GPS,IRS or INS GS
The GPS ,IRS or INS speed is difficult to use at high altitude. However it has been done by a B 747 400 crew who flew into a volcanic ash cloud over Alaska many years ago. Apart from multiple flame outs and opaque windows they managed to land safely at Anchorage using their IRS/GPS ground speed for reference during the remainder of the flight and approach.
Good Flying!
John