Abstract: Systems and methods are described for synthesis of total surface current vector maps by fitting normal modes to radar data. A method includes extracting a scalar data set from a radar signal from a radar. Velocity components are calculated from the radar signal. The velocity components are fitted to a set of scalar eigenfunctions and eigenvalues to simultaneously solve for the best set of normal modes and the corresponding set of constants. The corresponding set of constants represent a corresponding set of amplitudes. The set of constants and the set of normal modes are used to create a two dimensional vector field used in creating a total vector map.

Abstract: Systems and methods are described for HF radar frequency sharing with GPS time modulation multiplexing. A method is provided that includes generating clock signals from the time information contained in a GPS signal. Radio frequency signals are transmitted and received in a sequence whose start times are dictated by the clock signals. The clock signals also control the modulation of the radio frequency signals. The radio frequency signals are modulated by using a sweep modulation. An apparatus to implement the method includes a GPS receiver, a state machine, a clock generator, a microprocessor, a memory chip, a signal synthesizer, and a digital data output device. The GPS receiver extracts time information from GPS signals. The state machine controls radar functions versus time. The microprocessor performs modulation multiplexing on radar signals.

Abstract: An apparatus and method for target-angle determination using lower-frequency radars having compact non-moving antennas over broad viewing sectors. Use of direction finding (DF) in place of beam forming and scanning eliminates the need for conventional, physically large phased-array antenna systems. The described DF algorithm advances the art over previously described least-squares DF by allowing numerically efficient and robust resolution of multiple targets at closely spaced angles. When used with coastal HF ocean surface current and wave monitoring radars where sea echo is the target, the method extracts complex current patterns. The high degree of singularity of the antenna signal covariance matrix is exploited and used as the basis for extracting angles with minimal averaging. More receive antenna elements can be added at convenient locations to handle more complex target angle scenarios.

Abstract: A lower-frequency compact radar system for wide-angle surveillance. Direction-finding receive antennas consisting of colocated orthogonal electric and magnetic dipoles provide target angles from the radar. The size of this antenna unit is reduced to the point where internal noise is comparable to external to achieve maximum compactness. High sensitivity is achieved with an efficient class of pulsed/gated, linearly swept-frequency waveforms that are generated and processed digitally. For backscatter radars, close to 50% duty factors are realized. The rules for waveform design and processing overcome problems of range/Doppler aliasing and/or blind zones. After mixing in the receiver, processing bandwidths are much less than RF signal bandwidths, so that simple, inexpensive personal computers are used for real-time signal processing. Digital FFT algorithms determine target range and Doppler, and DF algorithms determine its angles.

Abstract: A system for radar remote sensing of near surface ocean currents in coastal regions. The system employs a pair of low power, transportable high frequency radar units to scatter signals from the shore off to the ocean waves. Underlying surface currents impart a slight change in velocity to the ocean waves which is detected by the radar units. Each radar unit can determine the angular direction of arrival of the radar echo signals by comparing the phase of the signals received at three short antennas on the shore. Signals scattered from the same point on the ocean by each of the two geographically separated radar units are used to construct a complete current vector for that point. The radar pair takes simultaneous measurements over an ocean area with a predetermined grid pattern. Vectors are constructed for each square section of the grid, and a map of the near surface current field is output in real-time by an on-site minicomputer.