Forget doppler in 1500-2000ft for hovering within 50ft range. The aberration of doppler in your time limit and in this altitude is to much. May be a special DGPS unit with near based ground station will have the needed accuracy. 15ft in 1000ft i believe as published but only for a fixed measurement from a fixed measuring point with digital indication, but not for measuring in an any time at least small moving helicopter.
Is the SAGEM 85T31 AP now with hovering mode???
