by Tillmann Mohr*
The first launches of artificial satellites beginning with Sputnik on 4 October 1957 by the Soviet Union and with Explorer I by the United States of America on 2 January 1958 heralded a new era of Earth observation. A few years later, on 1 April 1960, the first meteorological satellite, TIROS–1, was launched, providing the first-ever pictures of the distribution of clouds, images previously undreamed of (Figure 1). Although the spacecraft operated only for 78 days, meteorologists worldwide were ecstatic over the pictures of Earth and its cloud cover.
|Figure 1 — TIROS-I, first weather satellite image, 1 April 1960. The picture shows the New England Coast of the United States of America and Canada’s Maritime Provinces, north of the St. Lawrence River.|
Thus began the satellite revolution, which was to forever change how people observed the planet. These advances in computer and space technology at the end of the 1950s and the beginning of the 1960s stimulated the creation of the WMO World Weather Watch, and ultimately the WMO Global Satellite Observing System. The Global Satellite Observing System has had unparalleled success in bringing together the countries of the world to scientifically collaborate and transform how meteorologists study the planet and the atmosphere.
Getting the initial boost
In June 1962, two outstanding scientists, Soviet academician V. Bugaev and American H. Wexler, prepared a report that highlighted the enormous potential of satellite data for both the operational and research meteorological community, and they proposed a new structure, the World Weather Watch (WWW). Submitted by WMO to the United Nations, the report was a response to the Resolution 1721 (XVI) of the General Assembly of the United Nations of 20 December 1961 on “International Co-operation in the Peaceful Uses of Outer Space”. Based on their report, the General Assembly requested in its Resolution 1802 (XVII) of 1962 that the development of meteorology and atmospheric science “be for the benefit of all mankind”.
As a result, the WWW concept was further elaborated and the idea of a Global Atmospheric Research Programme (GARP) emerged during the following years. In 1963, the Fourth WMO Congress approved the concept of the WWW with its sub-systems: Global Observing System (GOS), Global Data Processing System and Global Telecommunication System. And in May 1967, the Fifth Congress approved the WWW Plan and Implementation Programme.
Creating a space-based sub-system
In the first plan, GOS comprised five conventional observing components and the meteorological satellites. At this time, only polar-orbiting satellites existed, and the system needed only one or two of such satellites. In addition the plan under the heading “Meteorological Satellites” made a very important statement: “The WMO should assist in bringing about co-ordination of the satellite programmes of individual countries (or groups of countries)” (Figure 2).
|Figure 2 — The WMO Global Satellite Observing System, 1961|
During the following years, two important technical developments took place that would underscore the international coordination to come. On 28 February 1966, ESSA-2, which was the first operational polar-orbiting meteorological satellite equipped with an operational real-time picture transmission, the so-called APT, was launched by the United States. It allowed the countries of the world to receive in real time twice a day imagery data in their area of reception (Figure 3). In December of the same year, a technology demonstration communication satellite ATS-I flew in geostationary orbit with a meteorological payload. This satellite successfully confirmed the potential of frequent satellite observations (every 30 minutes) from geostationary orbit – an orbit 35 800 kilometres above the equator that maintains the same position relative to Earth. One year later, ATS-III was launched, the first geostationary satellite with three channels in the visible spectrum, which for the first time enabled colour images (Figure 4).
|Figure 3 — ESSA‑8, cyclone over the North Atlantic, composite of two images, 29 March 1970||
Figure 4 — ATS-III, 18 November 1967
SSEC, Madison, Wisconsin, USA
These advances paved the way for significant progress in the development of GOS and GARP, specifically in the planning for the First Global GARP Experiment (FGGE). This experiment, conducted by a wide range of organizations, studied the entire global atmosphere in detail for a period of one year (December 1978 to November 1979). Both the upgraded WWW Plan and Implementation Programme for 1972 to 1975, as well as the planning documents for the FGGE, contained new requirements for the satellite configuration of GOS and the observing system of the FGGE. Two or three polar-orbiting and four geostationary satellites were now required.
In the early 1970s, the United States launched its Synchronous Meteorological Satellites SMS‑A and SMS‑B as forerunners of its Geostationary Operational Environmental Satellites (GOES), which were stationed at 60 West and 140 West longitudes, respectively. At the same time the European Space Research Organization (ESRO) — which later became the European Space Agency (ESA) — and Japan, started their geostationary satellite projects to fill the gaps over 0 degrees and 120 East longitude in time for the FGGE.
