Radiation budget Measurements Made by Earth Observation Satellites

CEOS EO HANDBOOK – MEASUREMENTS

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Radiation budget

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. 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.

Detailed Measurement	Description*	Instruments	Timeline
Diffuse attenuation coefficient (DAC)	Former name: “Water clarity”. Parameter extracted from ocean colour observation. Indicative of water turbidity and vertical processes in the ocean. Requested in both open ocean and coastal zone - Physical unit: [ m-1 ] - Accuracy unit: [m-1 ].	4 instruments
Downward long-wave irradiance at Earth surface Link:	Flux density of radiation emitted by the gases, aerosols and clouds of the atmosphere to the Earth's surface - Physical unit [ W/m2 ], Accuracy unit [ W/m2 ]	11 instruments
Downward short-wave irradiance at Earth surface Link:	Flux density of the solar radiation at the Earth surface - Physical unit [ W/m2 ], Accuracy unit [ W/m2 ]	8 instruments
Downwelling (Incoming) solar radiation at TOA Link:	Flux density of the solar radiation at the top of the atmosphere - Physical unit [ W/m2 ], Accuracy unit [ W/m2 ]	14 instruments
Long-wave cloud emissivity	Fraction of emitted radiation in respect of a black-body at the same temperature as the cloud top. Varies with wave-length. [Unit of measurement -dimensionless]	0 instruments
Long-wave Earth surface emissivity	Emissivity of the Earth’s surface in the thermal IR, function of the wavelength - Physical unit: [ % ] - Accuracy unit: [ % ].	16 instruments
Short-wave cloud reflectance	Reflectance of the solar radiation from clouds - Physical unit: [ % ] - Accuracy unit: [ % ].	2 instruments
Short-wave Earth surface bi-directional reflectance	Reflectance of the Earth’s surface function of the viewing angle and the illumination conditions in the range 0.4-0.7 µm (or other specific short-wave ranges) - Physical unit: [ % ] - Accuracy unit: [ % ].	18 instruments
Solar Spectral Irradiance Link:	Wavelength-dependent energy input to the top of the Earth's atmosphere, at a standard distance of one Astronomical Unit from the Sun - Physical unit: [ W m-2 nm-1]	2 instruments
Upward long-wave irradiance at TOA Link:	Flux of the terrestrial radiation in the range 4-200 µm (thermal emission) moving to space through the top of the atmosphere - Physical unit [ W/m2 ], Accuracy unit [ W/m2 ]	18 instruments
Upward short-wave irradiance at TOA Link:	Flux of the terrestrial radiation in the range 0.2-4 µm (reflected solar radiation) moving to space through the top of the atmosphere - Physical unit [ W/m2 ], Accuracy unit [ W/m2 ]	11 instruments
Upwelling (Outgoing) long-wave radiation at Earth surface	Flux of thermal radiation from the Earth’s surface - Physical unit: [ W/m2 ] - Accuracy unit: [ W/m2 ].	8 instruments
Upwelling (Outgoing) Short-wave Radiation at the Earth Surface	Flux of short-wave radiation from the Earth’s surface - Physical unit: [ W/m2 ] - Accuracy unit: [ W/m2 ].	5 instruments
Upwelling (Outgoing) spectral radiance at TOA	Level-1 product. Spectral range 0.2-200 mm. Resolving power l/∆l = 1000. Accuracy quoted as SNR (Signal-to-Noise-Ratio), actually SNR-1 so that smaller figure means better performance, as usual. WMO and IOCCG quote accuracy in [ % ]	6 instruments

* Description adapted from WMO.