Study On Remote Sensing Method Of Sea Surface Currents With Shipborne High Frequency Surface Wave Radar

By utilizing the vertical polarization electromagnetic wave(3~30 MHz), highfrequency surface wave radar(HFSWR) can be used for detection and track of ship targets on the sea and aircrafts at low altitude beyond the horizon, and used for remote sensing of sea states(such as surface currents, wind field and wave height) over a large area and all-weather operations. Shipborne HFSWR is the development of land-based HFSWR technology. Besides the advantages inheriting from the land-based radars, the main feature of shipborne HFSWR is the platform’s maneuverability. With this characterisitc, it can get the ocean area of interest rapidly for detection of targets or remote sensing of sea states. Thus, shipborne HFSWR will have a bright future and potential application value in both military and civil fields.So far, the theories and applicaion technologies for remote sensing of sea states based on land-based HFSWR are relatively mature, and various land-based HFSWR systems have been developed successfully and applied widely at home and abroad. However, the theories and application technologies for remote sensing of sea states based on shipborne HFSWR are nearly blank. This paper takes shipborne HFSWR as the study platform, takes the sea surface currents as the research object, and studies on remote sensing method of sea surface currents with shipborne HFSWR. The research achievements will provide new theoretical basis and methods for our country to study on remote sensing of sea states using shipborne HFSWR, and have important reference value for the deeper research and further development of radio oceanography. The main research contents are as following:1. Briefly introduce the basis theory of remote sensing of sea surface currents with land-based HFSWR, and then analyze the spreading mechanism of shipborne HFSWR sea echo Doppler spectra and explain the main problems needed to be solved in the application for the remote sensing of sea surface currents based on this basis, such as direction-of-arrival(DOA) estimation problem of sea surface radial currents, space-time coupling problem of the first-order sea echo, and estimation problem of sea surface vector currents with single station.2. In order to deal with the DOA estimation problems in measurement of sea surface radial currents with shipborne HFSWR such as the limited number of sensors and snapshots, the targets appeared in the spreading sea echo Doppler spectra, and low reconstruction accuracy and high computational complexity in the most existing complex-valued sparse representation methods, this paper analyzes the sparsity of shipborne HFSWR sea echo at a given range and Doppler resolution cell theoretically, and mainly studies the sparse representation methods of real-valued array signal and real-valued array signal covariance matrix. The validity of the two proposed methods is verified by the computer simulation results and the measured data processing results of shipborne HFSWR.3. In order to deal with the space-time coupling problem in the sea echo of shipborne HFSWR, this paper firstly analyzes the eigen-spectrum of the sea echo of shipborne HFSWR and its distribution characteristics theoretically, study the rank estimation method(i.e., the number of significant eigenvalues in the sea echo eigen-spectrum) of the sea echo covariance matrix of shipborne HFSWR; and then we theoretically analyzes the sea echo sparsity of shipborne HFSWR in the whole space-time domain with the rank estimation method, mainly studies the sparse representation-based space-time multiple signal classification(MUSIC) method and uses it for shipborne HFSWR sea echo space-time processing. Finally, the validity of the rank estimation method of the sea echo covariance matrix of shipborne HFSWR and the sparse representation-based space-time MUSIC method is verified by computer simulation results.4. In order to deal with the problem that single HFSWR is difficult to obtain the sea surface vector currents directly, this paper analyzes the distribution features of sea surface vector currents and the measurement errors of shipborne HFSWR sea surface radial currents, and studies an estimation method for measuring the sea surface vector currents using single shipborne HFSWR based on the first-order stream function. The validity of the estimation method for the uniform current field and simple non-uniform current field is verified by the computer simulation results.