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AtmosphericModel/atmosphericModel.py
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#!/usr/bin/env Python3
import numpy as np
from scipy import integrate
'''
@ Author: Joost van den Born
@ Contact: born@astron.nl
@ Description: This script offers a complete model of the atmospheric refraction
and dispersion. It uses the Ciddor1996 paper to calculate the
index of refraction for a wide range of conditions, with corresponding
error propagation if needed.
The actual refraction is calculated by any of the following models:
- Plane parallel atmosphere
- Cassini spherical homogeneous atmosphere
- Other methods described in Corbard et al., 2019.
'''
class Observatory:
def __init__(self, dT=0.2, dP=20, dH=0.02, dCO2=20, dl=0.001):
self.dT = dT # in K
self.dP = dP # in Pa
self.dH = dH # relative humidity between 0 and 1
self.dCO2 = dCO2 # in ppm
self.dl = dl # in micron
def n_as(self, l):
'''
Formula that calculate the refractive index for standard atmospheric
conditions, i.e. 15 C, 101,325 Pa, 0% RH, 450 ppm CO2.
It returns n_as, not (n_as - 1) * 1e8!
'''
_s = 1 / l
_k0 = 238.0185 # um^-2
_k1 = 5792105 # um^-2
_k2 = 57.362 # um^-2
_k3 = 167917 # um^-2
return (_k1 / (_k0 - _s**2) + _k3 / (_k2 - _s**2)) / 1e8 + 1
def n_axs(self, l, xc):
'''
Formula that calculate the refractive index for standard atmospheric
conditions, i.e. 15 C, 101,325 Pa, 0% RH, but with xc ppm of CO2.
It returns n_axs, not (n_axs - 1)
'''
_n_as = self.n_as(l)
return ( (_n_as - 1) * (1 + 0.534e-6 * (xc - 450) ) ) + 1
def n_ws(self, l):
'''
Formula that calculates the refractivity of air for standard moist conditions
as defined by B&S (1939), i.e. 20 C, 1333 Pa
Returns n_ws, not (n_ws - 1) * 1e8
'''
_s = 1 / l
_cf = 1.022
_w0 = 295.235 # um^-2
_w1 = 2.6422 # um^-2
_w2 = -0.032380 # um^-4
_w3 = 0.004028 # um^-6
return (_cf * (_w0 + _w1 * _s**2 + _w2 * _s**4 + _w3 * _s**6) ) / 1e8 + 1
def f(self, p, T):
'''
Enhancement factor of water vapour in air
t in degrees celsius
p in Pascal (Pa)
'''
_t = T - 273.15
_a = 1.00062
_b = 3.14e-8 # Pa^-1
_c = 5.6e-7 # deg C^-2
return _a + _b * p + _c * _t**2
def svp(self, T):
'''
Saturation vapour pressure in Pa.
'''
_A = 1.2378847e-5 # K^-2
_B = -1.9121316e-2 # K^-2
_C = 33.93711047
_D = -6.3431645e3 # K^-2
return np.exp(_A*T**2 + _B*T + _C + _D/T)
def svp2(self, T):
'''
Calculation of svp from IAPWS formula, based on documentation by NIST toolbox.
'''
K1 = 1.16705214528e+03
K2 = -7.24213167032e+05
K3 = -1.70738469401e+01
K4 = 1.20208247025e+04
K5 = -3.23255503223e+06
K6 = 1.49151086135e+01
K7 = -4.82326573616e+03
K8 = 4.05113405421e+05
K9 = -2.38555575678e-01
K10 = 6.50175348448e+02
_W = T + K9 / (T - K10)
_A = _W**2 + K1*_W + K2
_B = K3*_W**2 + K4*_W + K5
_C = K6*_W**2 + K7*_W + K8
_X = -_B + np.sqrt(_B**2 - 4*_A*_C)
return (2*_C / _X)**4 * 1e6
def xw(self, p, T, RH):
'''
Molar fraction of water vapour in moist air.
'''
_f = self.f(p, T)
_svp = self.svp(T)
return _f * RH * _svp / p
def Z(self, p, T, RH, xw=''):
'''
Compressibility of moist air
'''
_a0 = 1.58123e-6 # K Pa^-1
_a1 = -2.9331e-8 # Pa^-1
_a2 = 1.1043e-10 # K^-1 Pa^-1
_b0 = 5.707e-6 # K Pa^-1
_b1 = -2.051e-8 # Pa^-1
_c0 = 1.9898e-4 # K Pa^-1
_c1 = -2.376e-6 # Pa^-1
_d = 1.83e-11 # K^2 Pa^-2
_e = -0.765e-8 # K^2 Pa^-2
_t = T - 273.15
if xw == '':
_xw = self.xw(p, T, RH)
else:
_xw = xw
Z = 1 - (p/T) * (_a0 + _a1*_t + _a2*_t**2 + (_b0 + _b1*_t)*_xw + (_c0 + _c1*_t)*_xw**2) + (p/T)**2 * (_d + _e*_xw**2)
return Z
def rho(self, p, T, RH, xc, xw=''):
'''
Calculates the density of air for the given parameters.
T in Kelvin
p in Pascal
RH between 0 and 1
xc in ppm
'''
_Ma = 1e-3 * (28.9635 + 12.011e-6 * (xc - 400) ) # Molar mass in kg/mol of dry air containing xc ppm of CO2
_Mw = 0.018015 # kg/mol
_R = 8.314510 # J mol^-1 K^-1, gas constant
if xw == '':
_xw = self.xw(p, T, RH)
else:
_xw = xw
_Z = self.Z(p, T, RH, xw=_xw)
return ( ( p * _Ma ) / (_Z * _R * T) ) * ( 1 - _xw * (1 - _Mw/_Ma))
def n_tph(self, l, T, p, RH, xc):
'''
Calculates the refraction of the atmosphere for any conditions.
'''
_n_a = self.n_axs(l, xc)
_n_w = self.n_ws(l)
_La = (_n_a**2 - 1) / (_n_a**2 + 2)
_Lw = (_n_w**2 - 1) / (_n_w**2 + 2)
# Calculate the density of the dry air components, using the partial pressure of the dry air, i.e. p_dry = p_atm - p_water
_rho_a = self.rho(p=p-RH*self.svp(T), T=T, RH=0, xc=xc) # Dry air component for the actual conditions.
_rho_axs = self.rho(p=101325, T=288.15, RH=0, xc=xc) # Dry air component at standard conditions.
if RH == 0:
# nan is returned for _rho_w if we put in a (partial) pressure of 0
_rho_w = 0
else:
# Partial pressure of water vapour is p_water = h*svp
_rho_w = self.rho(p=RH*self.svp(T), T=T, RH=RH, xc=xc) # Moist air component for the actual conditions.
