E o s , Vol . 7 4 , N o . 1 2 , M a r c h 2 3 , 1 9 9 3

Global Distribution of Fires Seen from PAGES 129, 135

Space Meinrat O. Andreae

Biomass burning is one of the major pol­lution sources of the Earth's atmosphere, releasing large amounts of gaseous (CO, N 0 X , hydrocarbons, etc.) and particulate (aerosol) emissions [Crutzen and Andreae, 1990; Andreae, 1991; Leuine, 1991]. Further­more, fires in forests and savannas have an important ecological influence, especially in the tropics [Goldammer, 1990; Kozlowski andAhlgren, 1974] . Yet, no global survey of fire incidence as a function of time and geo­graphic region is available at this time. The recent release of the NASA/Space Shuttle Earth Observations Project (SSEOP) data base provides an opportunity to investigate the global distribution of large fires. For an example of such a fire, see Figure 1. Biom­ass fires or smoke plumes are evident in over 1000 of the data base images. Almost half of these fires are in Africa, a quarter are in South America, and the rest are scattered throughout the world. The data set suggests that burning follows a rather complex sea­sonal distribution.

Hand-held photography has been part of the manned space program since its begin­nings with the Mercury program. Larger crews and frequent space flights in the Space Shuttle program have resulted in a substantial number of Earth photographs being taken of features such as volcanos, vegetation fires, and meteorological phenom­ena [e.g., Helfert and Lulla, 1990; Wood and Nelson, 1991]. These images have been cata­loged in a computerized data base, which now contains descriptions of over 100,000 images taken on space missions beginning with Mercury-Redstone 3 in July 1961 through Space Shuttle mission STS-49 in May 1992. This data base is accessible on-line via computer networks (Internet sseop.jsc.na-sa.gov) or modem. For information, contact D. E. Pitts at NASA Johnson Space Center, Mail Code SN15, Houston, TX 77058; e-mail pit ts@sn.jsc.nasa.gov. The data include geo­graphical coordinates of image center and

Biogeochemistry Department, Max Planck Institute for Chemistry, PO Box 3060 , D-6500 Mainz, Ger­many

spacecraft nadir point, date, time, and a de­scription of features visible in the image.

I searched the entire data base for im­ages in which the words "fire" or "smoke" are mentioned in the features description

and then inspected the approximately 1400 records in more detail to eliminate cases depicting the Kuwait oil fires, ship fires, and smoke from industrial and power plants, etc. The remaining 1030 records are of large bio­mass fires, which are evidently flames, large smoke plumes, or smoke palls.

This data base has several limitations that reduce its reliability as a statistical and geographical tool. Coverage is not truly global because it is restricted by the inclina­tion of the spacecraft's orbit. Of the forty-six STS missions in the data base, only seven­teen had an orbital inclination > 2 8 . 6 ° , limit-

Fig. 1 Fires on eastern Melville Island, off the northern coast of Australia (11.1% 131.3°E). The photograph was taken on August 3, 1992, by the crew of the Space Shuttle, Mission 46. This near-vertical, cloud-free view shows several fires and associated smoke plumes. The widespread burning indicates the process of renewing pasture under open-canopy wood­lands. (Photo courtesy of the Space Shuttle Earth Observations Program/Flight Science Branch, NASA Johnson Space Center, Houston, Tex. Image analysis and interpretation by Ka-mlesh Lulla, Lead Mission Scientist, Earth Observations.) [Original color image appears in the the back of this volume.]

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E o s , T R A N S A C T I O N S , A M E R I C A N G E O P H Y S I C A L U N I O N

VOLUME 74, NUMBER 12

MARCH 23, 1993

PAGES 129-144

E o s , Vol . 7 4 , N o . 1 2 , M a r c h 2 3 , 1 9 9 3

60°N

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30°

60°S

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F/g. 2. Global distri­bution of fires as seen from manned space flights. Shown are the center points of pho­tographs that contain evidence of vegetation fires.

