English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The objective of the National Aeronautics and Space Administration's (NASA)Orbiting Carbon Observatory-2 (OCO-2) mission is to retrieve thecolumn-averaged carbon dioxide (CO2) dry air mole fraction(XCO2) from satellite measurements of reflectedsunlight in the near-infrared. These estimates can be biased by clouds andaerosols, i.e., contamination, within the instrument's field of view.Screening of the most contaminated soundings minimizes unnecessary calls tothe computationally expensive Level 2 (L2) XCO2retrieval algorithm. Hence, robust cloud screening methods have been animportant focus of the OCO-2 algorithm development team. Two distinct,computationally inexpensive cloud screening algorithms have been developedfor this application. The A-Band Preprocessor (ABP) retrieves the surfacepressure using measurements in the 0.76 µm O2 A band,neglecting scattering by clouds and aerosols, which introduce photonpath-length differences that can cause large deviations between theexpected and retrieved surface pressure. The Iterative Maximum A Posteriori (IMAP)Differential Optical Absorption Spectroscopy (DOAS) Preprocessor (IDP)retrieves independent estimates of the CO2 and H2O column abundancesusing observations taken at 1.61 µm (weak CO2 band) and2.06 µm (strong CO2 band), while neglecting atmosphericscattering. The CO2 and H2O column abundances retrieved in these twospectral regions differ significantly in the presence of cloud and scatteringaerosols. The combination of these two algorithms, which are sensitive to differentfeatures in the spectra, provides the basis for cloud screening of the OCO-2data set. To validate the OCO-2 cloud screening approach, collocated measurements fromNASA's Moderate Resolution Imaging Spectrometer (MODIS), aboard the Aquaplatform, were compared to results from the two OCO-2 cloud screeningalgorithms. With tuning of algorithmic threshold parameters that allows forprocessing of  ≃ 20–25 % of all OCO-2 soundings, agreement between theOCO-2 and MODIS cloud screening methods is found to be  ≃ 85 % overfour 16-day orbit repeat cycles in both the winter (December) and spring(April–May) for OCO-2 nadir-land, glint-land and glint-water observations. No major, systematic, spatial or temporal dependencies were found, althoughslight differences in the seasonal data sets do exist and validation is moreproblematic with increasing solar zenith angle and when surfaces are coveredin snow and ice and have complex topography. To further analyze theperformance of the cloud screening algorithms, an initial comparison of OCO-2observations was made to collocated measurements from the Cloud-Aerosol Lidarwith Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar andInfrared Pathfinder Satellite Observations (CALIPSO). These comparisonshighlight the strength of the OCO-2 cloud screening algorithms in identifyinghigh, thin clouds but suggest some difficulty in identifying some clouds nearthe surface, even when the optical thicknesses are greater than 1

Orbiting Carbon Observatory-2 (OCO-2) cloud screening algorithms: validation against collocated MODIS and CALIOP data