Abstract
A vegetation fire plume is a weakly ionised gaseous medium. Electrons in the plume are mainly due to thermal ionisation of incumbent alkali impurities. The medium is highly collisional with free electron - neutral particle been the dominant particle interaction mechanism. Signal strength of an incident millimetre wave (MM-Wave) may be significantly attenuated in the plume depending on the extent of ionisation. A numerical experiment was set to investigate signal power loss of a MM-Wave incident on a simulated weakly ionised fire plume with flame maximum (seat) temperature ranging from 1000–1150 K. The simulated fire plume had alkali impurities (potassium) content of 1.0% per unit volume. MM-Wave frequency range investigated in the experiment is from 30–60 GHz. The simulation has application in the prediction of MM-Wave propagation in a crown forest fire and may also be applied in remote sensing studies of forest fire environments. Simulated attenuation per unit path length for the MM-Wave frequencies ranged from 0.06–24.00 dBm−1. Phase change per unit path length was simulated to range from 2.97–306.17°m−1 while transmission power coefficients ranged from maximum of 0.9996 for a fire plume at 1000 K to a minimum value of 0.8265 for a plume at a temperature of 1150 K over a plume depth of 1.20 m. Absorption power coefficient ranged from a minimum value of 0.0004 to maximum value of 0.1585 at a seat temperature of 1150 K over the plume depth.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
B. W. Butler, J. Cohen, D. J. Latham, R. D. Schuette, P. Sopko, K. S. Shannan, D. Jimenet, and L. S. Bradshaw, Measurements of radiant emission power and temperature in crown fires. Can. J. For. Res. 34, 1577–1587 (2003).
T. Foster, Bushfire: History, Prevention and Control (A. H. and A.W. Reed Pty Ltd, Sydney, 1976).
P. R. Williams, R. A. Congdon, and P. Clarke, Effect of fire regimes on plant abundance in tropical eucalyptus savanna of North-Eastern Australia. Aust. Ecol. 28, 324–338 (2003).
D. W. Williams, J. S. Adams, J. J. Batten, G. F. Whitty, and G. T. Richardson, “Operation Euroka: An Australian Mass Fire Experiment,” Report 386, Defense Standards Laboratory, Maribyrnor, Victoria Australia, 1970.
C. J. Gibbins and R. Chadha, Millimetre-wave propagation through hydrocarbon flame, IEE Proc., H Microw. Antennas Propag. 134, 169–173 (1987).
K. M. Mphale and M. Heron, Plant alkali content and radio wave communication efficiency in high intensity savanna wildfires, J. Atmos. Sol.-Terr. Phys. 69, 471–484 (2007).
K. Mphale, M. Jacob, and M. Heron, Prediction and measurement of electron density and collision frequency in a weakly ionised pine fire, Int. J. Infrared Millim. Waves 28, 251–262 (2007).
M. Radojevic, Chemistry of forest fires and regional haze with emphasis on Southeast Asia, Pure Appl. Geophys. 12, 157–187 (2003).
D. Latham, Space charge generated by wind tunnel fires, Atmos. Res. 51, 267–278 (1999).
C. J. Butler and A. N. Hayhurst, Kinetics of gas-phase ionization of an alkali metal, A, by the electron and proton transfer reactions: A + H3O+ → A +.H20 +H; AOH + AOH2+ H20 in fuel-rich flames at 1800–2250 K, J. Chem. Soc. Faraday Trans. 98, 2729–2734 (1998).
J. Santoru and D. J. Gregorie, Electromagnetic wave absorption in highly collisional plasma, J. Appl. Phys. 74, 3736–3743 (1993).
K. Akhtar, E. J. Scharer, S. M. Tysk, and E. Kho, Plasma interferometry at high pressures, Rev. Sci. Instrum. 74, 996–1001 (2003).
S. Zang, X. Hu, Z. Jiang, M. Liu, and Y. He, Propagation of an electromagnetic wave in an atmospheric pressure plasma: Numerical solutions, Phys. Plasmas 13, 013502 (2006).
J. L. Dupuy and M. Larini, Fire spread through a porous forest fuel bed: A radiative and convective model including fire-induced flow effect, Int. J. Wildland Fire 9, 155–172 (1999).
T. Marcelli, P. A. Santoni, A. Simeoni, E. Leoni, and B. Porterie, Fire spread across pine needle fuel beds: Characterization of temperature and velocity distributions within the plume, Int. J. Wildland Fire 13, 37–48 (2004).
Y. Itikawa, Effective collision frequency of electrons in gases. Phys. Fluids 16, 831–835 (1973).
T. Okuno, N. Sonoyama, J. Hayashi, C. Li, C. Sathe, and T. Chiba, Primary release of alkali and alkaline earth metallic species during pyrolysis of pulverized biomass, Energy Fuels 19, 2164–2171 (2005).
L. S. Frost, Conductivity of seeded atmospheric pressure plasmas, J. Appl. Phys. 32, 2029–2036 (1961).
M. Laroussi and J. R. Roth, Numerical calculation of the reflection, absorption and transmission of microwave by a nonuniform plasma slab, IEEE Trans. Plasma Sci. 21, 366–372 (1993).
D. L. Tang, A. P. Sun, X. M. Qiu, and P. Chu, Interaction of electromagnetic waves with a magnetized nonuniform plasma slab, IEEE Trans. Plasma Sci. 31, 405–410 (2003).
Acknowledgements
We would like gratefully to acknowledge the Staff Development Office of the University of Botswana. The work was partly supported by Emergency Management Australia under project no. 60/2001.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Mphale, K., Heron, M. Absorption and Transmission Power Coefficients for Millimeter Waves in a Weakly Ionised Vegetation Fire. Int J Infrared Milli Waves 28, 865–879 (2007). https://doi.org/10.1007/s10762-007-9264-2
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10762-007-9264-2