| Autor: |
Yu, Shanshan, Rosenberg, Robert, Bruegge, Carol, Chapsky, Lars, Fu, Dejian, Keller Rodrigues, Graziela, Crisp, David, Eldering, Annmarie, Taylor, Thomas, Cronk, Heather, O'Dell, Christopher, Angal, Amit, Xiong, Jack |
| Rok vydání: |
2020 |
| Zdroj: |
Conference on Characterization and Radiometric Calibration for Remote Sensing (CALCON) |
| Popis: |
The Orbiting Carbon Observatory 2 (OCO-2) and the Orbiting Carbon Observatory 3 (OCO-3) are NASA Earth Science missions designed to measure carbon dioxide in Earth’s atmosphere. OCO-2 was inserted at the front of the 705 km Afternoon Constellation (A-Train) in August 2014, and flies about 7 minutes ahead of the Aqua spacecraft. OCO-3 was mounted on the Japanese Experiment Module Exposed Facility onboard the International Space Station (ISS) in May 2019. OCO-2 and OCO-3 use three-channel grating spectrometers to measure reflected sunlight within the O2 band at 0.76 micron and two CO2 bands at 1.61 micron and 2.06 micron. The grating of each channel disperses light onto 1016 spectral channels of a focal plane array, yielding spectra with a resolution of ~ 0.04, 0.08, and 0.1 nm, respectively. OCO-2 uses onboard lamps, solar observations, and lunar measurements as well as surface targets for radiometric calibration/validation. OCO-3 is equipped with onboard lamps, and can also observe the Moon a few times each year, but cannot observe the Sun due to its configuration onboard ISS. The OCO missions require a 5% accuracy on absolute radiometric calibration to meet their CO2 accuracy requirements. Here, we describe results from the radiometric comparisons of OCO-2 and Aqua MODIS using OCO-2 nadir observations over eight desert sites and nearly simultaneous MODIS observations with sensor viewing zenith angles of 15±0.5 degree. The MODIS data are collocated into the OCO-2 geolocation grid using a 1 km circular region around each OCO-2 footprint. Without correcting for viewing geometry differences and mismatched spectral response functions, the mean and standard OCO-2/MODIS radiance ratio over the eight sites are determined to be 1.103±0.010, 1.120±0.007, 1.233±0.016 for the OCO-2 three bands, respectively. Here, we report the OCO-2 absolute radiometric calibration obtained from ongoing efforts to develop bi-directional reflectance distribution function (BRDF) models to account for the viewing geometry differences and to reduce the seasonal variations, and by correcting biases due to mismatched spectral response functions. We will also discuss the absolute radiometric comparison of OCO-2 and OCO-3 using simultaneous nadir overpasses of these desert sites. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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