Variability in SCIAMACHY Earth-reflected solar spectral radiance: Guidance for climate benchmarking

The difference between the solar radiation incident at the top-of-the-atmosphere and that reflected to space establishes the infrared emission required for radiative equilibrium and thus represents the most fundamental equation of climate. Detecting climate change signatures in reflected solar radiance has been hindered by instrument accuracy and stability, insufficient spectral coverage and resolution, and inherent sampling limitations from low-Earth orbit observations. The primary goal of the Decadal Survey's Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission is to obtain climate “benchmark” data records with sufficient accuracy for identifying climate variability on decadal time scales and with sufficient information content to attribute change to underlying causality. Measurements of Earth-reflected solar spectral radiance from the ESA SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) have proven useful in defining a number of requirements for future missions that will establish climate benchmark data records. This paper presents results of CLARREO science definition studies utilizing the variability in SCIAMACHY spectra over spatial and temporal domains that can assist in defining the requirements of an Earth-viewing shortwave spectrometer for climate benchmarking. These same methods of analysis may also be applied to the detection of climate trends, and examples using SCIAMACHY spectra illustrate this capability.