2.3.1 spase://NASA/NumericalData/GOLD/L2/O2DEN/PT1200S Gold Level L2 Molecular Oxygen Density Profile 2020-09-14T16:47:17Z O2 is derived from measurements of stellar occultation in the Shumann Runge continuum. As the star rises or sets relative to the satellite position the stellar spectrum is measured across the GOLD spectral bandpass, from 132 to 162 nm. Geolocation of the OCC L1B data provides the line-of-sight tangent altitude vs. time during the occultation. This results in a 2-dimensional map of the stellar signal, in counts or calibrated geophysical units (irradiance), vs. wavelength and tangent altitude. A sample of this image is represented in the top left panel of the OCC L1D image in Figure 3-22. The measured counts profile is then normalized by the unattenuated, exo-atmospheric spectrum, yielding the slant path transmission profile vs. wavelength at the native L1C spectral sampling of 0.12 nm. The defining characteristic of the atmospheric transmission is that it is completely independent of instrument calibration or absolute accuracy. The full transmission spectrum is binned into a small number of 2-nm spectral channels for use in the retrievals. These retrieval channels are chosen to span the spectral dependence of the O2 absorption cross-section in order to maximize the O2 retrieval altitude range (approximately 120-240 km). In the Version 1 O2DEN data set two spectral channels are used, centered at 142- and 159-nm. Since stars rise or set at approximately 3 km/sec, as observed from orbit, the 100-msec occultation cadence results in a measurement of extremely high (sub-km) vertical resolution. The data are binned to enhance signal-to-noise, producing an effective vertical resolution of 10 km or less, which is sufficient to easily resolve the scale height of the O2 thermospheric profile. The algorithm uses an optimal estimation routine, which provide a complete error analysis and retrieval diagnostics such as averaging kernels and information content. A data vector constructed from the multiple spectral channels of slant path transmission is used to derive the atmospheric state vector – O2 density vs. geometric altitude – via a nonlinear, iterative inversion. The retrieved O2 density profile is reported on a fixed altitude grid with 5-km spacing. The valid altitude range varies for each event, but generally ranges from ~120 – 240. National Aeronautics and Space Administration; Dr. Richard Eastes spase://SMWG/Person/Richard.Eastes PrincipalInvestigator spase://SMWG/Person/James.M.Weygand MetadataContact GOLD Homepage web page https://gold.cs.ucf.edu/ GOLD web page with news and other information. GOLD Missions Space Science Reviews Article https://doi.org/10.1007/s11214-017-0392-2 Eastes, R.W., McClintock, W.E., Burns, A.G. et al. Space Sci. Rev. (2017) vol. 212, pp.383. spase://VSPO/NumericalData/GOLD/L2/O2DEN/PT1200S spase://NASA/NumericalData/SES-14/GOLD/L2/O2DEN/PT1200S spase://SMWG/Repository/NASA/GSFC/SPDF Online Open FTPS from SPDF (not with most browsers) ftps://spdf.gsfc.nasa.gov/pub/data/gold/level2/ FTPS access to Gold Level L2 data HTTPS from SPDF https://spdf.gsfc.nasa.gov/pub/data/gold/level2/ HTTPS access to Gold Level L2 data NetCDF Space Physics Data Facility of the NASA Goddard Space Flight Center; Robert E McGuire Calibrated GOLD Gold Level L2 Molecular Oxygen Density Profile Level 2 1 spase://SMWG/Instrument/GOLD ImageIntensity 2018-10-19T00:00:00 P1D PT1200S Earth.NearSurface.Ionosphere Day disk data GOLD SES-14 Spectral Width spectral_width Width of each data spectral channel. The size of the data array varies with the number of stellar occultations. PT1200S nm 0 10 9.9692e+36 Photon Scalar Wavelength O2 Density Random Uncertainty o2den_unc_ran Random uncertainty of retrieved O2. The size of the data array varies with the number of stellar occultations. PT1200S mol/cm^3 100000 999999986991104 9.9692e+36 Uncertainty Other Reference Longitude lon_ref Longitude at 225 km tangent point. The size of the data array varies with the number of stellar occultations. PT1200S degrees -180 180 9.9692e+36 Direction Positional O2 Density Model Uncertainty o2den_unc_mod Model uncertainty of retrieved O2. The size of the data array varies with the number of stellar occultations. PT1200S mol/cm^3 100000 999999986991104 9.9692e+36 Uncertainty Other Temperature temperature Assumed temperature profile. The size of the data array varies with the number of stellar