This study deployed receivers and sources of sound on the Songhua River and the Arctic Ice Station—areas covered with ice—in field experiments to examine and verify the feasibility of the passive detection of narrowband signals of underwater targets across ice. The classic method for the detection of narrowband signals based on power spectrum estimation was used. However, the spectrum was noisy, making it difficult to establish a detection threshold, which in turn, affected the results of detection. To solve this problem, an α-comparative detector based on the one-dimensional Kalman filter was developed to smoothen the frequency domain and improve detection capability. The results of experimental data processing show that under special impulse noise interference in areas covered with ice, the proposed method of signal processing reduced signal interference in the frequency domain to enable a clearer observation of narrowband signals. The feasibility of using the proposed method for the passive detection of narrowband signals of underwater targets across ice was also verified.