The artificial night sky brightness mapped from DMSP satellite Operational Linescan System measurements

We present a method to map the artificial sky brightness across large territories in astronomical photometric bands with a resolution of approximately 1 km. This is of use in quantifying the situation regarding night sky pollution, recognizing potential astronomical sites and allowing future monitoring of trends. The artificial sky brightness present in the chosen direction at a given position on the surface of the Earth is obtained by the integration of the contributions produced by every surface area in the surroundings . Each contribution is computed via detailed models for the propagation in the atmosphere of the upward light flux emitted by the area. The light flux is measured with top-of-atmosphere radiometric observations made by the Defense Meteorological Satellite Program (DMSP) Operational Linescan System.
We have applied the described method to Europe, obtaining maps of artificial sky brightness in the V and B bands.     

The first World Atlas of the artificial night sky brightness

We present the first World Atlas of the zenith artificial night sky brightness at sea level. Based on radiance-calibrated high-resolution DMSP satellite data and on accurate modelling of light propagation in the atmosphere, it provides a nearly global picture of how mankind is proceeding to envelop itself in a luminous fog. Comparing the Atlas with the United States Department of Energy (DOE) population density data base, we determined the fraction of population who are living under a sky of given brightness. About two-thirds of the World population and 99 per cent of the population in the United States (excluding Alaska and Hawaii) and European Union live in areas where the night sky is above the threshold set for polluted status. Assuming average eye functionality, about one-fifth of the World population, more than two-thirds of the United States population and more than one half of the European Union population have already lost naked eye visibility of the Milky Way. Finally, about one-tenth of the World population, more than 40 per cent of the United States population and one sixth of the European Union population no longer view the heavens with the eye adapted to night vision, because of the sky brightness.     

Moon night sky brightness simulation for the Xinglong stationSong Yao

Using a sky brightness monitor at the Xinglong station of National Astronomical Observatories,Chinese Academy of Sciences,we collected data from22 dark clear nights and 90 moon nights.We first measured the sky brightness variation with time for dark nights and found a clear correlation between sky brightness and human activity.Then with a modified sky brightness model of moon nights and data from these nights,we derived the typical value for several important parameters in the model.With these results,we calculated the sky brightness distribution under a given moon condition for the Xinglong station.Furthermore,we simulated the sky brightness distribution of a moon night for a telescope with a 5 field of view（such as LAMOST）.These simulations will be helpful for determining the limiting magnitude and exposure time,as well as planning the survey for LAMOST during moon nights.     

A site-testing campaign at the Calar Alto Observatory with GSM and DIMM instruments

The main atmospheric optical parameters have been measured at the Calar Alto Observatory simultaneously using the Generalized Seeing Monitor (GSM) and a Differential Image Motion Monitor (DIMM) during several nights in 2002 May. The temporal evolution of the seeing, the outer scale, the isoplanatic angle and the coherence time have been analysed. There is excellent agreement between the seeing measurements provided by the two instruments, particularly when the turbulence is slow. Indeed, the GSM measurements are corrected from the exposure time when the DIMM data were recorded for at least 5 ms. From almost three years of DIMM (at 5 m height above ground) data, a seeing of 0.92 arcsec with a standard deviation of 0.31 arcsec has been obtained for this site. The outer scale     , the isoplanatic angle  θ₀  and the coherence time  τ₀  measured with the GSM are well fitted with log-normal distributions with median values of 22.9 m, 2.27 arcsec and 3.7 ms, respectively.     

Characterization of the mesospheric sodium layer at La Palma

We present the results of a mesospheric sodium monitoring programme at La Palma carried out through five campaigns of one week each, from 1999 September to 2000 August. The yearly averaged parameters of the layer (the sodium column density and the width) are given. We show that the short time-scale dynamics of the layer are governed by the sporadic layers with an average frequency of one event per night. The influence of the short time-scale dynamics of the layer on an adaptive optics system working on the William Herschel Telescope is quantified. It appears that it is a small effect in terms of defocus error. Finally, we present data obtained during the Perseid meteor shower and show that the dynamics of the sodium layer undergoes a transition with the meteoric activity.     

