Survey Performance Expectations

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This page will summarize the various experiment definitions. The data products referred to are located on the NERSC system under /project/projectdirs/cmbs4/expt_xx

Experiment Definition 02, 02b, 02c

This is an update from 01 which differs in the following ways:

1) Addition of 20GHz band and (slight) changes to the band/detector optimization as per [Victor's May 15 posting in the logbook].

2) Addition of 3 delensing bands 95/155/220GHz with same number of detectors as the low res equivalent bands but beam size 4x higher. This adds up to approximately the same number of detectors but clearly one should reoptimize once they are not all at the same freq. Since we are still quite far from having real lensing reconstruction and realistic (non-Gaussian) high ell foregrounds this probably is OK for this round.

3) Addition of tensors - even number realizations have r=0.003, odd number have r=0. This is a sky change, not an experiment change, so shouldn't be here.

4) Set 02 is the same nominal 3% sky patch as set 01. We now add 02b which is 1% round patch with center the same as the BICEP/Keck patch (RA=0, Dec=-57.5), and 02c which is 10% round patch centered on RA=15deg, Dec=-35.

These products appear on NERSC under /project/projectdirs/cmbs4/expt_xx/02 etc.

Experiment Definition 01

This is intended to be basically the same as the assumptions made for the Fisher calculations done for the Science Book. The parameters come from [Victor's Dec 21 posting in the logbook] with the addition of bandwidths from Colin's Nov 4 posting and are summarized in the following table:

Frequency (GHz) 30 40 85 95 145 155 220 270 155 HR
Bandwidth (GHz) 9.0 12.0 20.4 22.8 31.9 34.1 48.4 59.4 34.1
Beam FWHM (arcmin) 76.6 57.5 27.0 24.2 15.9 14.8 10.7 8.5 4.0
white noise level TT (uK-arcmin) 12.97 13.22 2.30 1.89 5.31 5.48 11.86 17.72 5.48
ell knee TT 175 175 175 175 230 230 230 230 500
1/f exponent TT -4.1 -4.1 -4.1 -4.1 -3.8 -3.8 -3.8 -3.8 -3.8
white noise level EE (uK-arcmin) 10.85 11.06 1.93 1.58 2.49 2.56 5.55 8.30 2.56
ell knee EE 50 50 50 50 65 65 65 65 200
1/f exponent EE -2.0 -2.0 -2.0 -2.0 -3.0 -3.0 -3.0 -3.0 -3.0
white noise level BB (uK-arcmin) 10.59 10.79 1.88 1.54 2.38 2.45 5.30 7.93 2.45
ell knee BB 50 50 50 50 60 60 60 60 200
1/f exponent BB -2.0 -2.0 -2.0 -2.0 -3.0 -3.0 -3.0 -3.0 -3.0
ell min 30 30 30 30 30 30 30 30 100
nside 512 512 512 512 512 512 512 512 2048

These parameters are in the file expt_xx/01/params.dat and give rise to the window functions in expt_xx/01/wfunc and the noise spectra in expt_xx/01/noise/cls. The intent of the low ell cutoff is to approximate the effect of the timestream filtering which is commonly done in ground based experiments (and as some kind of acknowledgement that the largest angular scales may anyway be corrupted by systematic effects).

Additionally expt_xx/01/rhits/fsky03bk_n0512.fits is supposed to represent the "relative hits" with which the sky has been observed. This is a circular pattern centred at RA=0, Dec=-45 (a bit below the BICEP/Keck patch) which is flat at one out to r=12deg and then rolls down to zero as cosine squared over an additional 15 deg. This is some kind of approximation as to what small apertures might deliver (given their large instantaneous field of view).

From the noise spectra sets of alms are generated (with nlmax=4096) with names like expt_xx/01/noise/alm/noise_f155_b15_ellmin30_alm_mc_0000.fits where 155 is the frequency, 15 is the beam size (in arcmin), and 0000 is the realization number.

From these full sky maps are rendered at nside=512 and nlmax=1024. No beam smoothing is applied as is appropriate for noise. The maps have names like expt_xx/01/noise/map/noise_f155_b15_ellmin30_map_0512_mc_0000.fits.

The full sky noise is then divided by the square-root of the rhits mask and the result stored in files like data_xx.yy/01.YY/cmbs4_01_noise_f155_b15_ellmin30_map_0512_mc_0000.fits - these are the noise realizations that one would have access to in a real experiment - the noise blows up around the edge.

Including beam sizes in the names of unsmoothed data files is confusing

These masked noise realizations are then added to the sky model (LCDM+dust+sync+) and stored in names like data_xx.yy/01.YY/cmbs4_01pYY_comb_f155_b15_ellmin30_map_0512_mc_0000.fits. As a crude simulation of delensing these combined maps are also provided with the lensing effect reduced to 30, 10 and 3% of reality by combining lensed and unlensed LCDM - look for files with names like data_xx.yy/01.YY/cmbs4_01pYY_comb_AL0p3_f155_b15_ellmin30_map_0512_mc_0000.fits. Maps with partial lensing are constructed by the following combination: partially_lensed_map = sqrt(A_L) * lensed_map + (1 - sqrt(A_L)) * unlensed_map.

To analyze these maps one should use only the expt_xx/01/params.dat file and the maps under data_xx.yy/01.YY. A thousand realizations are present. We can see these maps in this posting

The last column of the table above shows one additional tweak - a second 155GHz band with a higher 1/f knee and smaller beam size - this is supposed to represent the maps made by higher resolution telescopes running in concert with small apertures in a hybrid approach. These maps can in principle be used to reconstruct the lensing potential and delens explicitly - instead of cheating by using the AL0p3 files etc. At the moment the noise spectrum in these maps is provisional. Additionally we may wish to add additional frequency bands at higher resolution so foreground cleaning before delensing can be done. We can see these maps in this posting.

(The filtered LLCDM realizations are also copied in data_xx.yy/01.YY as these are needed to build the bandpower covariance matrix in the multi-component cross spectrum approach used by the BK group. It seems reasonable that one would always have realizations of a known spectrum signal passed through an experimental simulation.)