Understanding planet Earth

The biggest environmental issue we face is global change, which encompasses not only climate change but also the large-scale impact that a growing global population and continued economic growth are having on the environment. Earth Explorers provide an important contribution to the global endeavour to further our understanding of Earth.

Earth Explorer missions form the science and research element of ESA's Living Planet Programme and focus on the atmosphere, biosphere, hydrosphere, cryosphere and Earth's interior. However, the emphasis is also on learning more about the interactions between these components and the impact that human activity is having on natural Earth processes.

Earth Explorer missions are divided into two categories: Core and Opportunity. Core missions respond directly to specific areas of public concern and are selected through widespread consultation with the science community. Opportunity missions are smaller, low-cost satellites that are relatively quick to implement to address areas of immediate environmental concern.

The user-driven approach is fundamental for both type of mission. The process of mission selection has given the Earth science community an efficient tool for advancing the understanding of the Earth system. The science questions addressed also form the basis for development of new applications of Earth observation.

To date, there have been three Core missions and three Opportunity missions selected for implementation.

Core missions:

GOCE
The Gravity field and steady-state Ocean Circulation Explorer (GOCE), the first Earth Explorer Core mission, was placed in orbit on 17 March 2009. GOCE is providing high spatial resolution gravity-gradient data with which to improve global and regional models of Earth's gravity field and geoid.

ADM-Aeolus
The prime aim of the Atmospheric Dynamics Mission is to demonstrate measurements of vertical wind profiles from space. The mission employs a high-performance Doppler wind lidar based on direct-detection interferometric techniques. ADM-Aeolus is due for launch in 2014.

EarthCARE
Earth Clouds Aerosols and Radiation Explorer (EarthCARE) will improve the representation and understanding of Earth's radiative balance in climate and numerical forecast models. EarthCARE is due for launch in 2015.

Opportunity missions:

SMOS
The Soil Moisture and Ocean Salinity (SMOS) mission, launched on 2 November 2009, is exploiting an innovative two-dimensional interferometer to acquire brightness temperature observations at L-band (1.4 GHz). These observations translate into information on the moisture held in soil and salinity in the surface layers of the oceans, which are needed to further our understanding of Earth's water cycle.

CryoSat-2
CryoSat-2, which was launched on 8 April 2010, will measure fluctuations in the thickness of ice on both land and sea determine how Earth's ice is changing. This information will lead to a better understanding of the relationship between ice and global climate. CryoSat-2 carries an innovative SAR/interferometric radar altimeter.

Swarm
The objective of this mission is to provide the best-ever survey of the geomagnetic field and its temporal evolution. The geomagnetic models resulting from the mission will provide new insights into Earth’s interior. This information will lead to a better understanding of atmospheric processes, and also have practical applications in areas such as space weather and radiation hazards. Swarm is due for launch in 2012.

Earth Explorer 7
Following the Earth Explorer selection process, there are currently three candidate missions undergoing feasibility study, after which one mission will be selected as ESA's seventh Earth Explorer mission:

Biomass – to take global measurements of forest biomass.

CoReH2O (Cold Regions Hydrology High-resolution Observatory – to make detailed observations of key snow, ice and water cycle characteristics.

PREMIER (PRocess Exploration through Measurements of Infrared and millimetre-wave Emitted Radiation) – to understand processes that link trace gases, radiation, chemistry and climate in the atmosphere.

Earth Explorer 8
As a result of the Call for Proposals for the eighth Earth Explorer released in October 2009, the Fluorescence Explorer (FLEX) and CarbonSat missions have been approved to move forward to Phase A/B1. Approval was given by ESA's Earth Observation Programme Board on 24 November 2010.