Originally Posted by
ASIP
Basic trigonometry will tell you that the apparent size, elevation and speed of a high-altitude airliner and a lower-altitude turboprop are virtually indistinguishable from the ground.
Basic trigonometry immediately tells you the altitude if you know the angle and distance (the two parameters Buk operator always sees).
A quick calculation shows angles of 18 or 21 degrees; not a lot in it for an inexperienced operator.
Speed, or rather rate of closure, might be measured by the system or alternatively left of operator assessment.
As we don't know (I think) if the launcher/operator was fully exploited and trained or only semi-trained the differentiation may not have been that obvious.