Heavy Sea Research Articles

Detection and Extraction of Target With Micromotion in Spiky Sea Clutter Via Short-Time Fractional Fourier Transform

In order to effectively detect moving targets in heavy sea clutter, the micro-Doppler (m-D) effect is studied and an effective algorithm based on short-time fractional Fourier transform (STFRFT) is proposed for target detection and m-D signal extraction. Firstly, the mathematical model of target with micromotion at sea, including translation and rotation movement, is established, which can be approximated as the sum of linear-frequency-modulated signals within a short time. Then, due to the high-power, time-varying, and target-like properties of sea spikes, which may result in poor detection performance, sea spikes are identified and eliminated before target detection to improve signal-to-clutter ratio (SCR). By taking the absolute amplitude of signals in the best STFRFT domain (STFRFD) as the test statistic, and comparing it with the threshold determined by a constant false alarm rate detector, micromotion target can be declared or not. STFRFT with Gaussian window is employed to provide time-frequency distribution of m-D signals, and the instantaneous frequency of each component can be extracted and estimated precisely by STFRFD filtering. In the end, datasets from the intelligent pixel processing radar with HH and VV polarizations are used to verify the validity of this proposed algorithm. Two shore-based experiments are also conducted using an X-band sea search radar and an S-band sea surveillance radar, respectively. The results demonstrate that the proposed method not only achieves high detection probability in a low-SCR environment but also outperforms the short-time Fourier transform-based method.

Ship Route Design for Avoiding Heavy Weather and Sea Conditions

This paper covers the current state of maritime oil transportation in the Baltic Sea and the development of oil transportation in the 2000s, as well as estimations of transported oil volumes in 2020 and 2030 in the Gulf of Finland. The scenarios were formulated on the basis of a current state analysis, energy and transportation strategies and scenarios and expert assessments. The study showed that the volumes of oil transportation in the Gulf of Finland will increase only moderately compared to the current status: 9.5-33.8 %, depending on the scenario. Green energy policy favours renewable energy sources, which can be seen in the smaller volumes of transported oil in the 2030 scenarios compared to the 2020 scenarios. In the Slow development 2020 scenario, oil transport volumes for 2020 are expected to be 170.6 Mt (million tonnes), in the Average development 2020 187.1 Mt and in the Strong development 2020 201.5 Mt. The corresponding oil volumes for the 2030 scenarios were 165 Mt for the Stagnating development 2030 scenario, 177.5 Mt for the Towards a greener society 2030 scenario and 169.5 Mt in the Decarbonising society 2030 scenario.

Miniscale Modelling Of Gyroscopic Effect with Application to Sheep Steering.

A gyroscope is a device for measuring or maintaining orientation, based on the principles of momentum. Mechanically, a gyroscope is a spinning wheel or disc in which the axle is free to assume any orientation. Although this orientation does not remain fixed, it changes in response to an external torque much less and in a different direction, than it would without the large angular momentum associated with the disc's high rate of spin and inertia. Ships or sea vessels require stabilization when they face heavy sea waves. A disturbing couple acts on the ships due to sea waves, hence stabilization of ship is necessary. Due to sea waves, ship will either roll or pitch. The amplitude of rolling is much higher than amplitude of pitching. The gyroscope can be used for reducing the amplitude of rolling and hence, stabilizing the ship. The fundamental requirement of gyroscopic stabilization is that, the gyroscopic must be made to precess by some external means (example: electric motor) in such a way that the relative gyroscopic couple exerted by the rotor should oppose any disturbing couple which may act on the ship. The gyroscope used in larger marine equipment is connected to PLC. PLC generates the signal and controls the movement of the ships. This paper presents development of various ship roll motion control system together with the challenges associated with their design. It discuss the assessment of performance, the applicability of difference modals, and the control methods that have been applied in the past. This also present outlook on what are believed to be potential area of research with in this topic.

