Earth Observation Data and Information Access: Internetworking for an International Application Demonstrator
Hermann Ludwig MOELLER <firstname.lastname@example.org>
Roberto DONADIO <email@example.com>
The present paper describes how the synergy of Internet-centric middleware solutions based on CORBA and a supporting TCP/IP-based communications infrastructure can benefit large-scale, internationally distributed information services in the domain of earth observation from space.
Earth Observation Information Systems (EOIS) handle tens of millions of data and information items worldwide, representing several hundred of terabytes of archived data, with new data from spacecraft entering a federation of systems at a rate above one terabyte per day and with user retrieval rates expected to exceed that rate considerably.
In preparation for future EOIS, a proof-of-concept initiative, based on different technology research and demonstration projects, has been set up by ESA and the EC, under participation of Japanese partners (NASDA, for example), and European industry has created a system consisting of
As an example of an environmental application, oil-pollution monitoring in the Mediterranean Sea, the paper illustrates how the demonstrator system is being applied to the requirements of earth observation. The paper concludes with an outlook on possible extensions to new partners (in the United States,for example), focus on the further validation of selected demonstrator components, and planned standardization efforts.
Earth Observation data holdings, created by an increasing number of remote sensing satellites worldwide, are going to increase dramatically over the coming five years. Globally, archives today contain more than 300Tbytes of information, mostly image based, organized in several tens of millions of data items and distributed over data centers in the United States, Europe, Japan and other regions. As from 1998, a new series of satellites will start augmenting the ingest rates of new data sets to reach 1Tbyte per day, i.e., one year of new data will equal about the total of all presently archived data.
Data is inherently distributed, and networked services, based
on Internet technology, are becoming a key element in effective
exploitation. A portfolio of different network services will be
required to best support the different levels of Earth Observation
Ground Systems which can be structured in three levels:
Each level has a different emphasis in terms of networking requirements. Data Level systems are concerned with high quality, reliable data management, data exchange and distribution, e.g., data base updates between archives in Japan, e.g., NASDA, and Europe, e.g., ESA. Information Level systems increasingly demand the networked federation of data and services, e.g., allowing the image processing of a data set at a VAC computing facility after ingestion from a satellite operators system. End-User Level systems focus on low-cost information access and retrieval, e.g., serving asymmetrical data flows, e.g., distribution of a processed VAC image toward a single user PC.
Data and Information Level Internetworking is provided primarily through Intranet and Extranet solutions, e.g., ESINet, the ESA Intranet, partners Internet/Intranet implementations, e.g., NASA's Science Internet (NSI), and outsourced Intranet solutions offered by Internet Service Providers (ISP) and Telecom Operators, and are complemented by public networks and access to National Research Networks (NRN). End-User Level networking at present still relies largely on the public Internet, with its current capabilities and level of saturation effectively slowing down further evolution of networked applications. Figure 1 illustrates the present scenario for ESA and its related internetworking infrastructures [Ref.1].
With focus on data level systems, the European Space Agency and other organizations in Europe and worldwide have engaged in the development of significant, large-scale Earth Observation Data and Information Systems for data exploitation. In Europe, these infrastructures involve facilities for acquisition, archiving and processing of satellite data and user services facilities, e.g., in Germany, the United Kingdom, France, Sweden, Spain, and Italy. The systems are capable of
Data Level systems provide large-scale User Information Systems, such as ESA's Multi-Mission User Information System (MUIS), providing access to several million inventory records through general purpose data search and discovery interfaces (see http://earthnet.esrin.esa.it). European systems interoperate with each other and with other such infrastructures associated with an increasing number of international satellite missions exchanging data globally, e.g., NASA's Earth Observing Data and Information System (EOSDIS) (see http://harp.gsfc.nasa.gov/~imswww/pub/imswelcome).
Recent developments are concerned with the creation and vertical interoperation of networked systems at Information Level, i.e., systems supporting services at VACs, data centers and scientific institutions, upstream toward large-scale systems (Data Level) and downstream towards end-users (End-User Level) (e.g., see NASA's "Prototype Earth Science Information Partnerships in Support of Earth System Science," http://www.hq.nasa.gov/office/mtpe/can97mtpe01/can97mtpe01.html).
The emergence of open, network centric middleware, in particular CORBA, and the recent evolution of advanced communication networks provide essential elements for the required underlying infrastructure for distributed services involving all three ground segment levels [Ref. 2, 3].
