Experimental determination of significant waveheight by OSMAR071: Comparison with results from buoy

Abstract

OSMAR071 is the latest product of the OSMAR (ocean state monitor and analysis radar) series of high frequency surface wave radar (HFSWR), which was developed by the Radiowave Propagation Laboratory of Wuhan University. It adopts a modified Barrick waveheight inversion model. The modifications are introduced to improve the model's performances under the effect of noises and interferences and in the case of broad beam radar detection. The two unknown coefficients in the modified model are figured out by fitting the HFSWR significant waveheight results to those output from a wave buoy located in the radiating coverage of the radar site. The model is applied to inverse the waveheights from radar data for the duration from Dec. 1st, 2008 to Feb. 25th, 2009, and then the radar waveheights are compared with the buoy measurements. Results show that the rms difference between radar-derived significant waveheights and those from the buoy is 0.38 m and the correlation coefficient between the two series is 0.66. This study describes OSMAR071 observation of significant waveheight with relatively satisfactory accuracy during about three months.High frequency surface wave radar (HFSWR) operated in the HF band (3-30 MHz), as the name suggests, employs the ground wave mode of radio wave propagation, in which the radar signal is guided by a good conducting surface such as the ocean surface to follow a path that essentially matches the earth's curvature. It is capable of all-weather remote sensing of large-area ocean surface dynamics with relatively high precision [1] . After more than 40 years' development, its capability of current detection has been considered to satisfy the requirements for routine marine observations while its wind and wave outputs have not reached the matched status [2] . Currents information can be extracted from the broadening of the Bragg peaks (which are also called as the first-order peaks) in the sea echoes' Doppler spectra. The second-order continuum which contain the information of waves and winds is relatively weak (20-40 dB lower than the Bragg peaks) and susceptible to the effect of noise and interference, so the extraction of waves and winds information is difficult [3] and the corresponding inversion theory and technology are still currently under development. Much progress has been made to understand the relationship between the Doppler spectrum of the radar backscatter signals and the ocean wave spectrum [4] . In 1977 Barrick proposed an inversion model of significant waveheight [5] , which can work robustiously in practice [6,7] . It is different from several other algorithms, which relate the inversion of wave spectra to the second-order sea echoes directly. Therefore, the significant

Study on the Shear and Bending Mechanical Properties of Millet Stem

“…For the three varieties of millet studied, the first internode of the stem exhibited the highest shear strength, while the patterns of shear strength for the second, third, fourth, and fifth internodes were not distinct. This conclusion differed slightly from the findings of Wu et al [31] in their study of millet straw. The difference was attributed to Wu's selection of overwintered straw, which had a lower moisture content, leading to larger differences in shear strength between internodes.…”

Assessment of Significant Wave Height in the Taiwan Strait Measured by a Single HF Radar System

“…This can be explained by the relatively greater effects of noise and interference in the case of low sea states where second-order sea echoes are weak in comparison with higher sea states. In this study, the OS081H-A HF radar was operated at 7.8 MHz, while the wavelength of a resonant sea wave was about 20 m; thus, such waves failed to obtain sufficient energy to develop, meaning the echoes were weak and of poor stability, which led to the poor results (Barrick 1972;Wu et al 2009). Based on the inversion theory of radar-derived Hs, the value of h generally meets the condition 0.1 # kh # 1 (Hs ' 2h), where k is the radar wavenumber and h is RMS wave height (Barrick 1977a;Wyatt 2002).…”

“…A OS081H-A system is composed of two separate antenna arrays, an eight-element nonlinear receiving array and a three-element Yagi-Uda antenna for transmitting frequency-modulated interrupted continuous wave pulses. The spatial superresolution algorithm known as the minimum variance method (MVM; which is another type of beam-forming algorithm but with an adaptive weighting) is applied in the field of spatial spectrum estimation (Capon 1969;Wu et al 2001). Based on the MVM algorithm, the Hs was measured by the single radar system with range and bearing resolutions of 5 km and 108, respectively.…”

Assessment of HF Radar in Mapping Surface Currents under Different Sea States

“…In China, the study of HF radar in ocean surface currents and sea state monitoring was conducted from the late 1980s, and the first HF radar system was developed for ocean surface state surveillance by researchers of Wuhan University in 1993. Many subsequent validation studies have contributed to the growing acceptance and wide use of the series of Ocean State Monitoring and Analyzing Radar (OSMAR) systems in China (Hou et al 1997;Lai et al 2017Lai et al , 2018Liu et al 2007;Wu et al 2001;Wu et al 2009;Yang et al 2005). The OSMAR071 HF radar is the product developed by Wuhan University and the China Precise Ocean Detection Technology Co., Ltd. During January-March 2013, two OSMAR071 HF radars were deployed on the coast of Dongshan County (DOSA) and Longhai County (LOHI) of Fujian Province (Fig.…”