occultations. PT1200S K 0 1000 9.9692e+36 Molecule Temperature 16 Retrieval geometric altitude grid zret Retrieval geometric altitude grid. The size of the data array varies with the number of stellar occultations. PT1200S km 0 1000 9.9692e+36 Direction Positional O2 Density o2den Retrieved O2 density. The size of the data array varies with the number of stellar occultations. PT1200S mol/cm^3 100000 999999986991104 9.9692e+36 Molecule NumberDensity 16 Number of Data Points nzdat Number of points in data altitude grid. The size of the data array varies with the number of stellar occultations. PT1200S -2147483647 Scalar Other UTC time TIME_UTC UTC date/time string: "2017-06-21T23:46:38.015Z". The size of the data array varies with the number of stellar occultations. PT1200S date/time ' ' Magnitude Temporal Number of Iterations n_iter Number of iterations to converge. The size of the data array varies with the number of stellar occultations. PT1200S number -2147483647 Scalar Other Convergence flag convergence Retrieval convergence flag (= 1 if retrieval converged). The size of the data array varies with the number of stellar occultations. PT1200S -2147483647 Scalar Other Number of Levels in Retrieval Altitude Grid nzret Number of levels in retrieval altitude grid. The size of the data array varies with the number of stellar occultations. PT1200S number -2147483647 Scalar Other L1C File Name input_l1c_file L1C file name for each occultation. The size of the data array varies with the number of stellar occultations. PT1200S ' ' Scalar Other O2 Systematic Uncertainty o2den_unc_sys Systematic uncertainty of retrieved O2. The size of the data array varies with the number of stellar occultations. PT1200S 100000 999999986991104 9.9692e+36 Uncertainty Other Reference Latitude lat_ref Latitude at 225 km tangent point. The size of the data array varies with the number of stellar occultations. PT1200S degrees -90 90 9.9692e+36 Direction Positional Normalization normalization Transmission normalization factor (unattenuated stellar brightness). The size of the data array varies with the number of stellar occultations. PT1200S counts 0 90 NaN Scalar Other O2 Data Quality o2den_dqi O2 data quality indicator per altitude (see table in The GOLD Public Science Data Products Guide). The size of the data array varies with the number of stellar occultations. PT1200S 0 2147483647 -2147483647 Scalar Other Channel channel GOLD channel (‘A’ or ‘B’). The size of the data array varies with the number of stellar occultations. PT1200S Scalar Other Central Wavelength central_wavelength Center wavelength of each data channel. The size of the data array varies with the number of stellar occultations. PT1200S nm 0 400 9.9692e+36 Photon Scalar Wavelength Signal to Noise signal_to_noise Effective signal to noise (above atmosphere). The size of the data array varies with the number of stellar occultations. PT1200S Scalar Other Number of Points in Data Altitude Grid zdat Number of points in data altitude grid. The size of the data array varies with the number of stellar occultations. PT1200S number Scalar Other Overall Quality Flag dqi Overall data quality index per scan (see table below). The size of the data array varies with the number of stellar occultations. PT1200S 0 1000 9.9692e+36 Scalar Other Model Fit Data transmission_fit Forward model fit to data. The size of the data array varies with the number of stellar occultations. PT1200S 0 10 9.9692e+36 Scalar Other Transmission Profile transmission Measured slant path transmission profile. The size of the data array varies with the number of stellar occultations. PT1200S 0 10 9.9692e+36 Scalar Other A Priori O2 Density o2_apriori A priori O2 density used in retrieval. The size of the data array varies with the number of stellar occultations. PT1200S mol/cm^3 100000 999999986991104 9.9692e+36 Molecule NumberDensity 16 Solar Zenith Angle at 225 km sza_ref Solar zenith angle at 225 km tangent point. The size of the data array varies with the number of stellar occultations. PT1200S degrees 0 180 9.9692e+36 Direction Positional Transmission Profile Uncertainty transmission_unc Transmission variance. The size of the data array varies with the number of stellar occultations. PT1200S 0 10 9.9692e+36 Scalar Other Name of Target Star target_star Name of target star. The size of the data array varies with the number of stellar occultations. PT1200S 0 5 9.9692e+36 Scalar Other