Pub Date : 2014-04-07DOI: 10.1109/OCEANS-TAIPEI.2014.6964507
H. Sugimatsu, J. Kojima, T. Ura, K. Mizuno, A. Asada, R. Bahl, S. Behera, H. Singh, V. Sagar, Rupak De
Around 15-20 Ganges river dolphins (platanista gangetica) inhabit the 12-km stretch from Karnavas to Narora Barrage in the Ganges river system. However, more than 10 dolphins were carried away downstream after the flood of June-July 2013. In order to urgently conduct a quick census to secure the dolphins in the original habitat, the existing compact four-hydrophone array system (J-Array) was remodeled for towing, and a function to display the real-time acoustic data on a GUI (Graphical User Interface) on an operational PC at the site was added. Using the new J-Array system, the initial in-situ census in combination with acoustic and visual census was conducted for two days from 19 to 20 November 2013. The functions that were added to the new J-Array performed well. Immediately following the towing survey, using both the acoustic and visual census data, an estimate of the number of the dolphins was made at the site. It was estimated that a minimum of six dolphins were still in the habitat. Off-line acoustic data analysis results were also found in accordance with the in-situ census results. From this, the effectiveness of the new J-Array system for conducting in-situ census has been demonstrated.
{"title":"Development of a handy mobile 4-hydrophone array system for in-situ census of the Ganges river dolphins (platanista gangetica)","authors":"H. Sugimatsu, J. Kojima, T. Ura, K. Mizuno, A. Asada, R. Bahl, S. Behera, H. Singh, V. Sagar, Rupak De","doi":"10.1109/OCEANS-TAIPEI.2014.6964507","DOIUrl":"https://doi.org/10.1109/OCEANS-TAIPEI.2014.6964507","url":null,"abstract":"Around 15-20 Ganges river dolphins (platanista gangetica) inhabit the 12-km stretch from Karnavas to Narora Barrage in the Ganges river system. However, more than 10 dolphins were carried away downstream after the flood of June-July 2013. In order to urgently conduct a quick census to secure the dolphins in the original habitat, the existing compact four-hydrophone array system (J-Array) was remodeled for towing, and a function to display the real-time acoustic data on a GUI (Graphical User Interface) on an operational PC at the site was added. Using the new J-Array system, the initial in-situ census in combination with acoustic and visual census was conducted for two days from 19 to 20 November 2013. The functions that were added to the new J-Array performed well. Immediately following the towing survey, using both the acoustic and visual census data, an estimate of the number of the dolphins was made at the site. It was estimated that a minimum of six dolphins were still in the habitat. Off-line acoustic data analysis results were also found in accordance with the in-situ census results. From this, the effectiveness of the new J-Array system for conducting in-situ census has been demonstrated.","PeriodicalId":114739,"journal":{"name":"OCEANS 2014 - TAIPEI","volume":"127 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126715286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-04-07DOI: 10.1109/OCEANS-TAIPEI.2014.6964498
D. Hernandez, L. Adler, J. Isern, J. Cabrera, A. Dominguez, E. Fernandez, V. Prieto, M. Eichhorn
The special characteristics of the ocean gliders propulsion scheme endows these vehicles with an extremely high endurance, at the cost of a relatively low surge speed. Hence, gliders' trajectory is highly influenced by ocean currents, which can even exceed the vehicle's nominal velocity. This calls for intelligent path planning algorithms, fact that reflects in the high number of solutions proposed by researchers that can be found in recent bibliography. In this paper we propose a novel method to combine multiple ocean forecast models in order to feed the glider path-planner with as reliable as possible source information. The scheme is configured as a multi-evidence fusion that integrates factors such as sensor vs model validation, forecast stability and model historic performance.
