Guoxiang Ai

Gradients of the line-of-sight magnetic fields in active region NOAA 6659

The gradients of line-of-sight magnetic fields in active region NOAA 6659 on 1991 June 8 have been calculated based on the photospheric and chromospheric magnetograms taken at Huairou Solar Observing Station. We found that high gradients coincided with high strengths of the transverse magnetic fields, implying a complicated configuration of the magnetic field in the lower atmosphere.For this extraordinarily flare-prolific region, a possible relationship between the gradients and the flares was inferred.

Space Solar Telescope

Abstract The Space has idea observing conditions of astronomy: observable in all wavelengths; continuous temporal coverage; observable in all direction; avoid disturbances produced by the atmosphere (seeing and stray light); super coherence length and so on. Following the space technology is developed further, it is not slightly doubt that space astronomy will become the major part of the astronomy. The solar magnetic fields provide the major incentive to do solar physics. The small spatial extent of the magnetically constrained structures and processes in the solar atmosphere provide the major incentive for high resolution solar telescope. The super high spatial resolution, the visibility of the out solar atmosphere in the ultraviolet and X-ray domains, and continuous evolution study provide the major incentive for space solar observation. A Space Solar Telescope has been proposal. The satellite is consisted of an optical diffracting limited telescope with 1 M diameter, 2-D real time polarizing spectrograph, and four small attached telescope of UV, hard X-ray, soft X-ray and Hα image (full disk). The total weight is about 2.5 T, effect power about 1000 W, sun synchronous polar circular orbit the orbit altitude 500 KM, mission life 3–5 years, launch date is about 2001–2002, that time is just next solar maximum period.

The principle of a navigation constellation composed of SIGSO communication satellites

The Chinese Area Positioning System (CAPS), a navigation system based on geostationary orbit (GEO) communication satellites, was developed in 2002 by astronomers at Chinese Academy of Sciences. Extensive positioning experiments of CAPS have been performed since 2005. On the basis of CAPS, this paper studies the principle of a navigation constellation composed of slightly inclined geostationary orbit (SIGSO) communication satellites. SIGSO satellites are derived from GEO satellites which are near the end of their operational life and operating in inclined orbits. Considering the abundant frequency resources of SIGSO satellites, multi-frequency observations could be conducted to enhance the precision of pseudorange measurements and ameliorate the positioning performance. A constellation composed of two GEO satellites and four SIGSO satellites with an inclination of 5◦ can provide service to most of the territory of China with a maximum position dilution of precision over 24 h of less than 42. With synthetic utilization of the truncated precise code and a physical augmentation factor in four frequencies, the navigation system with this constellation is expected to obtain comparable positioning performance to that of the coarse acquisition code of the Global Positioning System (GPS). When the new method of code-carrier phase combinations is adopted, the system has the potential to possess commensurate accuracy with the precise code in GPS. Additionally, the copious frequency resources can also be used to develop new anti-interference techniques and integrate navigation and communication.

Vector magnetic field in solar polar region

By means of ‘deep integration’ observations of a videomagnetograph the vector magnetic field was first systematically measured near the solar south polar region on April 12, 1997 when the Sun was in the minimal phase between the 22nd and 23rd solar cycle. It was found that the polar magnetic field deviated from the normal of solar surface by about 42.2° ± 3.2°, a stronger magnetic element may have smaller inclination, and that within the polar cap above heliolatitude of 50°, the unsigned and net flux densities were 7.8 × 10−4) T and −3.4×10−4T, respectively, and consequently, the unsigned and net fluxes were about 5.5 × 1022 and − 2.5 × 1022 Mx. The net magnetic flux, which belongs to the large-scale global magnetic field of the Sun, roughly appmaches the order of the interplanetary magnetic field (IMF) measured at distance of 1 AU.

Progress in Space Solar Telescope

Abstract Space Solar Telescope (SST) is a space project for solar research, its main parameters are that total weight 2.0T, sun synchronous polar circular orbit, altitude of the orbit 730KM, 3 axis stabilized attitude system, power 1200W, telemetry of the downlink rate 30Mb/s, size 5 × 2 × 2M 3 , mission life 3 years. It is expected it will be launched in 2001 or later. The main objective is structure and evolution of solar vector magnetic field with very high spatial resolution. The payloads consist of 6 instruments: main optical telescope with 1-M diameter and diffraction limited resolution 0.1 are second, EUV imaging telescope with a bundle of four telescopes and 0.5 are second resolution, spectrometric optical coronagraph, wide band spectrometer, H-alpha and white light telescope and solar and interplanetary radiospectrometer. An assessment study between China and Germany is under operation.

