Occultation Sources

SASKTRAN2 can be used in pure occultation mode, i.e., to calculate transmittances instead of radiances. To do this, we disable all other sources and enable the occultation source.

import sasktran2 as sk

config = sk.Config()

config.single_scatter_source = sk.SingleScatterSource.NoSource
config.multiple_scatter_source = sk.MultipleScatterSource.NoSource
config.emission_source = sk.EmissionSource.NoSource

config.occultation_source = sk.OccultationSource.Standard

import numpy as np

model_geometry = sk.Geometry1D(cos_sza=0.6,
                                solar_azimuth=0,
                                earth_radius_m=6372000,
                                altitude_grid_m=np.arange(0, 65001, 1000),
                                interpolation_method=sk.InterpolationMethod.LinearInterpolation,
                                geometry_type=sk.GeometryType.Spherical)

viewing_geo = sk.ViewingGeometry()

for alt in [10000, 20000, 30000, 40000]:
    ray = sk.TangentAltitudeSolar(tangent_altitude_m=alt,
                                    relative_azimuth=0,
                                    observer_altitude_m=200000,
                                    cos_sza=0.6)
    viewing_geo.add_ray(ray)

wavel = np.arange(280.0, 800.0, 0.01)
atmosphere = sk.Atmosphere(model_geometry, config, wavelengths_nm=wavel)

atmosphere['rayleigh'] = sk.constituent.Rayleigh()

atmosphere['ozone'] = sk.climatology.mipas.constituent("O3", sk.optical.O3DBM())
atmosphere['no2'] = sk.climatology.mipas.constituent("NO2", sk.optical.NO2Vandaele())

sk.climatology.us76.add_us76_standard_atmosphere(atmosphere)

engine = sk.Engine(config, model_geometry, viewing_geo)

output = engine.calculate_radiance(atmosphere)


output['radiance'].isel(los=0).plot()

[<matplotlib.lines.Line2D at 0x764fb8305910>]

Note that in occultation mode the model produces transmittances, i.e., values between 0 and 1 where 0 is completely attenuated and 1 is no attenuation.

Relevant Configuration Options

sasktran2.Config.occultation_source

Sets which (if any) occultation source is to be used inside the calculation.