In [1]:
import mapsims
import numpy as np
import healpy as hp
import pysm3.units as u
from pathlib import Path
%matplotlib inline
import matplotlib.pyplot as plt

# Running on the fly simulations with mapsims¶

The mapsims package allows to generate maps on-the-fly, so they can be generated as needed inside other pipelines.

The interface is the SONoiseSimulator class, specify nside to work with HEALPix maps, shape and wcs for CAR (see lesson 6).

The class constructor just initializes the configuration of the class, doesn't load neither spectra nor hitmaps.

In [2]:
mapsims.SONoiseSimulator?
Init signature:
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',
)
Docstring:      <no docstring>
Init docstring:
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 :math:\ell,
we can zero that power specifying an integer :math:\ell value here.
The power spectra at :math:\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
File:           /global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/noise.py
Type:           type
Subclasses:
In [3]:
noise_sim = mapsims.SONoiseSimulator(nside=256)

The simulate method does all the processing, it loads the HEALPix or CAR hitmaps (from a path when run at NERSC or downloading and caching them locally) and calls the so_noise_models package to generate the expected spectra given the instrument configuration.

The hitmaps were generated in time domain executing parallel runs with TOAST and then saved to disk. They are only used as a relative weighting, the global noise properties are driven by the spectra from so_noise_models.

The simulate method gets the expected spectra, weights them by the sky fraction and then generates isotropic noise over the whole sky with synfast for HEALPix and sym_expand for CAR and then scales it by the relative hitmap.

It always simulates a dichroic tube at a time so that also the cross-correlation between the channels is simulated and captured in the output maps.

In [4]:
noise_sim.simulate?
Signature:
noise_sim.simulate(
tube,
output_units='uK_CMB',
seed=None,
nsplits=1,
atmosphere=True,
hitmap=None,
white_noise_rms=None,
)
Docstring:
Create a random realization of the noise power spectrum

Parameters
----------

tube : str
Specify a tube (for SO: ST0-ST3, LT0-LT6) see the tubes attribute
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.
See the band_id attribute of the Channel class
to identify which is the index of a Channel in the array.

The second dimension corresponds to independent split realizations
of the noise, e.g. it is 1 for full mission.

The third dimension corresponds to the three polarization
Stokes components I,Q,U

The last dimension is the number of pixels
File:      /global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/noise.py
Type:      method
In [5]:
tube = "LT1"
In [6]:
noise_maps = noise_sim.simulate(tube)
/global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/utils.py:71: UserWarning: Access data from /global/cfs/cdirs/sobs/www/so_mapsims_data/v0.2/healpix/LT1_UHF1_01_of_20.nominal_telescope_all_time_all_hmap.fits.gz
warnings.warn(f"Access data from {full_path}")
/global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/utils.py:71: UserWarning: Access data from /global/cfs/cdirs/sobs/www/so_mapsims_data/v0.2/healpix/LT1_UHF2_01_of_20.nominal_telescope_all_time_all_hmap.fits.gz
warnings.warn(f"Access data from {full_path}")
/global/common/software/sobs/mbs/lib/python3.7/site-packages/healpy/fitsfunc.py:352: UserWarning: If you are not specifying the input dtype and using the default np.float64 dtype of read_map(), please consider that it will change in a future version to None as to keep the same dtype of the input file: please explicitly set the dtype if it is important to you.
"If you are not specifying the input dtype and using the default "
In [7]:
noise_maps.shape
Out[7]:
(2, 1, 3, 786432)
In [8]:
channels = mapsims.parse_channels("tube:" + tube)[0]
In [9]:
channels
Out[9]:
(Channel LT1_UHF1, Channel LT1_UHF2)
In [10]:
for ch, m in zip(channels, noise_maps):
hp.mollview(m[0][1], title="EE map " + ch.tag, unit="uK", min=-10, max=10)

## Compare cross-spectra¶

We can take a cross-spectrum between the maps of the 2 tubes and compare with the expected spectrum from noise.get_fullsky_noise_spectra.

