RADAR DETERMINATION OF SHIP ROLL PERIOD IN ROUGH SEAS

Subject and Purpose. Understanding ship roll parameters in rough sea conditions is crucial for practical applications, such as evaluating a ship’s stability or classifying a vessel type. The primary roll parameters include the amplitude and frequency (or period) of the ship’s oscillations. Doppler spectra of signals reflected from sea vessels moving in turbulent waters are analyzed, aiming to determine the ship’s roll period through spectral processing of signals scattered by various types of vessels in realistic marine environments. Methods and Methodology. The study involves both mathematical calculations and full-scale experimental studies. Average ship roll periods are theoretically calculated using the hydrodynamic theory of ship roll in irregular waves. The sea wave heights in the full-scale experiment are within three to four. The ships in the study vary significantly in size and displacement. The ship roll period is determined by analysis of a sequence of instantaneous Doppler spectra of signals reflected from the ship. The mathematical calculation results are compared with the measurement outcomes. Results. The full-scale experimental studies conducted for two vessel types at different ranges provided instantaneous spectra of Doppler signals. The average roll periods and their variances obtained during experimental data processing were compared with the theoretically calculated values. The comparison results validate the initial assumptions that the reflected signals contain frequencies associated with ship roll. The comparative study between two different ships shows a good agreement of the data. Conclusions. The Doppler signals scattered by a moving vessel in rough sea conditions contain information whose relevant processing yields the average roll period of the ship. The possibility of remote measurements of roll periods enables addressing problems related to surface object recognition and navigation.