The optimization of satellite orbit for Space-VLBI observation

By sending one or more telescopes into space,Space-VLBI(SVLBI)is able to achieve even higher angular resolution and is therefore the trend of the VLBI technique.For the SVLBI program,the design of satellite orbits plays an important role for the success of planned observation.In this paper,we present our orbit optimization scheme,so as to facilitate the design of satellite orbits for SVLBI observation.To achieve that,we characterize the uv coverage with a measure index and minimize it by finding out the corresponding orbit configuration.In this way,the design of satellite orbit is converted to an optimization problem.We can prove that,with an appropriate global minimization method,the best orbit configuration can be found within the reasonable time.Besides that,we demonstrate that this scheme can be used for the scheduling of SVLBI observations.

Nonlinearity Correction of Fourier Transform Spectrometer in Solar Observation Using Simulated Annealing

A Fourier transform spectrometer(FTS)has been used to observe solar activities due to its ultra-high spectral resolution.However,the FTS in-band spectra are usually distorted and some artifacts appear in out-of-band regions due to nonlinear effects.Therefore,the FTS nonlinear problem must be corrected.In this study,we proposed a novel method to correct the nonlinear effects using simulated annealing.We simulated several nonlinear spectra to evaluate the performance of our method.The calculated quadratic coefficients are extremely close to the given values,demonstrating that the method is effective and accurate.The proposed method is further used to correct the blackbody and solar spectra with nonlinearity obtained by Bruker IFS-125HR installed at the Huairou Solar Observing Station,which is a pathfinder for the accurate infrared magnetic field measurements of the Sun project.To the blackbody spectra,the nonlinearity in low-and high-frequency regions are corrected by 89.09%and 60.84%.The nonlinear correction of the solar spectra in the low-and high-frequency regions have reached 65.34%and 81.04%,respectively.These results prove that our method can correct the nonlinear problem to improve the data accuracy.

A Novel Imaging Method Based on Reweighted Total Variation for an Interferometer Array on Lunar Orbit

Ground-based radio observations below 30 MHz are susceptible to the ionosphere of the Earth and the radio frequency interference.Compared with other space mission concepts,making low frequency observations using an interferometer array on lunar orbit is one of the most feasible ones due to a number of technical and economic advantages.Different from traditional interferometer arrays,the interferometer array on lunar orbit faces some complications such as the three-dimensional distribution of baselines and the changing sky blockage by the Moon.Although the brute-force method based on the linear mapping relationship between the visibilities and the sky temperature can produce satisfactory results in general,there are still large residual errors on account of the loss of the edge information.To obtain the full-sky maps with higher accuracy,in this paper we propose a novel imaging method based on reweighted total variation(RTV)for a lunar orbit interferometer array.Meanwhile,a split Bregman iteration method is introduced to optimize the proposed RTV model so as to decrease the computation time.The simulation results show that,compared with the traditional brute-force method,the RTV regularization method can effectively reduce the reconstruction errors and obtain more accurate sky maps,which proves the effectiveness of the proposed method.