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GCOS Atmospheric Upper Air ECV: Earth Radiation Budget (including Solar Irradiance) Introduction: The Earth’s radiation budget is the balance within the climate system between the energy that reaches the Earth from the Sun and the energy that returns from Earth to space. Satellite measurements offer a unique means of assessing the Earth’s radiation budget. The goal of such measurements is to determine the amount of energy emitted and reflected by the Earth. This is necessary to understand the processes by which the atmosphere, land and oceans transfer energy to achieve global radiative equilibrium, which in turn is necessary to simulate and predict climate. Systematic observations of the Earth System energy balance components are noted by the IPCC as being of key importance in narrowing the uncertainties associated with the climate system. In addition to these continuous global measurements of the radiation budget, which are necessary both to estimate any long term climatic trends and shorter term variations overlying these trends, measurements on a regional scale are useful to understand better the dynamics of certain events or phenomena and to assess the effect of climate change, for example on agriculture and urban areas. In general, three types of measurements are currently possible: the shortwave and longwave radiation budget at the top of the atmosphere; the shortwave radiation budget at the Earth’s surface; the total incoming broadband radiation flux. (from the CEOS web site) Satellite Observations: Since the mid-1960s, NASA has been measuring the net radiation with the ERBE, ACRIM, and CERES sensors. The MISR spectroradiometer (also on Terra with CERES) provides data on the top of the atmosphere, cloud and surface hemispheric albedos, and aerosol opacity. Continuity of Total Solar Irradiance (TSI) measurements was assured by the launch of the SORCE mission at the beginning of 2003, carrying 4 instruments (TIM, SOLSTICE, SIM, XPS) that operate over the 1 nm–2000 nm waveband and measure over 95% of the spectral contribution to TSI. ESA’s EarthCARE will embark a broadband radiometer (BBR) together with instruments providing profile information (ATLID, CPR). The French-Indian mission Megha-Tropiques (2010) will carry the broadband ScaRaB radiometer, similar to the instrument flown in the mid-1990s on the Russian Meteor satellites, for ERB measurements over the tropical and equatorial regions. An increasing number of radiation budget measurements are featuring on operational meteorology missions. These include: GERB (operating since September 2002 on Meteosat and measuring shortwave and longwave radiation every 15 minutes from a geostationary orbit); TSIS on NPOESS; and continued narrowband information from the HIRS, AVHRR, SEVIRI (top of atmosphere and surface radiative fluxes) and VIIRS instruments. An important component of the Earth Radiation Budget is the Outgoing Longwave Radiation (OLR). This is calculated from multi-spectral infrared imager observations, such as those from AVHRR or imagers on geostationary platforms. (from the CEOS web site) Problem with the Data Record: The past multi-satellite record of measurements suffers from an absence of absolute calibration. It is recognised that development of absolute, spectrally resolved measurements is needed to provide information on variations in climate forcings and responses, and to calibrate the operational meteorological satellite sensors. In addition, there is the likelihood of a measurements gap after 2020; the recent change in NPOESS plans for climate-relevant measurements calls for coordinated re-planning efforts. In support of the GCOS IP, CEOS aims by 2011 to make absolute, spectrally resolved measurements of radiance emitted and reflected to space by the Earth for information on variations in both climate forcings and responses. CEOS agencies will also participate in re-planning ERBS removed from the planned payload of NPOESS. (from the CEOS web site) Satellite Missions, present and future [ECV Matrix Main Page] [About the ECV Matrix] [Reference Documents] [Contact] |
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