No abstract

Decoupling the integrated microwave signal originating from soil and vegetation remains a challenge for all microwave remote sensing applications. To improve satellite and airborne microwave data products in forest environments, a precise and reliable estimation of the relative permittivity (ε = ε − iε ) of trees is required.We developed an open-ended coaxial probe suitable for in situ permittivity measurements of tree trunks at L-band frequencies (1-2 GHz). The probe is characterized by uncertainty ratios under 3.3 % for a broad range of relative permittivities (unitless), for ε and [0.1-20] for ε . We quantified the complex number describing the permittivity of seven different tree species in both frozen and thawed states: black spruce, larch, red spruce, balsam fir, red pine, aspen and black cherry. Permittivity variability is substantial and can range up to 300 % for certain species. Our results show that the permittivity of wood is linked to the freeze-thaw state of vegetation and that even short winter thaw events can lead to an increase in vegetation permittivity. The open-ended coaxial probe proved to be precise enough to capture the diurnal cycle of water storage inside the trunk for the length of the growing season.

This paper deals with a numerical simulation to predict the air flow behaviour inside the chamber of an OWC wave converter plant by use of FLUENT code. The flow is assumed to be compressible, viscous and unsteady. Calculations have been conducted by considering a typical geometry (PICO plant) with an oscillating water free surface. In our analyses, we have only considered the case of monochromatic sinusoidal excitations with various frequencies and fixed amplitude. Analyses are focused on the flow behaviour characteristics both in the chamber and in the duct in order to obtain the temporal variation of velocity, pressure, flow rate and pneumatic power fields. Also, the mean characteristics like RMS ones of these parameters are determined. A great attention is paid to show the process of energy generation inside the chamber which can be exploited by a rotating turbine. In our case, we have included in the model a linear law relating the pressure drop to the mass flow rate in order to take into account the presence of the turbine. This is achieved in FLUENT by considering a domain of porous media in the turbine location. Simulation results obtained for all frequencies show that this code is very powerful and suitable for flow prediction in such geometries. Also, the amount of energy and also the aerodynamic losses between the chamber and the duct are well calculated.

We present nondestructive measurements of dielectric properties of concrete and mortar. The measures are made using a coaxial probe with a 32.5 mm open end, engineered specially for this work. The frequency domain goes from 100 to 900 MHz and includes frequently found frequencies in radars used for the auscultation of concrete structures. The probe was calibrated, and the measures were validated successfully on two solutions of different salinity, as well as on limestone and granite samples. Measures were also carried out on two mortars and six concretes of different recipes. We studied the effect of porosity and water content on the measures. The statistical analysis of the results indicates thatthe dispersion of measurements on these heterogeneous materials (granulometry from 5 to 20 nm) is comparable to that observed in limestone and granite. Our results confirm those from other authors who used more complicated techniques.[Traduit par la Rédaction]

No abstract