Coordinating global satellites
When the Europeans and the Japanese announced their separate satellite programmes, it was realized that it was time to coordinate the different activities. A meeting was convened in Washington, D.C., on 19 September 1972 with participants from ESRO, Japan and the United States. WMO and the Joint Planning Staff for GARP attended as observers.
The meeting identified several areas for coordination, in particular for the collection of fixed and moving platforms and for the so-called WEFAX to transmit image data in analogue format. In 1973, at the second meeting, the group adopted the name Coordination of Geostationary Meteorological Satellites (CGMS). WMO, representing the user community, and the Soviet Union, when it announced its plan to set up a geostationary satellite project, also became members of CGMS.
The CGMS satellite operators were able to implement within a few years a constellation of five geostationary satellites in time for FGGE. The United States provided three, one over the Western Atlantic, another over the Eastern Pacific and a third over the Indian Ocean. Europe stationed one over 0 degrees and Japan one over 140 East longitude. This was a tremendous achievement.
India joined CGMS in 1979 after the decision to place an imaging radiometer on its series of geostationary telecommunication satellites, INSAT, the first of which was launched in 1983. EUMETSAT and China came on board in 1987 and 1989, respectively.
When EUMETSAT and China announced in the late 1980s their intentions to fly not only geostationary satellites but also polar-orbiting ones, it became obvious that there was a need to extend the coordination to include polar-orbiting satellites. Recommended by the WMO Executive Council Panel of Experts on Satellites in October 1989, CGMS agreed to incorporate this new task and adopted a new chapter by 31 January 1992. The group changed the name accordingly to Coordination Group for Meteorological Satellites. The Panel of the Executive Council further recommended extending the coordination to include the extraction of meteorological parameters and contingency planning.
Extracting meteorological parameters
During the first 10 years after the launch of TIROS-1, the images were applied in weather forecasting primarily by improving surface and upper air analyses with qualitative information on cloud texture, extent and formation. Such qualitative work helped to determine types of clouds, cloud coverage and the location of frontal systems and centres of cyclones and tropical storms. The first quantitative data derived were the cloud-tracked winds from the geostationary satellites.
Only with additional instruments, such as the first vertical sounders in the late 1960s, the extraction of quantitative parameters became possible. Now, satellite data produce more than 100 different parameters. They range from vertical humidity profiles and sea-surface temperatures, to cloud top heights, snow cover and ozone distribution. They are today the most significant input to numerical weather prediction models and other applications. Total inputs for numerical models on a single day exceed several million. The overwhelming improvement in numerical weather prediction models during the last 20 years is due to the input of satellite data, notwithstanding advances in theoretical meteorology and computer technology.
CGMS has played a significant role in the coordination of the extraction of data. It directed, rather early, its attention to the enhancement of the utilization and the improvement of the quality of satellite products. Under its auspices, the International TIROS Operational Vertical Sounder Study Conference has been meeting since 1983. This group was instrumental in developing and distributing common software packages for temperature and moisture profile retrieval algorithms to be used by the meteorological community. The Working Group on Cloud Motion Vectors, established in September 1991, focused their efforts on the science, operational development and use of atmospheric motion winds from geostationary and, since 2004, also from polar-orbiting imagery data. In 2000, a Working Group on Precipitation was added.
Making contingency plans
At the request of WMO to deal more actively with the important issue of contingency — what to do when things go wrong — a first meeting of the Working Group on Global Contingency Planning was called in October 1992 and was attended by EUMETSAT, Japan, the United States and WMO. Contingency planning is vital in light of the critical role satellites play in worldwide observations and the high costs of launching and maintaining them. The working group discussed that the only realistic way forward was to build global contingency planning based on regional plans using the “help your neighbour” philosophy. The possibility of redeployment of satellites was ruled out due to financial and technical constraints.
The “help your neighbour” philosophy had been tested several times over the years. When the data collection service onboard METEOSAT-2 failed in 1984, GOES-4 was moved over the middle of the Atlantic. The next positive demonstration took place in 1991 in response to a USA request when the only fully operational geostationary satellite, GOES-7, was left to cover the United States. METEOSAT-3 was moved to 50 West longitude by August 1991 and from February 1993 until May 1995, it moved again to 75 West longitude. As a result of this successful and very positive experience, EUMETSAT and the United States in July 1995 signed a long-term agreement on the backup of operational meteorological satellites (Figure 5).
|Figure 5 — Hurricane Andrew, METEOSAT-3, 24 August 1992|
Three other regional contingency activities have occurred. In the autumn of 1992, Japan provided support in the Pacific region for data collection of Regional Data Collection Platforms, and in January 1998, EUMETSAT moved its METEOSAT-5 over the Indian Ocean to 63 East longitude when the Russian geostationary satellite GOMS-Electro N1 failed. When the Japanese GMS-5 stopped operating, the United States helped out with GOES‑9 from May 2003 to July 2005 over the Eastern Pacific. This experience led to Japan and the United States signing a long-term agreement in February 2005 to guarantee continuous geostationary satellite coverage over East Asia and the Western Pacific.