In [11]:
ell, ps_T, ps_P = noise_sim.get_fullsky_noise_spectra(tube=tube)
In [12]:
hitmaps, ave_nhits = noise_sim.get_hitmaps(tube=tube)
In [13]:
sky_fraction = (hitmaps[0] > 0).sum() / len(hitmaps[0])
In [14]:
noise_maps.shape
Out[14]:
(2, 1, 3, 786432)
In [15]:
x_C_ell = hp.anafast(hp.ma(noise_maps[0][0])*hitmaps[0], hp.ma(noise_maps[1][0])*hitmaps[1]) / sky_fraction / np.mean(hitmaps[0]*hitmaps[1])
In [16]:
x_C_ell.shape
Out[16]:
(6, 768)
In [17]:
plt.figure(figsize=(8,5))
plt.loglog(ell, ps_P[2] * sky_fraction, lw=2, label="Input polarization Cross-spectrum")
plt.loglog(x_C_ell[1], label="EE Cross-spectrum", alpha=.5)
plt.loglog(x_C_ell[2], label="BB Cross-spectrum", alpha=.5)
plt.xlabel("$\ell$")
plt.ylabel("$C_\ell [\mu K^2]$")
plt.grid()
plt.ylim(1e-5, 1e-1)
plt.legend();

## Simulate multiple tubes¶

A single SONoiseSimulator object is capable of simulating noise for different tubes. See for example a loop to simulate all SAT channels.

In [18]:
tubes = ["ST{}".format(i) for i in range(4)]
In [19]:
for tube in tubes:
noise_maps = noise_sim.simulate(tube)
for ch, m in zip(mapsims.parse_channels("tube:" + tube)[0], noise_maps):
hp.mollview(m[0][1], title="EE map " + ch.tag, unit="$uK$", min=-10, max=10)
/global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/utils.py:71: UserWarning: Access data from /global/cfs/cdirs/sobs/www/so_mapsims_data/v0.2/healpix/ST0_UHF1_01_of_20.nominal_telescope_all_time_all_hmap.fits.gz
warnings.warn(f"Access data from {full_path}")
/global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/utils.py:71: UserWarning: Access data from /global/cfs/cdirs/sobs/www/so_mapsims_data/v0.2/healpix/ST0_UHF2_01_of_20.nominal_telescope_all_time_all_hmap.fits.gz
warnings.warn(f"Access data from {full_path}")
/global/common/software/sobs/mbs/lib/python3.7/site-packages/healpy/fitsfunc.py:352: UserWarning: If you are not specifying the input dtype and using the default np.float64 dtype of read_map(), please consider that it will change in a future version to None as to keep the same dtype of the input file: please explicitly set the dtype if it is important to you.
"If you are not specifying the input dtype and using the default "
/global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/utils.py:71: UserWarning: Access data from /global/cfs/cdirs/sobs/www/so_mapsims_data/v0.2/healpix/ST1_MFF1_01_of_20.nominal_telescope_all_time_all_hmap.fits.gz
warnings.warn(f"Access data from {full_path}")
/global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/utils.py:71: UserWarning: Access data from /global/cfs/cdirs/sobs/www/so_mapsims_data/v0.2/healpix/ST1_MFF2_01_of_20.nominal_telescope_all_time_all_hmap.fits.gz
warnings.warn(f"Access data from {full_path}")
/global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/utils.py:71: UserWarning: Access data from /global/cfs/cdirs/sobs/www/so_mapsims_data/v0.2/healpix/ST2_MFS1_01_of_20.nominal_telescope_all_time_all_hmap.fits.gz
warnings.warn(f"Access data from {full_path}")
/global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/utils.py:71: UserWarning: Access data from /global/cfs/cdirs/sobs/www/so_mapsims_data/v0.2/healpix/ST2_MFS2_01_of_20.nominal_telescope_all_time_all_hmap.fits.gz
warnings.warn(f"Access data from {full_path}")
/global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/utils.py:71: UserWarning: Access data from /global/cfs/cdirs/sobs/www/so_mapsims_data/v0.2/healpix/ST3_LF1_01_of_20.nominal_telescope_all_time_all_hmap.fits.gz
warnings.warn(f"Access data from {full_path}")
/global/common/software/sobs/mbs/lib/python3.7/site-packages/mapsims/utils.py:71: UserWarning: Access data from /global/cfs/cdirs/sobs/www/so_mapsims_data/v0.2/healpix/ST3_LF2_01_of_20.nominal_telescope_all_time_all_hmap.fits.gz
warnings.warn(f"Access data from {full_path}")