Physikalisch-Metorologisches Observatorium Davos -- World Radiation Center pmod-wrc

EArth radiation budGet ExploreR


Proposal for Earth Explorer Mission EE-9

Executive Summary:

There is scientific consensus that the global warming observed since about the 1950s is mainly of anthropogenic origin. However, both on the centennial and on the decadal scale it is still unclear which fraction of the observed changes is related to natural causes. With respect to the latter in particular reduced solar irradiance has been mentioned. The variable solar electromagnetic energy input is hence of special interest. This includes both Total Solar Irradiance (TSI) and Solar Spectral Irradiance (SSI). While the solar TSI and SSI and their variations define the energy input to the Earth´s atmosphere, the global energy budget at the top of the atmosphere (TOA) is a key parameter in relation to climate change. While the global mean temperature is defined by equilibrium of net incoming solar and outgoing longwave terrestrial radiation, anthropogenic and natural changes lead to an Earth´s energy imbalance connected with global warming.

To address these issues, the EArth radation budGet ExploreR (EAGER) mission will continuously observe both TSI and SSI, together with the TOA outgoing radiation, on a daily and global scale and with absolute calibration in space to guarantee long-term stability. In addition, Earth´s Albedo will be measured at a higher spatial while lower temporal resolution. For an overview of the EAGER science see Figure 1. The EAGER payload comprises of:

  • the Auto-Calibration XUV-IR Spectrometers SolACER (Solar Auto-Calibrating EUV/IR Spectrometers) to observe SSI in the wavelength range 10 nm - 2800 nm,
  • the space-verified Davos Absolute Radiometer DARA-TSI to observe TSI,
  • an adapted DARA instrument DARA-AES to observe Earth Albedo and Earth electromagnetic emission radiation, and
  • three space-verified BOS Bolometric Oscillation Sensors to observe outgoing Earth total radiation (emission and reflected solar radiation) at high temporal resolution (2 s cadence).

The key concept to guarantee stability and to enable in-flight calibration for the solar observations is to apply the very stable DARA TSI sensors in a combination with filters as a reference for the SolACER SSI observations, completed by ionisation chambers for the calibration in the extreme ultraviolet range. Similarly, for the Earth observations, the fast BOS sensors with low long-term stability will be calibrated by the stable Earth-pointing DARA-AES. Another key point is that both incoming solar TSI radiation and outgoing infrared and reflected solar radiation from the Earth will be measured simultaneously with the same instrument type, to guarantee stability of the Earth´s radiation balance observations.

DARA sensors represent updated versions of the CLARA sensor (Compact and Light-weight Absolute Radiometer), flown on NORSAT-1. SolACER is a wavelength-extended version of the SolACES experiment which have successfully observed EUV spectra on board the ISS over nine years. The BOS sensors have successfully been flown on the PICARD mission already.

The EAGER payload in total has a weight of 60 kg only, and will therefore be suitable to be operated on further missions as additional observations. During EAGER the instruments will be further characterised.

The space segment platform follows to a large extent the Airbus DS Astrobus S line, in order to take profit from already existing developments. As launcher VEGA-C is foreseen.

The mission is intended for a duration of 3 years, possible extension to 6 or 11 years will already deliver results of the Earth radiation budget variations within a half or full solar cycle, respectively. The orbit will be sun-synchronous to facilitate the scientific analysis of Earth radiation observations. During 1/3 of each orbit, the S/C will be oriented towards the sun for SSI and TSI observations, while the Earth observations will be in operation continuously.

During its mission, EAGER will deliver stable, reliable and daily observations of the solar radiation, together with daily TOA energy budget estimations. The observations will be used as an absolute standard for solar flux, and to serve as a benchmark for the Earth energy budget in climate modelling.

Proposing Institutes:

Dorfstrasse 33, CH-7260 Davos Dorf, Phone +41 58 467 51 11, Fax +41 58 467 51 00