The following document provides a summary of the results of the ET-SSUP work in the area of alternative dissemination methods.

 

 

The Open Programme Area Group on Integrated Observing System’s Expert Team on Satellite System Utilization and Products (ET-SSUP) has reviewed during the past two years the direct broadcasting from meteorological satellite concept. Tasked by CBS-XII and EC-LIV, based on current and planned satellite systems, taking into account the evolving telecommunication technology, and having regard to NMHSs’ requirements for a cost-optimized access to all necessary meteorological data/products, ET-SSUP has developed a proposal to extend the concept of Direct Broadcast (DB) to Alternative Dissemination Methods (ADM).

The ADM branches are open to merging with the other meteorological data streams. For example, this evolved concept will allow for a seamless inclusion of data/product sets from polar and geostationary operational satellites as well as from relevant R&D satellites. The concept as depicted in Fig. 1 was welcomed by CMGS and CM-2.

ET-SSUP has also discussed a set of preliminary user requirements, while leaving technical specifications to the telecommunication experts. The Expert Team could only provide preliminary views on such requirements in order to help define the order of magnitude and to initiate a dialogue with other experts. It was expected that the most demanding application would be NWP, and that NWP requirements (see tables in the text titled ADM Preliminary User Requirements) could thus be taken as a benchmark for sizing the data communication means.

The Inter-Programme Task Team On Future WMO Information Systems should take into consideration the OPAG IOS ET-SSUP proposal as well as provide feedback to the Expert Team to help guide its future work programme.

In December 2000, CBS-XII was informed that the Open Programme Area Group on Integrated Observing System’s Expert Team on Satellite System Utilization and Products (ET-SSUP) had reviewed the direct broadcasting from meteorological satellite concept that so far had very successfully and efficiently served the meteorological user community. CBS-XII also noted that ET-SSUP had proposed preliminary guidance for future telecommunication alternatives, noting certain shortcomings in the current receiving concept and the enormous increase in data through the next decade. CBS-XII agreed to further explore the possibilities that broadcast service onboard meteorological satellites could be complemented and supplemented by alternative telecommunications services with the ultimate goal for a smooth and orderly transition to the full use of alternative telecommunications service for broadcast service starting with the future generation of satellites. Thus, CBS-XII assigned a specific task to ET-SSUP in its terms of reference with regard to further studying alternative telecommunications services.

The following sections contain detailed information related to the ET-SSUP review provided to CBS-XII as well as the results of ET-SSUP meetings since CBS-XII. The section labelled SSUP-3 refers to the review prior to CBS-XII and sections labelled SSUP RG-1 and SSUP-4 refer to the work by the Expert Team in response to the task assigned to it by CBS-XII.

The fifty-fourth session of the WMO Executive Council also discussed alternative telecommunications services. In particular, the Executive Council noted the matter of Alternative Dissemination Methods (ADM) for the distribution of satellite data and products from the operational meteorological satellites. The Council urged the Commission for Basic Systems to review the ADM concept, as a matter of urgency, to include data and products from Research and Development satellites in order to provide WMO Members with guidance on how the valuable satellite information could be made available in an optimized distribution system. Candidates for ADM included Internet and commercial telecommunication satellites. The Council was pleased to learn that CBS had made significant progress in reviewing ADM with the expectation that the Commission would finalize a distribution concept at its next session.

Thus, it can be seen that the Executive Council has expectations that CBS Ext 2002 will provide further guidance on Alternative Dissemination Methods to WMO Members. SSUP-4 also agreed that it was extremely important for the close coordination between the Open Programme Area Groups on Integrated Observing Systems (IOS) and Information Systems and Services (ISS) in the further development of the ADM concept. This would allow the OPAG ISS to expand the future GTS while taking into account OPAG IOS requirements. Thus, SSUP-4 agreed to further research user requirements in terms of e.g. data volume, timeliness, number of sources and area covered. It also suggested that the Chair of OPAG IOS seek representation on relevant OPAG ISS meetings including the Inter-Programme Task Team On Future WMO Information Systems (TT-FWIS-4) meeting September 2002 in South-Africa).

