# A Novel Method for Ocean Wind Speed Detection Based on Energy Distribution of Beidou Reflections
## 5 Conclusions  
Two new observables that describe the energy distribution of delay waveform were proposed in this paper. To study the dependence of the reflected GNSS signal on the sea surface wind speed, we divided the complex waveform into two zones, i.e. low-energy zone and high-energy zone, and proposed two new observables as input for alternative methods for wind speed retrieval. EMR is the ratio of energy between the low-energy zone and the high-energy zone. EDR is based on  
Figure 11: (**a**) RMSE and (**b**) coefficient of determination \(R^{2}\) as a function of the coherent integration time. Case1 is the gentle wind scenario, Case 2 is in the UTOR scenario.  
the computation of the ratio of the pixel volume between the low-energy zone and the high-energy zone. This paper processed two periods of dataset from the Beidou GEO satellite during the coastal experiment in Yangjiang, which represented two typical different wind states: gentle and high wind scenarios. Both observables showed good wind speed retrieval performances in the gentle wind scenario. The wind speed retrieval errors were less than 1.0 m/s with correlation \(R^{2}\) of 0.76 when \(Threshold2=0.3\). In the high wind scenario, the dataset during Typhoon UTOR were processed. When \(Threshold2=0.25\), EMR and EDR showed a strong linear relationship with the high wind speed during Typhoon UTOR, which reached a RMSE of 3.10 m/s and 2.69 m/s with a correlation \(R^{2}\) of 0.822 and 0.866, respectively.  
To obtain an optimal retrieval result, the influences of threshold and coherent time on wind speed retrieval were analyzed. Finally, the optimal retrieval performances were obtained, with an RMSE of 2.63 m/s and a correlation of 0.871 in the high wind scenario. In the gentle wind scenario, the optimal RMSE of wind speed reached 0.89 m/s and the correlation was 0.769.  
We neglected the wind direction factor when we set up the wind speed retrieval models in this paper. In the future, the relationships between wind direction and delay waveform and influences of wind direction on waveform will be considered, which will be good for estimating a more efficient wind speed retrieval model. Besides, it should be remarked that the buoy is located near the gulf of the Yangjiang Island and the distance between the GNSS coastal experiment station and the in situ measurement station is around 10 km, which may introduce additional errors when fitting the retrieval model. By referring to more ocean meteorological information such as tide and swell during the experiment, this may provide more opportunity to investigate the relationship between wind speed and observables in the future.  
[PERSON] conceived the main idea of this article and wrote this paper. [PERSON] analyzed the wind retrieval method based on the coherent time. [PERSON] and [PERSON] discussed the influences of the factors on wind speed retrieval. [PERSON] and [PERSON] supplemented the theory part during the manuscript modification.  
This work was supported in part by the National Key R&D Program of China under Grant 2017 YFB0502802, in part by the National Science Foundation of China under Grant 61171070, in part by the National High technology Research and Development Program (863 Program) under Grant SS2013 aa120602.  
The authors declare no conflict of interest.