60° 60° 120° 180°E

ing the ability to record fires at higher lati­tudes. However, since most fires occur in the tropics, the results obtained were not seriously compromised. In Asia, including Indonesia and New Guinea, where much burning occurs [Malingreau et al., 1985, 1989] , photography is hampered by persis­tent cloudiness [Robinson, 1991] and shuttle mission profiles that often limit observations of this region, although considerable Indone­sian fire imagery was obtained on Shuttle flight STS-48 in September 1991.

Since the observations are not temporally continuous, analysis of the seasonal distribu­tion of fires from the SSEOP data base is dif­ficult. However, from August 1965, when the first photographs of fires were taken on Gemini Mission 5, to May 1992, the most recent available data set, flights were con­ducted at all times of the year. Table 1 lists the number of days that manned spacecraft were in orbit for each month. This shows that while coverage is uneven throughout the year, at least all seasons are reasonably well represented. Normalization of observations to flight frequency can be used to eliminate some of this bias. There is also a bias toward large fires, s ince they must be con­spicuous enough to attract the astronauts' attention from some 2 5 0 - 5 0 0 km away. Fi­nally, inspection of STS imagery reveals that identifiable fire-related characteristics are not mentioned in the "features" description in all cases . In spite of these limitations, I feel that this data set gives a unique global per­spective on the distribution of large-scale fires that is not currently available from any other source.

The center points o f all photographs that contain evidence of biomass fires are plotted over a world map in Figure 2. A number of interesting and somewhat surprising trends emerge. While numerous fires are seen in the "class ic" deforestation regions at the pe­rimeter of the Amazon Basin and in west Africa, many more are detected in areas where large vegetation fires have not been recognized to be abundant. Central America, Mexico, and the pampas belt in Southern Brazil, Paraguay, and Argentina, as well as

as

a-A

SSl Southern Hemisphere

H Northern Hemisphere

1 i J JL 1 2 3 4 5 6 7 8 9 1 0 11 1 2

Month

Fig. 3. Seasonality of fires in the Northern Hemisphere (dark shading) and the Southern Hemisphere (light shading) as ex­pressed by the fire frequency index de­fined as the ratio be­tween fire images and space flight days in a given month.

the Andean countries Bolivia, Peru, and Ec­uador are the sites of many large fires. In Africa, fires are evident throughout the sub-Saharan belt; the largest concentration of fires in the world appears to be in the sa­vanna regions of southern Africa—Zaire, An­gola, Zambia, Tanzania, Mozambique, and Madagascar. In Australia, most fires are seen in the Northern Territory and Queensland. The extratropical regions of the Northern Hemisphere show relatively few fires: some clusters are present in Siberia and Nepal, as well as in North America. In the United States, a number of fires are seen in the for­ests and agricultural land of coastal regions of the Pacific, the Gulf of Mexico, and the Atlantic, and in the Everglades grasslands of Florida. In Europe, large fires were seen only in the scrublands of Corsica and Rhodos in the Mediterranean and in the European part of Russia.

Of the 1030 cases investigated, 42 .6% are in Africa, 26 .5% in South America, 12.5% in Asia, 6.6% in Australia and Oceania, 6.8% in Central America and Mexico, 4 .2% in North America, and 0.8% in Europe. The concen­tration of fires on the land masses on either side of the Atlantic is consistent with aircraft

and remote-sensing observations of high lev­els of pollutants over Africa, South America, and the southern tropical Atlantic {Andreae et al., 1992; Fishman et al., 1990; Reichle et al., 1990]. As mentioned above, the relative scarcity of fires in Asia is probably at least in part due to the Shuttle mission profiles.

To investigate the seasonal distribution of the fires, the dates of the images were strati­fied by the month in which they were taken; the results for each hemisphere are given in Table 1. To reduce the bias due to the un­even distribution of the flights, I have di­vided the number of images in a given month by the number of spacecraft mission days in that month to obtain a fire frequency index (Figure 3 ) . This index must be seen as a semiquantitative parameter, since many subjective and objective factors—crew atten­tion, cloudiness, mission profiles, etc.—in­fluence the number of images obtained from fires present during a given flight.

