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.Version:2.3.1
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.| Role | Person | StartDate | StopDate | Note | |
|---|---|---|---|---|---|
| 1. | PrincipalInvestigator | spase://SMWG/Person/Richard.Eastes | |||
| 2. | MetadataContact | spase://SMWG/Person/James.M.Weygand |
GOLD web page with news and other information.
Eastes, R.W., McClintock, W.E., Burns, A.G. et al. Space Sci. Rev. (2017) vol. 212, pp.383.
FTPS access to Gold Level L2 data
HTTPS access to Gold Level L2 data
Width of each data spectral channel.
Random uncertainty of retrieved O2.
Longitude at 225 km tangent point.
Model uncertainty of retrieved O2.
Assumed temperature profile.
Retrieval geometric altitude grid.
Retrieved O2 density.
Number of points in data altitude grid.
UTC date/time string: "2017-06-21T23:46:38.015Z".
Number of iterations to converge.
Retrieval convergence flag (= 1 if retrieval converged).
Number of levels in retrieval altitude grid.
L1C file name for each occultation.
Systematic uncertainty of retrieved O2.
Latitude at 225 km tangent point.
Transmission normalization factor (unattenuated stellar brightness).
O2 data quality indicator per altitude (see table in The GOLD Public Science Data Products Guide).
GOLD channel (‘A’ or ‘B’).
Center wavelength of each data channel.
Effective signal to noise (above atmosphere).
Number of points in data altitude grid.
Overall data quality index per scan (see table below).
Forward model fit to data.
Measured slant path transmission profile.
A priori O2 density used in retrieval.
Solar zenith angle at 225 km tangent point.
Transmission variance.
Name of target star.