_rho_ws = self.rho(p=1333, T=293.15, RH=1333/self.svp(293.15), xc=xc) # Moist air component at standard conditions.
_Ltotal = ( _rho_a / _rho_axs ) * _La + ( _rho_w / _rho_ws ) * _Lw
# print 'Dry air component = ', (_rho_a/_rho_axs)*(_n_a-1)*1e8
# print 'Wet component = ', ( _rho_w / _rho_ws ) * (_n_w - 1)*1e8
# print 'Sum of components = ', (_rho_a/_rho_axs)*(_n_a-1)*1e8+( _rho_w / _rho_ws ) * (_n_w - 1)*1e8
return np.sqrt( (1 + 2 * _Ltotal) / (1 - _Ltotal) )
def dn_tph(self, l, T, p, RH, xc, dl=None, dT=None, dP=None, dRH=None, dCO2=None):
'''
Calculates the uncertainty in the refractive index, following the Ciddor model,
by using fully propagated error analysis.
This involves almost endless use of the chain rule and evaluation of both the moist
air and dry air components. Note: dry air does not contain any water, i.e. H=0, x_w=0, etc.
Parameters:
l - Wavelength in micron (0.4 - 2.5 micron)
T - Temperature in Kelvin
p - Pressure in Pascals
RH - Relative humidity (no units, don't use percentage but value 0<x<1)
xc - CO2 density in ppm
dl - Uncertainty in the blue wavelength
dT - Uncertainty in the temperature, default: 0.2 K
dP - Uncertainty in the pressure, default: 20 Pa
dRH - Uncertainty in the relative humidity, default: 0.02
dCO2- Uncertainty in the CO2 density, default: 20
'''
if dP == None:
dP = self.dP
if dT == None:
dT = self.dT
if dRH == None:
dRH = self.dH
if dCO2 == None:
dCO2 = self.dCO2
# constants
_cf = 1.022
_w0 = 295.235 # um^-2
_w1 = 2.6422 # um^-2
_w2 = -0.032380 # um^-4
_w3 = 0.004028 # um^-6
_k0 = 238.0185 # um^-2
_k1 = 5792105 # um^-2
_k2 = 57.362 # um^-2
_k3 = 167917 # um^-2
_A = 1.2378847e-5 # K^-2
_B = -1.9121316e-2 # K^-2
_C = 33.93711047
_D = -6.3431645e3 # K^-2
_Mw = 0.018015 # kg/mol
_R = 8.314510 # J mol^-1 K^-1, gas constant
_a0 = 1.58123e-6 # K Pa^-1
_a1 = -2.9331e-8 # Pa^-1
_a2 = 1.1043e-10 # K^-1 Pa^-1
_b0 = 5.707e-6 # K Pa^-1
_b1 = -2.051e-8 # Pa^-1
_c0 = 1.9898e-4 # K Pa^-1
_c1 = -2.376e-6 # Pa^-1
_d = 1.83e-11 # K^2 Pa^-2
_e = -0.765e-8 # K^2 Pa^-2
_t = T - 273.15
_aa = 1.00062
_bb = 3.14e-8 # Pa^-1
_cc = 5.6e-7 # deg C^-2
_RH_a = 0
_RH_w = RH
# Calculated values
# _rho_obs = self.rho(p, T, RH, xc)
# _ref = refraction(lat, h, p, _rho_obs)
# _alpha = _ref.rc * np.sin(np.deg2rad(z)) / (_ref.rc + _ref.H)
_p_a = p - RH*self.svp(T)
_p_w = RH*self.svp(T)
_x_w_a = self.xw(_p_a, T, _RH_a)
_x_w_w = self.f(_p_w, T)
_Z_a = self.Z(p=_p_a, T=T, RH=_RH_a)
_Z_w = self.Z(p=_p_w, T=T, RH=_RH_w, xw=_x_w_w)
_Ma = 1e-3 * (28.9635 + 12.011e-6 * (xc - 400) ) # Molar mass in kg/mol of dry air containing xc ppm of CO2
_p_sv = self.svp(T)
_rho_a = self.rho(p=p-RH*self.svp(T), T=T, RH=0, xc=xc)
_rho_axs = self.rho(p=101325, T=288.15, RH=0, xc=xc)
if RH == 0.0:
# nan is returned for _rho_w if we put in a (partial) pressure of 0
_rho_w = 0
else:
_rho_w = self.rho(p=RH*self.svp(T), T=T, RH=RH, xc=xc)
_rho_ws = self.rho(p=1333, T=293.15, RH=1333/self.svp(293.15), xc=xc)
_n_a1 = self.n_axs(l, xc)
_n_w1 = self.n_ws(l)
_L1_a = (_n_a1**2 - 1) / (_n_a1**2 + 2) # Dry air component of L
_L1_w = (_n_w1**2 - 1) / (_n_w1**2 + 2)
_L1 = ( _rho_a / _rho_axs ) * _L1_a + ( _rho_w / _rho_ws ) * _L1_w # Overall L
_n1 = np.sqrt( (1 + 2 * _L1) / (1 - _L1) )
# Partial derivatives for derivation to l1
_dn_wdl = _cf * 1e-8 * (-1 * _w1 * 2/l**3 - _w2 * 4/l**5 - _w3 * 6/l**7)
_dLdn_w1 = _rho_w / _rho_ws * 6 * _n_w1 / (_n_w1**2 + 2)**2
_dn_adl = 1e-8 * (1 + 0.534e-6 * (xc - 450)) * ( - (2 * _k1 * l ) / ((_k0 * l**2 - 1)**2) - (2 * _k3 * l) / ((_k2 * l**2 - 1)**2) )
_dLdn_a1 = _rho_a / _rho_axs * 6 * _n_a1 / (_n_a1**2 + 2)**2
_dndL1 = ( ( (1 + 2*_L1) / (1 - _L1)**2 ) + (2 / (1-_L1)) ) / (2 * np.sqrt( (1 + 2*_L1) / (1 - _L1) ) )
_dndl = _dndL1 * ( _dLdn_a1 * _dn_adl + _dLdn_w1 * _dn_wdl)
# # Partial derivatives for derivation to l2
# Partial derivatives for derivation to T
# Dry air parts:
_drho_adp_a = _Ma / (_Z_a * _R * T) * (1 - _x_w_a * (1 - _Mw / _Ma))
_dp_adp_sv = - RH
_dp_svdT = (2*_A*T + _B - _D/(T**2)) * np.exp(_A * T**2 + _B * T + _C + _D/T )
_drho_adTZ = - _p_a * _Ma / (_R * ( _Z_a * T)**2) * (1 - _x_w_a * (1 - _Mw / _Ma))
_dTZdT_a = _p_a / T * (_a2 * _t**2 + _a1 * _t + _a0 + (_b1*_t + _b0) * _x_w_a + (_c0 + _c1*_t) * _x_w_a**2 ) - _p_a * (_a1 + 2*_a2*_t + _b1*_x_w_a + _c1*_x_w_a**2) - 2*(_p_a/T)**2 * (_d + _e * _x_w_a**2) + _Z_a
