EGU2020-4109
https://doi.org/10.5194/egusphere-egu2020-4109
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Carbon dioxide retrieval from OCO-2 satellite observations using the nonlinear least squares four-dimensional variational method: observing system simulation experiments

Zhe Jin1,2 and Xiangjun Tian1,2,3
Zhe Jin and Xiangjun Tian
  • 1International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
  • 2University of Chinese Academy of Sciences, Beijing, China
  • 3Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing, China

In this study, we apply the nonlinear least squares four-dimensional variational (NLS-4DVar) method to the retrieval of the column-averaged dry air mole fraction of carbon dioxide (XCO2 ) from the Orbiting Carbon Observatory-2 (OCO-2) satellite observations. The NLS-4DVar method avoids the computation of the tangent linear and adjoint models of the forward model, which reduces the computational and implementation complexity greatly. We use the forward model from the Atmospheric CO2 Observations from Space (ACOS) XCO2 retrieval algorithm. The inverse model is constructed of two parts, generating samples and minimizing the cost function. For the CO2 profile, we apply an improved sampling algorithm based on ensemble singular value decomposition (SVD). For the other elements in the state vector, we apply a sampling algorithm based on normal distributions, and values of standard deviations of normal distributions are vital to the accuracy of retrieval. To minimize the cost function, the NLS-4Dvar method rewrite it into a nonlinear least squares problem, and solve it by a Gauss-Newton iterative method. We have tested our method in summer and winter at four sites through observing system simulation experiments, which are Lamont, Bremen, Wollongong and an ocean site in the North Pacific respectively. All the four sites show an improved XCO2 and CO2 profile after the retrieval.

How to cite: Jin, Z. and Tian, X.: Carbon dioxide retrieval from OCO-2 satellite observations using the nonlinear least squares four-dimensional variational method: observing system simulation experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4109, https://doi.org/10.5194/egusphere-egu2020-4109, 2020