Martin J. Wooster

Retrieval of biomass combustion rates and totals from fire radiative power observations: FRP derivation and calibration relationships between biomass consumption and fire radiative energy release

Estimates of wildfire aerosol and trace gas emissions are most commonly derived from assessments of biomass combusted. The radiative component of the energy liberated by burning fuel can be measured by remote sensing, and spaceborne fire radiative energy (FRE) measures can potentially provide detailed information on the amount and rate of biomass consumption over large areas. To implement the approach, spaceborne sensors must be able to derive fire radiative power (FRP) estimates from subpixel fires using observations in just one or two spectral channels, and calibration relationships between radiated energy and fuel consumption must be developed and validated. This paper presents results from a sensitivity analysis and from experimental fires conducted to investigate these issues. Within their methodological limits, the experimental work shows that FRP assessments made via independent hyperspectral and MIR radiance approaches in fact show good agreement, and fires are calculated to radiate 14 ± 3% [mean ± 1S.D.] of their theoretically available heat yield in a form capable of direct assessment by a nadir-viewing MIR imager. The relationship between FRE and fuel mass combusted is linear and highly significant (r2 = 0.98, n = 29, p < 0.0001), and FRP is well related to combustion rate (r2 = 0.90, n = 178, p < 0.0001), though radiation from the still-hot fuel bed can sometimes contribute significant FRP from areas where combustion has ceased. We conclude that FRE assessment offers a powerful tool for supplementing existing burned-area based fuel consumption measures, and thus shows significant promise for enhancing pyrogenic trace gas and aerosol emissions estimates

Fire radiative energy for quantitative study of biomass burning: derivation from the BIRD experimental satellite and comparison to MODIS fire products

A major focus in global change research is to quantify the amount of gaseous and particulate pollutants emitted from terrestrial vegetation fires. Determination of the emitted radiant energy released during biomass combustion episodes (the so-called fire radiative energy or FRE) has been suggested as a new tool for determining variations in biomass combustion rates and the rate of production of atmospheric pollutants. We review the physical principals behind the remote determination of FRE and present an alternative method for its derivation via analysis of ‘fire pixel’ radiances in the middle infrared spectral region. We compare our method to the existing FRE retrieval approach used in the EOS Moderate Resolution Imaging Spectro-radiometer (MODIS) fire products, and to retrievals of FRE based on derived fire temperature and area made via the so-called Bi-spectral method. We test each FRE retrieval method using both simulated data and imagery from a new experimental space mission, the Bi-spectral InfraRed Detection (BIRD) small satellite, which has sensors specifically designed for the study of active fires. We analyse near simultaneous MODIS and BIRD data of the fires that burned around Sydney, Australia in January 2002. Despite the markedly different pixel size and spectral coverage of these sensors, where the spatial extent of the fire pixel groups detected by MODIS and BIRD are similar, the derived values of FRE for these fires agree to within F15 %. However, in certain fires, the lower spatial resolution of MODIS appears to prevent many of the less intensely radiating fire pixels being detected as such, meaning MODIS underestimates FRE for these fires by up to 46% in comparison to BIRD. Though the FRE release of each of these low intensity fire pixels is relatively low, their comparatively large number makes their overall FRE significant. Thus, total FRE release of the Sydney fires on 5 January 2002 is estimated to be 6.5 � 10 9 Js � 1 via BIRD but 4.0 � 10 9 Js � 1 via MODIS. The ability of BIRD to resolve individual fire fronts further allows the first accurate calculation of ‘radiative’ fireline intensity from spaceborne measurements, providing values of 15–75 kJ s � 1 m � 1 for fire fronts that are up to 9 km in length. Finally, we analyse the effectiveness of the satellite-based FRE retrieval methods in estimating the FRE from the active flaming and smouldering components only (FREActive, believed to be proportional to the rate of biomass combustion), despite the sensor receiving additional radiance from the ‘cooling ground’. The MIR radiance method appears particularly strong in this regard, allowing FREActive to be estimated to within F30% in the range 100–100,000 J s � 1 m � 2 . These results provide further confidence in the ability of spaceborne missions to derive physically meaningful values of FRE that could be used to support biomass burning emissions inventories. Future comparisons between FRE derived via MODIS and those from higher spatial resolution BIRD or airborne imagery may allow the MODIS-derived FRE values to be ‘calibrated’ for any systematic underestimation. We therefore expect FRE to become an important tool for enhancing global studies of terrestrial vegetation fires with infrared remote sensing, particularly as the majority of large fires are now imaged four times per day via the MODIS instruments on the Terra and Aqua spacecraft. D 2003 Elsevier Science Inc. All rights reserved.