A laser beacon for monitoring the mesospheric sodium layer at La Palma

We report the results of the first laser beacon experiment at the astronomical site of La Palma (Canary Islands). A continuous wave low‐power laser (a few hundred mW) system has been set up. The laser, tuned on the sodium D₂ line at 589 nm, is launched close to the zenith angle. The emission of the mesospheric sodium layer is observed from a telescope located 160 m away from the laser. The layer is therefore resolved in altitude and the different features of its dynamics are investigated.     

Weather at Sierra Negra: 7.3-yr statistics and a new method to estimate the temporal fraction of cloud cover

Sierra Negra, one of the highest peaks in central Mexico, is the site of the Large Millimeter Telescope. We describe the first results of a comprehensive analysis of the weather data measured in situ from 2000 October to 2008 February to be used as a reference for future activity in the site. We compare the data from two different stations at the summit considering the accuracy of both instruments. We analysed the diurnal, seasonal and annual cycles for all the parameters. The thermal stability is remarkably good, crucial for a good performance of the telescopes. From the solar radiation data, we developed a new method to estimate the fraction of time when the sky is clear of clouds. We show that our measurements are consistent with a warm standard atmosphere model. The conditions at the site are benign and stable given its altitude, showing that Sierra Negra is an extremely good site for millimeter and high-energy observations.     

The seeing at the William Herschel Telescope

We present results from a study of the seeing quality at the 4.2-m William Herschel telescope at La Palma. The median intrinsic seeing at the site is found to be excellent, and is comparable to that at the Paranal and Mauna Kea observatories. Contributions to the seeing from turbulence within the telescope dome are insignificant. Furthermore, the optical quality and tracking stability of the telescope are good, so that long-exposure image widths close to the limit imposed by the site seeing can be expected.     

大气492 GHz亚毫米波不透明度的测量

使用移动式亚毫米波望远镜(POST)在位于青藏高原海拔3200米的紫金山天文台德令哈射电天文观测站址测量地球大气492GHz频率处天顶方向的不透明度(τ0)的结果．在1999—2000年冬季和2000—2001年冬季的两个观测季节内累计共进行了约870个小时的测量，取得了25842组τ0的有效数据．对数据的统计表明，观测季节内τ0值主要分布在1．5—3．0之间．观测时段内大气不透明度τ0≤1．0的时间比例约占3％．在给出实测资料的基础上，将所测量的亚毫米波不透明度与国际现有亚毫米波台址的不透明度进行了初步比较．     

High-altitude wind velocity at Oukaimeden observatory

This paper aims at studying the wind at 200 mbar over the Moroccan observatory Oukaimeden, as high-altitude winds have been adopted as a useful parameter for site characterization in terms of the suitability of a site for the development of some adaptive optics techniques. The data used come from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data base, which is widely acknowledged as being reliable. Statistical analyses of 200-mbar wind speed since 1983 are performed. Comparison with some of the main observatory sites worldwide qualifies Oukaimeden as one of the best observatory sites in terms of 200-mbar wind statistics. Our analysis of a record of seeing measurements during the years 2003 and 2004 concludes that while 200-mbar wind speed can be used as a parameter for ranking astronomical sites in term of their suitability for adaptive optics, it cannot be used for the whole atmospheric seeing prediction. A comparison of monthly values of the seeing parameter at Oukaimeden, La Silla and Paranal demonstrates the high seeing quality of Oukaimeden, as the seeing values measured were lower than those of La Silla and Paranal for most of the time during the comparison period. Furthermore, a statistical analysis of atmospheric stratified seeing, wavefront coherence time and isoplanatic angle measured with a Multi-Aperture Scintillation Sensor instrument over Paranal from 2004 to 2007 have been performed. We found good correlations between 200-mbar wind velocity and levels 4, 5 and 6 seeing, wavefront coherence time and isoplanatic angle, with corresponding correlation coefficients of 0.74, 0.79, 0.70, 0.97 and 0.78.     

