646 research outputs found
The Impact of Atmospheric Fluctuations on Degree-scale Imaging of the Cosmic Microwave Background
Fluctuations in the brightness of the Earth's atmosphere originating from
water vapor are an important source of noise for ground-based instruments
attempting to measure anisotropy in the Cosmic Microwave Background. This paper
presents a model for the atmospheric fluctuations and derives simple
expressions to predict the contribution of the atmosphere to experimental
measurements. Data from the South Pole and from the Atacama Desert in Chile,
two of the driest places on Earth, are used to assess the level of fluctuations
at each site.Comment: 29 pages, 7 figures, 1 table, appears in The Astrophysical Journa
A Spin Modulated Telescope to Make Two Dimensional CMB Maps
We describe the HEMT Advanced Cosmic Microwave Explorer (HACME), a balloon
borne experiment designed to measure sub-degree scale Cosmic Microwave
Background anisotropy over hundreds of square degrees, using a unique two
dimensional scanning strategy. A spinning flat mirror that is canted relative
to its spin axis modulates the direction of beam response in a nearly
elliptical path on the sky. The experiment was successfully flown in February
of 1996, achieving near laboratory performance for several hours at float
altitude. A map free of instrumental systematic effects is produced for a 3.5
hour observation of 630 square degrees, resulting in a flat band power upper
limit of (l(l+1)C_l/2 pi)^0.5 < 77 microK at l = 38 (95% confidence). The
experiment design, flight operations and data, including atmospheric effects
and noise performance, are discussed.Comment: 4 pages, 3 figure
Measurements of Anisotropy in the Cosmic Microwave Background Radiation at 0.5 Degree Angular Scales Near the Star Gamma Ursae Minoris
We present results from a four frequency observation of a 6 x 0.6 degree
strip of the sky centered near the star Gamma Ursae Minoris during the fourth
flight of the Millimeter-wave Anisotropy eXperiment (MAX). The observation was
made with a 1.4 degree peak-to-peak sinusoidal chop in all bands. The FWHM beam
sizes were 0.55 +/- 0.05 degrees at 3.5 cm-1 and 0.75 +/-0.05 degrees at 6, 9,
and 14 cm-1. During this observation significant correlated structure was
observed at 3.5, 6 and 9 cm-1 with amplitudes similar to those observed in the
GUM region during the second and third flights of MAX. The frequency spectrum
is consistent with CMB and inconsistent with thermal emission from interstellar
dust. The extrapolated amplitudes of synchrotron and free-free emission are too
small to account for the amplitude of the observed structure. If all of the
structure is attributed to CMB anisotropy with a Gaussian autocorrelation
function and a coherence angle of 25', then the most probable values of
DeltaT/TCMB in the 3.5, 6, and 9 cm-1 bands are 4.3 (+2.7, -1.6) x 10-5, 2.8
(+4.3, -1.1) x 10-5, and 3.5 (+3.0, -1.6) x 10-5 (95% confidence upper and
lower limits), respectively.Comment: 16 pages, postscrip
Measurements of Anisotropy in the Cosmic Microwave Background Radiation at Degree Angular Scales Near the Stars Sigma Hercules and Iota Draconis
We present results from two four-frequency observations centered near the
stars Sigma Hercules and Iota Draconis during the fourth flight of the
Millimeter-wave Anisotropy eXperiment (MAX). The observations were made of 6 x
0.6-degree strips of the sky with 1.4-degree peak to peak sinusoidal chop in
all bands. The FWHM beam sizes were 0.55+/-0.05 degrees at 3.5 cm-1 and a
0.75+/-0.05 degrees at 6, 9, and 14 cm-1. Significant correlated structures
were observed at 3.5, 6 and 9 cm-1. The spectra of these signals are
inconsistent with thermal emission from known interstellar dust populations.
