The chromosphere-corona transition zone above an active region

Intensities and profiles of ion emission lines between 1170 A and 1700 A from an active region on the Sun are measured from spectra obtained with the Naval Research Laboratory's High Resolution Telescope and Spectrograph - HRTS. The measurements provide simultaneous determination of line intensities, wavelength shifts and Doppler widths at 50 separate positions in the active region, with spatial resolution of 1 arc second and spectral resolution 0.07 A. Fine structure variation of intensities and gas flow velocities in the temperature range 20,000–200,000 K are determined. The density sensitive line pair I(1486 N IV)/I(1548 C IV) has been used to measure electron pressures. Derived emission measures imply filling factors of 0.05–0.1 to balance the divergence of conductive flux width radiative losses above 60,000 K.     

HRTS results from spacelab 2

The HRTS instrument flew on the Spacelab 2 mission from 29 July - 6 August 1985. HRTS consisted of a 30 cm Gregorian telescope, a slit spectrograph covering the 1190–1680 Å region with 0.05 Å spectral resolution, a broadband (90 Å FWHM) spectroheliograph tuned to 1550 Å, and an H-alpha filter system. The spectrograph slit was 920 arc sec, approximately 1 R₀, in length. Sub arc second spatial resolution along the slit is possible, but because of jitter in the Spacelab Instrument Pointing System (IPS) good exposures actually achieved 1–2 arc sec resolution. We describe the scientific results from HRTS.     

Ultraviolet spectroscopy of the chromosphere and transition zone at high spatial and temporal resolution

The third rocket flight of the NRL High Resolution Telescope and Spectrograph (HRTS) recorded UV spectra of the quiet Sun in a 10″ × 800″ region. By rastering the slit in 2′' increments, a time series with 20s resolution of two-dimensional spectra with 1′' spatial resolution was obtained. The spectrum includes strong chromospheric diagnostic lines of C I, Si I, and Fe II, transition zone lines of C IV and the continuum which is produced in the temperature minimum. Images of the network show that Fe II emission is well-correlated with dark Hα mottles, that the transition zone is produced in extended structures which are apparently continuations of the mottles, and that the strongest continuum emission is from near the base of the mottles. Time series of C I profiles show little variation in most features aside from the chromospheric jets which develop rapidly over timescales of 30s. The C IV profiles also show only gradual variations over most of the slit except for the numerous small explosive events.     

多谱段全日面极紫外成像仪

在极紫外波段对太阳进行成像观测是研究太阳活动、日冕中等离子体物理特性的重要手段.传统极紫外成像仪或光谱仪无法同时实现高光谱分辨率和大视场的太阳成像.本文设计了一种新型太阳极紫外多谱段成像系统,采用无狭缝光栅分光方式实现了高光谱分辨率和空间分辨率的全日面成像,成像视场可达47',光谱分辨率每像素2×10-3 nm,空间分辨率每像素1.4',全日面时间分辨率优于60s.通过分析谱线的全日面成像图和系统响应,表明成像仪能大范围的观测太阳活动形态演化,为太阳物理研究和空间天气预报提供更完整的观测数据.      

Great solar bursts of October 19, 22 and 23, 1989

Itapetinga measurements at 48 GHz with the multibeam technique are used to determine the relative position of solar burst centroid of emission with high spatial accuracy and time resolution. For the Great Bursts of October 19,22, 1989, with a large production of relativistic particles, and October 23, it is suggested that, at 48 GHz, the bursts might have originated in more then one source in space and time. Additionally the October 19 and 22 Ground Level Events exhibited very unusual intensity-time profiles including double component structures for the onset phase. The Bern observatory spectral radio emission data show a strong spectral flattening typical for large source inhomogeneties. The interpretation for this is that large solar flares are a superposition of a few strong bursts (separated both in space and time) in the same flaring region.     

