EOQ N°66 July 2000
meteorology – earthnet – remote sensing – solid earth – future programmes
Earth Observation Quarterly
The Earth Explorer Missions - Current Status
G. Mégie (1) and C.J. Readings (2)
(1) Institut Pierre-Simon Laplace, Université Pierre & Marie Curie, Paris, France (2) ESA-ESTEC, Earth Sciences Division, Noordwijk, The Netherlands
The ‘ESA Living Planet Programme’ [ESA SP-1234, 1998] describes the plans for the Agency's new strategy for Earth Observation in the post–2000 time frame. It marks a new era for European Earth Observation, based on a programme that is user-driven, spanning the whole spectrum of interests ranging from scientific research-driven Earth Explorer missions through to application-driven Earth Watch missions. The user community is therefore now able to look forward to a programme of more frequent but very specific missions directed at the fundamental problems of Earth system sciences.
Introduction In this Issue The Earth's environment is a complex many aspects of this Earth system are system which couples, at various still not understood and so there Earth Explorer Mission Special Issue temporal and spatial scales, the remains a need for a world-wide • The Earth Explorer Missions – atmosphere, the oceans, the scientific effort to better assess Current Status...... 1 biosphere and the cryosphere. knowledge of the various global • Call for Ideas ...... 4 Unfortunately, despite its importance, threats. These include climate change, • The Gravity Field and Steady- State Ocean Circulation Explorer Mission – GOCE...... 6 • The Atmospheric Dynamics Mission – ADM...... 12 • The Soil Moisture and Ocean Salinity Mission – SMOS ...... 18 • Envisat...... 27 • Conferences and Publications...... 28
Fig. 1: The Earth System Earth Explorer Missions 2
Fig. 2: The Earth Explorer Missions stratospheric ozone depletion and Earth sciences community. It funds Earth Explorer Core and Earth Explorer tropospheric pollution, as well as more many of the Agency's Earth Opportunity Missions. localised events such as the 1999 El Observation activities including the Niño, fires in South East Asia, floods in Earth Explorer missions (see ESA-SP- The purpose of this and the southern Africa and the devastating 1227, Earth Explorers: the Science and accompanying articles, is to describe earthquakes in Turkey. Research Elements of ESA's Living these selected missions which are now Planet Programme). These are in their implementation phase, setting To further enhance our capacity to research/demonstration missions them in the context of the Agency's predict the evolution of the Earth's intended to advance understanding of overall Earth Observation programme. environment, under the influence of the Earth's environment, which can both natural variability and man's also be used to demonstrate new The Earth Explorer Core Missions activities, the provision of data and observing techniques. There are two In May 1996 a user consultation their integration into appropriate complementary types of Earth Explorer meeting was held in Granada, Spain, models of the Earth system are of Missions, namely : following which (and the subsequent paramount importance. All elements of peer review) four Earth Explorer Core the system (atmosphere, land, – Earth Explorer Core Missions - Missions were selected for Phase-A cryosphere and oceans), as well as large research/demonstration study, namely: their couplings, have to be studied. So missions led by ESA. Earth observation from space has a – Earth Explorer Opportunity Missions – A Gravity Field and Steady-State crucial role to play as it can provide – smaller research/demonstration Ocean Circulation Mission the globally coherent data sets which missions not necessarily ESA led. – An Atmospheric Dynamics Mission are an essential complement to – An Earth Radiation Mission ground-based, airborne and ship- The Living Planet programme is a user- – A Land Surface Processes and borne measurements. led programme which requires regular Interactions Mission interactions between the Agency and These considerations underlie the the Earth sciences community. From The four Phase-A studies, together with establishment of the European Space the definition of several missions in accompanying scientific studies, were Agency's Living Planet programme, as both categories by scientists, a completed during the latter half of described in a previous issue of the selection process based on extensive 1999. They were presented at a Earth Observation Quarterly (EOQ interaction with the community, second Granada consultation N°63, September 1999). An aim of this assessment by the Earth Science workshop held in October 1999. programme is to provide a series of Advisory Committee and further Subsequently, following completion of regular flight opportunities, combining endorsement by the Programme Board a peer review by the Earth Sciences flexibility with certainty, to address the for Earth Observation, has led over the Advisory Committee (ESAC) and scientific issues highlighted by the past year to the selection of the first consideration by the Programme 3 Current Status
depth of the atmosphere, a notable deficiency of the current observing systems. With these data it will be possible to increase understanding of atmospheric processes for climate studies, particularly in tropical regions, as well as advancing the performance of numerical models used in weather forecasting. It is intended to improve understanding of atmospheric dynamics and global atmospheric transport as well as the global transfer of energy, water, aerosols and chemicals. This will lead to improved analyses of atmospheric state, providing the more complete three- dimensional picture of the atmosphere Fig. 3: The Gravity Field and Steady-State Ocean Circulation Mission (satellite which is required to: configuration and accommodation of the 3-axis gradiometer) – improve the parameterisations of Board for Earth Observation (PB-EO), it For this it is necessary to determine atmospheric processes in models; was agreed that the first two Earth the Earth’s gravity field and the geoid – advance climate and atmospheric Explorer Core Missions to be (i.e. the equipotential surface for a flow modelling; implemented (in order of hypothetical ocean at rest) to high – provide better initial conditions for implementation) should be the Gravity accuracy (1 mgal and 1 cm) and high weather forecasting. Field and Steady-State Ocean spatial resolution (~ 100 km). This will Circulation Mission (GOCE) and the be achieved with the aid of a three- A Doppler wind lidar, flying in a sun- Atmospheric Dynamics Mission (ADM). dimensional gradiometer. The mission synchronous orbit at about 400 km, will is scheduled for launch in 2004/5. be used to observe global winds in The Gravity and Steady-State Ocean More information