SSUP-3 reviewed the concept of direct broadcast from the space-based Global Observing System paying particular attention to advantages, limitations and challenges. It took into consideration rapid technological advances, in particular telecommunications, now occurring and expected to accelerate in the future.

SSUP-3 recalled that the Direct Broadcast Service (DBS) was a broadcast service available from most of the meteorological satellites operated by members of the Coordination Group for Meteorological Satellites (CGMS). Such broadcasts allowed the transmission of satellite sensor data and products in real or near real-time to user reception stations located within the broadcast field of view of the satellite.

SSUP-3 also noted the potential Internet provided for distribution of meteorological data as a complement to DBS, as well as for schools and amateurs, or as the main data source for training centres (within the VL concept) or for scientific users to access recently archived data and the ongoing activities by satellite operators to already provide subsets of satellite data to their users via the Internet. SSUP-3 was well aware of current shortcomings in the Internet system, but was generally of the opinion that an effective Internet system for data exchange could be expected globally in the coming years. SSUP-3 also agreed that the developments in this area should be kept under constant review.

SSUP-3 also considered new developments in telecommunication technology as related to satellite data dissemination including: the use of digital packaged transmissions, VSAT technology and emerging standards for digital video broadcast (DVB). SSUP-3 noted with some concern that radical changes in communications technology were taking place over a period of time far shorter than the life cycle of a meteorological satellite system. SSUP-3 considered that, wherever possible, advantage should be taken of such progress to improve access to data by the users.

SSUP-3 then considered several possible evolution paths for the DBS. It noted that user requirements were evolving, sophisticated instrument payloads were being proposed and designed to take advantage of developing technology and alternative data dissemination schemes were being considered. These alternatives included:

• The use of data relay between satellite systems;
• The use of commercially provided higher data rate services;
• The use of services such as the Internet.

Commercially provided services could be more reliable, as they may have greater potential for system redundancy. Furthermore, in the case of the geostationary satellites solely dedicated to meteorology or climate monitoring, not including the broadcast capability could simplify the design of the satellite, could reduce development costs, relax the need for very accurate station keeping, and thereby possibly extend the lifetime of the satellite. Additionally, the use of commercially provided broadcast services could facilitate the global development of low cost standard classes of user stations with smaller antennas with less stringent requirements for pointing accuracy and for a significant reduction in the need for specific training as concerns the operation and maintenance of the equipment. Relying on higher bandwidth commercial telecommunication systems offer the potential of improving the overall timeliness.However, SSUP-3 noted that an important point to consider with such broadcasts would be the telecommunication coverage. In order to ensure coverage within a region similar to that currently available from the meteorological satellite broadcasts, use of more than one telecommunications system may be required. SSUP-3 stressed, however, that to make any commercial proposal viable, the lower cost to the user of the telecommunication service should not offset this advantage, also bearing in mind the timeliness and coverage requirements.

SSUP-3 considered that any implementation of such a possible evolution would be a long-term objective and could be considered selectively in the following categories of satellite data flows:

A gradual implementation of near-real-time satellite data available through high bandwidth telecommunication means as a complement to the DBS: for example, GEO imagery from "foreign" satellites, satellite products derived from GEO and/or LEO satellites, global data from polar-orbiting satellites;

With the start of operations of future generation of meteorological satellites, a full set of real-time GEO data disseminated by normal telecommunication satellites, or other means, as a replacement to the DBS assuming it offers more cost-efficient solution with the same timeliness and coverage performance as dissemination by the meteorological spacecraft itself.

SSUP-3 stressed that any change to the broadcast concept would need long periods of notice for the users and long transition periods, which should be compatible with the lifecycle of receiving equipment and of relevant satellite series.

SSUP-3 also agreed that there was a requirement for system studies and demonstration before the impact of such major changes in broadcast system on the users could be assessed in more detail and recommended that this topic be added to the future work plan of the Expert Team.

