# S-Band Doppler Wave Radar System
## 1 Introduction  
The non-coherent and coherent method are the two main methods used in radio ocean remote sensing. The non-coherent method utilizes a non-coherent radar to acquire the backscatter images of the targeted ocean area. Then 3D-FFT(three dimensional fast fourier transformation) is applied to the acquired images to obtain the spectra. Finally, the ocean dynamic parameters are deduced by a spectral analysis of the spectra [1]. The radar used in this method can be modified from a marine navigation radar, which makes it a low-cost and flexible method of monitoring oceans. However, the modulation transfer function is always needed during the calibration of the results [2]. In the shallow water area, factors such as offshore winds could significantly influence the results [3]. The coherent method employs a Doppler coherent radar to measure the radial wave velocity [4], and the wave height spectra are derived via a certain relation between the radial velocity and the wave height spectrum. Eventually the ocean dynamic parameters are extracted from the wave height spectra [5]. Compared with the non-coherent method, the coherent method does not require calibration, and is adaptive in various bathymetry areas; therefore, the coherent method is promising for monitoring oceans with radars and worth further research.  
In 1985, [PERSON] et al. extracted the wave and current parameters from the echoes of an X-band marine radar [1]. Since then, the non-coherent method utilizing X-band radar has been well investigated. Multiple algorithms, such as the basic LS (Least Square) fitting method [1], weighted LS method [6], ILS (Iterative LS) approach [7], DiSC (dispersive surface classificatory) method [8], the Polar Current Shell algorithm [9], the Normalized Scalar Product method [10], have been examined by researchers to improve the non-coherent method. Research and measurements of the modulation transfer function have been completed [11; 12; 13]. Various mature systems, such as WaMos II, which was developed by OceanWaves GmbH in Germany, and WAVEX, which was developed by MIROS in Norway, have also been implemented. However, a precise modulation transfer function, which is difficult to obtain, is the decisive accuracy factor. The study of the coherent method began in the 1980s when [PERSON] and [PERSON] proposed a preliminary theory and approach for deducing wave height spectra from the velocity of water particles [14; 15]. In the 1990s, various experiments using microwave Doppler radar were conducted [16; 17; 18; 5; 19]; however, none of the experimental results fully obtained the directional wave height spectra. Recently, the coherent method has been applied on the X-band radar, and the results are very good [20]. SM050, which was developed by MIROS in Norway, is the only mature Doppler marine radar system and it functions in C band and is capable of outputting accurate results one range cell at a time.  
To achieve the coherent method, the use of MORSE (Microwave Ocean Remote SEnsor), a shore-based microwave Doppler marine radar system developed by Wuhan University, is proposed. The six antennas equipped with MORSE have a beam width of 30 degrees, which enables MORSE to obtain the full wave height spectrum. MORSE has been deployed in Zhuijajian, Zhejiang and Shanwei, Guangdong Province and it has successfully acquired the wave parameters of targeted ocean areas. In Section 2, we provide a brief description of the coherent wave measuring method. In Section 3, the MORSE system is introduced. In Section 4, a comparison between MORSE and a Waverider MKIII buoy is performed showed and discussed. Finally, in Section 5, the conclusions of the paper are presented.