频率标准对VLBI最高频率相干性的影响
The Impact of Frequency Standards on Coherence in VLBI at the Highest Frequencies
摘要：
我们进行了全成像模拟研究，探讨频率标准的毫米和亚毫米甚长基线干涉测量（VLBI）的影响，重点是相干时间和灵敏度。特别是，我们比较的H-脉泽，传统上用于VLBI，超稳定的低温冷却蓝宝石振荡器的性能在一系列的观测频率，天气条件和分析策略。我们的模拟结果表明，在最高频率下，氢脉泽不稳定性引起的损失与高质量对流层条件下的损失相当。我们发现显着的好处，在VLBI观测的频率在175 GHz以上的网站，具有最好的天气条件下，在350 GHz的频率，我们估计一个20-40%的灵敏度增加，当网站有H-脉泽，相干损失20- 10%，分别取代氢脉泽基于低温蓝宝石振荡器的频率参考。使用共置的水汽辐射计进行大气校正预计会带来最大效益。在这种情况下，我们估计在350 GHz的H-脉泽的灵敏度增加60-120%。
英文摘要：
We have carried out full imaging simulation studies to explore the impact of frequency standards in millimeter and sub-millimeter Very Long Baseline Interferometry (VLBI), focusing on the coherence time and sensitivity. In particular, we compare the performance of the H-maser, traditionally used in VLBI, to that of ultra-stable cryocooled sapphire oscillators over a range of observing frequencies, weather conditions and analysis strategies. Our simulations show that at the highest frequencies, the losses induced by H-maser instabilities are comparable to those from high quality tropospheric conditions. We find significant benefits in replacing H-masers with cryocooled sapphire oscillator based frequency references in VLBI observations at frequencies above 175 GHz in sites which have the best weather conditions; at 350 GHz we estimate a 20-40% increase in sensitivity, over that obtained when the sites have H-masers, for coherence losses of 20-10%, respectively. Maximum benefits are to be expected by using colocated Water Vapour Radiometers for atmospheric correction. In this case, we estimate a 60-120% increase in sensitivity over the H-maser at 350 GHz.
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