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Ocean observation and international cooperation
Space Policy 15 (1999) 23 — 25
Ocean observation and international cooperation Raymond Zaharia Programme d+Occeanographic Spatiale, CNES, 2 Place Maurice Quentin, 75039 Paris cedex 01, France
Abstract This article reports on the types of effects changes in the oceans can have on the Earth’s atmosphere and climate and on progress in monitoring and understanding these effects with particular reference to the French—US Topex-Poseidon satellite. It discusses the types of results that are now becoming available and describes some of the future satellites that are set to continue Topex—Poseidon’s work. This article was first published in Elsevier’s Nouvelle Revue d’Aeronautique et d’Astronautique, No. 3, May—June 1998. 1998 E¨ditions scientifiques et me´dicales Elsevier, Paris
1. The Topex-Poseidon experience
2. Monitoring the oceans in 2000
Topex-Poseidon is a space oceanography satellite, developed and operated under the terms of a cooperative agreement signed by CNES (Centre National d’Etudes Spatiales) and NASA (National Aeronautics and Space Administration) in 1987. This radar altimetry satellite which provides the data used for the study of marine currents, ocean topography and also the state of the sea, has been delivering results of major scientific significance since its launch in 1992. The satellite has enabled observations, with an unprecedented level of accuracy, of different phenomena related to variations in the level of the oceans and has also shown our capability to forecast certain climatic events. This was the case in May 1997 with respect to the particularly intense El Nino phenomenon. While the Topex-Poseidon satellite has exceeded its nominal lifetime, after six years in orbit, a new satellite, Jason-1, which is smaller (weighing less than 500 kg) but which has the same level of performance, is currently being developed by CNES and NASA for a launch date which has been set for May 2000. Apart from the Topex-Poseidon programmes and Jason-1, space oceanography activity is expanding rapidly. The scientific perspectives which it has opened for the study of the global climate, but also, in the coming years, for the operational implications of forecasting ocean conditions, are of vital importance.
One of the major problems facing humanity today is the role played by the oceans in the evolution of the Earth’s climate and environment. The oceans carry and exchange enormous quantities of elements (water vapour, carbon dioxide, etc.) or energy (heat, kinetic energy) with the atmosphere. In the past, the oceans’ average level has dropped by about 100 m. Their mass is about 300 times that of the atmosphere and they have a heat storage capacity which is 1200 times as great. In addition they contain 70 times more carbon. The oceans’ levels fluctuate over all scales of time and space, from a few hours to a few hundred years and from a few kilometres to several thousands of kilometres, thus greatly affecting the Earth’s environment. Swells, cyclones and tides, whose effects on the marine environment are well known, were some of the first phenomena which could be directly observed. Another famous example of the influence of the oceans on the environment is provided by the major currents on the Western edge, such as the Gulf stream in the North Atlantic or the Kuroshio in the North Pacific. The ocean also undergoes seasonal variations related to the varying intensity of winds and to cooling or solar heating of the water during different seasons. There is a direct relationship between oceanic seasons and atmospheric seasons, with, however, a time shift of about three months, because of the time taken by ocean water masses to react to atmospheric changes (this is why
0265-9646/99/$ — see front matter 1998 E¨ditions scientifiques et me´dicales Elsevier, Paris PII: S0265-9646(98)00041-1
24
R. Zaharia / Space Policy 15 (1999) 23—25
the oceanic summer occurs in autumn). This seasonal cycle may itself be disturbed by unusual events. The resulting imbalance may then have significant effects on the climate and hence on the socioeconomic activities of human beings. This is the case for the El Nin o phenomenon following the severe weakening of the trade winds in the equatorial Pacific area. The transfer of hot water masses towards the east and the wave systems which they cause result in a thorough perturbation of the climatic system in the Pacific Basin (droughts in the east, rainfall in the west), but also on a global scale via the upper layers of the atmosphere which travel around the globe. This is why such anomalies are also observed over other ocean basins. These few examples show how difficult it is to understand the ocean environment, its interaction with the atmosphere (and with emerged land masses) and hence its consequences for the global climate. Great progress has been made over the past 30 years, in particular owing to the development of new observation tools — satellites — which offer the possibility of a global, continuous and homogeneous vision of the oceans. During the same time, new, more efficient techniques were developed for in-situ measurements. The successive stages of the ‘observe, understand, predict’ approach were thus