Impact of survey design and acquisition technology on 3D Marine Mega-survey success, a recent example from Southern Australia

The objective of the seismic survey discussed here was to rapidly explore deep targets over 12000 km2 of frontier permits. Heavy seas with a strong south-westerly swell and strong ocean currents, coupled with stormy weather conditions create risk for both seismic quality and turnaround, limiting the survey to a tight weather window. These harsh metocean conditions were compunded by the remote setting; both factors strongly influenced the survey design and posed the biggest challenge to delivering a consistent high quality seismic dataset. The solution required a huge receiver spread covering over 11.5 square kilometers and modern equipment to withstand an extended period in these conditions. Two main technology solutions were also implemented to deliver the project. The first was Fan shooting where cables are laid out with greater spacing at the end or the spread compared to near the vessel. The second is termed intelligent infill modeling where variable coverage is modeled to determine acceptable offset gaps, and then the data quality impact is predicted from actual coverage during acquisition, to aid real time infill decisions. This was calibrated against real data decimation tests before the survey and found to be accurate. The wide and long receiver spread deployed in this project led to several vendor production records. These included production records for one day at 143.6km2, one week at 919 km2, and one month at 3,056km2, while still delivering very high quality seismic data. The design helped the acquisition to continue in severe swell conditions without introducing detrimental noise in the data, helped by real time, flexible, on-board seismic processing to confirm when swell noise could or could not be removed from the data. Infill management and fanning of the streamers contributed to an overall reduction of the infill.

Extreme Rapid Intensification of Typhoon Vicente (2012) in the South China Sea

Abstract One of the primary challenges for both tropical cyclone (TC) research and forecasting is the problem of intensity change. Accurately forecasting TC rapid intensification (RI) is particularly important to interests along coastlines and shipping routes, which are vulnerable to storm surge and heavy seas induced by intense tropical cyclones. One particular RI event in the western North Pacific Ocean with important scientific implications is the explosive deepening of Typhoon Vicente (2012). Vicente underwent extreme RI in the northern South China Sea just prior to landfall west of Hong Kong, China, with maximum sustained winds increasing from 50 kt (1 kt = 0.51 m s−1) at 0000 UTC 23 July to 115 kt at 1500 UTC 23 July. This increase of 65 kt in 15 h far exceeds established thresholds for TC RI. Just prior to this RI episode, Vicente exhibited a near-90° poleward track shift. The relationship between the track and intensity change is described, and the authors speculate that the passage of an upper-tropospheric (UT) “inverted” trough was a significant influence. An analysis of real-time numerical model guidance is provided and is discussed from an operational perspective, and high-resolution global model analyses are evaluated. Numerical model forecasts of the UT trough interaction with the TC circulation were determined to be a shortcoming that contributed to the intensity prediction errors for Vicente. This case study discusses the importance of considering UT features in TC intensity forecasting and establishes current modeling capabilities for future research.