The results in Figure 3 confirm the exis­tence of distinct fire seasons, particularly in the Southern Hemisphere, with a maximum in September and October. This seasonality is reflected in high ozone levels in the South Atlantic region at the same time of year

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E o s , Vol . 7 4 , N o . 1 2 , M a r c h 2 3 , 1 9 9 3

1 2 3 4 5 6 7 8 9 10 11 12

Month

Fig. 4. Occurrence of fires as function of latitude and time of year. The labeled clusters indi­cate the geographical region where most of the fires at a given time and latitude were ob­served.

[Fishman et al., 1990] . Figure 3 also shows, however, that numerous large fires occur in both hemispheres throughout the year. The widespread perception that fires are limited to hemisphere-wide "fire seasons" is an oversimplification. A more detailed analysis of the complex distribution of fires in space and time is presented in Figure 4, where the latitude of the fire images is plotted against time of year, showing the fire seasons of the various regions in the form of clusters. The clustering is, of course, partly due to the ten­dency of the astronauts to take a number of pictures of a conspicuous fire region. But in the case of most of the larger clusters, fires in the same region and season were ob­served from several flights over several years. For each of the clusters, the region where

most of the fire observations were made is indicated in Figure 4 , but most clusters also include fires observed in other regions at similar latitudes and times of year.

In the Northern Hemisphere, there is clear evidence of a shift in the latitude of fire frequency from the tropics early and late in the year to high latitudes in northern sum­mer. In the Southern Hemisphere, high-lati­tude fires are again concentrated in the sum­mer and fall months, while the tropical fires follow the regional dry seasons. In tropical Brazil, for example, almost all of the fires occurred from late August to early October, coinciding with the late part of the dry sea­son when the vegetation is driest and most suitable for forest clearing. This trend agrees with the findings of Setzer and Pereira [1991] , who used data from the National

Table 1. Temporal Distribution of Space Flights and Fire Observations by Month

Month Flight Days

Southern Hemisphere

Images Frequency

Northern Hemisphere

Images Frequency

1 6 0 41 0.68 72 1.20 2 18 1 0.06 4 0.22 3 37 6 0 .16 60 1.62 4 4 6 31 0.67 51 1.11 5 33 7 0.21 4 5 1.36 6 61 59 0.97 4 0.07 7 11 2 0.18 3 0.27 8 65 153 2 .35 27 0.42 9 22 175 7.95 2 5 1.14

10 42 170 4 .05 3 8 0 .90 11 65 38 0.58 13 0 .20 12 72 9 0.13 5 0.07

Listed are the total number of space flight days in a given month for the miss ions surveyed, the number o f images containing evidence of fires in that month, and the fire frequency index (the ratio between fire images and flight days) .

Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer (AVHRR) satellite sensor and found a sharp maximum of fire frequency in Amazonia in August and September. The grassland fires in Argentina and southernmost Brazil, on the other hand, occur from October to February, which is the dry season in that region. In Africa we see a migration of the fire distribu­tion from Zaire, which straddles the equator, from March to June, to southern Zaire, An­gola, Zambia, and Zimbabwe from June to July—the onset of the dry season—to Mada­gascar and Mozambique in October, the end of the dry season in that region.

In conclusion, the analysis of the SSEOP data base provides us with a first global and long-term view of large biomass fires. The images contain much more information, and further analysis should offer a more accurate understanding of vegetation fire patterns. Preliminary analysis shows an increase of burning in the Amazon from 1973 to 1985 and can provide estimates of the size of the areas exposed to fire [Helfert and Lulla, 1990; Wood and Nelson, 1991]. In conjunc­tion with remote sensing of fires from un­manned platforms, especially the AVHRR on the NOAA satellites [Malingreau et al., 1989; Kaufman et al., 1990], the Landsat Thematic Mapper and Systeme Probatoire d'Observa­tion de la Terre (SPOT) imagery [Brustet et al., 1991; Matson andHolben, 1987], and some sensors planned for the future, the analysis of hand-held imagery holds signifi­cant promise for investigating the role of fires in the environment.

Acknowledgments

The help of D. Pitts in accessing the SSEOP data base, K. Lulla and D. L. Amsbury in obtaining Space Shuttle images, and the late R. Brost in plotting the results are grate­fully acknowledged.

