AtmosphericModel/atmospheric refraction example.ipynb

Example: Calculating atmospheric dispersion for H-band

Using atmosphericModel.py is made as simple as importing the python file and calling its functions. Several parameters are needed, such as location, temperature, pressure and relative humidity. Then the dispersion model object is initiated, allowing us to calculate the index of refraction for any set of TPH and CO2 content values.

In [1]:

#!/usr/bin/env Python
import numpy as np
import matplotlib.pyplot as plt
from atmosphericModel import *


# Parameters at Cerro Armazones
T   = 279.65    # k
P   = 71200     # Pa
H   = 0.22
xc  = 450       # ppm
lat = -24.5983  # degrees
h   = 3064      # m
l1  = 1.49      # micron
l2  = 1.78      # micron

# Initializing dispersion model
at  = Ciddor1996(p=P, T=T, H=H, xc=xc)

# Calculating indices of refraction for l1 and l2
n1  = at.n_tph(l=l1, T=T, p=P, RH=H, xc=xc)
n2  = at.n_tph(l=l2, T=T, p=P, RH=H, xc=xc)

We can also calculate the density of the air, which will be useful when calculating the scale height of the atmosphere, necessary for the refraction calculations.

In [2]:

# Density of the atmosphere (following CIPM-81/91 equations)
rho = at.rho(p=P, T=T, RH=H, xc=xc)

# Initializing refraction model
ref = refraction(lat, h, P, rho)

The refraction for 1.49 um light at a zenith angle of 45 degrees, as calculated by the Cassini model, is found to be:

In [3]:

# Calculating refraction for edge FoV
zenith_obs = 45
refraction_obs = ref.cassini(n1, zenith_obs) * 3.6e3
print ('The refraction is %.03f arc seconds' %(refraction_obs))

The refraction is 40.697 arc seconds

Dispersion is simply the refraction differential between two wavelengths. This is calculated with this module by

In [4]:

# Initializing dispersion object
disp = dispersion(lat, h, P, rho)
dispersion_obs = disp.cassini(n1, n2, zenith=zenith_obs)*3.6e6
print ('The dispersion is %.03f milli arc seconds' %(dispersion_obs))

The dispersion is 31.019 milli arc seconds