Voyages at Sixteen

Voyages at Sixteen Robert Ashcom (bio) You would have expected the steel of the ship's forward deck to be smooth. But it wasn't. It was black and rough with the texture of a tar and gravel country road at home. It sloped sharply upward toward the bow and tapered from the centerline to the bulwarks so that in heavy seas the water would run off quickly. She was empty and riding high. Standing at the bow fifty feet above the water, I felt as if I were riding down the Hudson on a huge bobbing cork, leaving the Statue of Liberty to port, waiting for Sandy Hook and the Atlantic. The ship was quiet, the decks empty. It was Sunday evening and the late day summer sun hung like a flaming disk in the haze over New Jersey. I was fifteen, soon to be sixteen. It was June 1956. "You're the American boy aren't you?" I turned. "Yes, that seems to be what everybody calls me. Who are you?" "Mike. I'm the officers' mess boy. I can ship as an ordinary seaman (os), but I wanted to leave home in a hurry, so I took the first thing that came along. I just got fed up with home. I'm from Jamaica." "I could tell. You sound like Harry Belafonte." Mike looked hard at me for an instant to be sure there wasn't some kind of insult here. Then he said, "Yes, I do, don't I? What are you doing here? Couldn't you get a good job in an office ashore?" The words flooded out. "Whoa, and I'll tell you." I was now facing aft, with my back resting on the anchor ball pole. "I'm the starboard cabin boy. My sixteenth birthday is next week. I've read Moby-Dick. I just want to see some of the watery world, like Ishmael." Go somewhere straight away. My heart gave a sudden joyous lurch. Yes, straight away. I'm going. Mike looked at me strangely. "Do you understand? "I understand fine. That's why I am here too. I'm twenty-two. This is the fifth time I've shipped out, and I haven't seen much [End Page 560] of the world yet. A port's a port. The girls, too. They all look the same. Maybe it'll be different this time. Have you been to Newport News? They say the whole place stinks of coal. You know that's what we're loading—coal! For the Far East. I've never been to Japan before. They say the girls are something." That night, Gunnar, the second cook, whose cabin I shared, stared at me as I climbed into the upper bunk, carefully, without stepping on him. Gunnar, who was very tall and skinny, and was what we would call a neat freak, had jackknifed himself into his bunk and was reading a novel written in Norwegian, with a lurid cover of a near naked girl looking in fear at a man of exaggerated physique. The space was very small. When I leaned over the edge and said, "Goodnight," Gunnar grunted and went on reading. The motion and vibration of the ship put me to sleep. Thirty-six hours later we arrived at Hampton Roads, one day after my sixteenth birthday. I was unaware of our arrival before dawn, until the engine stopped and the anchor was released with a tremendous rush as the huge links passed through the hawse hole. I jerked awake and hit the close overhead so hard I thought I'd knocked myself out. There were a dozen or more ships anchored in the Roads, waiting to go alongside whatever pier their cargo required. All that day, as I was washing down the passageways, I occasionally ducked outside to see what was happening. Once the steward was standing at the forward rail of the boat deck. He was staring at me. When our eyes met, the man's head jerked as if he were waking from a daydream. I heard my name yelled in a Norwegian accent. The steward's hand gesture was clear: What...

The future of European teacher education in the heavy seas of higher education

The aim of this paper is to reconsider recent pan-European developments in teacher education and to discuss some aspects of its future. Teacher education across Europe has been largely ‘universitised’; therefore, both its present and future should be discussed within the context of the general changes in European higher education deeply marked by the Bologna Process and the emerging European Higher Education Area. The author relies on Goodlad’s and Clark’s discussion of teacher education from a higher education perspective and tries to continue in the context of European higher education reforms of the past decade. The central controversy of these reforms has concerned the length of traditional undergraduate courses at universities in most continental countries (4 to 5 years), particularly with regard to the relationship between ‘academic’ and ‘professional’ higher education. Until today, most teacher education institutions have adapted to the new system of two ‘Bologna’ cycles (Bachelor and Master). However, the reforms have led to different interpretations and their implementation has varied in different countries, thus opening new dilemmas about the future of European teacher education.

Detection of low observable moving target in sea clutter via fractal characteristics in fractional Fourier transform domain

Effective detection of low observable moving target at sea is important for remote sensing and radar signal processing. The non-Gaussian property of sea clutter and lack of accurate model make the detection difficult for statistics based detectors. Also the fractal techniques in time domain cannot achieve high detection probability in heavy sea clutter. To help solve the problems, fractal characteristics of IPIX datasets in fractional Fourier transform (FRFT) domain are analysed making use of the fluctuation of FRFT amplitudes and moving target detection algorithms are proposed based on the fractal characteristics in FRFT domain. Firstly, fractal model in FRFT domain is established with fractional Brownian motion model and two judgment and extraction methods are employed for calculating the fractal characteristics in FRFT domain. It is found that sea clutter of different polarisations exhibit fractal behaviours in FRFT domain, that is, self-similarity property, within its corresponding scale-invariant interval. Then, we find that four specific fractal statistics in the best FRFT domain can provide valuable information for developing simple and effective detectors. Finally, traditional amplitude detector and Hurst exponent detector in time domain are compared and the results prove the superior detection ability of low observable moving target without complex computations.

