Estimating target strength of young chum salmon (Oncorhynchus keta)

Although chum salmon (Oncorhynchus keta) is an important fishery resource in Japan, acoustic methods cannot be applied to biomass estimation because the target strength (TS) is unknown. This study clarified the TS for each fork length (FL: 5.5–33.5 cm) of young chum salmon inhabiting the Japanese coastal area to the Bering Sea by measuring free-swimming fish. The size dependences of the TS values were TSmean = 20 log10 FL – 68.0, for both 38 and 120 kHz. This facilitated the estimation of biomass of young salmon using acoustic methods.

Non-negative Intensity for Target Strength Identification in Marine Ecosystem Research

In this paper, we propose non-negative intensity (NNI) as an alternative intensity-based technique for target strength identification in marine ecosystem research. NNI identifies local surface regions of a body with positive-only sound power contributions. NNI is employed for sound scattering by fluid-loaded, fluid-filled elastic structures with weak scattering boundary conditions. Three numerical case studies are presented for which fully coupled fluid-structure interaction models based on the finite element method (FEM) and the boundary element method (BEM) are developed. To validate the three-way coupling between the structural and fluid domains, an elastic shell submerged in water and filled with different internal fluids is initially considered. Results for the scattered acoustic intensity obtained numerically are compared with analytical results from the literature. Models representing Antarctic krill of simple and complex geometry are developed. A 3×3 cylinder array representing a simplified aggregation of krill is also presented. Target strength is calculated using both the scattered intensity and NNI for different incident excitation angles. Results for NNI identify the surface regions of an individual organism or group of organisms with the greatest contribution to the scattered sound at the target strength locations.

Acoustic traits of bat-pollinated flowers compared to flowers of other pollination syndromes and their echo-based classification using convolutional neural networks

Bat-pollinated flowers have to attract their pollinators in absence of light and therefore some species developed specialized echoic floral parts. These parts are usually concave shaped and act like acoustic retroreflectors making the flowers acoustically conspicuous to the bats. Acoustic plant specializations only have been described for two bat-pollinated species in the Neotropics and one other bat-dependent plant in South East Asia. However, it remains unclear whether other bat-pollinated plant species also show acoustic adaptations. Moreover, acoustic traits have never been compared between bat-pollinated flowers and flowers belonging to other pollination syndromes. To investigate acoustic traits of bat-pollinated flowers we recorded a dataset of 32320 flower echoes, collected from 168 individual flowers belonging to 12 different species. 6 of these species were pollinated by bats and 6 species were pollinated by insects or hummingbirds. We analyzed the spectral target strength of the flowers and trained a convolutional neural network (CNN) on the spectrograms of the flower echoes. We found that bat-pollinated flowers have a significantly higher echo target strength, independent of their size, and differ in their morphology, specifically in the lower variance of their morphological features. We found that a good classification accuracy by our CNN (up to 84%) can be achieved with only one echo/spectrogram to classify the 12 different plant species, both bat-pollinated and otherwise, with bat-pollinated flowers being easier to classify. The higher classification performance of bat-pollinated flowers can be explained by the lower variance of their morphology.

Numerical Study on the Entrance Effect of Penetration into Concrete Targets

Investigation on penetration into concrete targets is of great importance as concrete is widely used as the fundamental construction material. To achieve a more accurate prediction of penetration depths of concrete targets, a further study was conducted to explore the entrance effect by using AUTODYN hydrocode in this study. The numerical results on both deceleration-time history and depth of penetration of projectiles are in good agreement with experimental data, which demonstrate the feasibility of the numerical model in these conditions. A new target model was established with a predrilled hole around the symmetry axis to simulate the entrance effect of the crater phase on the penetration process. Compared with the regular target, the predrilled target enters the peak of acceleration earlier, leading to the reduction of the depth of penetration. In addition, simulation results indicated that nose shape significantly influenced crater region depth, while the depth was independent of the impact velocity and the target strength. Based on the simulation of entrance effect, a modified formula of penetration depth has been proposed and validated in terms of different nose shapes. The crater region depths obtained from the simulations can improve the accuracy of the predictions of the penetration depths for the penetration of concrete targets.

