The Meteosat System

December 1998 TABLE OF CONTENTS

PREFACE ...... 5 Performance monitoring...... 21-22 Telecommunications ...... 22 System frequencies ...... 23 1 OVERVIEW...... 6 User frequencies ...... 23

Introduction ...... 6 Objectives...... 7 4 THE GROUND SEGMENT...... 24 Meteorological satellites ...... 7 Future programmes ...... 7 Ground segment facilities ...... 24 Meteosat history ...... 11 Primary Ground Station ...... 25 The programmes ...... 12 Overview ...... 26 Meteosat services ...... 12 Antennas ...... 26 Earth imaging ...... 13 Monitoring and control...... 26 Image dissemination...... 13 Equipment ...... 26 Data collection and distribution ...... 13 DCP Retransmission System...... 26 Meteorological Data Distribution...... 13 Back-up Satellite Control Centre...... 26 Meteorological and climatological The Mission Control Centre ...... 27 products ...... 13-14 Overview ...... 28 Archiving and retrieval...... 14 Core Facility...... 28 The MOSAIC concept ...... 14 Monitoring and control...... 28 Image processing...... 28 Dissemination ...... 28 2 OPERATIONAL ASPECTS ...... 15 User Station Display Facility...... 29 Data Collection System...... 30 System planning ...... 15 Meteorological products extraction...... 30 Satellite orbits ...... 15 Archive and retrieval facility...... 30 Routine operations...... 15-16 Other facilities ...... 30 Eclipse operations...... 16 The main communications links...... 30 Contingency planning...... 16 Back-up Ground Station...... 30 Satellites...... 16 Foreign satellite data relay station...... 30-31 Ground segment facilities ...... 16-17 MDD up-links...... 31 Joint contingency plans ...... 17 Land-Based Transponder...... 32 Support to INDOEX ...... 17 User systems...... 32 Support to MAP...... 17

5 IMAGE PROCESSING...... 32 3 THE SATELLITES...... 17 Overview ...... 32 The spacecraft...... 17 Data pre-processing ...... 32 Structure ...... 17 Rectification ...... 32-33 Power supply...... 18 Attitude and orbit control ...... 18-19 The radiometer ...... 19 6 METEOROLOGICAL PRODUCTS...... 33 The telescope...... 19 Scanning concept ...... 21 Segmentation ...... 33 Detectors ...... 21 Segment processing...... 34 Passive cooler...... 21 Meteorological products ...... 35

...... 2 Cloud motion winds...... 35-36 10 IMAGE AND PRODUCT Sea surface temperatures ...... 36-37 ARCHIVE ...... 55 Cloud analysis ...... 37 Upper tropospheric humidity...... 37 System description ...... 56 Clear sky radiances...... 37 Historical data ...... 56 Cloud top heights...... 38 Retrieval services ...... 56-57 Climate products...... 39 Climate data set ...... 39 ISCCP ...... 39 11 GLOBAL COORDINATION...... 58 GPCP ...... 39 Product quality...... 39 CGMS ...... 58 Quality control...... 39 Coordinated services...... 58-59 Calibration...... 39 Mutual support ...... 59 Quality monitoring...... 39-40 Geostationary satellite systems ...... 59 Distribution and archiving...... 40 Polar satellite systems ...... 60 EUMETSAT data policy...... 40

12 METEOSAT INTO ORBIT...... 61 7 IMAGE DISSEMINATION ...... 41 Satellite launches ...... 61 Dissemination system ...... 41 Launchers ...... 62 High Resolution Image dissemination ...... 42 Launch site ...... 62 Description...... 42 Launch services ...... 62-63 Primary Data User Stations...... 44 Launch activities ...... 63 WEFAX dissemination...... 45 Description...... 45 Secondary Data User Stations ...... 49 13 THE EUMETSAT USER SERVICE ...... 64 Operational aspects ...... 49 Registration ...... 49 Background...... 64 Operational information ...... 49 Addresses and points of contact ...... 64

8 DATA COLLECTION SYSTEM...... 50 14 EUMETSAT PUBLICATIONS...... 64

Data Collection Platforms ...... 50 Meteosat Data Collection System ...... 50 List of Figures...... 65 The International DCS ...... 51 List of Tables...... 65 DCP Retransmission System ...... 52 Glossary ...... 66

9 METEOROLOGICAL DATA DISTRIBUTION...... 53

The requirement ...... 53 The MDD system ...... 53 Up-link sites...... 54 User stations...... 54

...... 3 Figure 1 Colour enhanced Meteosat image. Full earth disc images are generated each half-hour, day and night.

...... 4 PREFACE

This document serves as a general introduction to the facilities and services provided by EUMETSAT through its Meteosat satellite system. It is a publication in the Technical Documentation (TD) series and provides an overview of the complete system, including both the ground segment and space segment, as well as operational aspects and the services and products of the system.

The basic service of Meteosat is the provision of images at 30 minute intervals of an area covering all of Europe, the Middle East, the entire continent of Africa, most of the North and South Atlantic oceans and some portions of South America. In addition there are many other supporting services and functionalities which this document seeks to introduce.

An earlier document with a similar name was published by the European Space Agency and describes the Meteosat system in its initial configuration. That original system served the user community well during the years since the launch of the first Meteosat satellite in 1977, but after nearly two decades of successful operations the time had come to completely update the ground segment. The present document therefore describes the EUMETSAT ground segment as brought into operation in December 1995.

It should be emphasised that, from the point of view of the user, there is a strong degree of continuity with the earlier system. There is of course no change to the satellites themselves and the basic products and services formerly provided through ESOC are also continued, with enhancements where appropriate.

...... 5 1 OVERVIEW

This chapter recalls the reasons why climatology, continuing the two funda- continuity of the Meteosat system and the meteorology and climatology are so mental concepts of data exchange and availability of data over nearly one quarter important to the global economy and the international cooperation which have been of the planet. The second level of contribution of meteorological satellites to traditional for more than 150 years. They cooperation is on a global scale, which those disciplines. The history of Meteosat provide vital data at frequent intervals over ensures the availability of satellite data is described briefly, and this is followed by wide areas, in the context of the over the entire Earth. a summary of the various Meteosat international cooperation needed to satellite programmes and an introduction ensure adequate worldwide data Meteosat is a European contribution to the to the Meteosat services. coverage. Cooperation exists at two levels. global observing system required for both First at the European level through those meteorology and climatology. The Introduction countries which have come together to following chapters describe both the establish EUMETSAT. This ensures the system itself and its place in the larger, Meteorological satellites have become worldwide context. essential for both meteorology and

Figure 1.1 The EUMETSAT headquarters, which was inaugurated in 1995 and contains the Mission Control Centre