Heavy metal concentrations in water, sediment and periwinkle (Tympanotonus fuscastus) samples harvested from the Niger Delta region of Nigeria

Heavy metal pollution of terrestrial and aquatic environments in Niger-delta region of Nigeria is on the increase due to increased urbanization and crude oil exploration. Tympanotonus fuscastus are mud dwellers and could bioaccumulate heavy metals; therefore consumption of heavy metal contaminated sea foods like periwinkle may breed lots of health problems. Heavy metal concentration in water, sediment and Periwinkle samples from three locations (Itu-River, Abuloma River and Oron River) in the Niger Delta Region of Nigeria were evaluated using atomic absorption flame photometry. Result showed that cadmium (Cd) concentration was highest in water samples from Abuloma River (0.106 mg/l) while lead (Pb) concentration was highest (0.01mg/l) in the water samples from Itu River. Cd and Pb concentrations (0.127 and 0.08 mg/kg, respectively) in sediment samples were highest in Abuloma River. The concentration of Cd in T. fuscastus samples was 0.11 mg/kg in Abuloma River, while concentration was 0.27 mg/kg in Oron River. Copper (Cu) was generally low in the water samples; the highest concentration (0.011 mg/kg) was obtained in water samples from Oron River. Sediment concentration of Cu was high (0.088 mg/kg) in Itu River, while its concentration in the periwinkle samples was 0.54 mg/kg in Abuloma River. The results also showed that Cr, As and Hg were below detectable concentration in tissues, soil and water samples from Itu and Abuloma Rivers, while Hg concentration in Oron River sediment was 64.2 mg/kg. Key words: Sea foods, heavy metals, pollution, environment, nutrition, bioaccumulation

Ecology of Sundarban, Bangladesh

Sundarban is the largest mangrove wetland in the world. It covers an area of about 1mha, of which 60% is located in Bangladesh and the remaining western portion, comprising 40%, lies in India. Mangrove ecosystems are of great ecological significance in the tropical and sub-tropical coast. They protect our coast from heavy wind, tidal waves, coastal erosion and sea water intrusion, generate substantial quantities of fishery resources and provide many useful forestry products. The Sundarban ecosystem supports rich fisheries diversity. This ecosystem support 27 families and 53 species of pelagic fish, 49 families 124 species of demersal fish, 5 families and 24 species of shrimps, 3 families and 7 species of crabs, 8 species of lobster. A total 334 plants, 165 algal, 13 special orchids, 17 fern, 87 monocotyledon and 230 dicotyledon belonging to 245 genera and 75 families from the sundarbans and adjacent area are found available. The principal tree species is Sundry (Heritiera fomes) which covers about 73% to total landmass and the second species is Gewa (Excoecaria agallocha) which covers about 16% of total forest area. The plant species include 35 legumes, 29 grasses, 19 sedges, and 18 euphorbias. Of the 50 true mangrove plant species recorded throughout the globe, the Sundarbans alone contain 35 species. The magnificent among the animals on land is Royal Bengal Tiger, Spotted deer, barking deer and wild boars are there in plenty. Besides those jungle cats, fishing cat, civet cat, monkey, bengal fox, jackle, water monitor, monitor lizard and snakes are important faunal spp. Moreover, abundant of the Sundarbans are purple heron, pond heron, cattle egret, little egret, open billed stork, smaller adjutant stork, brahmini kite, spotted dove, rose ringed parakeet, crow pheasant, wood pecker, bee eater, drongo, pide myna, jungle myna, bulbul, tailor bird, magpie robin, sparrow etc., Otherwise, recorded that wild Buffalo, 2 species of deer, javan rhinoceros extinct and presently 2 species of amphibians, 14 species of reptiles 25 species of birds and 5 species of mammals are considered as endangered species. This paper is to produce a new assessment of the mangroves ecology of Sundarbans. DOI: http://dx.doi.org/10.3329/jsf.v8i1-2.14618 J. Sci. Foundation, 8(1&2): 35-47, June-December 2010

Accidental exposure to polychlorinated biphenyls (PCB) in waste cargo after heavy seas. Global waste transport as a source of PCB exposure

