Search

Infrared remote sensing technique has been widely used for the characteristics of objects since ithas the advantage of higher atmospheric transmittance than visible wavelengths. However, theMid-Wave InfraRed (MWIR) region close to the visible band can be partially affected by solarradiation, so the solar radiation and attenuation in the atmosphere cause errors in the targetdetecting. In this study, an algorithm for retrieval of the mid-infrared surface temperature wasdeveloped by using a combination of the GEO-KOMPSAT-2A (GK-2A) satellite and Landsat data.Through the comparison with ground observations, it was found that the surface temperatures atMWIR band retrieved are less than 3K, and a statistically significant level of mutual comparisonwas obtained. Therefore, despite the limitations of the MWIR band, the new methodology can beapplied to determine the surface-level temperature through the coupling between the twodifferent orbit satellites.AcknowledgementThis research was supported by the Korea Aerospace Research Institute (FR22H00W01) in2022-2023.

Emission sources, meteorology, and topography are the major factors that make it difficult to predict aerosols in space and time. In this study, the moderate resolution imaging spectro-radiometer (MODIS) aerosol optical thickness (AOT) and the surface meteorology observed in Korea have been used to predict spatio-temporal AOT by using the machine learning with spatial analysis techniques. This method enables timeseries based prediction and spatial distribution modeling, and allows modeling values where there are no observation points. The model results show root mean square error (RMSE) 0.33 which is smaller than the standard deviation of the observed value 0.43. Using this technique, the trend of aerosol change in the future was estimated, and it was found that the aerosol in the area of interest decreased by about 7.4%. The methodology will be useful to analyze the regional scale aerosol evaluations, air quality, and climate study. AcknowledgementThis research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(NRF-2019R1I1A3A01062804)”

Multimode Tonpilz transducers operate at longitudinal and flexural vibration modes simultaneously. Consequently, they have wider bandwidths than conventional single-mode transducers. Generally, the performance of Tonpilz transducers is analyzed using the finite element method (FEM), whereas the equivalent circuit method (ECM) has proven to be a fast and efficient alternative to the FEM. However, the ECM for analyzing the acoustic characteristics of multimode Tonpilz transducers has not yet been developed. To address this issue, an equivalent circuit for the multimode Tonpilz transducer is developed herein. The proposed ECM encompasses the flexural characteristics of the Tonpilz head mass, which is impossible with conventional equivalent circuits. Furthermore, a prototype of the multimode Tonpilz transducer was fabricated to verify the validity of the developed ECM. Additionally, the accuracy and compliance of the ECM were confirmed by comparing the measured performance of the transducer with that from the equivalent circuit analysis.

In this study, a vector hydrophone was developed for a towed array sonar system using a shear type accelerometer. In general, inertia type vector hydrophones using accelerometers have higher sensitivity than multimode vector hydrophones. However, the sensitivity still needs to be enhanced as much as possible for practical application. For the purpose, the effect of the structural parameters of a shear type accelerometer on the receiving voltage sensitivity (RVS) of the vector hydrophone was rigorously analyzed, and the structure of the vector hydrophone was optimized to maximize the RVS. The developed vector hydrophone has an external diameter of 23 mm and the minimum RVS over the given frequency range of -201.4 dB. It was also verified that the designed vector hydrophone exhibits the characteristic of a dipole mode beam pattern. Furthermore, a prototype of the vector hydrophone was fabricated with the optimal dimensions, and its acoustic characteristics were measured to verify the validity of the design. The vector hydrophone developed in this work has the highest feasible RVS over the desired frequency range in comparison with other types of vector hydrophone like the multimode hydrophone.

Tonpilz transducers are desirable for their superior performance in underwater target detection and communication applications. Several design schemes to widen their bandwidth have been reported, but these schemes often involve a complex structure or arrangement of additional components. In this study, a simple design is proposed to improve the bandwidth of a multimode Tonpilz transducer by using a non-uniform drive section that consists of piezoelectric stacks of various thicknesses. The efficacy of the design is illustrated with a multimode Tonpilz transducer having three lead zirconate titanate (PZT) stacks of different thicknesses. A new equivalent circuit was developed to analyze the frequency response of the transducer incorporating the non-uniform drive section and was used for rigorous analysis of the effects of varying the position and thickness of the non-uniform stacks on the transmitting characteristics of the transducer. The validity of the design was verified through the fabrication and characterization of a prototype multimode Tonpilz transducer. The developed structure can be readily extended to an arbitrary number of stacks in the Tonpilz transducer with any number of PZT disks in each stack.