_dTZdxw_a = 2*_e*_p_a**2 / T * _x_w_a - _p_a * (_b1*_t + _b0 + 2 * (_c0 + _c1*_t) * _x_w_a)
_dxw_adf = _RH_a * _p_sv / _p_a
_dfdT = 2*_cc*_t
_dxw_adp_sv = self.f(_p_a, T) * _RH_a / _p_a
_drho_adxw_a = 0 # as rho_a has not water content, i.e. rho = p*M/ZRT
# Moist air parts:
_drho_wdp_w = _Ma / (_Z_w * _R * T) * (1 - _x_w_w * (1 - _Mw / _Ma))
_dp_wdp_sv = RH
_dp_svdT = (2*_A*T + _B - _D/(T**2)) * np.exp(_A * T**2 + _B * T + _C + _D/T )
_drho_wdTZ = - _p_w * _Ma / (_R * (_Z_w * T)**2) * (1 - _x_w_w * (1 - _Mw / _Ma))
_dTZdT_w = _p_w / T * (_a2 * _t**2 + _a1 * _t + _a0 + (_b1*_t + _b0) * _x_w_w + (_c0 + _c1*_t) * _x_w_w**2 ) - _p_w * (_a1 + 2*_a2*_t + _b1*_x_w_w + _c1*_x_w_w**2) - 2*(_p_w/T)**2 * (_d + _e * _x_w_w**2) + _Z_w
_dTZdxw_w = 2*_e*_p_w**2 / T * _x_w_w - _p_w * (_b1*_t + _b0 + 2 * (_c0 + _c1*_t) * _x_w_w)
_dxw_wdf = 1
_dfdT = 2*_cc*_t
_dxw_wdp_sv = self.f(_p_w, T) / _p_sv
_drho_wdxw_w = _p_w * _Ma / (_Z_w * _R * T) * (_Mw / _Ma - 1)
_tA = _drho_adp_a * _dp_adp_sv * _dp_svdT + _drho_adTZ * (_dTZdT_a + _dTZdxw_a * (_dxw_adf * _dfdT + _dxw_adp_sv * _dp_svdT) ) + _drho_adxw_a * ( _dxw_adf * _dfdT + _dxw_adp_sv * _dp_svdT )
_tB = _drho_wdp_w * _dp_wdp_sv * _dp_svdT + _drho_wdTZ * (_dTZdT_w + _dTZdxw_w * (_dxw_wdf * _dfdT + _dxw_wdp_sv * _dp_svdT) ) + _drho_wdxw_w * ( _dxw_wdf * _dfdT + _dxw_wdp_sv * _dp_svdT )
_dL1drho_a = _L1_a / _rho_axs
_dL1drho_w = _L1_w / _rho_ws
_dndT = _tA * (_dndL1 * _dL1drho_a) + _tB * (_dndL1 * _dL1drho_w)
# Partial derivatives for derivation to p
# Dry air parts:
_drho_adZ = - _p_a * _Ma / ( _Z_a**2 * _R * T) * (1 - _x_w_a * (1 - _Mw / _Ma))
_dZdp_a = - 1 / T * (_a0 + _a1 * _t + _a2 * _t**2 + (_b0 + _b1*_t)*_x_w_a + (_c0 + _c1*_t)*_x_w_a**2 ) + 2*_p_a/(T**2) * (_d + _e * _x_w_a**2)
_dfdp = _bb
_dxw_adp_a = - self.f(_p_a, T) * _RH_a * _p_sv / (_p_a)**2
# Moist air parts
_dZdp_w = - 1 / T * (_a0 + _a1 * _t + _a2 * _t**2 + (_b0 + _b1*_t)*_x_w_w + (_c0 + _c1*_t)*_x_w_w**2 ) + 2*_p_w/(T**2) * (_d + _e * _x_w_w**2)
# Not necessary, since dpwdp=0
_pA = _drho_adp_a + _drho_adZ * _dZdp_a + _drho_adxw_a * (_dxw_adf * _dfdp + _dxw_adp_a)
_dndP = _pA * (_dndL1 * _dL1drho_a)
# Partial derivatives for derivation to H
# Dry air parts:
_dp_adH = - _p_sv
_dZdxw_a = (_p_a / T)**2 * 2 * _e * _x_w_a - (_p_a / T) * ( (_b0 + _b1 * _t) + 2 * (_c0 + _c1 * _t) * _x_w_a )
_dxw_adH = self.f(_p_a, T) * _p_sv / _p_a
# Moist air parts:
_dp_wdH = _p_sv
_dZdxw_w = (_p_w / T)**2 * 2 * _e * _x_w_w - (_p_w / T) * ( (_b0 + _b1 * _t) + 2 * (_c0 + _c1 * _t) * _x_w_w )
_dxw_wdH = 0
_dxw_wdp_w = 0
_drho_wdZ = - _p_w * _Ma / ( _Z_w**2 * _R * T) * (1 - _x_w_w * (1 - _Mw / _Ma))
_hA = _drho_adp_a * _dp_adH + _drho_adZ * ( _dZdp_a * _dp_adH + _dZdxw_a * (_dxw_adH + _dxw_adp_a * _dp_adH + _dxw_adf * _dfdp * _dp_adH) ) + _drho_adxw_a * (_dxw_adH + _dxw_adp_a * _dp_adH + _dxw_adf * _dfdp * _dp_adH)
_hB = _drho_wdp_w * _dp_wdH + _drho_wdZ * ( _dZdp_w * _dp_wdH + _dZdxw_w * ( _bb * _p_sv ) ) + _drho_wdxw_w * ( _bb * _p_sv )
_dndRH = _hA * (_dndL1 * _dL1drho_a) + _hB * (_dndL1 * _dL1drho_w)
# Partial derivatives for derivation to xc
# Dry air parts:
_drho_adMa = _p_a * (1 - _x_w_a) / (_Z_a * _R * T)
_dL1drho_axs = - (_rho_a * _L1_a)/(_rho_axs**2)
_drho_axsdMa = _drho_adMa
_dL1dL_a = _rho_a / _rho_axs
_dL_adn_a1 = 6 * _n_a1 / (_n_a1**2 + 2)**2
# Moist air parts:
_drho_wdMa = _p_w * (1 - _x_w_w) / (_Z_w * _R * T)
_dL1drho_ws = - (_rho_w * _L1_w)/(_rho_ws**2)
_drho_wsdMa = _drho_wdMa
# Other parts:
_dMadx_c = 12.011e-9
_dn_adx_c1 = (self.n_as(l) - 1) * 0.534e-6
_dL1dx_c = _dL1drho_a * _drho_adMa * _dMadx_c + _dL1drho_w * _drho_wdMa * _dMadx_c + _dL1drho_axs * _drho_axsdMa * _dMadx_c + _dL1drho_ws * _drho_wsdMa * _dMadx_c + _dL1dL_a * _dL_adn_a1 * _dn_adx_c1
_dndCO2 = _dndL1 * _dL1dx_c
# Final error:
_nError = np.sqrt( (_dndl * dl)**2 + (_dndT * dT)**2 + (_dndP * dP)**2 + (_dndRH * dRH)**2 + (_dndCO2 * dCO2)**2 )
return _nError
class dispersion(Observatory):
def __init__(self, lat, h):
Observatory.__init__(self)
self.h = h # height above sea level in meters
self.lat = lat # Latitude of the observer in degrees
self.rc = self.set_rc() * 1000 # Radius of curvature of the earth at the observer
def setReducedHeight(self, P, rho):
self.H = self.set_H(P, rho) # Reduced height of the atmosphere assuming ideal gas law
def planeParallel(self, n1, n2, zenith):
'''
Refraction based on a flat atmosphere, easily derived from Snell's law.
