Abstract
As opposed to monostatic radars where incoherent backscattering dominates, in bistatic radars, such as Global Navigation Satellite Systems Reflectometry (GNSS-R), the forward scattered signals exhibit both an incoherent and a coherent component. Current models assume that either one or the other are dominant, and the calibration and geophysical parameter retrieval (e.g., wind speed, soil moisture, etc.) are developed accordingly. Even the presence of the coherent component of a GNSS reflected signal itself has been a matter of discussion in the last years. In this work, a method developed to separate the leakage of the direct signal in the reflected one is applied to a data set of GNSS-R signals collected over the ocean by the Microwave Interferometer Reflectometer (MIR) instrument, an airborne dual-band (L1/E1 and L5/E5a), multi-constellation (GPS and Galileo) GNSS-R instrument with two 19-elements antenna arrays with 4 beam-steered each. The presented results demonstrate the feasibility of the proposed technique to untangle the coherent and incoherent components from the total power waveform in GNSS reflected signals. This technique allows the processing of these components separately, which increases the calibration accuracy (as today both are mixed and processed together), allowing higher resolution applications since the spatial resolution of the coherent component is determined by the size of the first Fresnel zone (300–500 meters from a LEO satellite), and not by the size of the glistening zone (25 km from a LEO satellite). The identification of the coherent component enhances also the location of the specular reflection point by determining the peak maximum from this coherent component rather than the point of maximum derivative of the incoherent one, which is normally noisy and it is blurred by all the glistening zone contributions.
Highlights
During the last years, Global Navigation Satellite System-Reflectometry (GNSS-R) has been implemented mainly by performing the incoherent integration of a set of coherently integrated GNSS codes over short integration times (1–4 ms at most from space)
This work analyzes in more depth the presence of a coherent component with new data acquired by the Microwave Interferometer Reflectometer (MIR) instrument
Despite the evidences shown in the phase of the Delay-Doppler Map (DDM) over the ocean [11] and over land [7], the presence or not of a coherent component in the GNSS reflected signal and its magnitude has been the object of discussion during the last years
Summary
Global Navigation Satellite System-Reflectometry (GNSS-R) has been implemented mainly by performing the incoherent integration (the sum of the modulus square) of a set of coherently integrated GNSS codes over short integration times (1–4 ms at most from space) This integration basically removes any coherency present in the reflected signal. As shown in [6], the maximum interferometric delay is limited to about half the chip length, which puts a trade-off limit on the receiver height and on the satellite elevation angle (∼150 m for L1CA; ∼15 m for L5/E5a) This coherent component is almost negligible (but still present) in many reflections for airborne, high stratospheric balloons [7], and spaceborne instruments [8]. Despite the evidences shown in the phase of the Delay-Doppler Map (DDM) over the ocean [11] and over land [7], the presence or not of a coherent component in the GNSS reflected signal and its magnitude has been the object of discussion during the last years
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
