GPS-Reflectometry prototype for UACs and in flight data error analysis

The GNSS signals can be exploited for remote sensing purposes. In the past decade, lots of experiments have been conducted in the field of GNSS reflectometry, with the focus on the estimate of different parameters. Different methods have been presented to analyze the estimation errors, but a comprehensive analysis is still not trivial. In [1], as instance, a calibration method is presented for wind speed estimate and in [2] an error analysis for the same type of measurement is detailed. Another example is available in [3] where a calibration method is introduced for the soil moisture retrieval, using the Line-Of-Sight (LOS) Right Handed Circular Polarized (RHCP) signal and the reflected Left Handed (LHCP) signal. The aim of this work is to estimate the soil dielectric constant, by means of two reflected signals (both LHCP and RHCP) grabbed with a compact and low cost front-end, addressing the problem of the measurement error, which is fundamental in particular when using low cost devices. In this paper, a prototype of GNSS data grabber for soil moisture monitoring applications is described. It is compact to be mounted on board of an aircraft or on Unmanned Aerial Vehicle (UAV); four synchronized channels allows to simultaneously collect the LOS signal, together with the LHCP and the RHCP reflected signals. The techniques applied to process the data to retrieve the soil parameters are presented, with the focus on the measurement error in an in-flight dynamic environment.