Underwater sensors that detect the distance and direction of acoustic sources are critical for surveillance monitoring and target detection in the water. Here, we propose an axial vector sensor that utilizes a small (~1 cm3) compressive-type piezoelectric accelerometer using piezoelectric single crystals. Initially, finite element analysis (FEA) was used to optimize the structure that comprised piezoelectric Pb(Mb1/3Nb2/3)O3-28%PbTiO3 single crystals on a tungsten seismic mass. The receiving voltage sensitivity (RVS) was enhanced through geometric optimization of the thickness and sensing area of the piezoelectric material and the seismic mass. The estimated maximum RVS of the optimized vector sensor was &minus, 212 dB. FEA simulations and practical measurements were used to verify the directivity of the vector sensor design, which exhibited a dipole pattern. The dipole beam pattern was used to obtain cardioid patterns using the simulated and measured results for comparison. The results clearly showed the feasibility of using the proposed piezoelectric single-crystal accelerometer for a compressive-type vector sensor.

Typical hydrophones in line array sensors used to detect covert underwater targets can measure only sound pressure magnitude with the limitation of being unable to identify the direction of an incoming wave. In this paper, a thickness-shear mode vibrator is proposed as the main component of an inertia-type vector hydrophone to measure both the magnitude and direction of acoustic signals from targets. The piezoelectric single crystal lead magnesium niobate-lead titanate with rhombohedral 3 m symmetry constitutes the vibrator. The directional voltage response of the vibrator to an external force is derived, and the validity of the derived response is verified through fabrication of a piezoelectric single crystal vibrator and by comparison of its measured characteristics with the analysis results.

Recent underwater vehicles can operate with a much lower level of noise, which increases the need for an active sonobuoy with a high detection performance. These active sonobuoys mainly use bender transducers as a projector that emits sound waves. In this study, we designed a high-performance bender transducer and verified the validity of the design through experiments. For this purpose, first we analyzed the variation of the peak transmitting voltage response (TVR) level and peak TVR frequency of the bender transducer, in relation to its structural parameters. The performance of the bender transducer was analyzed using the finite element method. Then we derived the optimal structure of the bender transducer to achieve the highest TVR. Based on the design, a prototype of the bender transducer was fabricated and its acoustic properties were measured to confirm the validity of the design.

Commonly used underwater acoustic array types include planar and conformal arrays. The conformal array is favorable in practical active sonar systems as it offers superior acoustic performance, but its relatively complicated structure requires sophisticated analysis and design. In general, the characteristics of the array are analyzed using the finite element method (FEM). However, for complicated structures like the conformal array, the FEM is extremely time consuming and computation intensive. In this work, we developed a new equivalent circuit method (ECM) that can facilitate the analysis of the acoustical performance of a conformal array. The proposed ECM can include the effect of mutual interference between constitutive elements of the conformal array in addition to its own property of the array, which has not been possible with conventional equivalent circuits. The new ECM was applied to the analysis of the transmitting characteristics of a conformal array of multimode Tonpilz transducers. The Tonpilz transducer operated at both longitudinal- and flexural-mode resonances simultaneously to achieve a wide bandwidth. A new equivalent circuit to represent the multimodal properties of the Tonpilz transducer itself was derived as well. The validity and efficiency of the analysis of the Tonpilz transducer and the conformal array was verified by comparing the transmitting voltage response spectrum obtained by the ECM with those obtained by the FEM and experimental measurement. For the experimental validation, prototypes of the multimode Tonpilz transducers and their conformal array were fabricated and characterized.

