P A P E R A Study of a Rescue Device for Marine Accidents Using 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 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. The bistatic ra- wide area. The design of a rescue device Center, 1999). dar cross section is defined similarly for Table 2 other angles. Quantitatively, the RCS is Typical Radar Cross Sections (RCS). an effective surface area that intercepts the incident wave and scatters the energy isotropically in space. For the RCS, σ is defined in three dimensions (Knott et al., 2004) as: P 4πσ= r 2 s (2) Pi where σ is the RCS, Pi is the incident power density measured at the target, and Ps is the scattered power density seen at a distance R away from the target. In electromagnetic analysis, this is also commonly written as (Jay, 1984): E 2 = 4lim πσ r 2 s (3) r ∞→ 2 Ei

40 Marine Technology Society Journal 4. Maritime Application for maximum range at first detection, requires) of at least 10 m2. On the as- of RCS especially of small targets, is met whilst sumption that for at 4.1 Current Application for recognizing the physical constraints on sea generally use X-band of 9200-9500 Maritime Safety radar. Data produced from radar per- MHz frequencies, a round-shaped To avoid collisions between ships, formance modeling tools, radar range radar reflector, as shown in Figure 2, vessels of less than 15 m in length have tests and practical trials have all been should have at least 0.16 m of length to equip more than one radar reflector considered in reaching the proposed (L) from (4) and (5). constructed of steel panels (to improve figures. The ranges given in Table 3 reflectivity) in order to meet the stand- represent those that should be achieved (4) ards laid out by the British Standard BS in calm conditions with no clutter, 7380:1990 (ISO standard 8729, 1987), without evaporation ducting effects IMO performance standards and the and with all radar settings optimized. (5) DOT Marine Radar Reflector Specifi- As shown in Figure 2, dihedral or cation. By using a radar reflector, small trihedral corner reflectors have larger A square-shaped reflector should have ships have sufficient RCS to announce radar cross sections as compared to at least 0.13 m of length from (6) and 2 their presence to other nearby ships. flat, spherical and cylindrical reflectors. (7) in order to have 10 m of RCS. Recently, the subcommittee on safety Thus, most commercial radar reflec- of navigation (NAV) of the IMO tors for small vessels also have similar (6) has reviewed RCS characteristics for corner reflectors made of metal plates, maritime safety (IMO, 2004). For the as shown in Figure 3. (7) purposes of this review, typical RCS values in Table 2, averaged over 360° 4.2 Design of the New Personal in the azimuth where appropriate, have Rescue Device Figure 3 been used. To design radar reflectors for the Fundamental to this review of the new personal rescue device, practical Examples of commercial radar reflectors for small vessels: (a) an inflatable type; and considerations require a small device radar performance standard is ensur- (b) non-inflatable type. ing that the mariners’ requirement with a minimum RCS (as SOLAS (a)

Table 3

Minimum range at first detection in clutter-free conditions.

(b)

Winter 2008/2009 Volume 42, Number 4 41 To generate approximately the Figure 5 same RCS in any direction, the radar Personal rescue device designs: (a) balloon type; and (b) balloon hanged type. reflector should be shaped as shown in Figure 4, which is similar to the com- (a) (b) mercial reflectors shown in Figure 3. To meet the 10 m2 RCS requirement, a round-shaped radar reflector’s diameter should be at least 0.32 m and a square- shaped radar reflector’s width should be at least 0.26 m from (5) and (7). A radar reflector sized 0.32 m in diameter is compact, but still not small enough to equip to individual person- nel. Therefore, the radar reflector should be inflatable. To make an inflatable ra- dar reflector, we adapted metal-coated flexible radar reflective panels. detectable at a distance. The detectable personal rescue device described in this When a person uses the radar re- distance of navigation radar is deter- paper as shown in Figure 5. flector at sea, it should be free from mined by a function of radar height and When the floatable radar reflector back-scattering from the sea surface and target height from (8) (Harre, 2004) is used as a personal rescue device, the line between the case and the radar (8) reflector may strangle the neck of the Figure 4 user and could potentially cause serious Considered shapes for the radar reflector. where ha is the antenna height, ht is the injury. To prevent the injury, the radar target height. reflector should be kept in a human Round-shaped radar reflector Therefore, the radar reflector should head-sized long hard case. To ensure hang relatively high to have a sufficient the device is not misplaced during RCS. Higher hanging radar reflectors an emergency situation, the personal have additional advantages, as they also rescue device should be adhered to the minimize radio wave absorption from life jacket as shown in Figure 6. the water surface and avoid radio wave If the personal rescue device were disturbance by wave height. designed to operate automatically by To detect a signal at 20 km from a gas pressure when submerged, it could rescue vessel with a 15 m radar height potentially cause injury. To prevent and a cruising speed of 10 kts, the Figure 6 radar reflector should be hanging on approximately 35 m high in order to Strangle-free case design concept for the per- Square-shaped radar reflector rescue the sufferer within one hour—as sonal rescue device designs. determined from (8). For this reason, the radar reflector should be floatable or light enough to be hung from a bal- loon. To improve visibility, the radar reflector and balloon were designed with easily recognized colors such as yellow and red. Two models, a square- shaped radar reflector of 0.26 m width and a round-shaped radar reflector of 0.32 m diameter, were designed for the

42 Marine Technology Society Journal Figure 7

Structure of the personal rescue device designs: (a) structure; (b) tapping mechanism; (c) pulling mechanism.