'''
_R1 = np.arcsin(n1 * np.sin( np.deg2rad(zenith) )) - np.deg2rad(zenith)
_R2 = np.arcsin(n2 * np.sin( np.deg2rad(zenith) )) - np.deg2rad(zenith)
return np.degrees(_R1) - np.degrees(_R2)
def cassini(self, n1, n2, zenith, reduced_height=None):
'''
Refraction of spherical atmosphere, derived from geometry using Sine law
'''
if reduced_height:
H = reduced_height
else:
H = self.H
_R1 = np.arcsin(n1 * self.rc * np.sin(np.deg2rad(zenith)) / (self.rc + H)) - np.arcsin(self.rc * np.sin(np.deg2rad(zenith)) / (self.rc + H) )
_R2 = np.arcsin(n2 * self.rc * np.sin(np.deg2rad(zenith)) / (self.rc + H)) - np.arcsin(self.rc * np.sin(np.deg2rad(zenith)) / (self.rc + H) )
return np.degrees(_R1) - np.degrees(_R2)
def tan5(self, n1, n2, zenith, reduced_height=None):
'''
Same as oriani's theorem, but including a higher order term.
Found in Corbard et al., 2019.
'''
if reduced_height:
H = reduced_height
else:
H = self.H
_rList = []
for _n in [n1, n2]:
_a = _n - 1
_b = H / self.rc
_R = _a * (1 - _b) * np.tan( np.deg2rad(zenith) ) - _a * (_b - _a/2) * np.tan( np.deg2rad(zenith) )**3 + 3 * _a * (_b - _a/2)**2 * np.tan( np.deg2rad(zenith) )**5
_rList.append(np.degrees(_R))
return _rList[0] - _rList[1]
def oriani(self, n1, n2, zenith, reduced_height=None):
'''
Classic refraction formula with two tan(z) terms. This does not assume any
information about the structure of the atmosphere. Found with Oriani's theorem.
'''
if reduced_height:
H = reduced_height
else:
H = self.H
_rList = []
for _n in [n1, n2]:
_a = _n - 1
_b = H / self.rc
_R = _a * (1 - _b) * np.tan( np.deg2rad(zenith) ) - _a * (_b - _a/2) * np.tan( np.deg2rad(zenith) )**3
_rList.append(np.degrees(_R))
return _rList[0] - _rList[1]
def corbard(self, n1, n2, zenith, reduced_height=None):
'''
Corbard et al., 2019, mention an additional formula based on the error function.
Oriani's theorem can be derived from this equation by 'keeping only the three first
terms of its asymptotic expansion'.
'''
if reduced_height:
H = reduced_height
else:
H = self.H
_rList = []
for _n in [n1, n2]:
_a = _n - 1
_b = H / self.rc
_R = _a * ( (2 - _a) / (np.sqrt( 2*_b - _a )) ) * np.sin( np.deg2rad(zenith) ) * self.psi( (np.cos(np.deg2rad(zenith))) / np.sqrt(2*_b - _a) )
_rList.append(np.degrees(_R))
return _rList[0] - _rList[1]
def refractionIntegral(self, n1, n2, z0, R0=None, useStandardAtmosphere=True, heightData=None, rhoData=None):
'''
Using data that gives temperature, pressure and density as a function of height,
the gladstone-dale relation is invoked to calculate the path of a light ray
along the atmosphere. This is allows us to also include atmospheric activity in
different atmosphere layers.
Recommended use with the US Standard Atmosphere from 1976.
USSA1976 data generated from code supplied by http://www.pdas.com/atmos.html
The method described in eq. 3 in Auer & Standish (2000) is used for the calculation.
'''
if not R0:
R0 = self.rc
if useStandardAtmosphere:
_h, _, _, _, _Temp, _Press, _Dens,_,_,_ = np.genfromtxt('1976USSA.txt', unpack=True, skip_header=6)
else:
_Dens = rhoData
_h = heightData
_rList = []
z0 = np.deg2rad(z0)
# Integration of the refraction integral over the atmosphere layers.
for _n in [n1, n2]:
_Dens = np.asarray(_Dens)
_h = np.asarray(_h)
_R = R0 + _h * 1000
# Gladstone-Dale relation between refractive index and density
_n_h = 1 + (_n - 1) / _Dens[0] * _Dens
# Calculation of the zenith angle for given height and refractive index, from the refractive invariant
_z = np.arcsin( (_n * R0) / (_n_h * _R) * np.sin(z0) )
# Calculation of log space derivative of n and r
_lnn = np.log(_n_h)
_lnr = np.log(_R)
_dlnn = np.asarray([_lnn[i+1] - _lnn[i] for i in range(len(_lnn)-1)])
_dlnr = np.asarray([_lnr[i+1] - _lnr[i] for i in range(len(_lnr)-1)])
_dz = np.asarray([(_z[i] - _z[i+1]) for i in range(len(_z)-1)])
# Calculation of the integrand in eq. 3 in Auer & Standish
_Integrand = -1*(_dlnn/_dlnr) / (1 + _dlnn/_dlnr) * _dz
_rList.append(np.degrees(np.sum(_Integrand)))
return _rList[0] - _rList[1]
def psi(self, x):
_f = lambda a: np.exp(-a**2)
_int = integrate.quad(_f, x, np.inf)
return np.exp(x**2) * _int[0]
def set_rc(self):
'''
Returns the radius of the curvature at the observer in km,
taking into account the latitude of the observer and the corresponding
ellipsoidality of the earth.
'''
_A = 6378.137 # km
_B = 6356.752 # km
_phi = np.deg2rad(self.lat)
_rc0 = (_A*_B)**2 / (_A**2 * np.cos(_phi)**2 + _B**2 * np.sin(_phi)**2)**(3/2)
return _rc0 + self.h/1000
def set_H(self, P, rho):
'''
Calculates the reduced height of the atmosphere, assuming ideal gas law.
