Target Strength Research Articles

Deep-reinforcement-learning-based hull form optimization method for stealth submarine design

The stealth performance of submarines is closely related to their hull forms. In this study, an optimization method based on Deep Reinforcement Learning (DRL) was developed to design submarine hull forms, aimed at maximizing the stealth performance. The DRL optimization technique relied on the decision-making process of an agent for determining actions resulting in changes in the hull form, using stealth performance as the reward. The stealth performance of the submarine was evaluated through a Target Strength (TS) analysis model. Additionally, functional constraints of the examined hull forms were implemented in the optimization process, including geometric constraints related to the hull form and dynamic stability constraints pertaining to the hydrodynamic maneuvering characteristics. The TS of the final optimized hull form was 6.5 dB lower than that of the base model, indicating remarkable stealth performance and improved maneuverability. These results validated the effectiveness of the proposed DRL-based optimization method.

Geospatial analysis for prediction of potential fishing zones in the Banggai Waters using hydroacoustic data and satellite remote sensing

Banggai waters are a strategic area rich in fish resources and a source of livelihood for most of the local population. Mapping fish stocks is important to ensure the sustainability of fishing in the area. One of them uses hydroacoustic data and satellite imagery to provide more comprehensive results on fish stocks and more accurate predictions of potential fishing zones. This study will spatially estimate fish density in Banggai waters using hydroacoustic data and investigate the distribution of chlorophyll-a and sea surface temperature using Himawari-8 imagery. Hydroacoustic data processing will produce target strength (TS) and volume backscatter strength (Sv) values to determine the value and distribution of fish density. Meanwhile, ZPPI results are obtained from the overlay of chlorophyll-a and sea surface temperature. From the results of mapping the potential fishing zone, the high category has the highest percentage of 43%, low 28% and medium 29%. The ZPPI point distribution map then shows the concentration of ZPPI points in the southern Banggai waters. The fish density distribution map shows that the spatial distribution tends to be around the coast of Banggai Peninsula, dominated by small and very small fish categories. Correlation of fish density point distribution with ZPPI results and oceanographic parameters has a positive influence on fish density from GAM modelling.

Submarine Acoustic Target Strength Modeling at High-Frequency Asymptotic Scattering

Submarine Acoustic Target Strength Modeling at High-Frequency Asymptotic Scattering

Effect of elevated temperature on concrete incorporating zeolite, silica fume and fly ash as replacement for cement

In this study, the effect of utilizing zeolite and industrial by-products, silica fume, and Class C fly ash, as partial replacement for cement is investigated at room and elevated temperatures of 200°C, 400°C, and 600°C. Four different high-strength concrete mixes of M50 concrete grade with varying proportions of zeolite, silica fume, and Class C fly ash are tested and observed for workability, compressive strength, and microstructural characteristics using Scanning Electron Microscope analysis, and the optimum mix has arrived. The results indicate that the addition of zeolite, silica fume, and fly ash resulted in lesser early-age strength development but the strength after 28 days of curing is found satisfactory and the desired target strength is achieved. Temperature rise resulted in degradation of concrete properties for both conventional and optimum mix but the concrete cubes with 10% of zeolite, 7.5% of silica fume, and 10% of fly ash have higher retainment of strength at elevated temperatures compared with conventional mix. The results from the microstructural study are found to correlate with strength test results. Incorporation of 10% zeolite, 7.5% silica fume, and 10% fly ash improved mechanical and microstructural characteristics at room and elevated temperature, however, the replacement is effective for 28 days of curing.

Experimental study on the utilization of construction and demolition waste of recycled aggregate with GGBS and I-Crete in pavement quality concrete

This study investigates the mechanical properties of M40 concrete in Pavement Quality Concrete (PQC) by incorporating Recycled Aggregates (RA) from construction, demolition waste and industrial wastes, such as GGBS and I-Crete, for sustainable pavement construction. The research explores varying proportions of RA (25% to 100% by weight in 25% intervals). Results show concrete mechanical strength decreases with higher RA proportions but all mixes still meet target strength criteria (compressive, flexural, split tensile) at 7, 28, and 90 days of curing. Further testing on 100% RA (MRCA-100) with GGBS admixture from 5% to 35% in 5% increments found strength improves significantly up to 10% GGBS replacement by cement weight, with subsequent decreases at higher percentages Initially. Then introducing the mineral additive, I-Crete at 2% by weight of cement in 15% to 35% GGBS range results in notable strength enhancement, peaking at 25% GGBS replacement. Ultrasonic pulse velocity (UPV) and water absorption tests showed similar trends in 28-day strength across all mixes. Increased strength from better bonding was observed, with Scanning Electron Microscopy (SEM) showing enhanced hydration and bonding due to mineral admixture and additive. These findings underscore the efficacy of such additives in enhancing the mechanical strength of sustainable PQC.

