Directional Frequency Analysis And Recording Research Articles

Two-Dimensional Direction-of-Arrival Estimation Using Direct Data Processing Approach in Directional Frequency Analysis and Recording (DIFAR) Sonobuoy

Two-Dimensional Direction-of-Arrival Estimation Using Direct Data Processing Approach in Directional Frequency Analysis and Recording (DIFAR) Sonobuoy

South Georgia blue whales five decades after the end of whaling

Blue whalesBalaenoptera musculusat South Georgia were heavily exploited during 20thcentury industrial whaling, to the point of local near-extirpation. Although legal whaling for blue whales ceased in the 1960s, and there were indications of blue whale recovery across the wider Southern Ocean area, blue whales were seldom seen in South Georgia waters in subsequent years. We collated 30 yr of data comprising opportunistic sightings, systematic visual and acoustic surveys and photo-identification to assess the current distribution of blue whales in the waters surrounding South Georgia. Over 34000 km of systematic survey data between 1998 and 2018 resulted in only a single blue whale sighting, although opportunistic sightings were reported over that time period. However, since 2018 there have been increases in both sightings of blue whales and detections of their vocalisations. A survey in 2020 comprising visual line transect surveys and directional frequency analysis and recording (DIFAR) sonobuoy deployments resulted in 58 blue whale sightings from 2430 km of visual effort, including the photo-identification of 23 individual blue whales. Blue whale vocalisations were detected on all 31 sonobuoys deployed (114 h). In total, 41 blue whales were photo-identified from South Georgia between 2011 and 2020, none of which matched the 517 whales in the current Antarctic catalogue. These recent data suggest that blue whales have started to return to South Georgia waters, but continued visual and acoustic surveys are required to monitor any future changes in their distribution and abundance.

Displaying bioacoustic directional information from sonobuoys using "azigrams".

The AN/SSQ-53 Directional Frequency Analysis and Recording (DIFAR) sonobuoy is an expendable device that can derive acoustic particle velocity along two orthogonal horizontal axes, along with acoustic pressure. This information enables computation of azimuths of low-frequency acoustic sources from a single compact sensor. The standard approach for estimating azimuth from these sensors is by conventional beamforming (i.e., adding weighted time series), but the resulting "cardioid" beampattern is imprecise, computationally expensive, and vulnerable to directional noise contamination for weak signals. Demonstrated here is an alternative multiplicative processing scheme that computes the "active intensity" of an acoustic signal to obtain the dominant directionality of a noise field as a function of time and frequency. This information is conveniently displayed as an "azigram," which is analogous to a spectrogram, but uses color to indicate azimuth instead of intensity. Data from several locations demonstrate this approach, which can be computed without demultiplexing the raw signal. Azigrams have been used to help diagnose sonobuoy issues, improve detectability, and estimate bearings of low signal-to-noise ratio signals. Azigrams may also enhance the detection and potential classification of signals embedded in directional noise fields.

Software for real-time localization of baleen whale calls using directional sonobuoys: A case study on Antarctic blue whales.

Directional frequency analysis and recording (DIFAR) sonobuoys can allow real-time acoustic localization of baleen whales for underwater tracking and remote sensing, but limited availability of hardware and software has prevented wider usage. These software limitations were addressed by developing a module in the open-source software PAMGuard. A case study is presented demonstrating that this software provides greater efficiency and accessibility than previous methods for detecting, localizing, and tracking Antarctic blue whales in real time. Additionally, this software can easily be extended to track other low and mid frequency sounds including those from other cetaceans, pinnipeds, icebergs, shipping, and seismic airguns.

