Deng Yuanyong

Reports on Test Observations with the Multi-Channel Solar Telescope

In this paper, we have made a report on the test observations with a Multi-Channel Solar Telescope (MCST), which consists of 60 cm Nine-Channel Solar Telescope (NCST), 35 cm Solar Magnetic Field Telescope (SMFT), 8 cm Full Disc Telescope (FDT), 10 cm Full Disc Magnetic Field Telescope (FDMFT) and 14 cm Hα telescope. These observations demonstrate that the MCST has the following advantages: (a) It can work at more than nine visible spectral lines simultaneously. In this way, different solar layers of the photosphere and chromosphere can be observed at the same time; (b) every channel of the NCST is entirely equivalent to a videomagnetograph, by means of which the vector magnetic fields and line-of-sight velocity fields can be measured; (c) real-time monochromatic images of the photosphere and chromosphere can be obtained with the FDT, FDMFT, and Hα Telescope; (d) high-temporal-resolution full-disk magnetic fields can be measured with the FDMFT; (e) spectral profiles over a large field of view can be scanned with the NCST.In this paper, we have made a report on the test observations with a Multi-Channel Solar Telescope (MCST), which consists of 60 cm Nine-Channel Solar Telescope (NCST), 35 cm Solar Magnetic Field Telescope (SMFT), 8 cm Full Disc Telescope (FDT), 10 cm Full Disc Magnetic Field Telescope (FDMFT) and 14 cm Hα telescope. These observations demonstrate that the MCST has the following advantages: (a) It can work at more than nine visible spectral lines simultaneously. In this way, different solar layers of the photosphere and chromosphere can be observed at the same time; (b) every channel of the NCST is entirely equivalent to a videomagnetograph, by means of which the vector magnetic fields and line-of-sight velocity fields can be measured; (c) real-time monochromatic images of the photosphere and chromosphere can be obtained with the FDT, FDMFT, and Hα Telescope; (d) high-temporal-resolution full-disk magnetic fields can be measured with the FDMFT; (e) spectral profiles over a large field of view can be scanned with the NCST.

The measurement of flat fields and polarization offset from the routine observation data of a solar rotation

The correction of flat fields and polarization offset is a necessary step in the reduction of the full-disk solar observing data. The general used methods of the measurement of flat fields are summarized as follows. The first one is realized by randomly moving the solar telescope and making an average of thousands of observed images of the quiet region near the disk center, which is adopted by the large aperture solar telescopes with a small field-of-view. The second one is to shift the solar images with slightly different pointings, which is mostly used in the full-disk solar images. The third method is to use a diffuser to generate the uniform light source and it can be used in the full-disk solar images, too. Observing the nearby continuum of the selected working spectral line is generally used to obtain the polarization offset. It is worth to mention that, all these methods need special calibration observing mode and occupy the valuable scientific observation time. In the paper, we propose a new method to derive the flat fields and polarization offset from the routine observing data. Assuming that the flat fields and polarization offset do not change during a solar rotation, we firstly got the formula which can be used in the calculation of flat fields and polarization offset in the case of the ideal and real telescope guiding and pointing accuracy. The core algorithm in the formula is median process. Moreover, we obtained the flat fields and the crosstalk from Stokes I to Q , U and V using the above mentioned formula from series of the routine observed monochromatic image and Stokes Q / I , U / I and V / I images belonging to the Carrington Rotation 2144 observed by Huairou Solar Observing Station. The derived flat fields could not only reflect the small-scale dirty points but also the large-scale non-uniform pattern from the whole telescope system, which can be removed after the flat-fielding process. The distribution of the resulting Stokes V / I offset from Stokes I to V seems to be a Saddle surface, while that of the Stokes Q / I and U / I from I to Q , U is an upside-down bell shape. In order to evaluate the validity of the correction of the polarization offset we choose a quiet region near the solar limb as an example. The averaged value of Stokes V / I , Q / I and U / I in the region after polarization offset correction is −0.8×10−4, 0.9×10−4, 1.3×10−4, while that before correction is −6.8×10−4, 2×10−3, 1.7×10−3, respectively. It is quite clear that the Stokes V / I , Q / I and U / I improved a lot after the correction of the polarization offset. The main disadvantage of the method is that it can only correct the crosstalk from Stokes I to Q , U and V , incapable of the correction of that from Stokes V to Q and U . Some other methods are needed so as to make up the disadvantages. We suggest that the above mentioned method can be considered as one of the calibration methods for the space-borne or remote unattended full-disk solar observing instrument because it only uses the routine observation data without any other special calibration observation.