{"title":"Data uncertainty management in path planning for underwater ocean gliders","authors":"D. Hernandez, L. Adler, J. Isern, J. Cabrera, A. Dominguez, E. Fernandez, V. Prieto, M. Eichhorn","doi":"10.1109/OCEANS-TAIPEI.2014.6964498","DOIUrl":"https://doi.org/10.1109/OCEANS-TAIPEI.2014.6964498","url":null,"abstract":"The special characteristics of the ocean gliders propulsion scheme endows these vehicles with an extremely high endurance, at the cost of a relatively low surge speed. Hence, gliders' trajectory is highly influenced by ocean currents, which can even exceed the vehicle's nominal velocity. This calls for intelligent path planning algorithms, fact that reflects in the high number of solutions proposed by researchers that can be found in recent bibliography. In this paper we propose a novel method to combine multiple ocean forecast models in order to feed the glider path-planner with as reliable as possible source information. The scheme is configured as a multi-evidence fusion that integrates factors such as sensor vs model validation, forecast stability and model historic performance.","PeriodicalId":114739,"journal":{"name":"OCEANS 2014 - TAIPEI","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126551063","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-04-07DOI: 10.1109/OCEANS-TAIPEI.2014.6964527
Jianhua Wang, Xiaoyan Pei, Mengkai Zhao, A. Shen
Due to the special working environment, some problems should be taken into account for calibration of vision system used on autonomous surface vehicle (ASV). This paper discussed the relation between calibration parameters obtained from different distances. After a brief introduction to the imaging model of camera and the classical calibration methods, the relation between the distance from calibration rig to camera and calibration parameters is explored. By the least square algorithm, a functional relation is fitted. Based on equivalent transformation, a method to obtain the relatively accurate calibration parameters is proposed. Experiments show that the accuracy of calibration parameters is improved.
{"title":"Calibration of stereo vision system used on autonomous surface vehicle","authors":"Jianhua Wang, Xiaoyan Pei, Mengkai Zhao, A. Shen","doi":"10.1109/OCEANS-TAIPEI.2014.6964527","DOIUrl":"https://doi.org/10.1109/OCEANS-TAIPEI.2014.6964527","url":null,"abstract":"Due to the special working environment, some problems should be taken into account for calibration of vision system used on autonomous surface vehicle (ASV). This paper discussed the relation between calibration parameters obtained from different distances. After a brief introduction to the imaging model of camera and the classical calibration methods, the relation between the distance from calibration rig to camera and calibration parameters is explored. By the least square algorithm, a functional relation is fitted. Based on equivalent transformation, a method to obtain the relatively accurate calibration parameters is proposed. Experiments show that the accuracy of calibration parameters is improved.","PeriodicalId":114739,"journal":{"name":"OCEANS 2014 - TAIPEI","volume":"IA-20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126558866","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-04-07DOI: 10.1109/OCEANS-TAIPEI.2014.6964481
C. Berndt, G. Crutchley, I. Klaucke, M. Jegen, E. Lebas, S. Muff, K. Lieser, T. Roth, W. Chi, T. Feseker, S. Lin, C.‐S. Liu, L. Chen, H. Hsu
Formosa Ridge is one of many topographic ridges created by canyon incision into the eastern South China Sea margin. The northwestern termination of the ridge is caused by beheading of the ridge due to a westward shift of the canyon that originally formed to the eastern flank of Formosa Ridge. Below Formosa Ridge a bottom simulating reflector (BSR) exists. Its depth below sea floor coincides with the theoretical base of the gas hydrate stability zone and the reflection has reverse polarity suggesting that it is caused by free gas below gas hydrate accumulations. The BSR is ubiquitous but shows significant variations in depth below sea floor ranging from 150 ms TWT (or approximately 180 m) underneath the incised canyon in the north to up to 500 ms (or approximately 460 m) underneath the crest of Formosa Ridge. Predominantly this depth variation is the result of topography on subsurface temperature, but comparison with the average BSR depth underneath the surrounding canyons suggests that recent canyon incision in the north has perturbed the thermal state of the sediments. Formosa Ridge consists of a northern half that is dominated by refilled older canyons and a southern half that consists mainly of contourite deposits. However, judging by the reflection seismic data this difference in origin seems to have little effect on the distribution of gas hydrate.
