اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe Development of Single Star Scidar for Tibet and Dome A
518
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
A Single Star Scidar system(SSS) has been developed for remotely sensing atmospheric turbulence profiles. The SSS consists of computing the spatial auto/cross-correlation functions of short exposure images of the scintillation patterns produced by a single star, and provides the vertical profiles of optical turbulence intensity C2n(h) and wind speed V(h). The SSS needs only a 40 cm aperture telescope, so that can be portable and equipped easily to field candidate sites. Some experiments for the SSS have been made in Beijing last year, successfully retrieving atmospheric turbulence and wind profiles from the ground to 30 km. The SSS observations has recently been made at the Xinglong station of NAOC, characterizing atmospheric parameters at this station. We plan to automatize SSS instrument and run remote observation via internet; a more friendly auto-SSS system will be set up and make use at the candidate sites in Tibet and Dome A.
قيم البحث
اقرأ أيضاً
Knowledge of the Earths atmospheric optical turbulence is critical for astronomical instrumentation. Not only does it enable performance verification and optimisation of existing systems but it is required for the design of future instruments. As a m
inimum this includes integrated astro-atmospheric parameters such as seeing, coherence time and isoplanatic angle, but for more sophisticated systems such as wide field adaptive optics enabled instrumentation the vertical structure of the turbulence is also required. Stereo-SCIDAR is a technique specifically designed to characterise the Earths atmospheric turbulence with high altitude resolution and high sensitivity. Together with ESO, Durham University has commissioned a Stereo-SCIDAR instrument at Cerro Paranal, Chile, the site of the Very Large Telescope (VLT), and only 20~km from the site of the future Extremely Large Telescope (ELT). Here we provide results from the first 18 months of operation at ESO Paranal including instrument comparisons and atmospheric statistics. Based on a sample of 83 nights spread over 22 months covering all seasons, we find the median seeing to be 0.64 with 50% of the turbulence confined to an altitude below 2 km and 40% below 600 m. The median coherence time and isoplanatic angle are found as 4.18 ms and 1.75 respectively. A substantial campaign of inter-instrument comparison was also undertaken to assure the validity of the data. The Stereo-SCIDAR profiles (optical turbulence strength and velocity as a function of altitude) have been compared with the Surface-Layer SLODAR, MASS-DIMM and the ECMWF weather forecast model. The correlation coefficients are between 0.61 (isoplanatic angle) and 0.84 (seeing).
The Multi Aperture Scintillation Sensor (MASS) and the Generalized-Scintillation Detection and Ranging (Generalized SCIDAR) are two instruments conceived to measure the optical turbulence (OT) vertical distribution on the whole troposphere and low st
ratosphere (~ 20 km) widely used in the astronomical context. In this paper we perform a detailed analysis/comparison of measurements provided by the two instruments and taken during the extended site testing campaign carried out on 2007 at Cerro Paranal and promoted by the European Southern Observatory (ESO). The main and final goal of the study is to provide a detailed estimation of the measurements reliability i.e dispersion of turbulence measurements done by the two instruments at different heights above the ground. This information is directly related to our ability in estimating the absolute value of the turbulence stratification. To better analyse the uncertainties between the MASS and the GS we took advantage of the availability of measurements taken during the same campaign by a third independent instrument (DIMM - Differential Imaging Motion Monitor) measuring the integrated turbulence extended on the whole 20 km. Such a cross-check comparison permitted us to define the reliability of the instruments and their measurements, their limits and the contexts in which their use can present some risk.
In two recent papers the mesoscale model Meso-NH, joint with the Astro-Meso-NH package, has been validated at Dome C, Antarctica, for the characterization of the optical turbulence. It has been shown that the meteorological parameters (temperature an
d wind speed, from which the optical turbulence depends on) as well as the Cn2 profiles above Dome C were correctly statistically reproduced. The three most important derived parameters that characterize the optical turbulence above the internal antarctic plateau: the surface layer thickness, the seeing in the free-atmosphere and in the total atmosphere showed to be in a very good agreement with observations. Validation of Cn2 has been performed using all the measurements of the optical turbulence vertical distribution obtained in winter so far. In this paper, in order to investigate the ability of the model to discriminate between different turbulence conditions for site testing, we extend the study to two other potential astronomical sites in Antarctica: Dome A and South Pole, which we expect to be characterized by different turbulence conditions. The optical turbulence has been calculated above these two sites for the same 15 nights studied for Dome C and a comparison between the three sites has been performed.
The hybrid Tibet AS array was successfully constructed in 2014. It has 4500 m$^{2}$ underground water Cherenkov pools used as the muon detector (MD) and 789 scintillator detectors covering 36900 m$^{2}$ as the surface array. At 100 TeV, cosmic-ray ba
ckground events can be rejected by approximately 99.99%, according to the full Monte Carlo (MC) simulation for $gamma$-ray observations. In order to use the muon detector efficiently, we propose to extend the surface array area to 72900 m$^{2}$ by adding 120 scintillator detectors around the current array to increase the effective detection area. A new prototype scintillator detector is developed via optimizing the detector geometry and its optical surface, by selecting the reflective material and adopting dynode readout. This detector can meet our physics requirements with a positional non-uniformity of the output charge within 10% (with reference to the center of the scintillator), time resolution FWHM of $sim$2.2 ns, and dynamic range from 1 to 500 minimum ionization particles.
As telescopes become larger, into the era of ~40 m Extremely Large Telescopes, the high- resolution vertical profile of the optical turbulence strength is critical for the validation, optimization and operation of optical systems. The velocity of atm
ospheric optical turbulence is an important parameter for several applications including astronomical adaptive optics systems. Here, we compare the vertical profile of the velocity of the atmospheric wind above La Palma by means of a comparison of Stereo-SCIntillation Detection And Ranging (Stereo- SCIDAR) with the Global Forecast System models and nearby balloon-borne radiosondes. We use these data to validate the automated optical turbulence velocity identification from the Stereo-SCIDAR instrument mounted on the 2.5 m Isaac Newton Telescope, La Palma. By comparing these data we infer that the turbulence velocity and the wind velocity are consistent and that the automated turbulence velocity identification of the Stereo-SCIDAR is precise. The turbulence velocities can be used to increase the sensitivity of the turbulence strength profiles, as weaker turbulence that may be misinterpreted as noise can be detected with a velocity vector. The turbulence velocities can also be used to increase the altitude resolution of a detected layer, as the altitude of the velocity vectors can be identified to a greater precision than the native resolution of the system. We also show examples of complex velocity structure within a turbulent layer caused by wind shear at the interface of atmospheric zones.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
