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MissSoph created the topic: Height/ altitude/elevation
Hi everyone... met study and just wondering....pressure height can sometimes be referred to as pressure altitude? But then height is AGL , altitude is AMSL ..but pressure height talks about above sea level....am I just reading too much into it
John.Heddles replied the topic: Height/ altitude/elevation
Pressure Height and Pressure Altitude are interchangeable terms - they refer to AMSL.
'fraid that's not quite correct.
Pressure height (often written Hp) and pressure altitude are, indeed, equivalent terms for the same item. At least, I have never seen any authoritative claim that one differs from the other although I am quite happy to be proved wrong.
However, Hp is the altimeter reading in ISA above the assumed ISA SL datum for which the standard pressure is 1013.25 mb .. but let's just call it 1013 mb. It has naught, specifically, to do with AMSL. If the actual QNH happens to be 1013mb and the lapse rates happen to match ISA, then Hp will relate to AMSL on that occasion, coincidentally.
Thanks Bob and John - my explanation was most incomplete (mobile devices!) and in context wrong. I meant to say was it's AMSL in the ISA model but really Bob's example gets right to the point - it a measure of pressure.