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. The instantaneous frequency variance weighing method is used. The difference in instantaneous frequency energy fluctuation stability between the target line spectrum and background noise is utlized to assign different weights to frequency units with different instantaneous frequency variances within the band. Thus，the impact of environmental noise on the target sound source is suppressed，and the SNR performance of the modified sound intensity method for direction finding is improved. Simulation results verifies the effectiveness and superiority of the algorithm.
