Attenuation and depolarization data measured for scattered field inside Larch canopy

In this paper, measured attenuation and depolarization of electromagnetic fields propagating through a Larch plantation canopy in the Eastern Siberia are presented. The measurements were done with a vector antenna at 200 MHz and 1275 MHz. A spatial modulation of the received signal is observed, which is attributed to the interference among the direct, reflected, and scattered waves. Two dominant features of signal attenuation are identified. The first signal feature follows an exponential attenuation behavior while the second feature is characterized by a power-law attenuation as a function of horizontal distance from the transmitter. The latter may be attributed to a lateral wave, which propagates along the canopy-air interface shedding energy into the canopy as the signal propagates. The measured depolarization factor was found to take maximum values at locations where the field is maximum. Also, a horizontally polarized incidence wave appeared to depolarize more, as compared to vertical polarization. It is important to note that the difference in depolarization decreased at greater incidence angles, which confirms the theory that the predominant propagation mechanism is through a lateral wave. The data measured were also used for estimating an effective dielectric constant of the forest canopy as calculated from the multiple scattering theory approach.