Bridging the Gaps: A CubeSat Implementation to Enhance Earth’s Radiation Budget Observations from Space

The Compact Total Irradiance Monitor (CTIM) was a 6U CubeSat developed under the NASA In-Space Validation of Earth Science Technologies (InVEST) program to measure total solar irradiance (TSI). CTIM was launched in July 2022, collecting climate quality science data at an uncertainty of 0.016% until end-of-mission in November 2023. During orbital eclipse, CTIM was pointed in the nadir direction to measure Earth’s outgoing emission. These measurements have been compared to those from the Clouds and Earth’s Radiant Energy System (CERES) instruments flying on Terra, Aqua and NOAA-20. Initial comparative analyses of longwave radiance between coincident CTIM and CERES observations show relative agreement of 1.3%, within the respective uncertainties of CERES and CTIM. We apply additional adjustment factors for CERES non-nadir viewing observations derived from radiative transfer simulations over a variety of scene types and atmospheric conditions to better match the CTIM nadir observations and explain some of the variance exhibited between measurements.

CERES initiated the longest continuous record of Earth radiation budget (ERB) data record that is now 24-years long. The follow-on to CERES, Libera, launches in 2027 and has a 5-year prime mission lifetime, beyond which plans for ERB continuity remain uncertain. The study suggests that a leveraging of novel CubeSat technology to demonstrate CTIM’s opportunistic Earth-observing applications may complement heritage ERB missions and reduce the risk of gaps in future ERB observations from space. Moreover, it provides a potential pathway for the direct measurement of Earth’s energy imbalance using the same systems for Earth and Sun measurements.