'''
_phi = np.deg2rad(self.lat)
_c1 = 5.2790414e-3
_c2 = 2.32718e-5
_c3 = 1.262e-7
_c4 = 7e-10
_g0 = 9.780327 # m/s^2
_g0_local = _g0 * (1 + _c1 * np.sin(_phi)**2 + _c2 * np.sin(_phi)**4 + _c3 * np.sin(_phi)**6 + _c4 * np.sin(_phi)**8)
_g = _g0_local - (3.0877e-6 - 4.3e-9 * np.sin(_phi)**2) * self.h + 7.2e-13 * self.h**2
return P / (rho * _g)
def H_isotherm(self, T):
'''
Calculates the reduced height of the atmosphere, assuming an isotherm distribution.
'''
_kb = 1.38064852e-23 # kg m2 s-2 K-1
_m = 4.809651698e-26 # kg (weight per molecule of air, assuming dry air)
_phi = np.deg2rad(self.lat)
_c1 = 5.2790414e-3
_c2 = 2.32718e-5
_c3 = 1.262e-7
_c4 = 7e-10
_g0 = 9.780327 # m/s^2
_g0_local = _g0 * (1 + _c1 * np.sin(_phi)**2 + _c2 * np.sin(_phi)**4 + _c3 * np.sin(_phi)**6 + _c4 * np.sin(_phi)**8)
return (_kb*T) / (_m * _g0_local)
def cassiniError(self, z, l1, l2, T, p, RH, xc, dl1=0, dl2=0, dT=0.2, dP=20, dRH=0.02, dCO2=20, dz=0, lat=None, h=None):
'''
Calculates the uncertainty in the atmospheric dispersion, following the Cassini model,
by using fully propagated error analysis.
This involves almost endless use of the chain rule and evaluation of both the moist
air and dry air components. Note: dry air does not contain any water, i.e. H=0, x_w=0, etc.
Not taken into account is the errror propagation in the scale height of the atmosphere or
the zenith error, from my results this should give a small or even negligible difference.
Parameters:
z - Zenith angle in degrees
l1 - Bluest wavelength in micron (0.4 - 2.5 micron)
l2 - Reddest wavelength in micron (0.4 - 2.5 micron)
T - Temperature in Kelvin
p - Pressure in Pascals
RH - Relative humidity (no units, don't use percentage but value 0<x<1)
xc - CO2 density in ppm
dl1 - Uncertainty in the blue wavelength
dl2 - Uncertainty in the red wavelength
dT - Uncertainty in the temperature, default: 0.2 K
dP - Uncertainty in the pressure, default: 20 Pa
dRH - Uncertainty in the relative humidity, default: 0.02
dCO2- Uncertainty in the CO2 density, default: 20
lat - [Optional] Latitude of the observatory in degrees
h - [Optional] Height in m of the observatory
'''
if lat == None:
lat = self.lat
else:
self.lat = lat
if h == None:
h = self.h
else:
self.h = h
# constants
_cf = 1.022
_w0 = 295.235 # um^-2
_w1 = 2.6422 # um^-2
_w2 = -0.032380 # um^-4
_w3 = 0.004028 # um^-6
_k0 = 238.0185 # um^-2
_k1 = 5792105 # um^-2
_k2 = 57.362 # um^-2
_k3 = 167917 # um^-2
_A = 1.2378847e-5 # K^-2
_B = -1.9121316e-2 # K^-2
_C = 33.93711047
_D = -6.3431645e3 # K^-2
_Mw = 0.018015 # kg/mol
_R = 8.314510 # J mol^-1 K^-1, gas constant
_a0 = 1.58123e-6 # K Pa^-1
_a1 = -2.9331e-8 # Pa^-1
_a2 = 1.1043e-10 # K^-1 Pa^-1
_b0 = 5.707e-6 # K Pa^-1
_b1 = -2.051e-8 # Pa^-1
_c0 = 1.9898e-4 # K Pa^-1
_c1 = -2.376e-6 # Pa^-1
_d = 1.83e-11 # K^2 Pa^-2
_e = -0.765e-8 # K^2 Pa^-2
_t = T - 273.15
_aa = 1.00062
_bb = 3.14e-8 # Pa^-1
_cc = 5.6e-7 # deg C^-2
_RH_a = 0
_RH_w = RH
# Calculated values
_rho_obs = self.rho(p, T, RH, xc)
self.rc = self.set_rc() * 1000
self.H = self.set_H(p, _rho_obs)
_alpha = self.rc * np.sin(np.deg2rad(z)) / (self.rc + self.H)
_p_a = p - RH*self.svp(T)
_p_w = RH*self.svp(T)
_x_w_a = self.xw(_p_a, T, _RH_a)
_x_w_w = self.f(_p_w, T)
_Z_a = self.Z(p=_p_a, T=T, RH=_RH_a)
_Z_w = self.Z(p=_p_w, T=T, RH=_RH_w, xw=_x_w_w)
_Ma = 1e-3 * (28.9635 + 12.011e-6 * (xc - 400) ) # Molar mass in kg/mol of dry air containing xc ppm of CO2
_p_sv = self.svp(T)
_rho_a = self.rho(p=p-RH*self.svp(T), T=T, RH=0, xc=xc)
_rho_axs = self.rho(p=101325, T=288.15, RH=0, xc=xc)
if RH == 0.0:
# nan is returned for _rho_w if we put in a (partial) pressure of 0
_rho_w = 0
else:
_rho_w = self.rho(p=RH*self.svp(T), T=T, RH=RH, xc=xc)
_rho_ws = self.rho(p=1333, T=293.15, RH=1333/self.svp(293.15), xc=xc)
_n_a1 = self.n_axs(l1, xc)
_n_w1 = self.n_ws(l1)
_n_a2 = self.n_axs(l2, xc)
_n_w2 = self.n_ws(l2)
_L1_a = (_n_a1**2 - 1) / (_n_a1**2 + 2) # Dry air component of L
_L1_w = (_n_w1**2 - 1) / (_n_w1**2 + 2)
_L1 = ( _rho_a / _rho_axs ) * _L1_a + ( _rho_w / _rho_ws ) * _L1_w # Overall L
