Latest Progress of the Chinese Meteorological Satellite Program and Core Data Processing Technologies

In this paper,the latest progress,major achievements and future plans of Chinese meteorological satellites and the core data processing techniques are discussed.First,the latest three FengYun(FY)meteorological satellites(FY-2H,FY-3D,and FY-4A)and their primary objectives are introduced Second,the core image navigation techniques and accuracies of the FY meteorological satellites are elaborated,including the latest geostationary(FY-2/4)and polar-orbit(FY-3)satellites.Third,the radiometric calibration techniques and accuracies of reflective solar bands,thermal infrared bands,and passive microwave bands for FY meteorological satellites are discussed.It also illustrates the latest progress of real-time calibration with the onboard calibration system and validation with different methods,including the vicarious China radiance calibration site calibration,pseudo invariant calibration site calibration,deep convective clouds calibration,and lunar calibration.Fourth,recent progress of meteorological satellite data assimilation applications and quantitative science produce are summarized at length.The main progress is in meteorological satellite data assimilation by using microwave and hyper-spectral infrared sensors in global and regional numerical weather prediction models.Lastly,the latest progress in radiative transfer,absorption and scattering calculations for satellite remote sensing is summarized,and some important research using a new radiative transfer model are illustrated.

Validation of Column-Averaged Dry-Air Mole Fraction of CO_2 Retrieved from OCO-2 Using Ground-Based FTS Measurements

In order to correctly use the column-averaged atmospheric COdry-air mole fraction(XCO) data in the COflux studies, XCOmeasurements retrieved from the Orbiting Carbon Observatory-2(OCO-2) in 2015 were compared with those obtained from the global ground-based high-resolution Fourier Transform Spectrometer(FTS) participating in the Total Carbon Column Observing Network(TCCON). The XCOretrieved from three observing modes adopted by OCO-2, i.e., nadir, target, and glint, were separately validated by the FTS measurements at up to eight TCCON stations located in different areas. These comparisons show that OCO-2 glint mode yields the best qualitative estimations of COconcentration among the three operational approaches. The overall results regarding the glint mode show no obvious systematic biases. These facts may indicate that the glint concept is appropriate for not only oceans but also land regions. Negative systematic biases in nadir and target modes have been found at most TCCON sites. The standard deviations of XCOretrieved from target and nadir modes within the observation period are similar, and larger than those from glint mode. We also used the FTS site in Beijing, China, to assess the OCO-2 XCOin 2016. This site is located in a typical urban area, which has been absent in previous studies. Overall, OCO-2 XCOagrees well with that from FTS at this site. Such a study will benefit the validation of the newly launched TanSat products in China.

Jacobian matrix for near-infrared remote sensing based on vector radiative transfer model

Due to the polarization effects of the Earth’s surface reflection and atmospheric particles’scattering,high-precision retrieval of atmospheric parameters from near-infrared satellite data requires accurate vector atmospheric radiative transfer simulations.This paper presents a near-infrared vector radiative transfer model based on the doubling and adding method.This new model utilizes approximate calculations of the atmospheric transmittance,reflection,and solar scattering radiance for a finitely thin atmospheric layer.To verify its accuracy,the results for four typical scenarios(single molecular layer with Rayleigh scattering,single aerosol layer scattering,multi-layer Rayleigh scattering,and true atmospheric with multi-layer molecular absorption,Rayleigh and aerosol scattering)were compared with benchmarks from a well-known model.The comparison revealed an excellent agreement between the results and the reference data,with accuracy within a few thousandths.Besides,to fulfill the retrieval algorithm,a numerical differentiation-based Jacobian calculation method is developed for the atmospheric and surface parameters.This is coupled with the adding and doubling process for the radiative transfer calculation.The Jacobian matrix produced by the new algorithm is evaluated by comparison with that from the perturbation method.The relative Jacobian matrix deviations between the two methods are within a few thousandths for carbon dioxide and less than 1.0×10-3%for aerosol optical depth.The two methods are consistent for surface albedo,with a deviation below 2.03×10-4%.All validation results suggest that the accuracy of the proposed radiative transfer model is suitable for inversion applications.This model exhibits the potential for simulating near-infrared measurements of greenhouse gas monitoring instruments.