SONoiseSimulator

class mapsims.SONoiseSimulator(nside=None, shape=None, wcs=None, ell_max=None, return_uK_CMB=True, sensitivity_mode='baseline', apply_beam_correction=False, apply_kludge_correction=True, homogeneous=False, no_power_below_ell=None, rolloff_ell=50, survey_efficiency=0.2, full_covariance=True, LA_years=5, LA_noise_model='SOLatV3point1', elevation=50, SA_years=5, SA_one_over_f_mode='pessimistic', sky_fraction=None, cache_hitmaps=True, boolean_sky_fraction=False, instrument_parameters='simonsobs_instrument_parameters_2020.06')

Bases: object

Simulate noise maps for Simons Observatory

Simulate the noise power spectrum in spherical harmonics domain and then generate a map in microK_CMB or microK_RJ (based on return_uK_CMB)

In the constructor, this object calls the published 20180822 noise simulator and generates the expected noise power spectra for all channels. Then you need to call the simulate method with a channel identifier to create a simulated map.

Parameters:

nside : int

nside of HEALPix map. If None, uses rectangular pixel geometry specified through shape and wcs.

shape : tuple of ints

shape of ndmap array (see pixell.pixell.enmap). Must also specify wcs.

wcs : astropy.wcs.wcs.WCS instance

World Coordinate System for geometry of map (see pixell.pixell.enmap). Must also specify shape.

ell_max : int

Maximum ell for the angular power spectrum, if not provided set to 3 * nside when using healpix or 10000 * (1.0 / pixel_height_arcmin) when using CAR, corresponding roughly to the Nyquist frequency.

return_uK_CMB : bool

True, output is in microK_CMB, False output is in microK_RJ

sensitivity_mode : str

Value should be threshold, baseline or goal to use predefined sensitivities

apply_beam_correction : bool

Include the effect of the beam in the noise angular power spectrum

apply_kludge_correction : bool

If True, reduce the hitcount by a factor of 0.85 to account for not-uniformity in the scanning

homogeneous : bool

Set to True to generate full-sky maps with no hit-count variation, with noise curves corresponding to a survey that covers a sky fraction of sky_fraction (defaults to 1).

no_power_below_ell : int

The input spectra have significant power at low \(\ell\), we can zero that power specifying an integer \(\ell\) value here. The power spectra at \(\ell < \ell_0\) are set to zero.

rolloff_ell : int

Low ell power damping, see the docstring of so_noise_models.so_models_v3.SO_Noise_Calculator_Public_v3_1_1.rolloff

survey_efficiency : float

Fraction of calendar time that may be used to compute map depth.

full_covariance : bool

Whether or not to include the intra-tube covariance between bands. If white noise (atmosphere=False) sims are requested, no covariance is included regardless of the value of full_covariance.

LA_years : int

Total number of years for the Large Aperture telescopes survey

LA_noise_model : str

Noise model among the ones available in so_noise_model, “SOLatV3point1” is default, “SOLatV3” is the model released in 2018 which had a bug in the atmosphere contribution

elevation : float

Elevation of the scans in degrees, the V3.1.1 noise model includes elevation dependence for the LAT. This should reproduced original V3 results at the reference elevation of 50 degrees.

SA_years : int

Total number of years for the Small Aperture telescopes survey

SA_one_over_f_mode : {“pessimistic”, “optimistic”, “none”}

Correlated noise performance of the detectors on the Small Aperture telescopes

sky_fraction : optional,float

If homogeneous is True, this sky_fraction is used for the noise curves.

cache_hitmaps : bool

If True, caches hitmaps.

boolean_sky_fraction: bool

If True, determines sky fraction based on fraction of hitmap that is zero. If False, determines sky_fraction from <Nhits>.

instrument_parameters : Path or str

See the help of MapSims

Methods Summary

get_beam_fwhm(self, tube[, band])	Get beam FWHMs in arcminutes corresponding to the tueb.
get_fullsky_noise_spectra(self, tube[, …])	Get the noise power spectra corresponding to the requested tube from the SO noise model code.
get_hitmaps(self[, tube, hitmap])	Get and process hitmaps and sky fractions for the provided tube or provided an external one.
get_inverse_variance(self, tube[, …])	Get the inverse noise variance in each pixel for the requested tube.
get_noise_indices(self, tube[, band])	Gets indices in the so_noise_model package of a channel or the 2 channels of a tube
get_noise_properties(self, tube[, nsplits, …])	Get noise curves scaled with the hitmaps and the hitmaps themselves
get_white_noise_power(self, tube, sky_fraction)	Get white noise power in uK^2-sr (units=’sr’) or uK^2-arcmin^2 (units=’arcmin2’) corresponding to the tube name tube.
simulate(self, tube[, output_units, seed, …])	Create a random realization of the noise power spectrum

Methods Documentation

get_beam_fwhm(self, tube, band=None)

Get beam FWHMs in arcminutes corresponding to the tueb. This is useful if non-beam-deconvolved sims are requested and you want to know what beam to apply to your signal simulation.

Parameters:

tube : str

Specify a tube.

band : str,optional

Optionally specify the band name within the tube to get just its white noise.

Returns:

beam : tuple of floats

The beam FWHM in arcminutes either as a tuple for the pair of bands in the tube, or just for the specific band requested.

get_fullsky_noise_spectra(self, tube, ncurve_sky_fraction=1, return_corr=False)

Get the noise power spectra corresponding to the requested tube from the SO noise model code.

