Jonathan Israel

Sensitivity Analysis of Multiple Scattering Theory Applied to Tree Canopies at Microwave Frequencies

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 canopys 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.

A New Model for Scattering From Tree Canopies Based on Physical Optics and Multiple Scattering Theory

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.

Asymptotically efficient GNSS trilateration

Localization based on the reception of radio-frequency waveforms is a crucial problem in many civilian or military applications. It is also the main objective of all Global Navigation Satellite System (GNSS). Given delayed and Doppler shifted replicas of the satellites transmitted signals, the most widespread approach consists in a suboptimal two-step procedure. First, estimate the delays and Dopplers from each satellite independently, then estimate the user position and speed thanks to a Least Square (LS) minimization. More accurate and robust techniques, such as a direct Maximum Likelihood (ML) maximization, that exploit the links in between the different channels exist but suffer from an heavy computational burden that prevent their use in real time applications. Two-steps procedures with an appropriate Weighted LS (WLS) minimization are shown to be asymptotically equivalent to the ML procedure. In this paper, we develop a closed-form expression of this WLS asymptotically efficient solution. We show that this simple expression is the sum of two terms. The first one, depending on the pseudo-ranges is the widespread used WLS solution. The second one is a Doppler-aided corrective term that should be taken into account to improve the position estimation when the observation time increases. HighlightsClosed-form expression of the optimal GNSS trilateration procedure.The standard WLS algorithm is asymptotically efficient only for short integration times.The complete solution is a simple Doppler-aided procedure.

A new GNSS integrity monitoring based on channels joint characterization

Many GNSS (Global Navigation Satellites System) applications need high integrity performances. Receiver Autonomous Integrity Monitoring (RAIM), or similar method, is commonly used. Initially developed for aeronautics, RAIM techniques may not be fully adapted for terrestrial navigation, especially in urban environments. Those techniques use basically the pseudoranges to derive an integrity criterion. In this paper, we introduce a new integrity criterion based on the correlation quality of each channel. This quality assessment is computed from the correlation levels for each channel, all based on a single position and speed. Hence, as the so-called Direct Position Estimation (DPE), we exploit the joint behaviour of all channels to detect any incoherence at an upstream step of the processing. This Direct RAIM (D-RAIM) allows detecting possible integrity problems before it can be seen on a classical RAIM scheme that only exploits the outputs of each channel.