HITRAN_units and OmegaGrid not implemented in absorptionCoefficient_Voigt

[eli-miller]

Currently, there is an optional parameter for HITRAN_units in absorptionCoefficient_Voigt (and the other lineshape versions of this function), however it is never used within the function. I'm assuming that this should be handled using the volumeConcentration function from hapi to convert using molecules/cm^3. @RomanKochanov, can you comment on this?

Additionally, OmegaGrid is specified as an optional parameter, but ABSCOEF_FAST only take in WavenumberGrid. It seems like this is attempted to be handled with:

    # are deprecated and given for backward compatibility with the older versions.
    if WavenumberRange is not None:
        OmegaRange = WavenumberRange
    if WavenumberStep is not None:
        OmegaStep = WavenumberStep
    if WavenumberWing is not None:
        OmegaWing = WavenumberWing
    if WavenumberWingHW is not None:
        OmegaWingHW = WavenumberWingHW
    if WavenumberGrid is not None:
        OmegaGrid = WavenumberGrid

This is a backward implementation. If the user provides OmegaGrid, but not WavenumberGrid, the ABSCOEF_FAST function will recieve None for the wavelength axis.

[eli-miller]

Additionally, I'm noticing that the absorption simulations is not correctly using the molecular ID and isotopic ID specified when calling the function. I.e, if you are simulating with a table that contains multiple isotope values, and you specific Components=(1,1,0.01), it will still simulate all isotope values found in the source table. This is different than the expected behavior.

[HelyaHsiung]

According to my thoughts and guesses, this version of the HITRAN API is currently under development.
And this is my current pipeline of hapi2, wrote in utils.py as following:

from hapi2.db.models import Molecule
from hapi2.web import fetch_info, fetch_molecules, fetch_isotopologues, fetch_transitions, fetch_partition_functions
from hapi2.db.sqlalchemy.legacy import storage2cache
from hapi2.opacity.lbl.numba.fast_abscoef import arange_
from hapi2.opacity.lbl.numba import absorptionCoefficient_Voigt


def compute_absorption_voigt(
    molecule_name,
    numin,
    numax,
    T=296.0,
    P=1.0,
    HITRAN_units=True,
    diluent=None,
    step=0.01,
    wing_factor=50
):
    """
    Line-by-line absorption coefficient calculation using Voigt profile.

    Parameters
    ----------
    molecule_name : str
        HITRAN molecule name, e.g. 'CH4'
    numin, numax : float
        Requested spectral range (cm^-1)
    T : float
        Temperature (K)
    P : float
        Pressure (atm)
    diluent : dict or None
        Diluent definition, e.g. {'air':1.0}
        If None, defaults to air-broadening
    step : float
        Wavenumber grid spacing (cm^-1)
    wing_factor : float
        Line-wing extent in units of max Lorentz HWHM
    """

    if diluent is None:
        diluent = {'air': 1.0}

    table_name = f'{molecule_name}_{int(numin)}_{int(numax)}'

    # --- Molecule & isotopologue ---
    try:
        mol = Molecule(molecule_name)
    except:
        fetch_info()
        fetch_molecules()
        mol = Molecule(molecule_name)

    if len(mol.isotopologues) == 0:
        fetch_isotopologues([mol])

    main_iso = max(mol.isotopologues, key=lambda x: x.abundance)

    # Partition function is required for line intensity
    fetch_partition_functions([main_iso])

    # --- Transitions ---
    if main_iso.transitions.count() == 0:
        print(f"Download {molecule_name} spectral line: [{numin}-{numax} cm-1] ...")
        fetch_transitions([main_iso], numin, numax, table_name)

    print(f"Downloaded {table_name}: {main_iso.transitions.count()} n_points.\n")

    # --- Automatic wavenumber grid ---
    nu0 = [tr.nu for tr in main_iso.transitions]
    nu_min = min(nu0)
    nu_max = max(nu0)

    gamma_max = max(tr.gamma_air for tr in main_iso.transitions)
    margin = wing_factor * gamma_max

    wngrid = arange_(nu_min - margin, nu_max + margin, step)

    # --- Cache transitions ---
    storage2cache(table_name)

    # --- Absorption coefficient ---
    wavenumber, alpha = absorptionCoefficient_Voigt(
        SourceTables=[table_name],
        Environment={'T': T, 'p': P},
        HITRAN_units=HITRAN_units,
        Diluent=diluent,
        WavenumberGrid=wngrid
    )

    return wavenumber, alpha

Moreover, belowing is the usage example of function compute_absorption_voigt in main.py:

import matplotlib.pyplot as plt
from utils import compute_absorption_voigt


if __name__ == '__main__':
    nu, coef = compute_absorption_voigt('CH4', 1e4/12, 1e4/2)

    plt.figure(figsize=(10, 6))
    plt.plot(1e4 / nu, coef, color='gray', linewidth=0.8, label='Voigt Profile')
    plt.title(f'CH4 Absorption (Lorentz Profile)')
    plt.xlabel('Wavelength ($\mu m$)')
    plt.ylabel('Absorption Coefficient Cross Section ($cm^2/molecule$)')
    plt.grid(True, which='both', alpha=0.3)
    plt.legend()
    plt.show()

    print("All Job Were Done!")

I hope it will provide convenience to you.