Real-Time Determination of Earth Radiation Budget Spectral Signatures for Nonlinear Unfiltering of Results from MERBE

Among the best ways to gain more certainty in climate model prediction is to compare and constrain simulations with worldwide satellite measurements of the Earth radiation budget (ERB) short- and longwave radiant fluxes (SW and LW), which drive climate processes. Recent calls to ensure orbital ERB measurements track true climate, rather than instrument changes, led to the creation of the Moon and Earth Radiation Budget Experiment (MERBE). This independent project is recalibrating multiple existing ERB devices from different international space agencies so they adhere to common SI-traceable radiometric standards, by regularly sampling the unaltering constants of lunar reflectivity/emissivity, thus ensuring no artificial trends exist. This work details the use of MODTRAN to give an instantaneous SW and LW Earth spectrum for all scenes viewed by devices in the project, to then be used with instrument spectral responses for unfiltering radiances. In the majority of cases when data from a collocated imager are available, a dual-layer unfiltering is also performed separately on cloudy and cloud-free areas, yielding clear and overcast ERB spectral results. Additionally, use is made of improved in-flight methods to derive spectral responses from a previous American Meteorological Society study, and comparisons between Earth MERBE radiances from two identical devices operating on Terra/Aqua are shown along with results from the CERES project. These demonstrate an order of magnitude improvement in relative accuracy for edition 1 MERBE results over CERES and show that the latest CERES data are less accurate and stable than claimed.