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P A P E R A Study of a Rescue Device for Marine Accidents Using Radar Cross Section Characteristics A U T H ORS ABSTRACT Hee Jin Kang Despite continued advances in life-saving technological devices, communica- Dongkon Lee tions, and search and rescue, people continue to lose their lives at sea. Search time Maritime & Ocean Engineering is a very important factor in determining the success of rescue operations. However, Research Institute, KORDI visual searches by aircraft and ship can be restricted by weather conditions and Jong-Gye Shin are impossible at nighttime. The personal-use light stick is not bright enough at Research Institute of Marine System daytime. Search and Rescue Transponders (SART) for life-saving appliances are too Engineering, Seoul National University large and too heavy to equip individual personnel, and moreover have limited range. Emergency Position Indicating Radio Beacons (EPIRBs) using satellite communica- Cheol-Soo Park tion also require large and expensive equipment, and generally have an error range Beom Jin Park of 3 nautical miles. Therefore, a new device that is simple, convenient and efficient Jin Choi is required to reduce search time and prevent loss of life at sea. Maritime & Ocean Engineering In this paper, we undertake a study of a new rescue device based on Radar Research Institute, KORDI Cross Section characteristics to improve search and rescue (SAR) activities. First, the characteristics of current rescue devices were investigated; the characteristics of Radar Cross Section (RCS), which is the measure of a target’s ability to reflect radar signals, were also reviewed. New radar-reflecting rescue devices for personal 1. Introduction and life-saving use were also designed, and the RCS of these designed devices was he design of a ship’s safety margin is analyzed. The proposed device will aid in SAR activities and save lives. based on rules imposed by classification T People with only a life jacket cannot (U.S. Search and Rescue Task Force, societies and international regulations. Therefore, the possibility of major casu- survive for an extended period of time 2008). The table shows that the rescue alties caused by capsizing or sinking in in cold water because body tempera- activity should be completed within maritime accidents is extremely low. tures drop rapidly. Experiments have 1-6 hours if lives are to be saved when Nevertheless, accidents at sea do occur shown that, in cold water, people shiver the water temperature is within the and can potentially cause huge losses at a body temperature of 36°C, experi- range of 10–16°C. of human life. ence amnesia at approximately 34°C, Therefore, search time is the most As a standard procedure, people unconsciousness at 30°C and finally die important factor in SAR activities. To will embark on life boats and/or life at approximately 26°C. Table 1 shows reduce search time and to save lives, a rafts when they have sufficient time expected survival time in cold water good means for determining victims’ to evacuate. In these cases, crews also TABLE 1 send a distress signal with their location information. However, in more severe Expected Survival Time in Cold Water. emergencies, such as explosions, large fires, and rapid flooding, people may be Water Temperature Exhaustion or Unconsciousness in Expected Survival Time forced to dive into the sea with only a 21–27°C 3–12 hours 3 hours – indefinitely life jacket. Life boats, rafts and people 16–21°C 2–7 hours 2–40 hours wearing life jackets will drift due to 10–16°C 1–2 hours 1–6 hours waves, wind and ocean currents, mak- 4–10°C 30–60 minutes 1–3 hours ing it difficult for search and rescue 0–4°C 15–30 minutes 30–90 minutes teams to find them. < 0°C Under 15 minutes Under 15–45 minutes 38 Marine Technology Society Journal exact location is required. This solution within a range of approximately 8 nau- (Digital) that can be used to alert must be effective even under difficult tical miles. It is relatively large, heavy to SAR authorities of the distress of the conditions, such as nighttime, fog, rain, equip to individual personnel and has stricken vessel nearly immediately. SAR and high wave height. a limited detection range. response to anonymous analog type Current devices, such as light sticks Distress radio beacons, also col- beacons can be delayed by 4-6 hours, for personal use, Search and Rescue lectively known as distress beacons, and sometimes by as much as 12 hours. Transponders (SART) and Emergency emergency beacons, or simply as EPIRBs using satellite communica- Position Indicating Radio Beacons beacons, are tracking transmitters that tion require expensive equipment and (EPIRBs), are good rescue devices but aid in the detection and location of generally have an error range of about are prone to error and