## 6 Conclusions  
The GNSS-R ocean surface measurements were shown to be a good estimator of sea surface roughness and wave heights in the reflection zone. The grazing angle measurements additionally have the potential of delivering climate change input by monitoring the following ocean phenomena when including signal reception from more GNSS frequency bands from several global navigations systems (GPS, GALILEO, BEIDOU, and GLONASS) [7]:  
* Ocean mesoscale eddies and fronts (with horizontal spatial scales of 5-1000 km and temporal scales of 1 day-1 year),
* Mean ocean height variations (horizontal scales of 10-1000 m and temporal scales of 1 h-1 week),
* Ocean surface mean-square slopes/tilts (horizontal scales of 1-100 km and temporal scales of 5-50 h),
* Directional changes in the wind field patterns (horizontal scales of 10 m-100 km and temporal scales of 1 min-10 h). Combining all these measurements in the field of view of the receiving antennas leads to a range of reflection zones in the vicinity of the reflection zones from the GPS signals, which will have enough resolution to identify the abovementioned parameters and sea conditions. It was also shown that the signal spectra can be approximated by a relatively simple model, where the model constant is a function of the sea state. The retrieved mean wave-heights are almost proportional to the square of the wind speed, and the spectral variances from the measurements of setting and rising GNSS satellites link directly to the ocean surface roughness. Similar results were obtained in the performed multiphase screen wave propagation simulations. The relationships presented here can be used in practice to estimate sea states and wave-heights. The field of reflectometry is a relatively new research area with great potential for the retrieval of new and more precise geophysical parameters such as sea surface roughness, wave height, horizontal and vertical wind patterns, ocean tilt, ocean water salinity, ocean heat dissipation and evaporation transport, boundary layer humidity, and lower-troposphere turbulence. This great potential can also be seen from the relatively large number of satellite missions emerging in the near future. Thus, it is important to have the necessary tools to perform appropriate simulations and algorithms for assessing the actual performance of the technique, deriving the mentioned geophysical parameters. The spectral surface model, used here to represent the air-sea interaction, is a relatively simple model. More accurate models should be developed as in [23], making the relationship between wind speed and ocean wave-heights more accurate for both high and low wave numbers. It should also be mentioned that the relations for the smooth and rough impedances given in the paper are approximations to more general expressions. Further measurement campaigns under different geophysical conditions and locations than presented here would strengthen the validating and performance of the presented models and simulation tools. Both authors contributed to the preparation of the article. Conceptualization, P.H. and A.C.; methodology, P.H. and A.C.; software, P.H. and A.C.; validation, P.H. ; formal analysis, P.H. ; investigation, P.H. ; resources, P.H. and A.C.; data curation, P.H. and A.C.; writing--original draft preparation, P.H. and A.C.; writing--review and editing, P.H. and A.C.; visualization, P.H. ; supervision, P.H. ; project administration, P.H. ; funding acquisition, P.H. and A.C. All authors have read and agreed to the published version of the manuscript. The research was made available by internal grants at University of Oslo, Norway, and the company Beyond Gravity, Sweden. Measurements from the five datasets are available upon request to the authors. **Acknowledgments:** The authors want to acknowledge [PERSON], University of Oslo, Department of Physics, in Norway for his support to the research necessary for obtaining the results in the article. The assistance of the University of Hawaii in realizing the observations is very much appreciated.