A Review of Optical Sky Brightness and Extinction at Dome C, Antarctica

ABSTRACTWe present optical (UBVRI) sky brightness measurements from 1992 through 2006. The data are based on CCD imagery obtained with the CTIO 0.9, 1.3, and 1.5 m telescopes. The B‐ and V‐band data are in reasonable agreement with measurements previously made at Mauna Kea, although on the basis of a small number of images per year, there are discrepancies for the years 1992 through 1994. Our CCD‐based data are not significantly different than values obtained at Cerro Paranal. We find that the yearly averages of V‐band sky brightness are best correlated with the 10.7 cm solar flux taken 5 days prior to the sky brightness measurements. This implies an average speed of 350 km s−1 for the solar wind. While we can measure an enhancement of the night‐sky levels over La Serena 10° above the horizon, at elevation angles above 45°, we find no evidence that the night‐sky brightness at Cerro Tololo is affected by artificial light of nearby towns and cities.

Dome C, Antarctica is a prime site for astronomical observations in terms of climate, wind speeds, turbulence, and infrared and terahertz sky backgrounds (for example, see Aristidi et al. 2005; Storey et al. 2005). However, at present little is known about the optical sky brightness and atmospheric extinction. Using a variety of modelling techniques, together with data from the South Pole, the brightness of the night sky at Dome C is estimated in Kenyon & Storey (2006) including the contributions from scattered sunlight, moonlight, aurorae, airglow, zodiacal light, integrated starlight, diffuse Galactic light and artificial sources. The results are compared to Mauna Kea, Hawaii. We summarise the main conclusions.

The summit of the Antarctic plateau, Dome A, is proving to be an excellent site for optical, near-infrared, and terahertz astronomical observations. Gattini is a wide-field camera installed on the PLATO instrument module as part of the Chinese-led traverse to Dome A in 2009 January. We present here the measurements of sky brightness with the Gattini ultra-large field of view ( ) in the photometric B-, V-, and R-bands; cloud cover statistics measured during the 2009 winter season; and an estimate of the sky transparency. A cumulative probability distribution indicates that the darkest 10% of the nights at Dome A have sky brightness of S B = 22.98, S V = 21.86, and S R = 21.68 mag arcsec−2. These values were obtained during the year 2009 with minimum aurora, and they are comparable to the faintest sky brightness at Maunakea and the best sites of northern Chile. Since every filter includes strong auroral lines that effectively contaminate the sky brightness measurements, for instruments working around the auroral lines, either with custom filters or with high spectral resolution instruments, these values could be easily obtained on a more routine basis. In addition, we present example light curves for bright targets to emphasize the unprecedented observational window function available from this ground-based site. These light curves will be published in a future paper.

The Gattini cameras are two site testing instruments for the measurement of optical sky brightness, large area cloud cover and auroral detection of the night sky above the high altitude Dome C site in Antarctica. The cameras have been in operation since January 2006. The cameras are transit in nature and are virtually identical, both adopting Apogee Alta ccd detectors. The camera called Gattini-SBC images a 6 degree field centred on the South Pole, an elevation of 75° at the Dome C site. The camera takes repeated images of the same 6 degree field in the Sloan g' band (centred on 477nm) and, by adopting a lens with sufficiently long focal length, one can integrate the sky background photons and directly compare to the equivalent values of the stars within the field. The second camera, called Gattini-allsky, incorporates a fish-eye lens and images ~110 degree field centred on local zenith. By taking frequent images of the night sky we will obtain long term cloud cover statistics, measure the sky background intensity as a function of solar and lunar altitude and phase and directly measure the spatial extent of bright aurora if present and when they occur. An overview of the project is presented together with preliminary results from data taken since operation of the cameras in January 2006.

Nigel is a fiber-fed UV/visible grating spectrograph with a thermoelectrically-cooled 256×1024 pixel CCD camera, designed to measure the twilight and night sky brightness from 300nm to 850 nm. Nigel has three pairs of fibers, each with a field-of-view with an angular diameter of 25 degrees, pointing in three fixed positions towards the sky. The bare fibers are exposed to the sky with no additional optics. The instrument was deployed at Dome A, Antarctica in January 2009 as part of the PLATO (PLATeau Observatory) robotic observatory. During the 2009 winter, Nigel made approximately six months of continuous observations of the sky, with typically 104 deadtime between exposures. The resulting spectra provide quantitative information on the sky brightness, the auroral contribution, and the water vapour content of the atmosphere. We present details of the design, construction and calibration of the Nigel spectrometer, as well some sample spectra from a preliminary analysis.

