Journal of Marine Science and Engineering

Research

26 pages, 14781 KiB

Open AccessArticle

Combined Motion Compensation Method for Long Synthetic Aperture Radar Based on Subaperture Processing

by Yuan Zhang, Limin Huang, Zhichao Xu, Zihao Wang and Biao Chen

J. Mar. Sci. Eng. 2025, 13(2), 355; https://doi.org/10.3390/jmse13020355 - 14 Feb 2025

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Long synthetic aperture radar (SAR) offers the advantage of achieving higher resolution by utilizing longer synthetic aperture times, which makes it a promising technology for ocean observation in the future. However, compared to SAR systems with shorter synthetic aperture times, it suffers more [...] Read more.

Long synthetic aperture radar (SAR) offers the advantage of achieving higher resolution by utilizing longer synthetic aperture times, which makes it a promising technology for ocean observation in the future. However, compared to SAR systems with shorter synthetic aperture times, it suffers more severely from issues such as image defocusing, blurring and artifacts during the observation of maritime targets, due to motion errors. To improve the quality of SAR imaging against motion errors in long synthetic aperture time scenarios, this paper proposes a combined motion compensation (MOCO) method based on subaperture processing. The method first divides the full aperture data into several subapertures. Within each subaperture, the platform is assumed to move at approximately constant velocity. The major imaging step is then combined with two motion compensation operations, which are performed individually within each subaperture. Then, the processed subaperture data are stitched together, and finally, the residual errors are compensated by the third MOCO, resulting in the final image. By simulating maritime observation targets with point targets, simulation results demonstrate that the proposed MOCO algorithm effectively reduce the influence of motion errors, suppress the sidelobe interference to the imaging, and improve the focusing accuracy. Compared with other classical MOCO algorithms, the ISLR_r and ISLR_a metrics show improvements of 0.2662 and 0.8170 dB, respectively. Further verification of the proposed method is conducted by processing the imaging results of measured sea surface data. The proposed algorithm produces clearer wave textures and achieves better imaging performance on targets such as ships in the sea. This result validates the effectiveness and superiority of the proposed method. The proposed method effectively addresses the need for high-precision motion error compensation in high-resolution imaging within long synthetic aperture time system. Full article

(This article belongs to the Special Issue Ocean Observations)

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12 pages, 1377 KiB

Open AccessArticle

Population Genetic Structure with Mitochondrial DNA of the Chub Mackerel Scomber japonicus in Korean Coastal Waters

by Woo-Seok Gwak

J. Mar. Sci. Eng. 2025, 13(2), 252; https://doi.org/10.3390/jmse13020252 - 29 Jan 2025

Viewed by 593

Abstract

Scomber japonicus, commonly known as chub mackerel, is a fish species of economic significance in Korea, China, and Japan, whose natural abundance has reduced dramatically due to overfishing and environmental changes. To investigate the genetic differentiation and population structure of S. japonicus [...] Read more.

Scomber japonicus, commonly known as chub mackerel, is a fish species of economic significance in Korea, China, and Japan, whose natural abundance has reduced dramatically due to overfishing and environmental changes. To investigate the genetic differentiation and population structure of S. japonicus, a 359 base pair segment of the mitochondrial DNA (mtDNA) control region sequence was analyzed in 96 individuals sampled from three locations in Korean waters. Sixty-six haplotypes were recognized, of which 61 (92.42%) were population specific, whereas only five haplotypes were shared by multiple populations (8%). Two clades were revealed with low support values, and no specific genealogical branches were recognized according to geographical locations. Significant genetic differentiations, however, were detected among the three populations, with F_ST values (p < 0.05). These results indicate that populations of S. japonicus in Korean waters are genetically subdivided. Migration patterns, spawning site fidelity, and current temperature could be the possible causes of this subdivision. Consequently, it is thought that each of the genetically unique S. japonicus stocks found in Korean waters requires a different approach to management. Full article

(This article belongs to the Special Issue Ocean Observations)

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17 pages, 4267 KiB

Open AccessArticle

An Improved MG Model for Turbulent Mixing Parameterization in the Northwestern South China Sea

by Minghao Hu, Lingling Xie, Mingming Li, Quanan Zheng, Feihong Zeng and Xiaotong Chen

J. Mar. Sci. Eng. 2025, 13(1), 46; https://doi.org/10.3390/jmse13010046 - 30 Dec 2024

Viewed by 549

Abstract

Using in situ microstructure observations from 2010 to 2018, this study assesses the applicability of turbulent mixing parameterization schemes in the northwestern South China Sea (NSCS) and improves the MG model proposed by MacKinnon and Gregg in 2003 using machine learning methods. The [...] Read more.