After cargo with PCB-containing transformer oil waste was damaged in heavy seas, the vessel crew exposed to PCB developed itching and acne-form eruption of the skin. The objective of our study was to analyse this work-related incident and its effects on health. Air and wipe test samples were taken in the ship for analysis of PCB (28/52/101/138/153/180); clinical investigations of all seafarers (n = 6) included lung function, chest X-ray, clinical chemistry and biomonitoring (plasma PCBs, chlorophenols in urine) measured after a latency of 7 weeks. The biomonitoring data were adjusted according to age-related reference values and validated against controls (n = 96). Biomonitoring showed elevated PCB-28-/52/-102/-138 congeners (mean 1.16/0.91/136, ∑PCB: 5.82 μg/l), which correlates with the dust samples from the cargo hold (∑PCB. 9,440 mg/m(2)) and with 6.1 and 5.0 μg/m(3) in stern and bow cargo air samples. IgE elevation in two seafarers and substantial blood sedimentation rate increase with anaemia or pulmonary emphysema were unlikely to be caused by PCB exposure. Although two members showed slightly elevated airway resistance values, other lung function parameters were normal and reactive airways dysfunction syndrome due to PCBs could be excluded. Elevated chlorophenols in urine could contribute to the manifestation of chloracne. PCB-52/-101/-138 found in plasma and in air samples confirm exposure to PCB. Acne-form skin eruptions were from occupational exposure to polychlorinated biphenyls in the spilt transformer oil. There were no other abnormal findings in medical and clinical examinations that could be attributed to PCBs. This does not exclude possible long-term effects.

Comparison study between observation and simulation for sea fog over the Yellow Sea in May 2009

In this paper, almost all available observational data and the latest 6.0 version of Regional Atmospheric Modeling System (RAMS) model were employed to investigate a heavy sea fog event occurring over the Yellow Sea from 2 to 5 May 2009. The evolutionary process of this event was documented by using Multifunctional Transport Satellites-1 (MTSAT-1) visible satellite imagery. The synoptic situation, sounding profiles at two selected stations were analyzed. The difference between the air temperature and sea surface temperature during the sea fog event over the entire sea region was also analyzed. In order to better understand this event, an RAMS modeling with a 15 km×15 km resolution was performed. The model successfully reproduced the main characteristics of this sea fog event. The simulated height of fog top and the area of lower atmospheric visibility derived from the RAMS modeling results showed good agreement with the sea fog area identified from the satellite imagery. Examinations of both observational data and RAMS modeling results suggested that advection cooling seemed to play an important role in the formation of this sea fog event.

Effects of climate change on an emperor penguin population: analysis of coupled demographic and climate models

Sea ice conditions in the Antarctic affect the life cycle of the emperor penguin (Aptenodytes forsteri). We present a population projection for the emperor penguin population of Terre Adélie, Antarctica, by linking demographic models (stage-structured, seasonal, nonlinear, two-sex matrix population models) to sea ice forecasts from an ensemble of IPCC climate models. Based on maximum likelihood capture-mark-recapture analysis, we find that seasonal sea ice concentration anomalies (SICa ) affect adult survival and breeding success. Demographic models show that both deterministic and stochastic population growth rates are maximized at intermediate values of annual SICa , because neither the complete absence of sea ice, nor heavy and persistent sea ice, would provide satisfactory conditions for the emperor penguin. We show that under some conditions the stochastic growth rate is positively affected by the variance in SICa . We identify an ensemble of five general circulation climate models whose output closely matches the historical record of sea ice concentration in Terre Adélie. The output of this ensemble is used to produce stochastic forecasts of SICa , which in turn drive the population model. Uncertainty is included by incorporating multiple climate models and by a parametric bootstrap procedure that includes parameter uncertainty due to both model selection and estimation error. The median of these simulations predicts a decline of the Terre Adélie emperor penguin population of 81% by the year 2100. We find a 43% chance of an even greater decline, of 90% or more. The uncertainty in population projections reflects large differences among climate models in their forecasts of future sea ice conditions. One such model predicts population increases over much of the century, but overall, the ensemble of models predicts that population declines are far more likely than population increases. We conclude that climate change is a significant risk for the emperor penguin. Our analytical approach, in which demographic models are linked to IPCC climate models, is powerful and generally applicable to other species and systems.

