Abstract
We argue that the Earth Polychromatic Imaging Camera (EPIC) on the Deep Space Climate ObserVatoRy (DSCOVR) platform has blazed new pathways in observational technology, starting with its ∼ 1.5 × 106 km stand-off distance, but also in remote sensing science. We focus here on EPIC’s two oxygen absorption channels that 1) are unique in their spectral sampling and 2) have stimulated deep innovation in cloud remote sensing using Differential Oxygen Absorption Spectroscopy (DO2AS). Although first formulated 6 decades ago, DO2AS-based cloud probing from overhead assets is still an emerging observational technique. It is indeed somewhat paradoxical that one should use absorption by a gas to assay scattering by particles. After surveying the history of space-based DO2AS, and looking into its future, we see that EPIC/DSCOVR marks an inflection point in this important development. EPIC’s unique DO2AS capability motivated a notable sequence of papers revisited here. This research indeed spawned a rare occurrence of information content analysis coming from radically different—yet complementary—perspectives. First, we adopted the increasingly popular machinery of optimal estimation (OE) that is grounded in Bayesian statistics and uses a somehow linearized radiative transfer (RT) model. Nonetheless, OE feels like a black-box algorithm that outputs a number of “degrees of freedom” (a.k.a. independent pieces of information about clouds under observation). However, the very same conclusions are reached using fully transparent physics-based modeling for the RT, with a few approximations that enable closed-form analytical formulation. Lastly, we preview a novel DO2AS technique for regaining shortwave sensitivity to cloud optical thickness past the threshold where cloud reflectivity flattens off.
Highlights
AND OUTLINESince the beginning of operational satellite meteorology, NASA’s TIROS-1, we have been accustomed to seeing clouds as a dynamical 2D map projected onto the Earth’s surface
Another worthwhile review would focus on ground-based cloud studies with O2 absorption spectroscopy
another should focus on using O2 absorption spectroscopy
Summary
Since the beginning of operational satellite meteorology, NASA’s TIROS-1 (launched 1960), we have been accustomed to seeing clouds as a dynamical 2D map projected onto the Earth’s surface. A Second Workshop on “Remote Sensing in Oxygen Absorption Bands” was planned to happen in Berlin, Germany, in 2020, but has been postponed because of the COVID-19 pandemic to a future date in 2022 At any rate, this shows that there is a well-defined scientific community engaged in DO2AS, for clouds and from space in particular. As part of NASA’s generation of Earth observing satellites, the Atmospheric Observing System (AOS) implements the 2017 Decadal Survey’s ACCP element; it will include a UV-VIS imaging spectrometer in polar orbit that covers the O2 A-band at low spectral and moderate spatial resolutions, with a launch date in the late 2020s
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