can be found in clear air in the troposphere. The Circulation Earth Explorer Core Mission another article in this issue of the EOQ. instrument will operate in the ultraviolet (ESA/SP-1233(1)) is intended to (355 nm) and will be able to detect address the needs of the Solid Earth The Atmospheric Dynamics Earth backscattered signals from both physics, geodetic and oceanographic Explorer Core Mission (ESA/SP- aerosols and molecules. The mission is communities by measuring the Earth's 1233(4)) will, for the first time, provide, scheduled for launch in 2006/7. gravity field and a derived geoid to with the aid of a Doppler wind lidar, Further details will be found in an unprecedented accuracy and direct observations on global scale of accompanying article in this issue of resolution, using a three-axis atmospheric wind profiles over the EOQ. gradiometer. This will help to advance knowledge of the Earth's interior structure and provide a much better reference for oceanographic and climate studies. Specifically it will focus on the use of better knowledge of the Earth's gravity field for studies in:
– Solid Earth physics – anomalous density structure of lithosphere and upper mantle; – oceanography – dynamic ocean topography and absolute ocean circulation; – ice sheet dynamics – ice sheet mass balance; – geodesy – unified height systems, "levelling by GPS"; – sea level change. Fig. 4: The Atmospheric Dynamics Mission Satellite Earth Explorer Missions 4
Although the Land Surface Processes divergence of radiative energy in the and Interactions Mission (ESA/SP- atmosphere, aerosol-cloud-radiation As result, it was agreed that the first 1233(2)) and the Earth Radiation interactions, the vertical distribution of Earth Explorer Opportunity Mission to Mission (ESA SP-1233(3)) were not water and ice, and their transport by be launched should be Cryosat selected for implementation, both clouds, and cloud-precipitation followed by SMOS. Progress would be were highly commended, being seen interactions. It would have maintained on a third mission, namely as of crucial importance to the determined the vertical profiles of the ACE so that it could serve as a "hot" Agency’s Living Planet Programme. radiative properties of clouds and spare in the event of unforeseen Work should continue in support of both missions.
The main research objectives of the Land Surface Processes and Interactions Mission were to increase knowledge of land surface processes, including the carbon cycle. It would have supported the investigation of geo-biospheric processes for environmental research and climate modelling, to advance work on surface/atmospheric exchange processes. An imaging spectrometer, supported by a large number of well equipped experimental sites and field stations, would have been used to Fig. 5: Possible satellite concept for Cryosat obtain the required data. aerosol on a global scale, providing problems on Cryosat or SMOS. Two The Earth Radiation Mission was data for numerical modelling and other missions, SWARM and SWIFT, intended to advance knowledge of the atmospheric process studies. In were placed on a reserve list. particular it would have exploited the capabilities of a backscatter lidar and Cryosat is being designed to measure a cloud radar. variations in the thickness of the polar A Call for Ideas for the Next Earth ice sheets and the thickness of Explorer Core Missions Iterations continue on both missions, floating sea ice. Its data are intended notably for the radiation mission with to be used for the study of the mass Japanese agencies and scientists balances of the Antarctic and This issue of the Earth Observation who have shown a clear interest in an Greenland ice sheets, to investigate Quarterly provides an overview of the advanced Earth Radiation Mission. the influence of the cryosphere on status of the Earth Explorer missions The next milestone in the long term global sea level rise and to provide and it can be seen that, during the implementation of the Living Planet important observations of sea ice course of last year, two Earth Explorer Programme will be the issue of a Call thickness for use in Arctic and global Opportunity Missions and Two Earth for Ideas for the next Earth Explorer climate studies. It will fly in a high Explorer Core Missions have been Core Missions which start a new inclination orbit at around 600 km, selected for launch. Reference is also phase of implementation (see exploiting a Ku-band radar altimeter. It made to the future, notably the issue announcement on this page). is scheduled for launch in 2003. The of a Call for Ideas for the Next Earth mission was described in EOQ N°63 Explorer Core Missions. The Earth Explorer Opportunity (September 1999). This was discussed during the meeting Missions of the Programme Board for Earth In parallel with the work on the Earth SMOS is intended to demonstrate the Observation on 24-25 May and it was Explorer Core Missions there has also observation of two key variables of the agreed that the Call should be issued been considerable activity on the Earth system, namely soil moisture on 1 June 2000 with a deadline of Earth Explorer Opportunity Missions over land and salinity over oceans, to 1 September 2000 for the receipt of front. A call for proposals was issued advance the development of responses. Full details, including in July 1998 and no less than 27 full climatological, meteorological and instructions of how to submit a proposals were received in response. hydrological models. In addition, the response, will be found on These were subject to peer review by mission should provide new insights the ESAC and to consideration by the into snow and ice structure, so
the cryosphere. It is proposed to use a passive microwave radiometer, operating at L-band (1.4 GHz). The mission is scheduled for launch 2005. It is more fully described in an accompanying article in this issue of the EOQ.
The implementation of ACE involves the provision of two different instruments, namely GRAS and COALA. GRAS would exploit the atmospheric refraction of signals from GNSS satellites, to provide observations of temperature and humidity in the upper atmosphere. These data would be used in atmospheric analysis and modelling as well as for energy balance and transport studies. An array of 6 satellites would be deployed. Only this option is being retained as the "hot" spare.
The other instrument associated with the original ACE proposal (i.e. COALA) is being considered Fig. 6: SMOS (courtesy Alcatel) separately and is retained on the reserve list. COALA seeks to measure ozone and other chemical species by exploiting stellar occultation. Concluding Remarks Further information on the Earth This article has provided an overview Explorer Missions will also be found The aim of SWARM is to measure the of the current status of the Earth on