Using in situ microstructure observations from 2010 to 2018, this study assesses the applicability of turbulent mixing parameterization schemes in the northwestern South China Sea (NSCS) and improves the MG model proposed by MacKinnon and Gregg in 2003 using machine learning methods. The results show that the estimation error of the MG model is still more than one order of magnitude in the NSCS. Also, the importance of parameters obtained from machine learning indicates that the normalized depth (D) is one of the most relevant parameters to the turbulent kinetic energy dissipation rate ε. Therefore, in this study, D is introduced into the MG model to obtain an improved MG model (IMG). The IMG model has an average correlation (r) between the estimated and observed log₁₀ε of 0.79, which is at least 49% higher than the MG model, and an average root mean square error (RMSE) of 0.25, which is at least 42% lower than that of the MG model. The IMG model accurately estimates the multi-year turbulent mixing observed in the NSCS, including before and after tropical cyclone passages. This provides a new perspective to study the physical principles and spatial and temporal distribution of turbulent mixing. Full article

(This article belongs to the Special Issue Ocean Observations)

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19 pages, 12202 KiB

Open AccessArticle

Research on a Marine Animal Behavior Recording Tag System Based on Combined Positioning and Recovery

by Chuan Tian, Shiyao Shen, Zejin Sun, Dazhen Xu, Peng Luo, Yuanjie Song, Zhentong Wang, Chen Wang, Shengzong Zhang and Chong Shen

J. Mar. Sci. Eng. 2024, 12(12), 2292; https://doi.org/10.3390/jmse12122292 - 12 Dec 2024

Viewed by 1080

Abstract

The ocean represents the cradle of life on Earth, making it essential to comprehend the complex interactions between marine animal behaviors and the physical microstructure of their environments in order to study their behavioral ecology. Due to the vastness of the ocean, traditional [...] Read more.

The ocean represents the cradle of life on Earth, making it essential to comprehend the complex interactions between marine animal behaviors and the physical microstructure of their environments in order to study their behavioral ecology. Due to the vastness of the ocean, traditional observational techniques are constrained by distance, which poses significant challenges for conducting extended and continuous research on marine animal behavior and ecology. To overcome these challenges, this paper introduces a behavior recording tag system incorporating temperature, pressure, and miniature inertial measurement unit (MIMU) sensors as data collection modules. These sensors are integrated with a main control module and a data storage module to gather and archive behavioral and environmental information. A combined positioning recovery method is proposed, developed, and validated to address the issue of retrieving the tag system post data collection. The behavior recording tag system’s performance was assessed through laboratory and pool tests. The findings show that the accuracy of temperature sensor is about 0.01 °C, the accuracy of pressure sensor is approximately 0.5% of full scale, the continuous data collection duration can extend to 3 days, and the recovery window time after surfacing exceeds 7 days, underscoring its viability as a marine animal behavior recorder. Full article

(This article belongs to the Special Issue Ocean Observations)

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15 pages, 16510 KiB

Open AccessArticle

Mosaicking and Correction Method of Gaofen-3 ScanSAR Images in Coastal Areas with Subswath Overlap Range Constraints

by Jiajun Wang, Guowang Jin, Xin Xiong, Jiahao Li, Hao Ye and He Yang

J. Mar. Sci. Eng. 2024, 12(12), 2277; https://doi.org/10.3390/jmse12122277 - 11 Dec 2024

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Abstract

The ScanSAR mode image obtained by the Gaofen-3 (GF-3) satellite has an imaging width of up to 130–500 km, which is of great significance in monitoring oceanography, meteorology, water conservancy, and transportation. To address the issues of subswath misalignment and the inability to [...] Read more.

