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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/amt-2018-94
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
11 Apr 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).
A cloud algorithm based on the O2-O2 477 nm absorption band featuring an advanced spectral fitting method and the use of surface geometry-dependent Lambertian-equivalent reflectivity
Alexander Vasilkov1, Eun-Su Yang1, Sergey Marchenko1, Wenhan Qin1, Lok Lamsal2, Joanna Joiner3, Nickolay Krotkov3, David Haffner1, Pawan Bhartia3, and Robert Spurr4 1Science Systems and Applications Inc., Lanham, MD, USA
2Universities Space Research Association, Columbia, MD, USA
3NASA Goddard Space Flight Center, Greenbelt, MD, USA
4RT Solutions Inc., Cambridge, MA, USA
Abstract. We discuss a new cloud algorithm that retrieves an effective cloud pressure, also known as cloud optical centroid pressure (OCP), from oxygen dimer (O2-O2) absorption at 477 nm after determining an effective cloud fraction (ECF) at 466 nm, a wavelength not significantly affected by trace gas absorption and rotational-Raman scattering. The retrieved cloud products are intended for use as inputs to the operational nitrogen dioxide (NO2) retrieval algorithm for the Ozone Monitoring Instrument (OMI) flying on the Aura satellite. The cloud algorithm uses temperature-dependent O2-O2 cross-sections and incorporates flexible spectral fitting techniques that account for specifics of the surface reflectivity. The fitting procedure derives O2-O2 slant column densities (SCD) from radiances after O3, NO2, and H2O absorption features have been removed based on estimates of the amounts of these species from independent OMI algorithms. The cloud algorithm is based on the frequently used Mixed Lambert-Equivalent Reflectivity (MLER) concept. A geometry-dependent Lambertian-equivalent reflectivity (GLER) is used for the ground reflectivity in our implementation of the MLER approach. The OCP is derived from a match of the measured O2-O2 SCD to that calculated with the MLER method. Temperature profiles needed for computation of vertical column densities are taken from the Global Modeling Initiative (GMI) model. We investigate the effect of using GLER instead of climatological LER on the retrieved ECF and OCP. For evaluation purposes, the retrieved ECFs and OCPs are compared with those from the operational OMI cloud product which is also based on the same O2-O2 absorption band. Impacts of the application of the newly developed cloud algorithm to the OMI NO2 retrieval are discussed.
Citation: Vasilkov, A., Yang, E.-S., Marchenko, S., Qin, W., Lamsal, L., Joiner, J., Krotkov, N., Haffner, D., Bhartia, P., and Spurr, R.: A cloud algorithm based on the O2-O2 477 nm absorption band featuring an advanced spectral fitting method and the use of surface geometry-dependent Lambertian-equivalent reflectivity, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2018-94, in review, 2018.
Alexander Vasilkov et al.
Alexander Vasilkov et al.
Alexander Vasilkov et al.

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Short summary
We discuss a new cloud algorithm that retrieves cloud fraction and cloud altitude/pressure. The algorithm accounts for how changes in the sun-satellite geometry affect the surface reflection. The cloud fraction and pressure are used as inputs to the OMI algorithm that retrieves a pollutant gas called nitrogen dioxide.
We discuss a new cloud algorithm that retrieves cloud fraction and cloud altitude/pressure. The...
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