Motion tracking of fish and bubble clouds in synthetic aperture sonar data.

Data captured by a Synthetic Aperture Sonar (SAS) near Mobile Bay during the 2021 Undersea Remote Sensing experiment funded by the Office of Naval Research reveals near surface bubble clouds from wave breaking events and a large aggregation of fish. Tools developed for using SAS data to image hydrodynamic features in the water column were applied to observations of the bubble clouds and fish aggregation. Combining imagery and height data captured by the sonar array with a detection and tracking algorithm enables the trajectories, velocities, and behavior of fish in the aggregation to be observed. Fitting the velocity and height data of the tracked objects to a Gaussian mixture model and performing cluster analysis enables an estimate of the near-surface ambient velocity via observation of the movement of the bubble traces and the general direction of motion of the fish aggregation. We find that the velocity traces associated with bubbles are consistent with ambient currents as opposed to the direction of propagating wave crests while velocities of fish indicate relatively large, pelagic species.

A systematic review of literature on homicide followed by suicide and mental state of perpetrators.

BACKGROUND: Homicide followed by suicide is rare, devastating and perpetrated worldwide. It is commonly assumed that the perpetrator had a mental disorder, raising concomitant questions about prevention. Though events have been reported, there has been no previous systematic review of the mental health of perpetrators. AIMS: Our aims were twofold. First, to identify whether there are recognisable subgroups of homicide-suicides in published literature and, secondly, to investigate the relationship between perpetrator mental state and aspects of the incident. METHODS: We conducted a systematic review of published literature on studies of homicide followed within 24 h by suicide or serious suicide attempt that included measures of perpetrator mental state. RESULTS: Sixty studies were identified, most from North America or Europe. Methodologically, studies were too heterogeneous for meta-analysis. They fell into three main groups: family, mass shooter, and terrorist with an additional small mixed group. There was evidence of mental illness in a minority of perpetrators; its absence in the remainder was only partially evidenced. There was no clear association between any specific mental illness and homicide-suicide type, although depression was most cited. Social role disjunction, motive, substance misuse and relevant risk or threat behaviours were themes identified across all groups. Pre-established ideology was relevant in the mass shooter and terrorism groups. Prior trauma history was notable in the terrorist group. CONCLUSION: Research data were necessarily collected post-incident and in most cases without a standardised approach, so findings must be interpreted cautiously. Nevertheless, they suggest at least some preventive role for mental health professionals. Those presenting to services with depression, suicidal ideation, relationship difficulties and actual, or perceived, changes in social position or role would merit detailed, supportive assessment over time.

Three-dimensional observations of tidal plume fronts in estuaries using a synthetic aperture sonar array.

Synthetic aperture sonar (sas) systems are designed to observe stationary scatterers located near the sediment interface. Less commonly, a sas system may be used to observe scattering features located above the sonar in the water column. The Undersea Remote Sensing (USRS) project, sponsored by the Office of Naval Research, was a collaborative Directed Research Initiative (DRI) focused on studying dynamic estuarine water column features. During the USRS DRI, researchers from multiple institutions gathered to observe tidal features at various estuaries along the coast of the United States using both in situ and remote sensing techniques, including sas. The first studied estuary was the mouth of the Connecticut River (CTR). Data captured by a sas system deployed during a tidal event were post-processed to create three-dimensional observations of the structure of the leading edge of the CTR's ebb plume front. From these observations, lobed structures similar in scale to previously reported instabilities are revealed, with the present observations providing additional insight regarding the structure of the bubble distribution behind the front. Velocity estimates of plume features were also determined from sas data and shown to compare favorably with concurrent marine radar estimates.

Classification of broadband target spectra in the mesopelagic using physics-informed machine learning.