In order to validate these infrastructures and technologies and to assess their synergy, ESA and the EC, together with European industry and with the involvement of Japanese partners, e.g., NASDA, have initiated a large-scale prototype. It applies a common CORBA based architecture to a limited number of applications, e.g., environmental monitoring, and demonstrates applications developed on top of that architecture with real end-users networked across Europe and Japan. Validation sites are established at Spotimage/Toulouse-France, the Joint Research Center (JRC) of the European Commission Ispra-Italy, and the European Space Agency's Earth Observation Exploitation Center as part of ESA's Directorate of Applications Programs and located at ESRIN, Frascati-Italy. International interconnections are provided to the Earth Observing Center (EOC)/ NASDA, Japan and may be extended to the United States, e.g., Goddard Space Flight Center (GSFC)/ NASA. An advanced satellite/terrestrial based user access network is covering large parts of Europe and the Mediterranean basin.
Figure 2 depicts the various distributed functions implemented through ISIS, the Interactive Satellite Image Server project (see http://aisws22.jrc.it), and constituting a core element of the prototype [Ref. 4]. It illustrates their interconnection through a common bus, based on the Common Object Request Broker Architecture (CORBA) of the Object Management Group (OMG).
The architecture distinguishes the following functional objects:
The EOCF architecture is open to "plug in" multiple instances of functional blocks and to allocate server functions to different geographical locations. This allows for the creation of data, information and application specific modules and for the distribution of them between the parties involved, e.g., data providers, VAC and end-users.
Different degrees of distribution over Wide Area Networks (WAN) are possible. In a traditional scenario (figure 3), only limited functions are made available at the client end, e.g., for display and overlays of geographical information and verification of local attributes. This can be achieved through simple JAVA applets and requires no particular networking effort. WAN protocols can either be http only or include IIOP, the Internet InterORB Protocol.
In an advanced scenario (figure 4), the Information/(VAC) level may serve the application workflow represented by the Application Server module (RAS), which contains the knowledge that EOCF functions to activate as well as of which parameters or algorithms would apply to a specific user request. A minimum level of Quality of network Service is desirable between the VAC location and the data center, to ensure proper workflow control between server functions. An Intranet configuration may be required and IIOP becomes the WAN protocol of choice between VAC and Data Provider premises.
The architecture may also be exploited to effectively distribute functions of processing, cataloguing or integration of geographical information to the VACs, leaving modules for ingest and interfaces to large scale archives at the data provider level (fig.5). Such distribution, however, relies on higher bandwidth interconnections, e.g., to ensure efficient image transfers between the archives at data provider premises and the processing services at VAC. Single image transfers can involve multiple Mbyte of data. Depending on the workflow constraints set by the application server, e.g., fulfillment of an interactive user request within seconds, processing and networking requirements can be advanced. Quality of Service targets need to be balanced in particular against associated network service cost, despite deregulation still a dominant factor guiding the conception of high-volume trans-European information services.
In a federation of systems and services, the tiers of such vertically distributed entities (fig. 3-5) can also interoperate horizontally as figure 6 illustrates.
Largely based on IIOP, data and information flows between the
different elements in such federated architecture relate to
For a number of constellations, a satellite-based network shared by a federation of EOCF and interfacing Data Level systems can be a cost effective solution, in particular for supporting a trans-European federation.
Information level systems, as the distributed system described under 2.1, rely on data level systems in order to identify, order and receive delivery of standard images for ingest into the application architecture.
Data Level systems, e.g., ESA's MUIS or NASA's EOSDIS, are prototyping a common catalogue interoperability protocol, allowing distributed searches across catalogues of different agencies. This functionality is essential for effective identification of standard data sets for subsequent ingestion into Information Level systems. The Catalogue Interoperability Protocol, CIP, allows for the structuring of data sets according to given thematic criteria, e.g., oil slick radar images from the European Remote Sensing Satellite ERS for the Sicily Strait (see http://ceos.ccrs.nrcan.gc.ca/taskteam/cip.html).
CIP as interface to the existing data provider infrastructures enables VAC users to identify, order and ask for ftp-ingestion of standard data sets. A RAS/CIP gateway and a ftp pick-up point connected on the one hand to the Tbytes of archived standard products in the CIP sphere and on the other hand to the ingestion server (IS) provide the required interoperation (see figure 7). Individual orders can result in image transfers with individual images amounting to more than 50 Mbyte, and therefore require considerable network support.