Target strength measurement of Caroun croaker (Johnius sp.) and acoustic fish density estimation in Musi Estuary, South Sumatra

Caroun Croaker ( Johnius sp.) is one of the dominant estuarine fish that has a reasonably high economic value. The target strength (TS) value measurement is essential in calculating the density of fish stocks using the hydroacoustic method. Target strength measurement of Caroun Croaker (Johnius sp.) and an acoustic survey in Musi Estuary Waters of South Sumatra Province was conducted in December 2019. The result of TS measurement will be used to estimate the acoustic density along the survey area. The TS measurement used the standard tethered method, tying placing the fish in a fixed cage, transmitting the acoustic pulse, and analyzing its return using the scientific acoustic instrument Biosonic DT-X 200 KHz. The fisheries acoustic survey was carried out in the area around the Musi estuary with a predetermined survey design. The results of the measurements have obtained the TS-length relationship, as TS= 20 LOG L-78.79 with determinant value of R2= 0.67 for fish length ranges from 18.1-23.3 cm, and an acoustic survey showed that the estimated stock density value was 286 kg/ha for the total surveyed area of 1.612 ha.

Analisis Akustik Target Strength Penyu Hijau (Chelonia Mydas) Melalui Pengukuran Secara Terkontrol Pada Frekuensi 200 kHz

ABSTRACT Turtles are reptiles that live in the sea and are able to migrate over long distances along the Indian Ocean, Pacific Ocean and Southeast Asia. Currently the number of turtle populations in nature has greatly decreased. This population decline is caused by natural factors and human activities that endanger the population directly or indirectly. At this time the tagging set technique (ID tag code) is a method that is often used to detect the presence of turtles by attaching tags to female turtles who are landing to lay eggs on the beach or while in captivity or the discovery of the mother turtle by fishermen. One other method that can be used to detect the presence of turtles is to use the acoustic method. The purpose of this study was to analyze the characteristics of the acoustic backscattering energy of the green turtle (Chelonia mydes) and to analyze the relationship between target strength and total body length of the green turtle (Chelonia mydas). This research was conducted in the Tapak Paderi waters pond, Bengkulu City, in August-October 2020. The average target strength (TS) value for green turtles was -48.07 dB. Based on the regression equation, the value of determination (R2) obtained is 0.78. Where this value shows that the total length of the green turtle has an effect of 78% on the average target strength (TS) value, while for 22% it is caused by other factors such as body shape, environmental factors and other factors. Based on the ANOVA test, it can be concluded that there is a relationship between the total length and the value of the target strength (TS) on the green turtle or the value of the total length has an influence on the value of the target strength (TS) on the green turtle.

Kajian Hambur Balik Akustik Dari Tukik Penyu Lekang (Lepidochelys olivacea) Melalui Pengukuran Secara Terkontrol Pada Frekuensi 200 kHz

Turtles are marine reptiles that are protected because of their endangered population. The Convention on International Trade in Endangered of Wild Flora and Fauna (CITES) stipulates seven species of sea turtles in the world into Appendix I as endangered, protected and not exploited in any form. The number of hatchlings that managed to reach the sea is currently difficult to know, one method that can be used to detect the presence of hatchlings in nature is by using the acoustic method. This study aims to analyze the backscatter characteristics of the turtle hatchlings and to determine the relationship between backscattering and body length of the turtle hatchlings. The benefits of this research are expected to be able to provide information about the value of backscatter and the relationship to the body length of hatchlings that can be used as a basis for estimating the stock or abundance of hatchlings in nature. This research was conducted in the waters of the Tapak Padri pond, Bengkulu City. The research implementation takes about 3 months, from August to October 2020. Acoustic data processing is carried out at the Marine Acoustic and Resource Exploration Laboratory, Marine Department, FMIPA, Sriwijaya University, Palembang. The results obtained are that the average value of TS ranges from -52.74 to -48.45 dB for hatchlings length of 7-9.3 cm. Based on the regression equation, the coefficient of determination (R2) obtained is 0.57, so it is known that the total length affects the target strength value by 57% and 43% is influenced by other factors. it can be concluded that there is a relationship between the total length of the hatchlings with the TS value of the hatchlings or the total length has an influence on the magnitude of the TS value in the hatchlings.

Research on the Rapid Strengthening Mechanism of Microwave Field-Controlled Gypsum-Cemented Analog Materials

Various geotechnical experiments have used gypsum-cemented analog geotechnical materials. However, this material needs a long curing time, and the target strength is not easy to control. Therefore, this research adopted microwave heating as the curing method for this kind of material. Objectively, the authors investigated the variations in the material strength versus heating power and heating time. On this basis, we clarified the influence mechanism of microwaves on the strength of analog materials by analyzing material temperature, moisture content, and microstructure, which eventually led to an experimental control method for rapid strengthening of microwave field-controlled gypsum-cemented analog materials. Consequently, we drew the following conclusions. The stable strength of the material under high-power microwave curing was much lower than that under natural curing, while the material strength under low-power microwave curing was the closest to the material under natural curing.