Broadband echosounders measure the scattering response of an organism over a range of frequencies. When compared with acoustic scattering models, this response can provide insight into the type of organism measured. Here, we train the k-Nearest Neighbors algorithm using scattering models and use it to group target spectra (25-40 kHz) measured in the mesopelagic near the New England continental shelf break. Compared to an unsupervised approach, this creates groupings defined by their scattering physics and does not require significant tuning. The model classifies human-annotated target spectra as gas-bearing organisms (at, below, or above resonance) or fluid-like organisms with a weighted F1-score of 0.90. Class-specific F1-scores varied-the F1-score exceeded 0.89 for all gas-bearing organisms, while fluid-like organisms were classified with an F1-score of 0.73. Analysis of classified target spectra provides insight into the size and distribution of organisms in the mesopelagic and allows for the assessment of assumptions used to calculate organism abundance. Organisms with resonance peaks between 25 and 40 kHz account for 43% of detections, but a disproportionately high fraction of volume backscatter. Results suggest gas bearing organisms account for 98.9% of volume backscattering concurrently measured using a 38 kHz shipboard echosounder between 200 and 800 m depth.

Frequency- and depth-dependent target strength measurements of individual mesopelagic scatterers.

Recent estimates based on shipboard echosounders suggest that 50% or more of global fish biomass may reside in the mesopelagic zone (depths of ∼200-1000 m). Nonetheless, little is known about the acoustic target strengths (TS) of mesopelagic animals because ship-based measurements cannot resolve individual targets. As a result, biomass estimates of mesopelagic organisms are poorly constrained. Using an instrumented tow-body, broadband (18-90 kHz) TS measurements were obtained at depths from 70 to 850 m. A comparison between TS measurements at-depth and values used in a recent global estimate of mesopelagic biomass suggests lower target densities at most depths.

Direct inference of first-year sea ice thickness using broadband acoustic backscattering.

Accurate measurements of sea ice thickness are critical to better understand climate change, to provide situational awareness in ice-covered waters, and to reduce risks for communities that rely on sea ice. Nonetheless, remotely measuring the thickness of sea ice is difficult. The only regularly employed technique that accurately measures the full ice thickness involves drilling a hole through the ice. Other presently used methods are either embedded in or through the ice (e.g., ice mass balance buoys) or calculate thickness from indirect measurements (e.g., ice freeboard from altimetry; ice draft using sonars; total snow and ice thickness using electromagnetic techniques). Acoustic techniques, however, may provide an alternative approach to measure the total ice thickness. Here laboratory-grown sea ice thicknesses, estimated by inverting the time delay between echoes from the water-ice and ice-air interfaces, are compared to those measured using ice cores. A time-domain model capturing the dominant scattering mechanisms is developed to explore the viability of broadband acoustic techniques for measuring sea ice thickness, to compare with experimental measurements, and to investigate optimal frequencies for in situ applications. This approach decouples ice thickness estimates from water column properties and does not preclude ice draft measurements using the same data.

Acoustically relevant properties of four crude oils at oceanographic temperatures and pressures.

Inversions of models of broadband acoustic scattering to detect and quantify weakly scattering targets, such as oil droplets in seawater, require precise knowledge of the physical properties that determine scattering. When the characteristic impedance contrast between a target and the surrounding medium is weak, small differences between the true and modeled impedance can cause significant errors in modeled scattering. For crude oil, currently available empirical models of density and sound speed are derived from measurements made at reservoir conditions (high temperature and pressure), which may not be relevant to oceanographic conditions due to phase changes in the oil. Measurements of the density and sound speed, as well as thermal characterization of phase changes via differential scanning calorimetry, of four crude oils at oceanographically relevant temperatures and pressures were made and compared to a commonly used empirical model for sound speed and density. Significant deviations between the measured and modeled values were found and different empirically fit models were developed. A literature review of sound speed data was also performed, and the innovative empirical model shows improvement over the commonly used empirical model for both the data measured here and the measurements in the literature.

Broadband acoustic backscatter from crude oil under laboratory-grown sea ice.

In ice-covered seas, traditional air-side oil spill detection methods face practical challenges. Conversely, under-ice remote sensing techniques are increasingly viable due to improving operational capabilities of autonomous and remotely operated vehicles. To investigate the potential for under-ice detection of oil spills using active acoustics, laboratory measurements of high-frequency, broadband backscatter (75-590 kHz) from crude oil layers (0.7-8.1 cm) under and encapsulated within sea ice were performed at normal and 20° incidence angles. Discrete interfaces (water-oil, oil-ice, and ice-oil) are identifiable in observations following oil injections under the ice and during the subsequent encapsulation. A one-dimensional model for the total normal incidence backscatter from oil under ice, constrained by oil sound speed measurements from -10 °C to 20 °C and improved environmental measurements compared to previous studies, agrees well with pre-encapsulation observations. At 20° incidence angles echoes from the ice and oil under ice are more complex and spatially variable than normal incidence observations, most likely due to interface roughness and volume inhomogeneities. Encapsulated oil layers are only detected at normal incidence. The results suggest that high-frequency, broadband backscatter techniques may allow under-ice remote sensing for the detection and quantification of oil spills.

