With the rapid development of society and the economy, an increasing number of human activities have gradually destroyed the marine environment. Marine environment monitoring is a vital problem and has increasingly attracted a great deal of research and development attention. During the past decade, various marine environment monitoring systems have been developed. The traditional marine environment monitoring system using an oceanographic research vessel is expensive and time-consuming and has a low resolution both in time and space. Wireless Sensor Networks (WSNs) have recently been considered as potentially promising alternatives for monitoring marine environments since they have a number of advantages such as unmanned operation, easy deployment, real-time monitoring, and relatively low cost. This paper provides a comprehensive review of the state-of-the-art technologies in the field of marine environment monitoring using wireless sensor networks. It first describes application areas, a common architecture of WSN-based oceanographic monitoring systems, a general architecture of an oceanographic sensor node, sensing parameters and sensors, and wireless communication technologies. Then, it presents a detailed review of some related projects, systems, techniques, approaches and algorithms. It also discusses challenges and opportunities in the research, development, and deployment of wireless sensor networks for marine environment monitoring.

Applications of Wireless Sensor Networks in Marine Environment Monitoring: A Survey

Alternative power sources for remote sensors: A review

The performance of a network of five CODAR (Coastal Ocean Dynamics Application Radar) SeaSonde high-frequency (HF) radars, broadcasting near 13 MHz and using the Multiple Signal Classification (MUSIC) algorithm for direction finding, is described based on comparisons with an array of nine moorings in the Santa Barbara Channel and Santa Maria basin deployed between June 1997 and November 1999. Eight of the moorings carried vector-measuring current meters (VMCMs), the ninth had an upward-looking ADCP. Coverage areas of the HF radars and moorings included diverse flow and sea-state regimes. Measurement depths were ∼1 m for the HF radars, 5 m for the VMCMs, and 3.2 m for the ADCP bin nearest to the surface. Comparison of radial current components from 18 HF radar–mooring pairs yielded rms speed differences of 7–19 cm s−1 and correlation coefficients squared (r2) in the range of 0.39–0.77. Spectral analysis showed significant coherence for frequencies below 0.1 cph (periods longer than 10 h). At highe...

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Evaluating Radial Current Measurements from CODAR High-Frequency Radars with Moored Current Meters

This paper investigates the transport structure of surface currents around the Monterey Bay, CA region. Currents measured by radar stations around Monterey Bay indicate the presence of strong, spatial and temporal, nonlinear patterns. To understand the geometry of the flow in the bay, Lagrangian coherent structures (LCS) are computed. These structures are mobile separatrices that divide the flow into regions of qualitatively different dynamics. They provide direct information about the flow structure but are geometrically simpler than particle trajectories themselves. The LCS patterns were used to reveal the mesoscale flow conditions observed during the 2003 Autonomous Ocean Sampling Network (AOSN-II) experiment.

Drifter paths from the AOSN experiment were compared to the patterns induced by the LCS computed from high-frequency radar data. We verify that the fate of the drifters can be better characterized based on the LCS than direct interpretation of the current data. This property can be exploited to optimize drifter deployment.

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The correlation between surface drifters and coherent structures based on high-frequency radar data in Monterey Bay

This paper focuses on the validation of remotely sensed ocean surface currents from SeaSonde-type high-frequency (HF) radar systems. Hourly observations during the period July 22, 2003 through September 9, 2003 are used from four separate radar sites deployed around the shores of Monterey Bay, CA. Calibration of direction-finding techniques is addressed through the comparisons of results obtained using measured and ideal (i.e., perfect) antenna patterns. Radial currents are compared with observations from a moored current meter and from 16 surface drifter trajectories. In addition, four overwater baselines are used for radar-to-radar comparisons. Use of measured antenna patterns improves system performance in almost all cases. Antenna-pattern measurements repeated one year later at three of the four radar locations exhibit only minor changes indicating that pattern distortions are stable. Calibrated results show root-mean-square (rms) radial velocity differences in the range of 9.8-13.0 cm/s, which suggest radar observation error levels in the range of 6.9-9.2 cm/s. In most cases, clear evidence of bearing errors can be seen, which range up to 30deg for uncalibrated radar-derived radial currents and up to 15deg for currents obtained using measured antenna patterns. Bearing errors are not, however, constant with angle. The results recommend use of measured antenna patterns in all SeaSonde-type applications. They also recommend an expanded simulation effort to better describe the effects of antenna-pattern distortions on bearing determination under a variety of ocean conditions

Calibration and Validation of Direction-Finding High-Frequency Radar Ocean Surface Current Observations

HF radar has become an important tool for mapping surface currents in the coastal ocean and has been used to determine wind direction. Here the author investigate further the ability of multifrequency HF radar to measure the vector wind field and the impact that such measurements have on the measurement of coastal wind fields over both the land and sea. In this study the author use data collected over Monterey Bay, California from Jan. to Aug. 2001. Their multifrequency coastal radars (MCR's) operated at 4.8, 6.8, 13.4 and 21.8 MHz, measuring currents at effective depths of about 2.5, 1.8, 0.9 and 0.6 m respectively. Here, the author move beyond their preliminary reports by examining the durability of their HF wind vector measurements over a seven-month data set. The results over this longer time span indicate standard errors of prediction (SEP's) of 1.2 and 1.1 m/s for the U and V wind speed components respectively with biases less than 0.15 m/s. The author also investigate a Kalman filtering modification to their partial least squares algorithm. Further, the author demonstrate the beneficial impact of multifrequency HF radar, wind field measurements, on estimation of the coastal wind field over both land and sea.

