"""Atmospheric functions and other operations.
This file keeps track of all of the functions and computations which deal
with the atmosphere. Note that seeing convolution and spectral convolution
is in the :py:mod:`lezargus.library.convolution` module.
"""
import numpy as np
import lezargus
from lezargus.library import hint
from lezargus.library import logging
[docs]
def airmass(zenith_angle: float | hint.ndarray) -> float | hint.ndarray:
"""Calculate the airmass from the zenith angle.
This function calculates the airmass provided a zenith angle. For most
cases the plane-parallel atmosphere method works, and it is what this
function uses. However, we also use a more accurate formula for airmass at
higher zenith angles (>80 degree), namely from DOI:10.1364/AO.28.004735.
We use a weighted average between 75 < z < 80 degrees to allow for a
smooth transition.
Parameters
----------
zenith_angle : float or ndarray
The zenith angle, in radians.
Returns
-------
airmass_value : float or ndarray
The airmass. The variable name is to avoid name conflicts.
"""
# The bounds of the spline region.
low_spline_deg = 75
high_spline_deg = 80
# For the Kasten Young 1989 equation, we need the zenith angle in degrees.
zenith_angle_degree = np.rad2deg(zenith_angle)
# We either use the faster secant version for zenith angles.
secant_airmass = 1 / np.cos(zenith_angle)
kasten_young_airmass = 1 / (
np.cos(zenith_angle)
+ 0.50572 * (6.07995 + 90 - zenith_angle_degree) ** (-1.6364)
)
# The two modes of calculation.
airmass_value = np.where(
zenith_angle_degree <= high_spline_deg,
secant_airmass,
kasten_young_airmass,
)
# Creating the average splice between the two regions.
splice_index = (zenith_angle_degree >= low_spline_deg) & (
zenith_angle_degree <= high_spline_deg
)
kasten_young_weights = (
zenith_angle_degree[splice_index] - low_spline_deg
) / 5.0
secant_weights = 1 - kasten_young_weights
airmass_value[splice_index] = (
secant_airmass[splice_index] * secant_weights
) + (kasten_young_airmass[splice_index] * kasten_young_weights)
# All done.
return airmass_value
[docs]
def index_of_refraction_ideal_air(wavelength: hint.ndarray) -> hint.ndarray:
"""Calculate the ideal refraction of air over wavelength.
The index of refraction of air depends slightly on wavelength, we use
the updated Edlen equations found in DOI: 10.1088/0026-1394/30/3/004.
Parameters
----------
wavelength : ndarray
The wavelength that we are calculating the index of refraction over.
This must in meters.
Returns
-------
ior_ideal_air : ndarray
The ideal air index of refraction.
"""
# The formal equation accepts only inverse micrometers, so we need to
# convert. The wave number is actually used more in these equations.
wavelength_um = lezargus.library.conversion.convert_units(
value=wavelength,
value_unit="m",
result_unit="um",
)
wavenumber = 1 / wavelength_um
# Calculating the index of refraction, left hand then right hand side of
# the equation.
ior_ideal_air_num = (
8342.54
+ 2406147 / (130 - wavenumber**2)
+ 15998 / (38.9 - wavenumber**2)
)
ior_ideal_air = ior_ideal_air_num / 1e8 + 1
return ior_ideal_air
[docs]
def index_of_refraction_dry_air(
wavelength: hint.ndarray,
pressure: float,
temperature: float,
) -> hint.ndarray:
"""Calculate the refraction of air of pressured warm dry air.
The index of refraction depends on wavelength, pressure and temperature, we
use the updated Edlén equations found in DOI: 10.1088/0026-1394/30/3/004.
Parameters
----------
wavelength : ndarray
The wavelength that we are calculating the index of refraction over.
This must in meters.
pressure : float
The pressure of the atmosphere, in Pascals.
temperature : float
The temperature of the atmosphere, in Kelvin.
Returns
-------
ior_dry_air : ndarray
The dry air index of refraction.
"""
# We need the ideal air case first.
ior_ideal_air = index_of_refraction_ideal_air(wavelength=wavelength)
# The Edlén equations use Celsius as the temperature unit, we need to
# convert from the standard Kelvin.
temperature = temperature - 273.15
if temperature < 0:
logging.warning(
warning_type=logging.AlgorithmWarning,
message=(
"The temperature specified for the Edlén equation for the index"
" of refraction is lower than 0 C. The applicability is of this"
" temperature is unknown."
),
)
# Calculating the pressure and temperature term.
pt_factor = (pressure / 96095.43) * (
(1 + pressure * (0.601 - 0.009723 * temperature) * 1e-8)
/ (1 + 0.003661 * temperature)
)
# Calculating the index of refraction of dry air.
ior_dry_air = (ior_ideal_air - 1) * pt_factor
ior_dry_air = ior_dry_air + 1
return ior_dry_air
[docs]
def index_of_refraction_moist_air(
wavelength: hint.ndarray,
temperature: float,
pressure: float,
water_pressure: float,
) -> hint.ndarray:
"""Calculate the refraction of air of pressured warm moist air.