Attitude control and high precision pointing control system of a large balloon borne solar telescope

Abstract In this paper, we have discussed the development of a large Control Moment Gyroscope (51 N.M.S. CMG) and use CMG as the driving component to realize precise attitude control of a large balloon borne gondola (total weight 1.5 ton) on which the solar telescope, 80 cm in diameter, is equatorially mounted. On ground test, the pointing accuracy of the gondola of better than 1 arc-minute (R.M.S.) at its plumb line have finally been achieved. In addition, we have established a control model of the large balloon borne telescope pointing control system. By computer simulation and actual test on ground, we have achieved the pointing accuracy of better than 10 arc-seconds (R.M.S.) for the solar telescope.

An analysis of photospheric vector magnetograms, Hα images and soft X-ray images in a superactive region NOAA 7321

Based on the photospheric vector magnetograms taken at Huairou Solar Observing Station (HSOS), Hα images taken at Hiraiso Solar Terrestrial Research Center of Communication Research Laboratory, soft X-ray images taken by Yohkoh and an extrapolation method, the magnetic field structures and some active phenomena of the active region AR 7321 around 04:12 UT on 27 October 1992 are analyzed in this paper. A divergence of the transverse magnetic field, located at a newly formed spot, was found. At least four highly sheared magnetic field systems separately spread from this divergence to four other sites around this divergence. Vertical current concentrations are upward in this region and downward in the other four sites, and the corresponding Hα bright patches and soft X-ray bright loops coincide with these structures, confirming the existence of these four systems. The extrapolated magnetic force lines reconstructed by the Boundary Element Method (BEM), force-free field assumption, and boundary condition of observed photospheric vector magnetic field, coincide in space with the Hα bright patches and soft X-ray bright loops, showing that this extrapolation method is very effective and suggesting that the Hα bright patches and soft X-ray bright loops in this case represent the magnetic field structures in the upper atmosphere of the Sun.The bright structures in the Hα images and the soft X-ray images have a close correlation with the non-potential characteristics of the magnetic fields.

The Distributions of HDOP and VDOP in GNSS and a Corresponding New Algorithm of Fast Selecting Satellites

In Global Navigation Satellite System (GNSS), the accuracy of position estimates depends upon the measurement geometry and pseudorange measurement errors. The Dilution of Precision (DOP) provides a simple characterization of the user-satellite geometry. An in-depth study of DOP distribution characteristics is conducted in this paper, with emphasis on performance bounds of Horizontal Dilution of Precision (HDOP) and Vertical Dilution of Precision (VDOP) for four satellites in varied hypothetical constellations. The distributions of HDOP and VDOP in 16 major world cities are analyzed by simulated calculations using the TLE sets of GPS satellites. According to the theoretical analyses about the distributions of HDOP and VDOP, this paper also proposes a new algorithm of fast selecting satellites based on HDOP and VDOP, which requires a shorter computing time than the general method and provides a feasible way to quickly achieve a high-accuracy positioning.

Conical beam monopole antenna design for Chinese area positioning system

This article describes the operational principle of the satellite-based Chinese Area Positioning System (CAPS) and proposes a monopole antenna for a large anchored buoy platform in harshmarine environment. The proposed antenna is highly omnidirectional with sufficiently wide half-power beamwidth (HPBW) greater than 40° (i.e., not less than ±20° swing) by using a conical ground plane, taking into account the geostationary satellite position, link budget, sea conditions, volume and cost. The impedance bandwidth defined by 10 dB return loss is 750 MHz (5.60–6.35 GHz), and the main lobe direction and the half-power beamwidth are about 46° and 43° at the operating frequency 5.885 GHz, respectively. The antenna prototype has been installed on-site to test its performance in sea. The results confirm that the proposed antenna is a suitable candidate for a variety of CAPS applications in China.

Study of Ranging Using Dual Orthogonal Linear Polarized Antenna in Chinese Area Positioning System

The constellation for Chinese Area Positioning System (CAPS) consists of commercial communication satellites in the geosynchronous orbit. CAPS signals afford 3 dB polarization loss, since they are transmitted between linear polarized antenna of communication satellites and circular polarization antennas of receivers. In order to reduce the signal power loss, the receivers adopts a dual orthogonal linear polarized antenna to acquire signals from all directions with almost full power. In the current work, a method is proposed based on weighted combination of two pseudoranges measured by the dual orthogonal linear polarized antenna. The theoretical and simulation analysis show that this method improves the CAPS ranging precision approximately to that of signal with full power. Compared with 3 dB polarization loss of circular polarized antenna, this method is equivalent to 2.7 dB compensation for signal carrier to noise ratio. By applying the method to the experimental measured pseudoranges of the dual orthogonal linear polarized antenna, the precision of pseudorange is remarkably improved.