achieved in a relatively short time owing to this new information. Numerical models are of great importance here. They alone can be used for a horizontal, vertical and temporal interpolation of the observed phenomena and their extrapolation in the future. Highresolution models of the global ocean are currently being developed, based on more regional modelling experiments. With respect to chaotic phenomena, observations are first of all necessary in order to achieve a better description of the physical complexity involved, then to initialize and regularly ‘adjust’ the trajectories of models. Such an integrated approach, combining numerical models, space observations and in-situ measurements, opens up the possibility of operational oceanography, capable of providing realistic forecasts of the dynamics of ocean masses (known as oceanic circulation) on the global or regional scale for periods from a few weeks to a few months. Future ocean/atmosphere-coupled models will then enable us to make realistic climate forecasts over several months. The ‘space observations’ aspect of such an integrated system are based in particular on the dedicated satellite Topex-Poseidon. This satellite measures the level of the sea to an accuracy of about one centimetre. This sea-level parameter is extremely sensitive to variations which affect oceanic circulation and the corresponding energy and matter which it transports. Topex-Poseidon, which has completed its sixth year of successful operation in orbit (it was launched in August 1992), is the result of an outstanding cooperation between CNES and NASA which began more than 10 years
ago. Its measurements are used by more than 200 teams of scientists around the world and are combined with results provided by other instruments (altimeters, scatterometers and radiometers on the ERS (European Remote Sensing Satellite) and NOAA (National Oceanic and Atmospheric Administration) satellites). Noteworthy results, based on this indispensable integrated approach, and stimulated by a large cooperation with the international scientific community, have already been achieved or are about to be achieved. They include: (1) knowledge of the state of the ocean some three to four weeks ahead of time for the benefit of commercial shipping, offshore platforms, ocean currents and eddies for fishing fleets, as well as navies; (2) the use of ocean/ atmosphere- coupled models to observe and forecast ‘abnormal’ climatic events; (3) ocean weather forecasting for coastal areas (for studies of erosion, installing of public works or buildings, pollution scatter, whether permanent or accidental); (4) the monitoring of variations in mean sea level — by extending the six years of high precision Topex-Poseidon measurements which are already available, this monitoring will make it possible to use various models for long-term evolution of the climate in an attempt to find answers to basic questions such as the rate of global heating, the role of carbon dioxide emissions and the regulatory role of the ocean, etc.
3. Upcoming space programmes New satellites will be launched in the near future. In May 2000, Jason-1 will take over from Topex-Poseidon. Like its predecessor, this dedicated satellite is being built as a joint effort by France and the USA. It will be placed in orbit at the same time as NASA’s TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite, by a Delta-2 rocket for a double launch. Jason-1 falls into the mini-satellite category ((500 kg), but will nevertheless offer the same outstanding levels of performance as Topex-Poseidon: its dedicated mission will make it possible to measure the topography of the ocean and the variations caused by the marine currents. This information will then be used as an accurate reference enabling the best advantage to be taken of all other radar altimeter observations, such as those made by ERS or, in the future, by ENVISAT (Environmental Satellite). Other satellites for observing the ocean, the environment or the climate are being built, namely ENVISAT, METOP (Mete´orologie Ope´rationnelle) and ADEOS 2 (Advanced Earth Observing System), which will be launched in the years to come. Their measurements of ocean topography, but also of temperatures and surface winds, will be an indispensable multi-sensor and multisample complement to existing means.
R. Zaharia / Space Policy 15 (1999) 23—25
Along with this incredible international armada for observing planet Earth, operational networks for in-situ measurements (such as those planned for Ifremer’s Coriolis project) and high-resolution global ocean models, suitable for operational use, will be implemented (in particular the GODAE (Global Ocean Data Assimilation Experiment) project, supported by CEOS (Committee on Earth Observation Satellite) on an international level and the MERCATOR inter-establishment project
25
in France). This range of means combined with ongoing research efforts, and in particular, in France, those of CNRS (Centre National de la Recherche Scientifique)/ INSU, SHOM (Service Hydrographique et Oce´anographique de la Marine) and ORSTOM, should lead in time to a truly operational service for ocean observation and weather forecasting by organizations such as EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites), Meteo France and NOAA.
