brazil, AFARI-97 Field Campaign held in Kenya in 1997, ZIBBEE (The Zambian International Biomass Burning Emissions Experiment) undertaken in 1997, the Africa Biofuels/Emissions Research Program, SAFARI 2000 held in Southern Africa during 2000, FIRESCAN (Fire Research Campaign Asia North) and SEAFIRE (Southeast Asia Fire) currently being developed in southeast Asia and ICFME (The International Crown Fire Modeling Experiment) in the Canadian Northwest Territories.

The long-range transport of aeolian material may generate not only regional, but also transcontinental and transoceanic atmospheric impacts. For example, there is increasing evidence that savanna fires in Africa might be responsible for the elevated tropical ozone anomaly spanning from the western coast of southern Africa to South America during the southern hemisphere dry season (Fishman et al., 1991; Andreae et al., 1992; Thompson et al., 1996).

Biomass burning is estimated to contribute about 38% of the tropospheric ozone, 32% of the global carbon monoxide, 10% of the global CH₄, more than 20% of the world's H₂, non-methane hydrocarbons (NMHC), CH₃Cl, CH₃Br and NOx and approximately 39% of the particulate organic carbon (Crutzen and Andreae, 1990; Levine, 1991; Andreae, 1993; Helas 1995: Lobert et al., 1999). The increasing concentrations of greenhouse gases, produced by biomass burning among other sources, provide one of the clearest manifestations of global change in the atmosphere.

Aerosols emitted during biomass burning may also play a significant role in forcing climate change. They may influence climate directly by reflecting solar radiation back into space. Furthermore, aerosols act as cloud condensation nuclei (CCN), and may thus affect climate indirectly by modifying cloud microphysics and sunlight reflectance (Kaufman and Nakajima, 1993; Kaufman and Fraser, 1997). In general, biomass burning aerosols are considered to produce a cooling effect and together with aerosols emitted from other sources they produce a global-average forcing of equal and opposite sign with that of the greenhouse gas effect. However, assessing the combined climatic impacts of greenhouse warming and aerosol cooling at the global-scale has been difficult and rather controversial due to the uneven spatial distribution of the two effects. Several related studies have been reviewed by Kondratyev (1999). Since fire activity is among the contributors to potential climate forcing factors it is important to improve its characterization and commit to a long-term monitoring of fire patterns and quantification of fire emissions.

Impacts on Ecosystems

Perturbations in biogeochemical cycling processes may occur in the fire-prone environments and have implications for the sustained productivity of natural ecosystems that are limited in these nutrients. Nitrogen is readily volatalized during fire and lost if not replenished through nitrogen input mechanisms e.g., nitrogen fixation and atmospheric deposition. Enhanced biogenic emissions of NO and N₂O from soils have been measured following burning, reinforcing thus the role of fire on climate change with inputs to the atmosphere beyond just the direct emissions from fires (Anderson et al., 1988; Poth et al., 1996; Parsons et al., 1996; Levine et al., 1996; Harris et al., 1996). Phosphorus and sulfur cycling losses also result from biomass burning and unlike nitrogen these nutrients cannot be fixed by biological processes but are replaced instead through atmospheric input or rock weathering (DeBano, 1990; Barnett, 1989). Furthermore, because the biogeochemical cyling of important species, such as carbon and nitrogen, are intimately coupled, atmospheric deposition may impact the nutrient cycling of an ecosystem in complex ways. For example, increased nitrogen deposition may temporarily stimulate carbon dioxide assimilation by plants but over long time scales the imbalances caused for example by acidification, may lead to reduced carbon sequestration in plants and soils (Asner et al., 1997).

Besides their effects in the atmosphere and the fire environments, pyrogenic trace gases and aerosols can impact nutrient deposition and the biogeochemical cycling of essential nutrients in far-removed ecosystems located downwind of fires. Deposition of nitrogenous pollutants into forest ecosystems in North America and Europe has been occurring at enhanced rates over the past 50 years and there is an increasing number of suggestions that it can influence nutrient cycling processes (Aber et al. 1989, Asner et al., 1997; Korontzi et al., 2000). Similar evidence also exists for other regions, such as in southern African savanna ecosystems, where biomass burning is a major source of trace gas and aerosol emissions. For example, atmospheric dry deposition may contribute by as much as 60% of the annual input of certain important nutrients, especially phosphorus in the form of phosphate in the Okavango Delta ecosystem (Garstang et al., 1998).

Fires may also modify ecosystem composition and functioning. Depending on the fire regimes, plant species are frequently eliminated by burning and the successional pathways following fire are altered within plant communities (Krefting and Ahlgren, 1974; Noble and Slatyer, 1980; Christensen, 1985). At the same time fire can also have beneficial effects on ecosystem resources. Positive impacts of fire include the management of vegetation structure and composition, the reduction of potentially flammable fuel loads, the improvement of grazing for livestock and pest control (Frost, and Robertson, 1987). Studies in Australian savanna landscapes have shown that traditional Aboriginal fire regimes have served to maximize biodiversity by maintaining habitat diversity, savanna patchiness and species diversity (Braithwaite, 1996). To establish sound fire management programs as part of an integrated ecosystem management strategy, the contrasting effects of fires need to be considered and evaluated and the resulting information need to be incorporated in the analysis of benefits and costs. As part of developing this management strategy it is important to understand the drivers of land cover and land use change and the causes of fire. The role of fire in perturbing biogeochemical cycles of carbon, nitrogen, sulfur and phosphorus needs to be understood both directly e.g. the effects of fire on soil nutrient cycling where burning takes place, and indirectly e.g. the transport and deposition of aerosols and trace gases produced during biomass burning. The impact of fire in changing biodiversity needs to be understood at the local and landscape scale. Similarly the impact of fire on modifying ecosystem composition and functioning modifications need to be understood.

Impacts on Hydrological Processes

Fire can also affect water resources by changing hydrological processes. Removal of plant canopy during fires reduces evapotranspiration losses but is often translated into increased water runoff. Furthermore, destruction of vegetative canopy and litter through fire results in intercept losses and increased soil erosion. Burning can also affect the infiltration properties of soils, resulting commonly in decreased infiltration and increased streamflow discharge. Furthermore, fires may impact water quality, by causing increases of NO₃^- and altering concentrations of cations in either soil solution or streamflow (Hibert et al., 1974; Tiedemann et al., 1979; Sims et al., 1981; Campbell et al., 1977).

In tropical forests, smoke from biomass burning impacts precipitation patterns. In a newly published study over Borneo, Indonesia, TRMM data revealed that in smoke-infested region rainfall was inhibited due to the blocking effects of heavy smoke in tropical clouds on the warm rain process of raindrop formation (Rosenfeld, 1999). In boreal forests fires cause melting of the permafrost layer and an increase in soil moisture in the active layer for a few years after the removal of the vegetation allows more solar radiation to reach the ground and decreased the albedo of the ground layer (Kasischke et al., 1992; French et al., 1999).

Send comments to MODIS FIRE User Support at University of Maryland Authorized by Christopher Justice, Fire and Thermal Anomalies Principal Investigator