Getting Started¶
To build your an instrument simulation you will need,
- An instance of class Instrument.
- An instance of class Platform.
- An instance of class ForwardModel.
- An instance of sasktran.Atmosphere
These components, once configured, can radiances at the front aperture of the instrument.
Step 1: Make the Instrument¶
To make the instrument we are going to derive an instrument class from Instrument. Within the constructor of the class
we are goint to define 2 fields of view and 3 spectral point spread functions. We will then define 6 spectral windows using various
combinations of the fields of view and spectral point spread functions:
import math
from skimpy import FOV_Rectangle, Wavelength_GaussianPSF, SpectralWindow, Instrument
#------------------------------------------------------------------------------
# TestInstrument
#------------------------------------------------------------------------------
class TestInstrument( Instrument ):
"""
A test instrument class to demonstrate usage.
"""
def __init__(self ):
super().__init__( )
self.configure_front_end_fields_of_view()
#------------------------------------------------------------------------------
# configure_front_end_fields_of_view
#------------------------------------------------------------------------------
def configure_front_end_fields_of_view(self):
aperture_area_cms = 25.0
fov0 = FOV_Rectangle(Hrange=( 5, math.radians(0.0), math.radians(0.5)), # Horizontal field of view is 5 points spanning 0.0 to 0.5 degrees in instrument control frame
Vrange=( 3, math.radians(0.0), math.radians(20.0 / 3600.0))) # Vertical field of view is 3 points spanning 0.0 to 20 arc seconds in instrument control frame
fov1 = FOV_Rectangle( Hrange=(5, math.radians(0.2), math.radians(0.5)), # Horizontal field of view is 5 points 0.2 to 0.5 degrees in instrument control frame
Vrange=(3, math.radians(0.0), math.radians(20.0 / 3600.0))) # Vertical field of view is 3 points spanning 0.0 to 20 arc seconds in instrument control frame
fovidx0 = self.add_field_of_view( fov0 ) # define the different fields of view
fovidx1 = self.add_field_of_view( fov1 ) # used by this instrument. Define in instrument control frame coordinates
wavidx0 = self.add_wavelength_range( Wavelength_GaussianPSF( 30, 450.0, 0.3, rtm_processing_scheme='hybrid' )) # wavelength region 1. 30 wavelengths across 450 nanometers, FWHM = 0.53 nm
wavidx1 = self.add_wavelength_range( Wavelength_GaussianPSF( 30, 452.0, 0.4, rtm_processing_scheme='preconvolved')) # The code will spectrally integrate over each wavelength region
wavidx2 = self.add_wavelength_range( Wavelength_GaussianPSF( 30, 454.0, 0.5, rtm_processing_scheme='hybrid' ))
self.add_spectral_window( SpectralWindow( self, fovidx0, wavidx0, aperture_area_cms) ) # define the spectral windows used in the simulation
self.add_spectral_window( SpectralWindow( self, fovidx0, wavidx1, aperture_area_cms) ) # Each spectral window is a combination of a wavelength range and a field of view
self.add_spectral_window( SpectralWindow( self, fovidx0, wavidx2, aperture_area_cms) ) # The front-end radiance will be integrated over the eavelength range and the field of view
self.add_spectral_window( SpectralWindow( self, fovidx1, wavidx0, aperture_area_cms) )
self.add_spectral_window( SpectralWindow( self, fovidx1, wavidx1, aperture_area_cms) )
self.add_spectral_window( SpectralWindow( self, fovidx1, wavidx2, aperture_area_cms) )
Step 2. Make the platform¶
We are going to make a simple platform located at 600 km above (50N, 0E). It will look due North at the tangent heights from 0 to 40 km in steps of 2 km:
import numpy as np
from skimpy import Platform
#------------------------------------------------------------------------------
# class TestPlatform
#------------------------------------------------------------------------------
class TestPlatform( Platform ):
def __init__(self):
super().__init__()
self.make_observation_set()
#------------------------------------------------------------------------------
# step_to_next_observation
#------------------------------------------------------------------------------
def make_observation_set(self):
self.clear_states() # Clear the current observation set
t = np.datetime64('2018-07-31T12:15:35.023456') # Set the time of the observations
heights = np.arange( 0.0, 40000.0, 2000) # set the required tangent height, 0 to 40 km in 2 km steps
bearing = 0.0 # Set the geographic bearing
self.set_nadir_mode( False ) # Ensure we are not using nadir mode, ie. limb mode
self.set_platform_location(latlonheightandt=(50, 0, 600000.0, t)) # Set the location of the platform to (50N, 0E)
self.add_tangent_heights ( heights, bearing, clear_states = True) # Set the location of the platform
Step 3. Create the Forward Model and the Atmosphere¶
Next we must create the atmosphere and forward model:
import sasktran as sk
#------------------------------------------------------------------------------
# create_model_and_atmosphere
#------------------------------------------------------------------------------
def create_model_and_atmosphere()
atmosphere = sk.Atmosphere()
atmosphere['air'] = sk.Species(sk.Rayleigh(), sk.MSIS90())
atmosphere['ozone'] = sk.Species(sk.O3DBM(), sk.Labow())
model = ForwardModel('HR')
return mode, atmosphere
Step 4. Execute and Plot¶
And finally we put it all together so we can run it and make some plots:
import matplotlib.pyplot as plt def test_model(): model, atmosphere = screate_model_and_atmosphere() instrument = TestInstrument() platform = TestPlatform() model.calculate_radiance( instrument, platform, atmosphere) plt.figure(1) for window in instrument.spectral_windows: plt.plot(window.radiance.radiance, '.') plt.figure(2) for window in instrument.spectral_windows: plt.plot(window.radiance.toa_albedo, '.') plt.figure(3) for window in instrument.spectral_windows: plt.plot(window.radiance.irradiance, '.') plt.figure(4) for window in instrument.spectral_windows: plt.plot(window.radiance.photon_flux, '.') plt.show() test_model()