See get_noise_properties to get spectra scaled with the proper hitmap

Parameters:

tube : str

Specify a tube.

ncurve_sky_fraction : float,optional

The sky fraction to report to the noise simulator code. In the current implementation, the default is to pass a sky fraction of 1, and scale the result by the corresponding sky fraction determined from each band’s hitmap.

return_corr : bool

If True, returns cross-correlation N_XY / sqrt(N_XX * N_YY) coeffient instead of cross-correlation power N_XY in the third row of the returned arrays. This is more convenient sometimes, e.g. when you need to scale the auto-correlation power by some factor.

Returns:

ell : (nells,) ndarray

Array of nells multipoles starting at ell=0 and spaced by delta_ell=1 corresponding to the noise power spectra nells_T and nells_P

nells_T : (3,nells) ndarray

The first two rows contain the temperature auto-correlation of the noise power spectra of each band in the tube. The third row contains the correlation power between the two bands by default, but you can get the cross-correlation coefficient instead by setting return_corr=True.

nells_P : (3,nells) ndarray

Same as for nells_T but for polarization.

get_hitmaps(self, tube=None, hitmap=None)

Get and process hitmaps and sky fractions for the provided tube or provided an external one.

Parameters:

tube : str

Specify a tube.

hitmap : string or map, optional

Provide the path to a hitmap to override the default used for the tube. You could also provide the hitmap as an array directly.

Returns:

hitmaps : ndarray or ndmap

Processed hitmaps.

sky_fractions : float

The sky fraction covered by the survey determined from the hitmaps.

get_inverse_variance(self, tube, output_units='uK_CMB', hitmap=None, white_noise_rms=None)

Get the inverse noise variance in each pixel for the requested tube.

Parameters:

tube : str

Specify a specific tube.

output_units : str

Output unit supported by PySM.units, e.g. uK_CMB or K_RJ

hitmap : string or map, optional

Provide the path to a hitmap to override the default used for the tube. You could also provide the hitmap as an array directly.

white_noise_rms : float or tuple of floats, optional

Optionally scale the simulation so that the small-scale limit white noise level is white_noise_rms in uK-arcmin (either a single number or a pair for the dichroic array).

Returns:

ivar_map : ndarray or ndmap

Numpy array with the HEALPix or CAR map of the inverse variance in each pixel. The default units are uK^(-2). This is an extensive quantity that depends on the size of pixels.

get_noise_indices(self, tube, band=None)

Gets indices in the so_noise_model package of a channel or the 2 channels of a tube

get_noise_properties(self, tube, nsplits=1, hitmap=None, white_noise_rms=None, atmosphere=True)

Get noise curves scaled with the hitmaps and the hitmaps themselves

Parameters:

see the docstring of simulate

Returns:

ell : np.array

Array of \(\ell\)

ps_T, ps_P : np.array

Tube noise spectra for T and P, one row per channel, the 3rd the crosscorrelation

fsky : np.array

Array of sky fractions computed as <normalized N_hits>

wnoise_power : np.array

White noise power (high-ell limit)

hitmaps : np.array

Array of the hitmaps for each channel

get_white_noise_power(self, tube, sky_fraction, band=None, units='sr')

Get white noise power in uK^2-sr (units=’sr’) or uK^2-arcmin^2 (units=’arcmin2’) corresponding to the tube name tube. This is useful if you want to generate your own simulations that do not have the atmospheric component.

Parameters:

tube : str

Specify a tube.

sky_fraction : float

The sky fraction covered by the survey.

band : str,optional

Optionally specify the band name within the tube to get just its white noise.

units: str

‘sr’ for white noise power in uK^2-steradian and ‘arcmin2’ for the same in uK^2-arcmin^2 units.

Returns:

wnoise : tuple of floats

The white noise variance in the requested units either as a tuple for the pair of bands in the tube, or just for the specific band requested.

simulate(self, tube, output_units='uK_CMB', seed=None, nsplits=1, mask_value=None, atmosphere=True, hitmap=None, white_noise_rms=None)

Create a random realization of the noise power spectrum

Parameters:

tube : str

Specify a specific tube.

output_units : str

Output unit supported by PySM.units, e.g. uK_CMB or K_RJ

seed : integer or tuple of integers, optional

Specify a seed. The seed is converted to a tuple if not already one and appended to (0,0,6,tube_id) to avoid collisions between tubes, with the signal sims and with ACT noise sims, where tube_id is the integer ID of the tube.

nsplits : integer, optional

Number of splits to generate. The splits will have independent noise realizations, with noise power scaled by a factor of nsplits, i.e. atmospheric noise is assumed to average down with observing time the same way the white noise does. By default, only one split (the coadd) is generated.

mask_value : float, optional

The value to set in masked (unobserved) regions. By default, it uses the value in default_mask_value, which for healpix is healpy.UNSEEN and for CAR is numpy.nan.

atmosphere : bool, optional

Whether to include the correlated 1/f from the noise model. This is True by default. If it is set to False, then a pure white noise map is generated from the white noise power in the noise model, and the covariance between arrays is ignored.

hitmap : string or map, optional

Provide the path to a hitmap to override the default used for the tube. You could also provide the hitmap as an array directly.

white_noise_rms : float or tuple of floats, optional

Optionally scale the simulation so that the small-scale limit white noise level is white_noise_rms in uK-arcmin (either a single number or a pair for the dichroic array).

Returns:

output_map : ndarray or ndmap

Numpy array with the HEALPix or CAR map realization of noise. The shape of the returned array is (2,3,nsplits,)+oshape, where oshape is (npix,) for HEALPix and (Ny,Nx) for CAR. The first dimension of size 2 corresponds to the two different bands within a dichroic tube. The second dimension corresponds the three polarization Stokes components I,Q,U and the third dimension corresponds to independent split realizations of the noise.