SOHO LASCO C2 Level 0.5 FITS Data

The LASCO C2 Raw FITS Data.

LASCO (Large Angle Spectroscopic Coronagraph) is comprised of three nested coronagraphs (C1, C2, and C3) that image the solar corona from 1.1--30 solar radii (C1: 1.1--3; C2: 1.5--6; and C3: 3--30). The inner coronagraph (C1) is a newly developed mirror version of the classic Lyot coronagraph without an external occulter, while the middle coronagraph (C2) and the outer one (C3) are externally occulted. C1 is equipped with a Fabry-Perot interferometer that can take monochromatic images over the whole field of view with a spectral resolution of 0.07 nm. By stepping the bandpass across a spectral line, line profiles and Doppler shifts can be derived from all 1024 x 1024 pixels simultaneously. With an equivalent pixel size of 5.6 arcsec, the spatial resolution of C1 is ~11 arcsec. The resolution is ~23 arcsec for C2, and 112 arcsec for C3. The calculated expected precision of the emission line measurements, for example, of the 637.4 nm Fe X line is 0.05 Km/s at 1.1 solar radii, 1.0 km/s at 2 solar radii, and 8.0 km/s at 3 solar radii, all for a 60 s exposure. All three devices use a 1024 x 1024 pixel CCD. The CCDs are passively cooled to 193 K, but can be heated above ambient temperatures to drive off condensed material. The readout rate is ~21 s for a full image, but any line on the CCD can be accessed within about 60 ms, the unwanted lines being dumped. The electronics box provides overall control, including observation programs and scheduling. An observation program can be scheduled to be run at an absolute time or just next in sequence. It can run for a certain number of iterations, an interval of time, or stop at an absolute time. The observation program tasks included, e.g., taking single images from one of the telescopes, a series of images through the three linear polarizers, and a sequence of images at a series of Fabry-Perot wavelength steps. The image processing tasks are primarily image compression, with seven different techniques being available. On average, the readout time should be ~6 minutes or about 200 images/day. This information is from the paper ``The Large Angle Spectroscopic Coronagraph (LASCO): Visible Light Coronal Imaging and Spectroscopy,'' by G. E. Brueckner et al. (Proceedings of the First SOHO Workshop, ESA SP-348, pp. 27-34, November 1992).

LASCO C2原始灵活图像传输系统（FITS）数据。LASCO（大角度光谱日冕仪，Large Angle Spectroscopic Coronagraph）由三台嵌套式日冕仪（C1、C2、C3）组成，可对1.1至30倍太阳半径范围内的日冕进行成像，其中C1覆盖1.1至3倍太阳半径，C2覆盖1.5至6倍太阳半径，C3覆盖3至30倍太阳半径。内层日冕仪C1为经典李奥日冕仪的镜像改进型，未配备外部掩盘；中层日冕仪C2与外层日冕仪C3均搭载外部掩盘。C1配备法布里-珀罗干涉仪（Fabry-Perot interferometer），可在全视场内获取单色成像，光谱分辨率达0.07 nm。通过将通带跨光谱线步进，可同时从全部1024×1024像素中提取谱线轮廓与多普勒频移。C1的等效像素尺寸为5.6角秒，空间分辨率约为11角秒；C2的空间分辨率约为23角秒，C3则为112角秒。以637.4 nm的Fe X谱线为例，经计算其发射线测量的预期精度为：1.1倍太阳半径处0.05 km/s，2倍太阳半径处1.0 km/s，3倍太阳半径处8.0 km/s，以上均为60秒曝光时长下的结果。三台仪器均搭载1024×1024像素的CCD（电荷耦合器件，Charge-Coupled Device）。CCD采用被动冷却至193 K，亦可加热至环境温度以上以去除冷凝物。整幅图像的读出时长约为21秒，但CCD上任意一行均可在约60毫秒内被读取，无需读取的行可直接丢弃。电子学机箱提供整体控制功能，涵盖观测程序与调度。观测程序可设置为在绝对时刻运行，或按序列依次执行；可运行指定次数、指定时长，或在绝对时刻停止。观测程序包含的任务例如：从任意一台望远镜获取单幅图像、通过三个线性偏振片拍摄一系列图像，以及按法布里-珀罗干涉仪的一系列波长步长拍摄图像序列。图像处理任务以图像压缩为主，共提供七种不同的压缩技术。平均而言，读出时长约为6分钟，单日可获取约200幅图像。本数据集相关信息源自G. E. 布鲁克纳等人发表的论文《大角度光谱日冕仪（LASCO）：可见光日冕成像与光谱学》，收录于第一届SOHO（太阳和日球层观测台，Solar and Heliospheric Observatory）研讨会论文集《ESA SP-348》，第27-34页，1992年11月。