Localization of humpback whale signals with two directional frequency analysis and recording sonobouys

For many years, the navy has used directional frequency analysis and recording (DIFAR) sonobouys to record and track ships. DIFAR sonobouys compute acoustic particle velocity for two bimodal perpendicular hydrophone elements, which, with a magnetic compass, gives a directional bearing to the sound recorded on a third omnidirectional hydrophone. Use of DIFAR represents an easily deployable alternative method to standard time-difference of arrival localization with towed or bottom-mounted hydrophone arrays. In this study, we used two tethered DIFAR sonobouys to record and track playbacks of humpback whale song. GPS positions of playbacks were recorded. Digital signals were recorded at the sonobouy before multiplexing. Song units were recorded on both sonobouys, and then matched between sonobouys using time from the sonobouy GPS. To localize the signals, azimuths from the DIFAR sonobouys were combined with the time difference of arrival parabola to create a three-dimensional likelihood surface that gives the probabilities that a signal originated at a specific point in space. The locations with maximum likelihood were used to estimate source level of whale calls, and singing whales were tracked over time. Comparisons will be made between DIFAR methods and GPS locations from the playback boat, to ground-truth this localization methodology.

Bryde's whale calls recorded in the Gulf of Mexico

Bryde's whale calls recorded in the Gulf of Mexico

DOA estimation based on fourth order cumulant beamforming for nonuniform linear array of DIFAR sonobuoys

The Directional Frequency Analysis and Recording (DIFAR) sonobuoy has been widely used in underwater target localization because it can capture more information than the Low Frequency Analysis and Recording (LOFAR) omnidirectional sonobuoy. Recently, array processing for fields of DIFAR sonobuoys has attracted considerable attention in order to enhance the direction of arrival (DOA) estimation performance and accuracy. DIFAR sonobuoys may become irregularly spaced due to the deployment method and the drift experienced once deployed, resulting in a nonuniform array. In this paper, we demonstrate the fourth-order cumulant beamforming (FOC-BF) technique to estimate the DOA for a nonuniform linear array of DIFAR sonobuoys. FOC-BF was compared with the conventional beamforming (CBF) through simulation works. The results show that FOC-BF provides better spatial spectrum with lower sidelobes than CBF. Furthermore, FOC-BF provides superior DOA estimation accuracy over CBF at very low signal to noise ratios (SNR).

높은 방향성 소음환경에서 DIFAR 수신센서 신호의 적응 빔형성에 의한 방위추정

높은 방향성 소음환경하에서 DIFAR (Directional Frequency Analysis and Recording) 소노부이 (sonobuoy)와 같이 채널의 자유도가 낮은 시스템에서 넓은 빔폭과 낮은 신호 대 잡음비를 갖는 일반 빔형성 기법을 이용하여 음원의 방위 정보를 획득하는 것은 비효율적이다. 본 논문에서는 높은 방향성 소음환경에서 DIFAR 수신센서와 같이 센서의 수가 극히 제한된 경우에 적응 빔형성 기법을 응용하여 적용성을 검증하였다. 일반 빔형성 기법과 적응 빔형성 기법들은 모의된 방향성 신호에 의해 비교 평가되었으며, 최종적으로 실 신호를 적용하여 성능을 검증하였다. Conventional beamforming is ineffective in producing directional information in system with sparse degree of the freedom such as DIFAR (DIrectional Frequency Analysis and Recording) sonobuoy and in the presence of high directional noise. In this paper, Adaptive beamforming techniques are applied to produce directional spectra from a small number of sensors in highly directional noise environment. Conventional method as well as minimum variance and eigenvectors as adaptive method are evaluated via numerical test and real data.

Direction of arrival estimation using virtual array search

This study explores the application of the advanced array interpolation technique for direction of arrival estimation. It uses an array of Global Positioning System (GPS) sonobuoys, as a method for enhancing the bearing estimation accuracy, improving target tracking capabilities. Currently, the bearing estimation of underwater targets using sonobuoys is based on fusion of bearings, obtained through individual element processing. This preserves the advantage of having a widely spread field of sonobuoys to detect underwater targets. However, the low levels of signal-to-noise ratio (SNR) jeopardise the bearing estimation accuracy. This can be improved using array processing of a directional frequency analysis and recording (DIFAR) sonobuoy field. The environmental conditions and deployment strategies impose limitations on the array processing of a DIFAR sonobuoy field. These factors mainly cause the array of sonobuoys to be a non-uniform sparse array. Advanced array interpolation is proposed to mitigate the current processing limitations degrading the system performance. This method is tested using acoustic level simulation. Simulation results show that the proposed method improves the processing of non-uniform sparse arrays based on the SNR and the inter-element distances of the array.