The demonstrator relies on
The following section presents the network prototype infrastructure and how it is and can be applied to support the EOCF for demonstrations.
The interconnection of data centers participating in the demonstrations, i.e., ESA-ESRIN/Frascati, Spotimage/Toulouse, JRC/Ispra, NASDA/Japan takes advantage of a trial infrastructure made available through a co-operating project, GAMMA (see http://www.estec.esa.nl/gamma/gamma.htm). Earth Observation applications, together with other applications, share a network established through a mixed terrestrial-satellite based set up which comprises the use of satellite links at megabit rates between Europe and Japan, and a 2 Mb/s European satellite network, together with a range of terrestrial based networking facilities. Ultimately links via the Atlantic Ocean CANTAT cable to Canada and the United States are planned.
The European-Japan interconnect is depicted in figure 8 with Yamaguchi as the Japanese landing point. Part of the European infrastructure is illustrated with figure 9, showing Leuk/Switzerland as the central node for an Intelsat link to Japan, an interconnection to a national and a European R&D network, and a Eutelsat link to one demonstrator site, ESA/ESRIN in Frascati. This infrastructure maps best on internetworking requirements between Data Provider and VAC premises, in both, the horizontal and vertical plane (see figure 6) and can also be used for ftp data ingest from Data Level system archives into the EOCF Information Level (Figure 7).
Following development and verification in an ESA Technology Research and Development (TRD) activity, a mixed satellite-terrestrial user access and distribution network has been made available. Supporting the EOCF demonstrator, it is comprised of three different elements:
The following network services are offered to the users via the satellite-based infrastructure:
The demonstrator makes use of these network services in mapping them in the most effective way on information service requirements. Three information services related to distributed systems are of particular interest:
The integration of the ESRIN services with the DDSC remains transparent to the accessed service, with the only noticeable difference being the improved quality of network service perceived by the user. The link to the DDSC and the DDSC itself can be seen conceptually as an extension of the ESRIN LAN. Figure 10 shows the different components of the demonstration infrastructure, in particular the LAN-interconnect service between ESRIN and the DDSC (Uplink facility), the Eutelsat link between the DDSC and the user and the return link from the user through DDSC to ESRIN. Data flow through DDSC is transparent.
The DVB/MPEG system provides a trans-European access component, including large parts of the Mediterranean basin (see figure 11).
The following experimental results have been measured during demonstrations:
Television is today the flagship application for communication satellites. The introduction of Digital Television, including a data transmission facility based on the standard known as DVB-MPEG, allows the possibility of handling not only video but also data, thus giving rise to the opportunity to offer a number of data services, broadening the scope of digital TV from mere entertainment to work, education and information tools. These new services can now be launched on a low cost platform such as the digital TV receivers, which will be widely available in the consumer market.
The most promising and interesting application for the extension of the DVB/MPEG digital television is to transport TCP/IP data packets encapsulated in the MPEG data stream, to provide high speed Internet connections to users. This allows for the creation of a "satellite access network" which can represent an alternative to other broadband services comparable to interactive cable-TV networks and ADSL networks.
Because low-cost digital satellite TV equipment available on the market is conceived for receive-only operation, an immediate solution for high speed Internet delivery via satellite is to utilize a hybrid approach, complementing the downstream communications link via satellite, based on the multiplexing of TCP/IP packets in the DVB/MPEG streams, with an upstream link via a dial-up connection to a local Internet Point-of-Presence (POP). Such an approach has been the object of trials in Europe both in DVB and non-DVB compatible framing and is now offered commercially by several service providers. Since the satellite link is intrinsically of broadcast type, an addressing scheme is associated to this type of link that allows implementation of point to point connections as well as multicast/broadcast distribution schemes, optionally protected by encryption mechanisms.
This hybrid configuration can be seen as a step in the direction of fully satellite-based configurations, which will become possible when the first DVB broadcast satellites including transponders suited for interactive operations will start becoming available in the early 1999.
