Study On The Inversion Of Ocean Sates By High-frequency Surface Wave Radar

High-Frequency Surface Wave Radar (HFSWR) works at high frequency band(3~30MHz), using vertically polarized electromagnetic wave propagationcharacteristics, which is able to detect the area over the horizon, so it has been calledHigh-Frequency Over The Horizon Radar (OTHR). Compared with other marinemonitoring devices, HFSWR has far detection range, large surveillance area and lessinvestment. For the radar systems are sited on the shore or installed on a platform, thesystem is seldom impacted by the natural environments, so it is capable of supprotingreal-time monitoring of the ocean. HFSWR plays an important role in the monitoringof China’s Exclusive Economic Zone (EEZ), safeguarding of national interests andprotecting of the marine environment.In recent decades, although researches of HF radar have made considerableprogress, for instance, the monitoring of moving targets and the mapping of oceansurface currents and wind fields, there are still many problems about ocean statesinversion and new system signal processing remains to be investigated. This papercarried out the following two tasks on the inversion of ocean states using HFSWR:1. The inversion of ocean wave spectrum from onshore HFSWR echo signal. Inthe classification of ocean wave spectrum inversions from HFSWR echo, widely usedBarrick’s backscatter formula belongs to the nonlinear first kind Fredholm integralequation. However, this kind of integral equation is Ill-posed, moreover, the SNR ofHFSWR echo is relatively low, and the inversion ocean wave spectrum is unstable. Inthis paper, a stable and low complexity inverse algorithm is presented, which uses thefirst-order peak to measure the wave direction, and then introduces the direction to theprogress of solving the integral function, which deduced the number of variables. Inorder to solve the instability problem of inversion results, we use ThikhonovRegularization methods. Generalized Cross Validation (GCV) method is applied todetermine the regularization coefficients. Simulation results show that this algorithmis stable and small calculating amount.2. The estimation of ocean surface currents from shipborne HFSWR echo signal.In this paper, MUltiple SIgnal Classification (MUSIC) algorithm is applied todetermine the Direction of Arrival (DOA) of ocean surface current by shipborneHFSWR moving with a constant velocity, based on principles of broadened first-orderBragg peaks. The velocity of the signal in DOA is compared with that of platform inthe same direction, from which the radial velocity of currents can be obtained. As theplatform moves forward, the currents are observed at different locations, thusobtaining the ocean surface vector currents. Simulation results show that thealgorithm performs well in the overlapping areas.