(a) (b) (c)

device. Figures 7(b) and (c) explain the Figure 8 operation of the personal rescue device Usage concept for the personal rescue device designs. by tapping and pulling, respectively. Figure 8 illustrates the concept of personal rescue device usage. When a person falls into the sea, he can easily operate the radar reflector by simply pulling or tapping. The floating radar reflector will be detected easily by nearby rescue planes or boats, regardless of surroundings. 4.3 Analysis of the Designed Personal Rescue Device To evaluate the effectiveness of the designed personal rescue device, its performance was analyzed by RCS analysis codes, Radar Modeling and Signature Evaluation Software this, a manual instrument was adapted. are required. Figure 7 illustrates the (Ramses) (IABG, 2002). The codes Pulling and tapping are suitable ways acting mechanism and structure of the assume that the incidence angle of the to activate the personal rescue device in designed personal rescue device. electro- is horizontal. The an emergency situation as they are easy As shown in Figure 7(a), the person- backscatter from the sea surface is not to perform. To operate the personal al rescue device consists of compressed considered, as the radar reflector will be rescue device with just a simple action, gas (such as helium), a folded radar floating in the air. Multiple scattering compressed gas and a percussion fuse reflector, a rolled line and a percussion effects are also not considered.

Figure 9

RCS reflector: (a) Sigma HH at 8 GHz; (b) Sigma VV at 8 Ghz; (c) Sigma HH at 10 GHz; and (d) Sigma VV at 10 GHz.

(a) (b) (c) (d)

Winter 2008/2009 Volume 42, Number 4 43 Figure 10

RCS analysis results of 0.32 m diameter round-shaped radar reflector: (a) Sigma HH at 8 GHz; (b) Sigma VV at 8 Ghz; (c) Sigma HH at 10 GHz; and (d) Sigma VV at 10 GHz.

(a) (b) (c) (d)

From the results of the analyses, the personal rescue device was carried out References square-shaped radar reflector, shown to improve SAR activities based on RCS Currie, J. 1798. The Effects of Water Cold in Figure 9, had a larger RCS than the characteristics. Firstly, characteristics of and Warm as a Remedy for Fever. London: round shaped RCS, shown in Figure current rescue devices were investigated, Cadell and Davis. 10. Though the maximum RCS value and characteristics of RCS were also Harre, I. 2004. RCS in Radar Range Calcula- is similar, the round-shaped reflector reviewed. A design for new rescue de- tions for Marine Targets. Bremen, Germany. meets the SOLAS requirement only at vices for personal and life-saving appli- its peak points: near 0, 90, 180, and ances was then put forth, and the RCS Jay, F. 1984. IEEE Standard Dictionary of 270 degrees. Therefore, the square of designed devices were analyzed. Electrical and Electronic Terms, 3rd Edition. shaped radar reflector is superior. The developed device demon- ANSI/IEEE Std 100-1984. New York: IEEE Press. From the results of this evaluation, we strates good performance, is simple confirmed the possibility that a 0.26 m and inexpensive, and is be suitable for IABG, 2002. RAMSES User Manual, IABG, square-shaped radar reflector meet the personal use. The personal rescue device Ottobrunn. requirement of SOLAS, as expected. has the potential to reduce search time IMO. 2004. Review of Performance standards Based on the analysis results, it is and thereby save many lives. It also can for Radar. NAV 50/9. believed that this new rescue device will be applied to life boats, and would be help improve rescue activities at sea. an effective substitution for (or supple- IMO. 2004. SOLAS Consolidated Edition. ISBN 92-801-4183-X. The personal rescue device proposed ment to) current rescue devices. here can also be applied, based on the To verify the performance of the IMO. 2006. Guide for Cold Water Survival. same concept, to other life-saving ap- radar reflector, some practical exercises MSC.1/Circ.1185. pliances such as life boats. on the field are needed. In addition, Knott.E.F, Shaeffer, J.F. and Truly, M.T. 2004. the scattering characteristics of a large Radar Cross Section. SciTech Publishing. group of the radar reflectors should ISBN 1-891121-25-1. be measured or estimated to make the 5. Conclusions Naval Air Systems Command, Naval Air personal rescue device practical. Generally, RCS characteristics Warfare Center. 1999. Electronic Warfare are analyzed by militaries in the de- and Radar Systems Engineering Handbook. velopment of stealth technology. In NAWCWPNS TP 8347. non-military applications, IMO for Acknowledgment U.S. Search and Rescue Task Force. 2008. maritime safety also issues RCS-related The contents of this paper are www.ussartf.org regulations to prevent collisions involv- the result of the MOERI/KORDI ing small ships. research project, "Development of In this paper, a new usage of RCS smart operation technologies for an characteristics was introduced for exploration fleet based on ubiquitous maritime safety. The study of a new computing."

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