Laboratory measurements of high-frequency, acoustic broadband backscattering from sea ice and crude oil.

Recent decreases in summer sea ice cover are spurring interest in hydrocarbon extraction and shipping in Arctic waters, increasing the risk of an oil spill in ice covered waters. With advances in unmanned vehicle operation, there is an interest in identifying techniques for remote, underwater detection of oil spills from below. High-frequency (200-565 kHz), broadband acoustic scattering data demonstrate that oil can be detected and quantified under laboratory grown sea ice and may be of use in natural settings. A simple scattering model based on the reflection coefficients from the interfaces agrees well with the data.

Flow-noise and turbulence in two tidal channels.

Flow-noise resulting from oceanic turbulence and interactions with pressure-sensitive transducers can interfere with ambient noise measurements. This noise source is particularly important in low-frequency measurements (f < 100 Hz) and in highly turbulent environments such as tidal channels. This work presents measurements made in the Chacao Channel, Chile, and in Admiralty Inlet, Puget Sound, WA. In both environments, peak currents exceed 3 m/s and pressure spectral densities attributed to flow-noise are observed at frequencies up to 500 Hz. At 20 Hz, flow-noise exceeds mean slack noise levels by more than 50 dB. Two semi-empirical flow-noise models are developed and applied to predict flow-noise at frequencies from 20 to 500 Hz using measurements of current velocity and turbulence. The first model directly applies mean velocity and turbulence spectra while the second model relies on scaling arguments that relate turbulent dissipation to the mean velocity. Both models, based on prior formulations for infrasonic (f < 20 Hz) flow-noise, agree well with observations in Chacao Channel. In Admiralty Inlet, good agreement is shown only with the model that applies mean velocity and turbulence spectra, as the measured turbulence violates the scaling assumption in the second model.

A vessel noise budget for Admiralty Inlet, Puget Sound, Washington (USA).

One calendar year of Automatic Identification System (AIS) ship-traffic data was paired with hydrophone recordings to assess ambient noise in northern Admiralty Inlet, Puget Sound, WA (USA) and to quantify the contribution of vessel traffic. The study region included inland waters of the Salish Sea within a 20 km radius of the hydrophone deployment site. Spectra and hourly, daily, and monthly ambient noise statistics for unweighted broadband (0.02-30 kHz) and marine mammal, or M-weighted, sound pressure levels showed variability driven largely by vessel traffic. Over the calendar year, 1363 unique AIS transmitting vessels were recorded, with at least one AIS transmitting vessel present in the study area 90% of the time. A vessel noise budget was calculated for all vessels equipped with AIS transponders. Cargo ships were the largest contributor to the vessel noise budget, followed by tugs and passenger vessels. A simple model to predict received levels at the site based on an incoherent summation of noise from different vessels resulted in a cumulative probability density function of broadband sound pressure levels that shows good agreement with 85% of the temporal data.

Comparison of mesopelagic organism abundance estimates using in situ target strength measurements and echo-counting techniques.

Recent studies using acoustic techniques suggest that the biomass of mesopelagic fishes may be an order of magnitude higher than previously estimated from trawls. However, there is uncertainty surrounding these estimates, which are derived from shipboard echosounder measurements using necessary, but poorly constrained, assumptions. Here, an echosounder is used to measure individual target strengths at depth. These measurements are used to infer mesopelagic organism density through echo-counting. Measured target strengths are used to estimate organism density by inverting shipboard echosounder measurements. The two sampling methods agree well, but highlight the importance of accurate target strength measurements.

Acoustic characterization of sensors used for marine environmental monitoring.