...... 6 Objectives found to be due to human activity, major an equatorial ring of geostationary actions may have to be taken to reverse meteorological satellites which fly at an The primary objective of the Meteosat the trends. altitude of 36,000 km and circle the Earth system is to provide cost-effective satellite at the same speed as the Earth itself data and related services which meet the The variations in weather and climate have rotates. These satellites are effectively requirements of the EUMETSAT Member enormous economic consequences which stationary over one point of the Earth and States. To the greatest extent possible the are increasing as the world population provide images and other data on an system also addresses the requirements grows and becomes more industrialised. almost continuous basis, each satellite expressed by the World Meteorological The need to understand, monitor and covering about one quarter of the Earths Organization. It offers services to all predict the weather and the changing surface. Meteosat is the European countries of the world able to receive the climate is becoming increasingly geostationary meteorological satellite data and is therefore truly international in important. The next section describes how system. scope. satellites contribute to this necessary understanding. Future programmes The data and services are mainly focused on the requirements of operational Meteorological satellites With developments in the accuracy of meteorology, with the emphasis on support numerical weather prediction, the need for to operational weather forecasting. Meteorology and climatology are two more frequent and comprehensive data However, the data are of use for all areas disciplines which require frequent from space has evolved. This has led to of this discipline, including marine, observational data at closely spaced the present work on the Meteosat Second agricultural and aviation meteorology, as locations over the entire globe. Con- Generation (MSG) system. The new well as, for example, climatology and the ventional, surface-based systems can satellites will be spin-stabilised like the monitoring of planet Earth. observe the atmosphere with great current generation, but with many design accuracy but could not, under any con- improvements including a new radiometer Precise and accurate weather forecasts ceivable circumstances, provide global which will produce images every fifteen are of much greater importance than their coverage. By contrast, meteorological minutes, in twelve spectral channels. The use for merely predicting if it will rain or satellites can and do provide the MSG data will help in the swift recognition not during the next hours or days. They necessary global coverage at the required and prediction of dangerous weather have become essential for the transport intervals. phenomena such as thunderstorms, fog industry to ensure efficient and reliable and explosive development of small but operations, for the construction and This became immediately evident with the intense depressions. agricultural industries to schedule first experimental weather satellite, activities which may be affected by launched by the USA into a low earth orbit In cooperation with EUMETSAT, the weather, and by the retail industry to plan in April 1960. For the first time European Space Agency (ESA) is stocks of food and clothing for which the meteorologists could actually see the responsible for the development of the first demand varies according to the weather. distribution of weather systems over the MSG satellite, planned for launch in the The energy industries also vary the surface of the Earth and no longer had to year 2000. available capacity of their plants according rely on inferences from widely scattered to weather-dependent predictions of conventional observations. Within a The lack of observational coverage in parts demands. Accurate weather forecasts are decade the USA had established the two of the globe such as the Pacific Ocean therefore a strong contributor to the classes of meteorological satellites and southern continents has increased the efficiency of the way in which many forming the basis of the systems which importance of polar-orbiting satellites in industries work and therefore a strong have been in operation since the late numerical weather prediction and climate contributor to national economies. 1970s. The first weather satellite was in a monitoring. The EUMETSAT Polar System low earth orbit, the so-called polar orbit. (EPS), now in preparation, is the European The need for climate data also has a Today these satellites fly at an altitude of component of a joint European/US polar strong economic justification. If weather about 850 km, circling the Earth every 100 satellite system. The Metop-1 satellite, patterns change, then agriculture will also minutes. They provide detailed obser- developed in cooperation with ESA and change and this may have a profound vations of the atmosphere, the clouds and planned for launch in 2003, will carry effect, both on individuals and on the the surface of the Earth itself, covering the EUMETSAT instruments. Later satellites economies of nations. If sea levels entire globe twice during each twenty-four in the series will provide a service well into change, expensive coastal defences may hour period. the second decade of the 21st century. become necessary, or populations may have to migrate. Where changes are The polar satellites are complemented by

Figure 1.2a Meteosat visible image - The Meteosat visible channel measures solar radiation reflected from the Earth's surface. The oceans appear as dark areas, while land surfaces are grey and clouds white.

Figure 1.2b Meteosat infrared image - The Meteosat infrared channel measures thermal radiation emitted from surfaces. Dark regions represent warm areas such as the oceans, land surfaces and low clouds. The white areas are cold and correspond to regions of high cloud or ice and snow.

Figure 1.2c Meteosat water vapour image - The Meteosat water vapour channel measures thermal radiation from water vapour in the middle atmosphere. The dark areas on the image correspond to areas of low atmospheric humidity.

...... 10 Meteosat history Austria, joining in late 1993. Under the terms of an agreement signed with ESA in The importance of satellites for both January 1987, EUMETSAT assumed meteorology and more general overall financial responsibility for the environmental issues was quickly realised Meteosat system while ESA continued to throughout the world, leading to the manage the programme and operate the development of satellite systems by those satellites on behalf of EUMETSAT. countries already in possession of, or wishing to establish, a space capability. The agreement between ESA and Europe was no exception and the EUMETSAT covered the period until the development of Meteosat followed an end of November 1995, and as that date initiative by France, which performed the approached it became clear that the first feasibility studies and undertook the funding community should take a more pre-development of the radiometer for a direct responsibility for its satellite systems. new geostationary satellite. By 1972 this In 1991 the EUMETSAT Council took the had been established as a European decision to establish its own independent programme undertaken by eight par- ground segment to replace the system ticipating States of the former European established by ESA in 1977. This new Space Research Organisation (ESRO), system was completed during 1995 and which later became the European Space installed in the new EUMETSAT Agency (ESA). That programme led to the headquarters building, in Darmstadt, launch of the first Meteosat satellite on Germany, coming into operation in 23 November 1977 and so to the start of December 1995, as planned. the successful Meteosat system. Meteosat services have continued without The first satellite provided a faultless interruption since 1981, the operational service for two complete years until the task having been assigned successively radiometer failed in November 1979. By to Meteosat-3, an old prototype satellite this time it had become an established part launched in 1988 in order to ensure of the meteorological observing system continuity, and then to Meteosat-4 and -5. and major efforts were made, not only to From February 1997 until June 1998 launch a replacement satellite as soon as Meteosat-6 was used operationally before possible, but also to establish a Meteosat-7 took over this responsibility. mechanism for the operational long-term continuation of the satellite series.

The second satellite was launched in 1981, the same year in which an Intergovernmental Conference of 17 European countries was convened to consider the matter of long-term continuity. The Conference decided that a new specialised operational organisation was needed and, in a second session in 1983, agreed on the Convention for the future EUMETSAT organisation. At the same time, the Member States of the European Space Agency agreed to initiate the construction of three further satellites which could, in due course, be handed over to EUMETSAT.

By 1986 the EUMETSAT Convention had been ratified and entered into force, initially with 16 Member States, the 17th Member,

...... 11 The programmes Programme (MOP) and from 1987 this was since been agreed to extend MTP conducted as a joint programme, under Operations until 2003 to provide an The Meteosat system is defined by a the overall authority of EUMETSAT. This overlap with the next generation of number of overlapping programmes which programme provided the framework for the satellites (MSG). The current system as establish the respective legal and financial construction and launch of three further defined in this document is therefore frameworks during particular periods. satellites of a slightly modified design, operated within the MTP framework. These programmatic arrangements do Meteosat-4, -5 and -6, as well as the not, in general, affect the user community operation of the complete system from Meteosat services to any great extent, but are often referred 1983 until the end of November 1995. to and are recalled here for the sake of The main service provided by the completeness. Since it had been decided that a new Meteosat system is the generation of generation of satellites would not be images of the Earth, showing its cloud The development and early operation of immediately available by the end of the systems both by day and by night, and Meteosat was covered by a series of ESA Meteosat Operational Programme, the transmission of these images to the programmes until 1983. These ensured EUMETSAT implemented the Meteosat users in the shortest practical time. There the development of the two original flight Transition Programme (MTP), which are several other important supporting models, and of the prototype which was includes provision and launch of a further services summarised in the following later refurbished and flown as Meteosat-3. satellite of the same design (Meteosat-7), sections and described in more detail in the development of a new ground system, later chapters. When EUMETSAT was defined in 1983, and routine operations from December ESA initiated the Meteosat Operational 1995 until the end of the year 2000. It has