Broadband Scattering Characteristic Quantization Technique for Single Fish Based on a Split-Beam Echosounder

The utilization of broadband quantization data increases the possibility of practical applications for fish target recognition based on the acoustic scattering theory. However, the quantification of broadband data is more complex than that of narrowband systems, requiring consideration of the broadband characteristics of split-beam transducers, seawater absorption, and circuits. This paper elucidates the scatterer acoustic field equation, transducer power equation, and signal processing flow in split-beam broadband quantization technology for engineering applications. A broadband calculation model based on transducer parameters is proposed to enhance the generalization ability of broadband quantization technology to different types of sonar. The classical echo integration method is combined with Fourier transform to meet the requirements of target strength (TS) estimation under broadband signals. This paper includes a series of experiments to prove the rationality and effectiveness of the method. The results demonstrate that the provided calculation model can more accurately reflect the backscattering characteristics of the scatterer, but certain errors remain. This article analyzes the sources of errors and validates the effectiveness of the new TS calculation method.

Quantitative processing of broadband data as implemented in a scientific split‐beam echosounder

Abstract The use of quantitative broadband echosounders for biological studies and surveys can offer considerable advantages over narrowband echosounders. These include improved spectral‐based target identification and significantly increased ability to resolve individual targets. An understanding of current processing steps is required to fully utilise and further develop broadband acoustic methods in marine ecology. We describe the steps involved in processing broadband acoustic data from raw data to frequency dependent target strength () and volume backscattering strength () using data from the EK80 broadband scientific echosounder as examples. Although the overall processing steps are described and build on established methods from the literature, multiple choices need to be made during implementation. To highlight and discuss some of these choices and facilitate a common understanding within the community, we have also developed a Python code which will be made publicly available and open source. The code follows the steps using raw data from two single pings, showing the step‐by‐step processing from raw data to and . This code can serve as a reference for developing custom code or implementation in existing processing pipelines, as an educational tool and as a starting point for further development of broadband acoustic methods in fisheries acoustics.

Broadband target strength of arabesque greenling, Pacific sand lance, and pointhead flounder

Abstract Measurement of target strength (TS) is important for estimating the abundance of species using fisheries acoustics. However, most researchers have only used a limited number of representative frequencies for acoustic measurements of fish without a swim bladder (bladderless fish). Here, we measured the broadband TS of three bladderless fish species, arabesque greenling (Pleurogrammus azonus), Pacific sand lance (Ammodytes personatus), and pointhead flounder (Cleisthenes pinetorum), using two broadband echosounders. TS measurements were conducted in a seawater tank over frequency ranges of 45–90 and 80–120 kHz using a tether method. Higher TS and directivity were observed at higher frequencies than at lower frequencies for pointhead flounder and arabesque greenling. However, the TS for Pacific sand lance was relatively flat over the measured frequency spectra. Additionally, the TS of pointhead flounder and Pacific sand lance could be expressed as a function of body length and the TS of arabesque greenling could be expressed as a function of body length and frequency, which could be used in fish species discriminations and size estimations.

Active Control of the Reflection Coefficient of an Underwater Surface

From a strategic point of view, it is essential to protect underwater vehicles from being detected by opponents. Modern mono- or bistatic sonar systems are capable of precisely determining the position of a watercraft. In order to triangulate the positions of watercrafts, the sonar sends out acoustic signals that are reflected by the vehicles’ surfaces. These deflected sound waves are subsequently detected and evaluated. How well an object can be detected using a sonar can be measured according to the target strength. Through their shape, construction and choice of materials, modern underwater vehicles are optimized in relation to minimizing their radiated and reflected sound waves; in this way, their target strength is minimized. These passive measures are particularly effective in the medium- and high-frequency range down to 1500 Hz. To effectively reduce reflections at lower frequencies, an active system is developed in this study and evaluated in a laboratory test with a water-filled impedance tube. The incident sound waves were measured in front of an active surface and then processed using an adaptive control system based on an FPGA platform. The system operates with a very thin piezoceramic applied to the surface in order to minimize the reflections of the sound waves. The laboratory tests showed the high effectiveness of the system under the influence of sonar-like signals.

