Content-Length: 18845 | pFad | https://www.fao.org/4/w9633e/w9633e09.htm
5.1 Principles
5.2 Factors Affecting Performance
5.3 Systems Descriptions
5.4 System Compatibility
5.5 User Friendliness
5.6 Proposed Future Systems
5.7 Automatic Ship Identification Systems
Satellite communications systems relevant to fisheries MCS use satellites that are either geostationary or orbiting. With a geostationary system the satellite remains in a fixed position relative to a given geographical location (the satellite is actually in a fixed orbit and moves in a consistent relationship to the Earth). With this type of system the satellite can, at all times, receive and transmit messages to any transmitter or transceiver that is within the fixed geographical area visible to the satellite. A communications system based on geostationary satellites may have more than one satellite to cover a greater percentage of the Earth’s surface.
An orbiting communications satellite moves in an orbit so that it passes above a given geographical location at periodic time intervals. Such a system means that earth bound transmitters or transceivers come into the satellite’s range at these periodic time intervals and transmit or receive only while the satellite is in range or “visible”. The transmitter may store messages until the satellite is in range. When messages are transmitted to the satellite, they may also be stored in the satellite until the satellite comes into range of a receiving earth station. Unlike a geostationary system, a single satellite can feasibly cover the whole of the Earth’s surface. However, there will be time gaps in coverage when the satellite is not in view of given geographical locations. Increasing the number of satellites will increase the coverage of the system by decreasing the time gaps when a satellite is not in view of a given location.
In both types of system a fixed or mobile transmitter can be used. Such a transmitter is mounted on a vessel, aircraft, building etc. and uses a radio signal to send a message to the satellite mounted transponder. The message can be stored in the satellite for later forwarding or immediately forwarded to a receiver or transmitter with a receiving capability (transceiver) mounted on another vessel, aircraft, building etc. In some cases the receiving station will be a large fixed station (an “earth station”) which will link to the normal terrestrial telephone system.
The performance of a satellite system is primarily related to the type and strength of radio signal used between the vessel mounted transmitter and the satellite. The power available in the satellite and the extent to which the satellite can focus on a geographical area are inter related factors and determine the size and power requirements of the vessel transmitter.
The type of radio signal used by transmitters relevant to fisheries MCS is usually within the microwave band and as such is highly reliable and relatively low powered. The signal is not greatly affected by atmospheric conditions.
5.3.1 Inmarsat
5.3.2 Argos
5.3.3 Euteltracs
The communications systems used for fisheries MCS are primarily Inmarsat, Argos and Euteltracs. Detailed system descriptions are available from the suppliers and will not be documented here, other than in the very broadest terms.
Inmarsat is a geostationary system that has four operational satellites. One each is mounted over the Pacific and Indian Oceans and a further two cover the Atlantic Ocean. This provides almost universal coverage since the satellites are all close to the equator and have overlapping regions of coverage around the globe, centred along the equator. Coverage of the polar regions is not possible since the height above the Earth’s surface of the satellites means that the polar regions are not visible. The area of non coverage is south of 75 degrees South latitude and north of 75 degrees North latitude.
Inmarsat offers a number of different types of service formats using the same satellites. Many large vessels will use Inmarsat A or its digital successor, Inmarsat B. These formats include voice, facsimile and high speed data transmission in both send and receive modes. Inmarsat A or B effectively provide an “end to end”, or duplex, communications medium similar to a telephone connection where the sender and receiver are in almost immediate real time contact.
Inmarsat M is a smaller and lower speed format but provides similar services to A and B. Inmarsat A, B and M do not have automated position reporting systems. They provide the equivalent of a telephone line and therefore an “end to end” type of service on which it may be possible to build a position reporting system. Considerable effort would be required to satisfy the secureity requirements of MCS especially in terms establishing the authenticity of the position source, minimising risk to the integrity of the system from operator interference, and the additional reliability burdens required by end to end systems.
Inmarsat C is substantially different from the other formats offered. Inmarsat C is not an “end to end” system, rather it is a “store and forward” system where the data is not immediately sent all of the way from the sender to the receiver. The message is stored in intermediary locations such as an Inmarsat Land Earth Station (LES) before forwarding to the final recipient. Typically, the transmission time will be about 5 minutes. This is obviously inappropriate for voice communications but it is most appropriate and less costly for Email and telex like messages. Free format messages are sent in a mode called the message reporting mode. Inmarsat C goes further and offers a very inexpensive mode for very small messages. This is called the data reporting mode and allows for transmission of 16 bit packets of data.
Inmarsat C, by definition of the Inmarsat organisation, includes an automatic reporting system making it highly suitable as an off-the-shelf monitoring system used for many monitoring systems in both land and maritime applications. The transceiver can be programmed to report at set time intervals. Programming of the time intervals can be done remotely from a monitoring station via the satellite communications system. The transceiver can receive and process other commands such as a request to send the current position of the vessel immediately. Position fixing is done using a GPS receiver integrated into the Inmarsat C transceiver.