Figure 1.3 Schematic of the Meteosat system showing main services

...... 12 Earth imaging Image dissemination anywhere in the world and are supported through the International Data Collection The Meteosat radiometer is the principal Meteosat is equipped with high power System (IDCS), which is coordinated by payload of the satellite. It provides the amplifiers used to transmit processed all of the geostationary meteorological basic data of the Meteosat system, in the earth images and other meteorological operators. form of radiances from the visible and information to user stations located infrared parts of the electromagnetic anywhere within the field of view of The DCP data are distributed by a variety spectrum. These form images of the full Meteosat (Figure 3.3). of means. The Meteosat DCP Retrans- earth disc, as seen from geostationary mission System (DRS) broadcasts DCP orbit. The radiometer operates in three The dissemination schedule is dominated data directly to small user terminals, while spectral bands: by the transmission of Meteosat imagery meteorological data from many DCPs are in all three spectral bands. However, these also transmitted over the Global images are complemented by image data Telecommunication System (GTS) of the 0.45 to 1.0 µm the visible band (VIS), from other geostationary satellites, World Meteorological Organization used for imaging during including the USA satellites GOES-E and (WMO). daylight, GOES-W over the western Atlantic and eastern Pacific, Japans GMS satellite over Meteorological Data Distribution 5.7 to 7.1 µm the water vapour the western Pacific and the Russian absorption band (WV), GOMS satellite over the Indian Ocean. Additional Meteosat telecommunication used for determining the Images from other satellites will be added links are used for the transmission of amount of water vapour as available, so that, with a single receiver conventional meteorological data, in the middle and antenna system, the Meteosat user including observations in meteorological atmosphere, station can acquire images covering most transmission codes and meteorological of the globe. charts containing both data analyses and 10.5 to 12.5 µm the thermal infrared forecasts. This is Meteosats unique (window) band (IR), The satellite carries two independent Meteorological Data Distribution (MDD) used for imaging by day dissemination channels, used to transmit service. The data are transmitted directly and by night and also image data with minimum delay to two to the satellite through three independent for determining the classes of user station. Digital data are up-link sites located at meteorological temperature of cloud transmitted to Primary Data User Stations centres in France, Italy and the UK, and tops and of the ocean's (PDUS), which are intended to serve the received by small user terminals. surface. larger meteorological centres and research centres, while analogue data are Meteorological and climatological transmitted to the less complex Secondary products Earth images are generated at 30 minute Data User Stations (SDUS), widely intervals. Each image is transmitted from implemented in smaller meteorological The Meteorological Products Extraction the satellite to the Primary Ground Station centres as well as in many schools and Facility (MPEF), located in the in Italy and relayed to the central facilities by private individuals. EUMETSAT headquarters, makes use of in Germany for further processing, the digital Meteosat image data to gene- distribution and archiving. As can be seen Data collection and distribution rate a variety of quantitative from the illustrations in this document, meteorological and climatological each image covers a substantial portion Besides its main dissemination channels, products. The meteorological products of the Earth, centred at the sub-satellite Meteosat has a further 66 telecom- include wind vectors obtained through the point, which is over the equator and munication channels used for the relay of automatic tracking of clouds as they move normally at 0o longitude. Using these environmental data from automatic or through the atmosphere. These Cloud images, meteorological features can be semi-automatic Data Collection Platforms Motion Winds (CMW) are of great identified and weather patterns tracked out (DCP). Regional DCPs may be located importance as inputs to the computer to nearly 70o of great circle arc from the anywhere within the Meteosat field of view models used for numerical weather sub-satellite point. The distorted (Figure 3.3) and are served exclusively by prediction, especially over tropical areas perspective introduced by the Earth's the Meteosat Data Collection System where there are few other observations of curvature makes quantitative use of the (DCS), which relays the data through the atmospheric dynamics. data less satisfactory at large distances satellite to the Primary Ground Station for from the sub-satellite point, but quanti- onward distribution. The so-called Inter- The facility also generates several climate tative products are generated routinely for national DCPs are mobile platforms, such products, including the data needed for the distances of at least 60o great circle arc. as ships and aircraft. These can move International Satellite Cloud Climatology

...... 13 Project (ISCCP). Clouds form a vital part receive frequent image data from of the Earth's climate system; they help to Meteosat and from other satellites around insulate the Earth from excessive solar the world. The same antenna can be used radiation during the day and to reduce heat as a DRS terminal to receive environmen- loss from the planet at night. The ISCCP, tal data from data collection platforms to which Meteosat contributes, has been located within the region of interest and systematically storing global cloud can also form part of an integrated MDD coverage parameters since 1983 and is a terminal for the reception of other major resource for climate studies. meteorological data. Furthermore, modern computer workstations or personal These, and other important products, are computer systems can be used to display, described in more detail in chapter 6. store and print all of the data in a cost efficient way. Low cost disk storage Archiving and retrieval systems may be used to provide a local image archive. Many meteorological The final component of the Meteosat centres have all of these facilities, which system is the Meteorological Archive and may be combined into a single integrated Retrieval Facility (MARF) which is also facility. located within the EUMETSAT headquarters in Darmstadt. This facility has been archiving all Meteosat image data and derived products in digital format since December 1995. It provides a comprehensive data retrieval service including on-line access to the data catalogues and other information.

The digital data are written to Digital Linear Tape (DLT), each having the capacity to store several days images. This is a different medium from that used to store images before December 1995 and the same retrieval mechanism cannot be used to directly retrieve the data archived prior to that date. However, the older data, extending back to 1977, remain available and can be retrieved using independent systems. A project to systematically transfer the old data from some 40,000 tapes and cartridges to the newer medium will take some years to complete.

The MOSAIC concept

MOSAIC (Meteosat Operational Systems for data Acquisition and InterChange) is not a separate service but indicates how all of the real-time Meteosat services can be brought together at a user site to provide a consolidated "one-stop- shopping" service, meeting many of the data requirements of small meteorological centres.

A single antenna system may be used to Figure 1.4 The MOSAIC Concept - an integrated user facility

...... 14 2 OPERATIONAL ASPECTS

This chapter describes some of the satellite and this, in turn, was succeeded uneven shape of the Earth, in particular operational aspects affecting the by Meteosat-7 in June 1998. Beyond the location of the deep oceans, which performance of the system. It starts with a Meteosat-7 it is expected that a new causes the gravitational field of the Earth general description of the EUMETSAT generation of satellites will become to depart from a true spherical shape. The launch plans and policies, then briefly operational by the end of the year 2000. effect is as if the satellites were located describes the factors affecting orbital on hills, which they may slide off, or in operation. This is followed by a summary Satellite orbits valleys, where they may remain stable. description of the mode of operation both There are two stable locations in during normal periods and during the Geostationary satellites fly at an altitude geostationary orbit, one of which is over eclipse seasons. The chapter concludes of about 36,000 km over the equator. The the Indian Ocean (the other is over the with a section on contingency planning. operational Meteosat is normally located eastern Pacific Ocean). Meteosat, at 0o close to 0o longitude, while the spare longitude, is on the gravitational slope System planning satellite may be located at 10oE or W, from leading to this "hole" and gradually drifts which positions it can be used occasionally towards the east. The satellite is normally The Meteosat satellites after the pre- for test purposes. These are nominal maintained within a defined box around operational series have a specified lifetime locations but, because of the uneven its nominal location. When it reaches the of five years and carry fuel reserves for shape of the Earth and the gravitational eastern extremity of the permitted box, the orbit station-keeping sufficient for at least influence of the moon and sun, the satellite thrusters are activated and the satellite is six or seven years of normal operations in does not stay precisely at the nominal moved back to the western extremity of orbit. location. There are two major effects, the the box, where the process starts again. gradual increase in satellite inclination, This cycle repeats every few months The EUMETSAT policy is to maintain one which affects the north-south position, and (depending on the current size of the satellite in operation at all times and to satellite drift, which affects the east-west permitted box), but is not expensive in fuel keep a further operable satellite in orbit position. utilisation. While the satellite stays within as an operational back-up. This ensures this box it is compliant with system a high level of reliability in the service. A The inclination of the satellite orbit is specification, and realignment of user new satellite is launched close to the date essentially the small angle between its antennas due to satellite movement is not at which the older of the two satellites orbital plane and the equatorial plane of necessary. already in orbit is expected to exhaust its the Earth. This causes an apparent daily on-board station-keeping fuel. Should a motion of the satellite in a figure of eight Under the terms of an intergovernmental satellite fail before the end of its nominal pattern, centred over its nominal location. agreement, spent satellites must be lifetime, then every effort would be made The maximum excursion north and south ejected from geostationary orbit at the end to launch a replacement as soon as of the equator is the same as that of the of life. A small amount of station-keeping possible. The actual launch date would inclination. While the inclination remains fuel has to be reserved for this purpose. depend on the nature of the failure, the less than 0.3o no action is taken to control Generally, the retired satellites are moved incident investigation and the availability this small movement. However, during the to a slightly higher orbit where they do not of a spare satellite and launch vehicle. lifetime of the satellite the inclination tends interfere with the operation of other to increase, and at intervals it is necessary geostationary satellites and where they A satellite rarely fails completely and there to perform a so-called "north-south may remain indefinitely. may be occasions when there is no single manoeuvre" to adjust the orbital plane of satellite able to provide all of the required the satellite. Routine operations services but there are two or more satellites which each have some North-south station-keeping is expensive The Meteosat system is operated 24 hours remaining functionalities. For such cases in fuel and is often the limiting factor in the a day, every day of the year, so that in the ground segment has the capability to lifetime of the satellite. When the fuel is general the user can expect to obtain the operate a so-called split mission, using two exhausted, the inclination increases full range of real-time operational services or more satellites simultaneously to continuously, at about 0.9o each year, and on a continuous basis. There is a high provide the services normally supported eventually the daily north-south movement degree of redundancy in the ground by a single satellite. makes reception of line data by user system in order to ensure reliable stations difficult. The precise inclination operations. This includes duplicate When EUMETSAT took over operations limits for successful reception of data antennas at the Primary Ground Station at the end of 1995 the operational satellite depend on the location and characteristics in Fucino, parallel communications links, was Meteosat-5, while the in-orbit spare of the individual user stations. via commercial satellite, between Fucino was Meteosat-6. In February 1997 and the central facilities in Darmstadt, and Meteosat-6 took over as operational A further orbital effect is caused by the duplicate computer networks in the central

