Vicarious Calibration of Orbiting Carbon Observatory-2
- 20 March 2019
- journal article
- research article
- Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Geoscience and Remote Sensing
- Vol. 57 (7), 5135-5145
- https://doi.org/10.1109/tgrs.2019.2897068
Abstract
Vicarious calibration methods use well-characterized surface sites to complement other on-orbit radiometric calibration techniques. Since 2009, NASA's Orbiting Carbon Observatory-2 (OCO-2) and Japan's Greenhouse gasses Observing SATellite teams have conducted annual campaigns at Railroad Valley, NV, USA, for this purpose. These sensors pose special challenges due to their large footprint sizes and view angles. OCO-2 sweeps the playa surface during a targeted overpass of the test site, and records data at a number of viewing angles. The smallest of these is selected for processing, thereby minimizing the off-nadir correction. Surface reflectances at nadir are recorded by the field team, and the Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance product is used to provide the small, off-nadir correction. Another MODIS product, the Level 1B top-of-atmosphere radiance product, is used to validate the results and to provide input into the OCO-2 calibration uncertainty estimate. From 11 experiments, the ratio of radiances reported by the OCO-2 Level 1B data product to those from the field campaigns is 1.01, 1.04, and 1.01 for the three OCO-2 spectral bands. These analyses validate the data product absolute calibration, to within the 5% requirement. The need for executing these experiments will be of continued importance to OCO-3. This sensor has an on-hoard calibrator that provides a dark signal and lamps for response trends but does not have the on-board solar-diffuser present on OCO-2, and thus cannot track degradations relative to the Sun.Keywords
Funding Information
- California Institute of Technology
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