SSUP-3 noted that new dissemination concepts could offer many opportunities for the wider distribution of satellite imagery and derived products from both GEO and LEO satellites on a more global scale and include both operational and R&D satellites.

SSUP-3 also noted that many aspects involved in this issue (e.g., observation, telecommunications, training, resources) would require coordination with other relevant OPAG working groups.

In conclusion, SSUP-3 agreed that direct broadcast service onboard meteorological satellites be complemented and supplemented by alternative telecommunications services with the ultimate goal for a smooth and orderly transition to the full use of alternative telecommunications service for broadcast service starting with the future generation of satellites.

RG-1 reviewed several activities related to existing and near future alternative dissemination methods (ADM) that had occurred since the twelfth session of CBS and which were relevant to discussions on the concept of direct broadcast from the space-based component of the GOS. The activities included a Workshop on Satellite Distribution on Meteorological Information hosted by Météo-France in Paris, France 6 November 2001, CGMS-XXIX held in Capri, Italy 22-25 October 2001, plans by EUMETSAT for an ATOVS Retransmission Service and the People’s Republic of China’s internal rebroadcast service for meteorological information.

After consideration of the above activities, RG-1 prepared the following summary statement on data access. RG-1 agreed that the summary statement should be used as input to the discussions on alternative dissemination methods at the next full session of the Expert Team.

Access to satellite data and products by WMO Members should be through a composite data access service comprised of both direct broadcast from satellite systems and ADM. ADM would be the baseline while direct broadcast reception would serve as back-up as well as for those WMO Members unable to take advantage of ADM.

As concerns ADM, RG-1 noted existing and current plans of some WMO Members and satellite operators to implement satellite-based broadcast system with regional coverage and noted the possibility to use them inter alia for satellite data and product dissemination. RG-1 was convinced that a few dedicated ground facilities could serve as entry points to feed such regional broadcast systems with all relevant satellite data in a standardized form for the benefit of the entire region. With regard to the ADM, on the basis of WMO Regions each satellite operator should cooperate with NMHSs to establish a new service to deliver the full suite of satellite data and products (to include the comparable data content delivered by the global dissemination broadcast) from its satellite systems to users (for example as planned with the ATOVS Retransmission Service but expanded to include all data and products). Each region may choose to have its distribution system different from other regions but such a regional service should exist. The regional distribution system should have the ability to selectively distribute data and products, i.e., all data and products would be available at the regional hub but only required data and products would be distributed to the end-users. All satellite operators should seek to connect their individual systems into the regional distribution system. The regional distribution systems should allow the injection of GTS data as well as data from other sources such as the R&D satellites.

As concerns direct broadcast, while recognizing that future satellite systems would not have duplicate instruments nor provide identical data, there would be a need for a direct broadcast capability as part of a global dissemination service based on the already approved CGMS global specification for AHRPT, i.e., a WMO standard. The global service should be provided by all satellite operators with near-polar-orbiting satellites. The global service should have a common frequency in the 1698-1710 MHz band and common bandwidth (TBC). Finally, the global service should have a comparable data content with Metop considered as a benchmark.

SSUP-4 reviewed the concept of data access for the space-based component of the Global Observing System (GOS). SSUP-4 agreed that DB meant that a transponder aboard the meteorological spacecraft itself performed data broadcasting to the user whereas the ADM concept meant that after downlink to a primary ground station (or Command and Data Acquisition station) the data distribution to the user community at large was performed through telecommunication services as available from telecommunication operators, which are not dedicated to meteorological data. ADM may rely on telecommunication satellites or terrestrial links or a combination of both, depending on what would be more cost-effective. However, in the present state of technology the most obvious alternative to DB would be the use of commercial satellite-based broadcast services. Therefore, in the following discussions, ADM was understood to be "near real time data distribution via commercial satellite telecommunication services".

SSUP-4 recalled that RG-1 held in December 2001 had reviewed the meteorological satellite operators’ plans as well as the development of the meteorological telecommunications systems. RG-1 had reconfirmed the need for an integrated strategy for dissemination of meteorological satellite data in particular.