Assessing the potential of recycled fine aggregate from freeze-thawed parent concrete for structural concrete

Recycled fine aggregate (RFA) generated from waste concrete, especially in harsh environment, can be considered as an alternative to natural sand. The yield rate, gradation and properties of RFA from natural aggregate concrete with the target strength of C40 as parent concrete (PC) every 200 freeze–thaw (FT) cycles are investigated. To more accurately evaluate the application potential of RFA, the mechanical properties and durability of recycled fine aggregate concrete (RFAC) is further studied. The results showed that as the FT cycles of PC increased, the yield rate of RFA decreases and the grading curve of RFA meets the requirements of Class II aggregate. The limit FT cycles of PC in Class II and III RFA are 148 and 450, respectively. For the compressive strength of RFAC that meets the design requirements, the FT cycles of PC are no more than 530. Based on 50 years of RFAC in Class D and Class E environments, the limit FT cycles of PC are 663 and 200, respectively. The limit FT cycles of PC are 221 based on 50 years of RFAC service in cold regions. Through the FT cycles of PC, the Class of RFA and the mechanical and durability of RFAC can be directly predicted. This provides a theoretical and data support for improving the utilization rate of waste concrete in FT environment.

Practical target strength of free-swimming chub mackerel Scomber japonicus

Practical target strength of free-swimming chub mackerel Scomber japonicus

Development of stealth design systems for advanced submarine hull forms to reduce underwater radiated noise and target strength

The stealth capability of a submarine is the key performance to be considered in submarine design since it is directly related to survivability and operational capability. In this study, a system that can be applied from the conceptual design stage for the submarine shape, including the hull forms and appendages, has been developed by considering the two key components that determine the stealth capability of underwater vessels: underwater radiated noise (URN) and target strength (TS). First, for submarine stealth design considering URN, a design optimization technique was developed that can reduce the high flow noise caused by the interaction between the propeller and the vortex generated in various parts of the hull and appendages. And for submarine stealth design considering TS, shape design technology that can minimize the reflections of active sonar was developed through an evaluation method with high adaptability to shape modifications. Finally, by developing the optimization design procedures that comprehensively cover URN and TS, the optimal shapes and arrangements of sail and rudders that can maximize stealth performance have been derived.

Individual Fish Echo Detection Method Based on Peak Delay Estimation and Instantaneous Frequency Characterization

In fisheries science research and farmed fish monitoring, acquiring individual fish echoes is the basis for the growth assessment, tracking, and target strength estimation of farmed fish. However, individual fish echo detection methods based on narrowband signal features cannot be applied well to high-density aquaculture scenarios. The broadband signaling system can improve the distance resolution of the detected target and can help to improve the performance of individual fish echo detection. In this study, for the broadband signal system and the characteristics of the underwater fish acoustic echoes, an individual fish echo detection method is proposed using the matched filter output envelope peak interval and instantaneous frequency characteristics of the echo as evaluation indices, and the simulation and experiments of the method are carried out in an anechoic water tank. The results show that the broadband signal system and the corresponding detection method perform better in detecting single target echoes than the narrowband signal system. Compared with the broadband single echo detection method that only relies on the peak interval of the matched filter envelope, the joint detection method that incorporates the instantaneous frequency characteristics of the echo signal has a better rejection capability for overlapping echoes, which can reduce the probability of misjudging the overlapping echoes. The combined detection methods may provide a better detection performance for individual fish echoes.

Performance evaluation and cost analysis of ternary blended geopolymers for sustainable built environment under different curing regimes

Geopolymer technology provides ecological and monetary benefits in supporting waste management. This study examines the influence of different aluminosilicate materials (85–100 % ground granulated blast furnace slag (GGBS), 0–15 % fly ash (FA), and 0–15 % waste glass powder (WGP)) and curing regimes (water and steam curing) on the mechanical and durability properties and production cost of geopolymers. The water-binder ratio, binder-fine aggregate, and alkaline activator-binder ratios were kept constant, whereas different amounts of superplasticizer were used in all the samples to achieve the target strength of 250 mm. The results revealed that the compressive and flexural strengths of specimens containing FA and WGP outperformed those of GGBS-based geopolymers. The compressive and flexural strength results demonstrated that the optimal FA and WGP replacement levels in ternary blended geopolymers were 10 % and 0–15 %, respectively; subsequent increases or decreases in FA and WGP replacement levels in most of the specimens resulted in mechanical properties similar to those of GGBS-based geopolymers without a significant increase in the production cost. Moreover, exposing specimens to freeze–thaw cycles led to higher compressive strength, ultrasonic velocity values, and weight irrespective of the curing regime, which can be credited to the continued geopolymerization reaction. Contrary to freeze–thaw cycles, only some specimens exhibited higher compressive and flexural strength once exposed to magnesium sulfate (MgSO4) solution. Like compressive and flexural strengths, the resistance of ternary blended geopolymers against freeze–thaw and sulfate attack is higher than that of GGBS-based geopolymers. It is also revealed that water- and steam-cured specimens provide better early- and later-age mechanical and durability properties; therefore, the choice of curing regime should be based on potential application. The positive results of this study indicate that ternary blended geopolymers have the potential to solve environmental challenges while also being futuristic and cost-effective in the production of eco-friendly and structural-grade materials.

