**1. Introduction**

380 Remote Sensing – Applications

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Maritime search and rescue (MSR- In the maritime publications, the abbreviation for search and rescue is also SAR. Here we use MSR to distinguish it from the abbreviation for Synthetic Aperture Radar.) became an enormous task with the vast growth of marine transportation and other marine activities. In the year of 2006, the MSR centers and maritime authorities in China organized and coordinated 1620 MSR operations, which involved 5322 vessels and 17498 human lives. The past few years have witnessed tremendous changes in the organizations of maritime rescue. A large part of this evolution stems from the involvement on an international scope and the contribution of the advanced technology. However, current maritime search operation, especially searching people over board, depends mostly on human eyes.

SOLAS (International convention for safety of life at sea) convention prescribes that ships must be equipped with GMDSS (Global maritime distress and safety system) equipments, which have improved the search and rescue. However, for many non SOLAS convention ships, such as fishing boats and small crafts, the detection results are not very much satisfied. With the complex sea environment, the searching of distress vessel becomes a nail-biting task. Because of the physiological characteristics of human eyes, it is difficult for the rescuer to find small target in the adverse background lighting, night or dark condition, wave or clustered seas. Continuous long time observation also causes fatigue of human eyes, resulting poor sensitivity of detection. All those factors decay the results of searching operation.

In order to improve the effect of MSR operations during the dark hours or in adverse lighting or sea conditions, remote sensing technique is a potential approach to overcome the limitation of human eyes in MSR, and thereby may hopefully improve the searching performance in complex environment or in a fatigued state of human being. Regarding ship monitoring, compared with shore-base, shipboard or airborne detecting devices, and other visible visible or infrared monitoring methods, the Synthetic Aperture Radar (SAR) remote sensing system possesses the capability of all-time, all weather, extensive and high resolution for detecting ships on the sea. Especially due to its working characteristics of not being limited by the sea surface, weather or human factors, it can detect the sea areas with geographical remote positions and hostile environment which cannot be entered directly.

In this chapter, some remote sensing techniques and algorithms concerned with the MSR are introduced. A Remote Sensing Monitoring System for Maritime Search and Rescue (RS-MSR)

Remote Sensing Application in the Maritime Search and Rescue 383

According to the requirement of the maritime search and rescue, the Synthetic Aperture Radar (SAR) imageries are used for this purpose. The algorithms concerned with the system

In the SAR images with high resolution, each target occupies several resolution units to form area target. So detecting the ship target in the SAR images with high resolution should regard the target as distributive target, and the assumption of point target under the traditional radar is not suitable any more. The project here proposes a distributed target detection method in the Gaussian scale-space. The distance relationship among the detected objects is adopted to identify the distributed target. In the situation of hardly estimating the background's scattering distribution or of low SNR (signal-to-noise ratio), this method can realize the distributive target detection more effectively than CFAR

In the SAR images with high resolution, the ship target can be divided into three categories according to their dimension, among which small ships(≤50m) are represented as point target, while the middle size ship(≤100m) as distributive target of single corner and big size ship(≥100m) as double corner distributive target. According to the relative positions of the corner and combining the orbit information (resolution ratio and incident angle) of the SAR

The imaging geometry of the SAR imagery is slant-range projection. So, due to the geometric distortions, such as layover, foreshortening, and shadows, there exits measurement error between the observed position and its actual location. In this method, using the directional texture of the wake of ship, the convergent point of the wake pattern can be calculated, which is the actual location of the stern. Then the position correcting

A bow wave is the wave that forms at the bow of a ship when it moves through the water. As the bow wave spreads out, it defines the outer limits of a ship's wake. Theoretically, the convergent point of the bow wave' outline must at the extended line of the ship's heading. The vanishing point can be calculated by the Hough transform, and the heading direction of

Wave direction estimation can be used to analyze the sea state of the target area and supply basis for search and rescue area decision. This method is set up on the basis of steerable filter, which is a filter set composed of an even-symmetric filter and an odd-symmetric filter. When the orthogonal filter set is rotated to the same orientation of the local texture, the oriented energy reaches its maximum. The orientation corresponding to the maximum

the ship can be calculated according to the coordinates of the bow and the stern.

**2.2.4 Wave direction estimation based on the partial energy direction** 

**2.2.1 Distributed target detection method in the Gaussian scale-space** 

image, the length, height and the direction of the ship will be worked out.

**2.2.3 Ship location correction and ship direction estimation method** 

**2.2 Algorithm introduction** 

method.

demand are introduced as follows.

**2.2.2 Ship size category estimation model** 

parameters can be worked out.

is presented. This work is a part of our project—Vision Enhancement System for Maritime Search and Rescue. The main task for the RS-MSR is to acquire general information in a wider scale. The distress ship is detected and located for guiding the search operation. Surrounding ships are also distinguished to coordinate the MSR operation. Some important data such as current and sea state are retrieved to help decision-making of the operation. Section 2 proposes the outline of the remote sensing methods for maritime search and rescue; Guided by the systematic functions and structures of the RS-MSR described in Section 2, Section 3 introduces the related algorithms used in RS-MSR. Section 4 describes the architecture of the remote sensing aided system for maritime search and rescue. The experiment design and the implementation performance are given in Section 5. Finally, Section 6 concludes the paper.