{"title":"Geological controls on the gas hydrate system of Formosa Ridge, South China Sea","authors":"C. Berndt, G. Crutchley, I. Klaucke, M. Jegen, E. Lebas, S. Muff, K. Lieser, T. Roth, W. Chi, T. Feseker, S. Lin, C.‐S. Liu, L. Chen, H. Hsu","doi":"10.1109/OCEANS-TAIPEI.2014.6964481","DOIUrl":"https://doi.org/10.1109/OCEANS-TAIPEI.2014.6964481","url":null,"abstract":"Formosa Ridge is one of many topographic ridges created by canyon incision into the eastern South China Sea margin. The northwestern termination of the ridge is caused by beheading of the ridge due to a westward shift of the canyon that originally formed to the eastern flank of Formosa Ridge. Below Formosa Ridge a bottom simulating reflector (BSR) exists. Its depth below sea floor coincides with the theoretical base of the gas hydrate stability zone and the reflection has reverse polarity suggesting that it is caused by free gas below gas hydrate accumulations. The BSR is ubiquitous but shows significant variations in depth below sea floor ranging from 150 ms TWT (or approximately 180 m) underneath the incised canyon in the north to up to 500 ms (or approximately 460 m) underneath the crest of Formosa Ridge. Predominantly this depth variation is the result of topography on subsurface temperature, but comparison with the average BSR depth underneath the surrounding canyons suggests that recent canyon incision in the north has perturbed the thermal state of the sediments. Formosa Ridge consists of a northern half that is dominated by refilled older canyons and a southern half that consists mainly of contourite deposits. However, judging by the reflection seismic data this difference in origin seems to have little effect on the distribution of gas hydrate.","PeriodicalId":114739,"journal":{"name":"OCEANS 2014 - TAIPEI","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122204095","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-04-07DOI: 10.1109/OCEANS-TAIPEI.2014.6964336
Li Baojun, W. Haiyan, Shen Xiaohong, Jiang Zhe
Subsea pipelines are very susceptible to encounter failure. One novel method based on underwater acoustic network (UAN) is proposed to monitor free span of subsea pipeline. It considers the characteristics of shallow water and complex response of subsea pipeline, defines the principle of parallel cooperative transmitting of data package and the scheme of cross layer design that take into physical layer, data link layer and network layer. The method, shown by simulation, can achieve good performance of throughput and energy consumption which exists minimum and can enhance lifespan of equipment and meanwhile reduce the cost of monitoring.
{"title":"One novel monitoring method for free span of subsea pipeline","authors":"Li Baojun, W. Haiyan, Shen Xiaohong, Jiang Zhe","doi":"10.1109/OCEANS-TAIPEI.2014.6964336","DOIUrl":"https://doi.org/10.1109/OCEANS-TAIPEI.2014.6964336","url":null,"abstract":"Subsea pipelines are very susceptible to encounter failure. One novel method based on underwater acoustic network (UAN) is proposed to monitor free span of subsea pipeline. It considers the characteristics of shallow water and complex response of subsea pipeline, defines the principle of parallel cooperative transmitting of data package and the scheme of cross layer design that take into physical layer, data link layer and network layer. The method, shown by simulation, can achieve good performance of throughput and energy consumption which exists minimum and can enhance lifespan of equipment and meanwhile reduce the cost of monitoring.","PeriodicalId":114739,"journal":{"name":"OCEANS 2014 - TAIPEI","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116248281","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-04-07DOI: 10.1109/OCEANS-TAIPEI.2014.6964402
Bian Yeping, Li Jiabiao, Chu Fengyou, Han Xi-bin, Jiang Zhimin, Chu Zhihui, K. Wolfgang
The palynological analysis of two marine core, MD06-3075 (6.4762°N, 125.8322°E; 1878 m water depth, 30.76 m in length) in the southern Philippines and MD98-2178 (3.6200°N, 118.7000°E; 1984 m water depth, 35.6 m in length) in the northwest Celebes Sea, the detailed oxygen isotope records, and other marine pollen records in the west Pacific, provide the regional vegetation and climate history during the Holocene. The record shows that, during the early Holocene, ~10.0-6 kyr B.P., the pollen percentage of the tropical montane forest decline, suggestting that the tropical montane forest distribute at the high altitude just like nowdays, which indicates a warm condition. The pollen from mangrove group is abundant, presenting the well-development of the mangrove along the coast of the adjacent islands. Meanwhile, the pollen from the herb is rare, but the value of the pteridophyte is much high, indicating a wet condition. During the mid-Holocene, the pollen percentage of the tropical mid-upper montane rainforest is very high at 6-5 kyr B.P, suggesting the downslope movement of the tropical montane forest, indicating a much cold condition at the time. Besides, it is a striking decline in mangrove pollen and a slight less abundance of the fern spore, indicating the vegetation group of mangrove and fern were suppressed during the mid-Holocene. During the late Holocene, a relatively high level of the herbaceous group provides a more open environment. These changes, are relatively the same as stalagmite record in this area, but different from palaeooceanographic records. This likely indicates that tropical vegetation changes have close relationship with the global monsoon.
