Baseline Measurement of the Antenna Array for the Chinese Spectral Radioheliograph in the Centimeter-to-Decameter Wave Range
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摘要: 日像仪采用综合孔径原理成像,利用不同基线单元的相关输出得到复可见度函数,经过傅里叶变换得到源的亮度分布,基线测量精度是影响成像质量的重要因素。提出了采用大地坐标测量结合观测天文源确定方向基准,进行厘米-分米波射电日像仪天线阵单元天线三维坐标位置测量,获得天线基线矢量的方案,并通过在国家天文台明安图观测站建立相对坐标测控网,对射电日像仪天线阵天线基线进行实测定位,整网平差计算结果表明测量方案合理可行,并满足日像仪基线间距离测量精度的要求和相关成图要求。Abstract: The Chinese Spectral Radioheliograph (CSRH) is a aperture synthesis telescope dedicated to solar observation. Its antenna array is aligned in a shape of triple-spiral arms in an area of about 10 square kilometers. A radioheliograph is a radio-astronomy instrument to obtain solar images in radio bands based on image synthesis. The surface-brightness distribution of the sun is recovered from an ensemble of measurements. The first step of the image recovery process is computing the three-dimensional inverse Fourier transformaion of the correlation outputs of different baselines of the entire radioheliograph antenna array.Here, the high-precision baseline-vector measurement is one of the key factors for imgae recovery with high confidence.In this paper, we propose a measurement method of the CSRH baseline vectors. We first set up a coordinate system with its original reference direction is determined by observing a star (e.g. Polaris). Geodetic surveys and high-precision theodolites are then used to measure the three-dimensional coordinates of all the CSRH antennae in this coordinate system. The triangle-network coordinate system with 31 monitoring points spaced at about 500 meters has now been established at the Mingantu Station of the National Astronomical Observatories where the CSRH is located.On November 2011, we measured with the error compensation the three-dimension baseline vectors in the network coordinates. This results in three-dimensional coordinates of the CSRH antennae with a precision better than 5mm rms. Such a precision meets the requirement of high-quality CSRH imaging. The precision can be improved as more measruements are carried out over time.
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Keywords:
- Aperture synthesis /
- Geodetic survey /
- Radioheliogragh /
- Baseline
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