# Airborne GNSS Reflectometry for Water Body Detection
## 8 Conclusions  
This airborne experiment studies the techniques for water body localization using GNSS-R. A GNSS-R setup of reduced size and weight was developed specifically to meet the requirements of this application. The utilization of the delay line in the GNSS-R setup is a significant contribution of this work. The delay line produces a delay that is sufficient enough to track the direct and reflected GNSS signals independently using a mono channel receiver which allows perfect synchronization of the RHCP and LHCP links. The observations are realized with high temporal and spatial resolution. We estimate the reflectivity measurements as the ratio of the amplitudes of the reflected LHCP antenna signals over the amplitudes of the direct RHCP antenna signals. The signals are segmented into stationary parts associated with different areas of reflection. We relate the 20 ms rate reflectivity measurements to the corresponding reflecting surfaces via a 20 ms localization of the specular points of reflection. We apply a real flight experimentation using a low-altitude airborne carrier with high rate observations of the surface reflectivity. We show that our method is able to differentiate surfaces, and thus detect water bodies in landforms, based on the difference in reflectivity measurements associated to each surface. We show that our radar technique is able to detect 96% of the total number of water body surfaces on the traces of the satellites footprints in study as compared to the up-to-date data provided by IGN maps. In a second analysis, we apply a manual inspection between the automatic edge localization provided by the radar technique and manual localization using Google Earth in order to assess the edge localization accuracy of the proposed approach. We show in this study that our proposed radar technique is highly sensitive to the changes in landforms with a meter precision regarding the water body edge localization.  
Conceptualization, H.I., G.S. and S.R.; Data curation, H.I.; Formal analysis, H.I. and S.R.; Funding acquisition, S.R.; Investigation, H.I., G.S. and S.R.; Methodology, H.I., G.S. and S.R.; Project administration, S.R.; Resources, H.I., G.S. and S.R.; Software, H.I. and S.R.; Supervision, G.S. and S.R.; Validation, H.I., G.S. and S.R.; Visualization, H.I.; Writing--original draft, H.I. and S.R.; Writing--review and editing, H.I., G.S., S.R., M.R. and G.F. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy restrictions. The authors would like to acknowledge the Universite du Littoral Cote d'Opale (ULCO) and the National Council for Scientific Research of Lebanon (CNRS-L) for granting a joint doctoral fellowship to [PERSON]. The authors would also like to thank the CPER MARCO project (Recherche marine et littorale en Cote d'Opale, des milieux aux ressources, aux usages et a la qualite des produits de la mer) for their financial support. The authors declare no conflict of interest.