SSUP-4 was informed that in February 2002, the second Consultative Meetings on High-Level Policy on Satellite Matters (CM-2) had discussed the space-based component of the GOS and in particular the inclusion of relevant R&D environmental satellites. In this context, CM-2 "felt that the issue of ADM was of utmost importance to WMO and that some Members had experience with examples of such systems that were very cost effective. CM-2 encouraged CBS to remain aware of the capabilities of future telecommunications systems for the distribution of satellite products from operational and R&D data streams". CM-2 "recognized that due to the large volumes of data expected from the satellite systems, ADM that would complement and supplement the existing DB service would be a necessity for the future space-based component of the GOS. It appreciated the ongoing initiatives within CGMS and CBS to address the issue and encouraged them to give the issue highest priority".

SSUP-4 then discussed the advantages of ADM. SSUP-4 remained convinced that the DB concept had been a remarkably efficient means for real-time data dissemination to a large number of users around the world during three decades, while no public or commercial telecommunication infrastructure was available to achieve a comparable performance. Presently however, the telecommunication market was offering a range of solutions covering all regions of the globe, which have the potential to at least complement - if not replace - DB.

SSUP-4 noted that the development and exploitation cycle of a meteorological satellite generation generally extended over at least two decades, which was very long compared to the development rate in the telecommunication sector. Therefore, the design of the telecommunication functions aboard meteorological satellites, which would be "frozen" long before the first launch, could not benefit from the latest available technology. There was a strong risk that the dissemination mission aboard a meteorological satellite would become rapidly obsolete.

SSUP-4 also agreed that if the dissemination function were to be assigned to a dedicated telecommunication system, separated from the meteorological spacecraft, it would be more likely updated and follow the state of the art in telecommunication technology and adapted to evolving user requirements. This was the primary rationale for further investigating ADM.

SSUP-4 also noted that ADM was likely to bring significant advantages mainly in the following areas:

High performance allowing high data rates of several Mb/s, thus providing access to a wide range of data and products with a good timeliness;

Flexibility allowing enhancement of dissemination during the lifetime of a satellite generation with additional products that were not included in the initial design of a satellite system, in response to evolving requirements and latest R&D results;

Capability to include data from spacecraft that were out of the visibility of the user;

Availability of standard user terminals, which would be optimized and serial manufactured for a wide and competitive market. In particular, use of relatively small antennas depended on the frequency band (e.g., RETIM-2000 uses 45 cm dishes, in Ku-band, while RETIM-Africa uses 180 cm dishes, in C-band). This resulted in low costs (one order of magnitude below the price of dedicated meteorological receiving stations), easy operation and maintenance;

The availability of low cost user terminals would make data access affordable for a larger number of users;

The availability of dedicated data receiving systems was indeed a limiting factor for the use of satellite data in several regions which argued in favour of enhancing data access through ADM;

By making the data available to a wider audience, the use of ADM could alleviate the need for further internal redistribution of very large volumes of data, with its implications on internal telecommunication infrastructure;

ADM could facilitate a smooth transition between different satellite generations for the user community. When all users obtained the data by direct readout, there would be a need to maintain two spacecraft systems in parallel operation during an overlap period, until users had upgraded or replaced their receiving devices. When data were disseminated by ADM, it would be possible to only duplicate the dissemination function during the overlap period, without operating two spacecraft in parallel. Furthermore, the proper software upgrade could be downloaded through the system itself;

As long as satellite data were disseminated by DB, they would require dedicated receiving devices that would be distinct from the other telecommunication systems used for meteorological operation. When using ADM, it would be possible to combine reception of satellite data with the reception of other meteorological data, which would save costs and facilitate operation, since the same or similar terminals could be used;

Dissemination via an ADM would allow alleviation of the constraints on spacecraft station keeping without requiring antenna re-pointing by the ADM user, thus extending the lifetime of satellites and reducing cost;

Dissemination via ADM would greatly facilitate contingency planning, whereby the impact of a satellite change could be transparent at the telecommunication level, and thus minimized for the user;

ADM would facilitate the acquisition of multiple satellite data in an integrated way, in order to produce multi-satellite composite products.

