The altimeter is an instrument which measures vertical distance with respect to a reference level. The altimeter is an instrument that measures the altitude of the land surface or any object such as an airplane. Louis Paul Cailletet was the French physicist who invented the altimeter and the high-pressure manometer.
Louis Paul Cailletet (1832-1913)
French physicist and inventor who in 1877-78 was the first to liquefy oxygen, hydrogen, nitrogen, and air.
Lloyd Espenschied invented the first radio altimeter in 1924. In 1938, the fm radio altimeter was first demonstrated in New York by Bell Labs. In the first public display of the device, radio signals were bounced off the ground, showing pilots the altitude of an aircraft.