by Tillmann Mohr 1 and Mark Dowell 2
The demand for climate services has increased considerably over recent decades. Key public and private sector interests such as insurance, agriculture, public health, energy and transportation have a fundamental need for authoritative climate information and services upon which to base strategic plans, investments and day-to-day decisions. The Global Framework for Climate Services (GFCS) provides a context for developing such services.
The GFCS recognizes that a strong observation and monitoring system, or “pillar” as the GFCS Implementation Plan defines it, is a critical foundation for climate services at the global, regional and national levels. The provision of more and higher quality observational data, together with advances in climate science, will improve the prediction of extreme events such as droughts, floods and tropical cyclones. Better predictions of, and preparation for, such events will save lives, protect property and improve economic resilience and public well-being and security.
A significant part of the required observations can only be provided in a synoptic manner by satellite systems. The large Numerical Weather Prediction centres around the world already use up to 80 million satellite observations per day in the framework of the World Weather Watch, but climate predictions will require much more. In fact, the observational requirements of the GFCS is one of the major driving forces for improving the architecture for climate monitoring from space (although the call for improvement was issued before the GFCS Implementation Plan was drafted). In 2011, the Sixteenth World Meteorological Congress decided “… that an architecture should be developed to provide a framework for the sustained and coordinated monitoring of Earth’s climate from space.”
A large part of the observation capabilities needed for climate monitoring are already available or being planned. Some critical gaps, however, remain, and the overall system needs to be better articulated to ensure that it is efficient and robust, and can effectively underpin climate applications and related decision-making.
The growing capabilities of satellites
The discussions being held today for climate monitoring are remarkably similar to the discussions for a globally coordinated “architecture” for weather monitoring held when building World Weather Watch (WWW) in 1963, which have led to the successful, globally coordinated meteorological system that we have today. Since the creation of the WWW, some 240 environmental satellite missions have taken place as a major component of the global observing system. The various on-board instrument technologies have permitted observation of the Earth through a wide range of the electromagnetic spectra. There are now more than 160 meteorological satellites in orbit, many of them in operational series of five or more spacecrafts. They are an integral part of the space segment of WMO Integrated Global Observing System (WIGOS), which is superseding WWW.
Many of these observation systems are optimised to support real-time weather monitoring and forecasting, but their scope is gradually expanding to provide a foundation for longstanding climate records of key atmospheric parameters. For example, the international geostationary network, currently maintained by seven satellite operators, will soon fly enhanced visible and infrared imagers, hyperspectral infrared sounders and lightning detectors. Towards the end of the decade, some series will include an additional payload for atmospheric composition.
Operational meteorological satellites on sun-synchronous low-Earth orbits, which perform multispectral imaging and vertical sounding as core missions, will progressively feature more advanced capabilities, including hyperspectral infrared sounding, Global Navigation Satellite System (GNSS) radio occultation sensors, some Earth Radiation Budget instrumentation, and atmospheric composition and space environment sensors. However, while providing a significant contribution to climate monitoring as part of the space component of WIGOS, operational meteorological satellites do not always achieve the level of accuracy needed for climate monitoring and do not observe all the variables involved in climate processes.
More than 30 satellite missions have already been deployed to specifically observe climate components, support climate process studies or demonstrate new technology to be used in climate monitoring. These missions provide a valuable reference source for future missions in support of sustained climate monitoring from space. The increased frequency of satellite measurements, improved satellite and sensor technology, and easier access to, and interpretation of, the Earth observation data that they provide will augment understanding of the role of satellite data in climate knowledge systems.
Another 140 satellites missions – carrying over 400 different instruments for measuring components of the climate system – are planned over the next 15 years. These satellites will gather new data on the chemistry, aerosol content and dynamics of the Earth’s atmosphere. Space-borne Lidar will provide new information on winds, in addition to cloud and aerosol observations. Observation of the Earth’s radiation budget, measured at the top of the atmosphere through a combination of measurements, will benefit from dedicated climate and operational meteorology missions. Building on capabilities built over more than a decade, global monitoring of the water cycle will be enhanced by spaceborne precipitation radar and passive microwave sensors coordinated by a large international network of satellites.
Global sea level rise 1992–2012, based on TOPEX/Poseidon
and Jason satellite data
Ocean surface topography measurements from radar altimetry and ocean surface wind vector measurements from scatterometry, initiated 20 years ago on an experimental basis, are expected to be strengthened by follow-up missions. New capabilities for measuring ocean salinity will also come online.
Operational meteorological and land monitoring satellite series will supply continuous observations of the land surface, vegetation parameters and ice sheets. Advanced Synthetic Aperture Radar (SAR) systems will yield new information on land surface properties, and active and passive microwave instruments will measure surface soil moisture. A new generation of sensors is also emerging with improved capabilities to remotely sense land surfaces, the ocean and the atmosphere, including their chemical composition.
There are several initiatives already in place for improving observations for climate science. Any strategy for improving space observation must consider these as well as the consistency and compatibility of observation and monitoring within the global architecture.
The developing Climate Change Service of the European Union’s Copernicus programme, for example, aims to provide information on climate change monitoring and prediction, which will support support adaptation and mitigation activities. The Service benefits from a sustained network of in situ and satellite-based observations and from re-analyses of climate data and modelling scenarios. Through the Climate Change Service it will be possible to access climate indicators – temperature increase, sea level rise, ice sheet melting, ocean warming – and climate indices – based on records of temperature, precipitation, and drought events – that describe both the identified climate drivers and the expected climate impacts.
Identifying and addressing gaps
The adequacy of current holdings and planned space-based capabilities is kept under review by the Global Climate Observing System (GCOS) community and evaluated in the “Systematic Observation Requirements for Satellite-Based Products for Climate (GCOS-154)” report. Gaps or deficiencies are identified or anticipated at almost every step in the value chain, from sensor to Climate Data Record.