Active acoustic sensors are widely used in oceanographic and environmental studies. Although many have nominal operating frequencies above the range of marine mammal hearing, they can produce out-of-band sound that may be audible to marine mammals. Acoustic emissions from four active acoustic transducers were characterized and compared to marine mammal hearing thresholds. All four transducers had nominal operating frequencies above the reported upper limit of marine mammal hearing, but produced measurable sound below 160 kHz. A spatial map of the acoustic emissions of each sonar is used to evaluate potential effects on marine mammal hearing when the transducer is continuously operated from a stationary platform. Based on the cumulative sound exposure level metric, the acoustic emissions from the transducers are unlikely to cause temporary threshold shifts in marine mammals, but could affect animal behavior. The extent of audibility is estimated to be, at most, on the order of 100 m.

Short article: Buried bumper syndrome in children: incidence and risk factors.

OBJECTIVE: Buried bumper syndrome (BBS) is a serious complication in gastrostomy-dependent children. Many need surgical correction. On account of comorbidities, this becomes a high-risk procedure. Our aim was to review the incidence of BBS in children and to identify the risk factors. PATIENTS AND METHODS: Retrospective review of patients' records over 10 years, 2006-2015, was carried out. Types of tubes, operative interventions, comorbidities and records were noted. Two-tailed Fisher's exact test was used for statistical analysis. RESULTS: A total of 535 patients were reviewed. Overall, 475 had only percutaneous endoscopic gastrostomy (PEG) and 60 had a jejunal extension with percutaneous endoscopic gastrostomy (PEG-J). Twenty-nine patients (PEG-J - 16/26; PEG - 13/26) had a total of 31 BBS episodes. The overall incidence of BBS in our study was 5.4%. The age at presentation ranged from 1 to 18 years (median 8.6 years). All had significant comorbidities (neurodevelopmental 26/29, cardiorespiratory 14/29, genetic 16/29). Overall, 27/29 had two or more comorbidities. The mean time to development of BBS was 1025±634 days. BBS was found in the second or the subsequent tube in four patients with PEGs (P<0.0004) and in 10 PEG-Js (P<0.0001). Twenty-five patients needed laparotomy. There were no postoperative deaths. CONCLUSION: In BBS, the two significant risk factors identified were a having PEG-J and two or more previous gastrostomy insertions. Vigilance in documentation and prolonged follow-up to provide regular education to carers can reduce the incidence of this preventable complication.

Functional outcomes in Hirschsprung disease: A single institution's 12-year experience.

AIMS: Hirschsprung disease (HD) is a chronic condition associated with long-term morbidity. We assessed the short and long-term functional outcomes of operated patients in a single institution over a 12-year period. MATERIALS AND METHODS: We conducted a retrospective review of all children operated for HD between 2002 and 2014. Postoperative functional outcomes were assessed using the Rintala Bowel Function Score (BFS, 0-20, 20=best score). We assessed hospital admissions, complications including Hirschsprung associated enterocolitis (HAEC) and the need for further surgical procedures. RESULTS: 72 (52 male) patients were studied, of whom, 6 (8%) had a positive family history, 5 (7%) had Trisomy 21 and 5 (7%) had total colonic HD. The median age at diagnosis was 6.5days (2 days-6.7 years) and median follow-up was 6years (1-12years). All patients except two underwent a Duhamel pull-through procedure. The median age at surgery was 4months (6days-90months). 37 (51%) procedures were performed single-stage and 7 (10%) were laparoscopically assisted. Our early complication rate was 15%; 11 (15%) patients were treated for HAEC and 43 (60%) did not require any further surgery. 12 (17%) underwent injection of botulinum toxin, 7 (10%) needed residual spur division and 4 (5%) required an unplanned, post pull-through enterostomy for obstructive defecation symptoms and HAEC. Two (3%) patients underwent an Antegrade Colonic Enema (ACE) stoma. The median BFS was 17 (5-20). There were two deaths both out of hospital. CONCLUSIONS: Long-term functional outcomes following Duhamel Pull-Through surgery are satisfactory although 40% of patients needed some form of further surgical intervention. The management of anal sphincter achalasia has improved with the use of botulinum toxin and we advocate aggressive and early management of this condition for symptoms of obstructive defecation and HAEC. LEVEL OF EVIDENCE: III.