Comparison of solar soft X-ray irradiance from broadband photometers to a high spectral resolution rocket observation

The solar soft X-ray (XUV; 1–30 nm) radiation is highly variable on all time scales and strongly affects the ionosphere and upper atmosphere of Earth, Mars, as well as the atmospheres and surfaces of other planets and moons in the solar system; consequently, the solar XUV irradiance is important for atmospheric studies and for space weather applications. While there have been several recent measurements of the solar XUV irradiance, detailed understanding of the solar XUV irradiance, especially its variability during flares, has been hampered by the lack of high spectral resolution measurements in this wavelength range. The conversion of the XUV photometer signal into irradiance requires the use of a solar spectral model, but there has not been direct validation of these spectral models for the XUV range. For example, the irradiance algorithm for the XUV Photometer System (XPS) measurements uses multiple CHIANTI spectral models, but validation has been limited to other solar broadband measurements or with comparisons of the atmospheric response to solar variations. A new rocket observation of the solar XUV irradiance with 0.1 nm resolution above 6 nm was obtained on 14 April 2008, and these new results provide a first direct validation of the spectral models used in the XPS data processing. The rocket observation indicates very large differences for the spectral model for many individual emission features, but the differences are significantly smaller at lower resolution, as expected since the spectral models are scaled to match the broadband measurements. While this rocket measurement can help improve a spectral model for quiet Sun conditions, many additional measurements over a wide range of solar activity are needed to fully address the spectral model variations. Such measurements are planned with a similar instrument included on NASA’s Solar Dynamics Observatory (SDO), whose launch is expected in 2009.     

I.U.E. high resolution observations of hot stars emitting coronal x-rays

The far UV resonance lines of a sample of 21 early-type stars, which were observed in the soft X-Ray band with the $\text{Einstein}$ satellite, are examined using I.U.E. high resolution spectra to search for possible correlation between the X-Ray coronal emission and far UV spectral properties. In particular, those quantities that can give information on the structure of the outer envelope (such as wind terminal velocities, emission-absorption ratios) are measured and compared with the observed X-Ray flux.     

WAMDII — A wide angle Michelson Doppler imaging interferometer for spacelab

A CCD imaging device has been designed which combines a spatial resolution of 0.1° with a spectral resolving power of 10⁵, sufficient to measure Doppler shifts and line widths of individual atmospheric emission lines. It will be flown aboard Spacelab and will be used to study neutral winds and temperatures as functions of height, latitude and time of day.     

Ultraviolet emissions from the upper atmospheres of the planets

A large number of atoms and molecules have strong emission lines in the vacuum ultraviolet. As a result, this spectral region is particularly suited to studying the upper atmospheres of the planets. The observed emissions not only identify the constituents, but also provide information on the solar and magnetospheric excitation processes. Long term monitoring of these emissions, particularly with modest spatial resolution, can elucidate the effects of variations in the solar input as well as changes in magnetospheric conditions. Also, earth orbiting telescopes generally provide better spectral resolution than is available on flyby vehicles. A modest beginning in planetary upper atmospheric studies from earth orbit has been made using orbiting observatories designed primarily for stellar astronomy. As examples of the power of this technique, some recent results will be reviewed with an emphasis on Jupiter and the Io torus. The unusual scheduling requirements and the effects of scattered intense long wavelength radiation put demands on orbiting planetary observatories which are somewhat different from those of stellar astronomy. The implications of these demands for continued advances in this area are discussed.     

The Fuse/Lyman observatory

The scientific interest in observing the 900–1200 Å spectral range is based on the fact that this spectral region contains the bulk of the accessible emission of hot objects (T ∼ 10⁵–10⁶ K) and the majority of the resonance lines of many astrophysically important atoms and ions. To pursue the pioneering work with Copernicus on bright objects in that spectral range, a high spectral resolution of 3 10⁴ should be attained. In addition, to have access to extragalactic targets (i.e. increase the cosmological return of this observatory) a large collecting area is needed. A design based on the use of 1m class grazing incidence telescope is now under study. Instrumentation at its focal plane may include a 3 10⁴ resolution spectrograph in the 900–1200 Å spectral range, a 10³ resolution spectrograph in the 100–300 Å spectral region and a 10⁴ resolution spectrograph in the 1200–2000 Å region.     