Initiatives to address these gaps in a coordinated fashion have been taken by space agencies through the Committee on Earth Observation Satellites (CEOS) and the Coordination Group for Meteorological Satellites (CGMS), as well as by WMO in response to the GCOS requirements.
Defining a common architecture
In January 2011 the Global Climate Observing System (GCOS) and the WMO Space Programme held a workshop for both policymakers and technical experts. The workshop proposed establishing an ad hoc team comprised of representatives from CEOS, CGMS and WMO to develop a strategy document for an architecture for climate monitoring from space. The final report, released in 2013 and entitled “Strategy Towards an Architecture for Climate Monitoring from Space,” focuses on satellite observations for climate monitoring and the need for an international architecture that ensures delivery of these observations over the time frames required for the long-term analysis of the Earth’s climate system.
The report outlines a strategy that is intentionally high-level, conceptual and inclusive so that broad consensus can be reached and all relevant entities can identify their potential contributions. The strategy, however, is not sufficient in and of itself. It limits itself to proposing a logical architecture to define the activities and functions that are required to develop an end-to-end system. Its four major components (see Fig. “Main Components of a Logical View”) include: sensing, climate data record generation, climate monitoring and analyses, and support to decision-making. The initial emphasis is expected to be placed on representing the processes “upstream” – sensing and climate data record generation. However, focus on “downstream” applications and services will be equally important.
The proposed physical architecture calls for research and operational satellites, broad and open data-sharing policies, and contingency planning and agreements. These elements are essential for bringing the same continuity to long-term and sustained climate observations that exists for weather observations. The task of climate monitoring, however, has requirements that go beyond the capabilities of one-time research missions and operational satellite systems in existence today.
The report underlines the necessity for both research and operational agencies to develop a joint framework for stewardship of climate information. Climate record processing requires a sustained expert understanding of new and legacy climate sensors as well as a sustained web of support activities, including calibration and validation and collaborative product assessment and intercomparison. This can only be delivered through the collaborative efforts of both research and operational agencies.
The report also identifies an imperative for further and broader coordination among all stakeholders, both technical and policy-related, in order to optimize efforts, ensure traceability and secure the necessary resources for implementation. From a technical perspective, the scientific community, relevant technical groups and other mechanisms must be more involved in both reviewing the proposed approach and in further developing the physical architecture. From a policy perspective, the proposed logical architecture must be verified through a top-down approach to ensure that it adequately supports the information flows from the decision-making process back to the sensing capacity and requirements. This is an essential step for policymakers to be able to appreciate and support the need for an integrated climate monitoring architecture that is capable of meeting the needs of themselves as well as other users. Lastly, the report includes a roadmap for the way forward and defines concrete actions.
The report provides evidence on the following:
- inventories are needed to document the contributions of current and planned observing systems for climate purposes as current observing systems have not been designed primarily from a climate perspective;
- requirements on mission continuity and contingency need refinement through international collaboration among space agencies;
- sustained Climate Data Record (CDR) programmes will provide an avenue to replace heritage algorithms and data sets with improved versions once they are successfully demonstrated, validated and available; and
- there is an imperative for further and wider coordination among all stakeholders in order to ensure traceability along harmonized practices.
While the strategy report emphasizes space-based observations, it is also expected that during the implementation phase, space agencies and associated programmes will start to address in earnest how the in-situ components of the climate monitoring system could be represented within the architecture. This integration process should take advantage of existing international activities and frameworks that coordinate in-situ observation networks. With this long-term ambition in mind, the logical architecture presented in the report has been made intentionally generic so that it can be readily adjusted to describe the functional components of the integrated space and in-situ monitoring system at some point in the future.
The report is aimed at the coordinating groups that undertook its writing, their members and governing or advisory authorities, and programmes with climate mandates or interests, in particular those that have provided technical reviews of the report – GCOS, the Group on Earth Observations (GEO) and the World Climate Research Programme (WCRP). It will be important that these bodies recognize the need for such an architecture and the benefits that international coordination and collaboration can bring, particularly through the optimization of resources for satellite systems. All of the climate programmes and frameworks should work internationally to strengthen and leverage climate observations and research. Their needs can be better met if the strategy for developing an architecture for climate monitoring from space is both technically and politically sound.
Implementation – the way forward
A concrete way forward is also proposed in the report, and CEOS, CGMS and WMO are now embarking on the next steps of this initiative. These include designing a physical architecture that captures the current and planned implementation strategies on an ECV-by-ECV (Essential Climate Variable) basis. An initial step in this process is the maintenace of an ECV Inventory 4 to provide a detailed overview of current and planned capability. To this end, CEOS and CGMS member agencies have completed a detailed questionaire at the product level, which forms the basis for an initial rendition of this inventory.
Main Components of a Logical View
Decomposition of the 4 pillars of the Architecture (with a focus on “Climate Record Creation and Preservation” and “Applications”)
Finally, a fundamental value of the architecture is its end-to-end nature, which, from a user perspective, flows back from a decision-making policy perspective through the required applications to the necessary datasets and ultimately the required observational capacity to sustain this information flow. In the short-term the plan is to verify that the proposed architecture adequately supports climate applications and derived decision-making. An application of the architecture in specific case studies at a variety of scales compatible with climate service development (i.e. global, regional, local) would address this. Policy-makers would appreciate the value of such an integrated climate monitoring capability that meets their needs.
1 Special Advisor to the WMO Secretary-General on Satellite
2 Institute for Environment and Sustainability, Joint Research
Centre, European Commission
4 The ECV Inventory in its current form is avaiable at http://ecv-inventory.com/