Role of material properties in acoustical target strength: Insights from two species lacking a swimbladder

Acoustic target strength (TS) is a key parameter for species identification and stock assessment in fisheries. The TS of fish is influenced by the contrast in acoustic impedance between their tissues and the surrounding water. While the swimbladder is responsible for most of the backscatter in fish with gas-filled swim bladders, the backscatter in bladderless fish is a combination of that of fish tissues. The aim of this paper is to explain the marked differences in acoustic properties reported between skipjack tuna and Atlantic mackerel, two important pelagic fish species that lack a swimbladder. The study measures the acoustic properties (density and sound speed) of their flesh and backbone. These measurements are then used to simulate acoustic backscattering using a numerical model based on the Method of Fundamental Solutions, covering a range of frequencies and fish lengths relevant to fisheries acoustics. The numerical estimation of the TS shows that the differences in the material properties of the tissues predict the reported differences in the reduced target strength of more than 10 dB greater for skipjack than for mackerel at 38 kHz and 120 kHz. The study contributes to the understanding of the complex acoustic field backscattered by bladderless fish species and provides insights into the role of fish tissue material properties in the interpretation of acoustic response differences between species.

A Method for Enhancing the Acoustic Scattering Characteristics of Underwater Acoustic Corner Reflectors in Vacuum Cavities

To alleviate the problem of unsatisfactory target strength and scattering stability of an underwater corner reflector, a method to enhance the acoustic scattering characteristics using a vacuum cavity as an acoustic reflecting layer is proposed. According to the principle of acoustic impedance mismatch of a water-reflecting layer, a vacuum cavity corner reflector is designed to take advantage of the property that sound waves cannot propagate under vacuum conditions. The acoustic vacuum reflecting layer has a theoretical acoustic reflecting coefficient of one. Comparative analyses are carried out with the single-layer metal corner reflector in terms of frequency and angle of incidence. For the concave structure of the underwater corner reflector, the structural finite element software ANSYS combined with the acoustic analysis software SYSNOISE is used to simulate and analyse the acoustic scattering characteristics, and the consistency of the simulation calculations and experimental data is verified through the pool experiments for typical cases. The results show that under the same reflection area, the vacuum cavity underwater corner reflector has large scattering intensity, good antiacoustic performance, no obvious frequency characteristics, and good decoupling effects. The target echo intensity value can be increased by 2 dB for better scattering stability. The overall weight is reduced by about 20 kg, with considerable engineering practicality, proving that the true cavity corner reflector is an ideal underwater acoustic counter-acoustic device.

Target strength measurements of individual sub-Arctic krill have frequency-dependent differences from scattering model predictions.

Target strength (TS) is commonly used to convert acoustic backscatter from marine organisms to numerical abundance estimates. Shipboard, tank-based TS measurements were made on four sub-Arctic krill species (Euphausia pacifica, Thysanoessa spinifera, Thysanoessa inermis, and Thysanoessa raschii) from the eastern Bering Sea and Gulf of Alaska at discrete frequencies between 42 and 455 kHz. These measurements were compared to scattering model predictions parameterized with data from the same (when possible) individual krill. Statistically significant differences between modeled and experimental estimates at 42, 45, 120, and 131 kHz exceeded 2 dB on average. Variability in the signal-to-noise ratio, animal length, and measurements from two separate narrowband and broadband transducer pairs (at those frequencies) did not account for these differences. Scattering predictions at 120 and 131 kHz were consistent with the expected transition from Rayleigh-to-geometric scattering where models become increasingly sensitive to orientation and body shape variability. Disagreement between modeled and measured TS may be due to using scattering models developed for, and validated on, larger krill (i.e., Euphausia superba) rather than smaller species of krill. Acoustic surveys of smaller (15-30 mm) krill may require further validation of both the generalizability and parameterization of applied scattering models.

Acoustic camouflage increases with body size and changes with bat echolocation frequency range in a community of nocturnally active Lepidoptera.