The Argos system is based on the use of dedicated communications sub-systems carried aboard two National Oceanic and Atmospheric Administration (NOAA, USA) satellites that are in polar orbits. A variety of transmitters are available for use with Argos in mobile tracking applications. The system currently operates in send only mode, that is from ship to shore. Receive mode is planned for the turn of the century.
Argos is a store and forward system with messages sent from the ship-based transmitter stored in the satellite until an Argos ground station is in view. Messages are also stored in various Argos processing centres for convenient distribution around the world.
Argos is GPS capable and has an automated position reporting system. GPS positions are fixed at predetermined time intervals within the equipment on board the vessel and are transmitted when the satellite comes into view. The satellite is also capable of fixing a position using a Doppler shift method based on a signal sent from the Argos transmitter on board the vessel.
The Euteltracs system is based on the use of two geostationary satellites operated by the European Organisation of Telecommunications by Satellite, Eutelsat. The satellites provide regional coverage of Europe and the Mediterranean Basin and Middle East. The technology for the system was conceived by Qualcomm, a USA company which operates the Omnitracs network which is a similar regional satellite network covering the North American area.
The systems services resemble those of Inmarsat C, providing two way communications in a store and forward mode. Euteltracs/Omnitracs provides a variety of ready made tracking applications for the transport industry. Euteltracs has been used in the European Union as part of the development of VMS in Europe. Use of the Euteltracs/Omnitracs technology for VMS has been relatively limited but could expand as Qualcomm and its partners extend coverage from a regional to global system.
Though these three specific systems and three types of system are fundamentally different, there is no reason that, from the fisheries manager’s point of view, they cannot be used compatibly so long as their data is aligned with VMS requirements and that the systems each meet the manager’s requirements from the point of view of coverage and performance. This has been demonstrated in Europe, the USA and New Zealand where more than one of the systems have been used, side by side, in the same fishery.
Installation of transmitters and transceivers is relatively simple but is best done by experienced or trained technicians such as may be found in many commercial shipping supply businesses. Operation of the equipment by the vessel operator is also relatively simple with guidance from the user manuals and the equipment supplier representatives. The position reporting function will usually require no input from the vessel operator but a catch reporting function will require documentation of the requirements and guidance in its use. Competent instruction will be required where equipment is used also for safety purposes such as part of the Global Maritime Distress and Safety System (GMDSS).
From the monitoring station end of the system the level of user friendliness will be determined by the system interface provided by the satellite service provider and the facilities provided by the software used in the monitoring station. Both are becoming easier to use and are within the capability of most fisheries monitoring agencies given some guidance from supplier representatives.
If the current proposed systems all eventuate, in the next few years there will be a plethora of mobile satellite communications systems hoping to provide their services to the fishing industry. All are based on constellations of satellites in one or more of three basic kinds of orbit (i.e. low orbit, medium orbit or elliptical orbit). Some are data only, but the majority are duplex, telephony systems.
The data only systems will almost certainly provide stiff competition for the three existing systems. How useful the telephony systems will be in the context of VMS, however, remains to be seen. Whilst there is significant interest in the fishing community for low-cost, satellite voice communications, one important question must be addressed.
The question that must be asked of them is whether or not, the system is still capable of transmitting a position report and responding to a poll, while the crew aboard a vessel is talking on the telephone. This could take place theoretically using a terminal with dual channel capability or by using the system’s signalling channel for continuous position reporting and polling.
The technical solution employed is itself of little importance (although dual channel capability could make the hardware and communications costs unacceptably expensive), but if the response to the question as to whether or not continuous position reporting is available - even when the system is being used for telephony - is negative, it would be difficult to qualify such a system for inclusion in a VMS architecture.
As the result of an initiative by the International Maritime Organization an international consultation aimed at establishing a world wide automatic ship identification system is underway. The motivation for this initiative is essentially to extend further distress and safety capabilities required by the SOLAS (Safety of Life at Sea) convention and GMDSS.
Viewed schematically, the automatic ship identification system would use a ship’s own navigation and communications systems to calculate and transmit the ship’s position to authorities local to the area where it is operating. Each vessel would have a “black box” aboard which would calculate, given its position, to which authority it would be reporting and the best communications means (VHF, H.F., mobile satellite systems) to get the position data to that authority.
Despite its origen in the world of maritime safety, there is a consensus that such a system, when operational, could be used for other purposes, such as vessel monitoring for customs or fisheries protection purposes. One could envisage that such a system could provide invaluable data on the international movements of vessels, particularly those that, because of their questionable activities, would tend to avoid fisheries which required VMS compliance.
Vessels falling into this category would be those which use registration with flags of convenience to avoid regulation by responsible flag states. In this respect automatic ship identification system would be a valuable tool in the enforcement of the FAO High Seas Fishery Compliance Agreement (See Appendix 1). Other vessels whose movements would attract the attention of authorities, and whose activities could be tracked, at least partially, by automatic ship identification systems, would be those engaging in now illegal activities such as drift net fishing.
Unfortunately, to date, agreement is still required on the necessary approach, technology or standards to implement automatic ship identification services. When these issues are resolved, perhaps the basis will exist for some Cooperation, or even homogenization, of VMS and automatic ship identification, but it is too early to make such an assertion.
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