I'd tend to suggest that a pressure sensing device, mounted on or near the nose of an aircraft, while that aircraft is perhaps both rotating and/or moving through ground effect may not be the most reliable indicator of absolute altitude. I've certainly seen the raw pressure data do unusual things during the unstick portion of a takeoff. I would suggest that the radalt has at least as good a chance of being an accurate indicator (with its own caveats regarding terrain profiles and the effect of pitch attitude, of course)