SDO/HMI line-of-sight Magnetogram

Magnetograms are maps of the observed solar magnetic field in the photosphere. The line-of-sight component of the field can be accurately measured as it evolves in time over the full visible disk of the Sun. The HMI instrument exploits the Zeeman effect, which allows the strength of the line-of-sight component of the magnetic field to be determined by measurements of the spectral line in circularly polarized light.

HMI makes two independent measurements of the line-of-sight component of the photospheric magnetic field. One is collected every 45 seconds with the HMI Doppler camera. The other is computed every 720 seconds using filtergrams recorded by the Vector Field camera. The spatial resolution is 1 arc second (half arc-second pixels) and the full disk images are collected on a 4096**2 detector. The noise level is nominally 6.3 Gauss. HMI really measures flux density in Mx/cm2 in each pixel.

磁图是观测到的太阳光球层磁场的映射。该场线的视向分量能够随着时间在太阳全视域内演化而精确测量。HMI仪器利用塞曼效应，通过测量圆偏振光中的光谱线，从而确定磁场视向分量的强度。HMI进行了两次独立的磁场视向分量测量。一次是通过HMI多普勒相机每45秒收集的数据，另一次则是利用矢量场相机记录的滤光图，每720秒计算一次。空间分辨率为1角秒（半角秒像素），全圆盘图像由4096**2探测器收集。噪声水平约为6.3高斯。HMI实际上是在每个像素中测量磁通密度，单位为Mx/cm2。