Ocean observation and international cooperation Raymond Zaharia Programme d+Occeanographic Spatiale, CNES, 2 Place Maurice Quentin, 75039 Paris cedex 01, France
Abstract This article reports on the types of effects changes in the oceans can have on the Earth’s atmosphere and climate and on progress in monitoring and understanding these effects with particular reference to the French—US Topex-Poseidon satellite. It discusses the types of results that are now becoming available and describes some of the future satellites that are set to continue Topex—Poseidon’s work. This article was first published in Elsevier’s Nouvelle Revue d’Aeronautique et d’Astronautique, No. 3, May—June 1998. 1998 E¨ditions scientifiques et me´dicales Elsevier, Paris
1. The Topex-Poseidon experience
2. Monitoring the oceans in 2000
Topex-Poseidon is a space oceanography satellite, developed and operated under the terms of a cooperative agreement signed by CNES (Centre National d’Etudes Spatiales) and NASA (National Aeronautics and Space Administration) in 1987. This radar altimetry satellite which provides the data used for the study of marine currents, ocean topography and also the state of the sea, has been delivering results of major scientific significance since its launch in 1992. The satellite has enabled observations, with an unprecedented level of accuracy, of different phenomena related to variations in the level of the oceans and has also shown our capability to forecast certain climatic events. This was the case in May 1997 with respect to the particularly intense El Nino phenomenon. While the Topex-Poseidon satellite has exceeded its nominal lifetime, after six years in orbit, a new satellite, Jason-1, which is smaller (weighing less than 500 kg) but which has the same level of performance, is currently being developed by CNES and NASA for a launch date which has been set for May 2000. Apart from the Topex-Poseidon programmes and Jason-1, space oceanography activity is expanding rapidly. The scientific perspectives which it has opened for the study of the global climate, but also, in the coming years, for the operational implications of forecasting ocean conditions, are of vital importance.
One of the major problems facing humanity today is the role played by the oceans in the evolution of the Earth’s climate and environment. The oceans carry and exchange enormous quantities of elements (water vapour, carbon dioxide, etc.) or energy (heat, kinetic energy) with the atmosphere. In the past, the oceans’ average level has dropped by about 100 m. Their mass is about 300 times that of the atmosphere and they have a heat storage capacity which is 1200 times as great. In addition they contain 70 times more carbon. The oceans’ levels fluctuate over all scales of time and space, from a few hours to a few hundred years and from a few kilometres to several thousands of kilometres, thus greatly affecting the Earth’s environment. Swells, cyclones and tides, whose effects on the marine environment are well known, were some of the first phenomena which could be directly observed. Another famous example of the influence of the oceans on the environment is provided by the major currents on the Western edge, such as the Gulf stream in the North Atlantic or the Kuroshio in the North Pacific. The ocean also undergoes seasonal variations related to the varying intensity of winds and to cooling or solar heating of the water during different seasons. There is a direct relationship between oceanic seasons and atmospheric seasons, with, however, a time shift of about three months, because of the time taken by ocean water masses to react to atmospheric changes (this is why
0265-9646/99/$ — see front matter 1998 E¨ditions scientifiques et me´dicales Elsevier, Paris PII: S0265-9646(98)00041-1
24
R. Zaharia / Space Policy 15 (1999) 23—25
the oceanic summer occurs in autumn). This seasonal cycle may itself be disturbed by unusual events. The resulting imbalance may then have significant effects on the climate and hence on the socioeconomic activities of human beings. This is the case for the El Nin o phenomenon following the severe weakening of the trade winds in the equatorial Pacific area. The transfer of hot water masses towards the east and the wave systems which they cause result in a thorough perturbation of the climatic system in the Pacific Basin (droughts in the east, rainfall in the west), but also on a global scale via the upper layers of the atmosphere which travel around the globe. This is why such anomalies are also observed over other ocean basins. These few examples show how difficult it is to understand the ocean environment, its interaction with the atmosphere (and with emerged land masses) and hence its consequences for the global climate. Great progress has been made over the past 30 years, in particular owing to the development of new observation tools — satellites — which offer the possibility of a global, continuous and homogeneous vision of the oceans. During the same time, new, more efficient techniques were developed for in-situ measurements. The successive stages of the ‘observe, understand, predict’ approach were thus achieved in a relatively short time owing to this new information. Numerical