References

Andreae, M. O., Biomass burning: Its history, use and distribution and its impact on environmental quality and global climate, in Global Biomass Burning: Atmospheric, Climatic and Biospheric Implications, edited by J . S. Levine, pp. 3 - 2 1 , MIT Press, Cambridge, Mass., 1991.

Andreae, M. O., A. Chapuis, B. Cros, J . Fontan, G. Helas, C. Justice, Y. J . Kaufman, A. Minga, and D. Nganga, Ozone and Aitken nuclei over equa­torial Africa: Airborne observations during DE-CAFE 88 , J. Geophys. Res., 97, 6137, 1992.

Brustet, J . M., J . B. Vickos, J . Fontan, K. Manissad-jan, A. Podaire, and F. Lavenu, Remote sensing of biomass burning in West Africa with NOAA-AVHRR, in Global Biomass Burning: Atmo­spheric, Climatic and Biospheric Implications, edited by J . S. Levine, pp. 4 7 - 5 2 , MIT Press, Cam­bridge, Mass., 1991.

Crutzen, P. J . , and M. O. Andreae, Biomass burn­ing in the tropics: Impact on atmospheric chem­istry and biogeochemical cycles, Science, 250, 1669, 1990.

Fishman, J . , C E. Watson, J . C. Larsen, and J . A. Logan, Distribution of tropospheric ozone deter­mined from satellite data, J. Geophys. Res., 95, 3599 , 1990.

Goldammer, J . G. (Ed.) , Fire in the Tropical Biota: Ecosystem Processes and Global Challenges, Springer-Verlag, Berlin-Heidelberg, 1990.

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E o s , Vol . 7 4 , N o . 1 2 , M a r c h 2 3 , 1 9 9 3

Helfert, M. R., and K. P. Lulla, Mapping continen­tal-scale biomass burning and smoke palls over the Amazon Basin as observed from the Space Shuttle, Photogramm. Eng. Remote Sens., 56, 1367, 1990.

Kaufman, Y. J . , C. J . Tucker, and I. Fung, Remote sensing of biomass burning in the tropics, J. Geophys. Res., 95, 9927, 1990.

Kozlowski, T. T., and C. E. Ahlgren, Fire and Eco­systems, 542 pp., Academic Press, New York, 1974.

Levine, J . S. (Ed.) , Global Biomass Burning: Atmo­spheric, Climatic, and Biospheric Implications, 569 pp., MIT Press, Cambridge, Mass., 1991.

Malingreau, J . P., G. Stephens, and L. Fellows, Re­mote sensing of forest fires: Kalimantan and North Borneo in 1 9 8 2 - 8 3 , 4 m 6 / o , 14, 314, 1985.

Malingreau, J . P., C. J . Tucker, and N. Laporte, AVHRR for monitoring global tropical deforesta­tion, Int. J. Remote Sens., 10, 855, 1989.

Matson, M., and D. Holben, Satellite detection of

tropical burning in Brazil, Int. J. Remote Sens., 8, 509, 1987.

Reichle, H. G., Jr . , V. S. Connors, J . A. Holland, R. T. Sherrill, H. A. Wallio, J . C. Casas, E. P. Con­don, B. B. Gormsen, and W. Seiler, The distribu­tion of middle tropospheric carbon monoxide during early October 1984, J . Geophys. Res., 95, 9845, 1990.

Robinson, J . M., Problems in global fire evaluation: Is remote sensing the solution?, in Global Biom­ass Burning: Atmospheric, Climatic and bio­spheric Implications, edited by J . S. Levine, pp. 6 7 - 7 3 , MIT Press, Cambridge, Mass., 1991.

Setzer, A. W., and M. C. Pereira, Amazon biomass burnings in 1987 and their tropospheric emis­sions, Ambio, 20, 19, 1991.

Wood, C. A., and R. Nelson, Astronaut observa­tions of global biomass burning, in Global Bio­mass Burning: Atmospheric, Climatic and Bio­spheric Implications, edited by J . S. Levine, pp. 2 9 - 4 0 , MIT Press, Cambridge, Mass., 1991.

