MK I K-Coronameter White Light Polarization Brightness Scans

The first K-coronameter (later known as MK I) was an internally occulted white light coronameter to record the polarization brightness (pB) of the Thomson scattered K-Corona continuum emission. The brightness of the polarized light was measured with a sensitive photoelectric polarimeter using electro-optic modulation of the light beam and a half-wave plate made of two quartz plates whose optical axes were crossed and had thicknesses that differed by half a wave length for 500 nm. These rotated at half the speed of a 360 degree scan around the corona (i.e. 8 minutes). Following the aperture stop the beam was modulated using a quarter-wave plate that included a ‘Z-cut’ crystal of ammonium dihydrogen phosphate (ADP) and a polaroid. The retardation of the beam was proportional to the voltage applied to the crystal. The voltage frequency, and the modulation of the light, was 50 Hz. A cone with a small hole drilled along its axis isolated the region of the corona for scanning around the Sun. A complete coronal scan took 4 minutes. Measurements were acquired every 5 degrees around the Sun. The half-angle of the cone could be varied to scan the corona at different heights from 1.125 out to 2 solar radii (as measured from Sun center). It was decommissioned in 1978. The K-Coronameter took daily scans of pB intensity at 3 heights in the corona. It did not take images of the corona. Daily scans at 1.5 solar radii are available as digitized synoptic maps in fits and gif format covering the later mission from June 1965 until January 1968. Hard copy daily scans early in the mission (September 1956 through November 1960) are available in pdf format. Digital synoptic maps from the MK II instrument are available from 1969 to 1978, superseding the MK I maps.

首台K日冕仪（K-coronameter，后称MK I）是一款内掩式白光日冕仪，用于记录汤姆逊散射（Thomson scattering）产生的K冕连续谱辐射的偏振亮度（polarization brightness, pB）。该仪器借助对光束进行电光调制的高灵敏度光电偏振计，以及由两片光轴正交、厚度差对应500 nm波长半波延迟的石英板组成的半波片（half-wave plate），来测量偏振光的亮度。该半波片的旋转速率为绕日360°扫描速率的一半（单次完整绕日扫描耗时8分钟）。光束经过孔径光阑（aperture stop）后，由搭载磷酸二氢铵（ammonium dihydrogen phosphate, ADP）Z切晶体与偏振片的四分之一波片（quarter-wave plate）完成调制。光束的延迟量与施加在晶体上的电压成正比，该电压的频率与光束调制频率均为50 Hz。沿轴线钻有小孔的锥光阑可隔离出太阳周围的扫描区域，单次完整日冕扫描耗时4分钟，测量数据沿太阳周向每5°采集一次。该锥光阑的半顶角可调节，从而能在距日心1.125至2倍太阳半径的不同高度对日冕进行扫描。该仪器于1978年退役。MK I K日冕仪可对日冕三个高度处的偏振亮度强度进行每日扫描，且未拍摄日冕图像。1965年6月至1968年1月的任务后期，1.5倍太阳半径处的每日扫描结果以数字化综合图形式提供，格式为FITS与GIF。任务早期（1956年9月至1960年11月）的每日扫描硬拷贝数据以PDF格式提供。MK II仪器的数字化综合图数据可获取自1969年至1978年，该数据集替代了MK I的观测图件。