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-rw-r--r--fg21sim/utils/convert.py65
1 files changed, 65 insertions, 0 deletions
diff --git a/fg21sim/utils/convert.py b/fg21sim/utils/convert.py
index 1212780..fc9a228 100644
--- a/fg21sim/utils/convert.py
+++ b/fg21sim/utils/convert.py
@@ -5,7 +5,9 @@
Utilities for conversion among common astronomical quantities.
"""
+import numpy as np
import astropy.units as au
+import numba
def Fnu_to_Tb(Fnu, omega, freq):
@@ -61,3 +63,66 @@ def Sb_to_Tb(Sb, freq):
omega = 1.0 * au.sr
Fnu = Sb * omega
return Fnu_to_Tb(Fnu, omega, freq)
+
+
+@numba.jit(nopython=True)
+def Sb_to_Tb_fast(Sb, freq):
+ """Convert surface brightness to brightness temperature, using the
+ Rayleigh-Jeans law, in the Rayleigh-Jeans limit.
+
+ This function does the calculations explicitly, and does NOT rely
+ on the `astropy.units`, therefore it is faster. However, the input
+ parameters must be in right units.
+
+ Tb = Sb * c^2 / (2 * k_B * nu^2)
+
+ where `SB` is the surface brightness density measured at a certain
+ frequency (unit: [ Jy/rad^2 ] = [ erg/s/cm^2/Hz/rad^2 ]).
+
+ Parameters
+ ----------
+ Sb : float
+ Input surface brightness, unit [ Jy/deg^2 ]
+ freq : float
+ Frequency where the flux density measured, unit [ MHz ]
+
+ Returns
+ -------
+ Tb : float
+ Calculated brightness temperature, unit [ K ]
+ """
+ # NOTE: `radian` is dimensionless
+ rad2_to_deg2 = np.rad2deg(1.0) * np.rad2deg(1.0)
+ Sb_rad2 = Sb * rad2_to_deg2 # unit: [ Jy/rad^2 ] -> [ Jy ]
+ c = 29979245800.0 # speed of light, [ cm/s ]
+ k_B = 1.3806488e-16 # Boltzmann constant, [ erg/K ]
+ coef = 1e-35 # take care the unit conversions
+ Tb = coef * (Sb_rad2 * c*c) / (2 * k_B * freq*freq) # unit: [ K ]
+ return Tb
+
+
+@numba.jit(nopython=True)
+def Fnu_to_Tb_fast(Fnu, omega, freq):
+ """Convert flux density to brightness temperature, using the
+ Rayleigh-Jeans law, in the Rayleigh-Jeans limit.
+
+ This function does the calculations explicitly, and does NOT rely
+ on the `astropy.units`, therefore it is faster. However, the input
+ parameters must be in right units.
+
+ Parameters
+ ----------
+ Fnu : float
+ Input flux density, unit [ Jy ]
+ omega : float
+ Source angular size/area, unit [ deg^2 ]
+ freq : float
+ Frequency where the flux density measured, unit [ MHz ]
+
+ Returns
+ -------
+ Tb : float
+ Calculated brightness temperature, unit [ K ]
+ """
+ Sb = Fnu / omega
+ return Sb_to_Tb_fast(Sb, freq)