SSUP-4 noted that there would be specific advantages for geostationary, polar-orbiting and environmental satellites. For geostationary satellites, there was a requirement for global coverage, whereby weather forecasting applications required access to imagery data from all geostationary locations as defined in the GOS. ADM could support such global coverage with minimum risk since data from any geostationary satellite corresponding to a given footprint could be relayed independently from the availability of the other satellites of the GOS. Additionally, composite imagery generated from two neighbouring satellites could be made available in the same manner, after relevant central processing, without any additional task for the user.

With regard to polar-orbiting satellites, the use of ADM would be most useful when the data coverage had a wider extension than the acquisition area for a single direct readout station. This would be the case when ADM would be fed by a Primary Ground Station where on-board recorded data were dumped (e.g., Near Real Time dissemination of global IJPS data in the EUMETSAT Polar System programme). This would also be the case when it merged data acquired by a network of single direct readout stations (e.g., EUMETSAT ATOVS Re-Transmission Service) since the resulting area covered would be the sum of all single acquisition areas.

With regard to environmental satellites (i.e., R&D or operational satellites which were relevant to environmental observation, but not considered as operational meteorological satellites), it was recognized that they would be contributing to the space-based component of the GOS. However, data dissemination from these spacecraft did not imply the same level of coordination as operational meteorological satellites since they were beyond the scope and mandate of CGMS at the present time. Thus, SSUP-4 recalled that there was an urgent need to take initiatives to establish near-real time dissemination data streams to the meteorological user community in a suitable way, i.e., without requiring that each WMO Member invest in a dedicated, expensive and complex receiving facility.

SSUP-4 noted the reaction by CGMS satellite operators to the ADM concept as follows:

EUMETSAT and NOAA/NESDIS both mentioned that they were in an early planning stage for the dissemination means of their future generations of geostationary satellites and would welcome any guidance from WMO;

EUMETSAT underlined that establishing an ADM was a new experience for a space agency such as EUMETSAT, concerning satisfying the requirements for operational quality of service;

CMA supported the approach which would allow access to global data, while noting that each region may have its own implementation plan which should be consistent with the resources available and the expected/targeted level of data utilization;

ROSHYDROMET noted that in the Russian Federation Internet was now the most widely used alternative to direct broadcast. The need for ADM was particularly relevant for R&D satellites that required specific receiving systems.

JMA saw a potential interest in ADM for Japan as regards the access to global data, and R&D satellite data in particular, as well as for contingency planning. The possible implementation of ADM in Eastern Asia should be reviewed with further information on the available communications satellites, preferably in coordination between CMA and JMA.

SSUP-4 discussed in depth the possibility to complement or replace DB with ADM in the context of the global utilization of future satellite systems. SSUP-4 agreed that access to satellite data and products by WMO Members should be through a composite data access service composed of both DB and ADM. DB would complement ADM and also serve as a back-up as well as to provide the possibility to receive data independently from a third party (besides the satellite operator).

SSUP-4 noted the continuing efforts by WMO towards standardization especially for the space-based component of the GOS. However, another point of justification for ADM was that it was not reasonable to expect total standardization across instruments, missions, data and products.

As concerns DB from polar-orbiting satellites, SSUP-4 recognized that future satellite systems would not have duplicate instruments nor provide identical data. Thus, there would be a continuing need for a DB capability as part of a global dissemination service provided in a similar way by all satellite operators with polar orbiting satellites. This would allow the development of direct readout stations compatible with different satellite systems. Furthermore, the global service should be based on the already approved CGMS global specification for AHRPT, i.e., a WMO standard. It should have a common frequency in the 1698-1710 MHz band and common bandwidth (TBC). The global service should have a comparable data content including basic imagery channels. METOP AHRPT dissemination was proposed as a benchmark. SSUP-4 discussed the issue of comparable data content in more detail, as recorded in the report from SSUP-4 under agenda item 5.

