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Map-based noise simulations based on the SAT mbs-noise-sims-sat time-domain simulations

Tag: mbs-s0014-20230920

Updates

  • 2023-09-20: first release.

Summary

300 realistic realizations of the SAT map noise, estimated from the mbs-noise-sims-sat time-domain noise simulations. Simulations cover the full SAT footprint and utilize the tiled noise model.

Noise model

This release is based on the mbs-noise-sims-sat time-domain simulations, available on NERSC at:

/global/cfs/cdirs/sobs/sims/sat-noise-sims/v1

These noise-only time-domain simulations include detector and atmospheric noise scaled to match a full year of sensitivity split into two disjoint maps for each frequency band. In more detail:

  • One year, three calendar days per month
  • Full SAT focalplanes
  • HWP demodulation
  • Variable mapmaking resolution
    • NSide=128 for 30 and 40GHz (LF)
    • NSide=512 for 90 and 150GHz (MF)
    • NSide=1024 for 230 and 290Ghz (HF)
  • Up to hour-long uninterrupted observations
  • Two time-domain filters:
    • 20th order ground polynomial filter
    • 1st order subscan polynomial filter
  • Noise and atmosphere scaled to match full year of sensitivity split into two disjoint maps

Using mnms, we generate 300 realizations of the noise using map-based methods. Specifically, we use the tiled model, governed by the configured parameters.

Notes:

  • The following releases were used: mnms v0.0.4 and sofind v0.0.4
  • Both time-domain and map-domain simulations are stored in HEALPix format. See examples below for further guidance.
  • A mask has been applied to the map-domain simulations. The masks are stored here: /global/cfs/cdirs/sobs/v4_sims/mbs/mbs_s0014_20230920/car/masks/coadd_SAT_{bands}_mask_obs_hp.fits.
  • See these slides for validation of the map-based simulations.

Available maps

Maps are available in the HEALPix format. Maps are in Equatorial Coordinates, K_CMB units, FITS format.

The maps are available on NERSC at:

/global/cfs/cdirs/sobs/v4_sims/mbs/mbs_s0014_20230920/out/run00

and have the following naming convention:

so_sat_v1_f1_tile_{band}_2way_set{split_num}_noise_sim_map{sim_num:04}.fits

where band is in [f030, f040, f090, f150, f230, f290], split_num is in [0-1] and sim_num is in [0000-0299]. Note that the split_num is 0-indexed for the map-based sims, while it is 1-indexed for the TOD sims.

The maps take up 215 GB.

Please open an issue here for any data access problems.

Example usage

import os
import numpy as np
import healpy as hp

opj = os.path.join

# First get some basic info like the path and the filename template.
fdir = '/global/cfs/cdirs/sobs/v4_sims/mbs/mbs_s0014_20230920/out/run00'
fbase_template = 'so_sat_v1_f1_tile_{band}_2way_set{split_num}_noise_sim_map{sim_num:04}.fits'

# Let's load the sim for e.g. f150, split 0, sim 123.
band = 'f150'
split_num = 0
sim_num = 123               # Has 4 digits (leading 0's), but padding done for us in template.

sim = hp.read_map(
    opj(fdir, fbase_template.format(
        band=band,
        split_num=split_num,
        sim_num=sim_num)
        ),
    field=None  # Load I, Q, and U maps in one go. First axis denotes Stokes I, Q and U.
    )
print(sim.shape, sim.dtype)

This should give:

(3, 3145728), float32

Drawing additional simulations

The runs/run00 script serves as an example of how to draw additional simulations. Note that the script was set up for use on the Simons Foundation cluster. For use on NERSC, the script has to be updated with the appropriate filepaths.

The covariance matrices from which simulations are drawn are available here:

/global/cfs/cdirs/sobs/v4_sims/mbs/mbs_s0014_20230920/models

The masks are stored here:

/global/cfs/cdirs/sobs/v4_sims/mbs/mbs_s0014_20230920/car/masks

Preprocessing the TOD simulations

To derive the models, the TOD sims have been preprocessed. This process consists of calling the project2car.py, compare_spectra.py, inpaint.py and get_masks.py scripts in order. This is not necessary to repeat, but scripts are included for completeness.

Feedback

If anything looks suspicious in the simulations, please do not hesitate to open an issue here.