Underwater acoustic transducers are used to detect and track targets by using sound waves in underwater environments. To enhance the performance, they can be arranged in various formations to create arrays. However, acoustic interaction between the constituent channels of array transducers is inevitable, and it distorts their characteristics. In this study, the transmitting voltage response (TVR) spectrum of an acoustic planar array transducer is analyzed by considering the crosstalk between channels. The transmitting performance of an array transducer is frequently analyzed using the conventional finite element method (FEM). However, when the size of the array is large, the time and cost of computation using the FEM increase to almost prohibitive levels. To overcome this problem, a new equivalent circuit method (ECM) is developed to analyze the acoustic characteristics of an underwater array transducer. The ECM is validated by comparing its TVR spectrum with that analyzed using the FEM. After validation, the ECM is utilized to design the optimal structure of a planar array transducer having the broadest bandwidth. The sample analysis conducted using the ECM was approximately 1780 times faster than that by the FEM. Therefore the ECM developed in this work can facilitate the design of an underwater planar array transducer with a superior speed and efficiency compared with those achievable with the conventional numerical analysis methods such as the FEM.

In this study, the optimum structure of a shear type accelerometer is designed to maximize the performance of a vector hydrophone used for a towed array sonar system. The effect of the structural elements of the accelerometer on the receiving voltage sensitivity (RVS) of the hydrophone is analyzed, and the optimal structure of the accelerometer is derived based on the analysis. The RVS of the acceleration designed by the optimization is -204.9 dB, which satisfies the design specification. In addition, it is confirmed that the accelerometer with the optimum structure has the dipole mode beam pattern required for a vector hydrophone. The dipole response when coupled with an omnidirectional hydrophone can generate a cardioid beam pattern that can detect not only magnitude of a sound pressure but also the direction of the external sound source. Precedent works have presented the concept of the vector hydrophone and proved its functionality without detailed design of its structure so far. This work is new in that we carried out full detailed design process to maximize the performance of the vector hydrophone based on the analysis of the effect of structural parameters constituting the accelerometer.

Department of Mechanical Engineering, Kyungpook National University, Daegu 702-010, Korea (Received May 21, 2013; Revised May 24, 2013; Accepted May 24, 2013)Abstract: With polymer properties and ceramic volume fraction as design variables, the optimal structure of 1-3 piezocomposites has been determined to maximize the thickness mode electromechanical coupling factor. When the piezocomposite vibrates in a thickness mode, inter-pillar resonant modes are likely to occur between lattice-structured piezoceramic pillars and polymer matrix, which significantly deteriorates the performance of the piezocomposite. In this work, a new method to design the structure of the 1-3 type piezocomposite is proposed to maximize the thickness mode electromechanical coupling factor while preventing the occurrence of the inter-pillar modes. Genetic algorithm was used for the optimal design, and the finite element analysis method was used for the analysis of the inter-pillar mode.Keywords: 1-3 piezocomposite, Inter-pillar mode, Optimization

A planar array transducer consists of several transducers arranged on an acoustic window, which causes crosstalk. The crosstalk is a phenomenon in which the acoustic pressure generated by a projector is transferred to adjacent hydrophones through the acoustic window and the transferred pressure generates noise signals in the hydrophones. The performance of the planar array transducer is deteriorated due to this acoustic interaction, which should be minimized for maximum array performance. Analysis of the crosstalk has been carried out with sophisticated numerical methods, which motivated the need to develop a simpler and accurate analysis method. In this work, an equivalent circuit has been developed to analyze the crosstalk level of the planar array transducer, and the validity of the developed method has been verified by comparing the result from the equivalent circuit analysis with that from finite element analysis.

The structure of 1–3 piezocomposites has been optimized with such design variables as volume fraction of piezoceramics inside the composite and the thickness and aspect ratio of the piezoceramic pillars to enhance the performance of an underwater acoustic transducer operating in the thickness mode of the piezocomposites. Influence of the design variables on the transducer performance was analyzed with equivalent circuits and finite element method. In operation of the transducer, inter-pillar modes of vibration were likely to occur between piezoceramic pillars due to the lattice-structure of the piezocomposite, which could deteriorate the performance of the transducer. The structure of the 1–3 piezocomposite plate has been optimized to maximize transmitting, receiving and transmitting–receiving performance of the underwater acoustic transducer while preventing the coupling of the thickness mode with inter-pillar modes within the frequency range of interest. As results, volume fraction (VF) of 40.5% and aspect ratio (AR) of 0.4 showed the highest transmitting performance while VF of 30.0% and AR of 0.5 showed the highest receiving performance. For the transmitting–receiving performance, VF of 43.7% and AR of 0.5 were the optimal. Genetic algorithm was used in the optimal design.