drift.core.visibility

Routines for calculating visibilities on the full sky.

Functions

cylinder_beam(sph_arr, zenith, cylwidth)	The beam function for a cylinder aligned N-S.
horizon(sph_arr, zenith)	The horizon function at particular location.
pol_IQU(sph_arr, zenith, feed1, feed2)	The polarisation tensors at each point, projected onto two feeds.
uv_plane_cart(zenith)	Fetch unit vectors in the UV plane.

drift.core.visibility.cylinder_beam(sph_arr, zenith, cylwidth)

The beam function for a cylinder aligned N-S.

Beam will be a thin strip in the N-S direction (controlled by the cylinder width in the E-W direction).

Parameters:

• sph_arr (np.ndarray) – Angular positions (in spherical polar co-ordinates).

• zenith (np.ndarray) – The zenith vector in spherical polar-coordinates.

• cylwidth (scalar) – The effective cylinder width.

Returns:

beam – The beam function at each angular position.

Return type:

np.ndarray

drift.core.visibility.horizon(sph_arr, zenith)

The horizon function at particular location.

Parameters:

• sph_arr (np.ndarray) – Angular positions (in spherical polar co-ordinates).

• zenith (np.ndarray) – The zenith vector in spherical polar-coordinates.

Returns:

horizon – The horizon function (including an angular projection term at each position).

Return type:

np.ndarray

drift.core.visibility.pol_IQU(sph_arr, zenith, feed1, feed2)

The polarisation tensors at each point, projected onto two feeds.

Parameters:

• sph_arr (np.ndarray) – Angular positions (in spherical polar co-ordinates).

• zenith (np.ndarray) – The zenith vector in spherical polar-coordinates.

• feed1 (np.ndarray) – Unit vectors for the two feeds. Should be given in (u,v) coordinates.

• feed2 (np.ndarray) – Unit vectors for the two feeds. Should be given in (u,v) coordinates.

Returns:

pI, pQ, pU – The projected polarisations at each angular position.

Return type:

np.ndarray

Notes

For each position \(\hat{n}\) in sph_arr calculate:

\[f_1^a f_2^b \mathcal{P}^X_{ab}\]

where X is one of I, Q or U.

The co-ordinate system defining the polarisation at each point is \((\hat{\theta}, \hat{\phi})\).

drift.core.visibility.uv_plane_cart(zenith)

Fetch unit vectors in the UV plane.

Parameters:

zenith (np.ndarray) – The zenith vector in spherical polar-coordinates.

Returns:

uhat, vhat – Unit vectors in the UV plane. uhat points East, and vhat points North.

Return type:

np.ndarray