The index of refraction depends on wavelength, pressure, temperature, and
humidity, we use the updated Edlen equations found in
DOI: 10.1088/0026-1394/30/3/004. We use the partial pressure of water in
the atmosphere as opposed to actual humidity.
Parameters
----------
wavelength : ndarray
The wavelength that we are calculating the index of refraction over.
This must in meters.
temperature : float
The temperature of the atmosphere, in Kelvin.
pressure : float
The pressure of the atmosphere, in Pascals.
water_pressure : float
The partial pressure of water in the atmosphere, Pascals.
Returns
-------
ior_moist_air : ndarray
The moist air index of refraction.
"""
# We need the dry air case first.
ior_dry_air = index_of_refraction_dry_air(
wavelength=wavelength,
pressure=pressure,
temperature=temperature,
)
# The wave number is actually used more in these equations. However, the
# wave number must be in inverse micrometers.
wavelength_um = lezargus.library.conversion.convert_units(
value=wavelength,
value_unit="m",
result_unit="um",
)
wavenumber = 1 / wavelength_um
# Calculating the water vapor factor.
wv_factor = -1 * water_pressure * (3.7345 - 0.0401 * wavenumber**2) * 1e-10
# Computing the moist air index of refraction.
ior_moist_air = ior_dry_air + wv_factor
return ior_moist_air
[docs]
def absolute_atmospheric_refraction_function(
wavelength: hint.ndarray,
zenith_angle: float,
temperature: float,
pressure: float,
water_pressure: float,
) -> hint.Callable[[hint.ndarray], hint.ndarray]:
"""Compute the absolute atmospheric refraction function.
The absolute atmospheric refraction is not as useful as the relative
atmospheric refraction function. To calculate how the atmosphere refracts
one's object, use that function instead.
Parameters
----------
wavelength : ndarray
The wavelength over which the absolute atmospheric refraction is
being computed over, in meters.
zenith_angle : float
The zenith angle of the sight line, in radians.
temperature : float
The temperature of the atmosphere, in Kelvin.
pressure : float
The pressure of the atmosphere, in Pascals.
water_pressure : float
The partial pressure of water in the atmosphere, Pascals.
Returns
-------
abs_atm_refr_func : Callable
The absolute atmospheric refraction function, as an actual callable
function. The input is wavelength in meters and output is refraction in
radians.
"""
# We need to determine the index of refraction for moist air.
ior_moist_air = index_of_refraction_moist_air(
wavelength=wavelength,
pressure=pressure,
temperature=temperature,
water_pressure=water_pressure,
)
# The constant of refraction.
const_of_refr = (ior_moist_air**2 - 1) / (2 * ior_moist_air**2)
# Incorporating the zenith angle.
abs_atm_refr = const_of_refr * np.tan(zenith_angle)
# Creating the function itself.
abs_atm_refr_func = (
lezargus.library.interpolate.spline_1d_interpolate_factory(
x=wavelength,
y=abs_atm_refr,
)
)
return abs_atm_refr_func
[docs]
def relative_atmospheric_refraction_function(
wavelength: hint.ndarray,
reference_wavelength: float,
zenith_angle: float,
temperature: float,
pressure: float,
water_pressure: float,
) -> hint.Callable[[hint.ndarray], hint.ndarray]:
"""Compute the relative atmospheric refraction function.
The relative refraction function is the same as the absolute refraction
function, however, it is all relative to some specific wavelength.
Parameters
----------
wavelength : ndarray
The wavelength over which the absolute atmospheric refraction is
being computed over, in meters.
reference_wavelength : float
The reference wavelength which the relative refraction is computed
against, in meters.
zenith_angle : float
The zenith angle of the sight line, in radians.
temperature : float
The temperature of the atmosphere, in Kelvin.
pressure : float
The pressure of the atmosphere, in Pascals.
water_pressure : float
The partial pressure of water in the atmosphere, Pascals.
Returns
-------
rel_atm_refr_func : Callable
The absolute atmospheric refraction function, as an actual callable
function. The input is wavelength in meters and output is refraction in
radians.
"""
# We need the absolute refraction function first.
abs_atm_refr_func = absolute_atmospheric_refraction_function(
wavelength=wavelength,
zenith_angle=zenith_angle,
pressure=pressure,
temperature=temperature,
water_pressure=water_pressure,
)
# The refraction at the reference wavelength.
ref_abs_refr = abs_atm_refr_func(reference_wavelength)
def rel_atm_refr_func(wave: hint.ndarray) -> hint.ndarray:
"""Relative refraction function.
Parameters
----------
wave : ndarray
The input wavelength for computation, in meters.
Returns
-------
rel_atm_refr : ndarray
The relative atmospheric refraction, in radians.
"""
rel_atm_refr = abs_atm_refr_func(wave) - ref_abs_refr
return rel_atm_refr
# All done.
return rel_atm_refr_func