SSUP-4 further suggested that satellite operators should make adequate pre-processing software (de-multiplexing, geo-location, calibration) available world-wide to enable direct readout users to efficiently use the data and locally prepare products in a consistent way.

SSUP-4 recalled that an ADM principal was to use the most cost-efficient and available technology in order to make ultimately more data available to a larger user community. An implication of ADM was also to alleviate the difficulty of the reception/acquisition task by making data available via a telecommunication standard (frequency, protocol), and in a format adapted to the needs and constraints of the user community within the footprint, rather than requiring the user community to adapt to each specific format of each individual satellite system. This was particularly relevant for the access to multiple satellite systems with different data formats. This adaptation should be achieved by an "editor" who can either be the data producer (i.e., the satellite operator) or another entity contributing to the system in partnership with the satellite operator.

SSUP-4 agreed that integration should be sought in two directions: amongst the various satellite systems globally and amongst satellite and non-satellite data in each WMO region. On the latter aspect, SSUP-4 recalled that some WMO Members had plans to implement satellite-based broadcast system with regional coverage and to propose them for inclusion in the GTS, in the framework of future GISC. In order to achieve integration, such systems should be used inter alia for satellite data and product dissemination.

On the basis of but not necessarily corresponding strictly to WMO Regions, each satellite operator should cooperate with WMO Members to establish a new service to deliver the full suite of data and products from its satellite systems. This should include, but not be limited to, the comparable data content delivered by the standardized global dissemination service.

The characteristics of the regional distribution system would depend on the specific requirements, constraints and capabilities of each Region, but it should exist in every Region. All satellite operators should be invited to ensure interfacing between their individual ground segments and the regional distribution system. The regional distribution system should have the ability to selectively distribute data and products, i.e., all data and products would be available at the regional hub, but only required data and products would be distributed to the end-users. It was felt that a few dedicated ground facilities should serve as entry points to feed the regional broadcast systems with all relevant satellite data in a standardized form for the benefit of the entire Region. The regional distribution system should allow the injection of GTS data as well as data from other sources such as relevant R&D environmental satellites.

For example, an important point was the capacity to interconnect different regional distribution systems, exchanging large data sets between regional "hubs", thus providing timely access to global data in every region. In the case of the METOP ground segment, the Near Real Time distribution of global data was currently planned via an ADM covering EUMETSAT Member-States and Cooperating States only, but an extension to a wider distribution could be considered, with the contribution of appropriate "hubs" and further distribution networks. In the same context, NOAA/NESDIS was investigating options for the wider distribution of GOES data and products beyond the coverage of DOMSAT.

The complementary role of DB, ADM and the other meteorological networks is illustrated in Figure 1.

In summary, SSUP-4 agreed that current telecommunication technology offered ADM with a large potential to enhance data access to existing and planned meteorological spacecraft. Such means would be required to cope with the multiple downlink formats and standards of the planned systems in both polar and geostationary orbit, especially when including relevant R&D or "environmental " satellites. There was an urgent need to converge on appropriate standards suitable for the meteorological community. Finally, the satellite operators, in partnership with WMO Members, should be invited to establish such facilities in every Region, in order to allow an adequate response to the meteorological and environmental data requirements.

SSUP-4 also agreed that it was extremely important for the close coordination between the Open Programme Area Groups on Integrated Observing Systems (IOS) and Information Systems and Services (ISS) in the further development of the ADM concept. This would allow the OPAG ISS to expand the future GTS while taking into account OPAG IOS requirements. Thus, SSUP-4 agreed to further research user requirements in terms of e.g. data volume, timeliness, number of sources and area covered. It also suggested that the Chair of OPAG IOS seek representation on relevant OPAG ISS meetings including the Inter-Programme Task Team On Future WMO Information Systems (TT-FWIS-4) meeting September 2002 in South-Africa).

