def freqs_to_vel(center_freq, fs, sc):
"""Convert frequency to radial Doppler velocity.
Accounts for movement of the earth relative to the sun and the sun relative to galactic center.
Args:
center_freq: frequency at zero velocity
fs: Quantity object representing frequencies
sc: SkyCoord object representing one or many coordinates (must have obstime and location set)
"""
# Convert from earth reference frame to solar reference frame using
# https://docs.astropy.org/en/stable/coordinates/velocities.html#radial-velocity-corrections
# Then convert from solar reference frame to Galactic Standard of Rest using
# https://docs.astropy.org/en/stable/generated/examples/coordinates/rv-to-gsr.html
pos_gal = sc.galactic
v_to_bary = pos_gal.radial_velocity_correction(kind='barycentric')
# Calculate the sun's velocity projected in the observing direction.
v_sun = Galactocentric().galcen_v_sun.to_cartesian()
cart_data = pos_gal.data.to_cartesian()
unit_vector = cart_data / cart_data.norm()
v_proj = v_sun.dot(unit_vector)
doppler_shift = u.doppler_radio(center_freq)
v_local = fs.to(u.km/u.s, doppler_shift)
v_bary = v_local + v_to_bary + v_local * v_to_bary / c
# v_bary is now barycentric; now we need to remove the solar system motion as well
return (v_bary + v_proj)
def freqs_to_vel(center_freq, fs, lcoord, bcoord):
# Convert from earth reference frame to solar reference frame using
# https://docs.astropy.org/en/stable/coordinates/velocities.html#radial-velocity-corrections
# Then convert from solar reference frame to Galactic Standard of Rest using
# https://docs.astropy.org/en/stable/generated/examples/coordinates/rv-to-gsr.html
pos_gal = SkyCoord(l=lcoord * u.degree,
b=bcoord * u.degree,
frame='galactic')
v_to_bary = pos_gal.radial_velocity_correction(
kind='barycentric',
obstime=get_time(),
location=radome_observer.location)
# Calculate the sun's velocity projected in the observing direction.
v_sun = Galactocentric().galcen_v_sun.to_cartesian()
cart_data = pos_gal.data.to_cartesian()
unit_vector = cart_data / cart_data.norm()
v_proj = v_sun.dot(unit_vector)
def freq_to_vel(f):
f = f * u.MHz
v_local = f.to(u.km / u.s, u.doppler_radio(center_freq * u.MHz))
v_bary = v_local + v_to_bary + v_local * v_to_bary / c
# v_bary is now barycentric; now we need to remove the solar system motion as well
return (v_bary + v_proj) / (u.km / u.s)
return [freq_to_vel(f) for f in fs]