- class eradiate.radprops.US76ApproxRadProfile(absorption_dataset, thermoprops=_Nothing.NOTHING, has_absorption=True, has_scattering=True)#
Radiative properties profile approximately corresponding to an atmospheric profile based on the original U.S. Standard Atmosphere 1976 atmosphere model.
xarray.Dataset) – Absorption coefficient data set.
us76.make_profile) – Thermophysical properties.
This class does not support
us76module implements the original U.S. Standard Atmosphere 1976 atmosphere model, as defined by the [NASA et al., 1976] technical report. In the original atmosphere model, the gases are assumed well-mixed below the altitude of 86 kilometers. In the present radiative properties profile, the absorption coefficient is computed using the
spectra-us76_u86_4absorption dataset. This dataset provides the absorption cross-section of a specific mixture of N2, O2, CO2 and CH4, the mixing ratio of which are those defined by the U.S. Standard Atmosphere 1976 model for the region of altitudes under 86 kilometers, where these four gas species are well-mixed. As a result, the dataset is representative of the U.S. Standard Atmosphere 1976 model only below 86 kilometers. Since the atmosphere is typically a hundred kilometers high or more in radiative transfer applications, and in order to make the radiative properties profile reach these altitudes, the absorption coefficient is nevertheless computed using the
spectra-us76_u86_4dataset. This approximation assumes that the absorption coefficient does not vary much whether the mixing ratios of the absorbing gas mixture are those below or above 86 km.
Furthermore, the U.S. Standard Atmosphere 1976 model includes other gas species than N2, O2, CO2 and CH4. They are: Ar, He, Ne, Kr, H, O, Xe, He and H2. All these species except H2 are absent from the HITRAN spectroscopic database. Since the absorption datasets are computed using HITRAN, the atomic species could not be included in
spectra-us76_u86_4. H2 was mistakenly forgotten and should be added to the dataset in a future revision.
We refer to the U.S. Standard Atmosphere 1976 atmosphere model as the model defined by the set of assumptions and equations in part 1 of the report, and “numerically” illustrated by the extensive tables in part 4 of the report. In particular, the part 3, entitled Trace constituents, which provides rough estimates and discussions on the amounts of trace constituents such as ozone, water vapor, nitrous oxide, methane, and so on, is not considered as part of the U.S. Standard Atmosphere 1976 atmosphere model because it does not clearly define the concentration values of all trace constituents at all altitudes, neither does it provide a way to compute them.
It seems that the identifier “US76” is commonly used to refer to a standard atmospheric profile used in radiative transfer applications. However, there appears to be some confusion around the definition of that standard atmospheric profile. In our understanding, what is called the “US76 standard atmospheric profile”, or “US76” in short, is not the U.S. Standard Atmosphere 1976 atmosphere model but instead the so-called “U.S. Standard (1976) atmospheric constituent profile model” in a AFGL technical report entitled AFGL Atmospheric Constituent Profiles (0-120km) and published in 1986 by Anderson et al. [Anderson et al., 1986]. Although the “U.S. Standard (1976) atmospheric profile model” of the AFGL’s report is based on the U.S. Standard Atmosphere 1976 atmosphere model (hence the name), it is significantly different when it comes about the gas species concentration profiles. Notably, the “U.S. Standard (1976) atmospheric profile model” of the AFGL’s report include radiatively active gases such as H2O, O3, N2O, and CO, that the U.S. Standard Atmosphere 1976 atmosphere model does not include.
- eval_albedo(si, zgrid=None)#
Evaluate albedo at given spectral index.
- eval_dataset(si, zgrid=None)#
Evaluate radiative properties at given spectral index.
- eval_sigma_a(si, zgrid=None)#
Evaluate absorption coefficient at given spectral index.
- eval_sigma_a_ckd(w, g, zgrid)#
Evaluate absorption coefficient spectrum in CKD modes.
- eval_sigma_a_mono(w, zgrid)#
Evaluate absorption coefficient spectrum in monochromatic modes.
- eval_sigma_s(si, zgrid=None)#
Evaluate scattering coefficient at given spectral index.
- eval_sigma_t(si, zgrid=None)#
Evaluate extinction coefficient at given spectral index.
- property levels#
Return level altitudes.
- property thermoprops#
Return thermophysical properties.
- property zgrid#
Default altitude grid used for profile evaluation.