Effusion rate trends at Etna and Krafla and their implications for eruptive mechanisms

Abstract Using effusion rates obtained from ground- and satellite-based data we build a data set of 381 effusion rate measurements during effusive activity at Etna and Krafla between 1980 and 1999. This allows us to construct detailed effusion rate curves for six fissure-fed eruptions at Etna and Krafla and four summit-fed eruptions at Etna. These define two trends: Type I and II. Type I trends have effusion rates that rise rapidly to an initial peak, before declining more slowly, resulting in an exponential decrease in eruption rate and declining growth in cumulative volume. Type II trends are characterised by steady effusion and eruption rates, and hence a linear increase in cumulative volume. The former is typical of fissure eruptions and can be explained by tapping of an enclosed, pressurised system. The latter are typical of persistent Etnean summit eruptions, plus one persistent effusive eruption at Stromboli (1985–1986) examined here, and can be explained by overflow of the time-averaged magma supply. We use our effusion rate data to assess the magma balance at Etna (1980–1995) and Krafla (1975–1984). Between 1980 and 1995, Etna was supplied at a time-averaged rate of 6.8±2.3 m 3 s −1 of which 13% was erupted. At Krafla 817±30×10 6 m 3 was erupted and intruded during 1975–1984, and the ratio of erupted to intruded volume was 0.3. At Etna there is evidence for intrusion of the unerupted magma within and beneath the edifice, as well as storage in the central magma column. At Krafla unerupted magma was intruded into a rift zone, but an increasing proportion of the supply was erupted from 1980 onwards, a result of the rift zone capacity being reached. Magma intruded prior to an eruptive event may also be entrained and/or pushed out during eruption to contribute to the initial high effusion rate phases of Type I events. The detail in our effusion rate curves was only possible using a thermal approach which estimates effusion rates using satellite data. We look forward to analysing satellite-derived effusion rate trends in real-time using data from current and soon-to-be-launched sensors.

A review of Ts/VI remote sensing based methods for the retrieval of land surface energy fluxes and soil surface moisture

Imagery from remote sensing systems, often combined with ancillary ground information, is able to provide repetitive, synoptic views of key parameters characterizing land surface interactions, including surface energy fluxes and surface soil moisture. Differing methodologies using a wide range of remote sensing data have been developed for this purpose. Approaches vary from purely empirical to more complex ones, including residual methods and those that have their basis in the biophysical properties characterizing a two-dimensional Ts/VI (surface temperature/ vegetation index) scatterplot domain derived from remote sensing observations. The present article aims to offer a comprehensive and systematic review of this latter group of methods, which differ in terms of the complexity and assumptions they entail as well as their requirement for field-based and other ancillary data. Prior to the review, the biophysical meanings and properties encapsulated in the Ts/VI feature space is elucidated, since these represent the building block upon which all the Ts/VI methods described herein are based. The overview of the Ts/VI methods is also very timely, as one such method is being scheduled in the operational retrieval of surface soil moisture content by the National Polar-orbiting Operational Environmental Satellite System (NPOESS), in a series of satellite platforms due to be launched in the next 12 years starting from 2016.

