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Knowledge of Earth energy (im)balance requires accurate measurements from which the differences between the incoming and outgoing radiation can be determined. The incoming energy is nearly all from the Sun, while the outgoing is a combination of reflected-solar and thermal-infrared radiation. This energy difference can be determined by separate measurements with good *absolute accuracy* of the incoming and outgoing radiation; or it can be determined, at least across the reflected-solar range, by good *relative* measurements of the two, which can lead to lower uncertainties due to many contributors being common mode to both measurements if acquired from a single instrument. This essentially allows Earth-reflectance measurements, which can be acquired with good relative precision, to provide outgoing Earth-radiation knowledge referenced to the well-known, SI-traceable, incoming spectral solar irradiance. We describe three instruments’ measurements and associated uncertainties that enable this approach along with a lunar-calibration means extending it to other instruments not able to directly measure the Sun’s irradiance: 1) Extant space assets provide daily measurements of the solar irradiance with good SI traceability; 2) The CLARREO Pathfinder’s HySICS instrument, to be launched in 2024, provides relative measurements of Earth-scene reflectances with < 0.3 % (k=1) uncertainties across most of the 350- to 2300-nm range with 8-nm resolution; and 3) The ARCSTONE, a 6U CubeSat with an anticipated mid-2024 launch date, will use a similar on-orbit solar cross-calibration approach to acquire spectral lunar irradiance measurements with uncertainties < 0.5 % (k=1) across the same wavelength range with 6-nm resolution. Via resulting improvements to lunar-irradiance models, these enable extending the SI-traceable lunar irradiance to other spaceborne assets viewing the Moon regardless of temporal overlap with these three instruments that will tie together SI traceability for Earth energy balance in the reflected-solar spectral region.
Topic : Theme 1: Earth Energy Balance.
Reference : T1-C20
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