Spectral study of microwave attenuation in a larch forest stand for oblique wave incidence

Height Dependence of Electromagnetic Field inside the Forest Canopy at Meter and Decimeter Wavelengths

“…The receiver antenna was installed in the forest canopy at the distance along horizontal line of 120m from the transmitter one. According to [2], at this distance and the wave frequency of 200 MGz, the wave reflected from ground was found to noticeably interfere with the line-of-site propagating wave, while a very weak interference between the two waves was observed in [2], at the frequency of 1000 MGz. Consequently, given the distance of propagation of 120 m was assigned, both mechanisms of wave propagation could be studied at the same location of the receiving antenna.…”

“…While for the VV polarization the interference pattern is less noticeable as, according to [2], in this case, the wave attenuation value exceeded that for the HH polarization wave by the value of 6 dB. With the rise of frequency from 400 to 1000 MHz, the direct wave attenuation increased from 10 to 21 dB (see [2]), allowing thus for the lateral wave field to become the major contributing component to the total field amplitude, at the frequency of 1000 MHz. As a result, the interference pattern of the height dependence appeared to get practically vanished, except for the case of HV polarization.…”

“…Though some more measurements have to be performed in order to better understand the impact of frequency variations on the height dependences observed. It is worth noticing that relevant considerations on this problem are available from papers [2][3][4][5][6]. Nevertheless, it was a distinct tendency for the field amplitude to grow with the height of receiver that took place in the case of prevailing lateral wave propagation mechanism.…”

“…As a result, the interference pattern of the height dependence appeared to get practically vanished, except for the case of HV polarization. According to [2], a lateral wave penetrates the forest canopy propagating nearly along the vertical line drawn from the receiver location. Due to this fact, the difference between the primarily VV and HH polarized waves was expected to decrease to a large extent.…”

“…Meanwhile, there is still need in on ground experimental data in order to both develop and validate the aerospace monitoring technologies [1], which are applicable to the forest environment. As follows from [2]- [6], two independent mechanisms of wave propagation are contributing to an overall field amplitude inside a forest canopy, provided the transmitter is placed on top the forest. The first of these is associated with the interference of two waves, one of which propagates along the line-of-sight, while the other reaches the receiver after being reflected from the ground.…”