The DVB standard [Ref. 5] includes the MPEG-2 compression algorithms and the definition of MPEG2 Transport Stream [Ref. 6], providing methods to multiplex several video, audio and data streams together. The DVB Data Broadcasting Standard [Ref. 7] defines four possible methods to map IP into a DVB stream. In the most straightforward case, the encapsulation of IP within MPEG packets can be achieved by segmenting the variable-size IP datagrams so that they can fit into the 184 bytes payload of a fixed-size MPEG-2 packet, to which 4 bytes of header are added, so that this sequence of MPEG packets forms a DVB Transport Stream, as shown in figure 12:
The data rates which can be reached with a hybrid satellite set up are well in excess of those available to most users, who access the Internet via modems or ISDN, and are limited by the type of service used as well as by the behavior of the protocols in conjunction with the satellite link characteristics. For the interactive services, the current implementations of TCP limit the maximum data rate on long-delay networks, the maximum theoretical value of the data rate being around 1Mbit/s for a TCP window of 64KB. The multicast and broadcast services, which do not rely on acknowledgements, are only limited by the bandwidth available on the downstream channel and the performance of the hardware on the receiving side.
EOCF aims to enable a wide range of EO applications. Large scale demonstrations of six different applications are being implemented on the common EOCF architecture and validated with selected end-user communities. In the following, the nature of one selected application and its implementation on the application architecture are illustrated.
Oil slicks have become the major risks in the Mediterranean Sea, badly affecting the large tourism and fishing industries, wildlife and marine ecosystems of the countries bordering the sea. Oil slicks accumulate on beaches producing tar balls, tainted sea food, tar stains on boats and clothing, etc. Large slicks can have a long lasting effect which is estimated to persist for up to 10 years. Light oils has toxic effects on fish and shellfish.
Annual traffic in the Mediterranean of ships of more than 100 tons is estimated at more than 220.000. Accidental oil spills, caused by collision of oil tankers and responsible for the largest catastrophes that have occurred, account for only 20% of the total oil slick pollution at sea, whereas, intentional oil spills, due to deliberate ship discharges of bilge and ballast water from oil tankers, unnoticed by media, produce 80% of the total marine pollution for oil slicks. According to the 1990 report of the Environmental Program for the Mediterranean (World Bank and European Investment Bank), about 30% of oil spilled in the Mediterranean accumulates as tar in the beaches of Algeria and Tunisia.
The aim of this demonstration application is to show that Remote Sensing techniques and tools are already available to identify and monitor oil slicks. One of the most promising Remote Sensing techniques to date is the use of satellite radar sensors ERS-1/2 SAR, resulting in different sea surface reflection patterns in case of oil slicks.
The OPM application allows End Users to interactively acquire information on oil slicks detection with two different data extraction methodologies being offered:
The first methodology is based on an automatic processing procedure that takes into account:
In this case the maps are computed by superimposing different layers and applying selection by several criteria.
The second methodology is based on:
That is, a user will be able to use the detection of possible oil spots by means of algorithms, or recognize the oil presence visually.
The user will be able to access the following information:
Once the user has selected a ROI, oil slick icons are displayed and the user can select a sub ROI area in order to see images.
Reflecting the chosen approach to the oil slick detection, i.e., how and by whom the slick was detected, the system will display "algorithm," DP or VAS oil slick icons in different colors (Fig. 13).
The user can select a sub ROI area by means of
In the same way, the user can modify the time selection.
The next step will be to show the images, so the user will select the resolution that can be (in pixels):
Subsequently the images extraction is initiated
Apart from the visual detection of the oil slicks, End Users are also interested to know additional information on the slicks such as dimensions, speed, movement direction, time forecast in reaching the coasts, etc.
Figure 14 illustrates the interaction between the user client (RAC) and the central services entry point (RAS) containing all the knowledge of the oil-slick application. It demonstrates the RAS support to the ROI selection at the client and the RAS control of the subsequently triggered image processing on the selected ROI within the processing function (IPS).
In the given example, once identified by the RAS as registered oil-slick application user
After a first selection, e.g., of an image icon
Following the use of additional vector information
Following further RAC-RAS interaction,
Figure 15 provides an example of an implementation detail, showing a CORBA based JAVA client application. The Web Server function is focused on the data transfer of its available resources to the client side, e.g., for downloads of Client ORB classes. Most RAC-RAS interaction is performed directly through Java Client ORBs. This option has become attractive since the recent introduction by OMG of a CORBA-Java mapping and COTS availability, e.g., IONA OrbixWeb 3.0.