_L2_a = (_n_a2**2 - 1) / (_n_a2**2 + 2) # Dry air component of L
_L2_w = (_n_w2**2 - 1) / (_n_w2**2 + 2)
_L2 = ( _rho_a / _rho_axs ) * _L2_a + ( _rho_w / _rho_ws ) * _L2_w # Overall L
_n1 = np.sqrt( (1 + 2 * _L1) / (1 - _L1) )
_n2 = np.sqrt( (1 + 2 * _L2) / (1 - _L2) )
# Partial derivatives for derivation to l1
_dn_wdl1 = _cf * 1e-8 * (-1 * _w1 * 2/l1**3 - _w2 * 4/l1**5 - _w3 * 6/l1**7)
_dLdn_w1 = _rho_w / _rho_ws * 6 * _n_w1 / (_n_w1**2 + 2)**2
_dn_adl1 = 1e-8 * (1 + 0.534e-6 * (xc - 450)) * ( - (2 * _k1 * l1 ) / ((_k0 * l1**2 - 1)**2) - (2 * _k3 * l1) / ((_k2 * l1**2 - 1)**2) )
_dLdn_a1 = _rho_a / _rho_axs * 6 * _n_a1 / (_n_a1**2 + 2)**2
_dndL1 = ( ( (1 + 2*_L1) / (1 - _L1)**2 ) + (2 / (1-_L1)) ) / (2 * np.sqrt( (1 + 2*_L1) / (1 - _L1) ) )
_dddn1 = _alpha / np.sqrt( 1 - _alpha**2 * _n1**2 )
_dddl1 = _dddn1 * _dndL1 * ( _dLdn_a1 * _dn_adl1 + _dLdn_w1 * _dn_wdl1)
# Partial derivatives for derivation to l2
_dn_wdl2 = _cf * 1e-8 * (-1 * _w1 * 2/l2**3 - _w2 * 4/l2**5 - _w3 * 6/l2**7)
_dLdn_w2 = _rho_w / _rho_ws * 6 * _n_w2 / (_n_w2**2 + 2)**2
_dn_adl2 = 1e-8 * (1 + 0.534e-6 * (xc - 450)) * ( - (2 * _k1 * l2 ) / ((_k0 * l2**2 - 1)**2) - (2 * _k3 * l2) / ((_k2 * l2**2 - 1)**2) )
_dLdn_a2 = _rho_a / _rho_axs * 6 * _n_a2 / (_n_a2**2 + 2)**2
_dndL2 = ( ( (1 + 2*_L2) / (1 - _L2)**2 ) + (2 / (1-_L2)) ) / (2 * np.sqrt( (1 + 2*_L2) / (1 - _L2) ) )
_dddn2 = _alpha / np.sqrt( 1 - _alpha**2 * _n2**2 )
_dddl2 = _dddn2 * _dndL2 * ( _dLdn_a2 * _dn_adl2 + _dLdn_w2 * _dn_wdl2)
# Partial derivatives for derivation to T
# Dry air parts:
_drho_adp_a = _Ma / (_Z_a * _R * T) * (1 - _x_w_a * (1 - _Mw / _Ma))
_dp_adp_sv = - RH
_dp_svdT = (2*_A*T + _B - _D/(T**2)) * np.exp(_A * T**2 + _B * T + _C + _D/T )
_drho_adTZ = - _p_a * _Ma / (_R * ( _Z_a * T)**2) * (1 - _x_w_a * (1 - _Mw / _Ma))
_dTZdT_a = _p_a / T * (_a2 * _t**2 + _a1 * _t + _a0 + (_b1*_t + _b0) * _x_w_a + (_c0 + _c1*_t) * _x_w_a**2 ) - _p_a * (_a1 + 2*_a2*_t + _b1*_x_w_a + _c1*_x_w_a**2) - 2*(_p_a/T)**2 * (_d + _e * _x_w_a**2) + _Z_a
_dTZdxw_a = 2*_e*_p_a**2 / T * _x_w_a - _p_a * (_b1*_t + _b0 + 2 * (_c0 + _c1*_t) * _x_w_a)
_dxw_adf = _RH_a * _p_sv / _p_a
_dfdT = 2*_cc*_t
_dxw_adp_sv = self.f(_p_a, T) * _RH_a / _p_a
_drho_adxw_a = 0 # as rho_a has not water content, i.e. rho = p*M/ZRT
# Moist air parts:
_drho_wdp_w = _Ma / (_Z_w * _R * T) * (1 - _x_w_w * (1 - _Mw / _Ma))
_dp_wdp_sv = RH
_dp_svdT = (2*_A*T + _B - _D/(T**2)) * np.exp(_A * T**2 + _B * T + _C + _D/T )
_drho_wdTZ = - _p_w * _Ma / (_R * (_Z_w * T)**2) * (1 - _x_w_w * (1 - _Mw / _Ma))
_dTZdT_w = _p_w / T * (_a2 * _t**2 + _a1 * _t + _a0 + (_b1*_t + _b0) * _x_w_w + (_c0 + _c1*_t) * _x_w_w**2 ) - _p_w * (_a1 + 2*_a2*_t + _b1*_x_w_w + _c1*_x_w_w**2) - 2*(_p_w/T)**2 * (_d + _e * _x_w_w**2) + _Z_w
_dTZdxw_w = 2*_e*_p_w**2 / T * _x_w_w - _p_w * (_b1*_t + _b0 + 2 * (_c0 + _c1*_t) * _x_w_w)
_dxw_wdf = 1 # _RH_w * _p_sv / _p_w
_dfdT = 2*_cc*_t
_dxw_wdp_sv = self.f(_p_w, T) / _p_sv # * _RH_w / _p_w
_drho_wdxw_w = _p_w * _Ma / (_Z_w * _R * T) * (_Mw / _Ma - 1)
_tA = _drho_adp_a * _dp_adp_sv * _dp_svdT + _drho_adTZ * (_dTZdT_a + _dTZdxw_a * (_dxw_adf * _dfdT + _dxw_adp_sv * _dp_svdT) ) + _drho_adxw_a * ( _dxw_adf * _dfdT + _dxw_adp_sv * _dp_svdT )
_tB = _drho_wdp_w * _dp_wdp_sv * _dp_svdT + _drho_wdTZ * (_dTZdT_w + _dTZdxw_w * (_dxw_wdf * _dfdT + _dxw_wdp_sv * _dp_svdT) ) + _drho_wdxw_w * ( _dxw_wdf * _dfdT + _dxw_wdp_sv * _dp_svdT )
_dL1drho_a = _L1_a / _rho_axs
_dL2drho_a = _L2_a / _rho_axs
_dL1drho_w = _L1_w / _rho_ws
_dL2drho_w = _L2_w / _rho_ws
_dddT = _tA * (_dddn1 * _dndL1 * _dL1drho_a - _dddn2 * _dndL2 * _dL2drho_a) + _tB * (_dddn1 * _dndL1 * _dL1drho_w - _dddn2 * _dndL2 * _dL2drho_w)
# Partial derivatives for derivation to p
# Dry air parts:
_drho_adZ = - _p_a * _Ma / ( _Z_a**2 * _R * T) * (1 - _x_w_a * (1 - _Mw / _Ma))
_dZdp_a = - 1 / T * (_a0 + _a1 * _t + _a2 * _t**2 + (_b0 + _b1*_t)*_x_w_a + (_c0 + _c1*_t)*_x_w_a**2 ) + 2*_p_a/(T**2) * (_d + _e * _x_w_a**2)
_dfdp = _bb
_dxw_adp_a = - self.f(_p_a, T) * _RH_a * _p_sv / (_p_a)**2
