---+ Atmospheric Subtraction

Two atmospheric subtraction methods:

• • These methods are equivalent for a frozen atmosphere (according to Crawford).
  • Principle Component Analysis ala Bolocam
    • principal_components.pdf: Very basic tutorial on principal component analysis (not specific to astronomy)
    • from bolo-bolo coveriance over a half scan (e.g. both spatial and time basis).
    • basically the data is put into a matrix, which we diagonalized and find the eigenvectors. We project out and subtract the N largest eigenvectors.
    • This will also subtract off things like 60Hz.
    • Good relative gain calibrations may not ne necessary.
  • Spatial Template Removal (also called Sawtooth Fourier Modes) - ala Tom Crawford for SPT or Bolocam
    • for each time sample, subtract a gradiant, quadrupole, etc across the array. (e.g. both spatial only)
    • you need to remove bolo offsets and gain variations before applying this.
    • Section 4.6 of Jack Sayer's Bolocam PhD Thesis, Dec 2007 Caltech.
  • 2006_AtmosphereCode Example code provided by friends.

Here are some notes for gaining an intuition about atmosphere 2006_AtmosphereSubtractionIntuition.

Relevant Papers:

• http://xxx.lanl.gov/abs/astro-ph/9905369 Lay and Halverson, "Impact of Atmospheric Fluctuations on Degree-scale Imaging of the Cosmic Microwave Background".
• http://lanl.arxiv.org/abs/astro-ph/0412031 Bussmann, Holzapfel, and Kuo (ACBAR), "Millimeter Wavelength Brightness Fluctuations of the Atmosphere Above the South Pole".
• http://lanl.arxiv.org/abs/astro-ph/0211134 Peterson et al., "Stability of the Submillimeter Brightness of the Atmosphere Above Mauna Kea, Chajnantor and the South Pole"

Glitch Flagging and Removing

• many astronomy applications use "kappa-sigma clipping" (e.g. for CCDs) to flag and recognize cosmic rays.

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This topic: APEX_SZ > WebHome > 2006_AtmosphereSubtraction Topic revision: r6 - 2008-05-13 - MattDobbs

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