Spectroscopy of the extreme ultraviolet background radiation

Observations in the far ultraviolet and soft x-ray bands suggest that the interstellar medium contains several components of high temperature gas and should be emitting in the extreme ultraviolet. Indeed diffuse radiation has been detected in the extreme ultraviolet with photometric instruments, but no spectral measurements exist below 520Å. We have designed a unique grazing incidence spectrometer to study the diffuse emission between 80 and 650Å with 10 to 20Å resolution. The instrument was launched on a Black Brant sounding rocket from White Sands Missile Range on April 22, 1986. Our preliminary analysis shows the expected geocoronal and interplanetary HeI 584Å emission, and possibly other features which may originate in the hot ionized interstellar gas. Flux limits to these possible emission lines are compatible with previous broad band measurements.     

Observational signatures of nanoflare heated solar stellar coronae

Using time-dependent dynamical models of the radiating gas in coronal flux tubes, we identify features in UV spectral line profiles that can reveal the direction in which energy flows through the solar transition region, in observations without temporal or spatial resolution. The profile features survive spatial and temporal averaging through non-linear dependencies of the line emission coefficients on thermal properties of the plasma that are correlated with the material velocity. This approach requires only low noise data of high spectral resolution and could naturally be applied to stars as well as the solar corona. We make predictions for the SUMER instrument that can in principle test whether energy propagates upwards or downwards in coronal flux tubes, suggesting a new angle of attack on the long standing problem of determining coronal heating mechanisms.     

X-ray spectral properties of non-magnetic cataclysmic variables using Chandra HETG

Results from a study of high resolution spectra obtained with the Chandra X-ray observatory for a sample of 6 Cataclysmic Variables (CVs) are presented. A global fit approach has been employed to obtain the spectral characteristics of the sources. The line-rich high-resolution spectra of these sources clearly indicate multi-temperature nature of the emitting plasma. Multi-temperature APEC models describe the spectra very well. Detection of significantly broad emission lines, indicates the presence of high velocity gas in SS Cyg and U Gem during the optical outbursts.     

Radio observations of total solar eclipse of November 3, 1994 at Chapecó (Brzil)

Radio observations of the eclipse on November 3, 1994, were carried out at Chapecó, Brazil by using a decimetric spectrograph having high spectral and time resolution. The light curve shows that: (1) Time variation of the radio flux before the totality was more compared to that after. (2) During the totality radio emission at 1.5 GHz was observed. Advantage of high spatial resolution ( 3.2 arc sec) possible during solar eclipse enabled us to determine the height of radio emission at 1.5 GHz. (3) Microwave bursts were observed associated with metric Type III-RS bursts. The source size of one of the microwave bursts was 7 arc sec and its physical parameters have been estimated. (4) The time difference between radio and optical contacts suggested for the first time asymmetrical limb brightening at 1.5 GHz.     

InfraRed Astronomy Satellite Swarm Interferometry (IRASSI): Overview and study results