When China and EUMETSAT established their respective polar-orbiting programmes in the 1990s, it became necessary to extend the contingency planning to polar-orbiting satellites. Based on the then-basic WMO requirement for two satellites in polar orbit, one in the morning and one in the afternoon orbit, a constellation of four polar-orbiting satellites was required to meet the contingency needs. Each of the satellites in the morning or the afternoon orbit would be backed up by one satellite.
Since then, based on the very positive impact of the sounding data from more than two polar-orbiting satellites in numerical weather prediction models, the number of satellites required by WMO in polar orbit has been increased from two to four. As a consequence, the discussion on contingency planning for polar-orbiting satellites is continuing. The main issues are backup arrangements and equator crossing times.
Reviewing GOS and further integration
At the end of the 1990s, the need for a review and update of GOS, including its space-based sub-system became evident. In 1999, CGMS reviewed the compliance of the space-based component of GOS in post-2010 time frame. It concluded that the upgraded component should not only include operational meteorological but also research and other Earth observing satellite systems.
Since 2000, the Consultative Meetings on High-Level Policy on Satellite Matters, involving the heads of the operational and research and development satellite operators and senior officials of WMO, have provided a forum for high-level policy discussions. It has paved the way for the inclusion of research and development Earth observing satellites into the space-based sub-system of GOS after approval by the fourteenth WMO Congress in June 2003.
Since that time, the number of satellites contributing to the system has increased significantly. Now, a fleet of satellites provides data to different user communities, in the field of meteorology, oceanography and climate (Figure 6).
|Figure 6 — The WMO Global Satellite Observing System, 2009|
WMO has placed emphasis on user communities since the 1980s, when it initiated the definition of user requirements by its programmes. The requirements subsequently included meteorology, hydrology, climatology, oceanography, climate and global change-related disciplines. The process also took into account the requirements for education and training. CGMS responded to this from 1995 onward with the establishment of a system of Regional Meteorological Training Centres, upgraded to centres of excellence in satellite meteorology and evenly distributed around the world by the continuing support of some of its member space agencies.
Over the years, several research and development space agencies have become members of CGMS (CNSA, CNES, ESA, JAXA, NASA and ROSCOSMOS). As early as 2001, the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific and Cultural Organization joined CGMS to represent the oceanographic community.
As a result, by 1 January 2004, WMO established a Space Programme, which together with the Consultative Meetings and the CGMS, pushed several initiatives ahead. The Integrated Global Data Dissemination System of WMO, based on the regional data dissemination systems of the operational CGMS members China Meteorological Administration, EUMETSAT and the United States National Oceanic and Atmospheric Administration, has been operational since the end of 2006. In April 2007, the Global Space-based Inter-Calibration System began its operation as a component of the space-based sub-system of GOS and, in the same year, the concept of a global network of centres for Sustained Coordinated Processing of Environmental Satellite Data for Climate Monitoring was approved by potential participants and started its pilot phase in 2009.
In February 2005, the Global Earth Observing System of Systems (GEOSS) was approved by its participating countries. Responsible for the implementation is the Intergovernmental Group on Earth Observations. Within this system, WMO leads or participates in the weather, water, climate and disaster Societal Benefit Areas of GEOSS and is a sponsor of component systems of GEOSS. The space-based sub-system of the GOS forms a component of the Space Segment of GEOSS.
Looking to the future
The development of GOS from a one-satellite system in 1967 to a constellation of a fleet of operational and research and development satellites is one of the most outstanding successes of WMO and its Members contributing to the system. The system serves not only the observational requirements of weather forecasting as it did in its first years but also a wide range of applications meeting the requirements of hydrology, climatology, oceanography and disaster prevention.
In the coming years, the emphasis will have to move to cover also the needs of climate change and global change-related disciplines. An international space observing architecture for the operational monitoring of climate change will have to be established. WMO is well suited to facilitate this endeavour. It can be anticipated that in a few years this architecture will be part of the space-based sub-system of the new WMO Integrated Global Observing System (WIGOS), which strives to provide a comprehensive global observing system that integrates diverse surface and space-based observations in the service of society.