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This paper presents a new model for scattering from tree canopies based on a modified physical optics approach. In this way, propagation through a canopy is accounted for by respecting the complex propagation constant, which can be obtained either by the multiple scattering theory (MST) or approximated based on the canopy specific attenuation. Unlike the case when MST is applied directly, the proposed approach offers significant benefits, including a straightforward software implementation, feasible computation times for high frequencies and electrically large canopies, and, most importantly, near-field calculations in regions close to a canopy. The new model is first tested against MST using two artificial single-tree scenarios at 2 and 10 GHz. Then, experimental data at 2 GHz obtained with the use of a remote controlled airship for an actual single-tree scenario are utilized as well. In this way, the model is thoroughly validated and its advantages over MST are presented in detail. [ABSTRACT FROM PUBLISHER]

Following the increasing popularity of unmanned aerial vehicles (UAVs) for remote sensing applications, the reliable operation under a number of various radio wave propagation conditions is required. Assuming common outdoor scenarios, the presence of trees in the vicinity of a UAV or its ground terminal is highly probable. However, such a scenario is very difficult to address from a radio wave propagation point of view. Recently, an approach based on physical optics (PO) and the multiple scattering theory (MST) has been proposed by the authors, which enables fast and straightforward predictions of tree-scattered fields at microwave frequencies. In this paper, this approach is developed further into a generative model capable of providing both the narrowband and wideband synthetic time series of received/transmitted signals which are needed for both UAV communications and remote sensing applications in the presence of scattering from tree canopies. The proposed channel synthesizer is validated using both an artificially-generated scenario and actual experimental dataset. [ABSTRACT FROM AUTHOR]

Detailed analysis of tree canopy interaction with incident radiowaves has mainly been limited to remote sensing for the purpose offorest classification among many other applications. This represents a monostatic configuration, unlike the case of communication links, which are bistatic. In general, link analyses have been limited to the application of simple, empirical formulas based on the use of specific attenuation values in dB/m and the traversed vegetated mass as, e.g., the model in Recommendation ITU-R P.833-8 [1]. In remote sensing, two main techniques are used: Multiple Scattering Theory (MST) [2--5] and Radiative Transfer Theory (RT), [5], [6], We have paid attention in the past to MST [7--10], It was shown that a full application of MST leads to very long computation times which are unacceptable in the case where we have to analyze a scenario with several trees. Extensive work using MST has been also presented by others in [11-16] showing the interest in this technique. We have proposed a simplified model for scattering from tree canopies based on a hybridization of MST and a modified physical optics (PO) approach [16]. We assume that propagation through a canopy is accounted for by using the complex valued propagation constant obtained by MST. Unlike the case when the full MST is applied, the proposed approach offers significant benefits including a direct software implementation and acceptable computation times even for high frequencies and electrically large canopies. The proposed model thus replaces the coherent component in MST, significant in the forward direction, but keeps the incoherent or diffuse scattering component present in all directions. The incoherent component can be calculated within reasonable times. Here, we present tests of the proposed model against MST using an artificial single-tree scenario at 2 GHz and 10 GHz. [ABSTRACT FROM AUTHOR]

A sensitivity analysis of the multiple scattering theory applied to propagation in tree canopies is presented. This analysis aims at addressing the influence of input parameters on the canopy's equivalent scattering amplitude as well as the overall coherent and incoherent scattered fields. The main input parameters of interest were identified as frequency, number densities and dielectric parameters of branches and leaves, polarization, and a canopy shape. A number of graphical results are provided enabling to identify the key parameters of corresponding radio-wave propagation models based on the multiple scattering theory. [ABSTRACT FROM PUBLISHER]