Body size is an important trait in predator-prey dynamics as it is often linked to detection, as well as the success of capture or escape. Larger prey, for example, often runs higher risk of detection by their predators, which imposes stronger selection on their anti-predator traits compared to smaller prey. Nocturnal Lepidoptera (moths) vary strongly in body size, which has consequences for their predation risk, as bigger moths return stronger echoes for echolocating bats. To compensate for increased predation risk, larger moths are therefore expected to have improved anti-predator defences. Moths are covered by different types of scales, which for a few species are known to absorb ultrasound, thus providing acoustic camouflage. Here, we assessed whether moths differ in their acoustic camouflage in a size-dependent way by focusing on their body scales and the different frequency ranges used by bats. We used a sonar head to measure 3D echo scans of a total of 111 moth specimens across 58 species, from eight different families of Lepidoptera. We scanned all the specimens and related their echo-acoustic target strength to various body size measurements. Next, we removed the scales covering the thorax and abdomen and scanned a subset of specimens again to assess the sound absorptive properties of these scales. Comparing intact specimens with descaled specimens, we found almost all species to absorb ultrasound, reducing detection risk on average by 8%. Furthermore, the sound absorptive capacities of body scales increased with body size suggesting that larger species benefit more from acoustic camouflage. The size-dependent effect of camouflage was in particular pronounced for the higher frequencies (above 29 kHz), with moth species belonging to large-bodied families consequently demonstrating similar target strengths compared to species from small-bodied families. Finally, we found the families to differ in frequency range that provided the largest reduction in detection risk, which may be related to differences in predation pressure and predator communities of these families. In general, our findings have important implications for predator-prey interactions across eco-evolutionary timescales and may suggest that acoustic camouflage played a role in body size evolution of nocturnally active Lepidoptera.

Effects of a Physical Activity Program that Incorporates Exercises Targeting Balance, Strength, and Proprioception on Cognitive Functions and Physical Performance in Old Adults with Mild Cognitive Impairment.

Aging often leads to cognitive function decline, sensory structure deterioration, and musculoskeletal system weakening. This impacts postural control during static and dynamic activities like walking, increasing the fall risk among the elderly. Older adults with mild cognitive impairment (MCI) face an elevated fall risk and cognitive decline, magnifying the public health concern. This study aimed to explore solutions by investigating the effects of a multi-component physical activity program on cognitive and motor functions in MCI patients. Twenty-three participants were enrolled in the study and assigned into two groups: an intervention group (n = 13; age = 85.7±5.5 years) and a control group (n = 9; age = 85±6.7 years). The study spanned two months, with participants engaging in three 60-minute weekly physical exercise sessions. The intervention focused on improving proprioception, muscle strength, and balance. Results demonstrated significant enhancements in physical performance, fall risk reduction, and balance (p < 0.05). Various tests, including the timed up and go test, Unipedal Stance test, Tinetti test, Short Physical Performance Battery, and 6-minute walking test, indicated these improvements. Cognitive function was evaluated with the Mini-Mental State Examination, revealing non-significant progress (p > 0.05). Predictive models for outcomes were developed using linear regression analysis during the follow-up stage. This study underscores the effectiveness of a multi-component physical activity program encompassing balance, proprioception, and muscle-strengthening exercises as a non-pharmaceutical approach in improving balance skills and playing a key role in mitigating the risk of falls among old adults with MCI.

Acoustic Target Strength of Jellyfish, Nemopilema nomurai, Measured at Multi-Frequency and Multi-Orientation

The jellyfish Nemopilema nomurai occupies an important position in the Northwest Pacific ecosystem, and monitoring its biomass is necessary to ensure the protection of fishery resources and the safety of offshore industrial production. The acoustic method has been proposed for jellyfish flux estimation and bloom warning, in which the target strength (TS) of the jellyfish is a crucial parameter. However, varied swimming orientations of jellyfish aggregation result in different backscatter strengths. The acoustic echo characteristics in horizontal swimming orientations and multi-frequency broadband signals are yet to be revealed. This study aims to obtain the TS of jellyfish in various orientations and to comprehensively investigate the jellyfish acoustic echo features at various frequency broadband sounds. In an anechoic tank, we used wide-band echosounder and 70 kHz, 120 kHz, and 200 kHz split-beam transducers to measure the TS of jellyfish swimming omnidirectionally. The results show a difference of approximately 4 dB in the jellyfish’s normalized TS at 70 kHz (frequency range: 45 kHz to 95 kHz) and 200 kHz (frequency range: 160 kHz to 260 kHz) center frequency. The normalized TS of jellyfish varies by around 8 dB between horizontal and vertical swimming orientations. For jellyfish swimming horizontally, the TS and bell diameter have the following least squares fits: T S D 70 k H z = 20 log D − 89.36 r 2 = 0.83 ; T S D 200 k H z = 20 log D − 93.85 r 2 = 0.83 . The swimming orientation has significant effects on TS estimation and model construction.