|INTERNATIONAL MARITIME ORGANIZATION
|SUB-COMMITTEE ON RADIOCOMMUNICATIONS AND SEARCH AND RESCUE
Agenda item 18
3 December 2004
ANY OTHER BUSINESS
Revision of the performance standards for Search and Rescue Radar Transponder (SART)
Submitted by Japan
This paper provides information of the results of the experimental study on search and rescue radar transponder (SART) using signals of circular polarization to improve the effectiveness of search and rescue operations, in addition to the proposal previously submitted to COMSAR 7 (COMSAR 7/11 by Japan)
Action to be taken: Paragraph 10
Related documents: Resolution A.802(19), COMSAR 7/11 and MSC 78/24/4
1 At the 7th session of the COMSAR Sub-Committee, Japan submitted a document which contained the result of an experimental study carried out by Japan and a proposed revision of the performance standards for survival craft radar transponders for use in search and rescue operations (Resolution A.802(19)) with a view to including circular polarization as effective polarization of SART. Japan also submitted a document which proposed to put the revision of performance standards of SART as the new work programme item of the Sub-Committee to MSC 78 and it was approved.
2 Japan carried out further experimental studies on the performance of circular polarization SART in rough weather conditions as it was pointed out at COMSAR 7 that there was no data which showed the validity of SART with circular polarization in such weather conditions in the document Japan previously submitted to the Sub-Committee (COMSAR 7/11).
3 This information paper includes the result of a recent Japanese experimental study on the performance of SART with circular polarization in rough weather conditions, and provides information on the effectiveness of SART which could be used as the basis of reconsideration of the performance standards for SART.
4 In the study, Japan developed an antenna for the transmission of a SART signal using circular polarization and it has been found that the SART signals of circular polarization appear clearer on plan position indicator (PPI) of marine radar than those of horizontal polarization.
5 It was also found that the SART signals of circular polarization were observed on radar PPI in a more stable manner and at a longer distance than that of horizontal polarization, and the loss of power of received signal, which was theoretically prospected to 3dB, was not observed. These were also observed in the results of the experiments in rough weather conditions.
6 The summaries of the results of this study are as follows:
.1 the received power of SART signals was measured by land-based radar during the sea trial, and it was found that the received power of SART signals of circular polarization was stronger than that of horizontal polarization and this differential in strength is greater in the area where the distance is almost at the distance of the limit of radio-visibility in calm weather conditions; and
.2 in rough weather conditions, though the difference between circular polarization and horizontal polarization is smaller than that in calm weather, the received power of SART signals of circular polarization was stronger than that of horizontal polarization in many cases.
Advantages of the circular polarization of the SART signal
7 The reasons of those advantages of the SART signal of circular polarization mentioned above can be considered as follows:
.1 as is well known, according to the radar equation for marine radar, wave is received as the mixture of direct transmission and reflected transmission at sea surface, and it happens in both ways from radar antenna to a SART (irradiation) and from SART to radar antenna (reflection). The phase of the wave of horizontal polarization changes by pi radian (180 degrees) at the sea surface but the degree of the phase changed at sea surface varies depending on the type of polarization of wave;
.2 the SART signal of circular polarization changes continuously with the polarization plane in 360 degrees and the phase changed at the sea surface is not constant as mixture of direct wave. The mixture of waves has much variety in circular polarization and the radars are more likely to receive the maximum power of the mixture. This fact extends the maximum visible distance of SART; and
.3 the SART antenna is always rolling at sea and this movement affects the polarization plane of the SART signal. The SART signal of circular polarization would have much possibility to be caught by radar antenna than that of horizontal polarization as horizontal polarization is more effective when polarization plane is maintained.
All reasons mentioned above show the superiority of circular polarization of the SART signal, and these have been proved by the sea trials in both calm and rough weather conditions.
Proposed amendments to resolution A.802(19)
8 Japan believes that the SART signal of circular polarization will promote the search and rescue capability by SART. Therefore, Japan proposes to amend the third sentence of paragraph 2.5 of the Annex to resolution A.802(19) as follows. This amendment has no effect on existing radars or existing standards for radar.
Insert "and/or any polarization which is received effectively by search radars" after "Horizontal polarization" in the third sentence of paragraph 2.5 of the Annex to Assembly resolution A.802(19).
The whole sentence would be:
"Horizontal polarization and/or any polarization which is received effectively by search radars should be used for transmission and reception."
9 This amendment will allow the use of circular polarization which will contribute to enhance maritime safety especially in search and rescue operations by providing following merits:
.1 it enables to develop new type of SART which needs less power to keep capability of radio-communications at sea;
.2 signals of SART using circular polarization can be observed stably by 9 GHz radar from a further distance than an existing SART which uses horizontal polarization;
.3 it allows more flexible design such as smaller, lighter SART. Such SART can be installed to small craft such as liferafts and lifeboats. It will also be possible to develop much smaller SART which can be fitted in lifejackets and float-free VDRs; and
.4 there is no need to change the existing radars and the existing standards for radars.
Action requested of the Sub-Committee
10 The Sub-Committee is invited to note the above and annexed information.
For reasons of economy, this document is printed in a limited number. Delegates are kindly asked to bring their copies to meetings and not to request additional copies.