The extrapolated amplitudes of synchrotron and free-free emission are too small
to account for the amplitude of the observed structures. If the observed
structures are attributed to CMB anisotropy with a Gaussian autocorrelation
function and a coherence angle of 25', then the most probable values are
DT/TCMB = (3.1 +1.7-1.3) x 10^-5 for the Sigma Hercules scan, and DT/TCMB =
(3.3 +/- 1.1) x 10^-5 for the Iota Draconis scan (95% confidence upper and
lower limits). Finally a comparison of all six MAX scans is presented.Comment: 13 pages, postscript file, 2 figure
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Radiological environmental monitoring report for Brookhaven National Laboratory 1967--1970
Brookhaven National Laboratory (BNL) was established in 1947 on the former Army Camp Upton site located in central Long Island, New York. From the very beginning, BNL has monitored the environment on and around the Laboratory site to assess the effects of its operations on the environment. This document summarizes the environmental data collected for the years 1967, 1968, 1969, and 1970. Thus, it fills a gap in the series of BNL annual environmental reports beginning in 1962. The data in this document reflect measurements for those four years of concentrations and/or amounts of airborne radioactivity, radioactivity in streams and ground water, and external radiation levels in the vicinity of BNL. Also included are estimates, made at that time, of BNL`s contribution to radioactivity in the environment. Among the major scientific facilities operated at BNL are the High Flux Beam Reactor, Medical Research Reactor, Brookhaven Graphite Research Reactor, Alternating Gradient Synchrotron, and the 60-inch Cyclotron
Optimization of Planck/LFI on--board data handling
To asses stability against 1/f noise, the Low Frequency Instrument (LFI)
onboard the Planck mission will acquire data at a rate much higher than the
data rate allowed by its telemetry bandwith of 35.5 kbps. The data are
processed by an onboard pipeline, followed onground by a reversing step. This
paper illustrates the LFI scientific onboard processing to fit the allowed
datarate. This is a lossy process tuned by using a set of 5 parameters Naver,
r1, r2, q, O for each of the 44 LFI detectors. The paper quantifies the level
of distortion introduced by the onboard processing, EpsilonQ, as a function of
these parameters. It describes the method of optimizing the onboard processing
chain. The tuning procedure is based on a optimization algorithm applied to
unprocessed and uncompressed raw data provided either by simulations, prelaunch
tests or data taken from LFI operating in diagnostic mode. All the needed
optimization steps are performed by an automated tool, OCA2, which ends with
optimized parameters and produces a set of statistical indicators, among them
the compression rate Cr and EpsilonQ. For Planck/LFI the requirements are Cr =
2.4 and EpsilonQ <= 10% of the rms of the instrumental white noise. To speedup
the process an analytical model is developed that is able to extract most of
the relevant information on EpsilonQ and Cr as a function of the signal
statistics and the processing parameters. This model will be of interest for
the instrument data analysis. The method was applied during ground tests when
the instrument was operating in conditions representative of flight. Optimized
parameters were obtained and the performance has been verified, the required
data rate of 35.5 Kbps has been achieved while keeping EpsilonQ at a level of
3.8% of white noise rms well within the requirements.Comment: 51 pages, 13 fig.s, 3 tables, pdflatex, needs JINST.csl, graphicx,
txfonts, rotating; Issue 1.0 10 nov 2009; Sub. to JINST 23Jun09, Accepted
10Nov09, Pub.: 29Dec09; This is a preprint, not the final versio
Off-line radiometric analysis of Planck/LFI data
The Planck Low Frequency Instrument (LFI) is an array of 22
pseudo-correlation radiometers on-board the Planck satellite to measure
temperature and polarization anisotropies in the Cosmic Microwave Background
(CMB) in three frequency bands (30, 44 and 70 GHz). To calibrate and verify the
performances of the LFI, a software suite named LIFE has been developed. Its
aims are to provide a common platform to use for analyzing the results of the
tests performed on the single components of the instrument (RCAs, Radiometric
Chain Assemblies) and on the integrated Radiometric Array Assembly (RAA).
Moreover, its analysis tools are designed to be used during the flight as well
to produce periodic reports on the status of the instrument. The LIFE suite has
been developed using a multi-layered, cross-platform approach. It implements a
number of analysis modules written in RSI IDL, each accessing the data through
a portable and heavily optimized library of functions written in C and C++. One
of the most important features of LIFE is its ability to run the same data
analysis codes both using ground test data and real flight data as input. The
LIFE software suite has been successfully used during the RCA/RAA tests and the
Planck Integrated System Tests. Moreover, the software has also passed the
verification for its in-flight use during the System Operations Verification
Tests, held in October 2008.Comment: Planck LFI technical papers published by JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/1748-022
B-mode polarization forecasts for GreenPol
We present tensor-to-scalar ratio forecasts for GreenPol, a hypothetical
ground-based B-mode experiment aiming to survey the cleanest regions of the
Northern Galactic hemisphere at five frequencies between 10 and 44 GHz. Its
primary science goal would be to measure large-scale CMB polarization
fluctuations at multipoles , and thereby constrain the
primordial tensor-to-scalar ratio. The observations for the suggested
experiment would take place at the Summit Station (72deg N, 38deg W) on
Greenland, at an altitude of 3216 meters above sea level. In this paper we
simulate various experimental setups, and derive limits on the tensor-to-scalar
ratio after CMB component separation using a Bayesian component separation
implementation called Commander. When combining the proposed experiment with
Planck HFI observations for constraining polarized thermal dust emission, we
find a projected limit of r<0.02 at 95 % confidence for the baseline
configuration. This limit is very robust with respect to a range of important
experimental parameters, including sky coverage, detector weighting, foreground
priors etc. Overall, GreenPol would have the possibility to provide deep CMB
polarization measurements of the Northern Galactic hemisphere at low
frequencies.Comment: 10 pages, 8 figures. To be submitted to A&
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