Model of optical turbulence profile at Cerro Pachón

New measurements of optical turbulence profile at the Cerro Pachón observatory in Chile are analysed jointly with previously published data to model the variations of the intensity and thickness of the ground layer and free atmosphere under a variety of observing conditions. This work is motivated by the need to predict statistically the performance of ground-layer adaptice optics. We find that the ground-layer profile can be represented by a decaying exponent with a scale height of 20–40 m, increasing to 100 m under bad conditions. The zone from 6 to 500 m contributes typically about 61 per cent to the total integral, the latter causing a median seeing of 0.77 arcsec. Turbulence integrals in the ground layer and in free atmosphere vary independently of each other, in 50 per cent of cases they deviate by less than 1.8 times from their respective median values. The existence of periods with low turbulence in the free atmosphere and their importance for adaptive optics is stressed.     

Adaptive optics parameters connection to wind speed at the Teide Observatory

Current projects for large telescopes demand a proper knowledge of atmospheric turbulence to design efficient adaptive optics systems in order to reach large Strehl ratios. However, the proper characterization of the turbulence above a particular site requires long-term monitoring. Because of the lack of long-term information on turbulence, high-altitude winds (in particular winds at the 200 mbar pressure level) were proposed as a parameter for estimating the total turbulence at a particular site, with the advantage of records of winds going back several decades. We present the first complete study of atmospheric adaptive optics parameters above the Teide Observatory (Canary Islands, Spain) in relation to wind speed. On-site measurements of   C ² _N ( h )  profiles (more than 20 200 turbulence profiles) from G-SCIDAR (Generalized Scintillation Detection and Ranging) observations and wind vertical profiles from balloons have been used to calculate the seeing, the isoplanatic angle and the coherence time. The connection of these parameters to wind speeds at ground and at 200 mbar pressure level are shown and discussed. Our results confirm the well-known high quality of the Canary Islands astronomical observatories.     

Telescope and instrument robotization at Dome C

This article reviews the situation for robotization of telescopes and instruments at the Antarctic station Concordia on Dome C. A brain‐storming meeting was held in Tenerife in March 2007 from which this review emerged.We describe and summarize the challenges for night‐time operations of various astronomical experiments at conditions “between Earth and Space” and conclude that robotization is likely a prerequisite for continuous astronomical data taking during the 2000‐hour night at Dome C. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modelling artificial night-sky brightness with a polarized multiple scattering radiative transfer computer code

As part of an ongoing investigation of radiative effects produced by hazy atmospheres, computational procedures have been developed for use in determining the brightening of the night sky as a result of urban illumination. The downwardly and upwardly directed radiances of multiply scattered light from an offending metropolitan source are computed by a straightforward Gauss–Seidel (G–S) iterative technique applied directly to the integrated form of Chandrasekhar's vectorized radiative transfer equation. Initial benchmark night-sky brightness tests of the present G–S model using fully consistent optical emission and extinction input parameters yield very encouraging results when compared with the double scattering treatment of Garstang, the only full-fledged previously available model.     

Comparison of the atmosphere above the South Pole, Dome C and Dome A: first attempt

The atmospheric properties above three sites (Dome C, Dome A and the South Pole) on the Internal Antarctic Plateau are investigated for astronomical applications using the monthly median of the analyses from ECMWF (the European Centre for Medium-Range Weather Forecasts). Radiosoundings extended on a yearly time-scale at the South Pole and Dome C are used to quantify the reliability of the ECMWF analyses in the free atmosphere as well as in the boundary and surface layers, and to characterize the median wind speed in the first 100 m above the two sites. Thermodynamic instability properties in the free atmosphere above the three sites are quantified with monthly median values of the Richardson number. We find that the probability to trigger thermodynamic instabilities above 100 m is smaller on the Internal Antarctic Plateau than on mid-latitude sites. In spite of the generally more stable atmospheric conditions of the Antarctic sites compared to mid-latitude sites, Dome C shows worse thermodynamic instability conditions than those predicted above the South Pole and Dome A above 100 m. A rank of the Antarctic sites done with respect to the strength of the wind speed in the free atmosphere (ECMWF analyses) as well as the wind shear in the surface layer (radiosoundings) is presented.