models are of great importance here. They alone can be used for a horizontal, vertical and temporal interpolation of the observed phenomena and their extrapolation in the future. Highresolution models of the global ocean are currently being developed, based on more regional modelling experiments. With respect to chaotic phenomena, observations are first of all necessary in order to achieve a better description of the physical complexity involved, then to initialize and regularly ‘adjust’ the trajectories of models. Such an integrated approach, combining numerical models, space observations and in-situ measurements, opens up the possibility of operational oceanography, capable of providing realistic forecasts of the dynamics of ocean masses (known as oceanic circulation) on the global or regional scale for periods from a few weeks to a few months. Future ocean/atmosphere-coupled models will then enable us to make realistic climate forecasts over several months. The ‘space observations’ aspect of such an integrated system are based in particular on the dedicated satellite Topex-Poseidon. This satellite measures the level of the sea to an accuracy of about one centimetre. This sea-level parameter is extremely sensitive to variations which affect oceanic circulation and the corresponding energy and matter which it transports. Topex-Poseidon, which has completed its sixth year of successful operation in orbit (it was launched in August 1992), is the result of an outstanding cooperation between CNES and NASA which began more than 10 years
ago. Its measurements are used by more than 200 teams of scientists around the world and are combined with results provided by other instruments (altimeters, scatterometers and radiometers on the ERS (European Remote Sensing Satellite) and NOAA (National Oceanic and Atmospheric Administration) satellites). Noteworthy results, based on this indispensable integrated approach, and stimulated by a large cooperation with the international scientific community, have already been achieved or are about to be achieved. They include: (1) knowledge of the state of the ocean some three to four weeks ahead of time for the benefit of commercial shipping, offshore platforms, ocean currents and eddies for fishing fleets, as well as navies; (2) the use of ocean/ atmosphere- coupled models to observe and forecast ‘abnormal’ climatic events; (3) ocean weather forecasting for coastal areas (for studies of erosion, installing of public works or buildings, pollution scatter, whether permanent or accidental); (4) the monitoring of variations in mean sea level — by extending the six years of high precision Topex-Poseidon measurements which are already available, this monitoring will make it possible to use various models for long-term evolution of the climate in an attempt to find answers to basic questions such as the rate of global heating, the role of carbon dioxide emissions and the regulatory role of the ocean, etc.
3. Upcoming space programmes New satellites will be launched in the near future. In May 2000, Jason-1 will take over from Topex-Poseidon. Like its predecessor, this dedicated satellite is being built as a joint effort by France and the USA. It will be placed in orbit at the same time as NASA’s TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite, by a Delta-2 rocket for a double launch. Jason-1 falls into the mini-satellite category ((500 kg), but will nevertheless offer the same outstanding levels of performance as Topex-Poseidon: its dedicated mission will make it possible to measure the topography of the ocean and the variations caused by the marine currents. This information will then be used as an accurate reference enabling the best advantage to be taken of all other radar altimeter observations, such as those made by ERS or, in the future, by ENVISAT (Environmental Satellite). Other satellites for observing the ocean, the environment or the climate are being built, namely ENVISAT, METOP (Mete´orologie Ope´rationnelle) and ADEOS 2 (Advanced Earth Observing System), which will be launched in the years to come. Their measurements of ocean topography, but also of temperatures and surface winds, will be an indispensable multi-sensor and multisample complement to existing means.
R. Zaharia / Space Policy 15 (1999) 23—25
Along with this incredible international armada for observing planet Earth, operational networks for in-situ measurements (such as those planned for Ifremer’s Coriolis project) and high-resolution global ocean models, suitable for operational use, will be implemented (in particular the GODAE (Global Ocean Data Assimilation Experiment) project, supported by CEOS (Committee on Earth Observation Satellite) on an international level and the MERCATOR inter-establishment project
25
in France). This range of means combined with ongoing research efforts, and in particular, in France, those of CNRS (Centre National de la Recherche Scientifique)/ INSU, SHOM (Service Hydrographique et Oce´anographique de la Marine) and ORSTOM, should lead in time to a truly operational service for ocean observation and weather forecasting by organizations such as EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites), Meteo France and NOAA.