The ScanSAR mode image obtained by the Gaofen-3 (GF-3) satellite has an imaging width of up to 130–500 km, which is of great significance in monitoring oceanography, meteorology, water conservancy, and transportation. To address the issues of subswath misalignment and the inability to correct in the processing of GF-3 ScanSAR images in coastal areas using software such as PIE, ENVI, and SNAP, a method for mosaicking and correcting GF-3 ScanSAR images with subswaths that overlap within specified range constraints is proposed. This method involves correlating the coefficients of each subswath thumbnail image in order to determine the extent of the overlap range. Given that the matching points are constrained to the overlap between subswaths, the normalized cross-correlation (NCC) matching algorithm is utilized to calculate the matching points between subswaths. Subsequently, the random sampling consistency (RANSAC) algorithm is employed to eliminate the mismatching points. Subsequently, the subswaths should be mosaicked together with the stitching translation of subswaths, based on the coordinates of the matching points. The image brightness correction coefficient is calculated based on the average grayscale value of pixels in the overlapping region. This is performed in order to correct the grayscale values of adjacent subswaths and thereby reducing the brightness difference at the junction of subswaths. The entire ScanSAR slant range image is produced. By employing the Range–Doppler model for indirect orthorectification, corrected images with geographic information are generated. The experiment utilized three coastal GF-3 ScanSAR images for mosaicking and correction, and the results were contrasted with those attained through PIE software V7.0 processing. This was conducted to substantiate the efficacy and precision of the methodology for mosaicking and correcting coastal GF-3 ScanSAR images. Full article

(This article belongs to the Special Issue Ocean Observations)

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18 pages, 7384 KiB

Open AccessArticle

Characteristics Analysis of Acoustic Doppler Current Profile Measurements in Northeast Taiwan Offshore

by Chung-Ru Ho, Kai-Ho Cheng, Zhe-Wen Zheng, Hung-Jen Lee and Tai-Wen Hsu

J. Mar. Sci. Eng. 2024, 12(9), 1632; https://doi.org/10.3390/jmse12091632 - 12 Sep 2024

Viewed by 883

Abstract

A comprehensive study was conducted at a wave energy device test site located off the northeastern coast of Taiwan to assess the influence of oceanic currents on experimental equipment. A bottom-mounted 600 kHz acoustic Doppler current profiler, equipped with integrated temperature and pressure [...] Read more.

A comprehensive study was conducted at a wave energy device test site located off the northeastern coast of Taiwan to assess the influence of oceanic currents on experimental equipment. A bottom-mounted 600 kHz acoustic Doppler current profiler, equipped with integrated temperature and pressure sensors, was deployed at a depth of approximately 31 m. This study, spanning from 6 June 2023 to 11 May 2024, recorded ocean current profiles by assembling data from 50 pings every 10 min, with a resolution of one meter per depth layer. The findings reveal that variations in water levels were predominantly influenced by the M2 tidal constituent, followed by the O1, K1, and S2 tides. Notably, seawater temperature fluctuations at the seabed were modulated by tides, especially the M2 tide. A significant drop in seawater temperature was also observed as the typhoon passed through the south of Taiwan. In terms of sea surface currents, the measured maximum current speed was 71.89 cm s⁻¹, but the average current speed was only 15.47 cm s⁻¹. Tidal currents indicated that the M4 and M2 tides were the most significant, with semimajor axes and inclination angles of 8.48 cm s⁻¹ and 102.60°, and 7.00 cm s⁻¹ and 97.76°, respectively. Seasonally, barotropic tidal currents were the strongest in winter. Additionally, internal tides were identified, with the first baroclinic mode being dominant. The zero-crossing depths varied between 14 and 18 m. During the summer, the M2 baroclinic tidal current displayed characteristics of the second baroclinic mode, with zero-crossing depths at approximately 7 m and 22 m. This node aligns with results from the empirical orthogonal function analysis and correlates with the depths’ significant shifts in seawater temperature as measured by a conductivity, temperature, and depth instrument. Despite the velocities of internal tides not being strong, the directional variance between surface and bottom flows presents critical considerations for the deployment and operation of moored wave energy devices. Full article

(This article belongs to the Special Issue Ocean Observations)

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26 pages, 15518 KiB

Open AccessArticle

Sequential Two-Mode Fusion Underwater Single-Photon Lidar Imaging Algorithm

by Tian Rong, Yuhang Wang, Qiguang Zhu, Chenxu Wang, Yanchao Zhang, Jianfeng Li, Zhiquan Zhou and Qinghua Luo

J. Mar. Sci. Eng. 2024, 12(9), 1595; https://doi.org/10.3390/jmse12091595 - 9 Sep 2024

Cited by 2 | Viewed by 1283

Abstract

Aiming at the demand for long-range and high-resolution imaging detection of small targets such as submerged submarine markers in shallow coastal waters, research on single-photon lidar imaging technology is carried out. This paper reports the sequential two-mode fusion imaging algorithm, which has a [...] Read more.

