Absorption and Transmission Power Coefficients for Millimeter Waves in a Weakly Ionised Vegetation Fire |
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Authors: | Kgakgamatso Mphale and Mal Heron |
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Institution: | (1) Physics Department, University of Botswana, Private Bag 0022, Gaborone, Botswana;(2) Marine Geophysical Laboratory, James Cook Univeristy, Townsville, QLD, 4811, Australia |
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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. |
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Keywords: | Signal attenuation Forest fire Weakly ionised gas Ionisation Phase change |
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