SSUP-4 then discussed preliminary requirements, which could be submitted as input to the Expert Team on Enhanced Use of Data Communication System in order to address the integration of ADM of satellite data into the overall telecommunications scheme for WMO.

It was understood that the focus should be on user requirements, while the technical specifications should best be addressed by telecommunication experts.

SSUP-4 recognized that different user communities could have different requirements and may thus be best served by different telecommunication means (e.g., near-real time satellite distribution or data pull from an Internet server).

SSUP-4 felt that end-user requirements should be expressed and reviewed by representatives of the relevant user communities. The Expert Team could only provide preliminary views on such requirements in order to help defining the order of magnitude and to initiate a dialogue with the Expert Team on Enhanced Use of Data Communication System. It was expected that the most demanding application would be NWP, and that NWP requirements could thus be taken as a benchmark for sizing the data communication means.

SSUP-4 was convinced that Level 0 data were required by the research community, while the operational users were expected to require mainly Level 1 or Level 2 data. Providing higher level data may facilitate the operation downstream, minimize the duplication of work and reduce the volume of data exchanged. However, it could also require some guarantee that the processing was made in a consistent fashion, especially if the processing were shared between different facilities.

In terms of timeliness, the following temporal requirements were available:

SSUP-4 also suggested the following table as an indication of the order of magnitude of the data volume to be exchanged as well as the data rate of the various relevant satellite systems:

As concerns GEO satellites, SSUP-4 noted that GOES-R would obviously be the most demanding in terms of telecommunication capacity. It was assumed that, in each region, there would be a requirement for the full data set from the geostationary satellites in direct visibility, while the data from other GEO satellites would also be required, although possibly with a lower temporal resolution. The maximum required data rate for global GEO data was expected to increase one order of magnitude over the coming decade (i.e., from 12 to 80 and ultimately to 150 Mbps) in taking into account all operational satellites.

As concerns operational LEO data, it was expected that the basic operational constellation would include at least 4 simultaneous satellites, depending on the final distribution of Equatorial Crossing Times. For sizing purpose, the total data rate was expected to include 4 data streams at the level of 20 Mbps each, i.e., 80 Mbps. Because of the requirement for global data at full resolution, this data flow was assumed to be permanent.

SSUP-4 noted that the relevant data flow from R&D satellites had not yet been addressed. It should be reviewed on the basis of the specific needs of thematic user communities.

SSUP-4 noted the need to define requirements with respect to telecommunication standards, frequency, IP protocol, error correction, reliability, commitment for long term continuity and quality of service. Additional requirements, which could be considered were the capability to selectively control the data access by user classes or individual users, to download receiving software upgrades and to guarantee a bandwidth for different classes of the data flow. Finally, SSUP-4 felt it important to consider WMO headers and filename conventions and imagery format and appropriate compression possibly to display imagery with standard display software.

In each region, there should be, for back-up purpose, at least two centres acting as editor and ingest point, each with the capacity to exchange the full volume of global data with the other centres.

SSUP-4 recommended that the Chair of OPAG-IOS present appropriate information concerning the ADM concept to CGMS.

ET-SSUP reviewed the direct broadcasting from meteorological satellite concept. Having regard to NMHSs’ requirements for a cost-optimized access to all necessary meteorological data/products and based on the notion of three different types of satellite data sources, ET-SSUP extended the present concept adding, as depicted in Fig. 1, to the direct broadcast (DB - retained as a back-up service) alternative dissemination branches (ADM – primary service) to be merged with the other meteorological data streams, and provided according to regional needs and available telecommunications technology. This evolved concept inter alia will allow also for a seamless inclusion of data/product sets from R&D satellites.

ET-SSUP already discussed preliminary user requirements, while leaving technical specifications to the telecommunication experts. The Expert Team could only provide preliminary views on such requirements in order to help defining the order of magnitude and to initiate a dialogue with other experts. It was expected that the most demanding application would be NWP, and that NWP requirements (see Tables) could thus be taken as a benchmark for sizing the data communication means.