Variability of aerosol optical parameters by advective processes

—The aim of this study is to detect elusive light that indicate the prayer time (Isha’). Therefore, we focused on optical sky brightness at dusk from May 2007 through April 2008 intermittently. The measurements of twilight sky brightness were covered at one (1) site covering; West coast of Peninsular Malaysia. The measurements were done by applying Sky Quality Meter (SQM) which covered between 400-700 nm in accordance of human eyes and SQM range. Results showed that there are clear indications of light changes when Sun at certain degree below horizon that visible by plateau form in twilight sky brightness dependences versus solar zenith angle. It is clarified that the yearly averages of solar depression by observation are best correlated within the range of 17.3o – 19.5o for Isha’. Index Terms —Twilight; prayer time; sky quality meter. I. I NTRODUCTION Early studies done by astronomers such as Ibn Muadh, al-Biruni, al-Qayini, Ibn Yunus etc.[1], [2]. Ibn al-Shatir adopted various value for each prayer times such as 17

The brightness of the night sky at an astronomical site is one of the principal factors that determine the quality of available optical observing time. At any site the optical night sky is always brightened with airglow, zodiacal light, integrated starlight, diffuse Galactic light and extra-galactic light. Further brightening can be caused by scattered sunlight, aurorae, moonlight and artificial sources. Dome C exhibits many characteristics that are extremely favourable to optical and IR astronomy; however, at this stage few measurements have been made of the brightness of the optical night sky. Nigel is a fibre-fed UV/visible grating spectrograph with a thermoelectrically cooled 256 × 1024 pixel CCD camera, and is designed to measure the twilight and night sky brightness at Dome C from 250 nm to 900 nm. We present details of the design, calibration and installation of Nigel in the AASTINO laboratory at Dome C, together with a summary of the known properties of the Dome C sky.

Inversion of visible optical extinction data for spheroid particle size distribution based on PCA

At the summit of the Antarctic plateau, Dome A offers an intriguing location for future large scale optical astronomical observatories. The Gattini Dome A project was created to measure the optical sky brightness and large area cloud cover of the winter-time sky above this high altitude Antarctic site. The wide field camera and multi-filter system was installed on the PLATO instrument module as part of the Chinese-led traverse to Dome A in January 2008. This automated wide field camera consists of an Apogee U4000 interline CCD coupled to a Nikon fisheye lens enclosed in a heated container with glass window. The system contains a filter mechanism providing a suite of standard astronomical photometric filters (Bessell B, V, R) and a long-pass red filter for the detection and monitoring of airglow emission. The system operated continuously throughout the 2009, and 2011 winter seasons and part-way through the 2010 season, recording long exposure images sequentially for each filter. We have in hand one complete winter-time dataset (2009) returned via a manned traverse. We present here the first measurements of sky brightness in the photometric V band, cloud cover statistics measured so far and an estimate of the extinction.

ABSTRACTDuring the austral summer of 1996, the mid‐infrared imaging polarimeter NIMPOL was operated at the Amundsen‐Scott South Pole Station, to obtain quantitative measurements of the 10 and 20 μm sky brightness and stability. These observations were conducted as part of the Joint Australian Centre for Astrophysical Research in Antarctica (JACARA) site testing program on the Antarctic Plateau. The results of this site testing program are presented. The observations show that the mid‐infrared sky brightness at the South Pole Station is much less than comparison sky brightness observations made at the Canberra base of the instrument. This reduction in sky brightness is attributed largely to the low emissivity of the atmosphere (because of its dryness and lack of aerosols), and the effect of the reduced atmospheric temperature (there is an expected decrease by a factor of 2.5 from the temperature difference between the two sites alone). The measured 11 μm sky emissivity at the South Pole is also lower than previous measurements of the sky emissivity at Mauna Kea Observatory in Hawaii. The sky brightness was also found to be more stable than at the warmer, mid‐latitude site (Canberra), and it is expected that “stare” mode operation of the instrument for astronomical observations would be quite feasible under these conditions. Measurements were also made during a period of “ice haze,” and the suspended ice crystals were observed to increase the sky background by 16% compared with clear weather and to add low‐frequency brightness variations. However, this variability could be removed by slow (2 Hz) chopping, allowing high‐sensitivity observing to continue through the “ice haze.”