...... 15 facilities. Redundant components, at the services. Users of the dissemination developed comprehensive contingency central facilities or at the Primary Ground services are informed in advance of such plans which seek to ensure continuity of Station, can easily be brought into use operations by means of administrative data and a proper protection of the when needed, either automatically or messages transmitted through the two investment. through software tools operated by the image dissemination systems. Relevant Mission Controller at the EUMETSAT information is also placed on the Internet. Satellites headquarters. These capabilities lead to a very high level of reliability with few gaps Eclipse operations As previously described, the first level of in operation even for routine maintenance. contingency planning is the policy to In addition to the above, Meteosat maintain a second operable satellite in The operational satellite does require operations are affected for the two eclipse orbit at all times. The satellite may not routine maintenance periodically which periods each year when the satellite always be located in the most suitable may lead to temporary gaps in service if undergoes an eclipse of the sun by the position for immediate use but could no spare satellite is immediately available. Earth. The two periods occur at the spring normally be reactivated up to full On several occasions each year, orbit and autumn equinoxes, and last from operational levels within a few days and station-keeping involves the use of the approximately 1 March to 15 April and from brought to the optimum orbital location thrusters and may disturb a few images 1 September to 15 October. During these within one or two weeks at most. This from time to time until the satellite is eclipse periods the satellite is in the Earths needs to be compared with the alternative restabilised. shadow for up to 70 minutes at around of launching a new satellite after failure of midnight. During the actual eclipse, certain the primary satellite, which might easily Longer periods of data loss may occur satellite functions, including earth imaging take 12 - 18 months, or even more. once or twice a year, especially in the early and all dissemination services, including Therefore the provision of an in-orbit spare stages in the life of the satellite, due to HRI, WEFAX, DRS and MDD, are is a major component of the EUMETSAT contamination of the cold optics by a film interrupted in order to save power. The contingency planning. of ice. The ice comes from water carried DCS is not affected. aloft with the satellite from the humid Ground segment facilities tropical launch site and held in the ther- A secondary effect may occur during the mal blanket material protecting the various eclipse period close to noon, when the sun In order to ensure the safety of the components of the satellite from extremes is precisely in line with the satellite as seen spacecraft there is appropriate of temperature. The ice tends to migrate from the Primary Ground Station. On these redundancy of the key ground segment over periods of time to the coldest part of occasions the reception of images and facilities. If the links to the Primary Ground the spacecraft. This happens to be the DCP messages suffers from interference. Station (PGS), or the PGS itself, should optical system used for the infrared and The dissemination service is suspended fail, then the Back-up Ground Station water vapour channels, which is usually during this time, increasing the power (BGS) could be brought into use maintained at a temperature close to 90 K. available on the satellite for the imaging immediately. The BGS would not provide Initially the contamination can be offset by and DCP services, thereby reducing the any of the user-related services but, by a gain change in the radiometer but effects of interference. A similar effect will relay of telecommands and telemetry eventually the performance is reduced to occur at any Meteosat user station. between the Mission Control Centre and an unacceptable level and it becomes the spacecraft, could keep the spacecraft necessary to decontaminate the system. Contingency planning safe until the problem is solved. Heating the affected optics evaporates the ice film and the radiometer is then allowed As an operational agency EUMETSAT is Similarly, if the Mission Control Centre to slowly cool again. The whole process conscious of the need for reliability of (MCC) itself or the links between the MCC takes about three days, during which service and the continuity of data. If and PGS should fail, there is a Back-up period the split mission capabilities of the Member States make operational use of Satellite Control Centre co-located with the system are usually exploited and the back- Meteosat data then they are entitled to PGS which could be used to monitor and up spacecraft is used for image-taking, expect access to Meteosat data on every control the spacecraft but, again, would whilst the nominal operational spacecraft day of the year on a continuous basis. not provide any user-related services. (which is undergoing decontamination) is EUMETSAT also wishes to ensure that the used for dissemination and the provision massive investment in the space segment The main communications links between of the DCS. - a satellite and its launcher cost more than the MCC and the PGS are also duplicated. MEUR 100 (M$ 130) - is protected and is If the primary channel through a In all cases where any scheduled not wasted through inadequate provision commercial satellite link should fail, there maintenance is to be performed, every in the ground segment. As a consequence is an alternative commercial satellite link effort is made to limit the interruptions to of these concerns, EUMETSAT has capable of supporting the complete

...... 16 3 THE SATELLITES

Meteosat data transmission requirements. High Resolution Imagery will be The Meteosat satellite system is an disseminated from Meteosat-5. Visible example of a very successful European In addition to this duplication of key channel images will be disseminated endeavour. First designed in the early functionalities, an appropriate level of during daylight with IR and WV imagery 1970s, the first model was launched in duplication of workstations and other available day and night. Derived products 1977, and the same design is expected to subsystems is available to enable tasks will be distributed on the GTS and also be in use until at least the end of 2003. to be easily reassigned to alternative archived in the MARF. The image data will The expected 26 years of operational systems in case of need. also be archived in the MARF. service amply justifies the initial development effort. A few relatively minor Joint contingency plans Support to MAP design changes were introduced after Meteosat-3, and it is this updated satellite The value of joint contingency plans From its location of approximately 10oW, specification which is now summarised. between satellite operators was the stand-by satellite, Meteosat-6, will be demonstrated when Europe was able to used to support the Mesoscale Alpine The spacecraft move Meteosat-3 to a new location at Programme (MAP) during the intensive 75oW and operate it as a temporary field phase from August until November The overall size of the satellite is 2.1 replacement for a failed USA satellite 1999. The Mesoscale Alpine Programme metres in diameter and 3.195 metres long. between 1992 and 1995. Following this is an international research initiative Its initial mass in orbit is 322 kg. Additio- initiative, EUMETSAT agreed with its devoted to the study of atmospheric and nal to this dry mass is the hydrazine partner in the USA that such provision hydrological processes over mountainous propellant used for station-keeping, could be reciprocated should a problem terrain. It aims towards expanding amounting to approximately a further 39 kg with Meteosat occur which EUMETSAT knowledge of weather and climate over at the beginning of life. In orbit, the satellite could not solve. In this case a GOES complex topography, and thereby to spins at 100 rpm around its main axis, satellite from the USA could be moved to improve current forecasting capabilities. which is aligned nearly parallel to the around 5oW and operated there by the Earths north-south axis. USA. EUMETSAT would make the Meteosat-6 will be used to provide rapid necessary emergency provision (for scanning over the Alpine region during Structure example, through the use of an old interesting weather features such as the Meteosat, or commercial satellite data buildup of deeply convective clouds. Meteosat is composed of a main cylin- broadcast) for the relay of the GOES During these episodes, up to eight mini- drical body, on top of which a drum-shaped image data to its user community. scans per half-hour slot will be scanned section and two further cylinders are and the resulting images archived in the stacked concentrically (Figure 3.1). The This is an extreme case which hopefully MARF for subsequent transfer to the MAP main cylindrical body contains most of the will never need implementation but serves database. satellite subsystems, including the to illustrate the commitment of EUMETSAT radiometer. Its surface is covered with the to operational data continuity. solar cells which provide the electrical power. Support to INDOEX The cylindrical surface of the smaller During the period from January until May drum-shaped section is covered with an 1998, Meteosat-5 was slowly moved from array of radiating dipole antenna elements. 10oW to 63oE in preparation for the support Electronics within the drum activate the to INDOEX (Indian Ocean Experiment). individual elements in sequence, in This is an international atmospheric field reverse order to the satellite spin sense. experiment with participation from the This subsystem constitutes an European Union, France, Germany, India, electronically-despun antenna whose the Netherlands, Sweden, the UK and the function is to ensure that the main USA. The objective is to analyse the transmissions in S-band are always transport of aerosols and pollutants by directed towards the Earth. The two tropical atmospheric dynamics, their cylinders mounted on top of the drum are evolution, and their interaction with clouds, toroidal pattern antennas for S-band and radiation and climate. The experiment low UHF respectively. started in February 1998 with an intensive field phase taking place in January to April 1999.

