diff options
| -rw-r--r-- | fg21sim/utils/convert.py | 88 |
1 files changed, 24 insertions, 64 deletions
diff --git a/fg21sim/utils/convert.py b/fg21sim/utils/convert.py index 9eb9061..0fd08b4 100644 --- a/fg21sim/utils/convert.py +++ b/fg21sim/utils/convert.py @@ -5,75 +5,14 @@ Utilities for conversion among common astronomical quantities. """ -import astropy.units as au - from .units import (UnitConversions as AUC, Constants as AC) -def Fnu_to_Tb(Fnu, omega, freq): - """ - Convert flux density to brightness temperature, using the - Rayleigh-Jeans law, in the Rayleigh-Jeans limit. - - Parameters - ---------- - Fnu : `~astropy.units.Quantity` - Input flux density, e.g., `1.0*au.Jy` - omega : `~astropy.units.Quantity` - Source angular size/area, e.g., `100*au.arcsec**2` - freq : `~astropy.units.Quantity` - Frequency where the flux density measured, e.g., `120*au.MHz` - - Returns - ------- - Tb : `~astropy.units.Quantity` - Brightness temperature, with default unit `au.K` - - References - ---------- - - Brightness and Flux - http://www.cv.nrao.edu/course/astr534/Brightness.html - - Wikipedia: Brightness Temperature - https://en.wikipedia.org/wiki/Brightness_temperature - - NJIT: Physics 728: Introduction to Radio Astronomy: Lecture #1 - https://web.njit.edu/~gary/728/Lecture1.html - - Astropy: Equivalencies: Brightness Temperature / Flux Density - http://docs.astropy.org/en/stable/units/equivalencies.html - """ - equiv = au.brightness_temperature(omega, freq) - Tb = Fnu.to(au.K, equivalencies=equiv) - return Tb - - def Sb_to_Tb(Sb, freq): """ Convert surface brightness to brightness temperature, using the Rayleigh-Jeans law, in the Rayleigh-Jeans limit. - Parameters - ---------- - Sb : `~astropy.units.Quantity` - Input surface brightness, e.g., `1.0*(au.Jy/au.arcsec**2)` - freq : `~astropy.units.Quantity` - Frequency where the flux density measured, e.g., `120*au.MHz` - - Returns - ------- - Tb : `~astropy.units.Quantity` - Brightness temperature, with default unit `au.K` - """ - omega = 1.0 * au.arcsec**2 - Fnu = (Sb * omega).to(au.Jy) # [Jy] - return Fnu_to_Tb(Fnu, omega, freq) - - -def Sb_to_Tb_fast(Sb, freq): - """ - Convert surface brightness to brightness temperature, using the - Rayleigh-Jeans law, in the Rayleigh-Jeans limit. - - Avoid using `astropy.units` to optimize the speed. - Tb = Sb * c^2 / (2 * k_B * nu^2) where `Sb` is the surface brightness density measured at a certain @@ -81,6 +20,16 @@ def Sb_to_Tb_fast(Sb, freq): 1 [Jy] = 1e-23 [erg/s/cm^2/Hz] = 1e-26 [W/m^2/Hz] + NOTE + ---- + It is very easy to use ``astropy.units`` for the conversion: + equiv = au.brightness_temperature(omega, freq) + Tb = Fnu.to(au.K, equivalencies=equiv) + + WARNING: + Using `astropy.units` for the conversion may be much slower. + This can be used as a cross check for the calculation. + Parameters ---------- Sb : float @@ -95,6 +44,17 @@ def Sb_to_Tb_fast(Sb, freq): Tb : float Calculated brightness temperature Unit: [K] + + References + ---------- + - Brightness and Flux + http://www.cv.nrao.edu/course/astr534/Brightness.html + - Wikipedia: Brightness Temperature + https://en.wikipedia.org/wiki/Brightness_temperature + - NJIT: Physics 728: Introduction to Radio Astronomy: Lecture #1 + https://web.njit.edu/~gary/728/Lecture1.html + - Astropy: Equivalencies: Brightness Temperature / Flux Density + http://docs.astropy.org/en/stable/units/equivalencies.html """ # NOTE: [rad] & [sr] are dimensionless arcsec2 = AUC.arcsec2rad ** 2 # [sr] @@ -104,7 +64,7 @@ def Sb_to_Tb_fast(Sb, freq): return Tb -def Fnu_to_Tb_fast(Fnu, omega, freq): +def Fnu_to_Tb(Fnu, omega, freq): """ Convert flux density to brightness temperature, using the Rayleigh-Jeans law, in the Rayleigh-Jeans limit. @@ -130,7 +90,7 @@ def Fnu_to_Tb_fast(Fnu, omega, freq): Unit: [K] """ Sb = Fnu / omega # [Jy/arcsec^2] - return Sb_to_Tb_fast(Sb, freq) + return Sb_to_Tb(Sb, freq) def JyPerPix_to_K(freq, pixelsize): @@ -146,5 +106,5 @@ def JyPerPix_to_K(freq, pixelsize): The pixel size. Unit: [arcsec] """ - factor = Fnu_to_Tb_fast(Fnu=1.0, omega=pixelsize**2, freq=freq) + factor = Fnu_to_Tb(Fnu=1.0, omega=pixelsize**2, freq=freq) return factor |