In this paper the ability of four radar sensors in detecting breath activity has been tested. In particular, range gating UWB, CMOS UWB, CW phase detecting, and FMCW radars have taken into account. Considering a realistic scenario, the radar antenna has been pointed towards the thorax of a breathing subject and the recorded signals have been compared with those of a piezoelectric belt placed around the thorax. Then the ability of the radars in detecting small movements has been tested by means of an oscillating copper plate placed at various distances from the radar antenna. All the considered radars were able to detect the plate movements with a distance-dependent resolution.

The mean power of the reflected Global Navigation Satellite System (GNSS) signals acquired by a GNSS-Reflectometry (GNSS-R) receiver can be modeled through the integral bistatic radar equation by weighting the contributions of all scatterers on the surface by the system impulse response. The geophysical properties of the scattering surface affect the magnitude of the reflected navigation signals through the bistatic scattering coefficient which, in case the observed surface is land, is a function of the soil dielectric properties, surface roughness, and vegetation cover. In this paper, the GNSS-R signal simulator developed in the framework of the Land MOnitoring with Navigation signal (LEiMON) Project, supported by European Space Agency, is presented. The simulator is able to predict the power reflected by land, taking as input the system and observation parameters, as well as the land surface parameters. The latter are used to simulate both the coherent and the incoherent scattering, taking advantage of widely used theoretical models of bistatic scattering from bare soils and vegetated surfaces. First, the geometrical formulation is discussed, and then, the problem of polarization mismatch due to real antennas at circular polarization is faced following the polarization synthesis approach. Finally, a comparison with some experimental data collected during the LEiMON campaign is presented. The simulations display the same trend of the experimental data, thus showing that the simulator can be used as an efficient tool for the interpretation of GNSS-R measurements.

The detection of the land surface scattering of the signal radiated by navigation satellites may help estimating geophysical parameters such as soil moisture and vegetation biomass. In fact, the modulation of the GNSS signal and its frequency (L band) are particularly effective to sense vegetation attenuation and change of soil permittivity due to moisture. An experiment has been carried out in Italy using a GNSS reflectometer (GNSS-R) developed by STARLAB, mounted on top of a crane and looking toward a couple of agricultural fields by two downlooking antennas operating at right and left circular polarization. The data collected during the experiment have been interpreted by comparing them to the output of a theoretical simulator, with the purpose of interpreting from an electromagnetic point of view the scattering mechanisms involved in the experiment. A summary of the simulator main feature and some comparison results is presented in this paper.

When considering a bistatic system made up of GNSS satellites and a receiver, the power at the receiver is modeled taking into account the matched filtering of the incoming signal with the PRN code modulation and Doppler filtering. In this paper, the simulator developed in the framework of the LEIMON Project supported by ESA, will be presented. The simulator is able to predict the power reflected by land taking as input the system and observation parameters, as well as the land surface parameters. The earth surface (represented by bare and vegetated soils) leaves its signature through the bistatic scattering coefficient which has been modeled by means of well established electromagnetic theories applicable at L-band. Experimental data collected during the LEIMON campaign will be compared with simulated data.