On the future of Earth radiation and energy imbalance measurements

Libera, NASA’s first Earth Venture Continuity Mission, is in preparation to provide seamless continuity to current Earth outgoing radiance measurements conducted and processed by the Clouds and Earth’s Radiant Energy System (CERES) project. Leveraging advanced detector technologies, Libera will measure the broadband total, longwave, and shortwave radiances akin to CERES and achieve radiometric uncertainty of approximately 0.2%. Beyond the crucial radiation budget continuity goal, Libera will carry a fourth radiometer in the shortwave near-infrared to advance our understanding of shortwave energy deposition in the climate system, such as related to the characterization of processes relevant for shortwave absorption, climate feedbacks, and Earth’s albedo variability with added insight into hemispheric albedo symmetry given the hemispheric differences in ocean, continent and cloud distributions. We use global model simulations and radiative transfer calculations as proxies for Libera’s future data record to demonstrate applications of the shortwave sub-band knowledge in climate science. Although Libera’s absolute accuracy is unprecedented, it is still insufficient to adequately close Earth’s energy budget. We will therefore discuss current and future avenues to indirectly and directly measure EEI from space. The latter is potentially feasible through sensing radiation pressure-induced accelerations acting on near-spherical spacecrafts, which under optimal conditions, are directly proportional to the net radiative flux experienced at the satellite’s location. This approach has been considered in the past, and the feasibility to achieve a measurement accuracy within 0.3 Wm^-2 is currently under investigation.