Studies of Millimeter-wave Atmospheric Noise above Mauna Kea
We report measurements of the fluctuations in atmospheric emission (atmospheric noise) above Mauna Kea recorded with Bolocam at 143 and 268 GHz from the Caltech Submillimeter Observatory. The 143 GHz data were collected during a 40 night observing run in late 2003, and the 268 GHz observations were made in early 2004 and early 2005 over a total of 60 nights. Below ≃0.5 Hz, the data time-streams are dominated by atmospheric noise in all observing conditions. The atmospheric noise data are consistent with a Kolmogorov–Taylor turbulence model for a thin wind-driven screen, and the median amplitude of the fluctuations is 280 mK2 rad−5/3 at 143 GHz and 4000 mK2 rad−5/3 at 268 GHz. Comparing our results with previous ACBAR data, we find that the normalization of the power spectrum of the atmospheric noise fluctuations is a factor of ≃80 larger above Mauna Kea than above the South Pole at millimeter wavelengths. Most of this difference is due to the fact that the atmosphere above the South Pole is much drier than the atmosphere above Mauna Kea. However, the atmosphere above the South Pole is slightly more stable as well: the fractional fluctuations in the column depth of precipitable water vapor are a factor of ≃√2 smaller at the South Pole compared to Mauna Kea. Based on our atmospheric modeling, we developed several algorithms to remove the atmospheric noise, and the best results were achieved when we described the fluctuations using a low-order polynomial in detector position over the 8' field of view. However, even with these algorithms, we were not able to reach photon-background-limited instrument photometer performance at frequencies below ≃0.5 Hz in any observing conditions. We also observed an excess low-frequency noise that is highly correlated between detectors separated by ≲(f/#)λ; this noise appears to be caused by atmospheric fluctuations, but we do not have an adequate model to explain its source. We hypothesize that the correlations arise from the classical coherence of the electromagnetic field across a distance of ≃(f/#)λ on the focal plane.
Additional Information© 2010 American Astronomical Society. Print publication: Issue 2 (2010 January 10); received 2009 April 24; accepted for publication 2009 November 24; published 2009 December 23. We acknowledge the assistance of the following: Minhee Yun and Anthony D. Turner of NASA's Jet Propulsion Laboratory, who fabricated the Bolocam science array; Toshiro Hatake of the JPL electronic packaging group, who wirebonded the array; Marty Gould of Zen Machine and Ricardo Paniagua and the Caltech PMA/GPS Instrument Shop, who fabricated much of the Bolocam hardware; Carole Tucker of Cardiff University, who tested metal-mesh reflective filters used in Bolocam; Ben Knowles of the University of Colorado, who contributed to the software pipeline, the day crew and Hilo staff of the Caltech Submillimeter Observatory, who provided invaluable assistance during commissioning and data-taking for this survey data set; high school teacher Tobias Jacoby and high school students Jonathon Graff, Gloria Lee, and Dalton Sargent, who helped as summer research assistants; and Kathy Deniston, who provided effective administrative support at Caltech. We thank W. L. Holzapfel for his many useful comments as referee of our manuscript. Bolocam was constructed and commissioned using funds from NSF/AST-9618798, NSF/AST-0098737, NSF/AST-9980846, NSF/AST-0229008, and NSF/AST-0206158. J.S. and G.L. were partially supported by NASA Graduate Student Research Fellowships, J.S. was partially supported by a NASA Postdoctoral Program Fellowship, J.A. was partially supported by a Jansky Postdoctoral Fellowship, and S.G. was partially supported by a R. A. Millikan Postdoctoral Fellowship at Caltech. The research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Facility: CSO
Published - Sayers2010p6717Astrophys_J.pdf