About the derivation of geomagnetic indices from digital data

Most of the present geomagnetic indices have been designed at a time when observatories were operated using analog variometers, and their derivation scheme therefore fits with the related requirements. They belong to the analog era. At present, more and more observatories are operated using digital magnetometers, and, in a near future, satellite remote data transmission will allow real time availability of the observations. Then the digital era will be entered, and the observatory routines should evolve accordingly. Some basic points that must be taken into account when geomagnetic indices are designed for the digital era are examined.