have limited boats and/or persons in distress. In the three nautical miles. range. Therefore, error-free and long- proper sense, the term refers specifi- range rescue devices are required to cally to the three types of radio beacons improve rescue activities. that interface with Cospas Sarsat, 3. Radar Cross Section In this paper, a study of a new the international satellite system for The radar cross section is the meas- rescue device was carried out based SAR activities. EPIRBs are intended ure of a target’s ability to reflect radar on RCS characteristics with the aim to signal maritime distress. Category signals in the direction of the radar of improving SAR activities. First, the I-EPIRBs are considered the best but receiver; i.e., it is a measure of the ratio characteristics of current rescue devices are also the most costly. The Category of backscatter power per steradian (unit were investigated; the characteristics I-type is recommended by the IMO solid angle) in the direction of the radar of RCS were also reviewed. New radar because a float free bracket is deployed (from the target) to the power density reflecting rescue devices for personal and automatically once the vessel sinks. that is intercepted by the target. The life-saving appliances were designed, Hence in the event of a disaster at RCS of a target can be viewed as a com- and the RCSs of these designed devices sea, the EPIRBs will automatically parison of the strength of the reflected were analyzed. The analysis revealed that be activated by immersion in water. signal from a target to the reflected these newly designed devices performed These EPIRBs are generally housed in a signal from a perfectly smooth sphere well and can potentially improve SAR specially designed bracket on the deck, with a cross sectional area of 1 m2. activities and save lives. and the buoyant beacon is designed The conceptual definition of RCS to rise to the surface and emit two includes the fact that not all of the signals: an emergency homing signal radiated energy falls on the target. A 2. Review of Current at 121.5 MHz (Analog) and a digital target’s RCS is most easily visualized as Personal Rescue Devices identification Hex Code at 406 MHz the product of three factors: The light stick is a simple, FIGURE 1 inexpensive, easy-to-handle and effective life-saving device, and it is Examples of: (a) Light stick; (b) SART; (c) and EPIRB. available in several colors. However, it does not have enough brightness in (a) (b) (c) the daytime and illumination time is limited to about 12 hours. Shipboard Global Maritime Distress Safety System (GMDSS) installations include one or more SART devices, which are used to locate a life boat or distressed vessel by creating a series of dots on a rescuing ship’s radar display. A SART will only respond to a 9 GHz X-band radar. It will not be seen on S- band or other radar bands. The SART may be triggered by any X-band radar Winter 2008/2009 Volume 42, Number 4 39 Radar Cross Section (RCS) = Geometric Cross FIGURE 2 Section × Reflectivity × Directivity RCS value (backscatter) from various shapes. where reflectivity is the percent of in- tercepted power reradiated (scattered) by the target and directivity means the ratio of the power scattered back in the radar’s direction to the power that would have been backscattered had the scattering been uniform in all directions. RCS (σ) can also be represented as: σ ∝ (Pbackscatter/Pintercepted) (1) where the power that is reflected toward the radar is Pbackscatter, and the power intercepted by the object is Pintercepted, both of which depend on the radar wavelength and the angle of incidence of the radio wave relative to the object. where Es and Ei are the scattered and with a large geometric cross section, re- When the object’s size spans several incident electric field intensities, re- flectivity and directivity will be helpful wavelengths, the RCS of a target ob- spectively. to rescue teams hoping to find people ject is equal to the cross-sectional area RCS reduction is chiefly important adrift at sea as quickly as possible. of a perfectly conducting sphere that in stealth technology for aircraft, mis- RCS is expressed as a product of would produce the same magnitude siles, ships, and other military vehicles projected area and directivity; some of reflection as that observed from the wishing to evade radar detection. In specific reflectors’ RCS values have target object. The usual definition or contrast, with respect to rescue activity been determined experimentally and RCS differs by a factor of (4π) from the a large RCS value is desirable as this will are shown in Figure. 2 (Naval Air Sys- standard geometric definition of cross aid in locating a small target within a tems Command and Naval Air Warfare section at 180 degrees.

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