Spectral mixture analysis to assess post-fire vegetation regeneration using Landsat Thematic Mapper imagery: Accounting for soil brightness variation     

S. Veraverbeke  B. Somers 《International Journal of Applied Earth Observation and Geoinformation》2012,14(1):1-11

Post-fire vegetation cover is a crucial parameter in rangeland management. This study aims to assess the post-fire vegetation recovery 3 years after the large 2007 Peloponnese (Greece) wildfires. Post-fire recovery landscapes typically are mixed vegetation-substrate environments which makes spectral mixture analysis (SMA) a very effective tool to derive fractional vegetation cover maps. Using a combination of field and simulation techniques this study aimed to account for the impact of background brightness variability on SMA model performance. The field data consisted out of a spectral library of in situ measured reflectance signals of vegetation and substrate and 78 line transect plots. In addition, a Landsat Thematic Mapper (TM) scene was employed in the study. A simple SMA, in which each constituting terrain feature is represented by its mean spectral signature, a multiple endmember SMA (MESMA) and a segmented SMA, which accounts for soil brightness variations by forcing the substrate endmember choice based on ancillary data (lithological map), were applied. In the study area two main spectrally different lithological units were present: relatively bright limestone and relatively dark flysch (sand-siltstone). Although the simple SMA model resulted in reasonable regression fits for the flysch and limestones subsets separately (coefficient of determination R² of respectively 0.67 and 0.72 between field and TM data), the performance of the regression model on the pooled dataset was considerably weaker (R² = 0.65). Moreover, the regression lines significantly diverged among the different subsets leading to systematic over-or underestimations of the vegetative fraction depending on the substrate type. MESMA did not solve the endmember variability issue. The MESMA model did not manage to select the proper substrate spectrum on a reliable basis due to the lack of shape differences between the flysch and limestone spectra,. The segmented SMA model which accounts for soil brightness variations minimized the variability problems. Compared to the simple SMA and MESMA models, the segmented SMA resulted in a higher overall correlation (R² = 0.70), its regression slope and intercept were more similar among the different substrate types and its resulting regression lines more closely resembled the expected one-one line. This paper demonstrates the improvement of a segmented approach in accounting for soil brightness variations in estimating vegetative cover using SMA. However, further research is required to evaluate the model's performance for other soil types, with other image data and at different post-fire timings.  相似文献   

应用DTM改善煤层自燃的热红外探测     

万余庆  张祥民 《遥感学报》1996,(4)

根据遥感物理基础，提出了应用ＤＴＭ计算出地表的太阳辐射强度，并以此为依据校正ＴＭ第６波段的象元值，消除地形的影响，突出由煤层自燃引起的地表热异常，为灭火工程及火区动态监测提供信息和指导。文中选择了新疆准南煤田的硫磺沟火区为试验区，展示了研究的成果。  相似文献   

鄂西山区森林火灾的分布特征及与地形气候的关系     

陈正洪 《地理研究》1992,11(3):98-100

本文揭示了鄂西山区森林火灾水平分布特征:1)森林火险具有地域差异性和邻近相似性,2)从北到南火险由高到低;3)高山林区为低火险区,4)23林区县市为低火险级;5)1600—2000m左右火灾最多发生,向上向下均减少。  相似文献   

辽宁海城7.3级地震死亡人数-年龄分布的分析   总被引：1，自引：0，他引：1  

贾燕  高建国 《中国地震》2004,20(4):394-398

2004年2月，我们在辽宁省海城市档案馆发现了《海城市县委关于全县干部人员受地震伤亡统计表名单》。通过对地震时死亡以及震后冻死、烧死、捂死和病死者年龄段的分析，得出不同的原因致死者所集中的年龄段不同。这个结论对于中国北方冬季的防震减灾有相当的参考价值，对今后的防震减灾工作有一定的指导意义。  相似文献   

Charcoal morphotypes in lake sediments from British Columbia (Canada): an assessment of their utility for the reconstruction of past fire and precipitation     

Mihaela D. Enache  Brian F. Cumming 《Journal of Paleolimnology》2007,38(3):347-363

Quantitative analysis of variations in morphological types of charcoal were undertaken in sediment cores from three lakes on the Interior Plateau (BC, Canada) over the period AD 1919–2000. Seven distinct morphological types of charcoal were identified based on particle shape and structural features and were compared with seasonal precipitation and recorded area burned within 20 km-radius of study lakes. Fragile-type charcoal fragments, termed type M, displayed significant relationships to recorded area burned in sediment cores from Prosser (r ² = 0.5; p = 0.0001) and Opatcho (r ² = 0.2; p = 0.02) lakes. However, nonsignificant correlations (p > 0.05) were found between total charcoal and area burned. Robust and highly elongated morphotypes C and F were correlated to recorded spring precipitation (r ² = 0.5; p = 0.002) in Opatcho Lake. Charcoal from a sediment core from Big Lake, the lake with the largest watershed, was significantly but inversely related to past fires (r ² = 0.44; p = 0.0003), suggesting important contributions from secondary transportation and deposition. Models were developed to infer relative area burned and precipitation for the study lakes. Our results suggest that charcoal morphotypes are related to the biogeoclimatic and lake watershed characteristics. This study also suggest that charcoal morphotypes can provide insights on past fire and climate, which was not possible based on traditional analysis of total charcoal.  相似文献   

Local boundary-layer development over burnt and unburnt tropical savanna: an observational study     

Chris K. Wendt  Jason Beringer  Nigel J. Tapper  Lindsay B. Hutley 《Boundary-Layer Meteorology》2007,124(2):291-304

