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Map-based noise simulations based on the LAT mss-0002 mission-scale time-domain simulations

Tag: mbs-s0015-20240504

Updates

  • 2024-06-10: first release, lmax=5400 simulations.

Summary

300 realistic realizations of the LAT map noise, given the single realization of the time-domain simulations. Simulations cover the full LAT footprint to a bandlimit of lmax=5400, and utilize the directional wavelet noise model.

Noise model

This release is based on the LAT mss-0002 time-domain simulations, available on NERSC at:

/global/cfs/cdirs/sobs/sims/mss-0002/RC1.r01

These time-domain simulations provide four noise splits for each frequency band. More information is available on the SO productdb.

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

Notes:

  • Simulations are bandlimited to lmax=5400. To save space, the simulations for the f090, f150, f230 and f280 bands are stored in a pixelization that is downgraded by a factor of 4 relative to the time-domain simulations (no downgrading was needed for the f030 and f040 maps) (shape=(..., 2640, 10800), 2 arcmin resolution vs. shape=(..., 10560, 43200) 0.5 arcmin resolution). See examples below for further guidance.
  • The following releases were used: mnms v0.0.7 and sofind v0.0.5
  • A mask has been applied to the map-domain simulations that removes a small amount of noisy pixels at the edges of the maps. The masks are stored here: /global/cfs/cdirs/sobs/v4_sims/mbs/mbs_s0015_20240504/masks/LAT_{bands}_mask_obs.fits.
  • See these slides for validation of the map-based simulations.

Available maps

Maps are available in the CAR (Fejer1 variant) pixelization. As above, the maps have a resolution of 2 arcmin. Maps are in Equatorial Coordinates, uK_CMB units, FITS format.

The maps are located here:

/global/cfs/cdirs/sobs/v4_sims/mbs/mbs_s0015_20240504/sims

and have the following naming convention:

so_lat_mbs_mss0002_fdw_{bands}_lmax5400_4way_set{split_num}_noise_sim_map{sim_num:04}.fits

where bands is in [lf_f030_lf_f040, mf_f090_mf_f150, uhf_f230_uhf_f290], split_num is in [0-3] and sim_num is in [0000-0299].

The simulations take up 2.3 TB.

Please open an issue here for any data access problems.

Available models

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

/global/cfs/cdirs/sobs/v4_sims/mbs/mbs_s0015_20240504/models

The /global/cfs/cdirs/sobs/v4_sims/mbs/mbs_s0015_20240504/renamed directory contains ancillary map files needed to draw from the covariance matrices or to generate new matrices. See the preprocess_maps.py script to see how these files were generated.

Metadata

The models correlate pairs of frequency bands on the same detector wafer. Therefore, the simulations are stored in a similar paired format. Thus, the shape of a given simulation file is (2, 1, 3, 2640, 10800):

  • The first axis is the frequency band
  • The second (singleton) axis follows mnms convention (reserved for map splits; since each simulation corresponds to one map split, the dimension of this axis is 1)
  • The third axis is Stokes component (I, Q, U)
  • The last axes are the map pixels

The geometry (including shape) of the maps is given in the FITS header:

SIMPLE  =                    T / conforms to FITS standard                      
BITPIX  =                  -32 / array data type                                
NAXIS   =
 5 / number of array dimensions                     
NAXIS1  =                10800                                                  
NAXIS2  =                 2640
NAXIS3  =                    3                                                  
NAXIS4  =                    1                                                  
NAXIS5  =                    2                                                  
WCSAXES =                    2 / Number of coordinate axes                      
CRPIX1  =               5401.0 / Pixel coordinate of reference point            
CRPIX2  =               1890.5 / Pixel coordinate of reference point            
CDELT1  =   -0.033333333333333 / [deg] Coordinate increment at reference point  
CDELT2  =    0.033333333333333 / [deg] Coordinate increment at reference point  
CUNIT1  = 'deg'                / Units of coordinate increment and value        
CUNIT2  = 'deg'                / Units of coordinate increment and value        
CTYPE1  = 'RA---CAR'           / Right ascension, plate caree projection        
CTYPE2  = 'DEC--CAR'           / Declination, plate caree projection            
CRVAL1  =                180.0 / [deg] Coordinate value at reference point      
CRVAL2  =                  0.0 / [deg] Coordinate value at reference point      
LONPOLE =                  0.0 / [deg] Native longitude of celestial pole       
LATPOLE =                 90.0 / [deg] Native latitude of celestial pole        
MJDREF  =                  0.0 / [d] MJD of fiducial time                       
RADESYS = 'ICRS'               / Equatorial coordinate system                   END

Example usage

For a simple example that loads and interacts with the simulations, see the example_usage.py script.

Additional simulations

If your analysis needs more simulations, it is possible to draw additional simulations from the provided noise models. This requires installing the mnms and sofind python libraries. Follow the "quick setup" described in the sofind readme.

An example of loading or simulating additional maps using mnms is provded in the additional_simulations.py script.

For an example of how to generate a larger set of simulations on a cluster, see the run01 script. For reference, drawing the simulations provided here took approximately 5 hours using 20 MPI tasks distributed over 5 128-core nodes.

Known issues

  • Small scales (l > 4000) f030/f040 has excess noise power. Large scales (l < 1000) in f030/f040 has excess TT noise power. Large scales (l < 500) in f150 has excess TT noise power and large scales (l < 1000) in f290 has excess TT noise power. All relatively small amounts. See these slides.

Feedback

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