A Triple-Photodetector System With Adaptive Optics for Enhanced Earth Energy Imbalance Monitoring

Earth’s Energy Imbalance (EEI)—the net difference between incoming solar radiation and outgoing terrestrial radiation at the Top of the Atmosphere (TOA)—is a fundamental indicator of climate change. Traditional radiometric systems (e.g., CERES) are limited by absolute uncertainties of ±0.3 W/m2, while acceleration-based “Space Ball” methods require idealized spherical spacecraft and are vulnerable to non-gravitational disturbances and calibration complexity. This paper presents a novel triple-photodetector system integrated with adaptive optics to enhance EEI assessment. It employs two high-quantum-efficiency detectors for solar and reflected shortwave radiation and a third optimized for longwave thermal emission. Fast Steering Mirrors (FSMs) and a Wavefront Sensing and Correction (WFSC) framework actively compensate for Angle-of-Arrival (AOA) deviations and wavefront distortions—key error sources in spaceborne radiometry. Numerical validation using CERES and CESM2 datasets demonstrates that, under strong optical turbulence (D/r0= 10), the system reduces EEI trend underestimation from ∼38% to just2decade vs. ideal 0.47 ± 0.17 ). On a spherical spacecraft, it achieves mean EEI agreement within < 0.5% of both radiation pressure acceleration and Electrical Substitution Radiometer (ESR) benchmarks. Crucially, it offers sub-hourly temporal resolution, geometric flexibility, and simpler calibration—enabling scalable deployment in satellite constellations. This approach provides a viable pathway toward the < 0.1% absolute radiometric accuracy required for definitive climate monitoring.