Map making in small field modulated CMB polarization experiments: approximating the maximum likelihood method
Map making in small field modulated CMB polarization experiments: approximating the maximum likelihood method
复制标题
小场调制 CMB 偏振实验中的制图：近似最大似然法
DOI：
10.1111/j.1365-2966.2008.14195.x
复制
发表时间：
2008
影响因子：
4.8
通讯作者：
K. Smith
中科院分区：
文献类型：
--
作者：
D. Sutton;B. Johnson;M. Brown;P. Cabella;P. Ferreira;K. Smith
地图制作是下一代千像素宇宙微波背景极化实验的一个重要的计算挑战。来自数千个探测器的多年时间有序数据（TOD）将需要压缩成T，Q和U斯托克斯参数的地图。这些实验的科学目标的基础，B模式的观察，是控制噪声和系统学的能力。在本文中，我们考虑一种替代的最大似然方法，称为去噪，其中的噪声被建模为一组离散的偏移函数，然后从时间流中减去。我们比较我们的striping代码（Descart：DEStriping CARTographer）的一个完整的最大似然映射器，将它们应用到200 Monte Carlo模拟的TOD从地面，部分天空偏振调制实验。在这些模拟中，噪声由探测器或大气1/f噪声主导。利用这种噪声的功率谱的先验信息，我们产生T，Q和U的striped映射，这些映射与最优映射的差异可以忽略不计。该方法不过滤信号或偏置E或B模式功率谱。取决于踩线基线的长度，该方法在计算时间上比最大似然算法提高了5到22倍。我们发现，对于单探测器映射的特定情况，即使Q和U信号由以5 Hz旋转的半波片调制，为了探测B模式，也必须去除大气1/f。
Map making presents a significant computational challenge to the next generation of kilopixel cosmic microwave background polarization experiments. Years worth of time ordered data (TOD) from thousands of detectors will need to be compressed into maps of the T, Q and U Stokes parameters. Fundamental to the science goal of these experiments, the observation of B modes, is the ability to control noise and systematics. In this paper, we consider an alternative to the maximum likelihood method, called destriping, where the noise is modelled as a set of discrete offset functions and then subtracted from the time stream. We compare our destriping code (Descart: the DEStriping CARTographer) to a full maximum likelihood mapmaker, applying them to 200 Monte Carlo simulations of TOD from a ground-based, partial-sky polarization modulation experiment. In these simulations, the noise is dominated by either detector or atmospheric 1/f noise. Using prior information of the power spectrum of this noise, we produce destriped maps of T, Q and U which are negligibly different from optimal. The method does not filter the signal or bias the E- or B-mode power spectra. Depending on the length of the destriping baseline, the method delivers between five and 22 times improvement in computation time over the maximum likelihood algorithm. We find that, for the specific case of single detector maps, it is essential to destripe the atmospheric 1/f in order to detect B modes, even though the Q and U signals are modulated by a half-wave plate spinning at 5Hz.