...... 17 Power supply

The main cylindrical body of Meteosat features more than eight thousand solar cells. These are mounted on five standard panels, each covering an arc of the body, and one special panel containing the large aperture for the radiometer telescope. The solar cells provide the main electrical power for operating the satellite, although two rechargeable batteries are also available and are used during eclipse periods and for peak power demands.

Attitude and orbit control

The spacecraft has four main (10 N) thrusters and two smaller thrusters rated at 2 N. All are fed by hydrazine propellant contained in three fully interconnected spherical tanks. These are sized to hold enough fuel for at least six years of station- keeping under normal operational conditions but the actual amount of fuel loaded is the maximum which the specific launch situation will allow. This subsystem is used to maintain Meteosats orientation in space, to make small adjustments to its orbit as described on page 15 and to move the satellite to a new nominal location if required for operational reasons.

Two of the main thrusters are mounted with their thrust axes parallel to, but offset from, Figure 3.1 Meteosat the satellite spin axis. They are used for north-south station-keeping for inclination control and as they can generate a torque about the spacecrafts centre of gravity they may also be used to make adjustments to the satellite spin axis. The other two main thrusters are radial thrusters acting with their axes at right angles to the spin axis. They are used for east-west station-keeping and are fired in very short bursts at the correct phase of the satellite spin cycle.

The small vernier motors act in a plane at about 12o to that of the radial thrusters and are also offset from the centre of gravity in opposition to each other. The torques thereby generated are used for spin rate The optical chain of the Meteosat radiometer control.

Figure 3.2a Schematic of the Meteosat radiometer

...... 18 In operation, the thrusters are activated by telecommands transmitted through the Primary Ground Station (PGS). The interval between manoeuvres is typically every three months or so for east-west station-keeping and about every six to eight months for inclination control.

Attitude measurement is achieved by Telescope means of two earth sensors which routinely search for the earth disc as the Primary aperture 400 mm diameter satellite rotates. Each can provide a pulse at the earth-to-space transition and at the Secondary aperture 140 mm diameter space-to-earth transition. In addition, two sun-slit sensors each give one sun pulse Image band VIS WV IR at each revolution of the spacecraft. These Spectral range (µm) 0.45 - 1.0 5.7 - 7.1 10.5 - 12.5 attitude data are transmitted to the PGS every 0.786 seconds to give constant Detector type Si photodiodes HgCdTe HgCdTe information on attitude. They are also used within the spacecraft to activate the image Focal length 3,650 mm 535 mm sampling during each line of earth scan, and for directional control of the Table 3.2.1 Principal characteristics of the Meteosat radiometer electronically-despun antenna.

The radiometer Image Channel Visible Water Vapour Infrared The Meteosat Visible and InfraRed Imager Spectral range (µm) 0.45 -1.0 5.7 - 7.1 10.5 - 12.5 (MVIRI) is a high resolution radiometer (Figure 3.2a) with three spectral bands, Number of detectors 2 (+2) 1 (+1) 1 (+1) and constitutes the main payload of (+ redundant) Meteosat. The instrument allows continuous imaging of the Earth. Radiance Lines per image 5,000 2,500 2,500 data from the full earth disc are acquired during a 25 minute period. This is followed Pixel samples per line 5,000 2,500 2,500 by a five minute retrace and stabilisation interval, so that one complete set of full Instantaneous field of earth disc images is available every half- view at sub-satellite 2.5 km 5 km 5 km hour. point Line duration 30 msec The telescope Line recurrence 600 msec The major feature of the radiometer optical Image duration 25 min system is a scanning Ritchey-Chrétien telescope with a primary aperture of Imaging recurrence 30 min 400 mm diameter and a focal length of 3,650 mm for visible light. The telescope Transmission to ground 333 kbps (normal) 2.7 Mbps (burst mode) is mounted on two flexible plate pivots and the scanning mechanism is a high Table 3.2.2 Earth imaging details precision jack screw driven by a step motor via a gearbox. A series of mirrors is used to collect the incoming visible, infrared and water vapour radiation and to direct the radiation onto the corresponding detectors.

...... 19 Figure 3.2b Scanning concept and distribution of detectors in the focal plane of the radiometer

...... 20 Scanning concept In total there are eight detectors: inward to the satellite body. The cold detectors and cold optics are located at The satellite scans the full earth disc within a redundant pair for infrared imagery, the apex of the inner cone, which is the a 30 minute period. Scanning from east to coldest part of the spacecraft. An west is achieved through the spin of the a redundant pair for water vapour equilibrium temperature is established, satellite. Scanning from south to north is imagery, corresponding to a balance between achieved by small incremental steps in the thermal inputs, for example from insulation pointing of the telescope. At each satellite two redundant pairs for visible imagery. deficiencies and from thermal conduction rotation during the imaging process, the along electrical leads, and thermal outputs, spin clock delivers a signal to the scanning At any given time, one infrared detector, in the form of radiation to space from the motor electronics, which has the effect of one water vapour detector and one pair surface of the cooler. rotating the telescope through an angle of visible detectors will be in operation. of 1.25 x 10-4 radians. Since the detectors are distributed across The inner conical reflector is protected the focal plane of the radiometer their from direct radiation from the sun and By this means, with every rotation of the respective fields of view on the earth scene Earth by the secondary conical reflector, spacecraft, the telescope scans a new line do not coincide but are displaced relative which serves both as a sun shield and as on the Earth approximately 5 km north of to each other. The misalignment due to a further radiator to space. the previous scan line. By successive scan these displacements is corrected by steps, the telescope is made to scan central on-ground image processing Fine tuning of the detector temperature to through 18 degrees in the direction from before the images are distributed to users. 90 K is ensured by a heater and thermistor south to north, generating a full earth scan Figure 3.2b indicates the effective fixed on the detector plate, giving a of 2,500 lines in 25 minutes. The telescope displacement for one Instantaneous Field constant temperature which ensures then retraces to its starting position in 2.5 Of View (IFOV) in all available channels constant spectral sensitivity. During the minutes, during which time a black body of the satellite. eclipse season the satellite passes into the calibration of the infrared and water vapour Earths shadow once a day and the ther- channels may be performed. A 2.5 minute The size of the IFOV at the Earths surface mal equilibrium of the cooler takes some stabilisation period allows for nutation of any detector is determined by the field time to stabilise, leading to slight variations damping before the next scanning period of view of the detector and the distance to in effective gain during these periods. is initiated. Thus the radiometer generates the Earths surface. In the case of the a new image in three spectral bands during visible detectors, the field of view is 0.07 At rare intervals, heaters are used to raise every half-hour period. mrad, giving an IFOV of about 2.5 km at the temperature of the detectors far above the sub-satellite point. The infrared and the normal operating temperature. This is The image radiance data are sampled water vapour detectors have a field of view in order to evaporate ice or other electronically 2,500 times as the telescope of 0.14 mrad, yielding an IFOV of about contaminants from the cooler and cold sweeps out each east-west line. 5 km at the sub-satellite point. detector area and, as mentioned earlier, Consequently, the infrared and water results in a loss of image-taking capability vapour images each comprise 2,500 lines The output of each detector passes for about three days. of 2,500 picture elements (pixels). The through an amplifier in which the gain may visible channel is sampled 5,000 times be varied by a factor of 1.2 in 16 separate Performance monitoring rather than 2,500 times, and there are two steps. This feature, used occasionally visible detectors in operation. The visible when the infrared and water vapour A mechanism is provided within the image therefore comprises a total of 5,000 detectors become contaminated by ice, radiometer to enable in-flight monitoring pixels in each of 5,000 lines, the lines allows a rather coarse control to maintain of the infrared and water vapour detector interleaved between the two detectors. the output of the detectors. performances.