# Moist air parts
_dZdp_w = - 1 / T * (_a0 + _a1 * _t + _a2 * _t**2 + (_b0 + _b1*_t)*_x_w_w + (_c0 + _c1*_t)*_x_w_w**2 ) + 2*_p_w/(T**2) * (_d + _e * _x_w_w**2)
# Not necessary, since dpwdp=0
_pA = _drho_adp_a + _drho_adZ * _dZdp_a + _drho_adxw_a * (_dxw_adf * _dfdp + _dxw_adp_a)
_dddP = _pA * (_dddn1 * _dndL1 * _dL1drho_a - _dddn2 * _dndL2 * _dL2drho_a)
# Partial derivatives for derivation to H
# Dry air parts:
_dp_adH = - _p_sv
_dZdxw_a = (_p_a / T)**2 * 2 * _e * _x_w_a - (_p_a / T) * ( (_b0 + _b1 * _t) + 2 * (_c0 + _c1 * _t) * _x_w_a )
_dxw_adH = self.f(_p_a, T) * _p_sv / _p_a
# Moist air parts:
_dp_wdH = _p_sv
_dZdxw_w = (_p_w / T)**2 * 2 * _e * _x_w_w - (_p_w / T) * ( (_b0 + _b1 * _t) + 2 * (_c0 + _c1 * _t) * _x_w_w )
_dxw_wdH = 0
_dxw_wdp_w = 0
_drho_wdZ = - _p_w * _Ma / ( _Z_w**2 * _R * T) * (1 - _x_w_w * (1 - _Mw / _Ma))
_hA = _drho_adp_a * _dp_adH + _drho_adZ * ( _dZdp_a * _dp_adH + _dZdxw_a * (_dxw_adH + _dxw_adp_a * _dp_adH + _dxw_adf * _dfdp * _dp_adH) ) + _drho_adxw_a * (_dxw_adH + _dxw_adp_a * _dp_adH + _dxw_adf * _dfdp * _dp_adH)
_hB = _drho_wdp_w * _dp_wdH + _drho_wdZ * ( _dZdp_w * _dp_wdH + _dZdxw_w * ( _bb * _p_sv ) ) + _drho_wdxw_w * ( _bb * _p_sv )
_dddRH = _hA * (_dddn1 * _dndL1 * _dL1drho_a - _dddn2 * _dndL2 * _dL2drho_a) + _hB * (_dddn1 * _dndL1 * _dL1drho_w - _dddn2 * _dndL2 * _dL2drho_w)
# Partial derivatives for derivation to xc
# Dry air parts:
_drho_adMa = _p_a * (1 - _x_w_a) / (_Z_a * _R * T)
_dL1drho_axs = - (_rho_a * _L1_a)/(_rho_axs**2)
_dL2drho_axs = - (_rho_a * _L2_a)/(_rho_axs**2)
_drho_axsdMa = _drho_adMa
_dL1dL_a = _rho_a / _rho_axs
_dL_adn_a1 = 6 * _n_a1 / (_n_a1**2 + 2)**2
_dL2dL_a = _dL1dL_a
_dL_adn_a2 = 6 * _n_a2 / (_n_a2**2 + 2)**2
# Moist air parts:
_drho_wdMa = _p_w * (1 - _x_w_w) / (_Z_w * _R * T)
_dL1drho_ws = - (_rho_w * _L1_w)/(_rho_ws**2)
_dL2drho_ws = - (_rho_w * _L2_w)/(_rho_ws**2)
_drho_wsdMa = _drho_wdMa
# Other parts:
_dMadx_c = 12.011e-9
_dn_adx_c1 = (self.n_as(l1) - 1) * 0.534e-6
_dn_adx_c2 = (self.n_as(l2) - 1) * 0.534e-6
_dL1dx_c = _dL1drho_a * _drho_adMa * _dMadx_c + _dL1drho_w * _drho_wdMa * _dMadx_c + _dL1drho_axs * _drho_axsdMa * _dMadx_c + _dL1drho_ws * _drho_wsdMa * _dMadx_c + _dL1dL_a * _dL_adn_a1 * _dn_adx_c1
_dL2dx_c = _dL2drho_a * _drho_adMa * _dMadx_c + _dL2drho_w * _drho_wdMa * _dMadx_c + _dL2drho_axs * _drho_axsdMa * _dMadx_c + _dL2drho_ws * _drho_wsdMa * _dMadx_c + _dL2dL_a * _dL_adn_a2 * _dn_adx_c2
_dddCO2 = _dddn1 * _dndL1 * _dL1dx_c - _dddn2 * _dndL2 * _dL2dx_c
# Partial derivatives for derivation to z
_zenith = np.deg2rad(z)
_dz = np.deg2rad(dz)
_R = self.rc
_H = self.H
_dddz = (_R * np.cos(_zenith)) / (_R + _H) * ( _n1 / np.sqrt(1-(_n1**2 * _R**2 * np.sin(_zenith)**2)/(_R + _H)**2) - _n2 / np.sqrt(1-(_n2**2 * _R**2 * np.sin(_zenith)**2)/(_R + _H)**2) )
# Final error:
_dispersionError = np.sqrt( (_dddl1 * dl1)**2 + (_dddl2 * dl2)**2 + (_dddT * dT)**2 + (_dddP * dP)**2 + (_dddRH * dRH)**2 + (_dddCO2 * dCO2)**2 + (_dddz * _dz)**2)
return np.degrees(_dispersionError)
class refraction(Observatory):
def __init__(self, lat, h):
Observatory.__init__(self)
self.h = h # height above sea level in meters
self.lat = lat # Latitude of the observer in degrees
self.rc = self.set_rc() * 1000 # Radius of curvature of the earth at the observer
# self.H2 = self.H_isotherm(T) # Reduced height of isotherm atmosphere
def setReducedHeight(self, P, rho):
self.H = self.set_H(P, rho) # Reduced height of the atmosphere assuming ideal gas law
def planeParallel(self, n, zenith):
'''
Refraction based on a flat atmosphere, easily derived from Snell's law.
'''
_R = np.arcsin(n * np.sin( np.deg2rad(zenith) )) - np.deg2rad(zenith)
return np.degrees(_R)
def cassini(self, n1, zenith, reduced_height=None):
'''
Refraction of spherical atmosphere, derived from geometry using Sine law
'''
if reduced_height:
H = reduced_height
else:
H = self.H
_R1 = np.arcsin(n1 * self.rc * np.sin(np.deg2rad(zenith)) / (self.rc + H)) - np.arcsin(self.rc * np.sin(np.deg2rad(zenith)) / (self.rc + H) )
return np.degrees(_R1)
def tan5(self, n1, zenith, reduced_height=None):
'''
Same as oriani's theorem, but including a higher order term.