Fire Detection and Fire Characterization Over Africa Using Meteosat SEVIRI

Africa is the single largest continental source of biomass burning emissions and one where emission source strengths are characterized by strong diurnal and seasonal cycles. This paper describes the development of a fire detection and characterization algorithm for generating high temporal resolution African pyrogenic emission data sets using data from the geostationary spinning enhanced visible and infrared imager (SEVIRI). The algorithm builds on a prototype approach tested previously with preoperational SEVIRI data and utilizes both spatial and spectral detection methods whose thresholds adapt contextually within and between imaging slots. Algorithm validation is carried out via comparison to data from ~800 temporally coincident moderate resolution imaging spectroradiometer (MODIS) scenes, and performance is significantly improved over the prior algorithm version, particularly in terms of detecting low fire radiative power (FRP) signals. On a per-fire basis, SEVIRI shows a good agreement with MODIS in terms of FRP measurement, with a small (3.7 MW) bias. In comparison to regional-scale total FRP derived from MODIS, SEVIRI underestimates this by, on average, 40% to 50% due to the nondetection of many low-intensity fire pixels (FRP < 50 MW). Frequency-magnitude analysis can be used to adjust fire radiative energy estimates for this effect, and taking this and other adjustments into account, SEVIRI-derived fuel consumption estimates for southern Africa from July to October 2004 are 259-339 Tg, with emission intensity peaking after midday and reducing by more than an order of magnitude each night.

Boreal forest fires burn less intensely in Russia than in North America

[1] Around 5–20 million hectares of boreal forest burns annually, mainly in Russia and North America. However, there are reports of significant differences in predominant fire type between these regions, which may have major implications for overall emissions of carbon, gases and aerosols. We examine boreal forest fire intensities via MODIS observations of fire radiative energy release rate. Results support the contention of a consistent difference in fire intensity and mean fuel consumption in Russia and North America, due to differences in dominant fire type. North American fires have higher mean intensities, increasing in proportion to percentage tree cover, characteristics indicating likely crown fire dominance. Russian fires have lower mean intensities, independent of percentage tree cover, characteristics more indicative of surface fire activity. Per unit area burnt, the results suggest Russian fires may burn less fuel and emit fewer products to the atmosphere than do those in North America. INDEX TERMS: 1615 Global Change: Biogeochemical processes (4805); 1640 Global Change: Remote sensing; 1694 Global Change: Instruments and techniques; 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions. Citation: Wooster, M. J., and Y. H. Zhang (2004), Boreal forest fires burn less intensely in Russia than in North America, Geophys. Res. Lett., 31, L20505, doi:10.1029/2004GL020805.

Major atmospheric emissions from peat fires in Southeast Asia during non-drought years: evidence from the 2013 Sumatran fires

Trans-boundary haze events in Southeast Asia are associated with large forest and peatland fires in Indonesia. These episodes of extreme air pollution usually occur during drought years induced by climate anomalies from the Pacific (El Niño Southern Oscillation) and Indian Oceans (Indian Ocean Dipole). However, in June 2013 – a non-drought year – Singapores 24-hr Pollutants Standards Index reached an all-time record 246 (rated “very unhealthy”). Here, we show using remote sensing, rainfall records and other data, that the Indonesian fires behind the 2013 haze followed a two-month dry spell in a wetter-than-average year. These fires were short-lived (one week) and limited to a localized area in Central Sumatra (1.6% of Indonesia): burning an estimated 163,336 ha, including 137,044 ha (84%) on peat. Most burning was confined to deforested lands (82%; 133,216 ha). The greenhouse gas (GHG) emissions during this brief, localized event were considerable: 172 ± 59 Tg CO2-eq (or 31 ± 12 Tg C), representing 5–10% of Indonesias mean annual GHG emissions for 2000–2005. Our observations show that extreme air pollution episodes in Southeast Asia are no longer restricted to drought years. We expect major haze events to be increasingly frequent because of ongoing deforestation of Indonesian peatlands.

Monthly burned area and forest fire carbon emission estimates for the Russian Federation from SPOT VGT

