import numpy as np
[docs]
def remove_phase_tracking(frequencies=None, wws_seconds=None,
num_time_steps=None, v_container=None,
num_baselines=None):
"""
WARNING - currently does not change the :math:`u,v,w` coordinates, so they
are still defined via the original phase centre. This function really is
just to feed uvfits into the RTS (which generates it's own u,v,w using the
antenna table)
Undoes phase tracking applied by WODEN - to phase track, a phase was applied
to counter the delay term caused by :math:`w` term of baseline - so just
apply the opposite effect of the w term, i.e.
.. math::
V^\\prime = V \\exp(2\pi i w)
where :math:`V` is the phase tracked visibility and :math:`V^\\prime` is
the visibility after removing phase tracking.
Parameters
----------
frequencies : float array
Frequencies of all fine channels (Hz)
wws_seconds : float array
The :math:`w` coordinates (seconds)
num_baselines : int
Number of baselines
v_container : float array
Complex visibility data out of WODEN with phase tracking, with
`shape=(num_time_steps*num_baselines,1,1,num_freq_channels,4,3))`
Returns
-------
v_container : float array
Same visibility data as before, with phase tracking returned.
"""
sign = 1
PhaseConst = 2j * np.pi * sign
num_freqs = len(frequencies)
# print("FREQS", frequencies)
for time_ind in np.arange(num_time_steps):
these_wws_secs = wws_seconds[time_ind*num_baselines:(time_ind + 1)*num_baselines]
for freq_ind, freq in enumerate(frequencies):
xx_re = v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,0,0]
xx_im = v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,0,1]
yy_re = v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,1,0]
yy_im = v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,1,1]
xy_re = v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,2,0]
xy_im = v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,2,1]
yx_re = v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,3,0]
yx_im = v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,3,1]
xx_comp = xx_re + 1j*xx_im
yy_comp = yy_re + 1j*yy_im
xy_comp = xy_re + 1j*xy_im
yx_comp = yx_re + 1j*yx_im
##theory - so normal phase delay is caused by path difference across
##a base line, which is u*l + v*m + w*n
##To phase track, you insert a phase to make sure there is no w contribution at
##phase centre; this is when n = 1, so you insert a phase thus:
##a base line, which is u*l + v*m + w*(n - 1)
##So we just need to remove the effect of the -w term
wws = these_wws_secs * freq
phase_rotate = np.exp( PhaseConst * wws)
xx_comp = xx_comp * phase_rotate
yy_comp = yy_comp * phase_rotate
xy_comp = xy_comp * phase_rotate
yx_comp = yx_comp * phase_rotate
v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,0,0] = np.real(xx_comp)
v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,0,1] = np.imag(xx_comp)
v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,1,0] = np.real(yy_comp)
v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,1,1] = np.imag(yy_comp)
v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,2,0] = np.real(xy_comp)
v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,2,1] = np.imag(xy_comp)
v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,3,0] = np.real(yx_comp)
v_container[time_ind*num_baselines:(time_ind + 1)*num_baselines,0,0,freq_ind,3,1] = np.imag(yx_comp)
return v_container