{"title":"Vegetation and climate change inferred from two marine pollen records in the west Pacific during the Holocene","authors":"Bian Yeping, Li Jiabiao, Chu Fengyou, Han Xi-bin, Jiang Zhimin, Chu Zhihui, K. Wolfgang","doi":"10.1109/OCEANS-TAIPEI.2014.6964402","DOIUrl":"https://doi.org/10.1109/OCEANS-TAIPEI.2014.6964402","url":null,"abstract":"The palynological analysis of two marine core, MD06-3075 (6.4762°N, 125.8322°E; 1878 m water depth, 30.76 m in length) in the southern Philippines and MD98-2178 (3.6200°N, 118.7000°E; 1984 m water depth, 35.6 m in length) in the northwest Celebes Sea, the detailed oxygen isotope records, and other marine pollen records in the west Pacific, provide the regional vegetation and climate history during the Holocene. The record shows that, during the early Holocene, ~10.0-6 kyr B.P., the pollen percentage of the tropical montane forest decline, suggestting that the tropical montane forest distribute at the high altitude just like nowdays, which indicates a warm condition. The pollen from mangrove group is abundant, presenting the well-development of the mangrove along the coast of the adjacent islands. Meanwhile, the pollen from the herb is rare, but the value of the pteridophyte is much high, indicating a wet condition. During the mid-Holocene, the pollen percentage of the tropical mid-upper montane rainforest is very high at 6-5 kyr B.P, suggesting the downslope movement of the tropical montane forest, indicating a much cold condition at the time. Besides, it is a striking decline in mangrove pollen and a slight less abundance of the fern spore, indicating the vegetation group of mangrove and fern were suppressed during the mid-Holocene. During the late Holocene, a relatively high level of the herbaceous group provides a more open environment. These changes, are relatively the same as stalagmite record in this area, but different from palaeooceanographic records. This likely indicates that tropical vegetation changes have close relationship with the global monsoon.","PeriodicalId":114739,"journal":{"name":"OCEANS 2014 - TAIPEI","volume":"95 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121744284","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-04-07DOI: 10.1109/OCEANS-TAIPEI.2014.6964580
Yao-Ting Tseng, Jian-Jiun Ding, J. Lou
Study results derived from global tide gauge data indicate that the global waters were simultaneously subject to the modulation of lunar nodal tide showing a period of 18.6 years and rose at a rate of about 2 mm per year in the past century. In contrast to other regions, those sitting along the east Atlantic Ocean coastal lines show strong semi-diurnal pattern and seemly do not suffer from extraordinary sea level rise problems. Without considering possibilities from local climatic and geological uplift or subsidence problems, the most severe sea level rise phenomenon of 13.24 mm per year happened at Manila, Philippines, a considerable contrast with the most extreme sea level falling rate of 10.11 mm/year at Churchill in Canada. From this study, we are not only able to identify the sea level rise rate for every gauge station from the global data but also be able to predict the timing of the next peak sea level of the 18.6-year tide, which is predicted in June 2025.
{"title":"Global sea level change in the past century","authors":"Yao-Ting Tseng, Jian-Jiun Ding, J. Lou","doi":"10.1109/OCEANS-TAIPEI.2014.6964580","DOIUrl":"https://doi.org/10.1109/OCEANS-TAIPEI.2014.6964580","url":null,"abstract":"Study results derived from global tide gauge data indicate that the global waters were simultaneously subject to the modulation of lunar nodal tide showing a period of 18.6 years and rose at a rate of about 2 mm per year in the past century. In contrast to other regions, those sitting along the east Atlantic Ocean coastal lines show strong semi-diurnal pattern and seemly do not suffer from extraordinary sea level rise problems. Without considering possibilities from local climatic and geological uplift or subsidence problems, the most severe sea level rise phenomenon of 13.24 mm per year happened at Manila, Philippines, a considerable contrast with the most extreme sea level falling rate of 10.11 mm/year at Churchill in Canada. From this study, we are not only able to identify the sea level rise rate for every gauge station from the global data but also be able to predict the timing of the next peak sea level of the 18.6-year tide, which is predicted in June 2025.","PeriodicalId":114739,"journal":{"name":"OCEANS 2014 - TAIPEI","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124930542","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-04-07DOI: 10.1109/OCEANS-TAIPEI.2014.6964516
Li Wang, Hao-Wen Li, Zhi-Hao Yang
This paper presents the analyzed results of an integration of an offshore wind farm (OWF) and a seashore wave farm (SWF) connected to an onshore large power grid through a high-voltage direct-current (HVDC) link to simultaneously achieve power-fluctuation mitigation and dynamic-stability enhancement. The performance of the studied OWF is simulated by three equivalent aggregated doubly-fed induction generators (DFIGs) driven by three equivalent aggregated wind turbines through three gearboxes. The characteristics of the studied SWF are simulated by three equivalent aggregated squirrel-cage induction generator (SCIG) driven by three equivalent aggregated Wells turbines through three gearboxes. A frequency-domain approach based on a linearized system model using eigenvalue analysis and a time-domain scheme based on a nonlinear system model subject to a torque disturbance are systematically carried out. It can be concluded from the simulation results that the proposed HVDC can effectively stabilize the studied integrated OWF and SWF under various disturbance conditions. The inherent power fluctuations injected to the power grid can also be effectively mitigated by the proposed control scheme.
