GNSS Measurement of Rain Rate by Polarimetric Phase Shift: Theoretical Analysis

Abstract

Abstract:In this paper, a novel method for rain rate estimation is researched by polarimetric phase shift of the Global Navigation Satellite System (GNSS). The physical process of GNSS signals propagating through rain-filled medium is investigated, by which the cause of polarimetric phase shift is explored. Then, a theoretical model between polarimetric phase shift ∆φ and rain rate R is established and simulated, which is based on the oblate spheroid raindrop model, four different popular raindrop size distribution models and raindrop canting angle distribution across the Space-Earth rain path. Additionally, effects of raindrop size distribution, rain path length, raindrop canting angle and temperature on the ∆φ-R relation are discussed systematically. Other factors in the slant path such as ice crystals, melting particles and ionosphere are also researched preliminarily. The results show that polarimetric phase shift of GNSS signals, which has a strong correlation with rain rate, can be used to estimate the rain rate, and these influencing factors, raindrop size distribution, rain path length, raindrop canting angle and temperature, are quite important in the process of rain rate measurement. It can be also found that the effect of ice crystals can be negligible, while that of melting particles should be considered, and though ionosphere effects are not obvious, the ionospheric anomalies cannot be neglected in future experiments. This method has potential applications in real-time, continuous, extreme precipitation reconnaissance and numerical weather prediction.

Rain Monitoring with Polarimetric GNSS Signals: Ground-Based Experimental Research

“…Its positive value comes from the contribution of hydrometeors, which includes not only raindrops but also ice crystals and melting particles. From our previous research, due to the fact that the number concentration of ice particles is often sparse at high altitude, the effect of ice crystals along the path is quite weak, which can be neglected [25]. Compared with the effect of larger and more concentrated raindrops, the melting particles have some effect but not that obvious.…”

“…Since the shapes of falling raindrops are always nonspherical, the depolarization of GNSS signals is inevitable when it passes through rain area [25]. Polarimetric phase shift, which is used to describe depolarization characteristic, is defined as…”

Feasibility Study of Rain Rate Monitoring from Polarimetric GNSS Propagation Parameters

“…Now, the scattering amplitudes for nonspherical drops can be computed from many algorithms [25]. However, considering the frequencies of GNSS signals (L-band) and the shape-size features of raindrops, the Rayleigh Scattering Approximation and T-matrix are used in this simulation research [16,34,35].…”

“…The L1 (1.57542 GHz) frequency of GPS is used in this paper to serve as an example. For the coordinate system in these algorithms, incident angle can be approximately equal to the elevation angle and is assumed to be 0 • here [25,34]. The environmental temperature of 20 • C is used.…”

“…Here, D eq is the diameter of the equivolumetric spherical drop in mm. Among these shape models, since the BC model introduced aerodynamic pressure to the equilibrium condition, it is more precise and often used in many calculations or regarded as a comparative object [19,24,25]. Therefore, it was selected for our following simulation research.…”