1. RTH AND NMC FUNCTIONS FOR GTS INFORMATION EXCHANGE T.K.RAY RTH,NEW DELHI,INDIA E mail:tkray@imd.ernet.in Training Seminar on information and communication Technology for the GTS Lecture Note no.2

2. THE GTS --GLOBAL SUPERHIGHWAY FOR MET. DATA EXCHANGE

4. 1. The GTS consists of an integrated network of point-to-point circuits, and multi-point circuits which interconnect meteorological telecommunication centres. The circuits of the GTS are composed of a combination of terrestrial and satellite telecommunication links. They comprise point-to-point circuits, point-to-multi-point circuits for data distribution, multi-point-to-point circuits for data collection, as well as two- way multi-point circuits. Figure 1 shows the structure of the the GTS. Meteorological Telecommunication Centres are responsible for receiving data and relaying it selectively on GTS circuits. The GTS is organized on a three level basis, namely: (a) The Main Telecommunication Network (MTN); (b) The Regional Meteorological Telecommunication Networks (RMTNs); (c) The National Meteorological Telecommunication Networks (NMTNs); 2. The Main Telecommunication Network is the core network of the GTS. It links together three World Meteorological Centres and 15 Regional Telecommunication Hubs. These are: (a) WMCs: Melbourne, Moscow and Washington; (b) RTHs: Algiers, Beijing, Bracknell, Brasilia, Buenos Aires, Cairo, Dakar, Jeddah, Nairobi, New Delhi, Offenbach, Toulouse, Prague, Sofia and Tokyo. The Main Telecommunication Network (MTN) has the function of providing an efficient and reliable communication service between its centres, in order to ensure the rapid and reliable global and interregional exchange of observational data, processed information and other data required by Members. 3. The Regional Meteorological Telecommunication Networks consist of an integrated network of circuits interconnecting meteorological centres, which are complemented by radio broadcasts where necessary. The Regional Meteorological Telecommunication Networks are to ensure the collection of observational data and the regional selective distribution of meteorological and other related information to Members. The RTHs on the MTN perform an interface function between the Regional Meteorological Telecommunication Networks and the MTN. There are six Regional Meteorological Telecommunication Networks: Africa, Asia, South America, North & Central America, South-West Pacific and Europe 4. The National Meteorological Telecommunication Networks enable the National Meteorological Centres to collect observational data and to receive and distribute meteorological information on a national level. 5. Satellite-based data collection and/or data distribution systems are integrated in the GTS as an essential element of the global, regional and national levels of the GTS. Datacollection systems operated via geostationary or near-polar orbiting meteorological/environmental satellites, including ARGOS, are widely used for the collection of observational data from Data Collection Platforms. Marine data are also collected through the International Maritime Mobile Service and through INMARSAT. International data distribution systems operated either via meteorological satellites such as the Meteorological Data Distribution (MDD) of METEOSAT, or via telecommunication satellites, such as RETIM or FAX-E via EUTELSAT are efficiently complementing the point-to-point GTS circuits. Several Countries, including Argentina, Canada, China, France, India, Indonesia, Mexico, Saudi Arabia, Thailand and the USA, have implemented satellite-based multi-point telecommunication systems for their national Meteorological Telecommunication Networks.

5. The basic design Principles of the GTS are : *Circuits and the Techniques used should be adequate to accomodate volume of data/information and their transmission within accepted time limits to meet the needs of WMCs,RSMCs & NMCs. *Planning of the CCTs should take into account of upto 80% of capacity only. *System be based mainly on interconnecting centres viz.NMCs,RSMCs,RTHs &WMCs. Integrated network for collection,exchange and distribution of data/information on world-wide basis with a view to meeting requirements of National Meteorological Services and also requirements of WMCs & RSMCs. *System should be integrated network of point-to-point,point-to-multipoint,multi point-to-point and broadcasts circuits.These circuits may be composed of a combination of terrestrial and satellite links.

6. Functions and Responsibilities of the Met.Telecommunication Centres WMCs (Telecomm. functions) and RTHs are responsible for : ( a) Collecting the observational data originating from their associated NMCs and transmitting such data on the MTN either directly or through appropriate WMC/RTH. (b)Relaying selectively on the circuits of the MTN as internationally agreed and in appropriate form. ©Transmitting over the MTN either directly or through a designated RTH as internationally agreed in appropriate form. (d)Ensuring selective distribution in appropriate form and speed, of meteorological and related information to the associated NMCs and to the RTHs not situated on the MTN. (e)Checking, correcting and monitoring for efficient WWW operations (f)Establishing data dissemination system (terrestrial and/or via satellite) as required in accordance with regional plans.

7. RSMCs not combined with RTHs should ensure distribution of their products by agreement with an appropriate GTS centre/centres. With regard to Telecommunications,NMCs shall be responsible for : Collecting observational data from their own Territory or that of one or more Members according to bilateral agreements,as well as observational data from aircraft and ships received by centres located within the area of responsibility. This collection shall take place as soon as possible and shall be completed within 15 minutes of the observing stations filing time. (a) Transmitting such data to the associated RTH or WMC. (b)Receiving and distributing for their benefit and that of Members that request them, in accordance with bilateral agreements, observational data and processed information,to meet the requirements of the Members concerned. (c)Checking and making corrections for standard procedures. (d)Carrying out monitoring of the operation of the GTS of WWW.

