11,565 research outputs found
The ArT\'eMiS wide-field submillimeter camera: preliminary on-sky performances at 350 microns
ArTeMiS is a wide-field submillimeter camera operating at three wavelengths
simultaneously (200, 350 and 450 microns). A preliminary version of the
instrument equipped with the 350 microns focal plane, has been successfully
installed and tested on APEX telescope in Chile during the 2013 and 2014
austral winters. This instrument is developed by CEA (Saclay and Grenoble,
France), IAS (France) and University of Manchester (UK) in collaboration with
ESO. We introduce the mechanical and optical design, as well as the cryogenics
and electronics of the ArTeMiS camera. ArTeMiS detectors are similar to the
ones developed for the Herschel PACS photometer but they are adapted to the
high optical load encountered at APEX site. Ultimately, ArTeMiS will contain 4
sub-arrays at 200 microns and 2x8 sub-arrays at 350 and 450 microns. We show
preliminary lab measurements like the responsivity of the instrument to hot and
cold loads illumination and NEP calculation. Details on the on-sky
commissioning runs made in 2013 and 2014 at APEX are shown. We used planets
(Mars, Saturn, Uranus) to determine the flat-field and to get the flux
calibration. A pointing model was established in the first days of the runs.
The average relative pointing accuracy is 3 arcsec. The beam at 350 microns has
been estimated to be 8.5 arcsec, which is in good agreement with the beam of
the 12 m APEX dish. Several observing modes have been tested, like On-The-Fly
for beam-maps or large maps, spirals or raster of spirals for compact sources.
With this preliminary version of ArTeMiS, we concluded that the mapping speed
is already more than 5 times better than the previous 350 microns instrument at
APEX. The median NEFD at 350 microns is 600 mJy.s1/2, with best values at 300
mJy.s1/2. The complete instrument with 5760 pixels and optimized settings will
be installed during the first half of 2015.Comment: 11 pages, 11 figures. Presented at SPIE Millimeter, Submillimeter,
and Far-Infrared Detectors and Instrumentation for Astronomy VII, June 24,
2014. To be published in Proceedings of SPIE Volume 915
Analysis of antenna position measurements and weather station network data during the ALMA Long Baseline Campaign of 2015
In a radio interferometer, the determination of geometrical antenna positions
relies on accurate calibration of the dry and wet delay of the atmosphere above
each antenna. For the Atacama Large Millimeter/Submillimeter Array (ALMA),
which has baseline lengths up to 16 kilometers, the geography of the site
forces the height above mean sea level of the more distant antenna pads to be
significantly lower than the central array. Thus, both the ground level
meteorological values and the total water column can be quite different between
antennas in the extended configurations. During 2015, a network of six
additional weather stations was installed to monitor pressure, temperature,
relative humidity and wind velocity, in order to test whether inclusion of
these parameters could improve the repeatability of antenna position
determinations in these configurations. We present an analysis of the data
obtained during the ALMA Long Baseline Campaign of Oct. through Nov. 2015. The
repeatability of antenna position measurements typically degrades as a function
of antenna distance. Also, the scatter is more than three times worse in the
vertical direction than in the local tangent plane, suggesting that a
systematic effect is limiting the measurements. So far we have explored
correcting the delay model for deviations from hydrostatic equilibrium in the
measured air pressure and separating the partial pressure of water from the
total pressure using water vapor radiometer (WVR) data. Correcting for these
combined effects still does not provide a good match to the residual position
errors in the vertical direction. One hypothesis is that the current model of
water vapor may be too simple to fully remove the day-to-day variations in the
wet delay. We describe possible avenues of improvement, including measuring and
applying more accurate values of the sky coupling efficiency of the WVRs.Comment: 19 pages, 14 figures, 1 table; presented at SPIE Astronomical
Telescopes + Instrumentation 2016, held in Edinburgh, UK on 26 June - 1 July
201
Preliminary results from the advanced photovoltaic experiment flight test
The Advanced Photovoltaic Experiment is a space flight test designed to provide reference cell standards for photovoltaic measurement as well as to investigate the solar spectrum and the effect of the space environment on solar cells. After a flight of 69 months in low earth orbit as part of the Long Duration Exposure Facility set of experiments, it was retrieved in January, 1990. The electronic data acquisition system functioned as designed, measuring and recording cell performance data over the first 358 days of flight; limited by battery lifetime. Significant physical changes are also readily apparent, including erosion of front surface paint, micrometeoroid and debris catering and contamination
High-resolution wide-band Fast Fourier Transform spectrometers
We describe the performance of our latest generations of sensitive wide-band
high-resolution digital Fast Fourier Transform Spectrometer (FFTS). Their
design, optimized for a wide range of radio astronomical applications, is
presented. Developed for operation with the GREAT far infrared heterodyne
spectrometer on-board SOFIA, the eXtended bandwidth FFTS (XFFTS) offers a high
instantaneous bandwidth of 2.5 GHz with 88.5 kHz spectral resolution and has
been in routine operation during SOFIA's Basic Science since July 2011. We
discuss the advanced field programmable gate array (FPGA) signal processing
pipeline, with an optimized multi-tap polyphase filter bank algorithm that
provides a nearly loss-less time-to-frequency data conversion with
significantly reduced frequency scallop and fast sidelobe fall-off. Our digital
spectrometers have been proven to be extremely reliable and robust, even under
the harsh environmental conditions of an airborne observatory, with
Allan-variance stability times of several 1000 seconds. An enhancement of the
present 2.5 GHz XFFTS will duplicate the number of spectral channels (64k),
offering spectroscopy with even better resolution during Cycle 1 observations.Comment: Accepted for publication in A&A (SOFIA/GREAT special issue
PICES Press, Vol. 7, No. 2, July 1999
Improving PICES CO2 measurement quality
The status of the Bering Sea: July - December 1998
The state of the eastern North Pacific since October 1998
The state of the western North Pacific in the second half of 1998
Paul Henry LeBlond
Report on the ICES/SCOR Symposium on Ecosystem Effects of Fishing
What is the carrying capacity of the North Pacific Ocean for salmonids?
Southeast Bering Sea Carrying Capacity (SEBSCC)
The Whole Earth System: The role of regional programs
Sub-Arctic Gyre Experiment in the North Pacific Ocean (SAGE)
The Alaska Predator Ecosystem Experiment (APEX): An integrated seabird and forage fish investigation sponsored by the Exxon Valdez Oil Spill Trustee Council
ICES and GOOS: A progress report
Report on GOOS Living Marine Resource Panel Meetin
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