Comparative Analysis of Errors in Monitoring the Earth’s Global Energy Budget by the Lunar Observatory and Orbiters

Abstract

The errors in measurements of the energy of the reflected solar radiation and the thermal radiation emitted from Earth entering space in all directions from the top of the atmosphere are analyzed. The potentials of measurements onboard the Lunar Observatory (LO) and spacecraft (SC) on geostationary and solar-synchronous orbits and at the L1 Lagrange point of the Sun–Earth system (SEL1) are compared. To take into account the radiation from the edge of the Earth’s disk, which cannot be observed from a geostationary orbiter at all phase angles, theoretical models should be constructed. The intensity distribution of radiation reflected to space through all other directions in dependence on the surface type, the radiation incidence angle, and the observation angle is also modeled. The actual inaccuracy of these methods is approximately 1%. At the SEL1 point, a SC may simultaneously observe the whole surface of the planet only at a phase angle α = 0° and only in the periods when the Moon does not eclipse the Earth’s disk. To take into account the radiation reflected to space at all other phase angles, it is necessary to construct theoretical models. This fact, as well as the lack of observations during lunar eclipses of the Earth, is connected with large errors in the required quantities. The system of two optical robotic telescopes mounted on the LO will sequentially survey the Earth’s surface almost in all ranges of phase angles. The annual averages of the Bond albedo and the emitted thermal radiation of the Earth as a planet determined at the LO and the corresponding deviations of the annual average global energy budget of the planet from the equilibrium state will be almost an order of magnitude more accurate than those determined from the data of any orbiter.