A Study Of Directional Acoustic Indices Based On Differential Microphone Arrays

With the impact of human activities on the ecological environment gradually deepened,ecological environment monitoring problem has been widespread concern.Acoustic index method,as a potential and efficient method for rapid assessment of biodiversity in the monitoring area,is becoming an active research direction in the field of ecological environment monitoring and evaluation in recent years.The acoustic index method aims to achieve rapid assessment of biodiversity information in the monitoring area through statistical analysis of the bioacoustic signals collected by the equipment.However,the acoustic index is extremely sensitive to human activity noise and can only be used for monitoring and evaluation in the central area of nature reserves.In areas with human activities,such as protected area margins,urban-rural integration,etc.,the acoustic index cannot reliably reflect the status and changes of biodiversity in the monitored area.In this paper,a directional acoustic index construction method based on the differential microphone array is proposed,in order to improve the application reliability of the acoustic index in the marginal area of the nature reserve and realize the rapid and accurate assessment of the biodiversity in the whole nature reserve.Firstly,two sets of back-to-back dual-delay differential array structures with delay factors of mutual prime are used for adaptive interference suppression processing to filter out interference signals from specific directions,using the advantages of differential microphone array processing with low complexity and the ability to quickly form a full-band spatial notch.Then,the two sets of spatial filtering outputs are used to suppress the grating lobe effect of the high-frequency pattern of the differential microphone array on the basis of the notch interleaving features in the two-dimensional space consisting of angle and frequency.In this step,the energy detection component of the bioacoustic signal is reconstructed through a complementary operation by taking the larger value at all time-frequency spectrum points,thereby restoring the time-frequency spectrum information of the bioacoustic signal without interference.Finally,the directional acoustic index results that accurately reflect the bioacoustic information are calculated.The results of simulation experiments and field measurements show that the method proposed in this paper can effectively suppress the artificial acoustic interference signals propagating from a specific direction,realize the ideal application of the acoustic diversity index in the whole airspace,and provide a feasible idea for the robust and accurate monitoring of bio-acoustic diversity in areas close to human activities.