Abstract
Abstract. NASA's Orbiting Carbon Observatory-2 (OCO-2) has been measuring carbon dioxide column-averaged dry-air mole fraction, XCO2, in the Earth's atmosphere for over 2 years. In this paper, we describe the comparisons between the first major release of the OCO-2 retrieval algorithm (B7r) and XCO2 from OCO-2's primary ground-based validation network: the Total Carbon Column Observing Network (TCCON). The OCO-2 XCO2 retrievals, after filtering and bias correction, agree well when aggregated around and coincident with TCCON data in nadir, glint, and target observation modes, with absolute median differences less than 0.4 ppm and RMS differences less than 1.5 ppm. After bias correction, residual biases remain. These biases appear to depend on latitude, surface properties, and scattering by aerosols. It is thus crucial to continue measurement comparisons with TCCON to monitor and evaluate the OCO-2 XCO2 data quality throughout its mission.
Highlights
The Orbiting Carbon Observatory-2 (OCO-2) is NASA’s first Earth-orbiting satellite dedicated to observing atmospheric carbon dioxide (CO2) to better understand the carbon cycle
Any differences with magnitudes less than 0.4 ppm could be attributable to Total Carbon Column Observing Network (TCCON) station site-to-site biases (Wunch et al, 2010), so we focus on the biases that are significantly larger and most likely attributable to the OCO-2 data
Aggregated OCO-2 XCO2 estimates filtered with warn level ≤ 11 and xco2_quality_flag = 0 generally compare well with coincident TCCON data at global scales, with absolute median biases less than 0.4 ppm and RMS differences less than
Summary
The Orbiting Carbon Observatory-2 (OCO-2) is NASA’s first Earth-orbiting satellite dedicated to observing atmospheric carbon dioxide (CO2) to better understand the carbon cycle. The OCO-2 observation scheme was optimized on 12 November 2015, to assign orbits that are almost entirely over ocean to always measure in glint mode This change occurred on 72 out of the 233 orbital paths: 15 over the Atlantic and 57 over the Pacific, resulting in higher data throughput due to the reduction in nadir soundings over ocean. During a target-mode maneuver, the OCO-2 satellite rotates from its nominal science mode to point at a selected ground location This transition takes approximately 5 min and rotates the spacecraft’s solar panels away from the Sun. The spacecraft scans across the site or “nods” as it passes overhead to sweep across the ground several times (see Fig. 2) over a period of about 4.5 min: these dithered measurements comprise the “target-mode data”. The target locations were carefully chosen to span a wide range of latitudes, longitudes, and surface types to challenge the OCO-2 retrieval algorithm (B7r) and reveal any biases it causes
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