Factors influencing the stable carbon isotopic composition of suspended and sinking organic matter in the coastal Antarctic sea ice environment

Abstract. A high resolution time-series analysis of stable carbon isotopic signatures in particulate organic carbon (δ13CPOC) and associated biogeochemical parameters in sea ice and surface waters provides an insight into the factors affecting δ13CPOC in the coastal western Antarctic Peninsula sea ice environment. The study covers two austral summer seasons in Ryder Bay, northern Marguerite Bay between 2004 and 2006. A shift in diatom species composition during the 2005/06 summer bloom to near-complete biomass dominance of Proboscia inermis is strongly correlated with a large ~10 ‰ negative isotopic shift in δ13CPOC that cannot be explained by a concurrent change in concentration or isotopic signature of CO2. We hypothesise that the δ13CPOC shift may be driven by the contrasting biochemical mechanisms and utilisation of carbon-concentrating mechanisms (CCMs) in different diatom species. Specifically, very low δ13CPOC in P. inermis may be caused by the lack of a CCM, whilst some diatom species abundant at times of higher δ13CPOC may employ CCMs. These short-lived yet pronounced negative δ13CPOC excursions drive a 4 ‰ decrease in the seasonal average δ13CPOC signal, which is transferred to sediment traps and core-top sediments and consequently has the potential for preservation in the sedimentary record. This 4 ‰ difference between seasons of contrasting sea ice conditions and upper water column stratification matches the full amplitude of glacial-interglacial Southern Ocean δ13CPOC variability and, as such, we invoke phytoplankton species changes as a potentially important factor influencing sedimentary δ13CPOC. We also find significantly higher δ13CPOC in sea ice than surface waters, consistent with autotrophic carbon fixation in a semi-closed environment and possible contributions from post-production degradation, biological utilisation of HCO3− and production of exopolymeric substances. This study demonstrates the importance of surface water diatom speciation effects and isotopically heavy sea ice-derived material for δ13CPOC in Antarctic coastal environments and underlying sediments, with consequences for the utility of diatom-based δ13CPOC in the sedimentary record.

荒天航海時の船体運動と海上輸送の安全・効率性の関係について

荒天航海時の船体運動と海上輸送の安全・効率性の関係について

Adaptive fractional Fourier transform-based detection algorithm for moving target in heavy sea clutter

Attention has been focused on the moving target detection in heavy sea clutter. On the basis of detection model of moving target with fluctuant amplitudes, a novel adaptive algorithm in fractional Fourier transform (FRFT) domain is proposed, which combines statistic-based and FRFT-based detection method. FRFT has good energy concentration property on linear frequency modulation (LFM) signal with the optimal transform angle, which is determined by calculating spectral kurtosis (SK) in FRFT domain. Grading iterative search method is used for good accuracy of parameter estimation and fast calculation speed. A novel adaptive line enhancer (ALE) in FRFT domain is proposed to suppress sea clutter and improve signal-to-clutter ratio (SCR), which provides less error and faster convergence. Leakage factor is introduced into the update equation of weight vector to reduce ‘memory effect’ and step size is normalised by the power of input signal with better convergence characteristic. In the end, both X-band and S-band real sea clutter is used for verification and the results present that the proposed algorithm has good convergence property and small mean square error (MSE). Weak moving target in low SCR environment (SCR=−6 dB) can be well detected and estimated, which indicates the effectiveness of the algorithm.

