Calibration of instruments measuring the Earth’s energy imbalance EEI as the difference of the total solar irradiance TSI and the total outgoing radiation of the Earth TOR requires precise, traceable TSI and TOR radiation standards with three congruent properties: spectral composition, power, and angular divergence. As there are no TSI and TOR standards available, EEI data should be considered estimates. To enable more accurate estimates, the proposed novel spectrometers are used. The innovative process behind it is called quasi-calibration and also compensates for the aging of the instruments. The data can be transferred to other instruments in space. SORACES allows the observation of spectral solar irradiance SSI and spectral outgoing radiation of the Earth SOR, which differ by about five orders of magnitude, with high statistical significance by the same detectors. It is equipped with a set of 16 compact Rowland spectrometers with 80 photomultiplier tubes (PMTs) and 32 radiation attenuators with transmissions from 10−1 to 10−5. The use of attenuators allows for a dynamic range of up to 12 orders of magnitude to be covered. The cadence of the spectra is one second. Based on the stability of the TSI data, quasi-calibrated measurement periods across a solar cycle are to be achieved. SORACES is intended to contribute time-stable estimated SOR data to climate research. By evaluating the spectral features of the data, annual changes in the global cover of the Earth’s green biomass due to global warming are to be derived.
Schmidtke et al. (Sun,) studied this question.