The far-infrared (FIR) regime is one of the few wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist yet. Neither of the medium-term satellite projects like SPICA, Millimetron or OST will resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, from highly excited carbon monoxide (CO) and especially from water lines would open the door for transformative science. These demands call for interferometric concepts. We present here first results of our feasibility study IRASSI (Infrared Astronomy Satellite Swarm Interferometry) for an FIR space interferometer. Extending on the principal concept of the previous study ESPRIT, it features heterodyne interferometry within a swarm of five satellite elements. The satellites can drift in and out within a range of several hundred meters, thereby achieving spatial resolutions of <0.1 arcsec over the whole wavelength range of 1–6 THz. Precise knowledge on the baselines will be ensured by metrology methods employing laser-based optical frequency combs, for which preliminary ground-based tests have been designed by members of our study team. We first give a motivation on how the science requirements translate into operational and design parameters for IRASSI. Our consortium has put much emphasis on the navigational aspects of such a free-flying swarm of satellites operating in relatively close vicinity. We hence present work on the formation geometry, the relative dynamics of the swarm, and aspects of our investigation towards attitude estimation. Furthermore, we discuss issues regarding the real-time capability of the autonomous relative positioning system, which is an important aspect for IRASSI where, due to the large raw data rates expected, the interferometric correlation has to be done onboard, in quasi-real-time. We also address questions regarding the spacecraft architecture and how a first thermomechanical model is used to study the effect of thermal perturbations on the spacecraft. This will have implications for the necessary internal calibration of the local tie between the laser metrology and the phase centres of the science signals and will ultimately affect the accuracy of the baseline estimations.     

An object-level strategy for pan-sharpening quality assessment of high-resolution satellite imagery

Current satellite imaging systems offer a trade-off between high spatial and high spectral resolution providing panchromatic images at a higher spatial resolution and multispectral images at a lower spatial resolution but rich in spectral information while a wide range of applications need the highest level of this information, simultaneously. Image fusion techniques as means of enhancing the information content of initial panchromatic and multispectral images produce new images, titled pan-sharpened, which inherent the advantages of the initial images. Considering the impact of fusion accuracy on the quality of corresponding applications, it is necessary to evaluate the quality of these processed images. During the last decade, a lot of quality evaluation metrics have been proposed which are mostly inspired by traditional image quality metrics. These methods are mostly based on applying quality metrics at the pixel level and evaluating final quality value based on averaging of obtained metric values through the whole image. However, obtained results clearly show that the behaviour of image fusion quality is inconsistent amongst different image objects. In this article, by applying image fusion quality metrics (IFQMs) to image objects, an object-level strategy for quality assessment of the image fusion process is proposed. The proposed strategy is applied to different satellite imagery covering residential and agricultural areas. Experimental results show higher capabilities of object-level quality assessment strategy in the quality assessment of the fusion process. Evaluating fusion quality at the object level provides the potential of fusion quality assessment for each individual image object in compliance with different parameters such as the type of objects and the effective size of objects in data set.     

Measurement of stratospheric trace constituent distributions from balloon-borne far infrared observations

Far infrared limb thermal emission spectra obtained from balloon borne measurements made as a part of the Balloon Intercomparison Campaign (BIC) have been analyzed for retrieval of stratospheric trace constituent distributions. The measurements were made with a high resolution Michelson Interferometer and covered the 15–180 cm⁻¹ spectral range with an unapodized spectral resolution of 0.0033 cm⁻¹. The retrieved vertical profiles of O₃, H₂O, HDO, HCN, CO and isotopes of O₃ are presented. The results are compared with the BIC measurements for O₃ and H₂O made from the same balloon gondola and with other published data. A comparison of the simultaneously retrieved profiles for several gases with the published data shows good agreement and indicates the validity of the far infrared data, the retrieval techniques and the accuracy of the inferred profiles.     

基于框架域的随机游走全色锐化方法

针对多光谱图像与全色图像的融合问题,提出了一种新的全色锐化方法。该方法首先通过亮度、色调、饱和度(IHS)变换与非下采样框架变换将原图像从空间域变换到框架域,然后利用基于图论的随机游走,建立高频框架系数的统计融合模型。此模型根据高频框架系数的邻域相关性与尺度相关性构造新的随机游走协调函数,将高频框架系数融合权重的估计转化为随机游走标记问题的求解。实验结果表明,该方法有利于保持图像的光谱信息和边缘轮廓信息,可以在降低融合图像光谱误差的同时提高空间分辨率,并且优于一些主流全色锐化方法。