{"title":"Stability improvement of an integrated offshore wind farm and seashore wave farm fed to a power grid using an HVDC link","authors":"Li Wang, Hao-Wen Li, Zhi-Hao Yang","doi":"10.1109/OCEANS-TAIPEI.2014.6964516","DOIUrl":"https://doi.org/10.1109/OCEANS-TAIPEI.2014.6964516","url":null,"abstract":"This paper presents the analyzed results of an integration of an offshore wind farm (OWF) and a seashore wave farm (SWF) connected to an onshore large power grid through a high-voltage direct-current (HVDC) link to simultaneously achieve power-fluctuation mitigation and dynamic-stability enhancement. The performance of the studied OWF is simulated by three equivalent aggregated doubly-fed induction generators (DFIGs) driven by three equivalent aggregated wind turbines through three gearboxes. The characteristics of the studied SWF are simulated by three equivalent aggregated squirrel-cage induction generator (SCIG) driven by three equivalent aggregated Wells turbines through three gearboxes. A frequency-domain approach based on a linearized system model using eigenvalue analysis and a time-domain scheme based on a nonlinear system model subject to a torque disturbance are systematically carried out. It can be concluded from the simulation results that the proposed HVDC can effectively stabilize the studied integrated OWF and SWF under various disturbance conditions. The inherent power fluctuations injected to the power grid can also be effectively mitigated by the proposed control scheme.","PeriodicalId":114739,"journal":{"name":"OCEANS 2014 - TAIPEI","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125334171","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-04-07DOI: 10.1109/OCEANS-TAIPEI.2014.6964519
Dali Liu, Yuntao Liu, H. Cai, Yongfeng Wang, Hong Zhang
Linear frequency-modulated continuous wave (LFMCW) is applied in continuous active sonar (CAS). Methods for echo detection and direct path interference (DPI) suppression are studied and evaluated by simulation and sea trial data. To detect the LFMCW echo, the received signal is first demodulated by the transmitting signal, resulting in a de-chirped signal, which is similar as in LFMCW radar. However, in active sonar case the target velocity is no longer negligible comparing with the sound velocity. Thus the de-chirped signal cannot be simplified as a CW signal. Instead, it is a LFM signal, with its sweep rate and center frequency related with the velocity and distance of the target. Time-frequency analysis methods which are generally used to detect and estimate LFM signals can then be used in LFMCW active sonar. In this work, the Fractional Fourier Transform (FRFT) is chosen. Simulations and experiments show that LFMCW active sonar with the de-chirp-FRFT receiver can get much higher processing gain than conventional LFM pulsed active sonar with a matched filter (MF) receiver. To reduce the direct path interference (DPI) from the transmitter, bi-static mode is preferred. DPI is eliminated by filtering the de-chirped signal in the frequency domain. The major drawback of this method is that targets close to the transmitter will be lost. The disadvantage of the de-chirp-FRFT algorithm is that the processing results can be obtained only once every long work cycle, which is not propitious to target tracking. The future work will be focused on the improvement of refresh rate.
