Underwater Extended Target Detection Based on Interframe Mutual Information in Range–Doppler Spatial Domain

Wideband signals exhibit significant advantages in reverberation suppression, range resolution, and target parameter estimation. Consequently, echoes acquired through wideband active sonar provide rich target information, facilitating tasks such as target detection and classification. However, as range resolution increases, target echoes spread across multiple range bins, resulting in energy accumulation loss and a reduced signal-to-reverberation ratio (SRR) within individual range cells, which ultimately degrades detection probability. To address this challenge, this paper proposes a detection method based on inter-frame mutual information (IFMI) in the range-Doppler (R-D) spatial domain. Received echo signals are segmented into frames and mapped into the R-D domain, forming multi-frame R-D subspace matrices. IFMI is introduced to quantify data association states between consecutive frames. This is achieved by computing the mutual information between corresponding rows of adjacent R-D subspace matrices. The minimum IFMI is designed as the final test statistic and compared against a decision threshold to achieve target detection. Furthermore, the proposed method preserves target information within the R-D domain. The extremum positions of the IFMI can be utilized to estimate target parameters, thus avoiding extensive two-dimensional searches in the R-D domain. The efficacy and superiority of the proposed method were validated through simulations and experimental analyses. The simulation results demonstrate that the proposed method significantly improves the detection performance for extended targets under low SRR conditions, achieving a detection probability of 85% even at -12dB SRR. Experimental results further verify that, compared to four existing methods, the proposed method increases the detection probability by at least 17% and reduces the false alarm probability by 10%.