Fragilariopsis diatom evolution in Pliocene and Pleistocene Antarctic shelf sediments

The late Pliocene – early Pleistocene sediment record in the AND-1B core from the McMurdo Sound, Ross Sea, Antarctica, displays a rich diversity and high abundance of diatoms, including several new morphologies within the genus Fragilariopsis. These new morphologies exhibit similarities to the extinct late Miocene/early Pliocene species Fragilariopsis aurica Gersonde and Fragilariopsis praecurta Gersonde, as well as to the modern sea ice-associated species Fragilariopsis ritscheri Hustedt and Fragilariopsis obliquecostata van Heurck. From the diverse morphologies present, we use light microscopy and scanning electron microscopy to identify and describe the characteristics of three new taxa, Fragilariopsis laqueata Riesselman, Fragilariopsis bohatyi Sjunneskog et Riesselman, and Fragilariopsis robusta Sjunneskog, which are common in the diatom-bearing intervals from ~3.2 to 1.95 Ma. Comparisons with extant and extinct species are made to assess possible environmental affinities, evolutionary relationships, and potential for future biostratigraphic utility. This complex of newmorphologies diversified as conditions cooled during the Pliocene, then went into decline as heavy sea ice conditions of the Pleistocene were established. Only the lineage of F. robusta appears to continue into the late Pleistocene, where it is interpreted to have evolved into F. obliquecostata.

Fog Detection over China’s Adjacent Sea Area by using the MTSAT Geostationary Satellite Data

AbstractA fog threshold method for the detection of sea fog from Multi-function Transport Satellite (MTSAT-1R) infrared (IR) channel data is presented. This method uses principle component analysis (PCA), texture analysis, and threshold detection to extract sea fog information. A heavy sea fog episode that occurred over China's adjacent sea area during 7-8 April 2008 was detected, indicating that the fog threshold method can effectively detect sea fog areas nearly 24 hours a day. MTSAT-1R data from March 2006, June 2007, and April 2008 were processed using the fog threshold method, and sea fog coverage information was compared with the meteorological observation report data from ships. The hit rate, miss rate, and false alarm rate of sea fog detection were 66.1%, 27.3%, and 33.9%, respectively. The results show that the fog threshold method can detect the formation, evolution, and dissipation of sea fog events over period of time and that the method has superior temporal and spatial resolution relative to...

SMALL TARGET DETECTION IN HEAVY SEA CLUTTER

This paper mainly deals with the detection problem of the target with low Radar Cross-Section (RCS) in heavy sea clutter with unknown Power Spectral Density (PSD). Since the performance of traditional single-scan detectors degrades as the target of interest is smaller and weaker, three adaptive detectors, based upon a two-step design procedure, are proposed within the framework of the multiple- scan signal model. Firstly, the Multiple-Scan Detectors (MSDs) are derived according to the Generalized Likelihood Ratio Test (GLRT), Rao and Wald tests respectively under the assumption that the PSD of primary data is known. Secondly, three strategies are resorted to estimate the unknown PSD, and their Constant False Alarm Rate (CFAR) properties are assessed. Finally, numerical simulation results show that the adaptive MSDs outperform the traditional single-scan detector using Monte Carlo method.

Numerical simulations of a fully submerged propeller subject to ventilation

Numerical simulations aimed at modeling the phenomenon of ventilation on a fully submerged propeller were performed. Ventilation occurs on thruster propellers operating at high loadings and heavy sea states, experiencing continuous cycles in and out-of water. This leads to sudden thrust losses and violent impact loads, which can damage shaft bearings and gears of azimuth and tunnel thrusters. Damages in rough seas were reported also during transit operations. In the simulated configuration the propeller is fully submerged ( h/ R=1.4) and working at high loading ( J=0.1), where the blade becomes surface-piercing only after ventilation occurs. The dynamic loads computed with the numerical model are in satisfactory agreement with the experimental data at the upright position where the blade is piercing the free-surface, whereas thrust is over-estimated at all the other angular positions. A thorough analysis of the causes of this deviation was performed, identifying the inability of the numerical simulation to properly resolve the tip vortex at some distance from the propeller blades as the most likely responsible factor. Unlike ventilation of surface-piercing propellers with super-cavitating profile, it was found that the tip vortex plays an important role in ventilation of conventional propellers, which is the object of the present study.