Using directional frequency sonobouys to localize singing humpback whales.

For many years, the navy has been using directional frequency analysis and recording (DIFAR) sonobouys to record and track ships. DIFAR sonobouys compute the acoustic particle velocity for two bimodal perpendicular hydrophone elements which, with an omnidirectional hydrophone and magnetic compass, gives a directional bearing to the sound. The omnidirectional hydrophone is also used to record sounds. DIFAR can be more accurate for low‐frequency whale calls than time of arrival methods, and only requires the three co‐located elements, which can function autonomously without a ship. In this study, we used two moored DIFAR sonobouys over a period of 4 days to record and track multiple singing humpback whales (Megaptera novaeangliae) off of Kaena Point, Oahu, HI. The distance between the two sonobouys was 1100 m. The digital acoustic signal was recoded at the sonobouy to preserve full dynamic range before multiplexing, and was analyzed in the laboratory using custom MATLAB programs. DIFAR localizations were correlated with visual observations from both the vessel and a 950 elevation land‐based location. Relative locations of singing humpbacks and durations of song were recorded. In addition, source levels for singing whales were also calculated.

Intensity processing of vector sensors in the bistatic regime

Acoustic intensity processing of signals from directional frequency analysis and recording (DIFAR) acoustic subsystems is used to enhance the detection of submerged bodies in bistatic sonar applications. In some directions, the scattered signals may be completely dominated by the incident blast from the source, depending upon the geometry, making the object undetectable by traditional scalar pressure measurements. Previous theoretical derivations suggest that acoustic vector intensity sensors, and the associated intensity processing, are a potential solution to this problem. Deep-water experiments conducted at Lake Pend Oreille in northern Idaho are described. A large body of revolution is located between a source and a number of SSQ-53D DIFAR sonobuoys positioned from 5 to 30 body lengths away from the scattering body. Scalar pressure measurements change by less than 0.5 dB when the scattering body is inserted in the field. However, the phase of the acoustic intensity component formed between the omnipressure and directional channel orthogonal to the direction of incident wave propagation varies by as much as 75. This metric is shown to be a repeatable and strong indicator of the presence of the scattering body. [Work supported by ONR, code 321MS.]

2-체널 링-코어 플럭스-게이트 콤파스의 위상검출 회로 설계와 구현에 관한 연구

항공 대잠수함전에 사용되는 방향주파수분석저장 소노부위 (DIFAR Sonobuoy)에 방위정보를 제공하는 플럭스-게이트 콤파스의 위상감응검출 (PSD) 회로 설계와 구현에 관해서 기술하였다. PSD 회로는 쌍동-T RC 회로망을 갖는 능동형 대역필터로 구성하였다. PSD 회로에 대한 성능실험 결과, 대역통과 필터가 지구자장 방향에 비례하는 2Fe의 2차 고조파 신호를 효과적으로 걸러냄을 확인하였다. 그 결과 방위 신호 정보를 획득할 수 있었다. This paper Presents a discussion on the design and realization for the Phase Sensitive Defector (PSD) circuitry of Flu<TEX>$\chi$</TEX>-gate Compass that gives direction information to the Directional Frequency Analysis and Recording (DIFAR) Sonobuoy in Air Anti-Submarine Warfare. PSD circuitry is realized with Twin-T RC networked active band-pass filter. Results of a performance test the PSD circuitry shows that the effectiveness of band-pass filtering of desired <TEX>$2F_0$</TEX> second harmonic signal, which is Pro- portional to the direction of earth's magnetic field. This resulted in the extraction of direction information.