{"title":"Linear frequency-modulated continuous wave active sonar signal processing","authors":"Dali Liu, Yuntao Liu, H. Cai, Yongfeng Wang, Hong Zhang","doi":"10.1109/OCEANS-TAIPEI.2014.6964519","DOIUrl":"https://doi.org/10.1109/OCEANS-TAIPEI.2014.6964519","url":null,"abstract":"Linear frequency-modulated continuous wave (LFMCW) is applied in continuous active sonar (CAS). Methods for echo detection and direct path interference (DPI) suppression are studied and evaluated by simulation and sea trial data. To detect the LFMCW echo, the received signal is first demodulated by the transmitting signal, resulting in a de-chirped signal, which is similar as in LFMCW radar. However, in active sonar case the target velocity is no longer negligible comparing with the sound velocity. Thus the de-chirped signal cannot be simplified as a CW signal. Instead, it is a LFM signal, with its sweep rate and center frequency related with the velocity and distance of the target. Time-frequency analysis methods which are generally used to detect and estimate LFM signals can then be used in LFMCW active sonar. In this work, the Fractional Fourier Transform (FRFT) is chosen. Simulations and experiments show that LFMCW active sonar with the de-chirp-FRFT receiver can get much higher processing gain than conventional LFM pulsed active sonar with a matched filter (MF) receiver. To reduce the direct path interference (DPI) from the transmitter, bi-static mode is preferred. DPI is eliminated by filtering the de-chirped signal in the frequency domain. The major drawback of this method is that targets close to the transmitter will be lost. The disadvantage of the de-chirp-FRFT algorithm is that the processing results can be obtained only once every long work cycle, which is not propitious to target tracking. The future work will be focused on the improvement of refresh rate.","PeriodicalId":114739,"journal":{"name":"OCEANS 2014 - TAIPEI","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127833807","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-04-07DOI: 10.1109/OCEANS-TAIPEI.2014.6964501
Qunyan Ren, J. Hermand
In coastal areas, the properties of the soft sediment are crucial for sound propagation prediction and relevant sonar applications. The noise of intense ship traffic is a convenient acoustic source in these areas for geoacoustic characterization. This paper introduces a sequential particle filter (PF) technique that can take advantage of the continuous ship sound field to predict the soft sediment properties along ship track. The PF is based a point mass (or “particle”) representation of the probability density function associated to different parameters. The particle set evolves recursively according to newly input data, which allows updating the estimation in real time and suitable for dynamical system monitoring if used properly. The approach is tested on synthesized vertical waveguide impedance data to characterize the sediment properties for the obtained bottom geoacoustic model offshore the Amazon River mouth. The vertical waveguide impedance is proven to be source spectrum independent and valuable for passive geoacoustic inversion. Simulation results demonstrate that the PF provides a statistical estimation of the geoacoustic parameters close to true values versus range, in addition, the intrinsic features of the PF filtering technique in successively updating the estimate suggest our approach is capable of characterizing more complex environments with varying geometries.
{"title":"Particle filtering for geoacoustic characterization of the soft sediment using ship noise","authors":"Qunyan Ren, J. Hermand","doi":"10.1109/OCEANS-TAIPEI.2014.6964501","DOIUrl":"https://doi.org/10.1109/OCEANS-TAIPEI.2014.6964501","url":null,"abstract":"In coastal areas, the properties of the soft sediment are crucial for sound propagation prediction and relevant sonar applications. The noise of intense ship traffic is a convenient acoustic source in these areas for geoacoustic characterization. This paper introduces a sequential particle filter (PF) technique that can take advantage of the continuous ship sound field to predict the soft sediment properties along ship track. The PF is based a point mass (or “particle”) representation of the probability density function associated to different parameters. The particle set evolves recursively according to newly input data, which allows updating the estimation in real time and suitable for dynamical system monitoring if used properly. The approach is tested on synthesized vertical waveguide impedance data to characterize the sediment properties for the obtained bottom geoacoustic model offshore the Amazon River mouth. The vertical waveguide impedance is proven to be source spectrum independent and valuable for passive geoacoustic inversion. Simulation results demonstrate that the PF provides a statistical estimation of the geoacoustic parameters close to true values versus range, in addition, the intrinsic features of the PF filtering technique in successively updating the estimate suggest our approach is capable of characterizing more complex environments with varying geometries.","PeriodicalId":114739,"journal":{"name":"OCEANS 2014 - TAIPEI","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133199046","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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