Geopotential Altitude Calculator
(for Aviation & Weather Stations
in Meteorology)

By: Jan Barani, Copyright © BARANI
DESIGN Technologies s.r.o.

BARANI DESIGN Technologies is a manufacturer of
professional micro weather stations and weather sensors that meet all
requirements of the WMO and NWS for professional climate monitoring.

This geopotential height or geopotential altitude (above standard mean sea level AMSL) calculator includes
corrections for the variability of earth's gravitational field due to
altitude, earth's centrifugal force, and earth's imperfect shape. Based on
WMO technical note 7 (also ref. WMO tech note 188).

Inputs

VARIABLE NAME

VALUE

UNITS

DESCRIPTION

Zp_m =


meters

Weather station altitude above mean sealevel (AMSL) in
geometric meters
(NOT gpm)

Lat_deg =


degrees

Latitude in degrees


Constants

g0 =

9.80665

m/s2

Standard
gravitational constant

g1 =

9.80616

m/s2

Gravitational constant @ 45° latitude used for corrections of
earth's centrifugal force


Conversions

Lat_rad =



Latitude converted to radians


Calculations

g_lat_o =



Correction due to lattitude (earth's centrifugal force)

b_lat =



g variation in free air or extended plateaus

g_lat_elev =



Combining both variations above


OUTPUT:
Hp_out =


gpm

OUTPUT: Weather station AMSL elevation in geopotential meters
(gpm) adjusted for variations in gravitational force with altitude and
latitude

Difference =





Geopotential altitude is used instead of geometric height and GPS altitude (in geometric units of meters, feet, ...) to simplify
mathematical calculations in meteorology and aviation. It allows one to use
gravitational acceleration as a constant fixed number (ɡ0 or ɡn = 9.80665 m/s2 (32.17405 ft/s2))
because variations in gravity around the earth's surface are already
accounted for in the geopotential altitude when given in geopotential units.
In short, geopotential altitude is just a
mathematical construct to make calculations simpler by allowing us to use
gravity as a constant/fixed number.

UNITS:
• Geopotential altitude/height = Geopotential meters (gpm) or geopotential
feet
• Geometric altitude/height (GPS altitude)= meters (m) or feet (ft) and
length many other units

In meteorology, weather stations like the MeteoHelix may be
located on high mountain ranges where geopotential altitude is used to
convert measured barometric pressure into the height of a standard isobaric
surface. This enables accurate determination of meteorological pressure highs
and lows, which drive weather patterns.