Aiming at the demand for long-range and high-resolution imaging detection of small targets such as submerged submarine markers in shallow coastal waters, research on single-photon lidar imaging technology is carried out. This paper reports the sequential two-mode fusion imaging algorithm, which has a strong information extraction capability and can reconstruct scene target depth and reflection intensity images from complex signal photon counts. The algorithm consists of four steps: data preprocessing, extremely large group value estimation, noise sieving, and total variation smoothing constraints to image the target with high quality. Simulation and test results show that the imaging performance and imaging characteristics of the method are better than the current high-performance first-photon group imaging algorithm, indicating that the method has a great advantage in sparse photon counting imaging, and the method proposed in this paper constructs a clear depth and reflectance intensity image of the target scene, even in the 50,828 Lux ambient strong light and strong interference, the 0.1 Lux low-light environment, or the underwater high-attenuation environment. Full article

(This article belongs to the Special Issue Ocean Observations)

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13 pages, 1229 KiB

Open AccessArticle

Advanced Capacitor-Based Battery Equalizer for Underwater Vehicles

by Kun-Che Ho

J. Mar. Sci. Eng. 2024, 12(8), 1357; https://doi.org/10.3390/jmse12081357 - 9 Aug 2024

Cited by 1 | Viewed by 952

Abstract

As maritime technology advances, exploration of the oceans has progressively moved from surface exploration to underwater ventures. Unmanned underwater vehicles (UUVs), now prevalent for such exploration, effectively reduce human labor and lower operational costs. These vehicles rely on an internal Battery Storage System [...] Read more.

As maritime technology advances, exploration of the oceans has progressively moved from surface exploration to underwater ventures. Unmanned underwater vehicles (UUVs), now prevalent for such exploration, effectively reduce human labor and lower operational costs. These vehicles rely on an internal Battery Storage System (BSS) that sustains device operation by extending operational duration and providing stable voltage. Typically arranged in series, BSSs face challenges due to differences in the chemical characteristics of individual batteries, which lead to discrepancies in battery voltages and cause imbalances during charge and discharge cycles. This results in varied utilization rates among the batteries and uneven aging of the battery pack, potentially decreasing operational efficiency and increasing failure rates, thus reducing reliability and safety. Considering the harsh environmental conditions and maintenance difficulties associated with underwater operations, this paper proposes a robust solution: a balancing system featuring a modular switch with electrical isolation. Through theoretical analysis and circuit simulation, this study constructs and tests a novel prototype of a capacitor-based equalizer circuit with electrical isolation, verifying its feasibility. Full article

(This article belongs to the Special Issue Ocean Observations)

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15 pages, 17356 KiB

Open AccessArticle

Multidimensional Evaluation of Altimetry Marine Gravity Models with Shipborne Gravity Data from a New Platform Marine Gravimeter

by Bo Wang, Lin Wu, Pengfei Wu, Qianqian Li, Lifeng Bao and Yong Wang

J. Mar. Sci. Eng. 2024, 12(8), 1314; https://doi.org/10.3390/jmse12081314 - 3 Aug 2024

Cited by 2 | Viewed by 1127

Abstract

With the development of satellite altimetry technology and the application of new altimetry satellites, the accuracy and resolution of altimeter-derived gravity field models have improved over the last decades. Nowadays, they are close enough to shipborne gravimetry. In this paper, multi-source shipborne gravity [...] Read more.

With the development of satellite altimetry technology and the application of new altimetry satellites, the accuracy and resolution of altimeter-derived gravity field models have improved over the last decades. Nowadays, they are close enough to shipborne gravimetry. In this paper, multi-source shipborne gravity data in the South China Sea were taken to evaluate the accuracies of two high-precision altimeter-derived marine gravity field models (SS V30.1, DTU17). In these shipborne gravity data, there are dozens of routes’ ship gravimetry data, obtained from the National Geophysical Data Center (NGDC); data were tracked from a marine survey with a commercial marine gravimeter (type KSS31M), and data were tracked from a marine gravimetry campaign that was conducted with a newly developed platform gravimeter (type JMG) in the South China Sea in September 2020. After various data filtering, processing, and calibrations, the shipborne gravity data were validated with crossover points analysis. Then, the processed shipborne data were employed to evaluate the accuracy of the altimeter-derived marine gravity field models. During this procedure, the quality of JMG shipborne gravity data was compared with the results of KSS31M and NGDC data. Analysis and evaluation results show that the crossover points verification accuracies of KSS31M and JMG are 0.70 mGal and 1.61 mGal, which are much better than the accuracy of NGDC, which is larger than 8.0 mGal. In the area where the bathymetry changes slowly, the root mean square error values between altimetry gravity models and KSS31M data are respectively 3.28 mGal and 4.54 mGal, and those of the JMG data are respectively 2.94 mGal and 2.60 mGal. According to the above results, we can conclude that the JMG has the same 1–2 mGal accuracy level as KSS31M and can meet the measurement requirements of marine gravity. Full article

