Baseline Measurement of the Antenna Array for the Chinese Spectral Radioheliograph in the Centimeter-to-Decameter Wave Range

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.