Wider SAT from the Pole II

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March 22, 2019 - Reijo Keskitalo and Julian Borrill


Background

We continue our exploration of wide field SAT observations from the Pole started in Wider SAT from the Pole. The results can also be compared to Deep SAT from the Pole. We have built observing schedules for the proposed wide field that divide the field into three latitude segments and two longitude halves. The splits are required to facilitate Sun and Moon avoidance and to balance the observing time with the area of each segment.

In this post we provide one year hit maps and depth maps corresponding to realistic detector noise as a function of observing elevation.

Here is the location of wide field and the segments:

Priority by pixel fwhm01 nbin10.full.pole.v3.png

The coordinates of the wide field are RA = -30..90 degrees, DEC = -60..-45 degrees.

The hitmaps and noise variance maps shown in this post are available at NERSC under /global/cscratch1/sd/keskital/cmbs4_scanning_simulations


Results

We ran a scanning simulation with a mock hexagonal focal plane with a 35-degree FOV and 217 pixels on a regular grid. Here is the resulting hit map scaled to match 100Hz observations with 1000 pixels:

Total hits.pole.png

The fsky numbers in the title correspond to raw, noise and signal-dominated versions of the same metric:

Fsky.png

Monthly hit maps show that the some of the tiles are not observable during the Austral summer due to the 45-degree solar avoidance region. The scheduler balances the integration time in the following months as Lunar avoidance permits:

Montly hits.pole.png

Due to the wide range of observing elevations, it is necessary to consider also the elevation-dependent noise in the detectors. We use the analytical fits to the 95GHz elevation profiles from S4 NET forecasts III and modulate the individual detector noise levels for each scan. The resulting depth map scaled to 1000 pixels is here:

Total wcov.pole.png


Further work

We also considered the possibility of lowering the minimum observing elevation from 45 degrees down to 40 degrees to allow access to a larger sky area. This adds an extra latitude segment to the wide field:

Priority by pixel fwhm01 nbin10.full.pole.v4.png

Here is the resulting depth map:

Total wcov.pole.low el test.png

The noise-driven fsky is increased by 12% while the depth is reduced by 7%. The coordinates of the even wider field are RA = -30..90 degrees, DEC = -60..-40 degrees.