Usage

ARC-ACTRIS is intended to be imported as a Python package.

from arc_actris import arc

The main entry point is the arc class.

Basic scattering cross section

from arc_actris import arc

rrs = arc(incident_wavelength=355)
cross_section_355 = rrs.cross_section(cross_section_type="full")

print(cross_section_355)

This calculates the Rayleigh scattering cross section at 355 nm by summing the polarized and depolarized molecular scattering components.

Backscattering cross section and MLDR

To calculate backscattering quantities, initialize the object with backscattering=True.

from arc_actris import arc

rrb = arc(
    incident_wavelength=355,
    backscattering=True,
)

bsc_cross_section_355 = rrb.cross_section(cross_section_type="full")
mldr_355 = rrb.mldr(mldr_type="full")

print(bsc_cross_section_355)
print(mldr_355)

The mldr method is available only for backscattering calculations.

Temperature

The atmospheric temperature is given in Kelvin. If no temperature is provided, ARC-ACTRIS uses 288.15 K.

from arc_actris import arc

rrs = arc(
    incident_wavelength=532,
    temperature=285.15,
)

print(rrs.cross_section(cross_section_type="full"))

Custom atmospheric mixture

The molar_fractions dictionary defines the relative contribution of the atmospheric gases.

from arc_actris import arc

molar_fractions = {
    "N2": 0.780796,
    "O2": 0.209448,
    "Ar": 0.009339,
    "CO2": 0.000416,
    "H2O": 0.0,
}

rrb = arc(
    incident_wavelength=532,
    temperature=285.15,
    molar_fractions=molar_fractions,
    backscattering=True,
)

print(rrb.cross_section(cross_section_type="full"))
print(rrb.mldr(mldr_type="full"))

Single-gas calculation

To calculate the contribution of one gas, set its molar fraction to 1.0 and the others to 0.0.

from arc_actris import arc

n2_only = {
    "N2": 1.0,
    "O2": 0.0,
    "Ar": 0.0,
    "CO2": 0.0,
    "H2O": 0.0,
}

rrb = arc(
    incident_wavelength=355,
    molar_fractions=n2_only,
    backscattering=True,
)

print(rrb.cross_section(cross_section_type="full"))

Raman calculation mode

The mode argument selects the type of Raman calculation.

Available modes:

• rotational_raman
• vibrational_raman_N2
• vibrational_raman_O2

Example:

from arc_actris import arc

rrb = arc(
    incident_wavelength=355,
    backscattering=True,
    mode="vibrational_raman_N2",
)

print(rrb.cross_section(cross_section_type="full"))

Cross-section types

The cross_section method accepts the following cross_section_type values:

Type	Description
full	All polarized and depolarized lines.
main_line	Polarized part and Q branch.
polarized	Polarized part only.
depolarized	Depolarized Raman part only.
O	Anti-Stokes branch only.
Q	Q branch only.
S	Stokes branch only.
wings	Stokes and anti-Stokes branches.

Example:

from arc_actris import arc

rrs = arc(incident_wavelength=355)

print(rrs.cross_section(cross_section_type="polarized"))
print(rrs.cross_section(cross_section_type="depolarized"))
print(rrs.cross_section(cross_section_type="wings"))

MLDR types

The mldr method accepts the following mldr_type values:

Type	Description
full	MLDR for the full molecular spectrum.
main_line	MLDR for the main line contribution.
polarized	Fixed MLDR of the polarized component.
depolarized	Fixed MLDR of the depolarized component.

Example:

from arc_actris import arc

rrb = arc(incident_wavelength=355, backscattering=True)

print(rrb.mldr(mldr_type="full"))
print(rrb.mldr(mldr_type="main_line"))

Interference filter example

An interference filter can be included through the filter_parameters dictionary. Filter calculations are meaningful for backscattering applications.

from arc_actris import arc

filter_parameters = {
    "transmission_shape": "Gaussian",
    "central_wavelength": 355.0,
    "bandwidth": 0.5,
    "peak_transmission": 1.0,
}

rrb = arc(
    incident_wavelength=355,
    backscattering=True,
    filter_parameters=filter_parameters,
)

print(rrb.cross_section(cross_section_type="full"))
print(rrb.cross_section(cross_section_type="full", normalize=True))
print(rrb.mldr(mldr_type="full"))