U.S. National Seismograph Network Improves Earthquake Monitoring PAGES 136-137

Ray Buland The concept of a United States National

Seismograph Network (USNSN) dates back nearly 30 years. The idea was revived several times over the decades but never funded. For example, a national network was pro­posed and discussed at great length in the so-called "Bolt Report" (U.S. Earthquake Ob­servatories: Recommendations for a New National Network, National Academy Press, Washington, D.C., 1980). From the begin­ning, a national network was viewed as aug­menting and complementing the dense, pre­dominantly short-period vertical coverage of selected areas provided by the Regional Seis­mograph Networks (RSNs) with a sparse, well-distributed network of three-component, observatory-quality, permanent stations.

The opportunity to develop a national network finally arose in 1986 with discus­sions between the U.S. Geological Survey and the Nuclear Regulatory Commission. Under the agreement signed in 1987, the NRC has provided $5 million in new funding for capital equipment (over 1987-1992) , and the USGS has provided personnel and facili­ties to develop, deploy, and operate the net­work. Because the NRC funding was ear­marked for the eastern U.S., new USNSN station deployments are mostly east of 105°W longitude, while the network in the western U.S. is made up mostly of cooperat­ing stations (stations meeting USNSN design goals but deployed and operated by other institutions that provide a logical extension to the USNSN).

USNSN Design and Implementation

The USNSN was designed, with extensive input from the seismological community and industry, to serve the purposes of the Na­tional Earthquake Information Service (NEIS), the NRC, and the seismological research community. The goals were to provide highly reliable, highly linear, real-time, three-com­ponent, well-calibrated, broadband, on-scale monitoring of moderate to large earthquakes at local, regional, and teleseismic distances. In short, the USNSN was intended to apply

observatory-quality instrumentation to conti­nental-scale seismological problems.

From 1987 to 1989, the USNSN was planned and specified and underwent a lengthy competitive procurement process, including rigorous production sample test­ing. Equipment for the field, telemetry, and the central control and processing system was selected. In 1990, hardware was deliv­ered and development began on the critical system integration software. The USNSN be­came operational and was dedicated in April 1991. Since then, extensive work has been done on stabilizing the real-time processes, enhancing functionality, deploying field equipment, and adding cooperating stations.

The USNSN is based on the following hardware:

1. In the field, Guralp Systems CMG-3 seismometers and CMG-5 accelerometers are interfaced with a six-channel, 80 sample/s, 24-bit Quanterra station processor. There is no local data storage except processor buffer memory. The principal band of interest is from 200 s to 30 Hz.

2. Telemetry is provided by a Scientific Atlanta Ku-band, time division multiple ac­cess , very small-aperture (satellite) terminal (VSAT) system. A VSAT connects each sta­tion processor to the master Earth station (MES) located at the National Earthquake Information Center (NEIC) in Golden, Colo., via the GE K-2 geosynchronous telecommu­nications satellite using the X.25 communi­cations protocol.

3. The network-processor system at the NEIC runs on four Digital Equipment Corpo­ration (DEC) IJLVAX 3000/4000 32-bit micro­computers (under the VMS operating system) configured as a local area VAXcluster. Scratch storage is provided by two System Industries Clustor III multiported disk sub­systems. The network processor receives X.25 data from the MES via Simpact copro­cessors. Archival data storage is provided by an Aquidneck Systems write once optical disk jukebox.

• USNSN STATIONS

• COOPERATING STATIONS

A USSN STATIONS

U.S. Geological Survey, Box 25046, M.S. 967, Den­ver Federal Center, Denver, CO 80225

Fig. 1. USNSN (filled circles) and cooperating USNSN stations (filled squares) in relation to the USSN stations (open triangles) excluding Alaska and Hawaii.

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Vol. 74, No. 12, March 23, 1993

Fig. 1 Fires on eastern Melville Island, off the northern coast of Australia (I I. JOS, 131.3°E). The photograph was taken on August 3, 1992, by the crew of the Space Shuttle, Mission 46.

This near·vertical, cloud-free view shows several fires and associated smoke plumes. The widespread burning indicates the process of renewing pasture under open-canopy wood­lands. (Photo courtesy of the Space Shuttle Earth Observations Program/Flight Science Branch, NASA Johnson Space Center, Houston, Tex. Image analysis and interpretation by Ka­mlesh Lulla, Lead Mission Scientist, Earth Observations.)