1 It has been passed three years since the Global Maritime Distress and Safety Systems (GMDSS) was enforced as the entirety. During the period, experiences on application of GMDSS including Search and Rescue Radar Transponder (SART) have been obtained. These experiences, among others, have shown the necessity of reviewing the performance standards of SART for further improvement of effective search and rescue operation.

　

2 In such a circumstance, Japan investigated the actual usage of SART at maritime distresses, and conducted, during the year of 1999 and 2000, an study "Research and study on performance improvement about SART". A summary of the report of the study is shown in ANNEX attached to this paper. As the result of the study, it has been recommended to review the existing performance standards of SART in IMO Assembly resolution A.802 (19), and to amend it for inclusion of new technology.

　

3 During the study, an antenna for transmission of SART signal in circular polarization was developed aiming at reducing the size of SART and it has been found that the SART signal of circular polarization appears clearer on marine radar PPI than SART signal of horizontal polarization, the letter of which is required by A.802 (19), through the following experimental measurements and observations.

　

.1 Measurement of receiving power of the SART signals, and observations of them on PPI(Plan Position Indicator), at radars installed on ships, aircrafts and a land-based facility, where the SART was positioned at sea (in on-sea trials); and

　

.2 Measurement of receiving power of the SART signals, and observations of them on PPI(Plan Position Indicator), at a radar where the SART and the radar were positioned at a towing tank facility.

　

4 It was also found that theoretically expected reduction (by 3 dB) of receiving power from SART signal was not observed in case that the polarization of SART signal was circular, and that the SART signal of circular polarization could be found, in more stable manner, on radar PPI in a longer distance than SARI signal of horizontal polarization could be.

　

5 The followings are the summary of the results of the study.

　

.1 The SART antennas were kept 1 metre high from the sea level, and distance between the SART and the ship, radar of which was used for observation of the SART signal, was altered. SART signal of circular polarization could be found on PPI of radar in the distance of 14 nautical miles (NM), while SART signal of horizontal polarization could be found on PPI in the distance of 11.5 NM, where the transmitting power of the antennas was the same. This means that the antenna of circular polarization is superior to the antenna of horizontal polarization.

　

.2 It was found, by the measurement of receiving power of SART signals at the land-based radar at the on-sea trial, that the received power of SART signal of circular polarization was clearly brighter than that of horizontal polarization in the distance of the limit of radio-visibility.

　

.3 In the measurement by the land-based radar, PPI visibility of SART signal of circular polarization was clearly stronger than that of horizontal polarization.

　

6 The reason why the SART signal of circular polarization is superior to that of horizontal polarization should be considered as follows:

　

.1 According to the equation of transmission of radar beam, received wave is the mixture of direct transmission and reflected transmission at sea Surface, in both ways from radar antenna to a object (irradiation) and from objects to radar antenna (reflection). The phase of the wave changes by pi radian (180 degrees) at the sea surface reflection. The difference of distance of wave passes between the direct transmission and the transmission reflected at sea surface causes the divergence of the phase at the mixture of both wave at receiving point (radar antenna and at objects). This divergence results in weakening the power of the mixture which decreases along the distance between the radar and the object in showing the maximum and the minimum. The phenomenon has been known well.

　

.2 It is also known well that the degree of the phase change at sea surface reflection depends on the polarization of wave which goes into the reflection point. The wave from radar, which polarization is horizontal, changes its phase at sea surface reflection by pi radian. Then its return signal from the object shows clear maximum and minimum of power at the receiver of the radar.

　

.3 The SART signal of circular polarization changes continuously the polarization plane in 360degrees. Therefore, the phase change at the sea surface is not constant. This results in the fact that the compensation happened at mixture of direct wave and reflected wave is not constant and the radar can receive the maximum power of the mixture. Then, this fact leads the extension of the maximum visible distance of SART of circular polarization.

　

.4 The SART antenna is always rolling at sea. This movement affects the polarization plane of the SART signal. The SART signal of circular polarization would have much probability to be caught by radar antenna which polarization of horizontal than SART signal of horizontal polarization would have.

　

All the reasons mentioned above show the superiority of circular polarization for SART signal, and these have been proved by the sea trials.

　

7 Japan believes that the SART signal of circular polarization will enhance the search and rescue capability by SART. Therefore, Japan proposes to amend the third sentence of paragraph 2.5 of ANNEX to the Assembly resolution A.802 (19) as follows. This amendment has no effect of existing radars or existing standards of radar.

　

　

So, the whole sentence should read:

"Horizontal polarization and/or any polarization which is received effectively by search radars should be used for transmission and reception."

　

8 This amendment will allow the use of circular polarization which shall contribute the enhance of maritime safety by the following merits:

　

.1 It will allow a development of a new type of SART which needs smaller power in keeping its capability of radio-communication at sea.

　

.2 The signal from such SART can be observed stably by 9GHz radar in further distance than existing SART can be.

　

.3 It will allow more flexible design of SART by not limiting the polarization in horizontal. Such SART may be of lighter weight and smaller and easy to install into liferafts and lifeboats. It will be also possible to develop a smaller SARI which can be fitted in lifejackets and float-free VDR

　

.4 There is no need to change the existing radars and the existing standards for radars.

　

9 The Sub-Committee is invited to consider the proposal described in paragraph 7 of this document, which will allow the use of SART signal of circular polarization and will allow people enjoying many substantial merits for enhancement of marine safety as described in paragraph 8 above, and take action as appropriate.