Observations of Running Penumbral Waves Emerging in a Sunspot

We present results from the investigation of 5 minute umbral oscillations in a single-polarity sunspot of active region NOAA 12132. The spectra of TiO, Hα, and 304 A are used for corresponding atmospheric heights from the photosphere to lower corona. Power spectrum analysis at the formation height of Hα – 0.6 A to the Hα center resulted in the detection of 5 minute oscillation signals in intensity interpreted as running waves outside the umbral center, mostly with vertical magnetic field inclination >15°. A phase-speed filter is used to extract the running wave signals with speed v ph > 4 km s−1, from the time series of Hα – 0.4 A images, and found twenty-four 3 minute umbral oscillatory events in a duration of one hour. Interestingly, the initial emergence of the 3 minute umbral oscillatory events are noticed closer to or at umbral boundaries. These 3 minute umbral oscillatory events are observed for the first time as propagating from a fraction of preceding running penumbral waves (RPWs). These fractional wavefronts rapidly separate from RPWs and move toward the umbral center, wherein they expand radially outwards suggesting the beginning of a new umbral oscillatory event. We found that most of these umbral oscillatory events develop further into RPWs. We speculate that the waveguides of running waves are twisted in spiral structures and hence the wavefronts are first seen at high latitudes of umbral boundaries and later at lower latitudes of the umbral center.

Flat-field measuring and correction method for full-disk solar image based on ground glass

Full-disk solar chromosphere and photosphere images are mainly used for monitoring solar activities. Flat-field correction of observation image is a basic work during data processing. In history, it is difficult to obtain uniform area light whose intensity is similar as sun. So flat-field measurement and correction of full-disk solar image usually depend on moving images and mathematical calculation. In order to overcome some disadvantages of traditional methods, such as large calculating quantity, complicated algorithms and difficult to realize automation, we research and design a new flat-field correction method based on ground glass. In this text, sunlight diffused by ground glass in field of view is used as uniform area light for flat-field measuring. We simulated the area light that sun diffused by ground glass, calculated the uniformity of area light in field of view. The uniformity of area light is more than 99%, so it can be used as uniform area light for flat-field measurement directly. We designed flat-field measurement device and formulate steps and methods for flat-field correction. After numerical stimulation and calculation, experiments carried out on solar chromospheres telescope and photosphere telescope separately. The result shows that the flat field obtained in this text could correct high-frequency information such as spots and non-uniformity of light path. Subjected to telescopes limited ability to eliminate stray light, flat-field measurement and correction also causes low-frequency information anamorphous because the angle of diffused light is much larger than normal observation. In order to amend low-frequency information distortion, we use multi-scale morphology filtering and median filtering to extract the low-frequency image from flat-field corrected image. Then the extracted low-frequency image is amended on the basis of theoretical limb darkening image. After flat-field correction and amendment, the correlation coefficient between corrected image and theoretical image is more than 0.99. At last, photosphere image of HMI and chromospheres image of GONG are used as reference images to quantitatively evaluate corresponding result in various field of view. The preprocessing of reference images includes three steps: (1) Centralization and geometric correction of experiment images and reference images; (2) unify reference images’ pixel resolution based on experiment images; (3) according to fitting intensity attenuation of experiment images’ margin, convolve the same Gaussian profile to unify the atmosphere effect on reference images and experiment images. The evaluation result shows that all indexes of corrected image are better than that of origin images. The flat-field measurement and correction method in this text is simple and convenient, and it is easy to realize automation. We suggest that the above mentioned method can be considered as a new method for full-disk solar telescope flat-field measurement and correction. In the future, we need to use diffuser which output angle is smaller during flat-field measurement to shorten exposure time and narrow the exposure time difference between flat-field measurement and normal observation. If a full-disk solar telescope wants to use this method to measure and correct flat-field, the ability of stray light elimination must be considered and optimized during design stage, and the data processing would be more simple and easy.

Solar flare forecasting model of combiningprincipal component analysis with support vector machine

Solar flare is an important event in the solar atmosphere. It is a main disturbance resource of space environment and has a dramatic impact on human activities. How to promote the forecast ability of solar flare has a great significance for human beings. To better predict solar flare, this paper used principal component analysis and support vector machine, which are two classic machine learning methods, to predict solar flare. In feature extraction part, principal component analysis is a generally adopted method, and it is a technique for linearly compressing multidimensional data into lower dimensions with minimal loss of information. In flare classification part, support vector machine is a learning machine based on the statistical learning theory. The support vector machine can deal with nonlinear problems in classification and regression easily by using kernel functions, which is necessary to map onto another high dimension linear space. In solar flare forecasting research, the relationship between solar flare and morphological evolution of sunspots plays an important role in daily flare forecasting. And there is evidence that sunspot parameters and 10.7 cm solar radio flux are extremely related with solar flare. With the predictors fully taken into account, a new method of combing principal component analysis with support vector machine is proposed to improve the forecast ability of solar flare. In this paper, the sunspot parameters are area of sunspot group, McIntosh classification, extended longitude, the sunspot number in the solar active region and magnetic classification. Using attribute coding and appropriate transform function, the initial data set of predictors is normalized to form the modeling data set. And based on this data set, principal component analysis and support vector machine are applied to build solar flare forecasting model. In experiment, the forecasting model is compared with other model, which works well in the solar flare short-term forecasting. This shows that the PCA-SVM prediction model has higher precision compared with the other one when either considering positive examples or negative samples. The results indicate that the Solar flare forecasting model of combining principal component analysis with support vector machine is an effective flare prediction model.