Using multifrequency HF radar to estimate ocean wind fields

Coastal nations have an interest in maritime domain awareness for applications in national security, coastal conservancy, fishery and stewardship of the exclusive economic zones (EEZs) along their coastlines. Using our previously developed HF radar and AIS ship detection models we find signal to noise ratio (SNR) as a function of range, including ducted propagation for the AIS radio signals. We use these SNR estimates to find probability of detection P d and then explore multiple systems and stations at variable spacings along the coast. Our example HF radar has significant power and aperture, similar to the Pisces radar. The AIS model is for high power (12.5 W) AIS and a significantly elevated receiver (≈ 250 ft asl). A combined system of HF radar and AIS shows good capability (P d > 0.9) to ranges of ≈ 125 km for small ships and to 200 km for large ships. Considering a system of sites separated by 100 km we find that a P d of > 0.9 can be maintained to a distance off shore of 130 km even for small, 120 ton, ships.

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A system trade model for the monitoring of coastal vessels using HF surface wave radar and ship automatic identification systems (AIS)

Maritime domain awareness is important for coastal nations in terms of applications to coastal conservancy, security, fishery and stewardship of their exclusive economic zones (EEZs). Maritime situational awareness involves knowing the location, speed, course and identity of ships and boats in the EEZ. HF radar is a useful tool in providing ship information in real time. It is especially effective when combined with information from ship-borne AIS beacons. However, ship detection by AIS alone is limited to ships with AIS beacons broadcasting. HF radar does not have this limitation, but is hampered by false targets related to wave echoes, interference and the high variability of HF echoes from ships. We have developed a ship detection and tracking system that accepts Codar SeaSonde range file data as input and proceeds through a ship detection algorithm to produce a target file every time step (range, radial speed and azimuth for each ship-like target). A Kalman filter algorithm is applied to the time history of target files to produce ship tracks as well as to remove false alarms. We demonstrate this ship tracking system using radar data from the Pescadero CA station in the COCMP HF radar network along the California coast. Available AIS data are used to verify the target locations and ship tracks. Although improvements are needed, we can now demonstrate a working end-to-end HF radar system for tracking non-cooperating ships in coastal waters using standard, Codar-SeaSonde-HF-radar output and software developed by the authors.

Ship tracking by HF radar in coastal waters

Maritime domain awareness is important for coastal nations in terms of applications to coastal conservancy, security, fishery and stewardship of their exclusive economic zones (EEZs). Maritime situational awareness involves knowing the location, speed and bearing of ships and boats in the EEZ. HF radar is a useful tool in providing ship information in real time. It is especially effective when combined with information from ship-borne AIS beacons. Our previously developed HF radar and AIS ship detection models estimate signal to noise ratio (SNR) as a function of range, including ducted propagation for the AIS radio signals. However, ship detection is hampered by false targets related to wave echoes, interference and the high variability of HF echoes from ships. This is due in part to the aspect and frequency dependence of ship radar cross-section and to the presence of clutter bands at known Doppler shifts from both the ground and ocean surfaces. Distinguishing ship echoes from false alarm echoes is significantly aided by identifying radar targets with ship-like behavior. Thus, tracking ships using their HF radar echoes becomes an important means for effectively monitoring the presence of ships in the coastal ocean. We demonstrate the application of Kalman filtering to the ship-tracking problem with examples using data from the COCMP HF radar network along the California coast. As with other radar tracking problems, the Kalman approach proves effective in this application as well.

Monitoring coastal vessels for environmental applications: Application of Kalman filtering

Marine situational awareness is a key factor in coastal activities, e.g. national security (terrorism, drug smuggling, etc.) and environmental protection (marine protected areas, fishery monitoring and regulation, oil spills, etc.). HF surface wave radar is a strong candidate to become a component of any large area, vessel-monitoring network. We discuss estimating the primary metrics for assessing performance for ship tracking radars (probabilities of detection Pd and false alarm Pfa) and their variation with parameters, such as range, azimuth and frequency, and number of observing modes. We discuss several design options for an HF radar, ship monitoring system, such as multiple or single frequency, multiple or single sites or method of target bearing determination (MUSIC or real aperture antenna) and present a model of the SNR for ship detection by HF radar and as well as observational examples of ship detection with single and multifrequency HF radars. Finally we suggest future experiments and draw conclusions.

K. Laws

Papers

Using multifrequency HF radar to estimate ocean wind fields

A system trade model for the monitoring of coastal vessels using HF surface wave radar and ship automatic identification systems (AIS)

Ship tracking by HF radar in coastal waters

Monitoring coastal vessels for environmental applications: Application of Kalman filtering

Monitoring of Coastal Vessels Using Surface Wave HF Radars: Multiple Frequency, Multiple Site and Multiple Antenna Considerations