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Remotely based fuels water content assessment applied to operational fire risk prevision: Requirements, situation and perspectives
Forest Ecology and Management 234S (2006) S35
Abstract
Remotely based fuels water content assessment applied to operational fire risk prevision: Requirements, situation and perspectives Jean-Franc¸ois Galtie´ GEODE UMR 5602 CNRS-Universite´ de Toulouse II, 5 alle´e Antonio Machado, 31058 Toulouse Cedex 9, France
Keywords: Operational fire prevision; Water content assessment and monitoring; Remote sensing; State of art; Ground-based photometry
Forecasting models for occurrences and behaviors of wildland fires assign a determining role to the susceptibility of plant combustibles to fire. A key variable of this dynamic, the hydric status of the plant material influences the main determinants of this susceptibility, namely the propensity to ignition and the behavior of the fire. The variations seen in space and time, under the combined action of physiological regulatory mechanisms and mesological factors, have a direct impact on the risk level. The operational implementation of these models is faced today with the difficulties found in the characterization of these variations, particularly concerning living combustibles. Remote detection of hydric status, is one possible way to surpass major limitations specific to traditional evaluative and monitoring techniques. Applications for operational forecasting nevertheless remain very limited. In this context, this paper has three objectives: (1) put remote detection of the hydric status back into the context of operational forecasting of fire risks, and of their needs and demands; (2) provide an inventory of technological and methodological offerings in this area while pointing out the major limitations and future prospects; (3) provide an account, within the framework of the two preceding objectives, of an exploratory approach in which the photometric instrumentation of the terrain and the transmittance measurements are evaluated as a potential source and real-time indicator of the hydric status of reference plant combustibles. The ideas laid out in objectives 1 and 2 are based on shared experiences and the outcome of
DOI: 10.1016/j.foreco.2006.08.051 E-mail address: [email protected] (J.-F. Galtie´).
exchanges, observations and field observations and measurements. Objective 3 is based on an experiment in the field conducted during the summer of 2005 in prospect to establish correlations in vivo between hydric status descriptors and spectral response for five Mediterranean plant species. Putting remote detection back into the dynamic context of hydric deficiencies and operational forecasting, the study identifies, specifies and quantifies four dominant criteria (nature and precision, updating, extrapolation and accessibility of data). Despite the potential recognized by various studies, it links the weakness of operational transposition to three overlapping limitations: the temporal availability of data (frequency of acquisition, accessibility, cost. . .), deciphering (nature and precision) and temporal calibration of the signal. The results of photometric experimentation in the field, with all plant species combined, show a strong dependence between transmittance at 1940 nm and the equivalent depth of water (r2 > 0.88). At the scale of the forest fire season in 2005 (July– September 2005), they show a strong relationship between the seasonal transmittance and fire risk dynamics, characterized by the average duration of ignition and the persistence of the flames (r2 > 0.86). They thus confirm the potential interest of photometry in the field and its propensity to provide timely, precise and inexpensive real-time information on the hydric status of vegetation. This potential interest is discussed in particular in the context of spatial-temporal monitoring of risk and of prospects related to the dynamic calibration of spatial remote-sensing data.
Abstract
Remotely based fuels water content assessment applied to operational fire risk prevision: Requirements, situation and perspectives Jean-Franc¸ois Galtie´ GEODE UMR 5602 CNRS-Universite´ de Toulouse II, 5 alle´e Antonio Machado, 31058 Toulouse Cedex 9, France
Keywords: Operational fire prevision; Water content assessment and monitoring; Remote sensing; State of art; Ground-based photometry
Forecasting models for occurrences and behaviors of wildland fires assign a determining role to the susceptibility of plant combustibles to fire. A key variable of this dynamic, the hydric status of the plant material influences the main determinants of this susceptibility, namely the propensity to ignition and the behavior of the fire. The variations seen in space and time, under the combined action of physiological regulatory mechanisms and mesological factors, have a direct impact on the risk level. The operational implementation of these models is faced today with the difficulties found in the characterization of these variations, particularly concerning living combustibles. Remote detection of hydric status, is one possible way to surpass major limitations specific to traditional evaluative and monitoring techniques. Applications for operational forecasting nevertheless remain very limited. In this context, this paper has three objectives: (1) put remote detection of the hydric status back into the context of operational forecasting of fire risks, and of their needs and demands; (2) provide an inventory of technological and methodological offerings in this area while pointing out the major limitations and future prospects; (3) provide an account, within the framework of the two preceding objectives, of an exploratory approach in which the photometric instrumentation of the terrain and the transmittance measurements are evaluated as a potential source and real-time indicator of the hydric status of reference plant combustibles. The ideas laid out in objectives 1 and 2 are based on shared experiences and the outcome of
DOI: 10.1016/j.foreco.2006.08.051 E-mail address: [email protected] (J.-F. Galtie´).
exchanges, observations and field observations and measurements. Objective 3 is based on an experiment in the field conducted during the summer of 2005 in prospect to establish correlations in vivo between hydric status descriptors and spectral response for five Mediterranean plant species. Putting remote detection back into the dynamic context of hydric deficiencies and operational forecasting, the study identifies, specifies and quantifies four dominant criteria (nature and precision, updating, extrapolation and accessibility of data). Despite the potential recognized by various studies, it links the weakness of operational transposition to three overlapping limitations: the temporal availability of data (frequency of acquisition, accessibility, cost. . .), deciphering (nature and precision) and temporal calibration of the signal. The results of photometric experimentation in the field, with all plant species combined, show a strong dependence between transmittance at 1940 nm and the equivalent depth of water (r2 > 0.88). At the scale of the forest fire season in 2005 (July– September 2005), they show a strong relationship between the seasonal transmittance and fire risk dynamics, characterized by the average duration of ignition and the persistence of the flames (r2 > 0.86). They thus confirm the potential interest of photometry in the field and its propensity to provide timely, precise and inexpensive real-time information on the hydric status of vegetation. This potential interest is discussed in particular in the context of spatial-temporal monitoring of risk and of prospects related to the dynamic calibration of spatial remote-sensing data.