SDO/HMI line-of-sight Dopplergram

Dopplergrams are maps of solar surface velocity. The HMI (Camera 2) instrument takes 72 filtergrams to construct a single dopplergram. Six filtergrams are taken in six positions across the nominal 6173.3 Å spectral line; each filtergram is taken in two polarization states (right circularly polarized (RCP), or Stokes I-V, and left circularly polarized (LCP), or I+V). Assuming that the absorption line is a Gaussian and that the HMI filter transmission profiles are delta functions, the Fourier coefficients can be calculated and are then used to estimate the line-of-sight magnetic field strength B.

多普勒图是太阳表面速度的映射。HMI（相机2）仪器通过采集72个滤光片图来构建单个多普勒图。在6173.3 Å的标准谱线上，从六个不同位置采集六个滤光片图；每个滤光片图均在两种偏振状态下采集（右旋圆偏振（RCP），或斯托克斯I-V，以及左旋圆偏振（LCP），或I+V）。在假设吸收线为高斯型且HMI滤光片的传输轮廓为δ函数的条件下，可计算傅里叶系数，进而用于估计视线方向的磁场强度B。