Interactions between the client and the application server can very well be served through asymmetrical hybrid terrestrial/satellite systems as the demonstrated MPEG/DVB configuration. The same system may be suited to also support transfers between other components of the CORBA bus, provided they are of asymmetrical nature, e.g., transfer of archived images to a processing module at a VAC premises.
A Version 0 of the prototype went online in November 1997 and has been demonstrated in a traditional configuration (figure 2) with the OPM application at a number of end-user locations in the Mediterranean region. Prior to that, a number of technical verifications of the MPEG/DVB network service (fig.10) had already taken place, and the Europe-Japan Intelsat link had been put in place. The data center interconnect at ESA-ESRIN was activated in January 1998 (fig.8).
At the time of writing, further European data centers, e.g., Spotimage/Toulouse, are scheduled to be inserted during spring 1998 at the same time as the interconnection to NASDA in Japan will be activated.
By the time of the INET98 Conference, Version 1 demonstrations are expected to be in their final phase with the full topology as described before being applied to six selected applications. At the same time, an 18 month follow-on initiative is expected to be kicked-off extending the trails to U.S. users, deepening demonstrations of the access network infrastructure, and to further advance on the distribution of EOCF functions over Wide Area Networks (figures 3 - 5). At the same time, a first initiative aiming at the standardization of EOCF in the OMG Business Object Architecture is expected to be launched.
The initiative will remain open to possible collaborations with partners in the Internet community interested in WAN high volume data exchange and service distribution over CORBA.
[Ref. 1] Trans-European Research Application Domains - Research Network Applications, the Space Sector and Earth Observations, Newsletter of ERCIM, the European Research Consortium for Informatics and Mathematics, - Special on Research Networking in Europe - No. 31 - October 1997, Hermann Ludwig Moeller
[Ref. 2] The use of CORBA in Earth Observation Application Systems, Committee on Earth Observation Satellites (CEOS) - Working Group on Information Systems and Services (WGISS) - Access/Network Subgroup (AS/NS), Earth Observation and Geo-Spatial Web and Internet Workshop, 17th - 19th of February 1998, Salzburg, Austria, Andrea Cicarelli, Luciano Foti, Sergio Vizzari, Hermann Ludwig Moeller [Ref. 3] European Earth Observation Application System Prototype, CODATA - Conference on Scientific and Technical Data Exchange and Integration, December 15-17, 1997, Bethesda, MD, THE UNITED STATES, Hermann Ludwig Moeller
[Ref. 4] The Interactive Satellite Image Server Project, International Society for Photogrammetry and Remote Sensing - ISPRS joint workshop "From Producer to User," October 1997, Boulder, Colorado, THE UNITED STATES, Hermann Ludwig Moeller
[Ref. 5] ETSI ETS 300 421, Digital broadcasting systems for television, sound and data services; Framing structure, channel coding and modulation for 11/12/Ghz satellite services
[Ref. 6] ISO/IEC, Generic Coding of Moving Pictures and Associated Audio: System, (MPEG-2 System Specification), ISO/IEC 13818-1, November 1994
[Ref. 7] TS/EN 301 192 DVB Data Broadcasting Standard
Related online resources:
The projects contributing to the EOCF demonstrator are funded under Programs of the European Commission:
The authors would like to acknowledge the contribution of the industrial, academic, and user partners in the initiatives supporting the demonstrator, i.e., Advanced Computer Systems (I), Alenia Aerospazio(I), Cap Gemini Italia (I), CSA(IRL), DASA-Dornier (Germany), EC-JRC-SAI, ESA-ESRIN, Etnoteam (I), Finsiel (I), France Telecom (F), ITC (NL), Matra Systems and Information (F), Newtec (UK), Nuova Telespazio(I), RAI-Centro Ricerche (I), RSC(DK), Swisscom (CH), Spotimage (F), VitroCiset (I), CGS (AU).
Special thanks to Jerome Bequignon (ESA), Neil Corlett (JRC), Andrea Cicarelli (ACS), Luciano Foti (CGI), Jean Francois Gallet (MS&I), Kevin Galligan (ESA), Lauren Garnier (MS&I), Marc Gorman (ESA), Yves Henaff (MS&I), Corinne Hinlopen (JRC), Fabrizio Jemma (Eurimage/ESA), D. Meehan (ESA), P. Meuret (Swisscom), B. Collini-Nocker (CGS), Tommaso Panetti (CGI), Sergio Vizzari (MS&I), Stefano Zatti (ESA).