A propagation experiment is described in which a stratospheric balloon served as a transmitter platform at 870 and 1502 MHz in simulation of a land mobile satellite. A vehicle followed the drifting balloon along roads of western Texas and New Mexico, collecting at L-band amplitude and phase, and at UHF amplitude information only for elevation angles between 25 degrees and 45 degrees . The data obtained has been analyzed and is presented along with results from modeling of multipath scattering and roadside tree attenuation. The signal, with variations caused by multipath propagation and tree shadowing, was reduced by 3 dB at L-band and 2 dB at UHF for one percent of all locations. A median ratio of 3.9 was found between peak-to-peak phase (degrees) and power (dB) fluctuations. The ratio between L-band and UHF dB attenuation averages varied from 1.3 to 1.0 at fade levels from 6 to 23 dB. Optical sky brightness was measured and used to predict fade distribution with great accuracy. A single-scatterer multipath model is introduced. It is used to duplicate some of the measured data and to show the dependence of power variations on satellite elevation angle. Using Fresnel diffraction theory, the attenuation caused by a model tree was calculated to be near 10 dB and the maximum fade was found to increase by the logarithm of the number of branches.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Infrared emission and optical scattering by the high galactic latitude dust cloud L1642

Lidar observations of the mesospheric Na layer were made at the south pole(90°S) and Syowa (69°S) during the winters of 1990 and 1985, respectively. These observations are used to characterize the gravity wave activity in the upper mesosphere at both sites. Strong wave activity is observed throughout the winter at both the south pole and Syowa and shows remarkable similarity with observations from several midlatitude and low‐latitude sites. The quasi‐monochromatic gravity waves exhibit the same general relationships between their wavelengths, observed periods, and amplitudes as observed at lower latitudes. The average growth length of these waves is approximately 26 km, indicating that the wave field at both Antarctic sites is strongly influenced by dissipation and saturation processes. The spectra and variances of the density perturbations associated with quasi‐random wave field at the south pole are reported. The vertical wavenumber and temporal frequency spectra follow power‐law shapes. The mean index of the vertical wavenumber spectrum is −2.4, and the mean characteristic wavelength is 14 km. The mean index of the temporal frequency spectrum is −1.7. The mean density variance at the south pole is (5.7%)2 and is similar in magnitude to that observed at a variety of lower‐latitude sites. With no tropospheric convection during the polar night and little orographic forcing over the relatively featureless Antarctic plateau, these observations suggest that nonlinear processes, rather than the source characteristics, primarily determine the characteristics of the gravity wave field in the upper mesosphere. These observations show two other distinct features. The mean Na layer over Antarctica is significantly lower and broader (centroid height ≈ 90 km and rms width ≈ 4.8 km) than at lower latitudes, reflecting the stronger downwelling and warmer winter temperatures in the mesopause region at high latitudes. Strong coherent oscillations were observed in the bottomside density contours of the Na layer with periods close to the inertial period. These oscillations were also observed in OH airglow measurements and appear to be associate with planetary scale waves.

We present the Gattini project: a multisite campaign to measure the optical sky properties above the two high altitude Antarctic astronomical sites of Dome C and Dome A. The Gattini-DomeC project, part of the IRAIT site testing campaign and ongoing since January 2006, consists of two cameras for the measurement of optical sky brightness, large area cloud cover and auroral detection above the DomeC site, home of the French-Italian Concordia station. The cameras are transit in nature and are virtually identical except for the nature of the lenses. The cameras have operated successfully throughout the past two Antarctic winter seasons and here we present the first results obtained from the returned 2006 dataset. The Gattini-DomeA project will place a similar site testing facility at the highest point on the Antarctic plateau, Dome A, with observations commencing in 2008. The project forms a small part of a much larger venture coordinated by the Polar Research Institute of China as part of the International Polar Year whereby an automated site testing facility called PLATO will be traversed into the DomeA site. The status of this exciting and ambitious project with regards to the Gattini-DomeA cameras will be presented.