Abstract Russian boreal forests contain around 25% of all global terrestrial carbon, some of which is released to the atmosphere when the forests burn. Whilst it is well known that fire is widespread in the boreal environment, there is a lack of good quality quantitative data on the extent of fire activity in Russian forests and on its interannual variation. This study provides one of the first comprehensive monthly satellite-based studies of fires occurring across the entire Russian Federation using a single, standardised methodology designed to map burned areas down to a size of 2 km 2 . Using data from SPOT VEGETATION (VGT), we detect newly burned pixels via a series of multi-temporal spectral reflectance differencing criteria. For the year 2001, the method is applied to 21 VGT 10-day syntheses (S10) scenes covering the Russian fire season. We map 2764 fires with a total area of 41,782 km 2 , and our methodology successfully detects all fires present in a comparison Landsat ETM+ data set, although it underestimates their size by on average of 18%. Using frequency–size relations, we estimate that 3790 fires of 1–2-km 2 area are likely to have remained unobserved by our method across the entire Russian region. Taking these corrections into account, we calculate the total burned area for the Russian Federation in 2001 as 51,546 km 2 , with 38,512 km 2 occurring in forest and 13,034 km 2 in other land use classes. Fire activity is strongest in August in Eastern Siberia and the northern part of the Russian Far East, and in May and October in the southern part of the Russian Far East. Using these data, we estimate direct carbon emissions from these Russian forest fires to be 39.3–55.4 Mt, five to eight times that from the 2001 North American boreal forest fires and around 11–17% of that years Russian industrial carbon emissions. This methodology will, in the future, be applied to the full VGT archive to quantify burned area and direct carbon emissions over a 5-year period in order to better assess the interannual variation in burned area and emissions and the relation to local climate.

Production of Landsat ETM+ reference imagery of burned areas within Southern African savannahs: comparison of methods and application to MODIS

Accurate production of regional burned area maps are necessary to reduce uncertainty in emission estimates from African savannah fires. Numerous methods have been developed that map burned and unburned surfaces. These methods are typically applied to coarse spatial resolution (1 km) data to produce regional estimates of the area burned, while higher spatial resolution (<30 m) data are used to assess their accuracy with little regard to the accuracy of the higher spatial resolution reference data. In this study we aimed to investigate whether Landsat Enhanced Thematic Mapper (ETM+)‐derived reference imagery can be more accurately produced using such spectrally informed methods. The efficacy of several spectral index methods to discriminate between burned and unburned surfaces over a series of spatial scales (ground, IKONOS, Landsat ETM+ and data from the MOderate Resolution Imaging Spectrometer, MODIS) were evaluated. The optimal Landsat ETM+ reference image of burned area was achieved using a charcoal fraction map derived by linear spectral unmixing (k = 1.00, a = 99.5%), where pixels were defined as burnt if the charcoal fraction per pixel exceeded 50%. Comparison of coincident Landsat ETM+ and IKONOS burned area maps of a neighbouring region in Mongu (Zambia) indicated that the charcoal fraction map method overestimated the area burned by 1.6%. This method was, however, unstable, with the optimal fixed threshold occurring at >65% at the MODIS scale, presumably because of the decrease in signal‐to‐noise ratio as compared to the Landsat scale. At the MODIS scale the Mid‐Infrared Bispectral Index (MIRBI) using a fixed threshold of >1.75 was determined to be the optimal regional burned area mapping index (slope = 0.99, r 2 = 0.95, SE = 61.40, y = Landsat burned area, x = MODIS burned area). Application of MIRBI to the entire MODIS temporal series measured the burned area as 10 267 km2 during the 2001 fire season. The char fraction map and the MIRBI methodologies, which both produced reasonable burned area maps within southern African savannah environments, should also be evaluated in woodland and forested environments.

Fire carbon emissions over maritime southeast Asia in 2015 largest since 1997

In September and October 2015 widespread forest and peatland fires burned over large parts of maritime southeast Asia, most notably Indonesia, releasing large amounts of terrestrially-stored carbon into the atmosphere, primarily in the form of CO2, CO and CH4. With a mean emission rate of 11.3 Tg CO2 per day during Sept-Oct 2015, emissions from these fires exceeded the fossil fuel CO2 release rate of the European Union (EU28) (8.9 Tg CO2 per day). Although seasonal fires are a frequent occurrence in the human modified landscapes found in Indonesia, the extent of the 2015 fires was greatly inflated by an extended drought period associated with a strong El Niño. We estimate carbon emissions from the 2015 fires to be the largest seen in maritime southeast Asia since those associated with the record breaking El Niño of 1997. Compared to that event, a much better constrained regional total carbon emission estimate can be made for the 2015 fires through the use of present-day satellite observations of the fire’s radiative power output and atmospheric CO concentrations, processed using the modelling and assimilation framework of the Copernicus Atmosphere Monitoring Service (CAMS) and combined with unique in situ smoke measurements made on Kalimantan.