GPS provides very accurate position locations of pressure
observations taken automatically by in-flight commercial aircraft worldwide.
The highly accurate location of these pressures provide a very accurate
analyses from which wind and other forecasts are made.
These observations are sent via satellite from remote areas such as over
oceans to weather centrals around the world. Within the US, the
observations are transmitted directly via air to ground communication
facilities.
In-flight pressure observations are then transmitted to weather
prediction centers to make upper level weather analyses from which automated
forecasts and flight plans are made. The results help pilots choose the
best cost-performance and safest flight routes.
Stan Doore
----- Original Message -----
From: <[email protected]>
To: "U.S. Metric Association" <[email protected]>
Sent: Sunday, April 18, 2010 11:32 PM
Subject: [USMA:47172] Re: Air flight altitudes in meters
What is the contribution of GPS data to the navigation of large aircraft?
Do GPS data dominate barametric data?
---- Original message ----
Date: Sun, 18 Apr 2010 18:10:10 -0700 (PDT)
From: "John M. Steele" <[email protected]>
Subject: [USMA:47170] Re: Air flight altitudes in meters
To: "U.S. Metric Association" <[email protected]>
Cc: "U.S. Metric Association" <[email protected]>
Actually, it is nominally based on height above
sealevel. Sitting on the runway, with altimeter
correction dialed in, it will read the published
height of the runway above sealevel.
At cruise levels, no altimeter correction is used
and reading is called flight level. It is the
height above sea level IF sea level were at 15 °C,
101.325 kPa, and a lapse rate of -6.5 K/km to the
stratosphere (11 km), and zero lapse rate above that
to 20 km. Further it it uses a height variable
called geopotential height, the height that would be
true if gravity were constant with height. There is
a transformation between that and geometric height
in the standard.
------------------------------------------------
From: James R. Frysinger <[email protected]>
To: U.S. Metric Association <[email protected]>
Cc: U.S. Metric Association <[email protected]>
Sent: Sun, April 18, 2010 8:47:07 PM
Subject: [USMA:47168] Re: Air flight altitudes in
meters
Altimeters work off of atmospheric pressure
readings, Pat. But the readout is in terms of height
above terrain. So assignments and reports are always
in length units. No human pressure to altitude
correlation procedures are used.
Jim
