Abstract:When the diameter to wavelength ratio does not meet the engineering approximation conditions, using the complex sound intensity method directly for azimuth estimation of a single pressure gradient vector hydrophone results in significant direction finding errors. While using the modified sound intensity method for azimuth estimation requires a higher signal-to-noise ratio (SNR). This paper provides an upper limit for the application of the diameter to wavelength ratio of a single pressure gradient vector hydrophone. This paper uses the instantaneous frequency variance weighting method. It utilizes the difference in instantaneous frequency energy fluctuation stability between the target line spectrum and background noise. This method assigns different weights to frequency units with different instantaneous frequency variances within the band. We suppress the impact of environmental noise on the target sound source in this way, improving the SNR performance of the modified sound intensity method for direction finding. The simulation results have verified the effectiveness and superiority of the algorithm.