Detectors Passive cooler The black body mechanism consists of two black bodies located on opposite sides of The optical visible, infrared and water The infrared and water vapour detectors the main optical path, one kept at ambient vapour signals are converted into and associated cold optics are cooled to temperature of about 290 K as a cold analogue electrical signals by the various the required operating temperature of 90 K reference and the other heated to about detectors. These are divided into two or less by a passive cooler filling the 50 degrees higher, as a warm reference. subsets: the visible detectors in one set, southern face of the satellite (the end of Two mirrors are mounted on a turning kept at ambient temperatures, and the the cylinder opposite to the antennas). The bracket which can be rotated by a torque infrared and water vapour detectors in the cooler consists of two concentric black motor, such that, in one extreme position other, cooled to below 90 K. cones with the apex of each pointing the infrared and water vapour detectors

...... 21 will look at the cold reference, and in the indication of calibration trends. The system system and thus serving to help calibrate other extreme position both detectors will cannot provide information on absolute the entire radiometer, not just the look at the warm reference. When the calibration because during calibration the detectors. turning bracket is at rest in its central main radiometer optics are not in the location, normal earth and space view optical path. These on-board calibration techniques are imaging operations can be carried out. supplemented by vicarious calibration, The view of cold space obtained during using surface-based measurements, The temperatures of the two black bodies normal imaging operations serves as a performed within the Meteorological are telemetered to the Primary Ground practical supplement to the on-board Products Extraction Facility (MPEF), as Station together with the corresponding calibration mechanism. This has the described in chapter 6. black body imaging values, to give an further benefit of using the entire optical

Telecommunications

Figure 3.3 Telecommunications coverage area

...... 22 System frequencies buffering of each line of image data during the earth scan so that it may be transmitted The spacecraft has a comprehensive during the much longer period (20 times telecommunications capability which can as long) when the radiometer is viewing be described under two headings: the space. If this on-board buffering is disabled system frequencies used for raw image then an alternative direct transmission reception, telemetry, telecommands and would be used at a data rate of 2.7 Mbps. for spacecraft orbit determination, described in this section; and the user All of these transmissions are intended for accessible frequencies, described in the point to point transmissions between the following section. satellite and the EUMETSAT PGS or BGS and are not broadcast for general use. For S-band in the range 2098 - 2110 MHz and security and copyright reasons the L-band in the range 1675 - 1690 MHz are transmissions are not available to the user the frequency bands used for system- community and are strictly reserved for related functions. system use.

These include: User frequencies

the transmission of the raw image from Data transmissions to user stations form the spacecraft to the Primary Ground part of the essential service of Meteosat Station in Fucino, and the frequencies used are, of course, available to registered users. the transmission of telemetry data from the spacecraft and telecommands to the The L-band is for user-related functions, spacecraft, including the following frequencies required to receive the specified Meteosat the transmission of DCP reports from the service: spacecraft to the Primary Ground Station, 1691.0 MHz WEFAX analogue image dissemination and the the up-link of image dissemination data DCP Retransmission from the Primary Ground Station to the System (DRS), spacecraft, 1694.5 MHz HRI digital image the up-link of MDD data from a maximum dissemination, with a of four ground stations, few WEFAX transmissions, the ranging signals transmitted between the Primary Ground Station in Fucino, 1695.605 - the spacecraft and the Land-Based 1695.935 MHz Meteorological Data Transponder (located in French Distribution, with up to Guiana), used for determination of the four channels spaced precise location of the satellite in orbit. at 30 kHz.

Housekeeping telemetry data is also In addition, Data Collection Platforms may repeated in S-band, within the range 2200 be given access to one of the 66 up-link - 2300 MHz, but this redundant link is channels in the UHF band between 402.0 maintained only as a back-up for and 402.2 MHz with 3 kHz channel emergencies and is not usually used. separation. A channel and precise time slots for data transmission are assigned The normal data rate of the raw image data to each individual DCP when registration from the spacecraft to the Primary Ground is accepted. Station is 333 kilobits per second (kbps). This is achieved through on-board

...... 23 4 THE GROUND SEGMENT

The Meteosat ground segment was almost totally renewed during 1995 and brought into operation under the direct control of EUMETSAT by December 1995. This chapter describes this system. Ground segment facilities

The Meteosat ground segment consists of a number of major components at different locations. These include:

the Primary Ground Station (PGS), used for all normal communications with the spacecraft,

the Mission Control Centre (MCC), where the complete system is monitored and controlled, and all data processing is undertaken,

the major communications facilities, which connect the PGS in Italy with the MCC in Germany,

a Back-up Ground Station (BGS), used in emergencies for monitoring and control of the spacecraft,

the Lannion facility, used to up-link image data from satellites other than Meteosat,

the up-link sites for the Meteorological Data Distribution (MDD) service, used to broadcast meteorological data through Meteosat,

the Land-Based Transponder (LBT), used for orbit determination,

the user facilities, located at user sites and under the direct control of the relevant users.

These components are described in the following sections.

Figure 4.1 Block diagram of the Meteosat system

...... 24 Primary Ground Station

Figure 4.2 Meteosat antennas at the Fucino Primary Ground Station

...... 25 Overview processed image dissemination, the Data In addition to this DRS activity, all DCP Collection System (DCS) and for messages received at the PGS are The Meteosat Primary Ground Station monitoring the Meteorological Data transmitted to the MCC for further (PGS) is established in Fucino, Italy. It is Distribution (MDD) service. In addition, in processing and distribution, depending on a facility fully owned by EUMETSAT, but order to support the INDOEX service (as the requirements of each operator. located within a commercially operated described in chapter 2) a third slightly centre which includes a major antenna smaller antenna was installed. The Back-up Satellite Control Centre farm serving many satellite systems. The antennas are situated within a few tens of actual site is in a wide valley in the metres away from a building used Also located at the PGS is a Back-up mountains some 150 km east of Rome. exclusively for the Meteosat equipment. Satellite Control Centre (BSCC) established as a functional extension of the The PGS serves as the main channel of Monitoring and control MCC in Darmstadt. In an emergency it communications with the Meteosat could be used in stand-alone mode to satellites and is an essential component The control of the PGS is actually monitor and control the spacecraft and the of the Meteosat system. The separate executed by a local monitor and control PGS, as well as to perform all essential Back-up Ground Station (BGS) in Weil- system located in Fucino and interacting flight dynamics activities. It is not designed heim, Germany, can be used in emer- with the MCC in Darmstadt. The PGS can to support the Meteosat user services but gencies for satellite control purposes, but operate in two different modes: remotely, does ensure the safety of the spacecraft only the PGS has the operational under the control of the MCC; or through until the problem is solved. capability to support the main user use of the system consoles in Fucino. This services, handling the raw image flexibility ensures maximum reliability in The BSCC can also be used in parallel transmissions from the satellite, and case of problems. with the MCC to operate the PGS and to transmitting the processed images back monitor the spacecraft. through the satellite to the users. The PGS Equipment also uniquely supports many other user- related functions and has the capability to The Fucino PGS is fully equipped to act as the Back-up Satellite Control Centre handle two complete Meteosat spacecraft, (BSCC), in the event of severe problems with additional redundancy of key at the Mission Control Centre (MCC) in components. The only exception to this the EUMETSAT headquarters or failure of philosophy is the support for the DCS, the main communications links between since it is envisaged that only one the MCC and PGS. spacecraft would support this service.

