Radio wave attenuation in bushfires : tropical cyclones and other severe atmospheric conditions / M. L. Heron and K. Mphale.

Cover title.

EMA Project 10/2001.

Includes bibliography (p. 30-35).

1. Background to the research report -- 2. Theory -- 3. Apllication to bushfires -- 4. Measurements on radio wave propagation -- 5. Extending the calculations to other frequency bands -- 6. Tropical cyclones and other severe atmospheric conditions -- 7. Summary and conclusions.

This report adapts classical physics of Maxwell?s Equations to apply to the propagation of radio waves through bushfires, represented as weakly ionised plasma. The theoretical development shows how to calculate the attenuation and phase change of waves in terms of the electron density and the collision frequency between electrons and neutral particles. The relevant collision frequency calculation is a contemporary research topic in plasma physics and a ?best practice? approximation was adopted. Literature which shows that the potassium content of bushfire fuel varies widely between species of plant, and the stage of growth was reviewed. By relating the potassium content of the fuel through the radio wave propagation theory it was shown that there are very significant differences in radio wave attenuation in bushfires supplied with high and low potassium fuel. The theory was used to make predictions across different radio communications bands. For operational radio communications, it is recommended that procedures be developed which take into consideration the type of fuel being burned in a bushfire.