(This article belongs to the Special Issue Ocean Observations)

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22 pages, 17643 KiB

Open AccessArticle

Response of Shallow-Water Temperature and Significant Wave Height to Sequential Tropical Cyclones in the Northeast Beibu Gulf

by Xiaotong Chen, Lingling Xie, Mingming Li, Ying Xu and Yulin Wang

J. Mar. Sci. Eng. 2024, 12(5), 790; https://doi.org/10.3390/jmse12050790 - 8 May 2024

Viewed by 1364

Abstract

Using shallow-water buoy observations, reanalysis data, and numerical models, this study analyzes the variations in sea temperature and significant wave height (SWH) caused by two sequential tropical cyclones (TCs) ‘Lionrock’ and ‘Kompasu’ in October 2021 in the northeast Beibu Gulf, South China Sea. [...] Read more.

Using shallow-water buoy observations, reanalysis data, and numerical models, this study analyzes the variations in sea temperature and significant wave height (SWH) caused by two sequential tropical cyclones (TCs) ‘Lionrock’ and ‘Kompasu’ in October 2021 in the northeast Beibu Gulf, South China Sea. The results show that the sea surface temperature (SST) cooling of the nearshore waters was larger than the offshore water in the basin of the gulf, with the cooling amplitude and rate decreasing and the cooling time lagging behind wind increasing from coast to offshore. The near-surface temperature at the buoy station had a maximum decrease of 2.8 °C after ‘Lionrock’, and the decrease increased slightly to 3 °C after the stronger wind of ‘Kompasu’. The total decrease of 4.6 °C indicates that the sequential TCs had a superimposed effect on the cooling of the Beibu Gulf. The heat budget analysis revealed that the sea surface heat loss and the Ekman pumping rate in the nearshore waters during ‘Kompasu’ (−535 W/m² and 5.8 × 10⁻⁴ m/s, respectively) were significantly higher than that (−418 W/m² and 4 × 10⁻⁴ m/s) during ‘Lionrock’. On the other hand, the SST cooling (−1.2 °C) during the second TC is smaller than (−1.6 °C) the first weaker TC in the gulf basin, probably due to the deepening of the mixed layer. During the observation period, the waves in the Beibu Gulf were predominantly wind-driven. The maximum SWHs reached 1.58 m and 2.3 m at the bouy station near shore during the two TCs, and the SWH variation was highly correlated to the wind variation with a correlation of 0.95. The SWH increases from the nearshore to offshore waters during the TCs. The SAWN and ARCIRC coupled model results suggest that wave variations in the Beibu Gulf are primarily influenced by water depth, bottom friction, and whitecapping. Two days after the TCs, sea surface cooling and high waves appeared again due to a cold air event. Full article

(This article belongs to the Special Issue Ocean Observations)

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18 pages, 5414 KiB

Open AccessArticle

Dynamic Doppler Characteristics of Maritime Airborne Corner Reflector

by Lingang Wu, Shengliang Hu, Chengxu Feng, Yasong Luo, Zhong Liu and Li Lin

J. Mar. Sci. Eng. 2024, 12(5), 727; https://doi.org/10.3390/jmse12050727 - 27 Apr 2024

Viewed by 1099

Abstract

The maritime airborne corner reflector (ACR) is a radar reflector that can measure wind speed in an unknown sea area in real time over a long distance. To improve our understanding of how the ACR works, we investigated the Doppler characteristics of the [...] Read more.

The maritime airborne corner reflector (ACR) is a radar reflector that can measure wind speed in an unknown sea area in real time over a long distance. To improve our understanding of how the ACR works, we investigated the Doppler characteristics of the ACR for the first time from a dynamic perspective. First, we constructed a radar echo signal model of the ACR. Then, we obtained the dynamic Doppler characteristics through pulse Doppler processing and discussed the special phenomenon of Doppler broadening. Finally, we proposed a rectangular window decomposition method to analyze the inner principle of the Doppler broadening phenomenon in more detail. In conclusion, this study provides valuable insights into the Doppler characterization of an ACR from a dynamic viewpoint, which contributes to enriching the basic theory of this equipment. Full article

(This article belongs to the Special Issue Ocean Observations)

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