Found in Corbard et al., 2019.
'''
if reduced_height:
H = reduced_height
else:
H = self.H
_a = n1 - 1
_b = H / self.rc
_R = _a * (1 - _b) * np.tan( np.deg2rad(zenith) ) - _a * (_b - _a/2) * np.tan( np.deg2rad(zenith) )**3 + 3 * _a * (_b - _a/2)**2 * np.tan( np.deg2rad(zenith) )**5
return np.degrees(_R)
def oriani(self, n1, zenith, reduced_height=None):
'''
Classic refraction formula with two tan(z) terms. This does not assume any
information about the structure of the atmosphere. Found with Oriani's theorem.
'''
if reduced_height:
H = reduced_height
else:
H = self.H
_a = n1 - 1
_b = H / self.rc
_R = _a * (1 - _b) * np.tan( np.deg2rad(zenith) ) - _a * (_b - _a/2) * np.tan( np.deg2rad(zenith) )**3
return np.degrees(_R)
def corbard(self, n1, zenith, reduced_height=None):
'''
Corbard et al., 2019, mention an additional formula based on the error function.
Oriani's theorem can be derived from this equation by 'keeping only the three first
terms of its asymptotic expansion'.
'''
if reduced_height:
H = reduced_height
else:
H = self.H
_a = n1 - 1
_b = H / self.rc
_R = _a * ( (2 - _a) / (np.sqrt( 2*_b - _a )) ) * np.sin( np.deg2rad(zenith) ) * self.psi( (np.cos(np.deg2rad(zenith))) / np.sqrt(2*_b - _a) )
return np.degrees(_R)
def refractionIntegral(self, n0, z0, R0=None, useStandardAtmosphere=True, heightData=None, rhoData=None):
'''
Using data that gives temperature, pressure and density as a function of height,
the gladstone-dale relation is invoked to calculate the path of a light ray
along the atmosphere. This is allows us to also include atmospheric activity in
different atmosphere layers.
Recommended use with the US Standard Atmosphere from 1976.
USSA1976 data generated from code supplied by http://www.pdas.com/atmos.html
'''
if not R0:
R0 = self.rc
if useStandardAtmosphere:
_h, _, _, _, _Temp, _Press, _Dens,_,_,_ = np.genfromtxt('1976USSA.txt', unpack=True, skip_header=6)
else:
_Dens = rhoData
_h = heightData
z0 = np.deg2rad(z0)
_Dens = np.asarray(_Dens)
_h = np.asarray(_h)
_R = R0 + _h * 1000
# Gladstone-Dale relation between refractive index and density
_n_h = 1 + (n0 - 1) / _Dens[0] * _Dens
# Calculation of the zenith angle for given height and refractive index, from the refractive invariant
_z = np.arcsin( (n0 * R0) / (_n_h * _R) * np.sin(z0) )
# Calculation of log space derivative of n and r
_lnn = np.log(_n_h)
_lnr = np.log(_R)
_dlnn = np.asarray([_lnn[i+1] - _lnn[i] for i in range(len(_lnn)-1)])
_dlnr = np.asarray([_lnr[i+1] - _lnr[i] for i in range(len(_lnr)-1)])
_dz = np.asarray([(_z[i] - _z[i+1]) for i in range(len(_z)-1)])
# Calculation of the integrand in eq. 3 in Auer & Standish
_Integrand = -1*(_dlnn/_dlnr) / (1 + _dlnn/_dlnr) * _dz
return np.degrees(np.sum(_Integrand))
def psi(self, x):
_f = lambda a: np.exp(-a**2)
_int = integrate.quad(_f, x, np.inf)
return np.exp(x**2) * _int[0]
def set_rc(self):
'''
Returns the radius of the curvature at the observer in km,
taking into account the latitude of the observer and the corresponding
ellipsoidality of the earth.
'''
_A = 6378.137 # km
_B = 6356.752 # km
_phi = np.deg2rad(self.lat)
_rc0 = (_A*_B)**2 / (_A**2 * np.cos(_phi)**2 + _B**2 * np.sin(_phi)**2)**(3/2)
return _rc0 + self.h/1000
def set_H(self, P, rho):
'''
Calculates the reduced height of the atmosphere, assuming ideal gas law.
'''
_phi = np.deg2rad(self.lat)
_c1 = 5.2790414e-3
_c2 = 2.32718e-5
_c3 = 1.262e-7
_c4 = 7e-10
_g0 = 9.780327 # m/s^2
_g0_local = _g0 * (1 + _c1 * np.sin(_phi)**2 + _c2 * np.sin(_phi)**4 + _c3 * np.sin(_phi)**6 + _c4 * np.sin(_phi)**8)
_g = _g0_local - (3.0877e-6 - 4.3e-9 * np.sin(_phi)**2) * self.h + 7.2e-13 * self.h**2
return P / (rho * _g)
def H_isotherm(self, T):
'''
Calculates the reduced height of the atmosphere, assuming an isotherm distribution.
'''
_kb = 1.38064852e-23 # kg m2 s-2 K-1
_m = 4.809651698e-26 # kg (weight per molecule of air, assuming dry air)
_phi = np.deg2rad(self.lat)
_c1 = 5.2790414e-3
_c2 = 2.32718e-5
_c3 = 1.262e-7
_c4 = 7e-10
_g0 = 9.780327 # m/s^2
_g0_local = _g0 * (1 + _c1 * np.sin(_phi)**2 + _c2 * np.sin(_phi)**4 + _c3 * np.sin(_phi)**6 + _c4 * np.sin(_phi)**8)
return (_kb*T) / (_m * _g0_local)
def cassiniError(self, n, dn, zenith, dz=0, reduced_height=None):
'''
Calculates the uncertainty in the refraction angle in degrees.
'''
if reduced_height:
_H = reduced_height
else:
_H = self.H
_zenith = np.deg2rad(zenith)
_dz = np.deg2rad(dz)
_R = self.rc
_dRdn = (_R * np.sin(_zenith)) / ((_R + _H) * np.sqrt(1 - ((n**2 * _R**2 * np.sin(_zenith)**2)/(_R + _H)**2)))
_dRdz = (_R * np.cos(_zenith)) / (_R + _H) * ( n / np.sqrt(1-(n**2 * _R**2 * np.sin(_zenith)**2)/(_R + _H)**2) - 1 / np.sqrt(1-(_R**2 * np.sin(_zenith)**2)/(_R + _H)**2) )
_dR = np.sqrt( (_dRdn * dn)**2 + (_dRdz * _dz)**2)
return np.degrees(_dR)
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