Solar Intensity Dispersing (SID) Concept for CubeSat Spectral CLARREO‐Like Radiance Measurements

Abstract

Abstract NRC Decadal Surveys stated that the most critical goal for orbital climate measurements was improving accuracy. This is so comparisons can be better made with models, tuning theory to match the truth. That gives confidence in model predictions of future global cloud albedo warming signals, estimated to be only 0.8%/decade or less. This work considers goals of a future mission CLARREO, currently in the development phase. CLARREO's Earth viewing optics intend to scan lunar radiance for tracking calibration changes, within both a high wavelength and high spatial resolution spectrometer. The current NASA CLARREO design will attempt absolute calibration from the space station by attenuating known solar flux, using pinholes and time under‐sampling. This study presents a cheaper and potentially more effective alternative, instead using the Sun as a near direct absolute calibration target. It does this spreading sunlight over a large solid angle, before integrating signals taken from a spinning orbiting CubeSat. Additionally, after reviewing actual orbital data comparisons, the realistic accuracy of cross‐orbit satellite to satellite calibration is shown several percent at best, even for a perfect CLARREO device (far short of the desired ±0.3% quoted by NASA). That is compared to the accuracy achievable from an absolute lunar spectral characterization from this CubeSat called “MERBE‐Sat,” acting as a transfer for a climate observation system, perhaps better than ±0.3% error. Although discussed individual components of MERBE‐Sat are mostly of high TRL Level, this work suggests experimentation to raise the net TRL level of the new entire concept.

Keywords

• climate change
• SI traceable calibration
• lunar calibration
• solar calibration
• CubeSat