Fire scars have the ability to radically alter the surface energy budget within a tropical savanna by reducing surface albedo, increasing available energy for partitioning into sensible and latent heat fluxes and increasing substrate heat flux. These changes have the potential to alter boundary-layer conditions and ultimately feedback to local and regional climate. We measured radiative and energy fluxes over burnt and unburnt tropical savanna near Howard Springs, Darwin, Australia. At the burnt site a low to moderate intensity fire, ranging between 1,000 and 3,500 kW m⁻¹, initially affected the land surface by removing all understorey vegetation, charring and blackening the ground surface, scorching the overstorey canopy and reducing the albedo. A reduction in latent heat fluxes to almost zero was seen immediately after the fire when the canopy was scorched. This was then followed by an increase in the sensible heat flux and a large increase in the ground heat flux over the burnt surface. Tethered balloon measurements showed that, despite the presence of pre-monsoonal rain events occurring during the measurement period, the lower boundary layer over the burnt site was up to 2^°C warmer than that over the unburnt site. This increase in boundary-layer heating when applied to fire scars at the landscape scale can have the ability to form or alter local mesoscale circulations and ultimately create a feedback to regional heating and precipitation patterns that may affect larger-scale processes such as the Australian monsoon.  相似文献   

Molecular characterization of dissolved black nitrogen via electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry     

《Organic Geochemistry》2015

Combustion produces a complex mixture of polycondensed aromatic compounds known as black carbon (BC). Such products can become remobilized from char and soil in the form of dissolved BC (DBC). Ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (ESI–FT-ICRMS) analysis of a variety of soil and char leachates showed that a significant proportion of DBC compounds contained one or more nitrogen atoms. While the presence of black nitrogen (DBN) in dissolved organic matter (DOM) has been reported, its molecular features were uncharacterized. Here we present results of FT-ICRMS characterization of DBN, where assigned formulae were validated on the basis on their ¹³C isotope signatures and fragmentation patterns obtained via collision induced dissociation. Possible chemical structures were assigned for several DBN formulae and suggest that nitrogen was incorporated into the core ring system as a pyrrole-type moiety. Most DBN compounds existed as part of homologous series where homologs differed by a mass corresponding to CO₂, suggesting that they were polysubstituted with carboxylic acid groups. The environmental contribution of such novel, aromatic, combustion-derived nitrogen compounds with respect to global nitrogen cycling remains elusive. The biogeochemical implications of the input of such fire-derived products to aquatic ecosystems as part of climate change therefore need to be assessed.  相似文献   

Monitoring the impact of aerosol contamination on the drought-induced decline of gross primary productivity     

《International Journal of Applied Earth Observation and Geoinformation》2015

Southwestern China experienced a period of severe drought from September 2009 to May 2010. It led to widespread decline in the enhanced vegetation index (EVI) and gross primary productivity (GPP) in the springtime of 2010 (March to May). However, this study observed a spatial inconsistency between drought-impacted vegetation decline and the precipitation deficit. Significant aerosol loads that correspond to inconsistent areas were also observed during the drought period. After analyzing both MODIS GPP/NPP Collection 5 (C5) and the newer Collection 5.5 (C55) data, a large area observed to be experiencing GPP decline in the eastern part of the study area proved to be unreliable. Based on EVI data, after atmospherically contaminated data were screened from analysis, approximately 20% of the study area exhibited browning whereas 33% displayed no change or greening and the remaining area (approximately 47%) lacked sufficient data to document changing conditions. Correlation analysis showed that fire occurrences, aerosol optical depth, and precipitation anomalies during the two drought periods (from September to February and from March to May) all contributed to a decrease in GPP. C55 data remains vulnerable to aerosol contamination due to a much higher correlation coefficient with aerosol optical depth compared to C5 data. In the future, users of remotely sensed data should be cautious of and take into account impacts related to atmospheric contamination, even during drought periods.  相似文献   

多普勒天气雷达在扑灭"7.29"井冈山火警中的应用     

董家祥  王华军  吕作范 《气象与减灾研究》2005,28(1):50-52

从多普勒天气雷达产品和天气形势分析入手,对利用人工增雨手段扑灭"7·29"井冈山火警过程进行了技术总结,得到了一些有益的结论一是井冈山区处副热带高压西南象限时,有利于人工增雨;二是中低空弱的冷平流有利于井冈山局部对流的发展;三是井冈山区对流单体在初始阶段的移向移速与700hPa风向风速对应较好;四是罗霄山脉中部的低空平均径向速度入流区的演变,与井冈山局部对流单体关系密切;五是应按山脉走向来布设人工增雨作业炮点.  相似文献   

The application of fire spread and evacuation simulation technology in large stadium     

Zhu Wei  Ding Hui  Wang Tong 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(4):433-439

Fire is a major danger in the large stadium due to fire accompanied with smoke flow and evacuation path. As a part of an effort to improve the life safety in large stadium, the simulation technology combined with fire spread and evacuation had been developed. Besides that, in order to decrease the rate of people death in the large stadium fire, the interface between fire and the evacuation people must be designed according to simulation results, based on the influence laws to human behavior by smoke temperature, CO concentration and extinction coefficient in fire condition. Therefore, the investigation of effect of fire spread on life safety is needed. In this paper, the dynamic changes of walking speed, route choice and mental state is obtained from automatic reading of fire data during the simulation of evacuation. The effect abruptly changes due to time-varying fire smoke parameters, especially local jamming and uneven efficiency of routes. From the simulation, the visual and tried evidences would be provided for safe evacuation in fire emergency in large stadiums.  相似文献