50 years of legacy in space accelerometer missions for measuring Earth's energy imbalance

For 50 years, ONERA has been developing space accelerometers for Geodesy or Fundamental Physics missions: CHAMP, GRACE series, GOCE, MAGIC, MICROSCOPE. For the latest one, the laboratory had the science responsibility and learned better understanding of mission design. By taking advantage of these experiences, we proposed to review the old 80’s concept mission called BIRAMIS aiming at measuring the Earth’s radiative energy imbalance (EEI). The EEI represents the difference between the incoming solar radiation and the outgoing longwave radiation at the top of the atmosphere and is fundamental to estimate the effect of anthropogenic greenhouse gases (GHG) emissions on our climate system.

Currently, EEI is known with a stability of ~+/- 0.2 W/m² over a decade. However, this estimate is biased due to the performance of radiometry and to limited in-flight calibration. Some improvement is brought by using in-situ oceanic and geodetic (gravimetry and altimetry) measurements to estimate the ocean heat uptake. These measurements helps to evaluate EEI with an accuracy of +/- 0.3 W/m² on the time mean.

The accelerometer performances used for the previous missions exhibit resolutions from 10 to 0.1 pico-g. That allows us to imagine a new mission with direct measurements of the radiation pressure on a satellite and to envisage accuracies much better than 0.1 W/m² on the time mean. Decadal-scale variations in EEI induced by solar cycles, volcanic eruptions and variations in GHG emissions could be closely monitored for the benefit of the study of climate change.