OTHR Impulsive Interference Suppression in Strong Clutter Background
External interferences can severely degrade the performance of an Over-the-horizon radar (OTHR), so suppression of external interferences in strong clutter environment is the prerequisite for the target detection. The traditional suppression solutions usually began with clutter suppression in either time or frequency domain, followed by the interference detection and suppression. Based on this traditional solution, this paper proposes a method characterized by joint clutter suppression and interference detection: by analyzing eigenvalues in a short-time moving window centered at different time position, clutter is suppressed by discarding the maximum three eigenvalues at every time position and meanwhile detection is achieved by analyzing the remained eigenvalues at different position. Then, restoration is achieved by forward-backward linear prediction using interference-free data surrounding the interference position. In the numeric computation, the eigenvalue decomposition (EVD) is replaced by singular values decomposition (SVD) based on the equivalence of these two processing. Data processing and experimental results show its efficiency of noise floor falling down about 10-20dB.
Fractal Features and Detection of Meteor Interference in OTHR
Backscatter signal from OTHR receiver may contain strong noise and interference background, among which the meteor echo is a typical and strong Impulsive interference. This meteor echo may inject transient but great power into the receiver, arise the noise floor in the range-Doppler map and decrease SNR. So it must be suppressed before target tracking. Many solutions are presented for meteor echo excisions, among which the meteor position must be estimated firstly. Usually the ocean clutter is so strong that it may cover other signals such as target and meteor, so it must be suppressed before position estimation. Different from these approaches, this paper proposes a novel algorithm of meteor position estimation without depressing clutter. The main idea is focused on the different fractal dimension corresponding to the ocean clutter and the meteor echo. Accounting for the real-time processing requirements, an effective of directional fractal dimension based on the fractional Brownian motion model is also proposed. Experiments prove that it is an effective method
Calculation of Complex Radiant Heat Load From Surrounding Radiator Surface Temperatures
Abstract A method for calculating the radiant heat exchange between an absorber and individual radiating components in its surroundings is reported. Radiator surface temperatures, ambient and absorber temperatures, and configuration factors for radiating components in the surroundings are used in the customary radiant heat exchange formulae. Simplified methods for calculating or estimating configuration factors for radiators of various shapes solely from angles, subtended at the absorber by the radiators are presented. The method has been verified in the laboratory under controlled conditions and has been used to advantage in the field studies. The method has advantages over the globe therometer method in certain applications.