SOHO LASCO C3 Polarized Brightness FITS Data

The Polarized Brightness data from the LASCO C3 coronagraph.

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).

本数据集为LASCO（Large Angle Spectroscopic Coronagraph，大角度光谱日冕仪）C3日冕仪的偏振亮度数据。LASCO由三台嵌套式日冕仪（C1、C2、C3）组成，可在1.1至30倍太阳半径范围内对日冕进行成像：其中C1覆盖1.1–3倍太阳半径，C2覆盖1.5–6倍，C3覆盖3–30倍。内部日冕仪C1为新型研制的经典李奥（Lyot）日冕仪反射式变体，无需外部掩盘；而中间的C2与外部的C3均采用外部掩盘式设计。C1搭载法布里-珀罗（Fabry-Perot）干涉仪，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（铁X）谱线为例，在60秒曝光时长的条件下，发射线测量的预期计算精度为：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。三台日冕仪均搭载1024×1024像素的电荷耦合器件（CCD），该类CCD采用被动冷却至193 K，也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，无需读出的行可直接丢弃。电子箱提供整体控制功能，涵盖观测程序与调度设置；观测程序可设定为在绝对时刻运行，或按序列依次执行，可按指定迭代次数、时间间隔运行，或在绝对时刻终止。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、通过三台线性偏振片组拍摄系列图像，以及按一系列法布里-珀罗波长步进拍摄图像序列。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，每日可获取约200幅图像。本段信息源自G. E. 布鲁克纳（G. E. Brueckner）等人于1992年11月第一届SOHO（Solar and Heliospheric Observatory，太阳和日球层观测台）研讨会发表的论文《大角度光谱日冕仪（LASCO）：可见光日冕成像与光谱学》（收录于ESA SP-348会议文集，第27-34页）。