Research On Inversion Algorithm Of Ocean Surface Current And Wind Direction With Uhf Radar

Ocean dynamic parameters as one of the important contents of ocean environment monitorning.The long-term and real-time monitoring of ocean dynamic parameters is conductive to the development and utilization of marine resources,which also pro-vide support for ocean scientific research and maritime safety.Especially the real-time monitoring of inshore ocean dynamic parameters is significant for the promotion and protection of coastal economic development.Due to the restrictions of theory and tech?nology,radio ocean remote sensing technology is difficult to apply in nearshore area.The high frequency ground wave(HF)radar plays an important role in the monitoring of ocean environmental parameters,who is widely utilized in marine development and utilization.However,it is difficult for HF radar to extract meticulous sea echo informa-tion,because HF radar's distance resolution unit is large and noise interference is more serious for high frequency.Ultra hig frequency(UHF)radar compared with HF radar has the characteristics of higher range resolution and lower power,which can extract infor-mation of both capillary and gravity wave with wavelength between high frequency and microwave.The noise interference of UHF radar is smaller.So it is possible to obtain precise monitoring of coastal coean dynamic parameters by UHF.This paper focus on researching and implementing the algorithm of extracting the velocity of ocaen surface and the ocean wind direction in coastal area.In the aspect of the extraction of ocean surface radial veolocity,radial veolocity is obtained by doppler shift which is formed by radar radio and ocean wave's Bragg scattering.As we all know that the offshore topography and ocean surface current are complex.UHF radar's wavelength is about 0.88m,which corrospends to both capillary wave and gravity wave information.Because the UHF radar has the characteristics that makes it possible to extract inshore surface velocity.It is different with HF radar echo spectrum that the first-order spectrum and the second-roder spectrum of the UHF radar's ocean echo spectrum is easier to be mixed together because of the shorter wave-length of UHF radar.It is difficult to extract first-order peak,therefore,multiple signal classification algorithm(MUSIC)is unavailable and digital beam-forming(DBF)is used in extracting the radial velocity.After a month,the radar and buoy data is highly correlated with a coefficient of 0.88,however,the root mean square error is large.The results show that the velocity of the ocean surface is influenced not only by the tidal effect and the rotation of the earth,but also by the local wind speed.In the aspect of the extraction of sea surface wind direction,the inversion is based on the theory of high frequency wind direction inversion that the ratio of the approach-recede first-order bragg lines is related to wind direction.As for HF radar,the accuracy of the wind direction result is very poor when the sea surface wind speed is low.UHF radar can respond to the ocean state under smaller wind speed because of the character-istics of short wavelength,which could be utilized in the inversion of sea surface wind direction.The angle information is extracted after digital beam-forming,and multi-beam least squares method is applied to eliminate ambiguity to determine reasonable wind direction.Over one week,the radar-derived wind direction has been highly corre-lated with buoy data,with coefficient of 0.85 and the root mean square error is about 25°.In addition,while small wind speed,the correlation coefficient and root mean square error of radar and buoy is 0.9 and 26°,respectively.The good experimental results shows that it is feasible and effective to monitor sea surface wind direction by UHF radar.Also,the results show that UHF can better monitor the ocean parameters under low sea state,which could compensate for disadvantage of HF radar under small wind speed with poor accuracy of wind direction results.It is possible for UHF radar to extract the wind direction under high wind speed whose average wind speed greater than 10m/s.However,the correlation coefficient and accuracy between radar and buoy is low.In this paper,the UHF radar is applied to the extraction of ocean surface velocity and ocean wind direction for the first time.It is verified that the feasibility of the application of UHF radar in ocean dynamic parameters monitoring in coastal area by means of the introduction of the inversion algorithm and analysis of the results.