8. Each member of WMO designates a National Meteorological Centre, or other *RTH/RMC,RSMC,WMC) centre as appropriate for preparing functions as stated above. Members are also responsible for operating centres who would collect observations from individual and stations and assemble reports/bulletins. Members are also responsible for collection of observations from sea (Ship) & aircraft (AIREP). Members should make necessary arrangement with Telecommunication authorities/administrations to establish procedures for collection of meteorological reports from ships through coast stations/satellite earth stations (INMARSAT). Members should be encouraged to develop use of automatic transmission from ships to the designated collecting centres automatically. Members responsible for collection of meteorological reports from ships shall provide the secretariat a list of the coast stations and coast earth stations designated for this purpose, including information on location, consigns, working transmission and reception frequencies. Members shall send necessary amendments, if any, on the above to the secretariat.

9. Responsibility for collection (Reception) of reports from aircraft Collecting centres designated in the ICAO Regional Air-navigation plans for the collection of aircraft weather reports shall send all available aircraft weather reports to the NMC situated in the respective country or to other meteorological centres designated by agreement between the aeronautical and meteorological authorities. RTHs shall collect the aircraft weather reports from the NMCs in their respective zones of responsibility. Responsibility for meteorological reports from automatic surface synoptic stations. Messages from automatic surface synoptic stations should be transmitted expeditiously to appropriate collecting centres. Messages directly transmitted by automatic stations should be transmitted with sufficient strength to ensure reception at the collecting centres.. Members operating automatic synoptic surface stations on drifting buoys should make every effort to communicate to other interested members all of the necessary information (Radio frequency and code forms). Other observational data from drifting buoys available at satellite data processing centres should also be made available to appropriate WMCs/RTHs for regional and global distribution over GTS.

10. Functions Specified within the framework of the GTS In order to obtain rapid collection and distribution of observational data or processed information for all national meteorological services, the Regional Meteorological Telecommunication Networks (RMTN) shall ensure : (a)Exchange and distribution of observational data within the region, to meet the needs of the members of the region; (b)Collection of observational data originating in are being received by, stations located in the region(e.g. reports from aircrafts and ships); (c)Collection of observational data from associated NMCs in adjacent regions provided that this is found to be of use to the GTS and provided that this is agreed by the members concerned and the corresponding Regional Associations. (d)Exchange and distribution of processed information as required to meet the needs of members of the region; (e)Interchange of observational data and processed information with other regions;

11. General functions of NMTN with the framework of WWW The National Meteorological Telecommunication Network (NMTN) shall be engineer so as to enable the NMCs perform functions specified above. Programmes of transmissions from NMCs to RTHs Transmissions from NMCs to the appropriate RTH/RTHs shall include the folowing: (a)Surface and upper air synoptic reports from land stations and fixed ships stations required by regional agreement for regional and inter-regional exchanges; (b)All reports from mobile ship stations and aircraft received either directly or from other collecting centres, within the area covered by the NMC transmission; (c)Other information as required by regional agreement; Satellite based data collection and dissemination Satellite based data collection and distribution system are integrated in the GTS essential element of the global, regional and national levels of the GTS. They should comply with the organization and principles of the GTS. They operate through communication functions of meteorological satellites and through public telecommunication services via satellite.

12. HF Radio broadcast of Meteorological Information Until the integrated network is completed, HF Radio Broadcast may be used in order to meet the requirements of the WWW for dissemination of Meteorological information. Responsibilities of the Members When a member establishes a routine meteorological broadcast intended for use by other members the member shall send following information to the secretariat: (a)Name and consign or other identification of transmitting station; (b) Power supplied to the antenna; (c)Class of emission, necessary bandwidth; (d)Frequencies (e)Contents, time schedules and WMO category of the broadcast; (f)Index of cooperation (IOC) and drum speed of facsimile transmitter; (g)Specific points or area in which the broadcast is intended to be received.

13. RTT Broadcasts ClassificationContentsInended reception areaResponsibility for operations A. TerrestrialMeteorological Information from the territory or territories of one or more Members and ship and aircraft reports as received in this territory or territories (a)At one or more designated RTHs (b)Within the area of origin of the information (c)In adjacent countries as regionally or inter- regionally agreed Mandatory for NMCs until a reliable point-to- point system is available to the associated RTH. Otherwise optional for national purposes B. Regional broadcasts Selection of meteorological Information as agreed regionally and coordinated inter- regionally as necessary (a)Within a specified area in a Region and in an inter- regionally agreed area WMCs and RTHs in accordance with the regional meteorological telecommunication plans

14. Radio-facsimile broadcasts ClassificationContentIntended reception areaResponsibility for operations Regional broadcasts Produces of the RSMCs in the Region, products of WMCs and other RSMCs as agreed regionally and coordinated inter- regionally as necessary Within a specified area in a Region and in an inter-regionally agreed area WMCs, RSMCs and RTHs in accordance with the regional meteorological telecommunication plans

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