Chirp Rate Estimation of LFM Signals Distorted by Underwater Acoustic Modal Dispersion

Low‐frequency sonar signals experience modal dispersion during long‐range propagation, leading to multipath effects and non‐linear phase distortion. This distortion causes the failure of traditional chirp rate estimation methods that rely on the linear frequency characteristics of linear frequency modulated (LFM) signals. This paper proposes a chirp rate estimation algorithm based on the fractional Fourier transform (FrFT) and modal dispersion compensation. The algorithm estimates the channel impulse response (CIR) by modifying the FrFT of the LFM signal, applies a de‐dispersion transform to eliminate modal dispersion in the CIR, and finally obtain the chirp rate estimate through a parameter search. Simulation and experimental results validate the effectiveness of the algorithm under dispersive conditions.