Analytical Computation of the Spatial Resolution in GNSS-R and Experimental Validation at L1 and L5

Adriano Camps,Joan Francesc Munoz-Martin

doi:10.3390/rs12233910

Abstract

Global navigation satellite systems reflectometry (GNSS-R) is a relatively novel remote sensing technique, but it can be understood as a multi-static radar using satellite navigation signals as signals of opportunity. The scattered signals over sea ice, flooded areas, and even under dense vegetation show a detectable coherent component that can be separated from the incoherent component and processed accordingly. This work derives an analytical formulation of the response of a GNSS-R instrument to a step function in the reflectivity using well-known principles of electromagnetic theory. The evaluation of the spatial resolution then requires a numerical evaluation of the proposed equations, as the width of the transition depends on the reflectivity values of two regions. However, it is found that results are fairly constant over a wide range of reflectivities, and they only vary faster for very high or very low reflectivity gradients. The predicted step response is then satisfactorily compared to airborne experimental results at L1 (1575.42 MHz) and L5 (1176.45 MHz) bands, acquired over a water reservoir south of Melbourne, in terms of width and ringing, and several examples are provided when the transition occurs from land to a rough ocean surface, where the coherent scattering component is no longer dominant.

Highlights

Global navigation satellite systems reflectometry (GNSS-R) is a relatively new remote sensing technique that uses navigation signals as signals of opportunity in a multi-static radar configuration [1].The spatial resolution of GNSS-R instruments was first analyzed in [2], and it was estimated from the dimensions of the area determined by the intersection of the first iso-delay and iso-Doppler lines
Global navigation satellite systems reflectometry (GNSS-R) is a relatively novel remote sensing technique, but it can be understood as a multi-static radar using satellite navigation signals as signals of opportunity
The predicted step response is satisfactorily compared to airborne experimental results at L1 (1575.42 MHz) and L5 (1176.45 MHz) bands, acquired over a water reservoir south of Melbourne, in terms of width and ringing, and several examples are provided when the transition occurs from land to a rough ocean surface, where the coherent scattering component is no longer dominant

Summary

Introduction

Global navigation satellite systems reflectometry (GNSS-R) is a relatively new remote sensing technique that uses navigation signals as signals of opportunity in a multi-static radar configuration [1]. This academic case is known as the “knife-edge diffraction”, and it is 4uosfe1d5 in radio communications to assess the propagation losses with respect to the free space caused by the RmottehhbmeeesodsttpreeTiuurShsiecmmentcsiaH.oot2ronnu0yd2ayb0wnag,yro1aey2tvnah,ewsxe,mFpraaOvor[n6iReudn]snP.ciE(itnpraEeislRndeuR,ccEhbauVnuraIviEblwWedeaiinanypgFtp,higleaituetcdrt.ehtIe4on)p.ctrohimme aplaruyttteewrtahtvheeiesflrewocntirltliacrtefsipeorlmdesseewnlathteetrhnteipmtareratnisosfitthtiheoenentfrvraoejelmo4cptoooefrn1yo5ef is partially obstructed by a conducting plane as illustrated, leaving a clearance h with respect to the line of sight. Gleracpanhicbael arepppreliseednttaotioconmofptuheteHtuhyegeelnesctdriifcfrfiacetlidons wprhinecnipplea.rt of the trajectory is partially obstructed by a conducting plane as illustrated, leaving a clearance h with respect to the line of sight This academic case is known as the “knife-edge diffraction”, and it is used in radio communications to assess the propagation losses with respect to the free space caused by the obstruction by a mountain, building, etc.

Babinet’s Principle

Principle of Superposition

Discussion

Conclusions