To accomplish these vital tasks a All of the 66 DCP channels can be considerable amount of redundancy is supported simultaneously, with primary incorporated in the station which, to a great and back-up DCS systems. extent, can function completely automatically. No operating staff are normally DCP Retransmission System required at the PGS; engineering support is available for maintenance purposes only Whilst most of the Meteosat data during normal working hours, while normal processing is performed at the MCC in operations are supervised by the MCC in Darmstadt, one service is conducted Darmstadt. entirely within the PGS, namely the DCP Retransmission System (DRS). DCP Antennas messages received in the PGS are selected according to a pre-defined list Two fully steerable 13.2 metre diameter and are then transmitted directly from the parabolic antennas (Figure 4.2) are PGS to the spacecraft in the gaps between located at the PGS and used exclusively the transmission of individual WEFAX to support all communications with image dissemination formats. This Meteosat. Each antenna is capable of normally ensures the delivery of DCP supporting all the transmissions and data messages within four minutes of reception required for one Meteosat observation to any user having a DRS data spacecraft and is used for telemetry and reception terminal. telecommands, raw image reception,

...... 26 The Mission Control Centre

Figure 4.3a The Mission Control Centre

...... 27 Overview operated by a shift team of two controllers: Image processing the Satellite Controller and the Ground The Mission Control Centre (MCC) is a Segment Controller. Apart from the control function, a primary dedicated facility incorporated in the task of the Core Facility is to process the operations wing of the EUMETSAT Monitoring and control image data in real-time. Raw images are headquarters building in Darmstadt, received from the Primary Ground Station Germany. Dedicated communications Meteosat monitoring and control functions and processed line-by-line to remove links connect it to the Primary Ground are executed within the Core Facility on a image imperfections. In particular, the data Station in Fucino and to the Back-up series of linked computer workstations, from the various on-board sensors are Ground Station in Weilheim. The MCC is each supporting standard display facilities realigned by resampling in order to make the core of the Meteosat ground segment. used by the human operators. They the image from each set of detectors The entire system is controlled from the display the necessary data using multiple coincide with the other images. At the MCC and this is also where all of the display windows on one screen to provide same time, the sampling removes the central processing is conducted. Facilities the maximum amount of information in the slight perturbations caused by the are installed for the monitoring and control most effective way. Display windows can movement of the spacecraft, thereby of the main components of the Meteosat be selected according to the focus of rectifying the image so that it appears to system, including the spacecraft, the activity at any given time and can easily come from the nominal location of the Primary Ground Station, the main be remapped or duplicated to other spacecraft. Adjustments to the individual communications links and the MCC itself. monitors to ensure the maximum flexibility data values are made according to Additional facilities are used to generate of operation. calibration information, then the image is meteorological products from the passed to the dissemination computers for Meteosat image data, to archive the The basis for the activity is the operations immediate relay to users and to the images and products, and to monitor the plan which governs the routine cycle of meteorological computers for further end-to-end performance of the system operations and is monitored using these processing. Additional details are given in from the point of view of an end-user. consoles. Routine spacecraft commands chapter 5. are stored in the computer system and Core Facility transmitted automatically in accordance Dissemination with a pre-defined schedule. Non-routine The Core Facility of the Mission Control commands are transmitted in accordance The dissemination of Meteosat images is Centre provides the required monitoring with pre-defined procedures. The also prepared in the Core Facility of the and control facilities as well as basic image transmission of the command sequences Mission Control Centre using dedicated processing, dissemination and the central and the telemetry from the spacecraft are workstations. Processed images are cut tasks of the Data Collection System. The all displayed on the consoles, colour into individual formats ranging in size from facility is based on networks of powerful coded according to the status of the activity the full earth disc to segments covering computer workstations interconnected or result. Many hundreds of parameters Europe or smaller areas. These formats through high speed local networks. There are monitored for each spacecraft and, are prepared according to a pre-defined are two independent processing chains, where any parameter exceeds pre-defined schedule for the two Meteosat dis- each capable of supporting the processing thresholds, an audible alarm is sounded semination channels and sent back down load from one spacecraft. In addition there and the parameter shown in distinctive the communications links to Fucino for up- is a development system for testing colours. link to the spacecraft and thence enhancements to the system and which transmitted to the users. The aim is to can also be used as a basic back-up The configuration of the spacecraft and of make the processed image data available configuration. The main system incorp- the ground segment can also be shown to the users with the minimum of delay. orates around 26 operational workstations, on the monitors, with mimic displays Priority is given to the European sectors, able to keep two spacecraft in full showing which of the redundant for which the processing is completed and operations and maintain a third in stand- components are in active use and which dissemination started within three minutes by mode. are available in stand-by mode. The of the completion of image acquisition. system permits reconfiguration of both the Transmission of the image covering the The total computer processing power is spacecraft and the ground station under full earth disc starts four minutes later, and substantial, actually exceeding the main- software control from the consoles. This the full earth imagery data are normally frame-based systems which it replaced. It enables remote operation and control of fully available on the users computer is arranged in a flexible way which can be the Primary Ground Station in Fucino. systems within a maximum of 20 minutes readily reconfigured in case of need but from the completion of image acquisition. obviating the need for a permanent shift Further details of the dissemination of computer operators. The facility is process are given in chapter 7.

...... 28 User Station Display Facility to know if there is a problem with the local transmitted data. By this means the system terminal or with the central facilities. operators can, at any stage, be aware of The dissemination of processed images Accordingly, a complete User Station any problem in the complete system and is the primary function of the Meteosat Display Facility (USDF) is co-located with take immediate action to rectify the system and is accomplished strictly the Core Facility. The USDF has its own situation. according to a pre-defined schedule independent antenna and receiving matching user requirements. The system, together with a display system operation of the central service is (Figure 4.3b), so that it can independently monitored by the Core Facility of the monitor the final results of the image Mission Control Centre but there may be dissemination system. The received rare occasions when the disseminated images from both communications images may be subject to some distortions channels are displayed on monitors and or errors which are not readily detected are used as a final check on quality. The by the mission monitoring computers. details of the received data are also monitored by the USDF computers and Alternatively, the system at a user site may passed back to the Core Facility for itself have problems and the user needs analysis and comparison with the

