Added Filippenko model, updated B&S refractivity

AstroAtmosphere/refractivityModels.py

@@ -9,7 +9,7 @@ import numpy as np
 				atmospheric dispersion, given a set of conditions.
 '''
 
-def BarrellAndSears(l, T=288.15, p=101325, RH=0):
+def BarrellAndSears(l, T=288.15, p=101325, RH=0, f=None):
 	'''
 		From Barrell & Sears, 1939
 		Equation 7.7, page 52
@@ -26,15 +26,20 @@ def BarrellAndSears(l, T=288.15, p=101325, RH=0):
 			Atmospheric pressure in Pascal
 		RH 	: 	float
 			Relative humidity (0=<H=<1)
+		f 	: 	float
+			Water vapour pressure in Pascal
 
 		Returns
 		-------
 		n 	: 	float
 			Refractive index of atmospheric air at the given conditions
 	'''
+	if f is None:
+		f = RH * svp(T)
+	f_mmHg = hPA2mmHg(f/100)
 	T = K2C(T)
 	P = hPA2mmHg(p/100)
-	R = (0.378125 + 0.0021414 / l**2 + 0.00001793 / l**4) * (P*(1 + (1.049 - 0.0157*T) * P * 1e-6)/(1 + 0.003661*T)) - (0.0624 - 0.000680 / l**2) * RH / (1 + 0.003661*T)
+	R = (0.378125 + 0.0021414 / l**2 + 0.00001793 / l**4) * (P*(1 + (1.049 - 0.0157*T) * P * 1e-6)/(1 + 0.003661*T)) - (0.0624 - 0.000680 / l**2) * f_mmHg / (1 + 0.003661*T)
 	n = R/1e6 + 1
 	return n
 
@@ -64,17 +69,25 @@ def Ciddor(l, CO2=450):
 	return n
 
 
-def Edlen1953(l):
+def Edlen1953(l, T=288.15, p=101325, RH=0, f=None):
 	'''
 		From Edlen, 1953
 		Equation 2
 
-		At standard conditions only
+		At standard conditions only.
+		Following Filippenko (1982), eqs. 2 & 3 we also include
+		the	modification proposed by Barrell in 1951.
 
 		Parameters
 		---------- 
 		l 	: 	float
 			Wavelength in microns
+		T 	: 	float
+			Temperature in Kelvin
+		p 	: 	float
+			Atmospheric pressure in Pascal
+		f 	: 	float
+			Water vapor pressure in Pascal
 
 		Returns
 		-------
@@ -83,7 +96,20 @@ def Edlen1953(l):
 	'''
 	s = 1 / l
 	R = 6432.8 + 2949810 / (146 - s**2) + 25540/(41-s**2)
-	n = R/1e8 + 1
+	n_standard = R/1e8 + 1
+
+	pHg = hPA2mmHg(p/100)
+	Tc  = K2C(T)
+	if f is None:
+		f = RH * svp(T)
+	f_mmHg = hPA2mmHg(f/100)
+
+	# Changes in temperature and pressure, from Barrell (1951)
+	n_tp = R/1e8 * (pHg * (1 + (1.049 - 0.0157*Tc) * 1e-6 * pHg ) ) / ( 720.883 * (1 + 0.003661 * Tc)) + 1
+
+	# Correction for water vapour pressure
+	n_svp = (n_tp - 1) * 1e6 - ( 0.0624 - 0.000680 * s**2 ) / (1 + 0.003661 * Tc) * f_mmHg
+	n = n_svp/1e6 + 1
 	return n
 
 
@@ -481,6 +507,7 @@ def Mathar(l, T=288.15, p=101325, RH=0):
 	return n 
 
 
+# Other necessary conversion or calculations
 def K2C(K):
 	'''
 		Kelvin to Celsius conversion
@@ -514,3 +541,23 @@ def hPA2mmHg(hPa):
 	'''
 	return 0.7500616827 * hPa
 
+
+def svp(T):
+	'''
+		Saturation vapour pressure in Pa.
+
+		Parameters
+		----------
+		T 	: float
+			Atmospheric temperature in Kelvin
+
+		Returns
+		-------
+		svp	: float
+			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)