Figure 4.3b A user display screen used for monitoring image reception

...... 29 Data Collection System the Meteosat archive. the users, which would have to be suspended in an extreme case for the The Data Collection System is also Archive and retrieval facility duration of the emergency. operated and monitored within the Mission Control Centre, in the Core Facility. The Meteorological Archive and Retrieval Foreign satellite data relay station Messages from Data Collection Platforms Facility (MARF) is the final component of (DCP) are received in the Primary Ground the MCC. It includes dedicated computer The satellite ground station facilities Station from the 66 Meteosat com- systems for receiving the image data from owned and operated by the French munications channels and transmitted the Core Facility and from the meteorological service in Lannion have immediately to the MCC in Darmstadt. Meteorological Products Extraction Facility been associated with the Meteosat system There they are compared with the master and archives all data on digital optical since the start of operations in 1977. list of expected DCP reports and disks. Equipment is available to provide EUMETSAT provides and maintains processed and distributed as appropriate. images to users in both digital and facilities at Lannion for the relay of image This is performed entirely automatically. photographic form in a variety of formats. data from additional satellites, to Malfunctions of the DCP, such as those complement the Meteosat images DCPs which report outside the expected Other facilities transmitted from the PGS. The primary frequency range or assigned time slot, are requirement is to relay images covering reported to the DCP owner and the The main communication links the western part of the Atlantic and the message itself may be suppressed from Americas. These images are obtained further dissemination. There are three The two main components of the Meteosat from the USA geostationary satellite methods of onward dissemination, the ground segment are the Mission Control known as GOES-E, which is usually primary method of distribution being the Centre, located in Darmstadt, Germany, located at 75oW. A large antenna at previously-mentioned DCP Retrans- and the Primary Ground Station, located Lannion receives image data directly from mission System (DRS). The other methods in Fucino, Italy. They are connected by GOES-E at three-hourly intervals. The are through the Global Telecommunication high speed data communication links to images are then reformatted on the System (GTS) of the World Meteorological enable the necessary transmission of data Lannion computers into the same format Organization (WMO), which is used to between them. Two independent links via as the normal Meteosat imagery. Trans- transmit environmental data to commercial satellites are provided in order mission then takes place from Lannion to meteorological services throughout the to ensure system reliability. Each has a users through the Meteosat spacecraft, world, and via the Internet. capacity of 640 kbps and a bit error rate exactly as if the transmission was of better than 1 in 108. The terminals for this Meteosat imagery. Meteorological products extraction service, including the necessary antennas, are located directly at the EUMETSAT Images from the Japanese GMS satellite, Another facility located within the Mission headquarters and at the Primary Ground located at 140oE, are received at Lannion Control Centre is the Meteorological Station. at three-hourly intervals using con- Products Extraction Facility (MPEF). This ventional land-based communications comprises another network of dedicated Back-up Ground Station systems, and are also up-linked to workstations which receives processed Meteosat as if they were Meteosat images. images from the Core Facility and uses In the unlikely event of a complete system Similar arrangements have been them, together with ancillary data, to failure at the PGS, or of a complete failure established for geostationary image data extract quantitative meteorological and of the main communications links between over the Indian Ocean now that a satellite climatological products. The powerful the MCC and PGS, it would still be is on station there (Meteosat-5, in support workstations have a windowed user necessary to control the spacecraft to of INDOEX, as described in chapter 2). interface similar to the other systems in ensure their safety. This would be the Mission Control Centre. The operators established through use of the Back-up Lannion thus contributes an essential use these consoles to monitor the Ground Station (BGS) located in Weilheim feature of the overall Meteosat system. progress of the automatic processing of in Germany. This facility is not owned by The Meteosat user station needs only a the image data and the dissemination of EUMETSAT and is not dedicated to single antenna and receiver to receive the final products. Processing takes place Meteosat operations, but an agreement is frequent images of most of the world. This within the hour following image reception in place for its use in an emergency to capability is vital for checking the analysed and most of the meteorological products communicate with and control the fields of global numerical prediction are distributed to the meteorological spacecraft. Control would continue to be models used in operational weather community over the GTS. The products, performed from the MCC in Darmstadt. forecasts. It is also vital for aviation including especially those of value for The BGS does not include a capability for meteorology, since the images can be climatology, are also stored indefinitely in provision of a full operational service for used to brief the air crews starting the

...... 30 long intercontinental flights which now where meteorological data are readily span half the globe without stopping. available. These stations are located in the meteorological centres in Toulouse MDD up-links (France), Rome (Italy) and Bracknell (UK).

The Meteorological Data Distribution Each of the up-link stations has a (MDD) service is a contribution by transmitter and antenna system and EUMETSAT to the Global Telecom- operates autonomously, transmitting munication System of the WMO. Its meteorological data on a free-flow purpose is to distribute vital meteorological schedule. The MCC can monitor data to WMO members, particularly in transmissions and can also initiate test those regions of the world where transmissions through the Meteosat PGS conventional communications are but is not otherwise responsible for the inadequate. MDD consists of four indepen- routine operation of the MDD up-links. dent dissemination channels on Meteosat, each of which can transmit data at 2,400 bps, and the corresponding up-link stations. Three up-link stations have been implemented by EUMETSAT at centres

Figure 4.4 Main system data flows

...... 31 5 IMAGE PROCESSING

Land-Based Transponder The raw images as initially transmitted from compensation is made for minor imaging the satellite are not in the most convenient system imperfections. The amplitude The Land-Based Transponder (LBT) is format for the end-user and are subject to response of the two visible channels is part of the system used to determine the variations which need to be adjusted. This also normalised to the same levels. position of the satellite in orbit by means is achieved through the on-ground image of ranging operations. Ranging signals processing, which is designed to ensure Rectification transmitted from the PGS are transmitted that the end-user has access to the best by the satellite back to the PGS (this is possible product in an easy to use format. No geostationary satellite stays precisely known as two-way ranging). The LBT can This aspect of the central ground at the nominal location. Meteosat is no also receive the same signals and send processing is described in the following exception, and in normal operation may them back to the PGS via the satellite text. be allowed to deviate by up to 1o of latitude (four-way ranging). The precise timing of and 1o of longitude from its nominal these sequences is established at the PGS Overview location. The spacecraft attitude with and transmitted to the MCC for use in orbit respect to the Earth's axis also varies and determination. A series of such Meteosat image processing is conducted these variations cause undesirable measurements, normally made at three- in two stages. First, the raw image is changes in the image perspective. hourly intervals, is needed to establish received at the Primary Ground Station in Variations in spin rate and the instant of accurate orbit information. Fucino and is subject to preliminary pre- line start also affect the image. All of these processing before transmission to the variations make the images appear The LBT consists of a parabolic 4.6 metre MCC in Darmstadt. This ensures a deformed with respect to a reference antenna and an equipment cabin, common format before transmission. The image which would be observed from the designed for continuous unattended pre-processing is completed within the nominal location under nominal operation in a tropical environment. It is Core Facility of the MCC, to ensure that conditions. These deformations occur located near Kourou, in French Guiana, the data are in the most suitable form for between images and, to a lesser extent, South America. further use, removing and compensating within one image. They make it much for the artifacts inherent in the radiometer harder for the user to locate individual User systems and satellite characteristics. scene features in terms of latitude and longitude and make it impossible to create In order to make use of the Meteosat Data pre-processing successful image sequences to be viewed systems, the user has to obtain the as animations. The rectification process necessary facilities. Images can be Image processing starts when individual is the means by which such effects are received on either a Primary Data User lines of raw image data arrive at the PGS removed. Station (PDUS) or a Secondary Data User in Fucino. The raw image might be affected Station (SDUS). Use of the Meteorological by variations in the satellite spin rate and The deviation of the actual image from the Data Distribution service, or the DCP by, in rare cases, the use of satellite data ideal reference image is known as the Retransmission System (DRS), requires transmission in the high speed burst mode deformation. This is calculated for specific an MDD or DRS terminal, respectively. instead of the nominal stretched data rate. points within each image by means of a More than 400 registered PDUS and These variations are eliminated at the mathematical model describing the orbit approximately 2000 registered SDUS are PGS and the image data are transmitted and attitude variations of the spacecraft. in operation. In addition, there are about in a standard format to the MCC. At this It is updated by means of measurements 115 MDD user stations in use. There are stage the data are still in the original line- made on each image as it is received, approximately 105 DCP operators by-line format as sampled by the including the automatic determination of operating almost 1400 platforms. spacecraft radiometer. Each line is the horizons and the location of key composed of 48-bit words containing landmarks. There is a feedback process All of these facilities are operated entirely interleaved visible, infrared and water from this stage to the image acquisition at the responsibility of the respective vapour data, corresponding to one line process, whereby the sampling start times users. EUMETSAT does not provide user scan of the Earth by the radiometer. are adjusted to ensure that subsequent facilities but can provide a list of the many Housekeeping telemetry data are included images are centred in the image frame to commercial Meteosat equipment in the line data. the maximum extent possible. suppliers. Within the MCC the first task is to The deformation vectors are then used to demultiplex (i.e. separate) the raw image resample the original image data, using data into the different radiometric channels. two-dimensional interpolation, to The individual data elements are adjusted determine the value of all the pixel to a common calibration standard and a elements corresponding to the nominal

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